From: "John Lyles" <jtml@losalamos.com>
Subject: [Amps] Distilled water in dummy load
Jim and all,
I've spent a lot of time for the past two years with high power liquid-cooled
loads. The globar resistor assembly sounds neat.
The popular high power resistor loads that have water hose connections (Bird
and Altronic at least) use a film resistor on ceramic core, not a bulk
carborundum element.
They run water through the center as well as around the outside of the element.
Altronics makes many of the elements for the other mfrs.
These resistors are made to run with tap water typically, as the R element is
50 ohms and it shunts the effective Z of the package with even slightly
conductive water (tap water).
Distilled or deionized water is tough on end contacts over time, so Altronics
doesn't recommend that practice. I have a 150 kW water cooled load running with
a pulsed amplifier, and it connected
to DI (deionized) loop out of necessity, not preference. I keep the flow very
low through it when it isn't powered, so as to not leave the harsh water in it
and then later flush this slug of water into my loop.
Same loop runs through the plate circuits of two tubes, so needs to be > 2
Megohm-cm resistivity to prevent > 0.5 mA through the fat water hoses.
You should be able to cool your globar load with tap water, but a check with a
network analyzer or antenna analyzer would be prudent. If you don't care about
VHF and above, then it will be easier.
It also helps to check the Z when it is hot, which, in my case, was simulated
with a New Mexico chili pot and a kW heating element along with a small
circulating pump.
Specific Heat of water is 0.997 BTU/lb/degF at 100F. Mineral oil is about 0.44.
50/50 Ethylene glycol/water is 0.855.
73
John
K5PRO
## Ok, the 4 x resistor's I bought from globar are type SP, and shiny black,
glass bodied types. So the altronics resistor's are a film resistor on a
ceramic core, I get it.
Rich measures used a single 500 watt SP globar... inside a pvc tube, complete
with a grnd return wire, to make the connection at the bottom of the resistor.
He then
used a garden hose on each end..and ran tap water through it. IF your water is
pure enough, you will get little or minimal scaling. Point here is that
regular tap water
will work with a type SP globar.
## As you say, tap water should work with my 'cantenna on steroids' . What I
propose to do is this. Get a new 1 gal paint can, fill it with tap water,
then remove the
top lid and resistor hanging from my heath cantenna... and re-use it on the
new 1 gal container, with tap water. Let's see if it works with the 90 watt
globar that's in the heath,
but immersed in tap water and not oil. If it's ok after a few months, I can
try 7 gals of tap water on the HB load.
## The 5 gal new paint can was not tall enough for my assy. There is a bulged
seam aprx 5" down from the top on these 5 gal cans. The entire 5 gal can is
slightly tapered.
They do this, so they will stack 25 of em, inside each other at the local paint
store. We bought 2 x 5 gal containers, then used a zip wheel to cut off
everything below the bulged out seam
on can #1. We took this top 5" portion from can #1..and stuffed it into the
top of can #2. Where the 2 x bulged out seams meet, it's a perfect place tp
braze em together.
## After brazing 360 deg, we tested with water..and very tiny drops coming out
in 2 x places, so these were re-brazed. No leaks the 2nd time around. So
now it's 7.5 gal. I just don't
trust this brazed seam with xfmr oil in it. It was suggested to perhaps
place the 7.5 gal dummy load inside a 2nd, bigger container, in case the load
leaked. Then put the entire mess on a
dolly, so it can be wheeled about the shop. We also installed a pressure
relief on the top lid, towards the outer edge, and a 7-16 DIN dead center in
the top lid.
### A buddy here in town has 3/4 of a 55 gal drum of xfmr oil, so oil is
available if needed. I'm incined to think that 7 x gals of tap water will look
pretty stale after a few months.
However, it could easily be changed out quickly, say 4 times a year. I will
wait to see what a heath load looks like in a new 1 gal container of water, swr
wise 1st. Then compare
swr/Z etc, with water at room temp, then again at say 50-60-70-80-90 deg C.
## I hate these steel paint cans. Steel doesn't conduct heat worth a damn.
Al or CU would be the real ticket. IF the tap water experiment works, I'd be
more inclined to add
an external HE /pump/fan assy to increase capacity.
## hey, I thought tap water will conduct AC ? Folks have been elctrocuted
with 120 vac devices falling into a bath tub. 5 kw = 500 vrms.. and 20 kw =
1000 vrms.
Tnx... Jim VE7RF
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