Dead battery!

[Burne S]

Question: Our team kinda lost (As in completely drained) a battery over the course of testing. We've tried almost every suggested place on the site, but nothing worked.

We need replacements and spares. Where might we find FIRST competition-legal batteries?
~Burne

[Sparks333]

Originally Posted by Burne S

Question: Our team kinda lost (As in completely drained) a battery over the course of testing. We've tried almost every suggested place on the site, but nothing worked.

We need replacements and spares. Where might we find FIRST competition-legal batteries?
~Burne

If you read a bit farther back, you'll notice that ahecht said that a sealed Lead Acid battery (the kind we use) will be trashed if voltage goes too low. That tallies with my own knowlege of SLAs, and I think others would agree. In short, I think that you guys are sunk. Look around for other batteries, or maybe contact FIRST.

Sparks

[Al Skierkiewicz]

Guys,
The gell cell batteries we use can be totally discharged without damage under normal loads. A dead short is not a normal load. In the event the battery we are discussing came in contact with the frame quickly, there is likely nothing more than a scrape where the contact took place. Arcing and burn marks are indications of high resistance contacts for low voltage DC. A completely discharged battery will take several hours to recharge even using the 6 amp charger.
Don't discount the possibility that the battery sustained mechanical damage when used in a robot that ran into a wall. You are dealing with a device that has a lot of mass, and that mass is concentrated in defined areas within the case. Lead is not nearly as strong as steel and a fracture in any connective structure (internal connections and plates) will result in battery failure.
The batteries are available from a variety of sources, including battery stores, McMaster and Digikey. Be sure that you order is the ES or EX type battery.
Most multimeters only can display and measure 10 amps or less and are internally fused for protection. The popular Fluke meters have two internal fuses, one for 300 mA and one for 10 Amp. To measure current on the robot, you need a current probe. Fluke makes a few nice ones but they are almost as expensive as the meter itself. They clamp on to wires under test. Remember that they can only measure current on one wire at a time. If you measure both the positive and negative leads of a motor at the same time with a clamp on probe, there will be no current measured.

[greencactus3]

Originally Posted by krhs_programmer

We went to disconnect the battery and when we grabed the connector we drew back in pain because it was burning hot! We let it cool and disconnected it and put the volt meter on it and it read .25 volts. The battery went from fully charged at 13.4 volt to .25. Please explain this!

by the way if you're wires are that burning hot id advise you to disconnetct first anyways because there just MIGHT be the chance it wont cool down (and keep getting hotter till sumthing blows or melts. at worst (with rc car experiences) you might even need to cut the wire. but never cut two wires at once.

[Sparks333]

Quick question regarding one of the above posts:
Were you able to charge the battery back up? If not, then you may have an internal short (SLAs depend on metal plates with acid between them. If the plates short, then you have a problem, but that doesn't explain the hot breaker wires). In any case, it sounds like you had a HUGE amount of current go somewhere really fast. That's downright dangerous. One thing is niggling, though: why is it that the wires did not actually melt? It seems to me that even a somewhat discharged battery, if it were to short using the breaker wires, would fry them in a heartbeat. If the voltage levels did drop that much, then it seems semi-logical that there would be scorch marks along the path the power took to whatever circuit it seems to have made. Make sure this gets solved before competiton!

Sparks