Be aware of battery and charger inconsistencies!
 

Anyone who has sufficient FRC experience knows that batteries are paramount to a robot's functionality. It can cause major problems if not properly taken care of. A loss of speed, general degradation of performance, and worst case is missing a goal and losing out on those points! We rather interestingly ran into this situation this year and actually found a good fix. We have noticed these symptoms in previous years but never really thought too much of it.

Short background story:
The issue arose when every time we did a battery swap the robot's performance seems to be altered. sometimes the balls would shoot higher, sometimes lower, the robot had a noticeable speed difference, and we couldn't figure out what in the world was going on. We had all good chargers and good batteries from last year. After some investigation we had concluded that our issue was the batteries! not just the batteries but the chargers as well!. The most typical problem is the connector coming lose but that wasn't the case for us. What I had noticed is that anytime a battery came off a specific charger it seemed to have much better performance. We had two of these chargers but the other one didn't perform as well. We also had two other newer style but those also didn't perform as well. Now you might be thinking they are defective, but i assure you they arn't they are all 100% fully functional.

Technical details:
-Battery age matters, avoid using batteries more than a year old
-connections matter
-chargers matter! just because you have two identical ones doesn't mean they will behave the same. we had 5 chargers and each one had charged the battery to a different voltage ranging from 12.8-13.3
-battery charge, you need to have enough batteries and chargers to keep your robot alive during competition! These batteries take a short while to discharge and long time to recharge so don't think 5 minutes on a charger and it will be good to go. Not only do you want a charged battery, but you want a FULLY charged battery to an optimal level.

Solution:
-Upon the recommendation of another team(sorry forgot which) we currently use: http://www.amazon.com/Stanley-BC1509...tanley+charger

(there are other types as well with higher current or other brands this is just one particular example i can vouch for)

for all our battery needs and are very happy with them so far. The key aspect is consistency. We have 3 of these chargers now and they will charge the batteries to the same point every time on every charger so we have resolved all of our battery inconsistency issues.

TLDR: get good chargers,test what your current ones do

Re: Be aware of battery and charger inconsistencies!
 

I'm sorry but that charger is illegal to use and will degrade battery life. The max recommended charging amperage of the FRC legal batteries is ~6 amps. Charging at a higher rate can cause overheating and over time damage to the battery.

That charger is intended to be used with an automotive sized battery not a FRC legal sized battery. It says that it "automatically" selects the charge rate but that is misleading. The battery is what sets the charge rate based on its voltage. Since the charger "thinks" that it is connected to a much larger battery it will charge at too high of a rate.

The reason you are seeing different voltages when you disconnect the charger is caused by a couple of factors. One is the state of charge when the battery is connected. That will set the charge voltage and rate. The other is the phenomenon known as a surface charge where you are seeing a little residual voltage on the surface of the plates. To test the batteries voltage you need to either let is sit for a number of hours, which is preferred, or remove the surface charge by connecting a light load to it for a couple of minutes. The max voltage of a fully charged lead acid battery that has had its surface charge removed or allowed to "soak" in is 12.77 volts.

Re: Be aware of battery and charger inconsistencies!
 

In addition, you should be testing your batteries before the competition season with something like this device:

http://www.westmountainradio.com/pro...oducts_id=cba4

We have easily found a half dozen batteries that looked 'good' but suddenly lost charge a number of amp hours into testing, proving they were actually bad over the past 5 years.

Re: Be aware of battery and charger inconsistencies!
 

we tried looking into the rules about which chargers are legal and we couldn't find any restrictions. We don't use batteries over a year old anyway so in regards to degrading them it's not really a concern. Can you point out where you see this restriction on chargers? It's not even a 1C charge rate.... The point about the voltages and chargers is that the same battery will have a different voltage from each different charger... this shouldn't be the case and from what we noticed it makes a big enough difference to effect robot performance to a rather noticeable and enough of a degree to make us miss shots and slow the robot down

Re: Be aware of battery and charger inconsistencies!
 

Which rule is it against? I looked & could not find it. I wonder if that was an oversight or intentional. Last years rule doesn't count. :)

Regardless of legality Al has a very considered opinion of not going over a 6 amp charge rate.

Re: Be aware of battery and charger inconsistencies!
 

You're correct. There is no "illegal" battery charger [this year]. We will definitely be seeing more event-specific guidance with power circuit limitations, however.

OP, the batteries can last for years, so I don't recommend the one-year limitation on inventory. We are currently using batteries that range from 1-5 years old. It is important to not fully discharge the batteries and keep them charged throughout the year to extend life.

For in-competition and general use, we use a Battery Beak to check the charge state. We also want to pick up the West Mountain Radio tester.

Re: Be aware of battery and charger inconsistencies!
 

Wow, didn't even notice the change. Not even a max charge rate this year. Could have sworn this was a rule, my mistake I guess.

I still think mechanisms should be limited by a control loop and not the state of your battery whenever possible.

Re: Be aware of battery and charger inconsistencies!
 

The one thing that got buried in a Safety Manual (I did have to do some searching to find it after a different thread referenced it) was that chargers should be limited by the manufacturer of the battery. In the case of these batteries, it is about 6.8A.

Re: Be aware of battery and charger inconsistencies!
 

Safety Manual, Page 8.

As said above, the recommended rate is 6 amps.

Re: Be aware of battery and charger inconsistencies!
 

The maximum charging current for FRC batteries is 5.4A per the spec sheet.
Charging batteries at a current lower than the maximum (i.e. 2A) will improve battery life. Charging at a higher current will speed up the time it takes to fully charge a battery.

Re: Be aware of battery and charger inconsistencies!
 

I am sorry to disagree with those that state there is no rule about chargers. It is found in the safety manual and as LRI's we have been told to enforce it. The highlight is mine but a direct quote. From the safety manual:

"Charging and Handling
 Keep the battery-charging area clean and orderly.
 Place your battery charger in an area where cooling air can freely circulate around
the charger. Battery chargers can fail without proper ventilation.
 Do not short out the battery terminals. If metal tools/parts contact the terminals
simultaneously, it will create a direct short circuit. This may cause high heat to
develop in the battery terminal/part/tool area and the battery could explode.
 If a quick disconnect is not available and you must use tools to disconnect the
battery, make sure metal tools don’t contact both terminals at the same time.
 Do not charge battery at greater than the manufacturer’s maximum recommended
rate."

