My Unusual DIY 500 Watt RF Dummy Load - Part 1

Follow me along as I attempt to construct a 500 watt dummy load for the 160 meter through 10 meter bands.
Below are some of the sources for parts I used.
100 Ohm / 250 Watt Flange Mount Resistors
eBay - www.ebay.com/i...
HP CPU Fan/Heatsink
www.ebay.com/s...
9 Volt Battery Holder
www.amazon.com...
9 Volt Rechargable Battery
www.amazon.com...

[@rfburns3472]

Hi friends. This design proved to have poor results above 60 Mhz. So, I redesigned it for excellent performance from 1 Mhz to 650 Mhz. Worst case SWR is at 1.4 GHz 1.4:1 Please see video Part 3 soon to be released this weekend. Thanks for watching!

[@Kult013]

Nice one! I made something similar. The PC coolers in computers dissipate about 75-100w of heat, the temperature delta is about 60 degrees Celsius. I quess that for short time it can dissipate few hundred wats untill the cooler and resistors get too hot. All the best ES5KML

[@rfburns3472]

Thanks Kult! In video Part 2, I pushed 340 watts into the DL for 2 minutes. The ambient temperature was 85 deg F. The highest resistor temperature was 188 degrees F. The temperature delta was 103 Degrees F. About all my amplifier can put out is 400 watts with a new set of tubes so, for now, the DL is handling the power quite well. 73's

[@WECB640]

Try tapping the RF and converting it to DC to power the fan. (next project)

[@rfburns3472]

Funny you should say that as I thought about it when I was watching the fan during the first test. Good idea WECB640! Has anyone tiried that?

[@WECB640]

@@rfburns3472 I think you'd be the first. Give it a try when you have time to experiment. The beauty of the RF power running the fan is twofold. 1. No more dead batteries that leak. 2. The fan is on when RF is applied, so there is no wait time for the thermal mass of the heatsink to trip the sensor and enable the fan. It should run cooler overall as a result. 73 OM

[@rfburns3472]

​@@WECB640 Your idea sounds "cool"❄but I'm afraid tapping onto the resistor network may cause a prohibitive change in the desired 50 ohm impedance. How about a thermoelectric generator that turns heat into electrical energy? Probably not enough heat to run the muffin fan though. 73 to you!

[@MichaelOfRohan]

Lm317 and some fat resistors can fit all in the battery box

[@rfburns3472]

@@MichaelOfRohan That would work. I found some rechargable lithium-ion 9V batteres that outlast the alkaline one I was using. www.amazon.com/Quzmo-Rechargeable-Lithium-ion-Multimeters-Walkie-Talkie/dp/B0CRYS8NYH/ref=sr_1_38?dib=eyJ2IjoiMSJ9.cEZnn1YZw9BvOkaWPQtAURTu01r4O5FAWpMbsHUpmjHGQvWCO1VuevpA6LTRUbwLPsI50NI3FnyxlhnhnlRiFpDPtsuvA7FgHIU8ZQ1jVU_oSRim8jA6-BTbELzKXYtcBOIzNS6eOIpcN3cbL18AardEpXSPatY4gTvDAeYO8NIurWU65_nRmiKpn6XYk0TqoIDzY8JYP33SsFKDTaN-O3Rup4ZwAw22MWx0jjMEk0sU4E9oWZ5ZlKpJtAkGppA-Yz1ehgMSTPjCAkLrj0WW9KQI430ErQVaYGpToIkoap0.svWl3QCfyw-MuM9R7HDW98LJd3S968CjUp6opabvKdE&dib_tag=se&keywords=9%2Bvolt%2Blithium%2Bbatteries&qid=1722625501&sr=8-38&th=1