Dummy Load

[alfaeire]

hey all.
Anyone make their own dummy loads?
Im looking for schematics for one rated to 300w

[pjeva]

You need dummy load resistor 50ohm or two of 100ohm in parallel an a heatsink. These are flanged resistors and they bolt onto the heatsink. You just need to solder connector or cable, there is no schematic...


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[alfaeire]

http://www.ebay.ie/itm/Dummy-Load-Resis ... 25aa8b14b4

this lad should be sufficient then im guessing.

[pjeva]

Yes. You just need good and big heatsink. Quality of heatsink is proportional to constant operating time. But you usually need less than a minute to see what you have on output...


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[alfaeire]

so what your saying is, a computer heatsink with a fan wont work

ill have a dig around and see if i have a aluminium one knocking about..

Couldnt it be put into mineral oil as well?

[teckniqs]

With all respect mate, from what I've read above I don't think you should be messing around with 300w transmitters!!!

[alfaeire]

the above was a joke, the other thread is not..
yeah i made an error, but im here to learn!

[pjeva]

This with mineral oil is not that bad as using wire to connect amp to antenna connector... I think that was the post teckniqs was reffering to...


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[alfaeire]

haha yeah, well ive learnt my lesson.

[thewisepranker]

You'd be better off with two 250 W, 100 Ohm flanged resistors in parallel, such as the Florida RF 31-1076-100-F.

You won't be able to afford an adequate heatsink to dissipate anywhere near 200 Watts from a single one of those 50 Ohm flanged resistors suggested, let alone 500 W as is written on the device. For the latter, you'd need a thermal resistance from junction to ambient of around 0.2°C/W, which is lower than the typical junction to case thermal resistance, let alone the rest. Dissipating 200 Watts only takes the required thermal resistance of the system up to 0.635°C/W, which is still largely unachievable at home.

You can find the Florida RF flanged resistors on eBay, here for example, for about 15 EUR each: http://www.ebay.co.uk/itm/RF-Resistor-R ... 1a02635255

Although forced cooling is effective, I would recommend against it for a dummy load, as you often require it in places where you don't have power available to drive the cooling fans.