Re: Be aware of battery and charger inconsistencies!
 

It's not that we limit it, it's that they simply aren't sufficiently usable. We have batteries going back a few years and 2012's and back simply don't perform as required so we just don't use them anymore. They are just used typically for a few rounds then we swap and continue this cycle for all batteries so other than normal robot use they don't see any abuse or misuse.

Re: Be aware of battery and charger inconsistencies!
 

the control loop only works when you have a reserve in power, not when you go all out and the battery top of level makes a huge impact in performance. For example our kicker. We just slam it with maximum power, there is no margin for a control loop here, if the battery isn't up to the required level a control loop will do nothing to fix that. You could argue the design shouldn't have to rely on that, but it's hard enough getting a working robot done much less something this tuned out.

Re: Be aware of battery and charger inconsistencies!
 

that's only a recommendation and the safety guidelines aren't really competition rules, they are just that, guidelines. We may not win a safety award but this doesn't seem illegal. Esp considering the chargers state automatic charge current setting with no specification for capacity rating so we believe we are working well within the design constraints of both the battery and charger. Worst case we use a 6A charger for bulk charge then these for top off and consistency guarantee.

Re: Be aware of battery and charger inconsistencies!
 

I guess that you didn't read my post. I am an LRI and we were told to enforce this safety RULE. You will notice that it says "DO NOT....."

Re: Be aware of battery and charger inconsistencies!
 

You can argue however much you want about how it isn't really a rule, but when the LRI tells you that it's not allowed to be used on your robot batteries, you aren't going to win. :rolleyes:

Re: Be aware of battery and charger inconsistencies!
 

Except that the Safety Manual is not just guidelines.
The spec sheet for the battery that I linked to in my post above states that the maximum charging rate for these batteries is 5.4A. You will damage you batteries if charge them above this rate.

Re: Be aware of battery and charger inconsistencies!
 

We consider the safety manual as guidelines not competition rules. If everything stated in that manual were enforced then every single team would be disqualified for one reason or another. Also the chargers state they automatically set he charge current. Even if they do deliver more than 7A it's not for a very long time either. Worst case is we do bulk charge on old 6A chargers then top off with these. That way they never do get charged higher than 6A but this is just playing around a technicality and more or less on a guideline rather than a competition rule anyway. Either way it won't really be an issue if that's all we have to adhere to.

Re: Be aware of battery and charger inconsistencies!
 

then we'll just play around it. do bulk charge on old 6A and top off with these, win-win?

Re: Be aware of battery and charger inconsistencies!
 

The charger you linked to is meant for car batteries, not FRC batteries. The charger does not know that the battery connected to it is not what it is designed for.
The safety rules are rules, and you will be told to follow them.

Re: Be aware of battery and charger inconsistencies!
 

It's not that we set the charge rate to 15A, the charger states: "automatically selects charge rate from 0 to 15 AMPS to maximize battery life, charge speed and maintenance" it also makes no claims as to a rating of battery it can/can't charge. From other online documentation I found there is no danger at charging up to 1C other than shortening the battery life, which you may consider damage I suppose though. Honestly i'm no worried since we can work around it by bulk charging on 6A then cycling to these for top off

At the week 1 event I inspected at, our LRI (Al) specifically asked us to look for chargers that operate above 6A, and instructed that they WOULD NOT be allowed, regardless of how you told us you would "program" or use them. OP there is no way for us to enforce that you are following what you are suggesting. I would highly recommend you bring other (i.e. legal) chargers to your event and consider leaving these at home.

Re: Be aware of battery and charger inconsistencies!
 

1C for a 40AH car battery is different and bigger than 1C for a 17AH FRC battery.

Re: Be aware of battery and charger inconsistencies!
 

actually it makes no claim as to what types of batteries it can and can't/shouldn't charge. The only indicator is: "automatically selects charge rate from 0 to 15 AMPS to maximize battery life, charge speed and maintenance"

From some online documentation it shows that batteries can be charged faster than manufacturer's recommended rate but it shortens their lifespan, which is fine.

Also from numerous places people are charging all kinds of batteries with these, including FRC batteries. It's a general purpose 12V lead acid battery charger, we are using fairly generic 12V lead acid batteries.

Even so we can easily adhere to the rules by bulk charging on old 6A then cycling to these for the top off

Re: Be aware of battery and charger inconsistencies!
 

there are a lot of things that you can't enforce what a team says they will do other than to take their word for it. As stated we can work within every single rule and planned on it anyway, that doesn't mean that just because something CAN be used in a way that violates the rules that it WILL and that doesn't mean it SHOULDN'T be used just because it might if not used properly. Kind of like the usage of a dremel.

Re: Be aware of battery and charger inconsistencies!
 

How is "cycling to these for the top off" adhering to the rules? If you can't use them, you can't use them.

Adhering to the rules would mean to use (and only use) LEGAL chargers at ALL times, while at the event. This would mean that the batteries never see the charger you are suggesting.

Save yourself the headache and space by leaving the charger at home when you compete.

Re: Be aware of battery and charger inconsistencies!
 

indeed it is, but battery ratings are in C which is relative to capacity and is more or less identical for each type of battery chemistry unless it was specifically designed a bit differently for some purpose. These are general purpose lead acid batteries, so as far as C ratings go the documentation talking about C ratings for generic lead acid batteries still applies. That's why the documentation does it this way, because it applies to all batteries of that chemistry regardless of capacity.

Re: Be aware of battery and charger inconsistencies!
 

How do you store your batteries during the off season?

Re: Be aware of battery and charger inconsistencies!
 

because there is no distinction to what is and isn't a legal or illegal charger. the rule states "Do not charge battery at greater than the manufacturer’s maximum recommended rate." which we can adhere to by doing bulk charge on 6A chargers then top them off with these where we know for a fact it won't draw even 2A. Just because something can be used it one way doesn't mean it will and so long as we adhere to the rule the usage of such a device is permitted.

