Massive Heat Sink for MosFet ?

[Theatronics]

Thermodynamics. Now there is a fun subject.  :
Well I wish it was.  Having to build my first SUPER circuit
I am having trouble handling the high current and temps
created and I was wondering if anyone had a good solution
for this type of challenge.

The design is a H-Bridge that is rated at 100A / 100V DC
it is built using 16 N channel MosFet parts in TO-220 cases.

I had thought about 'clamping' 4 of them at time between 2 aluminum
plates and using the metal tab as one of the connections for the power (Battery or Motor)

Then I could bolt the 8Ga Wire to the metal plates.

While the trigger lead is just a low current signal it can be soldered to a wire with shrink tubing over it and run back to the board.

The trouble comes with the 3rd and last lead.  How do I connect 8ga (AWG) wire to a little to-220 case lead.  In effect I am trying to solder a 8ga wire to a 22ga one. 

One method I had seen involved bolting the remaining lead to one of the plates and then insulating the two plates.  This would result in a 'Chip Sandwich'  The top and bottom plates would be the POWER buss and the Trigger gate connections would be soldered directly to the TO-220 case pins.

Any better ideas out there?

Thanks,
-Mike

 

[indulis]

You don't... the FET's "share" the current so it doesn't have to be as large. If you don't like that thought, then solder the the "third" leg to a "bus bar".

 

[Theatronics]

eh,
Sorry, like I said I slept through the (Heat Flows) part of the classes.
(I lost it when we started talking about Resistance to Heat flow, I wondered if
A high Heat flow through a High Heat flow resistance created something..?
V = I * R  so  What = Heat *  Insulation.  All I could come up with is "Kool-aid Stands"
then I passed out)

Anyway,
Yes they share the current. 
4 devices on one side of the H-Drive (Lower Left lets say) carry 100A.
Each will balance (Thanks to low Rds and Thermal compensation) a nearly equal share.
(25A each)

So here is my little dilemma:
I could run 4 OZ copper and put nice thick traces on a PCB but I would prefer to
mount these beasties off board.  While I can use the TAB as one electrical connection and it seems capable of the current load (Again 25A) I am still concerned about the itty bitty legs of the TO-220 case and how to connect them.  I hope that the package sinks enough heat away from the legs that they don't blow like fuses.

I guess I'll just go with my current plan.
Electronics isn’t beautiful!

thanks
-Mike

 

[J57ltr]

One thing I have used in the past was Solder wick kinda like a busbar if I have to travel any distance with the connection. Just a thought.

Jeff

 

[audioguru2]

I am still concerned about the itty bitty legs of the TO-220 case and how to connect them.

 

[J57ltr]

Back when I used to set up amplifiers for higher current use I used Solder wick because I had to usually remote mount parallel Mosfets about a half an inch or so from the main board so I needed something to handle the current and keep from melting the solder. This was back when the hottest Mosfet was the IRF Z40. Basically make the solder wick form a tube and slide it over the drain and source connections, twist it so that its tight to the lead and wick it all the way to the end of there the lead is makw your connections and then apply solder throughout the wick.

Jeff