Legal battery chargers this year.
 

My team was wondering about what chargers are legal this year. We have heard that in past years there has been a 6 amp limit but this year we cant find anything talking about chargers in either the game or administrative manual.

Does anyone have any clarification on this rule?

Re: Legal battery chargers this year.
 

You can not charge a battery at a rate higher then 6 amps, (about the max charge rate of the batteries we use) This is stated in the safety manual.

This is generally enforced by limiting chargers to a max rate of 6 amps. However certain special conditions could allow a charger with a max rate greater then 6 amps to be used.

Re: Legal battery chargers this year.
 

http://www.chiefdelphi.com/forums/sh...3&postcount=11

Re: Legal battery chargers this year.
 

Thanks for the help.

My team is also wondering how many batteries your team brings to competition. We have a 6 CIM drivetrain and are worried about not having enough batteries fully charged.

Re: Legal battery chargers this year.
 

I consider 6 batteries to be an absolute minimum for a competition. Now that we are a district, with 12 matches (at least) per event, this became an even more solid conviction. We have a charger cart with four chargers that makes us comfortable with 8 batteries. This partly due to doing only one match per battery and monitoring the battery state after each match just before it joins the charging cycle. At matches we set the charge rate to 4a.

Giving each battery a name will also help you keep track of the good versus the marginal performers and allow a cogent cycle of use to be formed for them. We use a battery beak to monitor the battery state. They are pricey, but the beak helps you manage your several hundred dollar investment in electron storage and feel confident that your robot has as decent a chance at getting through a match as you can give it. You also get the chance to see which of your stable of energy may only be suitable for practice or control system testing.

Re: Legal battery chargers this year.
 

With 6 CIMs, you'll most likely want a new battery every match. This will come up most in eliminations. There are extra batteries available for teams in eliminations that need to play back to back matches, but plan on having at least 6 batteries fully charged and ready to go for eliminations.

Re: Legal battery chargers this year.
 

We have a 3-charge bank and bring plenty of batteries. I think we bring 10-12ish, but I am not sure. We change the battery before every match.

Re: Legal battery chargers this year.
 

I think the amount of batteries will depend on how you use them. Previous years with us not using pneumatics, 4-6 batteries with two chargers was very adequate.

If you have a lot of pneumatics and plan on pre charging a bunch of tanks in queue you could need quite a few batteries and chargers to keep up.

This year we are using a lot of pneumatics and are bringing 10 new batteries and some of our previous years batteries for pit demos (LED shows and such for the pit visitors). We will be bringing 5 (6amp) chargers as well. We also plan on using the previous matches battery for the pneumatic pre charging and swapping in a fully charged battery when the robot is ready to load on the field.

Good luck this season,

Aloha!

Re: Legal battery chargers this year.
 

You might want to be worried about tripping the main breaker. At least two teams in Wisconsin tripped multiple times with a six motor drive train.

Re: Legal battery chargers this year.
 

We were kind of worried about this being an issue. I hope it doesn't end up being a huge problem.

Re: Legal battery chargers this year.
 

Oh, is that why 2481 kept dying during eliminations? I know in at least two (maybe it was three) matches, they dropped dead in the middle of the field (no signal light), after a rough pushing match.

Re: Legal battery chargers this year.
 

Yes in between SF 1 and SF 2 we switched out the main breaker. After that it never flipped again. We were also cooling it between matches. Realize we had 8 motors for our swerve drive. 4 CIMs and 4 BB RS775(I think). The wires between our battery and PDB were getting quite warm so we are planning on lowering the gauge for nationals to better handle the current.

Re: Legal battery chargers this year.
 

I saw three robots with tripped main breakers at the Boilermaker regional. In each case, only one of the wires was warm. The apparent cause was not too much current, but simply too much heat from a poor connection caused by a loose nut where the wire connects to the breaker.

Loose main power connections -- on battery terminals, SB-50 connectors, main circuit breakers, and/or Power Distribution Board inputs -- were unfortunately very common. It'll be interesting to see if the logging feature of next year's PDB will help convince certain teams that their general animosity toward "the FMS" is misplaced, and that their loss of robot control on the field can usually be prevented with a bit more attention in the pits to checking and maintaining the robot's electrical system.

Re: Legal battery chargers this year.
 

I didn't realize teams did anything different.

Re: Legal battery chargers this year.
 

Kyle,
I think the drivers just became a little less aggressive in the subsequent matches as I had suggested. If you go back to the old ways, this problem will revisit you. You know I have a vested interest in keeping you guys running, you gifted me and I am returning the favor.

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.