From: "Lukas Louw"
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Subject: Re: Question about linear derating factor for MOSFETs
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NNTP-Posting-Date: Tue, 12 Nov 2002 23:15:55 GMT
Organization: AT&T Worldnet
Date: Tue, 12 Nov 2002 23:15:55 GMT
No, being lazy, I just took a brute force approach - I have them mounted on
these huge amplifier heatsink extrusions, the extrusion is 8" wide,
baseplate about 1/2" , with 2" long fins, the resistors are mounted on the
flat baseplates. I simply had one of my clients send me 4 x 3 ft lengths of
these, for a 4 channel loadbank. Iv'e run 2KW continuous into 1 ohm loads,
and the sinks have never gotten much beyond 60 degrees C. Granted, I've not
run continuous power from these amplifiers for more that 20 minutes or so,
then I run them at 1/3 power sine, or a pseudo noise signal to simulate
music conditions, and then of course average power and resistor heat is
maybe 40% or so of continuous...
Any other power resistors will require the same heatsinking as these
> I was doing a few calculations (all I seem to be doing lately) and the
> derating of 8.73-degrees C/W is a real killer for those resistors.
> With a 4x4x1.25" bonded fin heat sink, with a fan, I can only get
> about 200W out of those resistors before I exceed the rating. The 600
> watt rating is only at a 70-degree C heat sink temperature (I'm
> assuming directly against the case).
> I'm hoping I made a mistake in the calculations though, the price of
> those resistors is amazing.
> Have you run the derating numbers for your load banks?
> >>>Nah, just 4 resistors and 6 heavy duty relays, some heatsink extrusion
> >>>little CMOS switching circuit, you can make a beefy switchable 1 ohm
> >>>watt, 2 ohm 1200 watt, 4 ohm 2400 watt and 8 ohm 1200 watt load