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moveon70's picture

Upgrading from SLA to LiFePO4

Some of you have been following my project to upgrade my little 180W ebike.
I have all ready posted on upgrading the hub motor from the 180W 36V system to the 1000W 48V system.
I promised to post on the performance when I got my new battery, and it finally came in.

I ordered a 48V 15Ahr LiFePO4 battery pack with BMS and charger from China off ebay for ~$250 shipped.
I hooked it up to the charger after unwrapping. I found the charger shut off after only 10minutes, so that means it did not self discharge during the 6 week boat trip it took to get here. Thats good news.
Another note is how they made it. Its simply duct taped together, but over all looks fine. IF I want to change the shape, I should be able to remove the tape and change it how I like.

In just a few minutes, I had it in the scooter.
There is nothing under the seat. That silver cube is the whole battery.
OK, its not pretty, but I will clean it up as time allows.

I finally got to go on a real test ride.
Here are the results:
Top speed is ~20MPH using a GPS.
It goes about the same speed up or down hill, so the speed must be governed by the controller.
It has plenty of torque. If I put my feet on the ground and pull the throttle, the front wheel will come up (but no, it wont wheelie while moving).
I can go up pretty steep hills with out loosing speed.
So far, I have gone about 8miles on the battery, and there is no noticeable drop in performance.
I pulled over and checked, and nothing (motor, controller, BMS or battery) was hot.

The only downer is that some times when accelerating from a stop (and pointing up hill) the current shuts off and then back on and off making a jerking motion. Since it did not do the same with the SLA batteries, I am sure that this is the BMS which came with the LiFePO4 system. It is protecting the battery from over current, or under voltage.
This tells me that I should have bought the 20Ahr battery, not for the additional range, but for the increased supply current under heavy load. Still, this issue is not common, and over all the bike is very ride-able, and I do not feel the need to order a larger battery.

So, the verdict:
Fun little scooter. Since I started with such a small frame, it is really light and maneuverable. The small LiFePO4 battery in the floor does not weigh much. The whole scooter weighs 32kg. It seems like is has plenty of range, and is fast enough to be usable. Also it is an e-bike, not a scooter. Only need a bike helmet, not license or registration. I am happy enough with it to want to finish off all the details like new lights and key switch. Get the regenerative breaking working and so on.

moveon70's picture

Upgrading my Electra Voy Bicycle

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.


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