Re: dumping a lot of heat

On Sun, 8 Dec 2024 00:19:37 +0100, Klaus Vestergaard Kragelund
<klauskvik@hotmail.com> wrote:

On 04-12-2024 22:29, john larkin wrote:

I'm thinking about building a biggish rackmount dummy load box. It
would simulate series resistance and inductance. Part of the problem
is that it will need to dump a lot of heat.
 
We are using copper CPU coolers on PC boards, which are great up to a
couple of hundred watts, but I'd like to do a kilowatt or two.
 
https://highlandtechnology.com/Product/P945
 
It would take a heap of expensive extruded heat sinks and fans to get
rid of a kilowatt. At 1 K/W, a pretty good heat sink, that's 1000 degC
temp rise.
 
A small hair dryer can dump a kilowatt. So some sort of red-hot
nichrome coils and a vicious fan might work.
 
I'd prefer to not use water.
 
I wonder if there is some sort of runs-red-hot power resistor.
 

I have thought many times, but never got around to make an electronic
load with many parallel circuits. At JLCPCB the mounting cost is low, so
no biggie
>
The idea is to spread the heat out, not relying on one element, but
many. Imagine a big PCB, like A3 size, spread out with 100 equal
circuits electronic loads. Frequency response would be high, power
dumping high also. Use a aluminum PCB like those used for LED lamps to
get even lower Rth

Needs a fan too, somewhere.

A CPU cooler is cheap and has a fan. It is a bit klunky to mount on a
PCB.

There are some nice heat-sinkable resistors. My TO-220s are cheap;
I'll TDR one and see how fast it is.

People make crazy high power aluminum nitride microstrip RF resistors
too.

I tested a Caddock DPAK surface-mount thick film resistor and it was
pretty good. I'd expect the cheaper flat Ohmites or Riedons to be
similar, likely better. I should TDR some.

https://www.dropbox.com/scl/fo/9ms2pdlhiqhhkuk6daviz/ADejWZO8YqocNAzyZD6i9cs?rlkey=j6y6vexfkpzmbyn36it0tjm9b&dl=0

It would be interesting to make a microstrip on one of those LED-type
aluminum boards. The white dielectric looks very thin.