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Unread 16-12-2010, 22:06
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DonRotolo DonRotolo is offline
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Re: Warming up the batteries

Quote:
Originally Posted by thelittlesister View Post
We haven't load-tested it. How would I do that?
You have any of several issues:
1. The chargers are all bad (unlikely)
2. The batteries are all bad (very likely)
3. The robot has a fault (possible)

You've read several suggestions to eliminate #3.

#1 is indeed unlikely, but possible. After a full charge (as indicated by the charger) measure the battery voltage with a multimeter. A normal reading for a battery just off the charger would be over 13.5 volts. Let the battery sit for a day, to eliminate the 'surface charge' and a normal reading should 12.6 volts.

#2 is easily determined with a load test. Al's recommendation of a West Mountain Radio CBA is excellent, but they are not free.

Instead, take about 10 feet of #10 wire (or 8 feet of #12), which should be about 1 Ohm. Measure the length of wire with an Ohmmeter (be sure to comensate for the resistance of the meter's test leads) to verify about 1.0 Ohms. (A high-wattage 1 Ohm resistor (25 Watts capacity) will do as well)

While measuring the voltage across the battery terminals, connect the 1 Ohm load (the wire or resistor) also across the battery's terminals. Count exactly 15 seconds. Write down the battery voltage at the 15 second mark.

A Very Good battery will read over 10 volts. An OK battery will read over 8.5 volts. Bad battery will drop below 8.5 volts. (NOTE: These numbers are debatable, but that's what I use).

If in 15 seconds with a 1 Ohm load your batteries all drop below 8.5 volts, and start above 12.5, they're bad. Buy new ones.

What causes a Lead-Acid battery to go "Bad"? Other than usage, sitting in a discharged state (terminal voltage less than 12.4 volts) for any period of time. Like over the summer. This kind of battery loses 50% of its charge in 90 days. On our team, we make sure they don't go more than 60 days without getting charged. Even then, we lose 3-4 batteries each year.
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