Electric Bike (ebike) Battery Question: Getting 24 Volts in a Lightweight Package?

Question

I'm in the planning stages of building an electric bike. Initially, I was going to buy a great quantity of lithium-ion cells (size 18650) and hook them up to provide me with 24 or 36 volts of power. But recently I have been thinking of using some quality lead-acid (think Optima!) batteries. The only problem is car batteries are pretty big! I am thinking that two Optima D51 batteries would be manageable-- they are Optima's smalles battery, but each one is still 26 pounds. They also provide 38 Ah (each!!!). Yah, that's a lot of power, but also a lot of weight. My question is this: is there a viable means of converting 12 volts to 24 volts without substantial power loss? I would rather just use one Optima battery, but they only come in 12 volts. Also, can anybody recommend some small deep-cycle lead acid batteries in which I could put two in a serial configuration? Any other advice? Cheers and thank:)

Answer 1

"converting 12 volts to 24 volts without substantial power loss?"

You don't get something for nothing. Yes, you could use a DC-DC converter, which would weigh a few pounds, but you would convert 12 volts at (eg) 10 amps to 24 volts at 5 amps, minus about 20 %, or 4 amps.

You need to go thru the numbers. Check the weight and power output of the Li-ion batteries, then check a 12v lead-acid with converter, then other alternatives. Calculate watt-hours per pound for each.

You can get watt-hours from amp-hours by multiplying it by the battery voltage. watt-hours is a unit of energy.

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