Re: dumping a lot of heat

On Fri, 6 Dec 2024 17:56:05 +0100, Lasse Langwadt <llc@fonz.dk> wrote:

On 12/4/24 22:55, Joe Gwinn wrote:

On Wed, 04 Dec 2024 13:29:03 -0800, 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.

 
Yes.  A toaster element: Nichrome wire woven onto a mica card in a
perforated metal box.
 
Already packaged, one can get ballast resistors for high-power VFDs
used to power machine tools.  The ballast resistor absorbs the energy
stored in a large chuck spinning fast, when it's time to come to a
stop quickly without over-voltage tripping the VFD.
 
.<https://www.automationdirect.com/adc/shopping/catalog/drives_-a-_soft_starters/ac_variable_frequency_drives_(vfd)/braking_units_-a-_resistors/br-n1-800w18p0>
 
Joe Gwinn

>
>
<https://www.reddit.com/r/CNC/comments/1es1d01/someone_didnt_believe_me_when_i_said_that_our/>

Yeah, small shops often do this kind of thing.  Cheap, and works just
fine.  Probably the original brake resistor had failed.

Joe Gwinn