F5 For Low Z Loads ?

[flg]

Originally Posted by jacco vermeulen

Problem in your case, someone else does the slapping.

And you slap yourself and wish someone else did?

[flg]

Originally Posted by Zen Mod

...I was slapped by Mr. Insomnia itself (G. Rollins)...

He's gone dude. who's Mr Insomnia himself now?

[Zen Mod]

dunno ;
Jacco ?

[flg]

Ya know, you could be right?

[jacco vermeulen]

Originally Posted by flg

someone else ?

Hardly.

I spend all of my time trying to recollect why i slapped myself.
And when i do remember, i have to slap myself again.
Next morning, the very 1st thought i have is : Why did i slap myself ?

But that's another story, at least i think it is, not sure.

[flg]

I've been busy and sick and busy but, I have some news on my high curent F5 project. I have some HeatSink USA 10.08" profile, 8" (200mm) sections that I tested for dissapation and temp rise. I used one like you see in the picture in post #23 mounted with 4 IRFP244s. I set up an adjustable current source with 1 ohm source resistors and a BC550 driving the gates. I used Kerafoil pads from Zhoufang on the transistors. I'm thinking I would like to have enough capacity in my sinks to dissapate 125W. effectively, the equivalent of 2 F5s.
The Sink was supported 3" above the table on the outer fins only, allowing for generous convective airflow on all sides. With room temp about 20C I adjusted the current for 1.3A/device with 24V D-S and let them sit for a while. After whaiting for hours, stabalization did not really take long, it was stable after the first hour. Device case temeratures rose to about 80C. The H.S. temp 1/2" from the device was about 70C. At the top of the H.S. the temp was almost 60C.
Although this is doable, I would really like to have more wiggle room. 60C at the H.S. outer extremes is a little hotter than I'ld like. I would also be happier if I could experiment with higher currents meaning, I need more H.S. I have some ideas towards improving things that I think will accomplish that.

[flg]

Not willing to settle for less idle current than my Heat Sinks will handle, in the next few day's I will hammer and chesil out another H.S. to aid the original. as in the sketch below.
Any other/better ideas?

[Andersonix]

If you want to go that way, to make the inside extra heatsink, I suggest cutting one the size of the main hs in half through the bandsaw (almost the way you show, but all the way across -- no waste, right?) and mounting it flush with the top of the main hs. You will need good ventilation through the bottom panel. Then turn the pcb or mount the outputs so they're are as close to the center of the assy as possible.

[flg]

Andersonix, I think I see what your your saying. There may also be issues of flatness in the 2 baseplates that require gap pad or gobs of Arctic Silver 5 or what ever to effectively make up for the lack of flatness/gaps. I could even use Arctic Silver epoxy and glue them together but, I am affraid of the end to end flatness, expansion of aluminium and maybe future use of my sink material. Although, I have used A.S. Thermal Epoxy, it's never been permanent for me. I've only used it to glue on thermal couples not for 80 insq of surface? Peices would aleviate much of that worry. I do have extra material to wack up though. I'm also conserned with making it look arteeestic and pretty, oh yea, WAF... I would be putting the In/Outs/+Gnd- on a plate across the ground away fins in the back and the PWR Supply in a seperate chasis in this case. One giant Mono Block of heat sink Mono Block would be cool.

[Andersonix]

Is this what you mean? It doesn't seem much more effective than just one heat sink.

Two side-by-side would be better, but that arrangement has its own problems.