Voltage Clamp Power Resistor Overheating

General discussion of using Roboclaw motor controllers
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Eoghan Killalea
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Joined: Thu Feb 07, 2019 10:44 am

Voltage Clamp Power Resistor Overheating

Post by Eoghan Killalea » Tue May 07, 2019 3:54 pm

Hi Everyone,

I have set up a voltage clamp circuit, and it has fixed the voltage spike problem. The voltage used to spike to 23 when operating at 12voltages, but instead has a spikes to 9 voltages which is fine. However my power resistor is overheating alot, just when I turn on the main power, involving no motor control.

I have a 10k ohm resisotr between the gate and the sourse which should keep the MOSFET off before any voltage spikes, or am I incorrect?

Thanks for any help

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Basicmicro Support
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Joined: Thu Feb 26, 2015 9:45 pm

Re: Voltage Clamp Power Resistor Overheating

Post by Basicmicro Support » Wed May 08, 2019 9:46 am

Check it isn't turning on before needed. I usually recommend setting your main battery voltage limit to 1 to 2v above the power supply voltage(as indicated in Motion Studio). You will also be able to see if it is triggering when it should be by looking at the main battery voltage error light in Motion Studio. If it is Yellow the voltage clamp is activated(assuming you setup a voltage clamp output). If the clamp is active alot/all the time the power resistor will over heat.

Also you should get almost NO voltage spikes above the limit you set. If you are this indicates either your power resistor isnt low enough resistance(recommend around 3 to 2ohm 50watt resistor). or your mosfet isnt turning on all the way(what mosfet are you using).

Note I also recommend a chassis mountable power resistor. Even under light regen you will generate quite a lot of heat in the power resistor and being able to mount it to a chassis/metal case will keep it cool.

Eoghan Killalea
Posts: 5
Joined: Thu Feb 07, 2019 10:44 am

Re: Voltage Clamp Power Resistor Overheating

Post by Eoghan Killalea » Wed May 08, 2019 1:28 pm

I can not see any yellow lights on the Micro Studio, and the clamp seems to be on all of the time. I assumed that the 10k Ohm resistor would ensure the mosfet stays off when there is no voltage spike, but that does not seem to be the case.

My mosfet is a FQP30N06.

Just to iterate. Instead of a voltage spike, I am getting a voltage drop when I connect the voltage clamp, and it does not matter what mode the Roboclaw is set too.

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Basicmicro Support
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Re: Voltage Clamp Power Resistor Overheating

Post by Basicmicro Support » Thu May 09, 2019 10:01 am

Then it is likely your clamping circuit is wired up wrong(based on the overheating and the voltage drop no matter what). I recommend taking a picture of everything and listing how you have it wired and emailing that to us at support@basicmicro.com. We will help you get up and running.

Note we now recommend a better mosfet. See this post: viewtopic.php?f=2&t=487

The old one will work(assuming it is properly wired and settings are setup correctly) but the new one is much more efficient(the mosfet will almost never heat up) because it will fully turn on.

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