Battery Chargers
 

So it's that time of year again - we're coming up to kickoff and we're frantically scrambling to make sure our labs are ready for the onslaught of activity. One of the things we're doing for this time-honored tradition is getting some new battery chargers.

So before I start discussing my options, I just want to make sure that I understand the recommended specs for FRC battery chargers. My understanding from experience and the spec sheets for the ES17-12 and NP18-12 tells me that battery chargers should (must) meet the following specs:

• Nominal output voltage between 14.4V and 15.0V
• Nominal output current between 4A and 6A, despite specified max charge currents
• Capable of charging 12V sealed lead acid AGM/gel batteries

Do correct me if I'm wrong.

That being said, there are the two obvious options: the Schumacher SC-600A and AM's AM-0026. I believe I've also seen CTEKs around.

While doing some browsing, I also came across this option, which says that it can support up to 6 batteries at once, and the spec sheet says that they have to be charged in parallel from the charger's single output - can anyone offer some insight into how exactly this works and whether it's a viable/safe option for us?

Alternatively, does anyone else have any other recommendations? (besides FIRST Choice).

Thanks!

Re: Battery Chargers
 

Do we know that both FRC batteries are indeed AGM and not gel? It's not specified in either of the datasheets.

Re: Battery Chargers
 

I recall seeing a post from Al way back when mentioning that both batteries are AGM, although I couldn't find it when I tried searching, so I could be wrong there.

I stand corrected. The ES17-12 is a AGM, the NP18-12 a gel.

Re: Battery Chargers
 

We have the three-bank charger from AndyMark, it has worked well for us. I much prefer the SB50 connectors to the clips.

Wetzel

Re: Battery Chargers
 

I recall 2815 using Schumacher chargers we bought from Walmart (but I've seen the same design with several other manufacturers' labels on them). They were about $25 each; we cut the leads and added an Anderson connector; they've held up fine for two seasons now.

(Fun fact: Once, we had a car with a dead battery at the shop. We took a spare Anderson connector, then connected jumper cables to the bare leads, then hooked THAT to the battery. Sure enough, car started.)

Re: Battery Chargers
 

Quick correction, last years rules specified the NP18-12 which is also an AGM design. For most types of lead acid batteries the charger is a voltage type. This means that the charger adjusts the output voltage as a method of controlling the charge current. An 8 amp charger uses a higher output voltage than a six amp charger. The Enersys data sheet recommends..."• Cyclic use: Apply constant voltage charging at 2.40-2.50 VPC. Initial charging current should be set at less than 0.25CA." Stated another way, 17.2AH * 0.25 = 4.3 amps and 2.5v * 6 cells is 15 volts. It is my opinion that 6 amp smart chargers will not stay at the full 6 amp charge currents for very long when charging these batteries making 6 amp chargers OK for our use. In discussion with MK engineers several years ago, they felt that higher charger currents (and the implied higher charge voltages) might cause internal cell arcing between the plates. This might lead to permanent damage to the cell(s) in the form of a internal short. There are a variety of factors that play into this so testing at higher charge voltages would not reveal consistent results but the specified max charging current is what MK felt was safe. For our purposes, most teams using 4-6 amp smart chargers have very little problems in charging or battery life. The critical factor for our use is the deep discharge and current demand we make on these batteries during competition. Under normal FRC usage, I tell teams to expect no more than about 400 charge/discharge cycles before the battery can no longer supply current for competition matches. If your robot is regularly depleting the battery in one match, life expectancy is even less. About 80 % of the failed batteries I see at competition are due to mishandling (dropping).
The charger shown above can be used but I would not recommend (nor was it legal in 2012) to charge at 8 amps.

Re: Battery Chargers
 

when I returned to Brazil after one month in U.S attending the FIRST , my car was dead and i did the same, worked perfectly:yikes:

Re: Battery Chargers
 

Th AndyMark triple charger am-2026 is a wonderful device. It does its job, and is foolproof and easy to use. You don't have a tangle of power cords, and the charging/ready lights are very easy to see.

I'd like to make a small mod to ours, to label the three charging connectors 1,2,3 so that it's easier to find which battery to unplug when a green light is showing.

Re: Battery Chargers
 

The problem with charging batteries in parallel from a single output is that each battery is in slightly different condition and state of charge. They try to work around this by giving the following conditions in the manual. I don't trust that you could ever guarantee this, so I don't think it's safe.
Additionally, notice that this is only to maintain the batteries, once they are fully charged. It won't charge 6 batteries.

Re: Battery Chargers
 

We also have two of the AndyMark am-2026 trichargers. We got them last year and love them, they allow for more batteries to be charging at once with less space required then the KoP chargers. If you are looking around, I would recommend the am-2026.

Re: Battery Chargers
 

Just to be clear, according to the datasheet, the NP18-12 is AGM. Check the 2013 rules (once released) to determine whether the NS18-12 is legal. (Are you sure that NS18-12 is even a valid part number?)

Re: Battery Chargers
 

Another related question...how many years do other teams use the same battery? It seems like after just a couple years of competitions, we've got some batteries that are bad. It can't help charging at such a high charge current during the days of competition (we have maybe 8 batteries total on our team?)

Re: Battery Chargers
 

And by "bad", I'm referring to the fact that for a couple of our 3 year old batteries have an internal resistance double that of one of last year's batteries. I assume oxidation buildup on the plates.

Re: Battery Chargers
 

Many teams get new competition batteries every year.

Re: Battery Chargers
 

How many batteries do your teams take to competition?
Ann

Re: Battery Chargers
 

We typically cycle them after every match. Around 8 total.

Re: Battery Chargers
 

We have around 9. We also cycle them every match.

Keep in mind every rookie will get 2 batteries, and every veteran will get 1.

Re: Battery Chargers
 

Going on precedent, but without the 2013 KoP list we don't actually know for sure...

Re: Battery Chargers
 

Re: Battery Chargers
 

Do not try to charge batteries in parallel please. I asked this question of MK and The Battery Association of America (I think that was the name) and both responded that the only way that was acceptable was if the batteries were all purchased at the same time, had been charged the same and had the same loads applied over their lifetime. And then it may work or it may damage all of the batteries. In other words if the batteries were assembled into a larger array and only used that way could other methods of charge and discharge be used. These batteries are not like the large arrays used on electric subs or in large UPSs where the acid is checked regularly and specific gravity is monitored cell by cell.
The best way to test batteries is to use an analyzer like the CBA III from West Mountain Radio. when they can no longer supply more than 15 amp hour, I would move them into the practice pile. When they fall to 10-12 amp hour, then it is time to recycle. If one cell dies before the others, recycle immediately, that cell is likely damaged internally. The Battery Beak from Cross the Road Electronics should also indicate when to remove the battery from competition.

Thanks! Missed that.

Re: Battery Chargers
 

I aim to please. :cool: :rolleyes:

Re: Battery Chargers
 

We bring 8. Enough for testing, matches and loaning.

Wetzel

Re: Battery Chargers
 

Typo on my behalf, I was referring to the NP18-12. Sorry!

We won't be getting the BatteryMINDER, but if we had my intent had been to run it at 4A, not 8A. I understand and see the reasoning behind your perspective that 6A is a purely nominal maximum setting, but I still can't help but be mildly uncomfortable charging batteries rated for max charge currents of 5.1A and 4.3A at "6A" (let alone 8A!)

I thought as much - I was rather skeptical of the method when I noticed it, because I just couldn't see charging them in parallel as a safe method, given that batteries often tend to differ from unit to unit. Thanks for confirming.

We buy a new batch of batteries every year, since most of our robots tend to err towards ridiculous power consumption. Our competition batteries tend to consist of mostly ones we buy that year, supplemented by ones from the previous two years that have good max charge records (we made a simple battery tester in-house that displays the battery voltage measured across a small load on an LCD screen; a "good" max charge record, with reference to our usage, tends to mean that it consistently charges up to 12.5V or higher).

