Balance Check

I have now driven more than 300km with the conversion and charged the battery pack nine times from about 1/3rd left. Everything seems to work real smooth. So I decided to check the cell voltages for any oddities, as I am relying only on bottom-balancing and there is no battery management system (BMS) used in my bike. As I went through them, every single cell of the 25 cells reported values within 0.01V from each other after driving to work and using almost 30Ah of energy. All the cells had values of 3.27-3.28V using the meter that gives a bit higher numbers than the other one I’ve used. So I’d say the pack is still in excellent balance, and there shouldn’t be no bad cells in the pack. I’d say I am now very confident with the bottom-balancing method. Also while opening the battery boxes for the inspection I added some extra insulation in the bottom pack, to make sure that the cells won’t bounce around and that the poles will have zero chance of hitting the bottom of the top box, which could potentially short circuit them.

Everything else went just fine, but as I worked in a rush, I managed to drop the DC-DC converter (stupid me) as I had to disconnect it so that I could get the upper battery box lifted. And I forgot to check it’s operation after the work was done. This morning I tested the 12V voltage and it looks like that I’ve either broken the DC-DC or disconnected some wire (also a very likely scenario) when I put the bike back together. The small lead-gel battery reads only 12.2 volts and the voltages do not jump back up to 13.5V as they used to do when the DC-DC worked and the bike was turned on. I’ll need to debug it this evening… Sigh.

EDIT (23pm): Just a disconnected wire. Failed crimping. Fixed…

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3 thoughts on “Balance Check

  1. Hi fella,
    With the 25 CALB 40ah batteries, would you recommend these for a 25 mile trip with an average speed of 55mph? I’m about to start an EV conversion and 40ah seems to be the right Ah for that range with some in reserve?

  2. At consistent 55mph speed I think it’s in the borderline if these are enough. If you make an efficient conversion you should be able to do the trip. But not sure if there’s much in reserve. My bike would probably use about 100-110Wh/mile in that speed so there would still be about 10-15% left in reserve after a trip like that. In my regular commuting at mix of 35 and 50mph limits my bike uses just less than 90Wh/miles (55Wh/km). (Going faster always uses more juice.)

  3. Hi Toni and thanks for the reply. You help and advice have been very valuable!
    I’m using a light weight bike alloy frame, from an Aprilia RS50. So hopefully the weight difference will give it better wh/mile, however the 25 mile trip is a to and from distance, I may see about recharging at work to get me the 13 miles home again. 60ah would fo it for sure, but I think the bike size will limit what size CALBs I could fit. Cheers

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