[TowerTalk] Film Power Resistors

[Hans Hammarquist]

Caddock, MP1000 100W resistor is derated to 50% @100 C. They don't like "short" overloads so causation is recommended. I use 10 pcs in a "linked" configuration That results in a low SWR up to 150 MHz. It's more a matter of wire layout than limitations in the resistors.


Hans - N2JFS 



-----Original Message-----
From: Bryan Swadener via TowerTalk <towertalk at contesting.com>
To: towertalk <towertalk at contesting.com>
Sent: Fri, Dec 4, 2015 5:16 pm
Subject: Re: [TowerTalk] TowerTalk Digest, Vol 156, Issue 13

The trouble with any kind of fluid in the can is the can itself. A fluid
with a low thermal resistance still has to get rid of the heat via the
can. If the can had a bunch more surface area exposed to atmosphere,
the cooling would be more effective. As it is, you heat the oil+can,

and wait for it to cool down. That's what I like about my forced air 
cooled DL. I can run it all day (unless I run out of air).
Unlike actual RF power resistors and terminators, the TO-220 resistors
are rated full power at 25C, and need to quickly be derated. The Anaren
pn RFP400-50R (http://tinyurl.com/RFP400-50R) that I used are typical,
with a rating of 100C before you need to derate.


vy 73 es gl,

Bryan WA7PRChttp://www.tinyurl.com/wa7prc-dummy


Date: Fri, 4 Dec 2015 12:45:20 -0500
>From: TexasRF at aol.com
>To: hanslg at aol.com, towertalk at contesting.com
>Subject: Re: [TowerTalk] Fwd:  Oil For Dummy Load
>
>What is wrong with using distilled water, $1.50 per gallon at Walmart? 
>Works just fine for amplifier cooling, no problem at 2000vdc and 1296 MHz.  Not 
>flammable either!
>
>73,
>Gerald K5GW
>
>
>
From: Hans - N2JFS>I dime  in the discussion, why not use something with the lowest viscosity 
>such as  kerosene. That way the heat would be more efficiently removed. 
>Kerosene has a  relatively low flam point so, unless you allow the temperature 
>to rise too  much.
>
>
>I, myself use a home made dummy load made from resistors  packed in TO-220 
>capsules and mounted on a large, flat heat  sink.
>
>
>Hans - N2JFS.
>
>
>
>From: Bryan WA7PRC
>Gary K4FMX asked only about the  derating chart.
>
>Fortunately for myself, oil viscosity is immaterial  
>since my HN31 won't ever see more than ~ 100W again 
>and I'll never  need to change the FREE transformer oil. 
>
>Instead, for high power  stuff, I use my scrap parts 
>1500W (100% D/C) DL that uses small  flange-mounted 
>RF resistors. It's actually smaller than my HN-31.  
>
>vy 73,
>Bryan WA7PRC
_______________________________________________



_______________________________________________
TowerTalk mailing list
TowerTalk at contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk