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I have a couple of old 36v eBike batteries lying around. I also have a Minn Kota Endura C2 30 electric trolling motor for my small boat which needs a battery. My previous experience with a large lead acid car battery for the boat motor was really negative (it was so heavy to carry to the boat and then it leaked some acid as well). This makes me wonder if I could use my old, useless but powerful lithium ion bike batteries to power the trolling motor instead? I imagine powering an eBike motor might need a roughly similar amount of power as a trolling motor.

The batteries are 36v and the motor is 12v though. Would it be possible to use a device like this buck converter to bring the battery voltage down to 12v and then just hook it up to the motor? https://www.ato.com/dc-dc-buck-converter-36v-to-12v

What other considerations should I make before possibly attempting this?

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  • \$\begingroup\$ I have a "55lb thrust" 12V trolling motor : it takes over 40Amps from a fresh battery, so if your "30" means 30lb thrust you'd need the 30A buck converter. Which is probably more expensive than a 12V battery. \$\endgroup\$
    – user16324
    Commented Jul 15, 2020 at 20:13
  • \$\begingroup\$ Not realistically, no. Questions on the usage of products are off-topic here. The only realistic option is to use motor/battery combinations which were designed to work together. \$\endgroup\$ Commented Jul 15, 2020 at 20:16
  • \$\begingroup\$ if you don't use full speed, thus keeping the amps down, a buck should work fine; 12v is 12v is 12v, until it's not... \$\endgroup\$
    – dandavis
    Commented Jul 16, 2020 at 5:48

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It may be possible, it depends on the current requirements of the motor (compared to the maximum output of the buck converter). The ebike battery pack would also need to provide a little more than 1/3 of the current required by the motor (multiplied by 3 minus power supply loss by the buck converter).

A better idea would be to rebuild the 36V ebike battery packs into 12.6V packs. You would need to add a 3S (12.6V) BMS to prevent over-discharge. This requires caution, you cannot just split the battery pack in three and connect the three parts in parallel (you have to at least use bleeder resistors between the packs to equalize the packs before directly connecting them together).

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