Dummy Load for Bench Power Supply - Resistors?

[DW1961]

Hopefully you've used a smear of heatsink compound underneath the resistors. With a milled / extruded surfaces, the actual metal to metal contact area is minimal, so the resistors will end up running significantly hotter than the heatsink.

I was going too, but if you look at the screw holes on the resistors, the design is bad. Both holes are on the same side. What I did do is tape down some emery cloth and sanded the bottom of the resistors until they were as flat as they are going to get. Then I did the same thing to the heat sink. It's transferring heat. Between the resistors, the heatsink was the same temp as the resistors. That heatsink is just way too small. It would probably help a lot if even just the fins were 1" instead of .38". That would nearly triple the area. Next time I'll insist on getting staggered screw holes, or even all corners, but hard to find on Amazon.

25 minutes for the first test, then I just let it run until the temp stabilized, around 10 minutes each after the initial 25 minute warm up time,.  each test. Ambient temp around 23C:
050W stable @ 054C: Low RPM 120mm computer case fan.
100W stable @ 073C: Higher RPM 120mm computer case fan.
150W stable @ 096C: Higher RPM 120mm computer case fan.

I accidentally threw away my Nidec Servo Gentle Typhoon 1850RPM CPU radiator fans. Those things moved 58CFM with high pressure. So I can't do a test with those wind tunnels. In any event, it looks like adding a fan, in some future configuration/open ended box, will cool that set up just fine. A better heat sink would allow higher wattage, though. Each resistor is rated at 100w.

As suggested above, I ran one set of 100W 6ohms resistors in parallel and another 100W 6ohms resistors in parallel and then ran those two parallel groups in a series to get 6 ohms. Since all of the resistors are 6 ohms, I'm assuming power is divided by each resistor?

If so, at 150 watts, each resistor is working at roughly 37.5 watts each? That's still far below their rated 100 watt rating, which means they could use much better cooling. I should be able to get 200+ watts out of them in this parallel configuration (derated 50%). And for short periods even 300 watts (75w each resistor).

[tkamiya]

Don't forget simple incandescent light bulbs!  A caveat is, as it heats up its ohmic value will increase (draws less current) if you just want to load it up, it's a cheap way to go.  Buy buy a piece of wood, a bunch of ceramic sockets, and some wires, you can make all kinds of dummy loads.  Replacement is cheap, too.

I actually have 40 watts, 60 watts, 100 watts, 150 watts, 500 watts, 1500 watts, and 2000 watts (all rated at 120 volts) bulbs.  They come in handy when I have to test extreme situations.  2000 watts bulb is about the size of a toddler's head!

[theHWcave]

Totally agree with @tkamiya. Don't forget light bulbs (incandescent of course). Another use case is wiring them in series with the mains input of a device as current limit in case there is a short circuit in the power supply. If the bulb(s) light up brightly, you have a problem.