[bensherman]

Originally Posted by Chris Mormile

Hi, I am the battery guy (aka Battman) for team 1676.
We have 10 good batteries and 6 chargers. Each battery is 18Ah. Each charger can charge at up to 6 amps. By basic math it takes a battery that is 1Ah (in capacity) that is being charged at 1 amp, 1 hour to charge. So our FIRST robot batteries will take 3 hours to charge because they are 18Ah and are being charged at 6 amps.

If we were to purchase chargers that could charge batteries at, lets say 8-10 amps (which would result in faster charge times). There is always the possibility that we could blow the batteries up. And if we didn't blow the batteries up we would wear out the batteries faster then if we charged them at a slower rate. Basically we would have to replace batteries every year rather than every 2-3 years. And that would cost teams a lot of money. As a set of 2 batteries from ANDYMARK are $83.00.

Also we could purchase non-competition legal batteries that were the same physical size or larger and use those during driver practice. But on the other hand you don't want to be driving around with a 40lb marine battery running your robot. you may get exceptional run-time but it will cut into the robot's performance. Batteries that are the same physical size but have a higher capacity would be ideal for use, but they would cost teams even more money, and could possibly run teams $100+ per battery.

Also there is another aspect to charging times. This applies to all batteries. As batteries become more charged they will start accepting less and less voltage. therefore it will take longer to charge. The first 75% of a battery charge will take approx. as long as the last 25%.

And finally the last factor in run-times is the heat that you generate. As you run your robot more and more electronics start to heat up naturally. But the parts that heat up the most are the connections from the battery terminals to the PDB. Also the motors Heat up quite nicely to the point that they will burn you. And finally if you have a compressor (we have had the past 2 years) your battery life will go out the drain (plus that heats up quite well too). Parts like the C-RIO and ESCs wont heat up as much for one of two reasons. 1) they have a fan or 2) they dont have as much power flowing through them.

I think i have covered all of the bases of run-time and charging time. Please let me know if you still have questions...

Chris, since FRC batteries never get down to 0v during competition (or practice), there's always some charge left on it, so it shouldn't take 3 hours to charge a battery that was normally used.