Also leaving them at home is not an option. Our older chargers are not acceptable for robot performance. Each one charges the battery differently which is a major problem for us. I'll post on the QA and look for an official response but regardless I believe we can easily adhere to the rules to there shouldn't be any problems.

Re: Be aware of battery and charger inconsistencies!
 

What "automatically selects charge rate" most likely means is that it does what most other "automatic" chargers do: cycles through a factory-set charging algorithm which changes the current and voltage supplied to the battery.
http://batterytender.com/resources/battery-basics.htm/

Re: Be aware of battery and charger inconsistencies!
 

we give them a charge and shelve them until needed again. though hey see periodic use throughout the year anyway

Re: Be aware of battery and charger inconsistencies!
 

How long do they typically sit on the shelf without any maintenance, and is the shelving area air conditioned?

Re: Be aware of battery and charger inconsistencies!
 

As others have already stated, the charger you are using is designed for automotive batteries where the value for C, in Amps, is much greater than the C value for the 18 Ahr batteries used in FRC. Automotive batteries rarely give an Ahr rating but they would typically be in the range of 35 to 85 Ahr. The claim about automatic charge rate selection is relevant ONLY when the charger is connected to an automotive battery. Using an automotive charger in the "automatic mode" would almost guarantee that you are charging your FRC batteries at currents well above the manufacturers recommendations for part of the time. This excessively high charging current leads to premature failure of the battery. The failure modes can consist of reduced battery capacity, shortened life and rupture of the case (possibly explosively) due to boiling of the electrolyte.

The automotive chargers use charge currents that are appropriate for automotive batteries and they change charge currents and transfer to trickle charge mode based on the battery voltage. Since the voltage at full charge is related the same for all the 12 V (nominal) batteries, irrespective of their Ahr rating, the automotive chargers are able to properly charge all automotive batteries no matter what their actual Ahr rating is.

Each week, where I work, we literally use tons of batteries just like the ones used in FRC (different Ahr rating) to build large Interruptible Power Supplies for industrial applications and data centers. These are sourced from one of the FRC legal suppliers. We CALCULATE our charging current based on the size and number of batteries in a battery bank and recommendations from the battery manufacturer. Neither we, nor any competitor that I know of, has the technology that would allow a charger to distinguish between batteries of different sizes and what charge rates are appropriate for that battery.

Re: Be aware of battery and charger inconsistencies!
 

I believe the RCM (reserve capacity in minutes) rating of automotive batteries follows an industry standard of 25 amps load until voltage drops to 10.5V.

If so, you could multiply the RCM by (25/60) to get an Ahr rating (at 25 amps down to 10.5V).

For many automotive batteries, the RCM rating is available.

Re: Be aware of battery and charger inconsistencies!
 

I'm still not sure how using a >6A charger after you've used some other charger adheres to the rules. But by all means, you should put in a Question on the Q&A to see what the answer is; that's absolutely the right approach. Good luck; I'm pretty sure I know who's going to process that question, and he's the one that tells the LRIs & his inspectors when he's the LRI to tell teams to remove chargers >6A.

So to answer this another way, and avoid illegal chargers: what is it about this charger that is apparently improving the OP's robot performance? Is there a process to follow with the "standard" chargers that should achieve the same result, but safely?

Re: Be aware of battery and charger inconsistencies!
 

There's no apparent competitive advantage. The issue is that charging over 6 amps is unsafe per manufacturer direction and can decrease the life of batteries.

Re: Be aware of battery and charger inconsistencies!
 

because the rules state nothing about chargers, the only rule that mentions anything about charging is the one that states they shouldn't be charged at a higher rating than manufacturer recommends, which is 6A. Using a 6A charger to do bulk charge, then the 15A charger for top off will be within the rules because the charge rate will never be higher than 6A. these new chargers will only top them off which will only draw a few amps at max, so we will be explicitly within what the rule states.

Re: Be aware of battery and charger inconsistencies!
 

How do you know that? Have you tried this proposed process and measured the current?

Re: Be aware of battery and charger inconsistencies!
 

the main issue we suffer from is inconsistencies, not necessarily any kind of improved performance over other good chargers. All of our previous chargers get different performance because they all charge the batteries to a different level. The max charge current is actually irrelevant to us, what matters is the state the batteries are in when they get taken off the chargers. These Stanly provide a consistent charge every time and every charger is the same. That is the key element we need, a consistent charge level that actually fully charges the batteries. We do not get that out of the 6 old ones we had(which there are three different types) but we do with these new ones.

Re: Be aware of battery and charger inconsistencies!
 

Because the old chargers can't put out more than 6 so they will charge them as much as they can until hey reach a fully charged status(which isn't really fully charged it seems like). At that point we will move over to the stanly, there is actually a current readout of the charge rate so yes we did measure it and once it reaches a certain point it goes into float charge which documentation states is not more than a few amps. So we can indeed for a fact know and guarantee that we will always be within this rule. This is what we were going to do from the start anyway. Just because we have 15A chargers doesn't mean they will ever be charging at that unless we put a dead battery on which there is no need to.

Re: Be aware of battery and charger inconsistencies!
 

How do you know that the charging rate will not be above 6A?

Also, 6A is pushing it for these batteries. You should charge your batteries at the lowest charging rate you can get away with to maximize the lifespan of the batteries. The only thing charging at a higher rate gives you is less time to charge.

Re: Be aware of battery and charger inconsistencies!
 

My tentative working hypothesis, based on the presently insufficient information available, is that the Stanley BC1509 is overcharging the FRC battery (for which it was not designed).

Some "smart" battery chargers are not smart enough. If you interrupt them in the middle of a charge cycle and then try to continue, they may mis-read the state of the battery and fail to complete the charge cycle. I know my Schumacher SC-1200A sometimes does this.

Re: Be aware of battery and charger inconsistencies!
 

we are aware it will decrease the battery life but we don't care. From the information I found online here "http://www.powerstream.com/SLA-fast-charge.htm" there is absolutely no danger what so ever in using this charger with these batteries. Possibly through missuse or abuse but under normal conditions nothing dangerous should happen.

Re: Be aware of battery and charger inconsistencies!
 

Note:

The Ahr rating will increase if measured with a lower current.

