View Single Post
  #4   Report Post  
Posted to uk.d-i-y
Newshound Newshound is offline
external usenet poster
 
Posts: 2,112
Default oil-filled electric motors, topping up?

On 15/04/2013 18:36, The Natural Philosopher wrote:
On 15/04/13 16:01, harry wrote:
On Apr 15, 3:01 pm, Jules Richardson
wrote:
I've got an electric sewer pump which uses an oil-filled motor - the
lower seal had a tiny leak which I fixed, but it could use a little
topping up before I use it in anger (the upper bearing's *just*
protruding above the oil surface, so it doesn't need much to cover it
again).

Now, I think that the correct stuff is termed dielectric oil (which I've
been unable to find locally) - but that this *might* be the same as
transformer oil? (I've not seen the latter locally either, but at least
it lets me broaden my search!)

I also saw TNP mention recently that big transformers are filled with
mineral oil; is that true? Mineral oil I can certainly get (and indeed I
have a bottle somewhere) - unless of course not all mineral oils are
created equal, and the consumer-grade stuff is a completely different
animal :-)

cheers

Jules

About twenty years ago many were filled with PCB, a carcinogen.
You can't use mineral oil but transformer oil should be OK.


'mineral oil' is a very broad category. AFAIK transformer oil IS a
mineral oil, but only one of many.

But I agree, transforner oil is a safe bet.

http://en.wikipedia.org/wiki/Transformer_oil


Not sure how easy it will be to buy in small quantities though.

Just to clarify, mineral oil just means oil which has been refined from
crude oil. Just carbon and hydrogen plus whatever impurities have been
left in (typically organic sulphur compounds, perhaps some fatty acids).

What you need in your case is something with broadly the same viscosity
as the existing oil. Not too many additives, so I wouldn't use motor
oil. The most pure mineral oil which is readily available in small
quantities is Liquid Paraffin BP from any chemist. Baby oil is nearly as
pure, but it has an added smell. (Baby oil is thinner than liquid
paraffin). If you are just topping up existing oil (say, less than 10%)
I'd probably go with liquid paraffin, but I think baby oil would work
too. (It works on sewing machines).

I expect it is a brushless motor. The electric fields are likely to be
trivial compared to conditions in a high voltage transformer, so the
selective formulations found in transformer oils give no benefit.