null Posted February 1, 2021 Share Posted February 1, 2021 Replacing my Sherman board soon, and I see the old one uses a thermal pad for the heatsink. Could there be any benefit switching to thermal paste (CPU type)? I've read everything and its opposite so I'm interested if anyone has an informed opinion for our use case. Thanks for any input. Quote Link to comment Share on other sites More sharing options...
Chriull Posted February 1, 2021 Share Posted February 1, 2021 4 hours ago, null said: Replacing my Sherman board soon, and I see the old one uses a thermal pad for the heatsink. Could there be any benefit switching to thermal paste (CPU type)? Depends on how the mounting is in detail. Thermal paste is great for two level and flat surfaces which have great metal to metal contact. The paste fills only the "holes by the surface roughness". As soon as the surface can get any spacing by for example bending thermal pads could be better. If one chooses a good one... Best again to prevent any spacing by design... And of course with thermal paste there is no electrical insulation, in case this would be needed... 1 Quote Link to comment Share on other sites More sharing options...
null Posted February 1, 2021 Author Share Posted February 1, 2021 Thanks for the reply, yes the mosfets are probably less flat than a CPU spreader. But then they should be fairly tight from the screws. Anyhow, I had heard kick scooter controllers (at least mini motors) often had sub standard paste, so I wondered whether it was worth changing this thermal interface while the board was accessible. So probably not worth it then. Quote Link to comment Share on other sites More sharing options...
Chriull Posted February 1, 2021 Share Posted February 1, 2021 2 hours ago, null said: Thanks for the reply, yes the mosfets are probably less flat than a CPU spreader. But then they should be fairly tight from the screws. Mosfets a level enough - just fastening them too much can bend them. In this case one needs in any case mica/ceramic plates for insulation additionally to the thermal paste. Plus insulation "rings" for the screws. This solution is much better than the used thermal pads, although some "real good" packs should exist? A test and comparison was posted here (youtube) when the ?nikola? had the problems with the plastics between mosfets and heatsink. 1 Quote Link to comment Share on other sites More sharing options...
null Posted February 1, 2021 Author Share Posted February 1, 2021 (edited) I see, it has to insulate and not just be non conductive. On the kick scooter controller I disassembled the mosfets went straight on the aluminium with paste, hence I thought that was enough. That controller had died so it wasn’t the best conception either. Here is the back of the Sherman board (sorry bad pics, will take better in daylight) not much to see. The charge port arrivals are really very close to each other. Edited February 1, 2021 by null Quote Link to comment Share on other sites More sharing options...
Chriull Posted February 1, 2021 Share Posted February 1, 2021 11 minutes ago, null said: I see, it has to insulate and not just be non conductive. Insulate and not conducting is theoretically the same - but yes, once it conducts the mosfets are burnt and one faceplants... 11 minutes ago, null said: On the kick scooter controller I disassembled the mosfets went straight on the aluminium with paste, hence I thought that was enough. That controller had died so it wasn’t the best conception either. One would have to look at the used components and how they are assembled. A design as used with our EUCs with all mosfets with just thermal paste on the heatsink would never work... Maybe sometime if the aluminium plate is eloxated... But by vibrations the shortcircuit/faceplant would be inevitable 11 minutes ago, null said: Here is the back of the Sherman board Ah great - the to247 package of the mosfets already has the insulation for the screws build in! Quote Link to comment Share on other sites More sharing options...
null Posted February 1, 2021 Author Share Posted February 1, 2021 (edited) 54 minutes ago, Chriull said: One would have to look at the used components and how they are assembled. A design as used with our EUCs with all mosfets with just thermal paste on the heatsink would never work... I remembered wrong, there was an alu strip grouping / isolating the mosfets already, the thermal paste was between it and the housing So good then, learned that today. Edited February 1, 2021 by null Quote Link to comment Share on other sites More sharing options...
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