So be careful when comparing FRC Ahr to automotive Ahr computed from RCM*(25/60).

I eyeballed some data from the discharge curves in NP-18-12 datasheet and plotted the actual Ahr of that FRC-legal battery vs discharge current.

At the RCM 25 amp rate, the FRC battery appears to be less than 7Ahr, which would correspond to an RCM of about 17 minutes.

Re: Be aware of battery and charger inconsistencies!
 

You should. Batteries are expensive, and you do plan on competing in FIRST for multiple years, right?

Re: Be aware of battery and charger inconsistencies!
 

it will to a dead battery but we never plan on putting a dead battery on these chargers. only batteries that are indicated as fully charged by our old chargers. essentially we are just taking a charged battery, and moving i to another charger to maintain trickle. So no, no rules will be violated since it will never get into that state where it can possibly output that much current. No commercial charger is "dumb" enough to output anywhere near that much current to a battery that's indicated as already fully charged. We can argue this until the cows come home but from our observations this state is never achieved so we do fall within the rules.

Re: Be aware of battery and charger inconsistencies!
 

according to the information here: http://www.powerstream.com/SLA-fast-charge.htm with the max charge voltage this thing outputs it can't go into an overcharge state. it can be a higher than 0.3C rating yes but no overcharge.

Re: Be aware of battery and charger inconsistencies!
 

we already have and will continue to. We get about 4 batteries every year and the ones from the previous year are still good so we can manage with those. We care more about battery performance during a game than longevity.

Re: Be aware of battery and charger inconsistencies!
 

I don't see a max output voltage spec for the Stanley BC1509 anywhere on the page you linked.

Re: Be aware of battery and charger inconsistencies!
 

Until you find that the state of a battery includes bulging sides & won't fit in your robot, or until it's smoking. :) Then the manufacture's max current spec may become more important to you.

And before you ask: no, I haven't seen either of these personally. However, I do trust Big Al, who has seen them & told his inspectors at Central IL (one of which was me) about it when he told us to look for >6A chargers.

I'll repeat what someone else said earlier: if it comes down to a disagreement on this -- regardless of the evidence you present -- between your team and the LRI, you're not going to win. Unless you have a Q&A answer that states your chargers are legal. When you craft your question, you should be specific about the charger you would like to use.

Re: Be aware of battery and charger inconsistencies!
 

Thought I might ask here,

We are currently using the Schumacher SSC-1000a 2/6/10amp charger.
It does support motorcycle/tractor/jetski batteries, which the FRC battery seems to resemble.

The amount of charge has to be selected after the battery is attached. We only use the 6a mode during competition and the 2a mode for overnight trickle charge / maintenance.

We are going to order a few more to bring to our regional competition. Is this charger NOT going to be allowed?

Here is a link to the charger information.

http://www.amazon.com/Schumacher-SSC-1000A-SpeedCharge-Battery-Maintainer/dp/B0009IBJE4/ref=sr_1_3?s=automotive&ie=UTF8&qid=1394141261&sr= 1-3&keywords=schumacher+sc1000a

Aloha,
Mr. H

Re: Be aware of battery and charger inconsistencies!
 

Of course the float charge will be very small.

What I was asking was how long does it take to get to that certain point, and what is the current while it is getting to that certain point.

Re: Be aware of battery and charger inconsistencies!
 

Are you actually measuring the state of charge with some test equipment?

Re: Be aware of battery and charger inconsistencies!
 

oh sorry it just tells you this when it's charging, when we do put dead batteries on it's 14.x i don't remember the last digit. I can grab a multimeter if need be bu from what i've seen it never goes above 15V which according to that info can't cause an overcharge state

Re: Be aware of battery and charger inconsistencies!
 

That is not necessarily true. It depends on design of the charger and the health and state-of-charge of the battery when the cycle is started.

Re: Be aware of battery and charger inconsistencies!
 

You're probably right. But that still doesn't make it legal. Have you posted to Q&A yet?

Re: Be aware of battery and charger inconsistencies!
 

I can't tell you exact numbers at this moment but i can get them and can use them as proof that we are within the rule. However it's not even really needed all we want to use these Stanley for is trickle. as stated we will be putting fully charged batteries(as indicated by our old chargers) on these stanly so they should only ever be in a trickle mode. even if they arnt' i wouldn't imagine it be more than a few amps anyway but can verify this and will when I get around to it.

Re: Be aware of battery and charger inconsistencies!
 

no not yet, but again the rules state nothing about chargers, only charge rate. I can prove that we fall within the rules with the method mentioned in several other replies of only putting fully charged batteries from old chargers on the Stanley simply to trickle charge. that's what really matters to us is the quality of the trickle charge, not the brunt current capability.

Re: Be aware of battery and charger inconsistencies!
 

I don't agree with inspectors not taking a team's word for it. As mentioned previously, the rule states that we shouldn't charge more than the manufacturer's spec charge rate, which is set at 5.4 Amps. If that's the case, why are you allowing chargers that go up to 6 Amps? If we're adhering strictly to the rules (and FIRST has a tendancy to do that), we shouldn't be charging at 6 Amps either. Most chargers have a selectable charge rate from 2 A, 4 A and 6 A. To satisfy the rule, we would have to charge at 4 Amps. But right there, you're taking the team's word for it that we're going to charge at 4 Amps. The rule doesn't say that chargers that are capable of charging more than that are against the rules. The rule states that teams shouldn't charge more than the recommended maximum charge rate. It's a subtle, yet important difference. If we ruled out all chargers that are capable of charging at greater than 5.4 Amps, then most every team in FRC will need to get new chargers. Take the team's word for it and be done with it.

Re: Be aware of battery and charger inconsistencies!
 

Your problem is that you are being logical. The Q&A is not always logical.

Re: Be aware of battery and charger inconsistencies!
 

The administrative manual says "Every team should know, understand and follow the safety rules found in the FIRST Safety Manual." That phrasing appears to be advisory (in that it does not create a requirement).

However, If event staff or officials feel that a hazard exists, they'll refer it to the regional director, who can determine the extent of the team's continued participation in the event, based on the hazard present and efforts to resolve it.

