Lyen controller not working at 37V

[cwah]

Yeah, but I wasn't sure about the voltage I would need. Better to have something adaptable rather than having to change the whole system. I found that the weight was identical to a normal controller, so I preferred to get a higher voltage one for safety

[NeilP]

Yes, se your point, but less current with the high voltage ones, so less acceleration

[Jeremy Harris]

Using a high voltage controller for a lower voltage application also means less efficiency. There is a fairly linear relationship between FET on resistance and maximum voltage, such that 100 V capable FETs will have around double the on resistance (and hence double the losses at a given current) than 50 V capable FETs.

It's for this reason that I changed the FETs in my boat controller (that works at around 20 V max) to IRLB3034 FETs (40 V maximum. These have only 38% of the loss that the 100 V max IRFB4110 FETs commonly used in ~80 V controllers, and only 15% of the loss of the 150 V max IRFB4115 FETs frquently used in 100 V + capable controllers.

If you want best efficiency, then go for a controller fitted with FETs that match your operating voltage range, don't go for a controller with an unnecessarily high voltage spec.

[NeilP]

Ah yes, forgotten about that.

Is this the same controller that you have the 400W for 12mph thread going about or is this a different bike? This could account for a few more watts lost. OK, probably not the full amount, but a little bit here and there, all soon adds up

[cwah]

Yes, it is the same controller. Actually I wanted to be able to transform my 74V8AH battery to 37V16AH for maximum distance when required. But I didn't know that higher voltage controller would be less efficient...

Hopefully, I know that I can always increase the speed and voltage If I want/need to!