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Heatsink for the FETs

Posted by animoose 
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animoose
Heatsink for the FETs
May 25, 2015 08:30PM
Should I add heatsinks to the FETs on a RAMPS 1.4 board? I've read various reports of them overheating, and I've got a few spare small heatsinks and some thermal paste lying around. Is it worth doing this as an extra safety measure?
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AndrewBCN
Re: Heatsink for the FETs
May 26, 2015 12:25AM
The heatbed MOSFET benefits from a heatsink, the other two don't need it. Since a small heatsink costs $0.20 or so, there is no excuse for not using one.
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enif
Re: Heatsink for the FETs
May 26, 2015 02:21AM
When adding a heatsink, don't forget that it will be at 12V when the MOSFET is off. So make sure not to damage anything by accidental shorting...
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o_lampe
Re: Heatsink for the FETs
May 26, 2015 07:26AM
Kapton tape between heatsink and FET would insulate the sink. As long, as the screw to fix the heatsink doesn´t make contact.
-Olaf
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AndrewBCN
Re: Heatsink for the FETs
May 26, 2015 07:46AM
Quote
o_lampe
Kapton tape between heatsink and FET would insulate the sink. As long, as the screw to fix the heatsink doesn´t make contact.
-Olaf

It would also act as a thermal insulator, defeating the purpose of adding the heatsink in the first place, so: not recommended. As enif wrote above, just make sure the heatsink does not touch anything else on the RAMPS, and everything should be fine.
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cdru
Re: Heatsink for the FETs
May 26, 2015 08:46AM
Or the other option is to replace the mosfet with a better one that doesn't need active cooling to survive.
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AndrewBCN
Re: Heatsink for the FETs
May 26, 2015 10:26AM
Quote
cdru
Or the other option is to replace the mosfet with a better one that doesn't need active cooling to survive.

Very true, a good solution, although it's a little bit more expensive ($1 for a new MOSFET - IRLB8743 recommended - vs. $0.20 for a small TO-220 heatsink!) winking smiley and does take a lot more work and time (about 20 minutes to unsolder the original MOSFET and solder the new one in, assuming average (de-)soldering skills, vs. 1 minute to install the small TO-220 heatsink). The advantage of a better MOSFET, besides dissipating less heat, is that it transfers more power to the heatbed i.e. it is more efficient as a switch.
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animoose
Re: Heatsink for the FETs
May 26, 2015 07:37PM
Thanks for the advice, everyone. Is the heatbed MOSFET is Q3 in this diagram (http://www.reprap.org/wiki/File:Arduinomega1-4connectors.png)? If so, it looks like there is plenty of clearance around it so I can attach a heatsink. The one I had in mind is a small (15mmx15mm) one from MCM (http://www.mcmelectronics.com/product/83-13677?utm_source=transactionalemail&utm_medium=email&utm_campaign=ConfirmEmail). I have some larger ones as well, but then I would be more worried about an accidental short.
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itchytweed
Re: Heatsink for the FETs
May 26, 2015 07:46PM
Even a small fan blowing over the device will help as well.
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AndrewBCN
Re: Heatsink for the FETs
May 26, 2015 09:36PM
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animoose
Thanks for the advice, everyone. Is the heatbed MOSFET Q3 in this diagram ? ...

Yes, that's the one.
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AndrewBCN
Re: Heatsink for the FETs
May 26, 2015 09:39PM
Quote
itchytweed
Even a small fan blowing over the device will help as well.

I fully agree and always recommend the use of an 80mm fan over the RAMPS, which insures the stepper drivers are properly cooled:


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animoose
Re: Heatsink for the FETs
May 26, 2015 09:49PM
Looks good. I have a spare fan somewhere. Looks like you have the mounts are something I could print ... hmmm ... if only my printer was finished.
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