In terms of the competition, noncompliance with the safety manual carries no specific penalty, and certainly none related to passing or failing inspection or playing the game. But, if charging the battery in a particular way has rendered a battery unsafe, the inspectors and referees will prohibit the use of that battery in competition.

Re: Be aware of battery and charger inconsistencies!
 

We do take the teams' word on a lot of things; there's no way to inspect every part of each robot and everything in each pit in a reasonable amount of time. We take everyone's word that they didn't start working before build season, that they bagged their robot on time, etc. Part of the inspection form is a signature by both the team captain and a coach stating that they followed the rules; we even take their word that they didn't lie when signing. On all of those things I think the vast, vast, majority of FRC teams tell the truth.

However, we don't take the teams' word for a number of things. That's why spec sheets for non-standard parts are required, for example. Ask in the Q&A; maybe non-standard battery chargers fall into that category.

Good question; I don't know. I do know what I've been told to look for, though. LRIs, while not infallible, do have a lot of room to use their discretion -- or not.

Re: Be aware of battery and charger inconsistencies!
 

Sorry. That was my understanding of how chargers work. I should have done more research. I have edited my post.

Re: Be aware of battery and charger inconsistencies!
 

We're using the KOP chargers. (With anderson outlets of course) Haven't had too many issues with these. We do a 2 amp charge overnight (Treat your batteries right when you can!) and a 6 amp charge during competition time to boost the charge speed, and to 'top off' batteries. (I've noticed that a 2 amp charge leaves about 12.6 volts in the battery, whereas a 6 amp charge gets us to 13.1, even with two year old batteries. Our robots haven't been big power drawers until this year, though.)

Higher voltage (as long as it isn't surface voltage) is always better. Duh. It means less voltage dipping through the match, etc.

But if you're experiencing inconsistent performance based on battery voltage, You have a bad design. You will experience voltage drop throughout the match, during movement, so basically, if your performance is hinging upon a perfectly (not fully) charged battery, you really need to rethink how you've built something. (Though this late in the season... what can you do? Maybe use the battery reading in your programming to do something like an open-loop control, or you can slap on a sensor to do closed-loop control.) (This is my #1 concern with all these motor-powered catapults this year...)

Re: Be aware of battery and charger inconsistencies!
 

Your 25/60 number is close to the 1/2 number I found for converting RCM to an approximate Ahr. Since the RCM is measured at a constant current, regardless of battery, it isn't the same as the Ahr rating though it is close.


The peak currents that a typical FRC drivetrain will draw during acceleration is well off the charts provided by Enersys. Since the design of these batteries were optimized for their storage capacity rather than high discharge rate, their "output resistance" will be rather high, guaranteeing that you will get severe voltage dips.

Choosing your battery charger to give you a consistent state of charge is one way of dealing with the battery variations. As Toa states, a more robust solution would involve making your robots performance insensitive to the variations in your battery's state of charge or output voltage. FIRST has already provided us with an example; the regulated 12V output of the PDB.

Learning to devise strategies that are independent of variables such as your battery voltage is part of the STEM education you should be getting from participating in this program.

Re: Be aware of battery and charger inconsistencies!
 

it's easy to say stuff like this, but in reality it's almost never the case. Having a feedback loop requires you to have overhead in power, which i don't think many if any robots actually have. Not sure how much you have worked with control loops but it's pretty much never perfect. We have tried it, and concluded it was a waste of time for our needs. It was simplest and best to just slam it full power, but as you stated this relies on battery state. Our main issue is our kicker. it's less about being 100% full and more about having a consistent charge so it shoots the same every battery swap we do. with a good battery off these chargers we can accurately and consistently shoot it from the white zone for autonomous, this isn't the case with our old chargers. Sure you're right it's not an optimal design but we don't have a bunch of control system engineers at our disposal and it's hard enough making a robot work to bag much less something this advanced.

Re: Be aware of battery and charger inconsistencies!
 

As an LRI in past years you know that we must follow directions. We were told no battery charger above 6A. Need I say more. You know that I questioned the rule so that it could be enforced and the safety manual was quoted as law. As LRI's we have no choice but to enforce. We will ask that the charger be removed from the pit area.

Re: Be aware of battery and charger inconsistencies!
 

RCM is how many minutes it takes to drain a (fully charged) lead acid battery down to 1.75 volts per cell (10.5 volts for 12V battery) with a constant current of 25 amps.

Thus if you divide RCM by 60 you will get the number of hours it takes, under those test conditions.

If you multiply that number of hours by 25 amps you will get the Ahr rating of the battery, under those test conditions. That's where the (25/60) number came from.

You will get a higher Ahr number if you run a test with a lower test current.

To compare the capacity of an FRC battery to an automotive battery, you have to compare apples to apples. That means running the same test conditions on each battery.

Discharge curves for the NP-18-12 are available in the datasheet. From these curves you can get a rough estimate of the FRC battery RCM rating. It's very roughly 17 minutes. That number can be compared to the RCM of an auto battery to get a rough idea of the relative capacity of the two.

Re: Be aware of battery and charger inconsistencies!
 

By not letting the charger in the pits, you are not enforcing the rule. If a team limits the charger to be under 5.4 Amps, they are not breaking the rules. Ferraris aren't illegal to drive on the street because they have the ability to go over the speed limit. It's up to the driver to limit its speed.

Re: Be aware of battery and charger inconsistencies!
 

This is more akin to the purpose behind electrical rules for robot construction. This is about safety. Can most teams pick and use chargers safely? Yes. If they let teams pick and use any charger they want, will somebody blow up a battery? Also - yes. It is just statistics. It will happen some time and some where. The inspectors stand on this is reasonable and makes common sense.

Re: Be aware of battery and charger inconsistencies!
 

So dremels, grinders, and etc also shouldn't be used either because they have the potential to cause sparks and catch something on fire? Drills and other power tools shouldn't be used either because someone may get injured? this is complete nonsense. A properly used battery charger is no different than a properly used dremel. And so long as all rules are fallowed, safety ones included, there shouldn't be arbitrary limitations. Is there also speed limits for robots? because you know that just isn't safe. Robot's shouldn't be allowed to be powered on in the pit either, because of course you know something might happen and it's a confined space. There is common sense, then there is going to unnecessary and unwarranted extremes.

