Dummy Load question

[nevetslab]

I make my own with precision and for peanuts out of cheap spiral wound nichrome wire intended for ultracheap food heaters (probably forbidden in lawyer happy First and Second World for safety reasons, since live and red hot wire is exposed).

You can not solder it so eyelets or screws are needed for contact.

Use them straight for low power tests (up to 100W), add a fan or drop (200W) them in a bucket of water or oil for scary high power dissipation (400W each resistor section) .





made for these:



Just stretch wire , measure 8 ohm sections, cut and mount each, combine as needed.

Remember mounting base must be insulating, resist red hot temperatures and , if used wet, stand water or oil.

I use Micanite, which is the sheet material normally used for such purposes .... wrongly called Mica which it is not.

Micanite is to Mica what chipboard or MDF is to wood.

You can get both out of a cheap hair dryer:



Notice the elements I mentioned: nichrome wire, micanite and eyelets.

You may even add an external power supply for the motor and fan and kludge an air cooled load resistor.

Motors are typically 6 to 12V or thereabouts and run in series with heater resistor, that´s why I suggest an external independent supply.

Here you can see the bridge rectifier so they get DC for motor.

Out of curiosity, have you ever swept the impedance of these nichrome heater coils? I've been meaning to do that on my large Dale load banks.

[Chuck H]

Out of curiosity, have you ever swept the impedance of these nichrome heater coils? I've been meaning to do that on my large Dale load banks.

Do you think it could be an issue? Well, maybe not for audio, but perhaps something like a ham station or something?

[soundmasterg]

For those who need up to 200 watts, Ted Weber sells a pretty nice unit that has inductance and resistance. I guess that is for a more accurate load that is closer to a speaker than a pure resistive load.

https://www.tedweber.com/tru-load

I have one of these that I use for general use, and I've also got a bunch of those huge Ohmite resistors that I can use if I need a pure resistive load. I put them in a chassis box and with eight 16 ohm 100 watt resistors with various combinations I can get a high enough power capability that even with an SVT at full tilt the resistors didn't even get hot.

Greg

[drewl]

I had no idea those dynamite stick Ohmmite's were so expensive.
We literally have boxes of all different values at work I can use.

Also a giant switchable load for testing huge power supplies.
It looks like a large space heater with all them coils.

[nevetslab]

Do you think it could be an issue? Well, maybe not for audio, but perhaps something like a ham station or something?

For general purpose testing......verifying the amp delivers nominal power to the load at full power and into clipping without having to listen to that on a speaker system, shouldn't be an issue. These being helical wound, I'd expect some inductive reactance, leading to a rise in the impedance with increasing frequency.

From the pure brute-force standpoint of having an inexpensive high power load that can handle lots of power without failure, it sure is a clever solution. If I didn't already have the two load banks I built years ago, I'd cobble some of these together. Mostly curious to see what the wideband impedance is.....where the rise in impedance occurs. It would differ based on the coil diameter/length & wire size, I'd guess. For use in getting accurate power measurements, one would need to know what the load impedance is at the test frequency. It turns out the two load banks I have, one built with Dale 4 ohm 1% RH-100 series resistors, the other with Pacific 2 ohm 3% 250W 250CH series resistors are NOT the non-inductive types that I thought I had. I'll post some impedance plots of these at some point when I get a chance.

[J M Fahey]

Never traced them but inductance should be low within the Audio band and anyway speakers are quite inductive, so ...