Arlo's power stage.... New pics and video on page 22 + 24

[Arlo1]

As you know I am working on a BLDC controller Here OK So Its time to design my power stage. From this I will build 3 6 fet prototypes to test irfp4568 x6 irfp4668 x6 and irfp4468 x6 to their destruction Probably on my X5 but we will see it it can handle the power.... Once done I will look at the make power numbers and max current to see what I was to build for running colossus.

The Plan its to build the best layout possible. What I am thinking is using aluminum to prototype with then maybe built the finished product with Copper if it shows any advantage.

My goals are in this order. Best location of parts, Best cooling, Best size, best weight, best price.

What I am thinking is 3 layers all horizontal to each other with the fets laid on their backs the drain from the metal back on the body and the leg both attached to the Positive rail on the Hi side fets and on the phase rail on the low side fets. To help cool as good as possible and to keep the resistance as low as possible!!!

SO can anyone point me to something that's good to use to electrical isolate three layers of copper or aluminum but conduct heat though so I can cool the bottom?

and or a non conductive liquid??? This it my schematic so far....

[Arlo1]

Simular to this.

[Arlo1]

Something like this.... http://www.lairdtech.com/Products/Therm ... ting-TIMs/. They have electricaly conductive and insulating thermal stuff!

[Arlo1]

So far dave linked me this stuff. http://search.digikey.com/ca/en/cat/fan ... 9751?k=PGS
It conductrs heat at 2-5 times better then copper! But its not cheep the thin .025mm stuff adds about $1 per fet its under!
I have found some pastes that conduct electricity with silver or aluminum or copper mixed into them. I think cooling the fets needs to be Tied for #1 with low resistance as priority. Here is a data sheet.

[Nuts&Volts]

This stuff works pretty well too http://www.graftech.com/ We used it to distribute heat along the surface of our battery cells

[Arlo1]

This is what I am thinking for my layout sorry I have not mastered google scetchup or anything. But I need to save time for other things right now.

[Arlo1]

Ok so today I bought 65$ worth of 68oz 12gauge copper I cut up what I need for a 6fet controller and here is what it will look like. Once I test this I will cut the rest to make a bigger 24 or 36 fet controller with TO-247 package fets of what voltage I find best to work with what winding works best as a package for colossus. I have seen the 100v fet on paper will produce ~3 times less heat so....

[Lebowski]

looks cool (double meaning)

maybe you can get mica sheet material somewhere and cut it to size for you insulator/heat conducting material ?

[Arlo1]

Yeh I have been recomended to use this stuff from Dave, http://search.digikey.com/ca/en/product ... ND/1630955 It has 2-5 times less thermal resistance than copper!!! The only thing better is diamond. I will use it under the fets and the thin stuff conducts electricitiy 2 times as good as iron. I will also solder the drain leg to the plate under the fet to make sure the electrical resistance is uber low!

[mlim]

I thought graphite only transmitted heat well in two dimensions (i.e. parallel to the plane of the material). Isn't it a pretty good insulator in the other direction (perpendicular to the plane of the material)?

[Arlo1]

I thought graphite only transmitted heat well in two dimensions (i.e. parallel to the plane of the material). Isn't it a pretty good insulator in the other direction (perpendicular to the plane of the material)?

IM not sure it says A-B plane... But it doesnt list anything for the other direction

[Arlo1]

This video show some examples so I think I will get some. http://bcove.me/tua8w67g

[parabellum]

This video show some examples so I think I will get some. http://bcove.me/tua8w67g

Is it electrically conductive as well?

[Arlo1]

This video show some examples so I think I will get some. http://bcove.me/tua8w67g

Is it electrically conductive as well?

You can get it plain as electricaly conductive and electricaly insulative as well.

[Kingfish]

You can get it plain as electricaly conductive and electricaly insulative as well.

Using my best Mr. Burns voice: "Excellent!"

...and exciting! Very good info; I can see many useful applications

Keenly observing from afar, KF

[bearing]

2-5 times less thermal resistance than copper

Good find!

Imagine if there were PCBs made with this stuff as core. Then you could make high power electronics with surface mount transistors instead of the big through hole ones. That way you could put more transistor in a small space, to get better current sharing. With a big heatsink on the bottom side of the PCB, cooling of the SMD components would be as good as, or better than, a TO220 on a heatsink.

[Arlo1]

This might take a while lol but it will be worth it and should not be to bad for replacing fets.

[Alan B]

Good conductor. Hard to solder without overheating the FETs.

[Arlo1]

Good conductor. Hard to solder without overheating the FETs.

I have a plan for that

[Arlo1]

2-5 times less thermal resistance than copper

Good find!

Imagine if there were PCBs made with this stuff as core. Then you could make high power electronics with surface mount transistors instead of the big through hole ones. That way you could put more transistor in a small space, to get better current sharing. With a big heatsink on the bottom side of the PCB, cooling of the SMD components would be as good as, or better than, a TO220 on a heatsink.

It doesnt conduct electricity as cood as copper...

[Arlo1]

Tomorow I will drill and tap the heat sync and solder it all together and build the driver stage!!!

[parabellum]

It doesnt conduct electricity as cood as copper...

I imagine that non conductive type just has a tin layer of other non graphite stuff inside or outside. I wonder how heat conductive it is and how many volts it can handle before spark jumps, also how resistant to cuts of sharp transistor edges.

[Arlo1]

It doesnt conduct electricity as cood as copper...

I imagine that non conductive type just has a tin layer of other non graphite stuff inside or outside. I wonder how heat conductive it is and how many volts it can handle before spark jumps, also how resistant to cuts of sharp transistor edges.

The backs of these IRFP4668 fets are metal in the center with plastic on the edges. Its all listed on the data sheet for heat transfer rates. And the way I made my layout is for the back of the fets TO conduct as well as the drain leg, I will test it with just metal on metal and Krypton paper in between the plates for now.

[Arlo1]

I just found this stuff its price is cheeper and the specs are better. http://www.digikey.ca/ca/en/ph/LairdTec ... eries.html
I also ordered some t gard for the plates.

[Teh Stork]

I really like your layout. Nearly the same as I've got here in my notes, will post it up later

As far as soldering problems go: I would try to get some 43Sn43Pb14Bi, it melts at 163 degrees C, and have good mechanical properties. (similar to 63Sn37Pb, but 20 degC lower melt temperature). Bismut allyos aren't THAT expencive, but Indium totally is xD