Re: Be aware of battery and charger inconsistencies!
 

Have you got an answer yet from Q&A?

Re: Be aware of battery and charger inconsistencies!
 

I am going to point you to this section of the Administrative manual

Re: Be aware of battery and charger inconsistencies!
 

Hint: Don't run your mechanisms at 100% power on a full battery, and scale appropriately. There are absolutely ways around this issue.

OP: This is the point of how to build a robust system. It should not have to rely on a maximum (and potentially illegally reached) voltage level to be effective. A robust solution would operate at less than perfect voltage and be able to compensate when the charge is higher.

Re: Be aware of battery and charger inconsistencies!
 

not when the force you need is only available with doing just that. As i mentioned before we have to slam our kicker with a mostly full battery to make it from the white zone. There is no overhead here. We have tried different transmission ratios and weights. higher ratio we don't develop the speed we need, lower ratio we don't have enough force to achieve the speed, etc. We can have a margin closer up, but what good does that do us if we want to shoot from further away? there may be some way to achieve all the goals and have this overhead but we arn't a team with two dozen engineers and a NASA machine shop. We just get a robot together that works and hopefully get it done by bag day. You should understand these types of limitations if you are part of an FRC team. You just have to work within the limitations and don't have the time or resources to redesign the whole system

Re: Be aware of battery and charger inconsistencies!
 

we just try to build a good enough working system, robustness is an afterthought. These types of things are easy to say but until you are up until midnight on bag day trying desperately to finish a robot you just won't understand what it means that you're out of time and there's nothing you can do about it and that there isn't anything more you could have done during the season simply because you don't have the resources. You can say all you want how there is a better more robust way to do it but frankly that just isn't even an option for most teams. They just try to make something work, not build a mars rover.

Also it's impossible for these chargers to charge the batteries to illegal voltages. As i have stated over and over, it's not about the current, it's not about the voltage, it's about the CONSISTENCY. the batteries are only at 13.5V when freshly pulled off the charger. They can't overcharge the batteries. and we will use them in a way which is within ALL rules anyway. I really don't think most people in this thread have any idea how batteries and chargers actually work. As someone else stated it's like saying a Ferrari is dangerous and shouldn't be allowed to be driven on the street just because it can easily break the speed limit even though when properly used it will fall within all laws(rules)

Re: Be aware of battery and charger inconsistencies!
 

didn't ask yet don't have the team login

Re: Be aware of battery and charger inconsistencies!
 

What about dremels? they can throw sparks when used on steel. As far as I know their usage is permitted though, just need to be used on materials that don't throw sparks like aluminum or plastics.

Re: Be aware of battery and charger inconsistencies!
 

Sanelss, if a cop pulls you over for going 65 in a 45 zone, are you going to protest that the speed limit is too low, and needs to be raised, and besides, you aren't speeding?


If your answer is no, then I suggest that you just got pulled over and protested on BOTH points. I highly recommend that you take the first step you should take when you find yourself in a hole: stop digging. By now, I would guess that half the inspectors in your event(s) have figured out which is the first pit to check for chargers that are illegal, and will be busy tipping off the other half on the first day of said event(s).

If your answer is yes, then I suggest reconsidering that mode of operation.



I could be even more blunt, but in order to save as much face as possible for all concerned, I will refrain from going that route.

Re: Be aware of battery and charger inconsistencies!
 

Yet in this case the cop is putting you over for going 45mph because your car can go 60mph and demands that you need a new car that has a max speed of 45mph, despite the fact that you were clearly going 45mph.


Edit:
Also, just though of something that could remove the chance of argument and burden of proof with inspectors, if you would to wire the chargers to the batteries with a 6amp slow blow fuse, wouldn't that be enough to show that the batteries are not being charged above the recommend rate?

Re: Be aware of battery and charger inconsistencies!
 

From what I've been hearing, the car was going 65 after going 45 most of the length of the stretch. Sorry, that's a no-go. You can argue the "can go" argument all you like, but the radar don't lie.


Let me make something clear to y'all. The rule is the rule is the rule is the rule. Because it is a rule, it is enforced, regardless of how dumb, idiotic, or moronic it may seem. If you violate the rule, and you get caught, you can expect the penalty. Again, regardless of how dumb it seems. (It's not like I have prior experience with seeing this happen or anything, I've only seen this general class of rule or ruling an average of once per year from a certain group of people...)

Re: Be aware of battery and charger inconsistencies!
 

From what I understand of their setup, they are using bulk chargers to charge the battery most of the way, then the move to the other chargers to top off/trickle charge at a low amperage.
Using the same example, you would be going at 45 with a car that only goes 45 for most of the trip, then switching to a car that is going 5mph but can go 65 for the rest of the trip.

Legally that would satisfy all of the rules.

The issue seems to come from "what if the other charger goes higher then 6 amps, for whatever reason, even though it shouldn't" which is where I would recommend fusing the charger with a 6 amp slow blow fuse, to enforce a limit. So it CAN NOT charge at a rate more then 6 amps and makes inspectors happy.

Re: Be aware of battery and charger inconsistencies!
 

But consider this: they are getting a competitive advantage out of it. Imagine that you're in a (distance) race, and most cars go 55 (most efficient speed, for a car) the whole way until they run out of fuel. But this one car goes 55 until it runs out of fuel... and pulls out a 1-gallon gas can, dumps it in their tank, and drives another 30 or so miles beyond the rest of 'em--because they pulled out that extra gas can--which may or may not be legal (we haven't clarified that yet, because SOMEONE hasn't asked Q&A!).


Again, the rule will be enforced. No amount of whining and complaining about how your entire design revolves around this particular setup will change that. (BTW, that's how this thread struck me last night--a bunch of whining and complaining and "I'm not doing anything wrong, see this other example" from some folks.)


One thing about that slow blow fuse: You'd have to show that you did that particular modification safely. Otherwise, the charger would be sent out of the pit not under being a potentially illegal charger, but under being a safety hazard.

Re: Be aware of battery and charger inconsistencies!
 

Any battery charger can be used, provided it does not charger higher then the rated charge rate of the battery, some battery chargers are better, some are worse. Could a team find a charger had the same effect and is rated less then 6 amps? Most probably yes. Would it be legal? Yes.

