Improve cooling

General topics and discussions about the VESC and its development.
michael_wintergarden
Posts: 85
Joined: 10 Aug 2016, 16:14

Improve cooling

Postby michael_wintergarden » 11 Aug 2016, 11:05

Hi guys,

Has anybody an idea how we could improve the cooling of the VESC?

I was thinking of desoldering the backside (Drain) and bending the Fets upwards so I could attach a big cooling plate directly on the backside of the fets.

Would this make sense?

thx

rew
Posts: 939
Joined: 25 Mar 2016, 12:29
Location: Delft, Netherlands.

Re: Improve cooling

Postby rew » 11 Aug 2016, 18:03

Yes. Note that cooling the "top" of the fets (the side you can see without desoldering) is useless. I've found a datasheet that mentions 10x the thermal resistance to that side of the case than to the side that you're planning on cooling. Note that the high-side-FET drains are all connected to "VMOT". So you can easily solder all three of them to a big copper plate (connect to VMOT as well!) and a heatsink.

On the other side, the three drains are connected to the motor phases. So you'd need an L-shaped copper conductor and then an insulated heatsink on that. Consider: There is also the IRFP7530. The problem is that it is a lot bigger: TO247.

Johannes94
Posts: 1
Joined: 17 Oct 2017, 09:47
Location: The Netherlands

Re: Improve cooling

Postby Johannes94 » 18 Oct 2017, 15:10

I know i am kicking up an old topic,

but would there be any other downsides to swapping to TO247 Fets, like the IRFP7530.
because i am interested in building a custom Vesc but with better cooling capability.

markorman
Posts: 14
Joined: 25 May 2016, 11:35

Re: Improve cooling

Postby markorman » 20 Oct 2017, 13:48

Best way to cool down smd mosfets is to solder them on top side, and have thermal vias to bottom side and then place heatsink on bottom side of pcb.

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Ecyclist
Posts: 30
Joined: 24 Jun 2017, 01:26
Location: San Diego, CA

Re: Improve cooling

Postby Ecyclist » 20 Dec 2017, 06:08

You can cool VESC like this.
VESC case 1.JPG
VESC case 1.JPG (52.9 KiB) Viewed 1187 times

VESC case 2.JPG
VESC case 2.JPG (59.85 KiB) Viewed 1187 times

VESC case 3.JPG
VESC case 3.JPG (41.69 KiB) Viewed 1187 times

rew
Posts: 939
Joined: 25 Mar 2016, 12:29
Location: Delft, Netherlands.

Re: Improve cooling

Postby rew » 23 Dec 2017, 23:42

Looks nice, but read my posting from 15 months ago: You are not effectively cooling the mosfets. any heat generated inside the mosfet has to travel through the 10x higher thermal resistance to the outside of the FET.

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Ecyclist
Posts: 30
Joined: 24 Jun 2017, 01:26
Location: San Diego, CA

Re: Improve cooling

Postby Ecyclist » 24 Dec 2017, 22:41

All my VESC fets are thermally connected to the case with Thermal Paste High Performance Heatsink Compound.
Am I missing something?
Thermal Paste High Performance Heatsink Compound.jpg
Thermal Paste High Performance Heatsink Compound.jpg (12.26 KiB) Viewed 1128 times

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TheFallen
Posts: 80
Joined: 26 Oct 2016, 10:49
Location: UK
Contact:

Re: Improve cooling

Postby TheFallen » 25 Dec 2017, 13:24

The heat in the MOSFET has to go from the silicon die, through the thick, insulating epoxy case then through your high thermal conductivity paste and the finally to your large aluminium heatsink. The epoxy dominateds the heat path and absorbs the heat eventually killing the MOSFETs.

For the IRFS7530 or D2Pak-7 the vast majority of the heat comes from the metal slug on the bottom of the case. For the VESC that means the heat goes directly into the PCB, from both sides. This makes any sort of effective cooling impossible. Ideally you'd want the metal slug to be soldered to a heatsunk PCB, not another MOSFET metal slug.

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Ecyclist
Posts: 30
Joined: 24 Jun 2017, 01:26
Location: San Diego, CA

Re: Improve cooling

Postby Ecyclist » 27 Dec 2017, 00:03

TheFallen wrote:The heat in the MOSFET has to go from the silicon die, through the thick, insulating epoxy case then through your high thermal conductivity paste and the finally to your large aluminium heatsink. The epoxy dominateds the heat path and absorbs the heat eventually killing the MOSFETs.

For the IRFS7530 or D2Pak-7 the vast majority of the heat comes from the metal slug on the bottom of the case. For the VESC that means the heat goes directly into the PCB, from both sides. This makes any sort of effective cooling impossible. Ideally you'd want the metal slug to be soldered to a heatsunk PCB, not another MOSFET metal slug.

Thank you for your explanation. So, it looks like I made a nice box to look at. You guys broke my hart. Do I understand correctly that VESC was not designed with the idea of effectively cooling MOSFETs?
Last edited by Ecyclist on 27 Dec 2017, 09:20, edited 1 time in total.

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TheFallen
Posts: 80
Joined: 26 Oct 2016, 10:49
Location: UK
Contact:

Re: Improve cooling

Postby TheFallen » 27 Dec 2017, 09:14

It is a very nice box to look at, and it fits really well with the rest of your bike.

As far as I can tell the VESC was not designed for lots of power or heat. It was designed to fit into tiny spaces which it does very well.

Someone tried attaching heat transfer pipes: viewtopic.php?f=7&t=622&p=3778&hilit=heat+pipe#p3773


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