Choice of Load resistor.

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Alan0354

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Joined 2014
#1
What is your opinion of using wire wound resistor for dummy load?

I am thinking about using 4 of the 16ohm, 25W or 50W wire wound resistors in parallel to get 4ohm load. I do this to lower the inductance with 4 in parallel compare to a single 4 ohm resistor.

It is hard to find and expensive to get a bulk resistor in that size.

Anyone have opinion on this or have other suggestions?

Thanks
 
#2
Electric water heater elements might be your best bet.

You can calculate their resistance via the usual equations knowing their rated voltage and wattage.

They tend to have low inductance and temperature coefficients.
 
#3
Actual speakers have both inductive and capacitive components, so a simple resistive load won't really give you the whole picture. Having said that, you can get closer to the truth by testing briefly with a resistive load that is 20 to 30% lower in resistance than the nominal impedance of interest. For example, if you want to get a good idea how well an amp will work with a nominal 4 ohm load, use a 3 ohm resistive load with a high enough power rating, just don't try running the amp long term at full power into that load, just run long enough to get you test done. But if you want to test for long term power output it's better to use a 4 ohm resistive load for that.

Mike
 
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#4
Thanks both of you for your answers.

Hi Michael, you almost make it sounds like it's a good thing to use wire wound resistor.

I mainly want to test the distortion, I don't care about testing the power output or even how much power it can handle. This is hifi amplifier, not guitar amp!!!
 
#8
Speaking of heater. If you want 4ohm heater, the heater has to draw 120V/4=30A for 120VAC. That will be a heater of 3600W. That's a huge heater!!!

I looked at some water warmer heater that you stick into a small jar to heat up water, those are only about 1600W!!!

More importantly, they are not cheap!!! I can get a non inductive resistor for $19 and much cheaper if just wire wound.

If you happen to have a heater at hand, it's ok. But if you have to go buy one, then it's a different story.
 
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#9
For what it's worth, just out of curiosity I just checked the power resistors I've been using to test my amplifiers. They're 10 ohms @ 100 watts wire wound (NOT non-inductive design) with an adjustment slider/collar that I scored at a surplus store for a couple of bucks each. With the slider set for 8 ohms the inductance is lower than .05 mH, which is the lower limit of the tester. So stray inductance is probably not an issue for this type of resistor for testing amps.

Mike
 
#11
Alan0354 said:
Speaking of heater. If you want 4ohm heater, the heater has to draw 120V/4=30A for 120VAC. That will be a heater of 3600W. That's a huge heater!!!
Click to expand...

I picked up some appropriately rated water heater resistors on eBay for about $10 each, which is pretty cheap for a resistor that can be run @ 3600 watts if immersed in water.

This is a resistor that I found sold for use as a dummy load that had excessive temperature coefficient:

http://www.ebay.com/itm/200W-8ohm-aluminium-shell-braking-resistor-resistance-Dummy-Load-for-Audio-/350924428591?pt=LH_DefaultDomain_0&hash=item51b4b9d52f


My daily drivers are 200 watt Arco and Dale* branded devices in the classic die-cast housings that cost money. But I've tested some of these more cost effective approaches for friends who want to get started in measurements.

* My audio club was given some Dale power resistors and other gear when a certain well-known audio magazine moved their offices in Manhattan. I believe that I have the AP System 1s and load resistors that were used by Julian Hirsch. His name was crudely scribbled on some of the boxes...
 
#12
Alan0354 said:
What is your opinion of using wire wound resistor for dummy load?

I am thinking about using 4 of the 16ohm, 25W or 50W wire wound resistors in parallel to get 4ohm load. I do this to lower the inductance with 4 in parallel compare to a single 4 ohm resistor.

It is hard to find and expensive to get a bulk resistor in that size.

Anyone have opinion on this or have other suggestions?

Thanks
Click to expand...

Lots of stuff like this for affordable prices on eBay.
 
#14
davidsrsb said:
The gold coloured high power wirewounds with mounting flanges need to be bolted to a slab of metal
Click to expand...

Those gold resistor used to be bigger in size for the power rating. I even have a a Dale 100W that is like 3" X 1.5" size. BUT when I ordered 4 of the 4ohm 100W resistors, they are like 2" X 0.75"!!! They looked like 25W if I have to guess. They definitely need to be mounted on the heat sink. My original Dale is questionable, it is big.
 
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