Controller (reverse) shunt mod?

[maarten_almighty]

Can a shunt mod be performed in reverse; as in: make the shunt thinner such that max amperage drawn by the controller is less?

my controller is capable of 150Amps (DC battery current) but my current battery can only handle 70A (will upgrade in the future).
I would like to make the shunt in the controller smaller so it (the controller) only draws approx 70A or a bit less maximum.

Are there usually 2 shunts (1 for the DC battery amps and one for the phase amps) in a controller? If so how do I know which one is which? (most likely phase amp shunt will be thicker since the phase amps will be higher than dc amps).. Perhaps only 1 shunt is used? Please correct me if I'm wrong on this

Are there any negative consequences this (downsizing shunt) can have?

(I know the acceleration will be limited by this but that's fine by me, 70A should give plenty of torque imo, top speed shouldn't be affected I think since at the motor's topspeed at my battery voltage only 60A DC current should be drawn (approximately). Is this correct (should top speed not be affected by downsizing the shunt)?

I am working with a non-programmable controller (hence I need to do it via shunt mod instead of via software).
This is the controller I want to buy (9kw version): https://nl.aliexpress.com/item/33055639740.html?srcSns=sns_WhatsApp&spreadType=socialShare&bizType=ProductDetail&social_params=60005594459&tt=MG&aff_platform=default&sk=_BSKbYA&aff_trace_key=95e0245bd8a54d1a8f249db32258e951-1608992028480-07719-_BSKbYA&shareId=60005594459&businessType=ProductDetail&platform=AE&terminal_id=40d9f3f985c84148bb2e58704e805c2a

Thank you! :wink:

 

[amberwolf]

Can a shunt mod be performed in reverse; as in: make the shunt thinner such that max amperage drawn by the controller is less?

Yes...but it's not a reversible modification. You would have to replace the shunts with new ones identical to the old ones to undo it.

It would be better to remove half of the shunts in the system to cut the current in half. So if it has four shunt wires, desolder two of them and remove them (or even just unsolder and lift one end of each). If it has two, desolder just one. If it has three, then you'd have to desolder two of them, and the current would be cut by two-thirds.

Are there usually 2 shunts (1 for the DC battery amps and one for the phase amps) in a controller?

Typically with "generic" controllers, only one or the other is used in a particular controller. Either it monitors battery amps, or phase amps. Almost all generics only do battery amps. If it monitors phase amps at all, it usually uses non-shunt type current monitors, where the actual phase wires pass thru a sensor, often it looks like a plastic block. The cheap ones only monitor two phases, while the good ones monitor all three.

If it is only monitoring phase amps, there no "easy and fast" mod you can just do to it to lower the current limit. You would need to reverse engineer the circuit used between the sensors and the MCU, and figure out how to scale the signal coming from the sensor back to the MCU to cut that signal in half.

Is this correct (should top speed not be affected by downsizing the shunt)?

If top speed under the conditions currently being ridden under requires more current than the limit you've created, then it will be lowered to whatever is possible at that limit.

Remember that hacking the current sensor of a controller means the controller doesnt' know what the actual current is anymore. So it's behavior may not be the same as if it was unmodified, and it is possible to get unexpected behaviors you may not be able to predict. Probably it will be normal, but if it is not, it might be related to the sensor mod.

 

[serious_sam]

If it's a torque based controller then you could add a resistor in series with the +5V wire going to the throttle, and just limit the throttle range.