A few questions about dummy loads

z-adamson

Addicted Member
1) Which dummy loads do you use?

2) If I have four 2ohm dummy loads that are rated at 120watts and I wire all four in series, that gives me an 8ohm load. But, what is the rated wattage for this particular 8ohm load? Each is rated at 120watts, but if I run them in series the heat is spread out across all four, so does that mean this 8ohm load good up to 480watts? Any reason NOT to run several low-ohm dummy loads in series?

3) Where is a good place to buy dummy loads? I can't find much other than parts express, ebay and amazon. I see the silver finned aluminum ones and the green tubular ones. Is this all there is to choose from? I currently use 300watt 8ohm green tubular dummy loads and man do those things run HOT, even when testing a 120watt amplifier.
 
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[1] Dale NH250-8

[2] The power distributes equally if the resistances are equal; series or parallel. The extra connections in a series hookup could make total resistance a bit high.

[3] Dale's NH250 series is the gold standard. They're available from Mouser and Digi-Key at eyewatering prices. Those green Chinese wirewounds are nonlinear enough to corrupt amplifier distortion measurements unless the analyzer is attached directly to the amplifier's output terminals.
 
[1] Dale NH250-8

[2] The power distributes equally if the resistances are equal; series or parallel. The extra connections in a series hookup could make total resistance a bit high.

[3] Dale's NH250 series is the gold standard. They're available from Mouser and Digi-Key at eyewatering prices. Those green Chinese wirewounds are nonlinear enough to corrupt amplifier distortion measurements unless the analyzer is attached directly to the amplifier's output terminals.
Wow, even with your warning of eye watering prices I was not prepared for that!
 
1) Which dummy loads do you use?

2) If I have four 2ohm dummy loads that are rated at 120watts and I wire all four in series, that gives me an 8ohm load. But, what is the rated wattage for this particular 8ohm load? Each is rated at 120watts, but if I run them in series the heat is spread out across all four, so does that mean this 8ohm load good up to 480watts? Any reason NOT to run several low-ohm dummy loads in series?

3) Where is a good place to buy dummy loads? I can't find much other than parts express, ebay and amazon. I see the silver finned aluminum ones and the green tubular ones. Is this all there is to choose from? I currently use 300watt 8ohm green tubular dummy loads and man do those things run HOT, even when testing a 120watt amplifier.

Are you using good heat sinking with those resistors? Check out how avionic has his mounted. And I know Ray Gianelli has posted pics of his heat sink creation.
 
DSC03371.JPG More eye candy
 

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must admit i dont use dummy loads . i use my 40w aiwa bookshelf's instead . never had any complaints . those things will handle 600w no problem .
if i did have dummy loads i would only use for 2 seconds at most for max power testing .
 
Are you using good heat sinking with those resistors? Check out how avionic has his mounted. And I know Ray Gianelli has posted pics of his heat sink creation.
As near as I can tell, there is no way to heatsink mount the dummy loads I use.
 

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i looked at some like that .. they look like escalator braking resistors . shouldn't need heat sinks .
I guess it depends how you define "need".

They do run hot. Wether or not that means they need heatsinks, I couldnt say, but it would be nice if they had a way to be heatsink mounted.
 
for example 100w is pretty hot . so long as they are run in tolerance they should be fine . maybe try a fan or submerse in oil ?
 
The gold colored heatsink was cannibalized from an ABB 3 phase freq drive. The large aluminum heatsink was cannibalized from a 36-volt forklift battery charger.
 
I bought some huge dummy loads from the auction site. Marked 1,000 watts 8 ohms:
20181030_072538.jpg

I mounted them on some large heat sinks I got from a friend who is an electronics recycler. I don't know what he salvaged them from:
20181030_072534.jpg
This is the finished product. I ran leads out the back and into my distortion analyzer, which will measure 2 channels at once:
20181120_051059.jpg
 
6x ATE 12 ohm 100w resistors wired series/parallel for 8 ohms and 8 kilos of heat sink. At 200w (40v) it only got lightly warm to the touch after 15 minutes. I was planning on adding a couple of fans but they weren't really needed.

DSC05212.jpg DSC05214.jpg DSC05220.jpg DSC05526.jpg

Cheers,
James
 
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