Battery Chargers

[tuXguy15]

This past season we used the 6amp charger on our batteries from andy mark. This gave us up to 13 volts for a full charge but the FRC batteries can go up to 15 max. Our team knew this would happen and knew that our batteries would be destroyed by the end of the season. Well we were right. So over the off season we plan to develop a battery charging cart that will charge the battery at 2 Amps for a while, then 4 Amps, and then 6 Amps to get our batteries at full complicity and keep them living longer. Does anyone have any ideas on how we can make this possible?

[jbsmithtx]

Your batteries were zapped after one season? I think there's a bigger problem here.. We've had 8 batteries now, and after 2 seasons none of them show any signs of slowing up any time soon... Nearly all of them charge up to about 13 every time.. Do you leave them on the charger over night? Was your robot intensely power draining?

[mman1506]

Originally Posted by tuXguy15

This past season we used the 6amp charger on our batteries from andy mark. This gave us up to 13 volts for a full charge but the FRC batteries can go up to 15 max. Our team knew this would happen and knew that our batteries would be destroyed by the end of the season. Well we were right. So over the off season we plan to develop a battery charging cart that will charge the battery at 2 Amps for a while, then 4 Amps, and then 6 Amps to get our batteries at full complicity and keep them living longer. Does anyone have any ideas on how we can make this possible?

Charging a battery to 15v will not make it last longer, it is the other way around. The 6 amp charger will go green at 13v but will charge up to 14.6 if you leave it to maintain the battery. The best way to charge a battery is by charging the battery at 6 amps then slowly lowering the amperage as it gets closer to a full charge.

If you want to charge to 15v every time get one of these (http://www.hobbyking.com/hobbyking/s...er_w_acc_.html (It dosen't list lead acid charging in the ad but it does have it). It has adjustable endpoints and charge rates.

[tuXguy15]

This year our robot drew a lot of current and it killed the batteries when we had to keep recharging them constantly. Also i know that 15 volts wont last longer. My point is that we are not managing our batteries right if we arent getting 15 volts. The 6 amps wont get it there because doing a 6 amp charge does not allow a peak and level type of charge that those types of batteries need. You do 2 amp until it peaks then 4 until it peaks then6 to finish charging it's.

[mman1506]

Originally Posted by tuXguy15

This year our robot drew a lot of current and it killed the batteries when we had to keep recharging them constantly. Also i know that 15 volts wont last longer. My point is that we are not managing our batteries right if we arent getting 15 volts. The 6 amps wont get it there because doing a 6 amp charge does not allow a peak and level type of charge that those types of batteries need. You do 2 amp until it peaks then 4 until it peaks then6 to finish charging it's.

No it's the other way around. once it peaks you lower the current, lowering the voltage under load allowing you to put more power in. http://batteryuniversity.com/learn/a...d_acid_battery

[Tom Line]

Originally Posted by tuXguy15

This year our robot drew a lot of current and it killed the batteries when we had to keep recharging them constantly. Also i know that 15 volts wont last longer. My point is that we are not managing our batteries right if we arent getting 15 volts. The 6 amps wont get it there because doing a 6 amp charge does not allow a peak and level type of charge that those types of batteries need. You do 2 amp until it peaks then 4 until it peaks then6 to finish charging it's.

Something is fishy.

We constantly charge our batteries. We have 10 'competition' batteries, with another couple that we keep to charge the inverter on our cart. We draw plenty of current from the battery, and it's not unheard of for us to see the batteries drop to 6-7 volts when we're driving on our practice field. Nothing you've said leads me to believe that your batteries should be dying.

Our batteries fresh off the charger come in at just a touch over 13 volts, but let sit for a couple minutes for the surface charges to drop, they go down to 12.8 - 12.6. When our batteries are not on the robot, they are always on charge. I question your assertion that the batteries should be at 15 volts. I have never once seen an FRC battery come off a charger at 15 volts, and would worry if they did.

I think we need some more info. Are you running matches on the batteries without fully charging them? Are you overheating them?

Again: these batteries (generally speaking) should not die after a season of FIRST use if handled correctly. We have heavily used batteries from 2008 still going strong, and our last 2007 ones just failed this past year.

