DIY ebike project

About mid 2018 I bought some ebike parts from China, including a rear-hub non-geared motor, controller and LCD-3 display.  The battery was built from 5Ah 20C LiPo cells from HobbyKing to make 48V at 20Ah.  Back then there were fewer kits available and prices were higher so from here in New Zealand it was cheaper to put it together yourself.

The goal was to assemble a bike that had a good range and was able to climb the local hilly gravel forestry roads.

My Recommendation Now:

If doing this again I would use a 300-500 watt geared rear-hub motor.  The reasons being that they are now much cheaper, easy to install and use, with the gearing (5:1) able to handle reasonable grades without too much trouble.



Battery Cell Failed

About 4 weeks into use one cell failed short-circuit which took out it’s 3 mates (4 cells in parallel).  I suspect this was just a “natural failure” and not induced by charging, discharging or temperature.  These 20C 5Ah cells should easily cope with the maximum 8A discharge current.

I ordered 8 new cells but these will take 4-8 weeks to arrive.  So I removed and bypassed the faulty cell turning the 48V battery into a 44V battery.

Test Ride:  The bike was fine on 12 cells.  At the same time I adjusted some settings to reduce the maximum power and reduce the peddle assist from standard to low.

Power and Peddle Assist – PAS

The controller allows maximum power to be set between half and full.  PAS can be set low, standard or high.

With the power set to maximum the LCD indicates up to 1500 watts being delivered.  Note: the controller is limited to 30Kph maximum speed (my choice for safety).  The motor being non-geared means that some rear wheel speed is needed for the power to be useful when climbing.  PAS-1 delivers 200 watts which is too much for general riding.

So I adjusted settings to reduce power to max/2 and PAS from standard to low.  PAS-1 is now only 50 watts and good for getting some exercise.  PAS-2 is now about 150 watts, so good.  The maximum power is now about 800 watts which is more than enough for general riding and may be enough for some gravel road hill tracks like Mt Climie.  On the flat PAS-1 of 50 watts is about 10Kph with no rider effort and was about 25Kph at 200 watts.