Voltage Clamp Issue

General discussion of using Roboclaw motor controllers
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Eoghan Killalea
Posts: 5
Joined: Thu Feb 07, 2019 10:44 am
Voltage Clamp Issue

Post by Eoghan Killalea »

Hi Everyone,

I was wondering if people could help me fix my voltage clamp issue. I currently have a Roboclaw Solo Micro Controller with the S3 mode set to Voltage clamp. My circuit layout is explained below.

The S3 is connected to the Gate of the MOSFET, the Source is connected to the ground of the battery, and the Drain is connected to a 10 Ohm Power Resistor connected to the positive side of the battery. There is a 10k ohm resistor accross the ground and the S3 line.

However when I use Basicmicro Motion Studio to slow down the motor very fast, there is still a huge spike in voltage, and the voltage clamp does not appear to do anything. There is no current flowing through the power resistor at all.

Is there something obvious that I am missing?

Thanks,
Eoghan
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Basicmicro Support
Posts: 1594
Joined: Thu Feb 26, 2015 9:45 pm
Re: Voltage Clamp Issue

Post by Basicmicro Support »

You can't use just any mosfet. It needs to be a logic level mosfet. Standard mosfets will not turn on from the output of the Roboclaw pin. We recommend using the BUK965R8 mosfet specifically because it has a very low turn on voltage.

Also, make sure the S3 pin is actually switching when an over voltage happens. The pin must be set as a voltage clamp output AND the maximum main battery voltage should be set 1 to 2v above the power supply voltage.

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