Oil for a leaking Tinsley standard resistor

[tggzzz]

I've got a Tinsley 1659 oil-filled 10ohm standard resistor, and some of the oil has leaked out. The datasheet indicates that "the standards are not filled with oil when supplied. The recommended oil is Castrol Whitemor WOM14 or if it is not obtainable any high-quality non-corrosive oil can be used such as Transformer Oil".

Firstly I have to clean the leaked oil off the outside, then decide whether or not to top up or refil the oil. The latest calibration markings are from 1995, so I think it is reasonable to assume there are no PCBs in the oil!

Thereafter I could just leave the remaining oil in the resistor with a 1-2cm airgap at the top, or drain the oil. Either would imply not putting 1A(!) through the coil, but I don't see any real problem with that.

Alternatively I could drain the oil and replace it. I've looked for Castrol Whitemor WOM14 (now called optileb wom 14), which turns out to be a "medicinal white oil" available in 208l drums - i.e. about 10³ times too much!

Fleabay has sellers of Shell Diala B "transformer oil", but it isn't clear that it is suitable. In particular it contains potassium hydroxide and (unsurprisingly) the electrical properties are changed if stored in non-airtight containers. The standard resistor will never be airtight! Having said that, in my application I'm more concerned about any corrosive properties of the KOH.

I'm aware of Ralf Richard Ohmberger's 1659 teardown at https://www.amplifier.cd/Test_Equipment/other/Tinsley-1659-Standard-Resistor.html , but he is careful to avoid claiming that oil is suitable.

I'd appreciate any comments on sources of Whitemor/Optileb oil, or alternatives that are known to be suitable.

[Gyro]

"medicinal white oil"  sounds a bit like medical grade liquid paraffin - used as a laxative (among other things).

[tggzzz]

Well, it is a "food grade lubricant", tasteless, and "complies with all of the purity requirements ... for Liquid Paraffin"!
https://www.kernow-oils.co.uk/food-grade-lubricants/castrol-whitemor-wom-14-medicinal-white-oils-6920/c-6920/

[Gyro]

I certainly remember hearing that Liquid Paraffin was used to lubricate the blades of industrial bread slicing (as in sliced loaf) machines... with slight laxative effect if you ate enough! It looks as if they've found a fancy brand name substitute.

[picburner]

If it were not for the addition of perfume and Isopropyl palmitate, you could use Johnson's baby oil which is exactly liquid paraffin in even 500ml bottles.
I don't know how much these additives can affect electrical properties.

[Gyro]

You can get medical grade liquid paraffin on Amazon (best to pick your seller with care).


Edit: Well veterinary grade anyway.

[Diabolo]

Hello,

http://www4.total.fr/pdf/lub-indus/ISOVOLTINE.pdf

Diabolo

[PartialDischarge]

Either Shell diala B or paraffin oil are totally fine for that application

[IRFP]

Bonjour,

Même avis que diabolo, de l'huile pour transformateur haute tension. J'ai fabriqué une référence de tension dans ce même type d'huile.

Cordialement,

[tggzzz]

Hello,

http://www4.total.fr/pdf/lub-indus/ISOVOLTINE.pdf

Diabolo

Fortunately google translate exists!

Thanks (and to IRFP). I can't see any source of less than 20l, which is a bit of a problem.

[tggzzz]

Either Shell diala B or paraffin oil are totally fine for that application

I have no reason to doubt that, but can you point to any supporting evidence?

I note (without conclusion) that both Diala B and Isovoltine have similar levels of KOH.

[tggzzz]

I note (without conclusion) that both Diala B and Isovoltine have similar levels of KOH.

On looking further, I see that indicates a gross misunderstanding of the specification.

The mgKOH/g value does not indicate how much KOH is in the oil, it indicates how much KOH would have to be added to neutralise any acid in the oil.

Hence a lower mgKOH/g is desirable, but not very relevant.

[ArthurDent]

Do you know what the correct oil level is? Filling the case with no air gap could result in expansion problems and cause leaks, especially dissipating up to 10 watts.

[tggzzz]

Do you know what the correct oil level is? Filling the case with no air gap could result in expansion problems and cause leaks, especially dissipating up to 10 watts.

No, but that doesn't worry me because:

• I don't plan on dissipating anywhere near 10W
• it isn't hermetically sealed; if it is upended it will leak
• there's a strange piston-like device for manually circulating the oul. That would move out if necessary

But thanks for the caution; in other circumstances it might have been very valuable

Overall the oil may not even be necessary: the resistors are normally delivered unfilled, and Ralf Richard Ohmberger's teardown claims cal labs use it unfilled.

Currently I'm moving towards either liquid paraffin BP (medical grade, no additives) or draining it and not refilling it.

[mzzj]

Ask your local pharmacy/drug store for white oil/paraffin oil. Even hardware stores should have food grade paraffin oil for oiling kitchen countertops.

[tggzzz]

Ask your local pharmacy/drug store for white oil/paraffin oil. Even hardware stores should have food grade paraffin oil for oiling kitchen countertops.

I tried a single pharmacy last night. Even after reflection and checking, they looked blank

You used to be able to get things like IPA and potassium permanganate at pharmacies here, but not any more.

[mzzj]

I tried a single pharmacy last night. Even after reflection and checking, they looked blank

You used to be able to get things like IPA and potassium permanganate at pharmacies here, but not any more.

