[Amps] SS amps watercooling - was PowerGenius XL

Jeff DePolo jd0 at broadsci.com
Mon Mar 6 13:32:07 EST 2017

> ##  IF conductivity is NOT an issue, then Id suggest using 
> what is already 
> being used in car eng radiator setups.  Distilled water + a 
> corrosion inhibitor. 
> Typ a 50-50 mix of glycol + distilled water is used.  The 
> glycol offers the 
> inhibitor properties, and also raises the boiling point by a 
> bunch, to typ 265 deg F,
> IF under  typ pressure of 10-15 psi.  Less, with lower 
> pressure, but still  more than
> 212 deg F.  That 50-50 mix  will also lower the freezing 
> point to aprx  -40 deg F.
> You can also buy the 50-50 premixed, just pour it in.  

I agree.

In liquid-cooled broadcast transmitters (both tube and solid-state), the
thermal transfer fluid is typically a 50/50 mix of distilled water and
Dowtherm SR-1.  SR-1 is ethylene glycol with corrosion inhibitors.  There
are a few manufacturers that recommend or specify something else; Rohde and
Schwarz comes to mind - they spec DEX-COOL for some of their rigs (and,
yeah, I know all of the GM DEX-COOL horror stories, though I've never
experienced any problems myself either in broadcast transmitters nor in my
own GM vehicles).

50/50 is a good all-around mix ratio for SR-1.  It provides freeze
protection down to around -35 degrees F, yields a healthy concentration of
corrosion inhibitors, and prevents bacterial growth/contamination.

Unless there is some anomaly that occurs during the life of the coolant that
results in contamination, the primary reason to replace coolant at regular
intervals is due to the natural change in pH.  When the system is initially
filled, the pH of the 50/50 glycol mix is about 9.3.  As the glycol ages,
and as the copper and aluminum in the plumbing and system components leach
into the coolant, the pH slowly falls.  We usually do a flush when the pH
falls below 8.0, and we never ever let it go below 7.5.  You don't want to
let it turn acidic.  While you can try to extend the lifespan of the coolant
by adding KOH to raise the pH, by the time the pH starts gets down near 8.0,
the corrosion inhibitors are likely nearing depletion anyway.

You can send a fluid sample out to a lab for testing of all the main
indicators of the health of the coolant (glycol concentration, pH, inhibitor
concentration, contaminants, etc.) -- probably overkill for ham amplifiers.
Dow will even do it for free if your system is large enough (as I recall, if
the volume of coolant in the system is over 200 gallons they do it for
nothing).  But, for home/ham use, I think that if you just do a visual on
the coolant to confirm it's the proper color and free of contaminants, and
you check the pH every few months and when it falls below 8.0 do a flush and
re-fill, you would be fine.

By the way, cleaning the system real well before the first fill is very
important.  A solution of a few percent TSP in distilled water is typically
used, and then flushed twice with distilled water before filling the system
with the 50/50 mix.

The usual disclaimers apply regarding the toxicity of ethylene glycol, the
proper disposal of the same, yada yada yada.

					--- Jeff WN3A

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