Legal battery chargers this year.

[Maximillian]

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?

[Nirvash]

Originally Posted by Maximillian

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?

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.

[swootton]

Originally Posted by Nirvash

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.

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.

[Alan Anderson]

Originally Posted by swootton

It's all about reading the manual correctly.

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.

[swootton]

Originally Posted by Alan Anderson

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.

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.

[Alan Anderson]

Originally Posted by swootton

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.

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.

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.

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."

[Tristan Lall]

Here's the document in question.

Originally Posted by Alan Anderson

That sure looks like a maximum discharge current spec to me.

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.)

[philso]

Originally Posted by swootton

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.

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).

[Bill_B]

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.

[MrForbes]

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.

[Ether]

Originally Posted by Maximillian

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?

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

[Maximillian]

Originally Posted by Ether

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

Originally Posted by Nirvash

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.

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.

[Bill_B]

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.

[cgmv123]

Originally Posted by Maximillian

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.

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.

[Calvin Hartley]

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.