Can a team buy several of every legal battery, load test them, find the best model. Then buy 50 - 100 of that model and test them all so they only use the best 10? Is that an advantage? Yes. Is it legal? Yes.

The rule is not to charge at a rate greater then X, there is no rule on the chargers themselves.

Also, do you change the output leads on battery chargers? I know must teams do, and I don't see how adding a fuse is much more unsafe.
Also I will point you to teams using custom made cases for their chargers.

Re: Be aware of battery and charger inconsistencies!
 

I would be quite confident in saying that if the Q&A didn't say otherwise, your robot would not pass inspection until you removed the chargers from your pits.

Since this seems to be getting to the point where all the arguments are becoming circular, it would be nice if someone asked the Q&A and closed this thread (or just close the thread, OP can make a new one when he gets an answer from Q&A).

Re: Be aware of battery and charger inconsistencies!
 

except i'm only going 30mph in a 40mph zone. I just have a car that can go 200. There is no rule that states which cars you can or can't use or what the top speed of a car can be, just a speed limit. and i will happily abide by that speed limit. you guys keep thinking some rule is being broken. IT'S NOT. we have equipment that can be used to break rules, but we AREN'T using them in such way. so your analogy is completely flawed. the inspectors can check all they want. Not a single rule is being broken.

you guys can be as blent and uptight about it as you want, but it states very clearly what the rules are and i stated very clearly of how we will abide by them. It makes no difference to me if others do or don't like it or if some inspector thinks there is a problem with it when there isn't...NO RULES ARE BEING BROKEN, WE ARE NOT USING ILLEGAL CHARGERS. is that blunt enough? The inspector guy said we can't use them, but there is not a single rule against what types of chargers, only charge current limits.

I will post in the Q&A when I can but I don't have the team login to do so at this moment.

Re: Be aware of battery and charger inconsistencies!
 

Let me put something straight, in BLACK and WHITE: The inspector says you cannot use them, and you use them ANYWAY, then you need a CLEAR RULE that says that the inspector in question is wrong, applied by the LEAD ROBOT INSPECTOR at the event, to use them. In other words, you need to prove the inspector wrong, by the rules. Guess what, you can't. On the other hand, you can't necessarily be proven wrong--but that means that you need to make 1000% sure that you are following the directive of the Safety Manual--which that charger doesn't help with. (Did I mention that this directive about the charger is coming through the LRI?)

The other factor here is the charger type. It's been brought up before--but charging this type of battery with a charger meant for car batteries (these are motorcycle batteries) could present a safety risk--and a safety risk that can be avoided is TO be avoided, especially in the pits.



I remind you that if the lead robot inspector rules that you're charging your batteries with a charger deemed illegal, then they can refuse to pass you at inspection. No pass, no play. No play, no rankings, no standings, no Saturday afternoon play. All because someone didn't know the difference between being stubborn and being obstinate. It's happened before, though under clearer circumstances.

Incidentally, I can think of a quicker, though obviously not official method. I'll see if I can get a particular person to weigh in--an electronics guy who happens to have an awful lot of clout in what actually gets inspected.

Re: Be aware of battery and charger inconsistencies!
 

As someone mentioned we can fuse it for 6A and that should remove all doubt from our situation and fallowing rules. From the previous linked documentation there is absolutely no danger even if it were to charged at 15A with these chargers, there simply is no safety risk other than a couple people's fear of what they don't have knowledge of. Well no more safety risk than any other charger that is. This is not a valid reason to restrict equipment when there is information showing it's perfectly reasonably safe.

I also don't see how a robot inspector can deem something illegal when he has no rules to base it off of and how the equipment you use can prevent a robot's inspection. The tools you use to maintain a robot have nothing to do with robot inspection requirements. He may state something is unnecessarily unsafe and needs to be addressed but he can't just outright deem something illegal of his own will when we can prove the opposite. Or maybe they have some secret powers i'm not aware of.

I know i'm being stubborn, both because our season depends on it and because i honestly don't think we're in the wrong. If it wasn't such a critical thing I would just let it go but it's not something we can just let go without having a dramatic and devastating effect on us. It's either we can use these for trickle which is within all rules, or we can't do 3 ball autonomous and we will probably miss most shots because of battery inconsistencies.

So our two options are find a way to use these, or give up hope on doing well this season since we know full well we can't perform if we can't use something better than our old chargers. I don't think i'm doing anything different than anyone else would.

I'll post for an official answer the soonest opportunity I have I just haven't had that opportunity yet.

Re: Be aware of battery and charger inconsistencies!
 

Under Section 5.5 of the Game Manual, if "Event Staff" deem something unsafe, their decision is what is followed. Robot Inspectors do count as "Event Staff"--especially Lead Robot Inspectors, who are trained by FRC Headquarters. If the LRI rules your charger is unsafe and needs to be removed from the venue, that rule right there is all that is needed, and nothing can change that. (Which is why Q&A is the proper place to ask, because that's the one thing that has a chance at changing his mind.) Incidentally, I've asked the Lead Lead Robot Inspector to weigh in on this discussion, bearing in mind that anything posted here is unofficial.

If you hadn't been absolutely positive that you were legal (which you are now finding that maybe you shouldn't have been so positive--it never hurts to ask questions earlier), would you have chosen the same path in design?

There's a reason the field sizes are given with a tolerance--expect variations to happen. One thing a number of longtime veterans have learned is that the specs given are not necessarily totally exact. Case in point, the balls have been noted to behave differently at competition than at a lot of team facilities, for reasons unknown. Maybe you don't quite need full power to shoot as far as you want to--but you won't know that for sure until practice matches.

Wrong. You have a third option: Adapt. For example, I don't know anything about your robot, other than that it's a "kicker" type. I know you've tried a bunch of variables--have you tried a smidge more weight, strategically placed? What about different tip surfaces? Slight change in geometry? You have all day Thursday with the practice field and the pit and the event machine shop and the combined resources of however many teams are there and as many inspectors as opt to give advice--if a competitive robot can be built in less than 8 hours at an event, why can't a robot that doesn't quite have the adaptability it needs gain that adaptability? I might also note that if you have a tough drivebase, you can probably play some pretty tough defense or counter-defense, which can make you an attractive alliance partner.

