What is the maximum current that can be fed to the 48v 201rpm Q128h

[John_S]

Hello.

I'm close to finishing converting a bike that I've fitted with a 48v 201rpm rear Q128h motor in a 24" wheel. The bike has 20a controller. I'm considering soldering the controller shunt a little bit to increase the current slightly. I'm aware that the Q128h is a smaller motor than the BPM or similar, and so I assume that it has a greater risk of overheating at high currents. Could anyone tell me what the maximum current is that this motor will be able to cope with? If I were to increase the current from 20a to 25a, would the motor be able to cope with that increase?

Thanks for your replies.

 

[Woosh]

I'd keep it at 20A. Mine starts whining a little on steep hills.

 

[Deleted member 4366]

The problem is not so much overheating, especially on a 201 rpm one, but the years will wear if you go with too much torque. If you're not worried about that, 25A should be OK.

If you have a KT controller, you can turn up the current in the LCD settings, which will keep the power display accurate.

 

[Nealh]

Other issue to consider is the battery, poor cells will sag and loose capacity a lot quicker, even at 20a a good celled battery is better.

 

[John_S]

Thanks for your responses.

The lcd that my bike has is the S-LCD3 from BMSBattery. It came as part of a pack with the Sine Wave Controller for 09-Case: https://bmsbattery.com/controller/698-sine-wave-controller-for-09-case-controller.html

Is this LCD one in which you can turn up the current using the settings?

 

[Deleted member 4366]

Thanks for your responses.

The lcd that my bike has is the S-LCD3 from BMSBattery. It came as part of a pack with the Sine Wave Controller for 09-Case: https://bmsbattery.com/controller/698-sine-wave-controller-for-09-case-controller.html

Is this LCD one in which you can turn up the current using the settings?

Parameter C5 adjusts it, but I think there are different software versions for the values. IIRC, originally, you could adjust it up and down by 5A. The last manual I downloaded shows that C5=10 is maximum current (20A), C5 = 1 is current divided by 1.1 (18A) and C5=8, 7, 6, 5, 4, 3 correspond to divide by 1.2, 1.25, 1.33, 1.5 and 2.0.

Previously, it was something like C5 = 10 is max current +5 amps and C = 0 is max current -5 amps, with the other values being steps in between.

You won't need to turn the current up above 20A. I think that you'll be turning it down. The motor limits the current when you're going fast, not the controller, so you could turn it up to 100 amps and you wouldn't go any faster.

 

[Nealh]

C5 only allows current decrease from the max setting which will be #10, each decrease in number is 0.5a so you have a setting range of - 5a from settings #10.

 

[John_S]

So from what you're saying, it is not possible to increase the current above 20a using the LCD. Is the maximum setting of 20a (C5=10) the one that is enabled by default?

If I were to solder the controller shunt, would this increase the current beyond 20a, or would the LCD still limit the current to 20a?

Thanks.

 

[Nealh]

The lcd doesn't know the amp setting all it does is allow max amps to be drawn if #10 is selected in C5, if you mod the shunt C5 #10 will allow the max amps depending on how much solder you add though the watt output on the lcd screen might not show this as extra W drawn. More solder lessens the resistance so don't go too mad, a simple watt meter can verify how much you have increased it by.
If you add to much solder you can reduce the draw by up to 5a.