Re: dumping a lot of heat

On Wed, 4 Dec 2024 22:32:33 +0000, liz@poppyrecords.invalid.invalid
(Liz Tuddenham) wrote:

john larkin <jl@glen--canyon.com> 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.

>
Cooker hob ring?
>

What's that in American ??!!

I once used three industrial fan heaters as the starting resistor for a
large 3-phase motor with a big inertial load.  They were wired in delta
but connected to the star point of the motor - an arrangement which gave
the required starting current and torque.  After a predetermined time, a
normal 3-phase contactor shorted them out and closed the star point,
allowing the motor to run up to full speed.  The system worked
flawlessly, up to 8 times a day, for several years.

This looks like junk

https://www.amazon.com/dp/B00B8NY03G?ref=ppx_yo2ov_dt_b_fed_asin_title

but the price is right. I didn't understand it, so I got one, and I
still don't understand it.

The heater element has four faston lugs: one common, two resistors
each 22 ohms to common, one n/c.

The wires and thermal link are mysteries to me.

But something like this with a squirrel-cage blower behind it would be
slick. (or a hedgehog or a platypus blower.)