Same here, anything more complex and they suspect that you are making bombs or drugs.  But paraffin oil they have for sure at least around here, sold as laxative and skin ointment.

Back in the day you could buy fuming nitric acid, sulfuric acid and ammonium nitrate  from the farmacy 
(that was 25 years ago when I was 15.. )

[Magnificent Bastard]

Here in the USA, it is called "mineral oil", and it is sold over-the-counter (that means without a doctor's prescription).  You can find it in CVS, Walgreens, Walmart, etc.  It's pretty common stuff, and chef's use it to oil their cutting boards (butcher blocks) also.  It is "pharmaceutical grade", which means it is about at pure as your going to find at ordinary prices.

[Bud]

The other source of mineral oil are livestock/farm supplies places. Apparently mineral oil is used to feed animals to treat constipation. I'd imagine they use it in big quantities and it is a no additives product. I learned it when was looking for oil replacement for a RF dummy load.

[Gyro]

I tried a single pharmacy last night. Even after reflection and checking, they looked blank

You used to be able to get things like IPA and potassium permanganate at pharmacies here, but not any more.

Same here, anything more complex and they suspect that you are making bombs or drugs.  But paraffin oil they have for sure at least around here, sold as laxative and skin ointment.

Back in the day you could buy fuming nitric acid, sulfuric acid and ammonium nitrate  from the farmacy 
(that was 25 years ago when I was 15.. )

I think it's only used as a horse and cattle laxative these days (although it is still the base of pretty much all of human skin emollient creams).

A sad story, my Grandfather saw his father die of bowel cancer (that would have been back in the early 1900s) and dosed himself daily with liquid paraffin (Edit: from the pharmacy). Sadly he died at about the age of 70... of bowel cancer, a bit ironic. It's probably best reserved for the vet and external use these days.

Here in the USA, it is called "mineral oil", and it is sold over-the-counter (that means without a doctor's prescription).  You can find it in CVS, Walgreens, Walmart, etc.  It's pretty common stuff, and chef's use it to oil their cutting boards (butcher blocks) also.  It is "pharmaceutical grade", which means it is about at pure as your going to find at ordinary prices.

Just as well that you included the USA bit, I was just going to make a crack about buying it in blocks in Antarctica. We know where to find you now. 

[Bud]

BTW i ended up using mineral oil from the pharmacy for my dummy load and i can tell the dielectric constant was very close to the original oil . I measured the load impedance with a VNA without oil and the Return Loss was way off the dummy load manufacturer specs. I then filled it with mineral oil and re-measured and the Return Loss was almost spot on with the specs across the frequency range. All things being the same, it would indicate the dielectric constant of the mineral oil was a good match to the originally used oil. 

[IRFP]

Good evening,
Get closer to a maintenance company for high voltage substations, I got a few liters that way.

[mzzj]

I think it's only used as a horse and cattle laxative these days (although it is still the base of pretty much all of human skin emollient creams).

Dunno how often its used but its certainly still sold for human use in most? countries. Apparently maybe not UK.
Also here in Finland its sold for human use but pharmacy website says that "commonly used earlier for constipation, nowadays modern alternatives are available"

From wikipedia:
"Liquid paraffin is primarily used as a pediatric laxative in medicine and is a popular treatment for constipation and encopresis.[1] Because of its ease of titration, the drug is convenient to synthesize. It acts primarily as a stool lubricant, and is thus not associated with abdominal cramps, diarrhea, flatulence, disturbances in electrolytes, or tolerance over long periods of usage, side effects that osmotic and stimulant laxatives often engender (however, some literature suggests that these may still occur).[1][3] The drug acts by softening the feces and coats the intestine with an oily film.[4] Hence, reduces the pain caused by certain conditions such as piles (haemorrhoids). These traits make the drug ideal for chronic childhood constipation and encopresis, when large doses or long-term usage is necessary.[1]

Consensus has not been entirely reached on the safety of the drug for children. While the drug is widely accepted for the management of childhood constipation in North America and Australia, the drug is used much less in the United Kingdom.[1] The drug is endorsed by the American Academy of Pediatrics and the North American Society for Gastroenterology and Nutrition, with the latter organization outlining it as a first choice for the management of pediatric constipation.[1] The drug is suggested to never be used in cases in which the patient is neurologically impaired or has a potential swallowing dysfunction due to potential respiration complications, though normally the airways tolerate this medicine quite well,[5] and some go as far as saying that it should never be used with children"

[drussell]

The hypo-allergenic versions of "Baby Oil" sold under various brand names is pure mineral oil and works fine for this kind of application or home chemistry.  The versions marked as hypo-allergenic should be well refined / distilled, although some brands like Johnson's still annoyingly add a small bit of smell back into it, so best to stick with the cheap generic brands and double check the ingredient list for things like added "perfume" like it says on the Johnson's bottle.

NurdRage looked into this while developing his alcohol-catalyzed magnesium + sodium hydroxide + mineral oil metallic sodium production process for the amateur home chemist. 

He figured out about needing a very pure mineral oil source as described in this video:

https://youtu.be/oiZf-O6vvbE?t=260

Watch the next 90 seconds from the linked start marker...

[Gyro]

As I noted previously, pure Liquid Paraffin BP can easily be purchased on Amazon (or ebay) in the UK.