Oil cooling your hub- NOT snake oil!

[wiuhh]

just my 2 cents. atf is some pretty amazing stuff with alot of engineering behind it. tho there are some detergents and other stuff as well(mechanic background not chemist). id recomend if your using silicon, to seal atf, you use a silicon from an automotive company that uses silicon instead of a transmision gasket. ie for many years chrysler was known as the best silicon available(i know chrysler????) because their silicon would stick anywhere. always. as it was designed to be put on wet as a pan gasket and imediatley filled with atf and driven etc. so anyway those in the know always kept a tube in our tool box for when it absolutley had to be sealed period.

 

[flathill]

The magnets weaken with heat which provides unintended flux weakening which actually will increase your top speed (less back emf)

As long as they cool down when you decelerate they will recover and you'll have full torque off the line

Sorry, but I need to correct this. When you overtemperature the magnets you "knock down" their flux. It does not recover when the magnets are cooled. Their flux is permanately "knocked down".

http://www.ndfeb-info.com/temperature_ratings.aspx

An irreversible but recoverable loss occurs when the output falls but does not return when the magnet cools down (e.g. the high temperature takes the Intrinsic working point beyond the knee of the Intrinsic curve, causing demagnetisation) but this would be recovered if the Neodymium magnet is remagnetised. For all extents and purposes, this output is lost because the magnet will not be remagnetised during practical application... When cooled, such a demagnetised magnet will have the original Hci but a lower Br (the Br will have increased by the reversible temperature coefficient amount applied to the reduced high temperature Br).

Thanks for clarifying. I only said the magnets will weaken with heat which is true in any case. They will recover to ~99.9% if you don't exceed their temp rating, but they will lose all their strenth just sitting there at room temp given enough time

 

[auraslip]

I've been laying in the bed for a bit unable to sleep pondering the idea of PRE-cooling the motor using peltier coolers to below freezing. Thermo-electric cooling is of too poor efficiency to use on an electric vehicle, but I really like the idea of having the coolers running while the bike is plugged in on standby. This way when you get on the bike, the motor is super efficient and peppy for the first few miles. I'm not sure how to quantify this though. HOW much more peppy? For how long will it last?

I just can't think of a way to use peltiers to cool the hub that doesn't require plugging it in each time you use it. As in: glue a peltier to the side of the hub and plug it in when you stop running. Now, this might be useful for races!

 

[Ben Wilson]

I just can't think of a way to use peltiers to cool the hub that doesn't require plugging it in each time you use it. As in: glue a peltier to the side of the hub and plug it in when you stop running. Now, this might be useful for races!

When I used to race RC cars, I experimented with using 'air duster' can to clean the car, I quickly discovered that it worked as freeze spray if you inverted the can. Pre freezing the motor gave a decent kick for the first second or so, but that was all. Air dusters are also surprisingly expensive for a can of nothing...

 

[auraslip]

That's an idea that's been covered before here: http://www.endless-sphere.com/forums/viewtopic.php?f=3&t=33254

and as you said it is not too effective

 

[amberwolf]

Another issue with pre-cooling a motor is if you cool it below ambient, it will then also absorb heat from the environment as well as from the active motor, negating some of the usefulness of pre-cooling (or rather, making the process less efficient than it could be as the energy used to cool the outer parts of the motor/covers that is then warmed by the environment is wasted).

 

[Spicerack]

New stator turned up today- thanks Paul!

I hope to tear the motor down on Friday and have it reborn on Sunday. I'm sure there's something significant about the next few days but it escapes me.

Just remembered- on Sunday it's chocolate egg day or something... :wink:

 

[stripedtuna]

Funny stuff.. lol..

I just took a quick look to see the difference between the old and the new.



Side by side, you can really see the sun tan you gave it.. lol.

Awesome...

 

[kfong]

This is really good news for the BMC/Mac crowd. I'm quite happy with my 1700watts consumption on my BMC. If increasing the performance another 1000w with reliability. This would be significant to those who have lots of hills or run them in hot climates. I might go this route for my DH build then I can push the BMC with even higher voltages and current. 3000w on a middrive setup is more than enough for my needs.

 

[Whiplash]

Indeed! I need that 12 fet now!!