Re: Be aware of battery and charger inconsistencies!
 

Fuses do not limit current. A 6 amp fuse can and will pass current in excess of 6 amps. It's been well stated that the FRC Safety Manual says to not charge in excess of 6 Amps.

Quote:

Originally Posted by FRC Game Manual At each event, the Lead ROBOT Inspector (LRI) has final authority on the legality of any COMPONENT, MECHANISM, or ROBOT. Inspectors may re-Inspect ROBOTS to ensure compliance with the rules.

Quote:

Originally Posted by T6 A Team is only permitted to participate in a Qualification or Elimination MATCH and receive Qualification Points if their ROBOT has passed Inspection. If it is discovered after the start of the MATCH that a ROBOT did not pass Inspection and the Team participated in the MATCH, the entire ALLIANCE receives a RED CARD for that MATCH.

I would strongly advise not going against the LRI. You won't win. Not just anyone can be a Robot Inspector, especially a Lead Inspector. LRI's, especially Big Al, who is the Lead Inspector of Lead Inspectors, have been in FRC for a long time and know what they're talking about.

Working within parameters is part of engineering. You had a specification that was given to you from the beginning of the season. Unlike many of the other rules, this one hasn't changed since I've been in FRC (2011). Successful teams will design robots that are impervious to as many outside factors, including battery charge.

You can modify your robot to account for the different battery characteristics. It's part of the engineering process.

Re: Be aware of battery and charger inconsistencies!
 

There is no need to get hysterical. You can follow advice from experienced FIRSTers and in my case 30+ years engineering experience OR you can ignore the advice and take your chances with the inspectors. It is always your choice.

The safety manual (quoted by others in this thread) limits many of your examples. Of course there will always be safety risks but some risks can be eliminated.

Let me make a constructive suggestion - why not drive forward a couple feet then shoot? It solves all your problems. You can't do a 2-ball autonomous anyways if one kick sucks the top end out of your battery.

Take a deep breath, solve the problem without risking the inspector's ire and good luck to you and your team!

Re: Be aware of battery and charger inconsistencies!
 

It may or may not be fair but you are DEAD wrong here. The LRI is the safety god for that weekend. Nothing one can say will change that.

You are talking about exposing your team to a huge risk. I can't caution you enough.

Good luck!

Re: Be aware of battery and charger inconsistencies!
 

A quick google search and looking at a fuse spec sheet later show that a 5 amp fuse will open in 2 seconds if exposed to a 6 amp current (For that model of fuse), while this does not 'limit' current, it does stop any flow of current if the level of current goes higher then rated for more then two seconds.
I don't see how any unsafe behavior can occur in that time.

And on another note, how many people have checked to see how many amps their chargers put out? Manufacturing tolerances do exist, and that 6 amp charger (which is already 'breaking' the rules) may put out slightly more.

If this enforcement of the rule was following the rules wording properly all chargers that have a 6 amp setting should not be allowed as they will go above the max charging current of 5.4 amps.

Re: Be aware of battery and charger inconsistencies!
 

I don't see how any unsafe behavior can occur in 2 seconds either, but I also don't see how a 10+ Amp charger will know that there's a 5 amp fuse and limit its current. You'll just blow the fuse every time you try and charge a battery.

Re: Be aware of battery and charger inconsistencies!
 

Yes because it's not the design that's in question. honestly we never imagine this would be an issue since we went through all rules and found no mentions. Even with the 6A rule it didn't bring the certainty into question either because we can easily abide by it. We know factually that we fall within all rules, so these claims that even though we know we are 100% completely legal yet run into the possibility of having something happen like this of something that isn't written down anywhere(like chargers over 15A being illegal according to the LRI) is absolutely ridiculous. It's a rule that's not stated as a rule. we worked within all constrains but now we find out that there are these other secret rules? what the hell that's completely unacceptable.

we may not, and that would help a lot, but until that moment we won't know and we will be counting on needing full power. But again the issue isn't the voltage they charge up to, it's the consistency that matters to us. If we have to be closer to make it fine, but when we do a battery swap currently the shots we made previously don't go in anymore, this is the issue i'm talking about. They are either too high or too low.


We tried everything at our disposal. Different transmission ratios, different speed controllers, different weights(in different locations),different kicker geometry, even different kicker transmissions types(from worm to bewel). Believe me when I say if it was within our capability we would have. We knew from the start it would creep up as an issue, and thought that getting good chargers was the fix.....what you said sounds like an absolute dream: "combined resources of however many teams are there" but that's not reality. There is nothing wrong with our kicker or robot, it's our chargers. all we want is a consistent charge, that's all and we thought we found the fix for that. Just like all the other things people mentioned saying stuff like this is easy, but actually doing it is a much different story esp considering the resources(in our case lack of). It sounds great on paper, but has no real basis in reality, at least from my own experiences.

Re: Be aware of battery and charger inconsistencies!
 

because it will never be in that state. when these chargers are used for trickle it will never draw more than a few amps. just because it can output 15A doesn't mean it will. I would be suprised if they output more than 1-2A in trickle and we'll put a 3A fuse on it in that case. The point is we can PROVE we don't break any rules yet this doesn't seem to be enough for these people.

Re: Be aware of battery and charger inconsistencies!
 

It would be very dumb for a smart charger to give a nearly fully charged battery 15 amps, the charger in question may, I don't have one and have no way to test that, but the fuse would ensure the charger falls on legal grounds.

Re: Be aware of battery and charger inconsistencies!
 

Do yourself and your team a favor and leave those chargers at home. If the robot's performance depends on an absolutely fully charged battery then invest in some high quality chargers that will pass the scrutiny of the LRI.

You keep saying that your season depends on using these chargers. As an LRI I say your season is in jeopardy due to bringing these chargers in the door.

Putting a fuse inline will not help matters. Using these chargers to "top off" the battery won't work unless you have either given them time for the surface charge to dissipate or you put a load on them to remove the surface charge. Option one means wait several hours minimum to charge and putting enough load on it to remove the surface charge quickly and consistently means that the starting charge rate of the charger will likely blow the fuse.