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Insulating Oil : What oil should I use?

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Xray

Sat Jan 01 2011, 10:32PM

Registered Member #3429 Joined: Sun Nov 21 2010, 02:04AM
Location: Minnesota, USA
Posts: 288

JozefC wrote ...

Yeah, I wouldn't use paraffin because any MOT can overheat and melt the wax without a ballast to limit the current. Not good. I can't seem to see anywhere to buy mineral oil which is a pain so I might just have to use corn or vegetable oil for the time being...

My guess is cooking oil contains too much water and impuritites that will make it not very suitable for hv projects over, say, 20KV (just a guess). Since you are playing with an MOT, which operates at about 2500 or so volts, then kitchen cooking oil may work Okay, especially if you can put it under vacuum for a few hours in order to remove moisture and gas. If you use a good 2-stage vacuum pump, then you should see the oil appear to "boil" like water! After some time, the "boiling" will stop, and you may see only a bubble or two every few seconds. At that point, the oil should be mostly free of water vapor and other disolved gases. The vacuum process is an essential step when I add new oil to repaired X-ray heads that operate at 70KV. Without it, the hv will arc through the oil and damage the internal components.

Kiwihvguy

Sat Jan 01 2011, 10:44PM

Registered Member #3395 Joined: Thu Nov 04 2010, 08:42AM
Location: Christchurch, New Zealand
Posts: 193

Alright... First, I don't even have a vacuum pump so I can't suck all the air and moisture out, so what the hell. I've seen that kind of effect before where the oil boils like water. Would a vacuum cleaner work or is that just a fail?

Xray

Sat Jan 01 2011, 10:59PM

Registered Member #3429 Joined: Sun Nov 21 2010, 02:04AM
Location: Minnesota, USA
Posts: 288

JozefC wrote ...

Alright... First, I don't even have a vacuum pump so I can't suck all the air and moisture out, so what the hell. I've seen that kind of effect before where the oil boils like water. Would a vacuum cleaner work or is that just a fail?

No, a vacuum cleaner produces only a little "suction", not even close to what you would call a true vacuum. Anyhow, I've read some posts on 4hv and other similar sites where hobbyists have used drug store mineral oil with good success in their hv projects (even without placing the oil under vacuum). The key issues are voltage and spacing between conductors. If you can keep your voltage relatively low, and the spacing wide, then you should be able to get by without using the vacuum process. I can't give you exact numbers for either parameter, so you will just have to experiment with it.

Kiwihvguy

Sat Jan 01 2011, 11:15PM

Registered Member #3395 Joined: Thu Nov 04 2010, 08:42AM
Location: Christchurch, New Zealand
Posts: 193

You mean you can get mineral oil at a pharmacy? Sweet...

Pinky's Brain

Sun Jan 02 2011, 12:35PM

Registered Member #2901 Joined: Thu Jun 03 2010, 01:25PM
Location:
Posts: 837

DIY vacuum pumps are generally constructed from refrigerator pumps.

dmg

Sun Jan 02 2011, 04:29PM

Registered Member #2628 Joined: Fri Jan 15 2010, 12:23AM
Location:
Posts: 627

Here is a thread I started a while ago, and up to this date, I still use baby oil for my homemade transformers.

The stuff is basicly mineral oil, with a few more ingrediants to make it smell nice, but so far Ive tested it with pretty high voltages, and didnt have a flashover or transformer failiure yet with it.
its pretty good IMO (and dirt cheap).

No matter what oil you do decide use, before you go dumping it in as an insulating oil, you should test it first for yourself.

Patrick

Sun Jan 02 2011, 06:16PM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

I have seen from experience and from good writen publications, that vacuum dried oil has about twice the dielectric strenth, then oil that is non-dried, so you can increase the distence if you dont have access to a pump.

Patric

Sun Jan 02 2011, 07:35PM

Registered Member #2899 Joined: Wed Jun 02 2010, 06:31PM
Location: Deinze, Belgium
Posts: 255

radhoo wrote ...

Patric wrote ...

I have very good experience with paraffin, it melts at 52Â°C.

paraffin goes well only up to 40-50KV . It can also develop small cracks that allow air to get close to the hv terminals, not very good.

for very high voltage mineral oil is the way to go, not paraffin. after the oil is added, ideally a pump should be use to suck out any air left in the container.

From Wikipedia: "Pure paraffin wax is an excellent electrical insulator, with an electrical resistivity of between 10!13 and 10!17 ohm metre.[4] This is better than nearly all other materials except some plastics (notably teflon)."
I use paraffin since years in a secondary from a tesla coil without any problem. My tesla capacitors are protected with paraffin too.

2Spoons

Sun Jan 02 2011, 10:44PM

Registered Member #2939 Joined: Fri Jun 25 2010, 04:25AM
Location:
Posts: 615

Paraffin can be modified by dissolving some polyethylene in it - this makes it tougher, slightly pliable, less likely to crack, and raises the melt point.
'Hot glue' sticks also work well as a modifier for paraffin.

Adam Munich

Mon Jan 03 2011, 12:12AM

Registered Member #2893 Joined: Tue Jun 01 2010, 09:25PM
Location: Cali-forn. i. a.
Posts: 2242

I've had nothing but good things to say about canola oil. I used it to insulate an x-ray transformer and I had no problems with it.

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