 

[GCinDC]

any suggestions how to prep a 9C? particularly the wiring/halls...?

 

[Spicerack]

any suggestions how to prep a 9C? particularly the wiring/halls...?

Prep it for oil cooling?

Make sure all wires are well tied down, maybe a few bits of epoxy here and there in the hall wires so they can't move. Then coat everything in an engine lacquer or windings lacquer. Seal the wires where they pass into the axle with automotive silicone (should have mentioned that before- don't use bathroom silicone as it won't hold up to the oil), then seal the whole motor up as described.

 

[GCinDC]

Then coat everything in an engine lacquer or windings lacquer.

here's a 9C that was painted with motor varnish and then baked, and you can see there's been a fair amount of flaking, presumably from installs.

i wonder if the ATF will erode the varnish more, considering it doesn't really appear to have bonded well...

and i wonder if it would be better just to varnish the halls and maybe phase wiring.

...Seal the wires where they pass into the axle with automotive silicone

Ok, so to try to fill the axle from the outside, moving around the wires as necessary to fill the end??

 

[fechter]

If the motor is filled with oil, rust should not be a problem, so the laminations shouldn't need any coating.
I've found it to be difficult to get a good seal around a bundle of wires. Yes, wiggle them around to make sure there aren't any gaps between them.

I suppose oil could have a tendency to wick into the stranded copper in the phase wires. It might be good to seal between the insulation and the copper on the ends of the wires. If the wires are tinned up to the end of the insulation, it should block the oil. Oil won't necessarily hurt the copper, but it will make it difficult to solder if contaminated with oil.

 

[Spicerack]

Fechter just beat me to it... But here's my response anyway! Great minds think alike...I guess that coating the windings and wires in varnish is just a case of old habits... With an oil bath you could probably not bother. I'd try to get as much of that flaky stuff off as possible. Still epoxy the wires to hold them together and if you can, epoxy the phase wires at the soldered join to the windings. If you seal this end of the wires there's going to be less oil wicking up the wires under the insulation. Use the silicone to seal on the inside where all the wires enter the axle- you could also use epoxy if you're feeling brave and don't mind a bit of work chipping it out if you have to change wires. Sealing up from the outside is probably as good but the wires do move a bit so there's more chance of breaking the seal and leakage.

 

[GCinDC]

If the motor is filled with oil, rust should not be a problem, so the laminations shouldn't need any coating.

good, that'll save me a step with this 9C, for which i've found some grody old sidecovers to (clean up and) replace the holy ones...

as you can see, the motor's very clean to start with, so this will be a good test...

now to find an auto parts store.. :lol:

 

[advancedelectricbikes]

Regular mineral oil is used for cooling transformers.

That would be my choice for cooling a hub motor. Mineral oil has been used for many years to cool transformers. It is a dielectric fluid and is readily available. Transformer manufacturers generally pull nitrogen and then pull vacuum to remove any water vapor prior to filling the tank with oil. This helps minimizes corona discharge.

 

[bigmoose]

I think I previously posted the reference to why I am recommending Dextron III oil. Don't make this more complicated than it needs to be. Dextron was run by the researchers that did the "Power Dense" motor at BGSU. These motors were also used in an aerospace development project with Dextron the stressed the oil far more than we ever will in a hub motor. It works, it's cheap, it has great temperature characteristics, and it has anti foam agents which has some bearing in this situation. Transformer oil is great stuff, but you do not need the exotic characteristics of dielectric strength, etc. Today's automatic transmissions have wiring, solenoids and epoxies all drenched in Dextron III and approach temperatures of 300 degrees F.

...just buy a quart of Dextron III and be done with it.

 

[gensem]

I might be wrong but the oil approach doesn't make much sense for a dd.. you ll have a faster way to heat the covers and maybe a little more room for a few hundred watts. But after heating the motor that should be it.
An oil/water radiator is missing for bigger power numbers.

 

[auraslip]

gensem - the oil conducts the heat from the windings much, much better than air. The oil then conducts the heat to the covers. Since the covers are much larger in surface area, they radiate heat much better than ventilated windings would. Also the covers get much better airflow then the windings.

 

[Spicerack]

As I said before, I follow the KISS principle. Keep It Simple, Stoopid!

