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I have an e-bike motor ( bbs02 48v 750watts ) which requires a 48v battery. I also have a 36v 13ah e-bike battery. Opening the battery and changing cells connection to make it 48 takes a lot of effort.

Is it a bad idea to use a step-up converter? I have a dc-dc converter which claims to have 95% efficiency. Any downside of using one?

If I would step up the 36v input to 50.92 volts using a step converter, will the e-bike motor meter still read the battery as full? Even if the battery goes below 50%, would the output of the step-up converter still be 50.92 volts? Or would the voltage drop?

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    \$\begingroup\$ Is that DC/DC converter rated for 750W? \$\endgroup\$ – Solar Mike Sep 29 '18 at 16:04
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    \$\begingroup\$ This is a bad idea, and will probably fail for one practical reason or another, especially with regard to the less usual circumstances the system can find itself in. As an example, consider that regenerative braking (either designed or accidental) would fail entirely, quite possibly destroying components in the process. In theory a system which worked this way could be engineered, but the components would have to be designed specifically for this use. In practice, the battery, controller, and motor are instead matched to each other. \$\endgroup\$ – Chris Stratton Sep 29 '18 at 16:06
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    \$\begingroup\$ The startup currents of the motor-----may be more than any cheap DC_DC converter can handle. \$\endgroup\$ – analogsystemsrf Sep 29 '18 at 16:32
  • \$\begingroup\$ Many e-bike motors have freewheel so they can't regen. My first had a motorised front wheel with freewheel for normal cycling. My current one has a Panasonic under-pedals motor which drives the chain. This freewheels on the rear sprocket as a normal bike. You'd need to check that but overall this looks like a bad idea. One big downside is that the motor controller won't know when the battery is flat until you've over-discharged it. \$\endgroup\$ – Transistor Sep 29 '18 at 17:50
  • \$\begingroup\$ In regards to the above comments, you would need a MPU programmed to monitor battery voltage, and a charger. Adding useful regenerative braking may take a machine shops help-and expense. Re-think this idea. \$\endgroup\$ – Sparky256 Sep 29 '18 at 21:09
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Yes, it is a bad idea.

You don’t know what the motor/battery controller expects and it would be hard piece of engineering to get 95% efficiency over a broad range of load currents.

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