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Electric Imp Testing Log April
17, 2003, Thursday - Testing Begins. May 13, 2003 -Tuesday Upping the Amps 3: This time the battery that failed is under one of the inverters. The inverter is unbolted and moved to rest on the motor. This means the crew does not have to disconnect the cooling system or the major cables. It does mean there is not a lot of room to work. Some trimming of the battery cover is done to make it easier to remove. After the battery is replaced, we record the voltages of each individual battery. We have been told that if the pack is not under some load or been sitting idle for at least 24 hours, the voltages will not be indicative of stage of charge. The pack has had 3.346 kWh removed since it was last charged. The car is put up on jacks and the car is turned on. The batteries run down at 4 amps until one battery hits 1.75 volts. The pack is reading 311 volts under load and has delivered 4.667 kWh. The pack, when new, should be able to deliver somewhere around 9.5 kWh at 2.55 amps. The Kilowatt/hours the pack can deliver will be less at higher amp draws (see peurkert equation for more detail). Some people hold that lead acid batteries are like muscles, they need to be used or they weaken. And a weakened battery can be brought back by gentle exercise. This seems somewhat reasonable. It is a chemical reaction within the battery which produces electricity. Prolonged inactivity could lead to stratification among the chemicals in the battery. Gentle use might provide some mixing even in a "starved electrolyte" cell. Our pack has been out of action for a very long time. An experienced EV'er reported success in recovering capacity in Hawker Batteries by discharging them at 4 amps until 1.75 volts and then recharging them for 16 hours. Repeat the cycle until capacity stops increasing. Capacity is easily measured by tracking how long it takes the battery to discharge at 4 amps. Longer means capacity has increased. It would be best to take each of our 178 batteries and individual follow this routine. We cannot afford that kind of time. Instead, we decide on a routine of running down the pack with test drives and then finish discharging the pack on the jack stands under a 4 amp draw. It means that only the lowest capacity battery will be fully discharged, but that battery should improve and it's capacity is the limit that we can use anyway. May
14, 2003, Wednesday - The pack is put on charge. back to Lead Acid Test Log menu All
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