Heat sinking a controller for passive temperature reduction?

[Fordulike]

I intend to run a fairly powerful controller inside a bag.
This poses the problem of no air flow, and little air space around the controller.
Would attaching a large heat sink, with a thermal adhesive pad to the top of the casing, provide a viable passive solution to dissipating heat?

Heatsink: Large Aluminium Heatsink Power Amplifier/ Power Supply/ Transistor/IC/FET/PA | eBay

Thermal pad: eBay - The UK's Online Marketplace

Click on the above two links to see an example of what could be used.

 

[Blew it]

Heatsinks require airflow

A difficult one. Firstly, the fets are usually fixed to the side of the controller housing, that's where an external heatsink would need to be attatched.

Secondly, heatsink radiators require airflow through the fins to be effective.

 

[Fordulike]

A difficult one. Firstly, the fets are usually fixed to the side of the controller housing, that's where an external heatsink would need to be attatched.

So primarily, I should aim to position the controller within the bag, so that it has as much air space around the FET side of the casing?

Surely, bike controllers have been designed to operate in environments where there is little air flow, otherwise they would have large fin heatsinks attached to the casing on the FET side?

 

[NRG]

Its the peak current that kills the FETs, high peak current = short term heating of the silicon junction inside the FET, too much and it blows. Heatsinks wont have any effect during short term peaks as the heat cant be drawn away from the junction fast enough.

The only advantage of extra heatsinking is if the controller is going to be run continuously at a known current, well within the rating of the FET....the heatsink can then be sized appropriately...but for the short term peaks that take the FETs out its no use...

 

[flecc]

My eZee ones, the originals with over 27 amp capability, are in a small closed plastic box behind the battery carrier and squeezed between the bottom of the battery and the rear mudguard so little airflow. Despite that both have given no trouble since mid 2006.

View on Quando

View on Torq 1 stripped (just ahead of brake)

I doubt a bagged heatsink would help much, the sink would have to have it's fins protuding to outside the bag.

 

[Scottyf]

I used to constantly run my controllers in a bag in a sepreate compartment to the batteries.
So I guess there wasn't as much air flow and it did get warm @ 66v 30amp.

But it always worked and never failed.
I think you have to really push a high amount of amps for a long time for the heat to really build up.

I never worried about it anyway.

Infact it was nice in the winter with lipo as the backpack became a little back heater and I could tell from the warmth how much I was pushing batteries / controller.

Still probably dangerous though.

Its better to get some air flow to the controller but I don't think its needed as much as what people seem to point at.

 

[NRG]

...as I said its not long term heating that kills them but short term high level peaks.