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NNTP-Posting-Date: Fri, 06 Dec 2024 21:23:04 +0000
From: Joe Gwinn <joegwinn@comcast.net>
Newsgroups: sci.electronics.design
Subject: Re: dumping a lot of heat
Date: Fri, 06 Dec 2024 16:23:04 -0500
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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