Oil cooling a motor with transformer oil/dielectric fluid - the next frontier?

Mineral oil sounds good except...

- low materials compatibility, known to eat plastic and eventually delaminate circuit boards over a long period of time
- breaks down / oxidizes faster than most cooling oils
- smoke point at 135C, kind of low for a hub motor
- more toxic
- carcinogenic if not extremely pure

A lot of people building high performance computers who have used mineral oil had components destroyed after a number of years and concluded is it not worth it.

I say that since we have close to the same variety of materials as a PC, mineral oil is not suitable long term for a hub motor.

Looking for something like opticool or even better.
 
I think it's been suggested before but assuming you check for any use of silicones inside the motor DOT5 brake fluid seems like a pretty good option all things considered. Very low viscosity even at low temperatures (lower than ATF but a decent bit, slightly lower than opticool at 50C), very good compatibility, maybe compatible with everything except silicones, relatively safe. Only downside I see is the same with other oils which is brake rotor contamination.

Now if the compatibility of silicone oil works it may be easy enough to find something more pure than DOT5 (I don't know if there are really many additives normally used in it) with the same or lower viscosity, silicone shock oils perhaps.
 
According to EEVblog, silicone oil will screw up rubber and plastic ( per some manufacturers of the stuff ):
Submerged mineral oil PC - but EE what would say on it? Finally... - Page 1

Silicone oil also has pretty low heat transfer properties.
I can only find one report of using silicone oil in computer cooling and it's in the above thread.

Brake fluid, unknown. I read that it has a high propensity to absorb water from air, which could make it conductive. It comes in differing formulations which have varying materials compatibility. I dunno if this would be suitable.

Opticool for comparison:

1707022743549.png
 
Last edited:
neptronix said:
Brake fluid, unknown. I read that it has a high propensity to absorb water from air, which could make it conductive. It comes in differing formulations which have varying materials compatibility. I dunno if this would be suitable.
Click to expand...
Brake fluid is extremely corrosive. I wouldn't put it anywhere near the motor.

Maybe I missed it but I haven't seen the most obvious option : regular engine oil.
It shouldn't harm other materials very much, it's widely available for cheap, it doesn't degrade, it prevents rust of the core (I've red some people talking about distilled water earlier... well the iron core would rust even faster in distilled water than regular water, it would completely destroy the motor in a matter of days/weeks!), it's a very poor electric conductor, and last but not least, some relatively thin motor oils are available, such as 0W20.

Sounds like something very easy to try for anyone who'd like to experiment.
 
Last edited:
DOT5 brake fluid is silicone oil, it is quite different than all the other flavors. Also as far as I can tell from research silicone oil is very compatible with all rubbers except silicone and Fluorosilicone. So as long as we check for and replace any silicones used in the motor, which doesn't sound that hard, it should be good. Also it seems like the thermal conductivity of silicone oil slightly better than opticool at 40C and slightly worse at 100C but pretty close either way.

All that being said if opticool is so great why don't we just use a similar product, been awhile since I skimmed through the thread but if I recall it was that it was too hard to get but a quick search for "Dielectric Coolant Fluid" comes up with some options at reasonable prices and while they are all different and some research would be needed they seem to be for the same application.
 
Last edited:
I was literally a professional operator at one point. it was a tonne of fun, still keep in touch with most the guys (well, ones that are still with us, not a lot of old guys left it seem).
 
Justin (Grin Tech owner/operator) suggested an alcohol might be a good cooling fluid. After his suggestion, I tried distilled water with Motul MoCool as a corrosion inhibitor in my MAC and it worked quite well. Nice thing about using my mixture was if it leaked on my brake disc, it didn't appreciably affect the braking performance like ATF did.

Geared hub motors like a MAC have a different requirement than Direct Drive hub motors like the Leaf because you need about five times as much cooling liquid to thermally connect the windings to the shell for the Geared motors so viscosity can be a bigger problem for the Geared motor.
 
Bullfrog said:
Justin (Grin Tech owner/operator) suggested an alcohol might be a good cooling fluid. After his suggestion, I tried distilled water with Motul MoCool as a corrosion inhibitor in my MAC and it worked quite well. Nice thing about using my mixture was if it leaked on my brake disc, it didn't appreciably affect the braking performance like ATF did.
Click to expand...
I was thinking about both of those the other day but was worried that the water/coolant may cause electrical conductivity problems, although I suppose that depends how well things are sealed which wouldn't be that hard and how much is in there. The alcohol I think would work quite well if you had a way to cool it well enough, without enough cooling like a vent to a radiator the alcohol would evaporate too fast. But if you could recondense the vapor the whole system could be a phase change cooling system, although even that may have to operate at some amount of pressure now that I think about it.
 
Many years ago I did an experiment with what I had on hand at the time which was chainsaw oil. Ran a '200W' hub at over 800W for many kms without issue. It did leak a bit, but not enough to cause problems.
In the end that motor overheated from a badly rubbing hub brake shoe transferring heat into the motor....ironically I hadn't noticed it was rubbing due to the increased power available.