ATF is thin, easily available and good for gears in a geared hub. It's also specifically engineered to also be good for bearings, like those found in a DD hub. I don't want you DD guys feeling left out here. This simple splash system should be good for most people. If you want to really turn the power up, sure, a radiator, pump etc is better but way more complicated.

I guess the downside of simple splash oil cooling is that if you let your oil get to more than 80 celcius constantly, you risk damaging your magnets. If that's the case then you have to either try the radiator approach or air cooling and turning the power down a bit. If you have alot of spare time on your hands, you could do the liquid cooling/radiator approach with a coolant channel formed around the base of the stator laminations like have been done on this site (the carbon fibre channel- nice). This would prevent any of the hot coolant getting at the magnets but it also wouldn't take heat directly away from the windings either so they would still be susceptible to burning.

Of course we could buy motors that are rated for the power that we desire.........nah!

 

[auraslip]

I've heard 80c is when they start to break down. But is this permanent? Can any someone quantify this? Is it immediate? Does the speed the damage occurs speed up lineally? This seems like VERY important information.

Also, I wonder what the difference between the measured temperature of the windings and the temp of the magnets will be. The magnets are glued to a big hunk of metal that gets lots of air flow.

 

[Kingfish]

Standard machine oils plainly have a limit of 180*F, whether it is ship or motor. They can take more abuse for a short time, however breakdown is ongoing once the limit (however defined) is reached.

Organic oils: Once separation occurs, that’s it – jig is up; break down begins and it cannot be reversed. Hydrogenated Paraffin looks like pudding or yoghurt; white mushy mass, waste of good materiel, frustrating to clean. Measured in buckets on modest ships at sea. Damaged oil is required to be replaced; there is no alternative, even with filtration; that only removes more paraffin.

Synthetics have much higher heat tolerance; they are less affected by natural agents that cause lubrication failure. Think Amsoil!

A long career studying lubrication awaits the capricious few; kingly is the sire that solves the elusive problems of heat transfer and fluid flow (no pun intended). The problem is ginormous: Isn’t it amazing that all society hinges on the effectiveness of a thin-film long-carbon chains at the boundary layer under punishable conditions is really all that keeps our world afloat? (a bankable pun)

FWIW, Amsoil was one of my clients in ’92, as was Standard Oil in ’98. The technology surrounding them, aside from being a most-eye-opening technical culture, is amazing! I didn’t say they were Scott-free on the environment, no! Just appreciative of the science and industry.

~KF

 

[motomech]

As I said before, I follow the KISS principle. Keep It Simple, Stoopid!

ATF is thin, easily available and good for gears in a geared hub. It's also specifically engineered to also be good for bearings, like those found in a DD hub. I don't want you DD guys feeling left out here. This simple splash system should be good for most people. If you want to really turn the power up, sure, a radiator, pump etc is better but way more complicated.

I guess the downside of simple splash oil cooling is that if you let your oil get to more than 80 celcius constantly, you risk damaging your magnets. If that's the case then you have to either try the radiator approach or air cooling and turning the power down a bit. If you have alot of spare time on your hands, you could do the liquid cooling/radiator approach with a coolant channel formed around the base of the stator laminations like have been done on this site (the carbon fibre channel- nice). This would prevent any of the hot coolant getting at the magnets but it also wouldn't take heat directly away from the windings either so they would still be susceptible to burning.

Of course we could buy motors that are rated for the power that we desire.........nah!

Anyone actually seen these damaged magnets?
My gut tells me this is a theoretical problem that is not going to manifest in practice. I thinking other things[like winding insulation and wiring] will be damaged long before the magnets lose any strenght.
At least that's my experience working as a motorcycle/automotive/heavy equipment mechanic for more decades than I care to admit.

 

[Spicerack]

Anyone actually seen these damaged magnets?
My gut tells me this is a theoretical problem that is not going to manifest in practice. I thinking other things[like winding insulation and wiring] will be damaged long before the magnets lose any strenght.
At least that's my experience working as a motorcycle/automotive/heavy equipment mechanic for more decades than I care to admit.

I haven't seen any. Just what has been told on this thread- perhaps if someone has a magnetic flux meter they could do a little experiment for us? :wink: