E-mil said:
BBSHD Voltage mod evaluation of options
Hi all,
I already have a light "stealth" eBike with a small hub motor and I am running it with 2x 18V Makita drill batteries in series (2x 5s = 10s). That works pretty well.
Now I am thinking of upgrading my downhill MTB with a BBSHD with a similar tactic. It must be a BBSHD since my bottom bracket is about 93mm wide.
I further like the 500C display that seems to be able to handle 24V/36V/48V/60V nominal voltage?!
The question is with which battery configuration I should go:
1.) 36V = 2x 18V (10s), (~42V max), as in my other bike but maybe too weak for the BBSHD?
2.) 46.8V = 2x 18V + 1x 10.8V (13s), (~54.6V max), needs 2 different types of batteries that I both already own, but it's a kind of battery mix then
3.) 50.8V = 2x 18V + 1x 14.4V (14s), (~58.8V max), needs 2 different types of batteries and I would need to buy the 14.4V batteries
4.) 54V = 3x 18V (15S), (~63V max), pushes to the limit of the stock BBSHD?
I would use batteries from the same manufacturer with the same cell capacities (3Ah 2p = 6Ah) and connect two serial lines in parallel with ideal PV diodes to prevent back currents. The result would be a 10s4p, 13s4p, 14s4p or 15s4p pack.
I personal would prefer the 54V (15s4p) solution since I would get the maximum performance and I already have many of these 18V batteries. But I am still not sure if it is worth to potentially run into troubles with the display and/or the controller.
I read that the resistor/diode display mod may or may not be needed.
The question is if this is still the case for the 500C display that should support 15s out of the box? Or is it an overvoltage protection inside the controller that must be manipulated over the display line?
I measured the max voltage of the drill batteries and I measured 20.7V. So for 15s I would get about 62.1V max instead of 63V. The ideal diodes (MOS circuits) may also have a very low voltage drop that may come handy. In my calculation the diodes should correspond to a resistance of 1.2mOhm and the voltage drop would be then something between 10mV and 20mV and that's to low to give a margin to the overvoltage. However, could this still work without modifying the display line of the 500C and without changing any capacitors of the controller? How good are my chances that this will work out of the box?
Performance of the motor is not so important for me as long as I always can climb every hill by selecting a lower gear. The bike currently has a SRAM eagle group on it. So I personally think that 750W could be powerfull enough for me but I am still not sure if a 10s is good enough in combination with the heavy BBSHD. And I don't like the higher currents.
Thank you for your work and I hope you could give me your opinions which way I should go.