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My Citicar has a 3.5hp, 36 volt motor according to the data plate. 3.5 HP is the continuous rating, but even after a 25 mile run at about twice the rated HP (drawing 100 amps, about 30 MPH), it didn't get particularly hot. The Citicar has two flavors - 3.5 HP and 6 HP. (they had 2.5 in a very few early production 36v models)
My Alltrax controller is a 4844, rated at 400 amps. Since flooded battery terminals get rather hot over 400 amps (IMHO), it seems like a reasonable limit. In reality, the 4844 will go to 600+ amps for a few seconds (according to the internal logs) during hard acceleration from a dead stop, kind of like contacts (but without the whiplash...) Unless you have lots of hills, or a great number of stop signs you probably won't see 400 amps for longer than a few seconds in a Citicar-size vehicle anyways.
I added two extra 6-volt batteries (60v total) to test out what would happen, and found that the top speed and acceleration were the same with 48v when I had the stock contactor setup. Probably limited by the motor. On the other end, I took out a 'bad' battery (down to 42v) and the top speed went from 32 MPH to 26 MPH. At least for this motor, 48v seems to be the right number.
I am still at stock voltage of 48 volts - It came with eight 6-volt batteries (US 2200), but to reduce weight (and battery cost) I installed six 8-volt batteries (US 8VCG). They have about 100 amps (1 hour rate) compared to 117 amps for the 6-volt batteries that they replaced. They weigh 67 pounds each.
They -could- be replaced by four 8D batteries (12v) but the 8D's are about three inches wider than a pair of 2200's/8VGC's, so they probably won't fit in the space under the seat. In newer C-cars the batteries are in the bumper, and it would be difficult to shoehorn them in there as well.
My 8VGC batteries were about $90 each six months ago, but the price has gone up.
My daily drive to-from work is a round trip of 10 miles, which is well within the 25 mile (actual - went that far once) range with six 8-volt batteries.
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