On 11/19/05, [EMAIL PROTECTED] <[EMAIL PROTECTED]> wrote:
My current 72v AGM battery weight is 258#s with 45 - 65 AHs each depending on whose spec you believe. This should produce 4680 WHrs (72v X 65AH). While the Hawkers would produce only 3120 WHrs (120v X 26). Are my calculations correct?
You are right about the formula:
Amp Hours * Volts = Watt Hours
The trick is figuring out how many amp hours you will actually get out, which depends on how fast you drain it, and the Peukert factor at that drain level. EV cars should have a much higher average amp load on the batteries, which is why they are downrated so much. The figure I have heard before is the standard 12v Yellow Top is 400 watt hours, in an EV car (~33 amp hours instead of the rated 45).
If you don't know what the average discharge rate is (probably don't know, unless you have tried before), I would recommend derating it 25% in terms of the number of amp hours you can get out to get to 100% discharge.
Then, you have to derate it again, to account for the fact that it is bad for AGMs to be fully discharged. Some say don't go below 80% typical discharge, some say only 50%. From the data I've seen, 50% is the better number, since the expect number of cycles goes dramatically up as compared with the 80% discharge numbers.
In terms of peak KW of power my configuration would in theory produce ~25KW of power (or 33.7 peak HP) at 350 amps. While 120 volts at 450 amps would produce ~54KW or 72 HP.What about the charging profile? What chargers work well with Hawkers?
I would recommend Rich Rudman's PFC charger (www.manzanitamicro.com). I borrowed a Beta unit for a while and it was awesome. Extremely efficient, top notch knowledge and service, and almost fully automates AGM charging.
If you are able to get some higher voltages that would seem to improve range, but I have always been under the impression that more amps equals better acceleration (which is my goal). If I were to go up, I would probably just go to 96 volts as a first step and see what the actual results are like first.
In my experience, there are three main advantages of going to a higher voltage:
1. More batteries equals more range, since you have more stored energy available
2. Higher voltage means lower losses at the higher amp draws and less loss to the Peukert factor
3. Your average amp draw will go down, since it takes fewer amps at the higher voltage to get the same watts
Of course, this has to be balanced against the other factors:
1. Overall weight may be too much
2. May have to change charger/controller
3. Space limitations
4. Maintenance and battery failure possibilities increase
5. More $$ to by more batteries
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Mark
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Mark