[fb39ca4]

This charger from HobbyKing is about half the price when you factor in shipping weight, and also charges at 6 amps. I have one for charging Li-Po batteries at home, but I brought it to a competition, and it works great for FRC batteries. http://www.hobbyking.com/hobbyking/s...cessories.html

Keep in mind for either one you will still need to find a power supply. Laptop chargers as long as they are >6A and 12V and ATX power supplies both work great.

[spydan]

This thread may be of use, our team purchases from this company:
http://www.chiefdelphi.com/forums/sh...d.php?t=110031

[Billfred]

Mind you, many other things (current draw on the robot, cycles of use on the robot, physical abuse seen on and off the robot, storage conditions) can also determine how long a battery will last before it's due to retire from the match rotation.

On 2815, our standard procedure is to charge at 2A at home and overnight at competitions, then 6A during the day at competitions to ensure we have enough batteries ready. We also started using a Battery Beak to spot-check battery health; if you don't have one, another team nearby might.

For the capacity of these batteries, 6A until automatic cutoff shouldn't have serious negative effects...but we figure it's better not to tempt fate.

And even if your batteries have weakened to the point that they're not optimal for match use, never underestimate the utility of batteries for powering your electrical board during testing, or for powering an inverter for laptops in the stands. (I've seen a scouting team with a small cart that held a robot battery, an inverter, and a network switch for their laptop-based scouting network. Kinda slick.)

[mman1506]

Originally Posted by fb39ca4

This charger from HobbyKing is about half the price when you factor in shipping weight, and also charges at 6 amps. I have one for charging Li-Po batteries at home, but I brought it to a competition, and it works great for FRC batteries. http://www.hobbyking.com/hobbyking/s...cessories.html

Keep in mind for either one you will still need to find a power supply. Laptop chargers as long as they are >6A and 12V and ATX power supplies both work great.

I have that charger but it only changers at 50w vs 150w on the other one(Meaning on a 12v battery it will charge up to 4.1 amps on the 50w or 12.5 amps on the 150w) A boat battery makes a great portable power source.

[fb39ca4]

Originally Posted by mman1506

I have that charger but it only changers at 50w vs 150w on the other one(Meaning on a 12v battery it will charge up to 4.1 amps on the 50w or 12.5 amps on the 150w) A boat battery makes a great portable power source.

It charges fine when I set it to 12v/6A. It just gets a little warm, that's all.

[mman1506]

Originally Posted by fb39ca4

It charges fine when I set it to 12v/6A. It just gets a little warm, that's all.

did you check the actual amperage on the screen. You can input up to 6A but it will only go up to 50 watts as it is the lower limit.

[Tristan Lall]

Originally Posted by tuXguy15

This past season we used the 6amp charger on our batteries from andy mark. This gave us up to 13 volts for a full charge but the FRC batteries can go up to 15 max.

While you can safely charge AGM 12 V batteries at 15 V in certain conditions (smart charger, proper current and relatively low ambient temperature), they won't hold 15 V for long, if at all.

Test them under a small load like the Battery Beak does to get a more reliable voltage measurement. Test them under a moderate load like the CBA tester does to get an idea of voltage performance throughout a full discharge cycle.

Here's some data for the MK batteries, and the old (no longer FRC-legal) Exides.

Also, Al will likely be around shortly to explain more thoroughly why various forms of overcharging are contraindicated.

[tuXguy15]

Ok thanks guys ill check into these and Billfred the issue is that when you constantly do a direct 6 Amp charge and not 2 and 4 it damages the batteries. The second we take them off the charger they start dropping voltage even when not being used. That is the effect of the constant 6 amp charge.

[protoserge]

Can you answer some more basic questions?

1. How many batteries did you use this season?
2. Did you have a process for use such as a serial number and a cycle schedule?
3. Were you fully charging batteries before taking them off the charger?
4. Were you putting them back on charge immediately after use?
5. Did you Battery Beak them before and after use?
6. Did you maintain their charge through the pre-season?
7. Did you fully charge them before first use?

You easily can kill batteries by the method you described if you are not cycling (keeping an even usage) and charging them appropriately.

I'm paging our battery experts. Hopefully they will chime in soon.