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Old 09-07-2009, 09:52 PM   #1 (permalink)
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Question any number crunchers out there?

Havent been around for a while, as I was testing out the truck. The kelly kdh 9500 quietly died(no smoke or full on, just quit). My range was another problem, so I did some load testing on 8 75 ah batteries. I hooked each one to the motor, and used a voltmeter and my amp gauge, and this is what I got. 6 of them ran the ADC 9 for 25 min average, at 45 amps. starting voltage was 12.5 and ending was 6.5. battery recovery was back up to 11.3 in a minute after running for 25 min. 2 of them went flat in 17 min from 12.5 to 5.5 with poor recovery. My question is, are the 6 working properly, or are they all shot? I was only able to get 5 to 6 miles to a charge. any thoughts? Watt

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Old 09-11-2009, 02:40 AM   #2 (permalink)
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45 amps for 25 minutes is roughly 33.33 amp/hr (about 1/2 of what you should have in a 75 ah battery.)

45 amps for 17 minutes is roughly 22.66 amp/hr (about 1/3 of what you should have.)

While there is some derating (Peukert number) that will make a battery deliver less amp/hr at high amp draw, 45 amps is not a particularly high discharge rate, so you should be getting at least an hour of run time at 45 amps (to full discharge). My estimate is that these batteries are at their end-of-life for an EV, but could probably be used as IC starting batteries a while longer.

Peukert Number Battery Life Calculator

That being said, your starting voltage was rather low. At 12.5 volts, you were starting at about 90% of charge - but just an estimate - hard to tell actual 'charge' without a hydrometer. If your batteries measured 12.5 volts after being charged, they have problems - perhaps your charger isn't doing a good job? - just something else to check. The charger should be putting out just over 120 volts at the end of the charge cycle (for a 96v pack of flooded batteries.)

Running a battery to 'dead' is really hard on the battery - Kind of like having a heart attack - you can only have so many before things don't recover... If you drive it to 'dead' every day, your pack probably won't last more than a few months.

If your batteries were new, you should be getting around 1.5 to 2 miles 'per battery' out of your pack to about 80% discharge (because they are relatively small amp-hr wise) on flat roads. I'd expect you should see 10 to 15 miles of range with eight 12v/75 ah batteries (much less if you have to go uphill...)

Even one bad battery can make range really poor. Since you appear to have two mostly bad ones, that probably explains why the 5 miles. When you do replace batteries, don't buy them one at a time - you'll have fewer headaches with batteries that are all the same age.
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Old 09-11-2009, 10:43 PM   #3 (permalink)
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Thumbs up RE: amp hr results

Thanks, Tom. I was hoping to have some info come back. Was wondering about the chargers myself. I charged each battery separately, and they all have 12.9 to 13.0. They are holding after a day, so that could have been part of it. I bought these 4 at a time from a local wal-mart(johnson controls). My controller also would drain them at a very quick rate, plus it was impossible to back up(backwards burnouts.)Due to this thing turning into a hole in the driveway I throw money into, I had to buy a smaller controller, and use one less battery. I will test the batteries again at the higher charge, and if they still dont last, I can turn them in for new ones. One year warranties are a good thing Will keep working with it. Thanks again. Watt

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