Re: Legal battery chargers this year.
 

Big thanks, Al! We did make some subtle adjustments to our drive style and the issue did not occur once after we made the breaker swap like Kyle mentioned. We were icing it down between matches, as well, and are looking at all of our options for making sure we keep that breaker cool and untripped in St. Louis whenever that defensive intensity cranks up. Thanks again for all your help!

Re: Legal battery chargers this year.
 

Anytime, Good Luck!

Re: Legal battery chargers this year.
 

I guess I'm hijacking the thread a bit but want to capture a potentially important "gotcha" issue related to battery connections that Alan's post helped to job some cobwebs in my brain.
Alan,
At the MI Howell district event we even had someone (FTA?, Inspector?) come by and inspect our PD distribution board connections (12V & ground) to the battery to help eliminate this potential problem issue (assume he was going around to all teams.. we had not reported any issue). I can't remember precisely but he quoted something like "teams commonly place a lock washer underneath the battery connection to the PD board when, if used, it should be placed on the top, next to the nut".

Al S, is there any "best practice" on this battery connection to the PD board and main breaker that teams are missing?
I assume there should be a direct connection from the battery connector to the PD board post. Should the FRC
documentation trail capture this somewhere?

Re: Legal battery chargers this year.
 

Marc,
It is likely that someone visited you because the tracking logs showed you undervolt. The terminals on the main breaker and the PD are hard metal compared to the soft material used for the battery terminals and they don't get handled as much. The lock washer between the battery terminal an the wire terminals keep the terminals from twisting and loosening the hardware. Both the PD and the main breaker have substantial hardware with lock washers. Most often these wires are also tied into the robot so that they cannot move and twist unlike the battery. Any loose connection in the primary wiring (All the #6 AWG) will cause significant voltage loss under the current demands of our typical robot. These losses are what shows as melted SB50 plugs and wiring and to a much lesser degree, tripped main breakers.

Re: Legal battery chargers this year.
 

I hate to disagree with all of you but if you read the Enersys application manual for our batteries it does clearly state the maximum charging rates on page 6. The confusion seems to be the fact that the bolted terminal line says 6CA. All the other columns are specifically amps. If you go to page 17 you will see the definition of CA and the line above with c-rate.

The actual max charging rate on our battery is 6 times the Ah rating or 6*17.2 for a max of 103.2A. Would anyone ever charge at that high a rate? I would expect not. If you look at the other columns in the chart on page 6, why on earth would you be able to charge at 75A maximum through a normal spade terminal and only 6A through a physically bolted connection. That just doesn't make any sense at all. The most important thing with these batteries is not the amperage that you charge at, it's the voltage which should be 2.35-2.45 volts per cell or 14.1-14.7 volts.

It's all about reading the manual correctly.

Re: Legal battery chargers this year.
 

What manual are you reading? The one I see says the maximum suggested charging current is 0.25CA, and it says the battery won't accept more than 2CA in any case.

Re: Legal battery chargers this year.
 

You are reading page 11 under initial charge current limit. Go to page 6 in the chart at the bottom which lists "Maximum Permissable Current(Amps)"
You will see "All bolt or recpetacle" lists 6CA which is 6 time the Ah rating of the battery. In our case 17.2 times 6 = 103.2A maximum Amps.

The battery charger should be a smart charger with voltage limiting based upon state of charge. I verified all this information with my battery supplier and was told that you cannot overcharge these batteries unless you charge at too high a voltage. He recommended no more than 30A or so, but for longer battery life 10-20A max would be ideal.

Re: Legal battery chargers this year.
 

That sure looks like a maximum discharge current spec to me. The maximum charge current of 0.25CA appears immediately below it, as well as being repeated in the charging section on pages 10-12.

I don't know what your battery supplier thinks he's telling you, but 30A is more than five times the recommended value. "High charging current can cause abnormal internal heating which may damage the battery."

Re: Legal battery chargers this year.
 

Here's the document in question.

I agree. That's the current that can safely flow through that particular type of terminal, which basically has to be a discharge (except in the standby case).

We should consult the charts and data in the rest of that manual for the actual recommended charge current for the entire battery, which in normal service is 4.3 A (i.e. 17.2 A·h capacity at a 0.25 C rate of charge).

Charging at 6 A may not necessarily kill the battery or be unsafe, but it is outside the manufacturer's specifications for normal use. You should contact an EnerSys application engineer for guidance; they may be able to advise that 6 A or more is acceptable, at the cost of shorter battery life. (If that's indeed what EnerSys says, feel free to post the correspondence here and forward it to frcparts@usfirst.org so that they can keep it in mind for future years' rules/safety manuals.)

Re: Legal battery chargers this year.
 

The table with the "6CA" reference gives the current ratings of the various types of terminals available with the Genesis product family. It is NOT any sort of current rating for any of their batteries, in any mode of operation.

The section below, titled "Charging", shows how to choose the charging current.

We install about a ton or two (literally) of batteries from this series each week in the industrial grade UPS' we manufacture where I work. Our UPS' charge the batteries at about 0.1CA to maximize the service life of the batteries. I have spoken with the Application Engineers at Enersys multiple times about service life issues. Using a charging current that is too high is one of the major factors that WILL reduce service life (along with over-charging, discharging too deeply, discharging at very high currents, operating in high ambient temperatures and not cycling the batteries).

Re: Legal battery chargers this year.
 

I've heard that term "cycling the batteries" before but I'm still uncertain of its precise meaning. I'm sure it has nothing to do with certain popular two-wheeled vehicles. :cool:

Re: Legal battery chargers this year.
 

Cycling the batteries, just means to use them occasionally. Don't let them sit for half a year without being discharged and then recharged.

And never let them sit after being discharged...always recharge before storing.