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.

-Upon the recommendation of another team(sorry forgot which) we currently use:

(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

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.

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

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.

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

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. :slight_smile:

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

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.

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.

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.

Safety Manual, Page 8.

Do not charge battery at greater than the manufacturer’s maximum recommended rate.

As said above, the recommended rate is 6 amps.

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.

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

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.

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.

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.

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…”

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:

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.

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.

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

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.