Cheers
 
Cowardlyduck said:
Many years ago I did an experiment with what I had on hand at the time which was chainsaw oil. Ran a '200W' hub at over 800W for many kms without issue. It did leak a bit, but not enough to cause problems.
In the end that motor overheated from a badly rubbing hub brake shoe transferring heat into the motor....ironically I hadn't noticed it was rubbing due to the increased power available.

Cheers
Click to expand...
Was that 2-stroke oil or bar and chain oil?
 
Really? You guys still discussing alternative oil for geared hub motors in 2024?

Whats wrong with ATF? I hate the smell of ATF like the next guy (only jet fuel smells worst) but ATF has the right viscosity and got all the necessary additives (foam inhibitors, friction inhibitors, etc, etc) to make it the best oil for the job.
 
Marc S. said:
Really? You guys still discussing alternative oil for geared hub motors in 2024?

Whats wrong with ATF? I hate the smell of ATF like the next guy (only jet fuel smells worst) but ATF has the right viscosity and got all the necessary additives (foam inhibitors, friction inhibitors, etc, etc) to make it the best oil for the job.
Click to expand...
Reminiscing would be more accurate...what I mentioned above was done in 2014 or 2015. Point was that it worked and worked well...I would do it again if I didn't want to bother getting ATF just like last time. :p

Cheers
 
Marc S. said:
Really? You guys still discussing alternative oil for geared hub motors in 2024?

Whats wrong with ATF? I hate the smell of ATF like the next guy (only jet fuel smells worst) but ATF has the right viscosity and got all the necessary additives (foam inhibitors, friction inhibitors, etc, etc) to make it the best oil for the job.
Click to expand...

Personally,
- If i'm going to add something is going to drip everywhere, i want it to have low toxicity. A few laps of ATF can kill a dog.. i have two cats in my home.
- I want to be sure the fluid won't destroy parts of the motor over a period of 5 years. I want the highest materials compatibility i can get.
 
neptronix said:
Personally,
- If i'm going to add something is going to drip everywhere, i want it to have low toxicity. A few laps of ATF can kill a dog.. i have two cats in my home.
Click to expand...
There are automatic transmissions everywhere, many of then leaking, but cats and dogs are mostly fine.
I think you're overthinking it a little too much, the real risk is getting oil on the tire, bu if it's sealed properly this is unlikely to happen.
neptronix said:
- I want to be sure the fluid won't destroy parts of the motor over a period of 5 years. I want the highest materials compatibility i can get.
Click to expand...
There is only one sure way to know the reliability: to try and see how it goes.

I don't think there will be any problem with it, we're all fine with the idea of leaving the motor filled with air and moisture which corrodes the magnets and more importantly the laminated cores, we don't even think of it being wrong when it's one of the main motor death causes. At least adding oil will solve this issue for sure, all the rest is hypothetical.
 
Never seen much on animals and transmission fluid, i have however heard inumerous times that leaving anitfreeze out is dangerous to animals, and from having to chase my dogs off the gravel where I rinse out things when I am done with them (it is a ghetto settling tank. 22x30x8 pan sunk in the ground and filled with gravel. I clean it out properly once a year and so far not even discoloured gravel, I am just paranoid about pollution)

Also.. I have rat issues due to living next to farmland. They are currently self regulating because one chewed into an anti-freeze container and died... so now that container is on it's side, on the top shelf with a little rat be gone in it. Hey, I don't like killing animals but if they are gonna move in, they gotta pay rent.
 
OK, i looked into Bullfrog's suggestion on motul mocool.
Link to MSDS

MSDS states there are 3 ingredients, one which makes up ~1% of the mocool mixure is significantly toxic. The others are not so bad and close to opticool.

I found some research about a lubricant that was 90% water. It states that the coefficient of friction is lower. The stuff looks impressive.

1711002818706.png

I'm surprised that bullfrog hasn't encountered any issues with gears using mostly water and mocool, neither which i think have lubricating properties. Add a small amount of lubricant and apparently you're outperforming synthetic oil..?


There appear to be a number of companies making water based lubricants/coolants with high materials compatibility and safety. Here is one i could find with the most detail.

Water-based lubricant provides new pathway for electric vehicle lubrication

Supposedly they have tested and vetted for materials compatibility in the applications. More info in their giant brochure

This stuff is also very new, about a year old.

1711004823241.png

1711004403668.png

Any thoughts?
 
Is your lubricant running low? Just add water - Drives and Controls Magazine

1711038383245.png

"However, until now, he adds, water has been of limited use as a lubricant because it is “subject to certain physical and biological limitations – like evaporation and freezing points, oxidation or microbiological growth”. But “by means of additives in the lubricant or technical solutions at the component concerned, these limits can be shifted, and the water-specific effects rendered beneficially usable. With a water-based product concept, we’ve even been able to reduce the friction involved far enough to bring the range of ‘super-lubricity’ within reach.”
 
You must log in or register to reply here.

Similar threads

Reid Welch
"Extreme MY1018" archival, closed out
Replies
11
Views
15,862
GIGATT
G
Back
Top