Antifreeze a NoNo?

I have read the “top mods” post of Nedman (how can i PM ppl here?).
He stated that you should never use Antifreeze in the cooling liquid.
Can you tell me why ( in general)?

What is the optimal temperature of the cooling liquid?

I would like to have a 10litre active coolbox (Peltier-element driven) as my
container for the cooling liquid.
It cools air way below 0°C. I estimate -20°C. So i guess it will cool down
the liquid down to that point as well if i would keep it running for a very long time.

Wouldnt be Antifreeze be the most sane thing to add to the distilled water i use?
Or is this Setup overkill (depends on what the optimal temp. for the cooling liquid is)?

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that is waay too cold for laser applications. Optimal temp is 15-20°C with no condensation forming on the laser tube and pipes. And short answer is that most antifreeze increase the conductivity of the water and cause issues with performance.

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We know exactly what conductive coolant causes [shortens LPS life] but we do not know why. More often than not chronic LPS failures have been associated with conductive coolant. Unfortunately we don’t know exactly what is the right range of conductivity… we do know that distilled water treated with algaecide has a good working conductivity.

My over simplistic theory is that the water jacket full of water capacitive-ly shunts to ground some of the current from the LPS. It is not uncommon to stick your hand in a coolant bucket while operating and get a tickle. Since this current is not in the cathodes circuit it does not show up on the meter and the operator does not see that the actual current being drawn from the supply is greater than it should be run at.
So maybe when running the machine at 20 ma maybe 10 ma is being robed (because the coolant is anifreeze) and the LPS is trying to put out 30ma which is above its recommended running current?

This seems fantastic but consider that:

  • The effective area of the jacket exposed to the voltage and the water is pretty big
  • The voltage on the tube is large 20,000 VDC
  • The max current the supply can handle is 30ma, so 10ma is 30% of the supply’s capacity
  • You can easy imagine 100’s of volts drop across the various effective capacitance’s. One user measured 300v across his coolant bucket.

So you could easily imagine a large plate capacitor with 20,000vdc across it coupled to earth ground through all of the coolant loops surface area.

I have not been able to test my theory cause I have not gotten a hold of an old tube yet to set up a proper test environment.

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Here is a great write up on coolants;

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Hey thanks to all you guys!
I am relaxing right now because standard purified/distilled water will not really become ice when the room temp hits sub 0.
As long as it is germ"free" it can stay liquid far below 0°C.
So i will read the Link provided (Coolants and Additives).

Do you think UV light along the path of the tubes would be a sufficiant germicide?

Thanks!

It’s not just whether it is frozen solid.

As @Domm434 points out, you want to keep the temperature above the dew point.

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With dew point you mean 0°C i guess?
That would be my next question.
Can i assume that you can safely operate the machine between +1°C to +20°C?
What about the range from +1°C to +15°C?
What is problematic about that range?
I am asking because +15°-+20° is stated as the optimal temp…

And i will keep discussions public unless it gets intimate.

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I wondered so I should ask… why is condensation a bad thing on/in a laser tube. Do we know why or is it an assumption?

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I believe it increases the chance of arcing from the tube to the chassis by acting as an intermediary between them. This sis only from what I have read as i dont let mine get that cold to tempt fate :slight_smile:

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