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!

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

[strike]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.[/strike]

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

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

Wetzel

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.)

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.

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:

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.

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.

BatteryMINDer 12248 maintenance charger
Desulphators can be used to maintain up to
six (6) 12-volt batteries at a time, providing each
battery is fully operational (no dead-dying cells),
free of sulphate and meeting the minimum full
charge “rested” (see pg. 9) voltage of 2.13 volts
/ cell, after being fully desulphated.

Additionally, notice that this is only to maintain the batteries, once they are fully charged. It won’t charge 6 batteries.

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.

Just to be clear, according to the datasheet, the N[b]P18-12 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?)

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?)

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.

Many teams get new competition batteries every year.

How many batteries do your teams take to competition?
Ann

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

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.

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

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.