We bring 8 with us. During qualification matches, we'll often have as many as 3 at full charge (the rest are either charging, in the robot for practice/testing/matches, or being used for auxiliary 120VAC through an inverter), but we make sure every battery is fully charged (or as many as possible) going into elims, because of the rapid turnaround time between matches.

Thanks to everyone for the outpour of feedback :)

I'm still curious if anyone has found success with alternatives to the Schumacher and Dual Pro. Speaking of which, it seems that Dual Pro makes an IS3 along the RS3, but I can't seem to identify a difference between the two... :confused:

Re: Battery Chargers
 

Our batteries last 2 or 3 seasons generally, sometimes more. It is critically important to keep them fully charged, even over the summer, since A) they are damaged by sitting even a little discharged and B) they have a self-discharge that requires charging every 60 days or so.

We have 10 to 12 batteries we bring to competition.

Re: Battery Chargers
 

My team usually ends up buying 2-4 batteries each year. We use the best ones at competitions and relegate the older ones for practice or shop testing.

After a team accumulates a lot of batteries, keeping track of their age and condition is a chore. I have ours labelled and we keep a log at competitions. We are careful to use them in sequence, so that the last one used gets to charge and rest while all the others are used. Every battery is labelled with a number and we follow that sequence.

We test every battery once at the beginning of the season on a West Mountain CBA-III. It's a wonderful device which gives a real picture of the battery's condition, but it is time-consuming, often more than an hour per battery.

This year, we are considering buying fresh batteries for competition and calling everything from previous years either practice batteries, or recycling. You can get through most regionals with 6 batteries as long as they are good ones. Use a fresh battery for every match - never more than one match. You have enough time to charge the battery from your first match well before you reach a seventh match.

Put one person on your pit crew in charge of batteries so that they always know what is going on with them. Have them keep a log on a clipboard to track what time the battery went on the charger and when it came off. Analyzing these logs later can identify both weak batteries and defective chargers.

We have a battery manual for the team and review it with the entire team once a season. It covers everything from theory to handling to use and charging to spill procedures and recycling. A copy is kept in the pits for reference.

Re: Battery Chargers
 

Does any one have a solution to running the robot from A/C power? A A/C to 12V converter that's safe for the circuitry.
I seem to recall seeing one on AndyMark, but I can't find it now. This would be handy for programming and imaging.

Thanks

Re: Battery Chargers
 

How much of the robot do you want to run?

A simple 12 volt power supply at a few amps will handle the control system and sensors. You can do a lot of software development that way. It's probably best to use a linear supply, as a fancier "switching" power supply is likely to balk at the boost regulators in the Power Distribution Board.

Motors are another thing entirely. If you want to be able to supply the same kinds of current you can get from a robot battery, you'll end up with something huge, heavy, and expensive.

Re: Battery Chargers
 

We started using these chargers last year after suffering with poor performance from past and present kit chargers, we were loosing them 1 by one.



http://smartercharger.com/products/b...-multi-us-4-3/

Our new battery cart with 6 of those things with all their LED's glowing on the front sure generated a lot of attention at the AZ regional last year.

It's the only charger I will use on small backup generators, and battery backups now too.



We also load tested and purged all of our old and failed batteries and got fresh ones so now we roll with 12 good batteries and 6 good chargers.

Re: Battery Chargers
 

Batteries or chargers? The charger shown appears to be a nice alternative.

Re: Battery Chargers
 

The chargers, 2 of our schumacher smart chargers failed last year.

It became very apparent at our pre regional event last year that we would be in a world of hurt if we didn't get out batteries in line quickly. We were putting out fully charged batteries according to some of the chargers only to have them go dead as soon at the drive team pushed the joystick forward.

We also had some of the older black dumb chargers in use and we ditched those too. 6 amps is too much current, and the user interface sucked, especially if you were in a hurry. I think that led to kids taking partially charged batteries and using them.

Our load tests also weeded out a few batteries that we had gotten our monies worth and then some.


Also all batteries are now dated and numbered instead of just dated so we can alternate and spread the wear and tear more evenly.