Hello All,
I been a TIG hobbyist for about 7 years, when I bought my Miller 180SD
Syncrowave new. Through the years I've occasionally come up against
both the high and low limits of the machine, and have always dreamed
of finding a used 250 Syncro on the cheap.
Well, I found a non-working 350 Syncro of 1990 vintage for cheap,
brought it home, cleaned it up, eventually found the problem (about $2
worth of components on PC1; a shorted tantalum cap that took out a
couple of resistors and a PCB trace). Fan was noisy, put new bearings
in the motor.
It now runs like a champ. Looks nice, welds nice. Plus it has the
built-in pulser option, so I'm pretty happy now. My 180SD has been a
great unit, but it's time for it to go to a new home.....
My largest torch today is a 17 aircooled, so I'm planning to get both
18 and 20 watercooled torches. Over the weekend, I found a good used
Miller Coolmate 3 for sale and brought it home.
So I started researching the whole coolant issue on this NG and other
forums. I wasn't aware when I bought the Coolmate of the pricey
Miller low-conductivity coolant ($30 a gallon! and I need 3 gals for
the Coolmate!)
So I started researching the various options. To sum up what I've
found, some folks just hook up to flowing tap water, some use
distilled water with their coolers if their keeping the unit in a warm
shop, some use the pink RV Propylene Glycol stuff, some use ordinary
auto antifreeze.(ethylene glycol mixes)
Obviously, Miller thinks that low conductivity is im****tant. And it
would seem to me that if your coolant is conductive, then you will
lose strength of the HF. I have found no data on relative
conductivity of various solutions, so tonight I rigged up a "kitchen
experiment", pretty non-scientific from an absolute sense, but pretty
good from a relative sense to check relative conductivity of various
solutions.
I went to Wally World today and picked up a gallon of Distilled Water,
a gallon of Prestone RV antifreeze, a gallon of Dow pink Dowfrost RV
antifreeze. I already had a gallon of Zerex auto antifreeze and a few
quarts of Pentosin Pink antifreeze in the garage.
I made a simple conductivity divider with a set of known resistances,
and used 240VAC as the excitation voltage. (yes; I know that the high
voltage of the HF output can have different conductivity
characteristcs, but I wasn't going to mess with any higher voltage)
I constructed a simple conductivity cell with a glass beaker and a
couple of stainless steel butter knives from the kitchen. (to keep
with the "kitchen experiment" theme, of course)
I then used my Fluke 179 DMM to measure the voltage across the cell
with various liquids in the cell. A pefect insulator would measure
240 VAC (actually 236 VAC according to my meter), a dead short would
be 0 VAC. I rinsed out the beaker with distilled water between
liquids.
Here's my findings:
Distilled Water: 42 VAC
Hard well tap water : 700 millivolts AC
Soft well tap water: 600 millivolts AC
Prestone RV antifreeze: 115 millivolts AC
Dow RV antifreeze: 175 millivolts AC
Pentosin/Distilled 50%: 600 millivolts AC
Zerex/distilled 50%: 550 millivolts AC
I investigated the theoretical conductivities of industrial ethylene
and propylene glycol aqueous mixtures, and both should be in the range
of near distilled water; around 5 micromhos/cm. I also found data
that the Dow RV stuff has a conductivity about 2,000 micromhos/cm, or
400 times that of distilled water. This is close to what I observed.
Obviously, both the RV and auto additives make the mixtures
dramatically more conductive than the base water and glycol mixes.
I've seen several assumptions in this NG that Miller doesn't recommend
auto antifreeze because of stop leak additives. I think they don't
recommend it because the damn stuff is so conductive....
Conclusions? Obviously distilled water is the way to go, but what
about if you need freeze protection? (my shop isn't heated full time;
rarely gets below freezing, but has a few times in the past) I would
NEVER use the pink RV stuff of any brand. It is basically a dead
short path for the HF back to your cooler. Tap water is much better,
(my tap water, anyway. YMMV) Automotive stuff is marginally better.
None of these are any good, really (IMHO.)
Here's my plan. I need 3 gallons for my system. The Miller low
conductivity stuff would set me back $90. I have found several
sources for both Propylene and Ethylene Glycol (industrial grade) for
about $30 a gallon. I can easily get by with a 33% mixture for my
shop, which will cost about $32 total, a $60 savings.
Here's a question to those running either tap water or especially pink
RV stuff: Have you noticed a degradation of HF power, from conduction
losses? Given my observations, it appears to me that you should. (Or
perhaps suffer poor component life in your welder's HF circuitry?)
HTH,
Jeff
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