Upgrading my Electra Voy Bicycle

moveon70's picture

I bought a used ebike purely for the experience of upgrading it.

I stared with a Electra Voy bike/scooter which I found on Craigslist and boght for $150. It has a 36V lead acid battery set which feed a 180W hub motor.
My ultimate goal (and I have all ready ordered parts) is to upgrade it to a 48V, 1000W, LiFePo4 system with regen breaking.
I ordered the motor and controller (with regen breaking) from "Golden Motor" ($400), and the LiFePo4 battery with Battery Management System from a Chinese distributor through ebay($400).

It will take a couple months for my new parts to come in, so until then I thought I would mess around with the current system. The 3 12V, 12Ahr batteries were shot. I picked up some used 12V 7Ahr batteries from a surplus house for $5 each and decided to see if I can make them work.

This scotter has allowances for two sets of batteries. When one set dies, you can switch to the other set. I was interested in putting two sets (a total of 6 batteries) but do not want to switch between them. If the two sets are simply wired in parallel, then one weak battery brings down both sets. Instead I decided to use some diodes to seperate them out. After drawing the schematic I realized that it was actually the same diode lay out as a bridege rectifier. (see attached file for schematic).
I bought an NTE5340 40A bridge rectifier from Fry's for $7 and it all ready has push on blade connectors, so it was easy.

So far, it works great. I can charge all 6 batteries with the 36V charger, and as I ride, the controller pulls the most current from the set with the most voltage. They basically drain together. Fantastic!

Next posting will be once I get some of my new parts in.
-Mark

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Series parallel battery pack.jpg4.17 KB

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