The first battery build is now done, plenty learned on the way. It’s a 14Ah at 48V (13s – 6p) and I took it for the first run today – it performed great
, attached to a 350W bafang geared hub via a 18amp controller. I set the C5 setting at 5 as this gave me 100w on setting 1, 180w on 2 up to 1000w on setting 5 – so plenty of power. I did 25 miles (all offroad) and the voltage dropped from 54.4v to 51.8v which should work out well when winter comes and I am ploughing through the mud. Nothing got hot and with the aluminium frame being held in with additional rivnuts so it is connected to the down tube, seat post and crossbar there were no rattles.
It is just lashed together with cable ties and tape at the moment, and I need to sort out the wiring a bit (basically shorten the various leads so they fit in better). The cover is also lashed up with cable ties, and I have not fitted an on/off switch yet, but I have used XT60’s for the main power connections and XT30s for the lights and USB port.
The spot welder worked a treat and was a million times (for me) easier than soldering the cells.
Also I tried this and it worked on three cells that were giving a reading of less than 1v (not using a dodgy DVM
) -
My main lessons learned are:
Check your digital volt meter is working correctly
, and have a spare battery for it.
Don’t use lead free solder, it needs more heat to melt.
Silicon coated wire is great because it is very flexible, but it is much fatter for the same current rating than solid core, so did not fit the BMS.
Forgot that the charging wires from the BMS would need a fitting compatible with my charger – else how was I going to charge it up
.
For the + and – leads that are connected to the first and last cell group I should have soldered the leads to the Nickel strip first and then spot welded the strip it in place. Trying to solder along the Nickel strip that was already spot welded onto the cells took ages and looks a dogs dinner.
The second build is underway and it will incorporate all the lessons learned (the image shows the cells being tested and sorted) this will take a few weeks to do.
This is an excellent resource if you are using old cells -
https://secondlifestorage.com/celldatabase.php
I intend to make three batteries of different capacity that can be fitted in the frame and connected together to give me options for distance vs weight for this bike. But the next project is going to be a Mid Drive (love the Zoobop) or I am seriously tempted by a two wheel drive mud plugger - 250w on the front, 350w on the back run at 52v, 26” wheels in a 27.5” frame with the fattest tyres what will fit
.