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Marko

Fri Feb 15 2008, 08:11PM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

Jan, don't use cooking oil as with long-term heat exposure like that it will turn rancid quickly and shi* up your transformer. I'd never do something like that myself, at least.

What core, and what voltage are you aiming for? Often singlelayer air winding (just like a TC secondary) will be enough for 10+kV on a double legged core. You would need to use very thin wire, but it's very flashover-proof at cost of some more heating in the copper.

To prevent flashover to core you can put another piece of plastic pipe over the wound one and pour resin into the gap.

I'd always try something like that before messing with the oil.

Marko

Dr. Dark Current

Fri Feb 15 2008, 08:32PM

Registered Member #152 Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384

Marko, it will be probably 8-10kV maximum (two 8kV coils w/ centertap) and there will be maybe 2-3mm airgap between the secs. and primary.
But the problem is that at several tens of KHz insulators turn into non-insulators pretty easily

when there's at least some air, corona will eat away the insulation sooner or later. (been there - a "standard" AC flyback will arc through anything plastic that is thinner than some 3mm or so (if you let it "spray" for a while), no matter that's the best insulator in the world.. this is pure AC coupling)

Ultra7

Fri Feb 15 2008, 08:37PM

Registered Member #1157 Joined: Thu Dec 06 2007, 12:11PM
Location: Houston, TX
Posts: 307

A place in India.

Conoco transformer oil.

Real Mineral oil. Petroleum based white mineral oil.

Proud Mary

Fri Feb 15 2008, 09:13PM

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

Dielectric fluids based on sunflower seed oil have breakdown voltages of >35kV for a standardized 2mm gap.

Food grade sunflower seed oil is highly refined with excellent high temperature stability, and a dielectric constant about 3.

The oxidation resistance of sunflower/canola oil blends in commercial high voltage transformers is usually improved by placing oxygen-scavenging chemical cartridges in the upper air-filled portion of the transformer housing. There is empirical evidence to suggest that transformer life is extended when using vegetable dielectric fluid as compared to petroleum-based mineral oil.

The flashpoint of vegetable dielectric fluid [~275 C] is almost double that of petroleum mineral oil [~145 C] making for a much reduced fire hazard, which is always an issue in transformer design.

There is a great deal of literature on the web about the growing use of vegetable dielectric fluids - which are the best oils to use, and so on - so I will rest my case for them here!

Mates

Sat Feb 16 2008, 12:15AM

Registered Member #1025 Joined: Sun Sept 23 2007, 07:53PM
Location: Czech Rep.
Posts: 566

I can tell you from my own experience that sunflower cooking oil works pretty well. I have my 50KV 6KHz ignition coil and all my fly-backs dipped in the same oil already more then half a year and there is no problem and no small. Actually Iâ€™m little bit surprised that so many people here see in everything such a big problem, recommending things which sounds great but are hardly achievable for amateur HV researcher with a limited budget. I also red pessimistic predications like my home made caps will be certainly eaten by corona and so on. I guess you are not going to built professional HV voltage transformer for long time operation which will be a part of live supporting facility. As I know cadency and longevity of your experiments just buy the cheapest cooking oil in supermarket and you'll get what you needâ€¦

Cheers Mates

jpsmith123

Sat Feb 16 2008, 04:32AM

Registered Member #1321 Joined: Sat Feb 16 2008, 03:22AM
Location:
Posts: 843

Coconut oil is supposed to work well also.

Tonic

Sat Feb 16 2008, 09:01AM

Registered Member #528 Joined: Fri Feb 16 2007, 10:32PM
Location: Warsaw, Poland
Posts: 166

I've had also problem with finding oil for my homemade transformer. What I have done is getting phone book, searching companys that winds transformers, writting few numbers and calling. One of company agreed to let me buy transformer oil, under one condition - I must have own container. The price was quite low, 3 euro per liter, if I remember correctly.

EDIT:

"Marko" wrote ...

To prevent flashover to core you can put another piece of plastic pipe over the wound one and pour resin into the gap.

I wouldn't recommend this. If it's decided to use oil, it's better not to fill with resin because it creates air bubbles, which are much inferior to oil in insulation terms. I know it's possible to avoid bubbles through vaccuming, but it complicates construction :)

cbfull

Mon Feb 18 2008, 12:11PM

Registered Member #187 Joined: Thu Feb 16 2006, 02:54PM
Location: Central Ohio
Posts: 140

If this helps, there is a wonderful little chemistry store that I often order odd things such as a large amount of mineral oil, and their prices are great. A gallon for 14 bucks isn't bad.

The Chemistry Store

Have a look and see if you like it. The fact that they can even supply a 55-gallon drum amazes me.

Avalanche

Mon Feb 18 2008, 09:02PM

Registered Member #103 Joined: Thu Feb 09 2006, 08:16PM
Location: Derby, UK
Posts: 845

How much do you need?

Could you crack open an ignition coil or two to get the right amount of oil? They should be easily available at scrapyards. Punch two holes through the casing and pour out the oil, avoid drilling so you don't get bits of crud swimming around in there.

Remember that transformer oil is quite 'thin', compared to some of the other things mentioned in this thread. If you try to pour in something too viscous, you're going to have problems getting out the air, and getting the stuff soaked in. The right stuff needs to be as close to water as you can find!

Which leads me onto another idea - couldn't automatic transmission fluid be used? I used this in my forks when I needed some good quality low viscousity(?) oilage.

teslacoolguy

Mon Feb 18 2008, 10:09PM

Registered Member #1107 Joined: Thu Nov 08 2007, 10:09PM
Location:
Posts: 792

definately get some mineral oil i one bought 12 bottles for a capacitor bank i once built and it works very well for me. also on the funny side i asked the lady at walgreens if they sold it by the case and she gave me this look like you have got to be kidding me

and than she said no im sorry but we dont (hoping i would just walk out of the store) so than i was like ok than ill just buy 12 bottles.

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