Controller shunt mods

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amberwolf   100 GW

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Re: Controller shunt mods

Post by amberwolf » Dec 02 2018 10:36pm


newbiehere   10 mW

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Re: Controller shunt mods

Post by newbiehere » Dec 05 2018 8:07pm

Yeah I think I found it, but its going to the chip that controls the Motor, maybe that chip has that capabilty built in as well. If it was going to an op amp, that means the amps across the shunt are at the micro level?

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Re: Controller shunt mods

Post by fechter » Dec 06 2018 9:10am

On newer designs, the op amp is built into the main MCU chip so all you see is maybe a RC filter between the shunt and the MCU.

The shunt resistors are generally in the neighborhood of 1 milliohm. Making an adjustable divider on the signal is pretty easy but most people just lower the shunt resistance and adjust the current limit in software.
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Re: Controller shunt mods

Post by newbiehere » Dec 06 2018 7:19pm

very informative thanks very much :thumb:

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Re: Controller shunt mods

Post by newbiehere » Dec 06 2018 7:31pm

thanks very much, I will hack the solder bridge shunt off a damaged controller and try that, for the voltage divider, I am lost trying to find it. i see a trace coming from the shunt towards a gate driver, but seems to be going under the driver to where, difficult to tell

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Re: Controller shunt mods

Post by newbiehere » Dec 07 2018 11:39pm

My controller has 6 mosfets, so if I increase the amp capacity of the shunt, I think i must add more mosfets. If I added 6 more mosfets, could I add them in parallel, or does this mod require a new board and controller?

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Re: Controller shunt mods

Post by fechter » Dec 08 2018 11:51am

newbiehere wrote:
Dec 07 2018 11:39pm
My controller has 6 mosfets, so if I increase the amp capacity of the shunt, I think i must add more mosfets. If I added 6 more mosfets, could I add them in parallel, or does this mod require a new board and controller?
It depends on the FETs and how much current you end up with. Many times you can get away with just cooling the outside of the controller adequately (mounted in the open where there is some air flow).

Can you read the numbers off the existing FETs?

Adding more in parallel makes it hard to cool the added ones. It's usually better to stay with 6 but maybe upgrade them to better ones.
"One test is worth a thousand opinions"

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Re: Controller shunt mods

Post by newbiehere » Dec 08 2018 8:22pm

IRF 3205

Yes I have some heat sinks out of old PC, was thinking about putting the 6 mosfets on it, but dont know if the leads to the gates etc will be too long. maybe use the PTC or NTC sensor with the arduino or nano to sense when the temp gets too high and power the fan on the heat sink, its out of an old desktop

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Re: Controller shunt mods

Post by newbiehere » Dec 08 2018 11:20pm

I see the drain current for the IRF 3805 is 98 amps so I think Im good as you said, no need to parallel any more mosfets just heat sink them or open air it

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Re: Controller shunt mods

Post by fechter » Dec 09 2018 1:22am

Those are rated for 55V and have an on resistance of 8 milliohms. For sure you can find FETs with much lower resistance. Less resistance will produce less heating. The legs will melt off the FETs around 70A, so the silicon rating is not the limiting factor.

I'd just try the stock FETs and see if it gets too hot. If they do, then replace them. Any kind of additional heat sinking or air flow will greatly reduce heating also.
"One test is worth a thousand opinions"

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