Battery Chargers

[Jon Lawton]

This year's battery is 12V at 18Ah, the charger is somwhere about 14V at 1A.

Last year's battery is 12V at 17.5Ah, the charger is some voltage I don't know off the top of my head, at 4A.

So... assuming the charging is 100% efficent (HAH!):

18A at 1A/hour = 18 hours
17.5A at 4A/hour = 4.375 hours

Remember though, these values are for a *totally* dead battery (and they are a little small, I can gaurentee that it won't charge at 100% efficency)!

I'd reccomend charging your batteries up all of the way, and putting some kind of ammeter on your robot and charger. This way you can have a pretty good idea of the charge state of the battery.

Why did FIRST give us this *WIMPY* charger this year? Why do they care what we use to put energy back into the battery? This, I think, is most uncool.

[Matt Reiland]

Were bringing last years chargers anyway, I can't see why if they were legal last year they wouldn't be this year, besides we now have four of them from over the years. I like the fact that the new one is small but our robot eats monster current this year and normally puts the low battery LED on after about 5 minutes tops.

[RicNic_team930]

I'm on a rookie team. We don't have anything from last year to use. or extra money (were going to nationals) 1 battery lasted for about 3 4 hours of testing and a full batery lasted more than 2 hours of continous compition we did with other WI teams so i dont see why 2 fully charged batteries won't last for a day.

[Wetzel]

*Not on control systems. I understand the concept*

It all depents on the load you are pulling. A bot with a 6 moter drivetrain will pull more than a 2 moter drivetrain. And if you spend all match in a tug-of-war, driving the moters near stall vs a ball getter where you are not running the moters so hard.
And if you are running the bot around alot, take breaks to protect to moters.

Hmm...
As I think about this, what if this was intended as an equalizer this year but no one noticed?

[Tom Fairchild]

Originally posted by Matt Reiland
our robot eats monster current this year and normally puts the low battery LED on after about 5 minutes tops.

I can tell you that the LED light that tells you if your battery is low is not really to be trusted. It turns on when the battery drops to a certain voltage and it doesn't matter if it stays there or not. Our robot you can drive for 30 sec. and the light will come on if you gas it full forward quickly. The thing to keep your eye on is the actual voltage on the control system display.

~Tom Fairchild~

[Al Skierkiewicz]

To All,
I saw some disturbing reports here and I want to make sure everyone is on the same page.
To the team that is charging from dead to full in one hour, cease and desist. The internal heat from that kind of charge cannot escape or conduct to the outside quick enough for you to stop the charge when the battery gets warm. If you are able to full charge in an hour you are most likely charging at 18-20 amps. This amount of current if it doesn't blow the battery will surely damage internals. The kind of damage will show up when you least expect it, like out on the floor.
The specification from the battery maker is specified at 4 amps max. Last year's charger was a step charger and speced at 2 amps. At 2 amps, constant current charging, a dead battery should take about 8-10 hours to reach full charge. At 1 amp twice that length of time or 16-20 hours.
Good Luck All