500W 50 ohm DUMMY LOAD

[unit_399]

I ordered 2 of these yesterday (10 pieces total). I want to build a 1kw dummy load. 10 of these in parallel mounted on an old linear heat sink with the cover and a small fan on one end should work. what do you guys think ??? Price is right.

- 399

http://www.ebay.com/itm/5pcs-100W-5...768640?hash=item4881a5bf80:g:g~AAAOSwkl5XdiK~

 

[Beetle]

Good luck. I don't know what the description means ("98% new and real shot"). Ten of them in parallel means you have ten times the potential failures. Then again, ten 50-ohm resistors in parallel results in a resistance of only FIVE ohms, not 50.

 

[Road Squawker]

Good luck. I don't know what the description means ("98% new and real shot")....

My knowledge of Chinglish tells me that means the picture is a real (actual) picture, shot (photographed) by the seller.

The 98%,...........??

 

[Klondike Mike]

...10 of these in parallel

?? - See below; I bought one of these awhile back. Just haven't found a suitable heat-sink for it yet (suitable meaning good price). As mentioned, one piece, no fuss.

http://www.ebay.ca/itm/800-Watt-Hyb...050379?hash=item56898f318b:g:zb8AAOSwDNdVhIeA

 

[fourstringburn]

I would personally have went with an oil can since the heat factor using one isn't much of an issue with big power.

But making your own is always a good learning experience.

Here is a good link with schematic:

https://www.flickr.com/photos/bswadener/sets/72157625292963590/

 

[Tallman]

I ordered 2 of these yesterday (10 pieces total). I want to build a 1kw dummy load. 10 of these in parallel mounted on an old linear heat sink with the cover and a small fan on one end should work. what do you guys think ??? Price is right.

- 399

http://www.ebay.com/itm/5pcs-100W-5...768640?hash=item4881a5bf80:g:g~AAAOSwkl5XdiK~

I would buy an item called "Cantenna". Watts no problem.

 

[Captain Kilowatt]

I would buy an item called "Cantenna". Watts no problem.

I have been trying to get away from oil filled loads. I have a home made load consisting of a Gates 1000 watt dummy load made from ten 100 watt 500 ohm Globar resistors in parallel. It is suspended in a 12 quart stock pot full of silicone load oil. It will take pretty much whatever i wanted to hit it with including 1000 watts of 100% modulated AM for expended periods of time until the oil gets hot. A few years ago I acquired a 200 watt Termaline (?) dry load. I also bought a pair of 100 ohm 800 watt ceramic chip resistors from Henry Radio and mounted them on a heatsink measuring 15 x 10.5 x 1.75 inches. It wortks well but I just don't have the power to really tax it. I have a couple more of those heatsinks and may build a better load with ceramic chip resistors. The best way to build one is to use a piece of think copper plate between the chip and the sink to help with rapid dispersal of heat over the area as copper will transfer the heat better than the aluminum.

 

[unit_399]

Then again, ten 50-ohm resistors in parallel results in a resistance of only FIVE ohms, not 50.

You're correct. I misstated. I should have said in " series-parallel "

- 399

 

[Captain Kilowatt]

You're correct. I misstated. I should have said in " series-parallel "View attachment 18376

- 399

Ah-ha........I was wondering how you were going to get 50 ohms using all ten resistors LOL Unless the leads are REALLY short then the SWR may be a bit high at the high end of the HF spectrum.

 

[bob85]

That works if you can insulate them from the heatsink & hook them up without introducing too much inductance or stray capacitance.

 

[unit_399]

That works if you can insulate them from the heatsink & hook them up without introducing too much inductance or stray capacitance.

I will probably use a large diameter hookup wire between the devices, and keep the lengths as short as possible. I was going to use Bergquist type 800 insulating material as insulators between the sink and the resistors. What do you think ??

- 399

 

[Robb]

What is the advantage of using sil-pads over thermal paste - BTW?

 

[bob85]

insulation robb,
399 has resistors that are normally bolted & electrically connected to the heatsink,
wiring them as per his schematic means insulating and clamping them while still been able to make short electrical connections to the wire leads & mounting flanges,

im sure its doable but not as simple as bolting some resistors to a sink and running wires between them,

i would not expect the full power rating using pads but they work ok in mosfet cb amps,

 

[Tallman]

I have been trying to get away from oil filled loads. I have a home made load consisting of a Gates 1000 watt dummy load made from ten 100 watt 500 ohm Globar resistors in parallel. It is suspended in a 12 quart stock pot full of silicone load oil. It will take pretty much whatever i wanted to hit it with including 1000 watts of 100% modulated AM for expended periods of time until the oil gets hot. A few years ago I acquired a 200 watt Termaline (?) .

I got this one off of eBay and it had fans on it and it sounded like a bomber squadron when I used it.

This one will handle full legal limit with the fans on it. I run it intermittently with no more than 500 watts with out the fans. Since this photo was taken I have put the fans back on with thermostatic control.

 

[Captain Kilowatt]

I will probably use a large diameter hookup wire between the devices, and keep the lengths as short as possible. I was going to use Bergquist type 800 insulating material as insulators between the sink and the resistors. What do you think ??

- 399

Don't forget that you also have to use insulated mounting hardware like nylon screws to mount the devices or at the very least a nylon flange washer under the head of a metal screw to insulate the mounting hardware from the device otherwise the mounting screws would simply short the device to the heatsink.