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Ben Solon

Sat Jun 23 2012, 02:33PM

Registered Member #3900 Joined: Thu May 19 2011, 08:28PM
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Posts: 600

I am going to use water cooling for my induction heater. The problem is that this is a multi kW ih, and there are more parts than just the work coil that I want to cool. When I feed the water through both the grounded water block for the igbts and the work coil and maybe a few other components, I see a problem coming up. Has anyone done this and found that then causes live water or shorts? Water is fairly resistive, especially when fed though tubing like this, but I have also read somewhere that it tends to be more capacitive than anything else. Help?

Nik

Sat Jun 23 2012, 02:57PM

Registered Member #53 Joined: Thu Feb 09 2006, 04:31AM
Location: Ontario, Canada
Posts: 638

It would lower the heat transfer but you might try coating the inside of your waterblocks with something insulating (like the insulating pads you can put between a heatsink and a live part).

Ash Small

Sat Jun 23 2012, 04:15PM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

Don't take my word for it, but unless you have a lot of impurities in the water I imagine it won't be a problem.

Electricity takes the path of least resistance, so will tend to flow through your conductors (the metal parts) rather than the water.

As an example, consider a high resistance 'bleed resistor' accross a capacitor. It has very little effect on the circuit during normal operation.

Ben Solon

Sat Jun 23 2012, 04:17PM

Registered Member #3900 Joined: Thu May 19 2011, 08:28PM
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I'll try that if nothing else works, but that seems like it would dramatically reduce the effectiveness of water cooling. As long as there isn't more than a couple mA flowing through the water, I don't really care about voltage- I can just ground the hell out of everything. I know that the most basic water cooling uses the capacitor terminals as the input and output for water flow, so if it was a HUGE problem, then people would be shorting a couple amps through their water supply, but I just don't know enough about how it behaves.

Alex M

Sat Jun 23 2012, 05:24PM

Registered Member #3943 Joined: Sun Jun 12 2011, 05:24PM
Location: The Shire, UK
Posts: 552

How about some of that liquid that is used in liquid cooled computers? That is made just for this purpose.

Another thing is if you are in a hard water area like me then regular tap water will cause lime-scale to appear, a bit of a pain when you have to replace the kettle every few months lol.

But yes the stuff they use for computer water cooling is what I would suggest.

Steve Conner

Sat Jun 23 2012, 05:39PM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

It won't pass enough current to blow anything up. If there is a net DC component, you'll get electrolytic corrosion that will plug your cooling pipes with gunge after a while. But if the current is purely AC that's not a problem.

Ben Solon

Sat Jun 23 2012, 06:14PM

Registered Member #3900 Joined: Thu May 19 2011, 08:28PM
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So the tank itself won't have any issues, it can't hold dc current if it tried. I don't know exactly how I will wire it yet, but piping water from any circuit to any other circuit will be fine as long as there is another path? I will try to keep any dc component out of the system, an I could put in a filter to trap any junk form the water electrolysis. I don't want to use coolant though, cause I need to pump a lot of fluid, and in the extreme cases I will just hook a hose up to it to eliminate the radiator. I dont mind putting some kind of substance in the piping to each component- most of it wil be rubber or plastic anyways. But inside each cooling junction there has to be minimal thermal resistance.

radiotech

Sat Jun 23 2012, 09:28PM

Registered Member #2463 Joined: Wed Nov 11 2009, 03:49AM
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Is the cooling water closed loop or just drained to a sewer?

Proud Mary

Sat Jun 23 2012, 10:08PM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

Freshly distilled water has a pH of about 7, and a resistance around 18MÎ© cm.

After a few hours exposure to the air, in an open system, the water takes on CO2, forming carbonic acid. The pH of the water will fall to ~5.75, and the resistance fall to ~1MÎ© cm.

Where atmospheric CO2 is abundant, the pH may fall to as low as 4.5, with correspondingly reduced resistance.

Moral of the story: where the dielectric properties of cooling water are important, only use freshly distilled water in an air-free closed system.

Ash Small

Sun Jun 24 2012, 12:33AM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

Putting in 'extra' piping between the heatsinks, for example, will greatly increase the 'already high' resistance, if you really want to minimize any effects.

Any 'DC component' will possibly, over a long period, lead to 'electrolytic corrosion', see here:

but you probably don't need to worry about these things. (I'm just posting this as 'additional information').

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