[Amps] Amps] water purity/conductivity in water cooled tube, > amplifiers
Steve Bookout
steve at nr4m.com
Wed Apr 18 22:20:24 EDT 2018
Hi John,
Thanks so much for your input. This is exactly the kind of info I was
looking for.
I'm familiar with the Pex tubing, but never thought of using it. It
sure would hold it's round cross section better than the softer silicone.
I have a metal lathe, that I have used for winding wire on large coil
forms. (Unfortunately, its' slowest speed is way too fast to use the
machine under power. I turn the chuck by hand.) I was thinking of
doing something like a bifilar filament choke like you would find on a
grounded grid amp. Maybe on a diameter of 2 to 3 inches. 6 or 8 turns
on a 3 inch dia would be a bunch.
I will surely kick around the info you provided.
73 de Steve, NR4M
On 4/15/2018 1:36:PM, John Lyles wrote:
> Steve,
> You have 3600 VDC and want to keep the leakage current small, in the
> uA, no mA. So if that is, say 100 uA, then R=3600/100e-6, or 36 Megohms.
>
> RCA recommended never lower than 10 Megohm path resistance to prevent
> electrolysis in the water connections.
>
> I use PEX tubing, used for home water pipes now, and it can be formed
> into a coil by heating it carefully with one or two heat guns and
> winding it around a wood dowel. Then it will retain it's form when
> cooled off. If you screw up, just reheat and form it again. Amazing
> stuff. I am not sure if it is available in 3/8 inch. Eimac recommends
> against silicone tubing in their literature, although I am using red
> silicone-based radiator hoses for megawatt amplifiers that I build for
> work.
>
> You have three variables, the ID of the insulated piping, the length
> from HV to ground through it and the resistivity of the water. I use
> resistivity not conductivity since the value is easy to understand and
> the dimensional units cancel out correctly in the formula. The pipe is
> a resistor of high value depending on what these variables are.
>
> With 3/8 tubing chosen, I will assume 0.375 inch ID for this example,
> but you can check the actual ID and correct if I guessed wrong.
> Convert it to SI units, 0.95 cm. Also, pick a length of your pipes
> that is convenient to fit in the cabinet, remembering that the hose
> must be floated on insulator or an insulated form for most of the
> length. I started with 12 inches, or 45.97 cm long per hose. 1
> Megohm-cm water chosen for this example. This is so short that coiling
> might not be needed depending on the cabinet space.
>
> Since the ID is 0.95 cm, area is 0.709 cm^2.
> R = resistivity x (L/A)
> L is 45.97 cm
> A is 0.709 cm^2
> resistivity is 1 Megohm-cm
> R= 64 Megohms
>
> This is twice what we wanted, so you can use 500 Kohm-com water with
> this length of tubing and diameter. If you double the length, the
> current goes in half, etc. I would recommend not going to below 500
> kohm-cm water though.
>
> Remember that this is per hose, so with two hoses (in and out) the
> total current loading on the power supply from the water pipes is
> twice what was calculated above. This is what a DC hipotter should
> measure if the tube is off, no filament power applied.
>
> Also, temp rise is dependent on flow and dissipation.
> P (kW) = 0.2648 x (Tout-Tin) x Flow (GPM) for water
> You don't want to create a very high linear water flow rate through
> the tube and piping that is beyond acceptable practice as it is noisy
> and can cause erosion as well as turbulent conditions in the anode. So
> that weighs into your 3/8 tubing decision.
>
> 73
> John
> K5PRO
>
>> Date: Fri, 13 Apr 2018 21:40:20 -0400
>> From: Steve Bookout <steve at nr4m.com>
>> Hello all,
> ...
>> My general plan was to use 3/8 inch silicone tubing, to and from, the
>> tube boiler.? In order to give myself some 'dielectric length', I was
>> going to wrap several turns of the tubing around a round form in a
>> single layer.? This would be kind of like coaxial choke some wrap on a
>> piece of PVC.? ??? I think I would rather have 3 or 4 feet of 'series
>> water', than have the HV only 10 inches of water from conductive
>> 'stuff'.
>>
>> Plan on putting a micro ammeter from a metal water fitting? to chassis
>> in order to measure the conductivity from the water to chassis, at some
>> point in the water circuit.
>>
>> I know that really pure water is actually corrosive and will do it's
>> best to gain ions in order to get to some natural level of
>> minerals/contaminants.??? I built the coolers out of several pieces of
>> brass and hard silver brazed it all together.? I know the electrical
>> current will cause an etching or eroding effect of the materials in the
>> cooler, but I used what I had.?? At this point, I have no idea how often
>> I will changing? out the water.? Could be after only 10 hours of use, or
>> it may be 100 hours and the cooler may rot out in no time.
>>
>> So, I need to know what the 'big boys' do in industry.? At what point,
>> in uS/cm, do I change out the water? The metering of the water
>> conductivity would be measure 3 or 4 feet from the tube boiler (@ 3600
>> volts)? How many inches (feet) of 3/8 inch dia distilled/low ion water,
>> in silicon tubing, do I need to have between 3600 volts and gnd (thru a
>> meter?)
>
> ...
>> 73 de Steve, NR4M
>> ------------------------------
>>
>> Message: 4
>> Date: Fri, 13 Apr 2018 21:43:33 -0400
>> From: Steve Bookout <steve at nr4m.com>
>> Subject: [Amps] more on water cooling an amp
>> I just realized that I could use my Hi-pot tester to test things and
>> help set it up.
>
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