Coolant for dummy loads

It gets extremely hot and catches fire, is hazardous if spilled and is a poor absorber of heat.

..... Phil

I recommend the use of either refined mineral oil or silicone oil. Baby oil is mostly mineral oil, but I have no idea what the impurities would do to your impedance.

Are your loads undersized, or do you just have a hefty transmitter?

We had an 8-channel FM combiner in St. Louis (all full power Class- C's, 100kW horiz, 100kW vert, or very close to it). The combiner put all the FM's on a single Harris antenna, having dual feedlines (one for top half of panel, the other for lower). Each station combiner module had a 5kW or maybe 10kW forced-air reject load. These could get pretty toasty over time. I think we had something on the order of 60 tons of air conditioning to cool the room.

The combiner was manufacturered by Dielectric (Raymond, Maine). I'm fairly sure it's still in use. (?) unless IBOC killed it. (?)

Good luck.

-mpm

The use of an oil dielectric will greatly reduce the physical size of the device. And you don't want the oil to absorb heat -- you want it to transfer the heat to the device's heat fins. The placement of the internal resistor (usually on a ceramic substrate) surround by oil, in the right shape cavity, will present a near perfect match (S11 response curve) to the transmitter.

-mpm

Or, 100% "food-grade" mineral oil. Check with local animal-feed dealers... if I recall correctly it's used as a laxative for cattle and horses, and is available relatively inexpensively in gallon quantities. You can also buy it in small bottles at a drugstore, but it's much more expensive that way.

Air or water cooled Phil? (something else?)

George H.

You can buy here: Link:

Mineral oil. Art

"George Herold Troll"

Air or water cooled Phil?

Water is the ideal coolant for dummy load resistors ( for non RF applications) since the worst it can do is reach 100C and begin to boil.

A 100 watt rated tubular resistor can easily absorb 1000 watts if submerged in a bucket of the stuff.

.... Phil

Sjouke Burry wrote in news:4bb54f8a$0$14133$ snipped-for-privacy@textnews.kpn.nl:

mineral oil.

Mineral Oil as everyone has suggested. Easy to get at most local pharmacy chains. Or you can get pure stuff speced for transformers at the link someone provided. (depending on how much you need) Works great. Note you DO NOT want any "real" transformer oil. It's mostly banned except in totally sealed devices and creates big disposal problems. And if it leaks can cause skin problems. And only works a tiny bit better than cheap old mineral oil anyway. And you don't want any of the cooking oils like peanut, sunflower etc. because they tend to turn rancid when oxidized. (peanut oil will smell great when hot, however :-)

Find an oil distributor that sells to industry.

Mineral oil it is. Thanks guys.

On Apr 2, 7:47=A0am, "Michael A. Terrell" wrote:

Correct, my dummy loads are for testing DC power protection circuitry. I intend to have two dummy loads in the same "can" with each consisting of four 8 ohm 20W wirewound resistors (Radio Shack specials) connected in parallel making it two 2 ohm 80W loads. Each load has its own binding posts so connecting in series gives me 4 ohms and in parallel gives me 1 ohm allowing for 1, 2 and 4 ohm selections. Maximum dissipation is expected to reach around 1KW for short durations. Duration can be such that using the resistors as is, without the oil, is not an option.

Cite reference.

-- "For a successful technology, reality must take precedence over public relations, for nature cannot be fooled." (Richard Feynman)

Inciting the wrath of "screwface Allison".....~~~Screwface know-a who fi frighten~~~ LOL!

I built the DL Saturday g>

On Tue, 6 Apr 2010 09:22:37 -0700 (PDT), mpm

How many babies does it take to make a quart?

Jim