If it helps we use dowfrost HD for coolant for solar collectors, has low ion flow due to trying to keep the copper from oxidizing
@Abe_Fouhy I see two reasons in the forums:
- want antifreeze to stop freezing where the unit can freeze (in garages). However I doubt its that effective.
- want to use the antifreeze as an algae-cide along with anti-freezing.
…
If you have a strong and quite vacuum system ported to the window you can use a K40 inside. Mine is located on an upper floor in and ported to an outside window.
However I am going to move mine to the garage for fear of fire. I have seen what one of these can do when a cut catches fire and I don’t want that in the house.
When I move it to the garage I probably will add in a heater for winter protection.
@donkjr Cool, that’s what I figured. That’s news about the fire danger. Good to know!
@Abe_Fouhy specs on dowfrost, its $140 for 5 gallons.
I will be sticking with distilled water and 1oz of Clorox:).
Yea, it’s spendy stuff. It’s made to run your solar system for 10-15y without getting flushed.
@donkjr just as a FYI I checked the chemical compatibility of common tubing types and dilute bleach appears to be fine for all.
@HP_Persson are you removing any electrical connections from the probe whilst the machine is in use?
I’ve got stage 1 of the cooling system sorted, flow rate is approx 1.5 litres a minute, hopefully this will be enough.
@John_Sturgess Yeah, the readings are off the chart if it´s powered while the machine is running, due to the charging of the water. It´s small but it´s there.
Not sure, but one arduino died while it was connected to the probe and machine running, no clue if it was because of that or regular china clone quality 
I have a timer on the pump, it runs for 15min when the machine is turned on and shows me a green light (pre-cooling), and when machine is turned off, it runs 15min again. When this is running, the probe is also active trough a relay. I get a reading before usage, and after.
Can probably be solved better, or in the program itself. But just testing it so far 
@HP_Persson @John_Sturgess so you guys are reading conductivity real time (when not firing laser)?
Do you think that its that critical to track every time machine operated or is this “nice to have”.
If there is no algae would you expect the conductivity to change over time?
I’m not and will only read conductivity when the machine is initially turned on. For me it’s a nice to have, I was already implementing an arduino to control the laser enable circuit so for the cost of a few bits of wire it makes sense to add it.
Why the arduino to control it? I’ve started a job a handful of times without running the pump and also with the conductivity test it’ll probably force me to swap out the water sooner than I previously would’ve done. This’ll be the first time I’ve ran anything other than straight tap water though.
@donkjr In order for the conductivity to change over time the solution chemistry needs to change. Let’s consider some scenarios:
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Organic compounds present in solution from the start could breakdown (oxidize) overtime into things that are more conductive. If the oxidation produces ionizable compounds (acids/bases) a conductivity meter could pick that up. However, there are compounds that are neutral in solution but could still undergo conductivity through electrolysis (redox reaction) that a conductivity meter would not pick up. Your conductivity meter uses AC voltage to measure conductivity to avoid polarizing the solution and to avoid electrolysis reactions. So, the meter is just measuring things that are already ionized and are just bouncing back and forth through the solution with the AC polarity changes. But in our case, if we accept the hypothesis that the problem is due to electrical conduction through the tube cooling solution, any neutral compounds that could undergo a redox reaction would participate under HV DC. As long are you start with reasonable pure water I don’t see this as a big issue unless some of the things below come into play.
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It’s possible that chemicals (ions, organics) could leach from the system (tubing/bucket) overtime and alter the solution conductivity. In general I don’t think this would be a big issue, especially for materials that had been in use for a while.
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In an open system, water can absorb atmospheric CO2 and form carbonic acid (CO2 + H2O ⇌ H2CO3) which will make the solution slightly acidic, raising the conductivity. If your solution happens to be basic to start with the amount of absorbed CO2 will be greater. But for relatively pure water amount of absorbed CO2 under standard atmospheric conditions should not raise the conductivity significantly.
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Algae growth – Algae takes nutrients from the water and CO2 from the air to grow. So, these little organisms will have an effect on solution chemistry. How much of an effect there will be, I’m not completely sure because I’m not a biologist. But, I know that they will typically make the solution slightly basic which increases the conductivity a small amount. The big unknown for me is to what extent algae cells would undergo electrolysis when exposed to a HV DC potential. This could very well be significant.
So in summary, I think as long as you control the algae growth the likelihood that your solution conductivity will increase significantly over time is small.
@Nedman that post really gave me a geekasm. Thank you for the awesome chemical breakdown. Chemistry rocks!
Lol @Abe_Fouhy You are certainly welcome. I’m not a high level electronics geek or hacker so I don’t often get to a chance to add to the the technical discussions.
@Nedman I hear ya, I dabble in it all, wouldn’t say I’m a master of any of it. Lifelong experimenter, working on my engineering degree.
Ok guys I may of found a solution, no pun intended. Have we thought about mineral oil? I remember it being used in my HV coil on my car so I googled it to see if it would be thermally conductive, it is!
From wiki “Mineral oil is used in a variety of industrial/mechanical capacities as a non-conductive coolant or thermal fluid in electric components as it does not conduct electricity, while simultaneously functioning to displace air and water. Some examples are in transformers, where it is known as transformer oil,[8] and in high-voltage switchgear, where mineral oil is used as an insulator and as a coolant to disperse switching arcs. The dielectric constant of mineral oil ranges from 2.3 at 50 °C to 2.1 at 200 °C.”
Since this is a byproduct of oil production and the base to oil we may be able to draw parallels to this white paper (https://www.google.com/url?sa=t&source=web&rct=j&url=http://www.tandfonline.com/doi/pdf/10.1080/00071617600650161&ved=0ahUKEwjc8NCD97_SAhVB5WMKHRpGBFgQFggkMAE&usg=AFQjCNGD0lZpW_r_QPM_NFm-1LMx4q7ZUQ&sig2=lB2xKYmpHOlWsQhYmb7cbw) that indicate that oil inhibits algea growth by preventing it’s ability to perform photosynthesis, preventing the growth and any growth that does happen will be surrounded by a nonconductive island of oil.
@Nedman awesome explanation!. So it seems the 1oz of Clorox in 5 gallons is backed up by science. Now we test the practice.
@Abe_Fouhy very punny. I am sticking with the clorox/distilled water. Oil is expensive and messy …would probably have to change pump types.
The oil is cheap too $15/gal for mineral oil too, https://www.amazon.com/gp/aw/d/B00OGKPJB0/ref=mp_s_a_1_5?ie=UTF8&qid=1488737541&sr=8-5&keywords=gallon+mineral+oil
@Abe_Fouhy add in new pumps and a DC supply with controls :).
Doubt you will pump oil effectively with a submersible, but never tried it 
@donkjr I could see that the impeller in the pump may degrade with oil, not sure about the viscosity as they are probally similar. I think you would want/need a different pump though. Are you guys still using the stock fountain pump that came with it?