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Battery sizing advice

Hi everybody,

I am building a tricycle around two 175-200 watt (Output Power) wheel chair motors. I don't know the exact output power because they were salvaged from an old wheel chair and the motors themselves have no identifying information. I've found other places online that claim they are in that range.

I would like to use them to push about 1,000 lbs of steel and human around at Burning Man. The contraption also has pedals that are geared mostly for very low speeds... like going up hill or getting un-stuck.

Right now it has the 24-60v motor control kit from ElectricScooterParts and two (probably faulty) 68Ah, 200CCA deep cycle batteries. They are fully charged (25.5v) but seem to drop down to about 23v when I let the motors go full on.

Now, the bulk of the question: What battery should I get to replace the two defective batteries? What information do you need from me to determine what it takes to make these things operate at full power load for 4 or 5 hours? What can I do to determine the actual power output of my electric motors? (Like I said, I'm only guessing at the power output)
Assuming that the two motors are around 200 Watts each, which is typical for wheel chair motors, and that the vehicle will be fairly heavy as far as electric tricycles go, you will need large batteries to do the job. I would look into using boat trolling deep cycle batteries because they are large, designed exactly for what you need them to do, fairly inexpensive, and available locally which is important because they are heavy and would be very expensive to ship.

There is no easy way to determine the motors actual power rating but I would say you are safe to assume that both of them running together are under 500 Watts.

It is hard to say how much run time you will get out of the batteries because there are so many variables such as speeds traveled during usage and rolling resistance. I would start off with buying two large deep cycle marine batteries that are the size of full size car batteries, such as group 27M through 31M, and test run the vehicle to see how many hours it goes with them. Then if that does not provide enough run time two more identical deep cycle batteries could be added to the battery pack.

           Large Deep Cycle Marine Battery

By the way that is a really cool looking frame on the trike. I like the way that just about every piece of the frame has an arch to it.

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