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Inmotion V12 MOSFET board replacement - Walkthrough & lessons learned.


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Nicely presented, and congratulations on the family addition!

Do you dare stress test the replacement board?

And yes, MOSFETs are static sensitive and can be damaged if they're zotted. It doesn't take an actual ZAP with spark to do them in, a discharge that you wouldn't ever notice can be sufficient. It's highly recommended to always wear a static protection wrist band when working with them (a real one, with the in line safety resistor, they aren't that expensive).

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6 hours ago, Richardo said:

* that Russian site's post if I googled. 

Just for completenes the link for the v12 articles there: https://ecodrift.ru/tag/inmotion-v12/

6 hours ago, Richardo said:

non-conductive thermal paste
* ideally you will have new, thick thermal pads. I don't know the dimensions, but some very thick like 5mm and some very thin possibly sub-1mm. If anyone knows the actual size of the thermal pads used, dm me and I'll update this post.

For thermal pads no thermal paste is needed - in contrary it's counterproductive. As in the link of the thermal pad you provided is written "Ideal Gap Filler"

Thermal paste is just needed to fill the "micro gaps" by the roughness of hard surfaces like metal and cermics/mica. And for this only in a minimal dose - every bit of thermal paste separating the metal and ceramics/mica decreases thermal conductivity!

6 hours ago, Richardo said:

21. replacement board already had thermal paste on the sides of the mosfets somehow? maybe a factory test.👇 

If it was already hard/dry then it sould be scraped/grinded/polished off!

Thermal paste just has a better thermal conductivity than air to fill out these micro gaps! But compared to the metal pieces the thermal conductivity is almost like a thermal insulator.

6 hours ago, Richardo said:

22. the insulator between mosfets and the heatsink. a very important piece of plastic!👇 

That's the "important real thermal pad". Unfortionately here (?all/most?) manufacturers combine thermal pads and thermal paste.

Best solution here would be an ceramic insulator (some kind of special ?Aluminium oxide?) followed by mica. For both of this thermal paste is needed. There afaik exist also very nice thermal pads (coming up to mica?)- which could be a nice upgrade.

Unfortionately there also exist many real bad thermal pads... :( Like hopefully here no "piece of plastic" was used to just insulate!

6 hours ago, Richardo said:

NB - after replacing then, use a continuity tester or the diode testing mode on a multimeter to check for continuity between the heat sink of the MOSFET and the black screw. I think the wheel will break if current can flow between the two.


Edited by Chriull
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