Another attempt at liquid cooling...

[itchynackers]

Not quite sure yet. On the motor I took off (beefed up 9c 8x8) I ended up running 40a battery current. Although, for a while, I ran peaks of 90a, but that was on 25s lipo (102.5v hot). Just didn't seem like I was getting that much better acceleration, so I backed it down. Just this week, I switched to 30s (123v hot), and the end of ride temps were definitely affected. Before I got about 70-82C temps. With 30s, I'm getting 80-92C. And these runs were not pushing it 100% from stop lights. Usually I ride this route (6.5 miles) to work. Generally, I arrive home at night hotter than morning, since I'm riding into the wind heading home. The last time, I hit 102C with 30mph head wind gusts. I rode at about 30mph and still hit 102c.

I think I'll try 40a peak for a bit (about 4800watts). If I see good results, I'll up the amps a bit.

[Spicerack]

Nice, so just a little bit hotter than mine which is running at 1300W. Shows how toasted my windings are! Can't wait to get my new stator in. Also a good indicator for my 8x8 9C... better get that all fixed up I guess!

[itchynackers]

Ok, for those interested, I have a few results.

6.5 mile usual ride to work.
Ambient temp = 5.5c
Ending (highest) temp = 50.1c (way below the usual range of 70-92c)
Used 51.2 wh/mi
51 amps peak

Took about 3 minutes to write down the results, then I rode home right away.
Starting temp (cools down quicker than before) = 42c
Highest temp (during ride) = 67.2c
Totaled 57.9wh/mile for the total of 13 miles

Notes: I pushed hard on the way home, which I never do, and still didn't reach a temp I normally would see.
My tire is still egg shaped, must fix.
Had some minor fluid leakage. Got about a drop or two out of the vent. Didn't get on the brake rotor. I'll have to work on that. Also, I must not have sealed the inside axle hole very well, since there were a few drops coming out the end of the axle. I'll have to fix that if I crack the motor open again. Also, there seems to be very minor leakage out a couple cover screws. I'll try thread locker or silicone sealant to seal those up. All in all, I'm quite happy and will turn up the amps a bit. I'll have to start monitoring controller temps (I have a habit of not doing that since it hasn't been an issue). Once I get the minor leakage worked out, this should be more of a worry-proof system.

[auraslip]

Good work!

[Spicerack]

Perpex window in a side cover for level checking, live with minor leaks and top up when neccessary. Easy!

[itchynackers]

I had thought about a clear window for level monitoring! Just have to think about it a bit more to work out some details. Also, it looks like I didn't tighten down all the cover screws, so that may have been why I got some minor seepage out a couple screws. I noticed it when I went to seal each screw with silicone sealant and none of the screws were tight, whoops. Anyway, the silicone is drying for 24 hours. Should be ready for a retest after work today.

Also, I'm thinking I may leave the vent hole unobstructed. It's only a 1.5mm hole to begin with. If I stick a small piece of plastic in there (that still leaves room for airflow) it should all but stop any drops from escaping. We shall see.

[itchynackers]

Ok, tight screws do make a difference. No leaking there at all. I'm still eyeing the vent hole. Got a half drop from it, so I put a piece of insulated wire in the hole after pulling out a few strands (to still allow some air flow). That seems to have worked. I think that is it! If I could just get my damn tire to inflate round instead of oblong, I'd be 100% happy. Incidentally, I checked my top speed after charging to 4.1v/cell and got to 42.8 on 30s lipo with lyen controller programmed to 100% throttle (haven't done 110 or 120% yet).

[Xanda2260]

Thanks for the detailed write up. I really want to try this on my 9x7. Would you mind posting a pic of your vent hole + wire mod? I'd rather not have oil all over my frame after each ride!

Many thank yous!

[itchynackers]

Looks like I'm still getting just a teeny tiny bit of oil out the vent hole for my 6.5 mile ride. Maybe 1/4 drop. I'm still working on something better.

[parabellum]

Looks like I'm still getting just a teeny tiny bit of oil out the vent hole for my 6.5 mile ride. Maybe 1/4 drop. I'm still working on something better.

Pictures?

[itchynackers]

Here is a pic of the vent with my first attempt at plugging it. The vent has filter material in it. That didn't work.



I can't seem to get the flash to work on my phone now. So I'll have to wait for favorable light conditions to get a current photo with the wire plug in the vent.

[itchynackers]

6.5 mile ride to work:

Fluid: 300ml
Ambient: 6C
Arrival: 60C max
Usage: 58wh/mile

[auraslip]

What about some thing like goretex that allows gasses through but not liquids?

[itchynackers]

Yes, I will try that. I'm not quite willing to chop up my good winter boots though... Hmm...

[auraslip]

IIRC you can order patches of it from somewhere.

[fechter]

I think most any material that covers the hole will get saturated with oil and expanding air will push some of it out as the motor heats and cools.

A short piece of tubing bent toward the axle might work as centrifugal force from the wheel spinning will tend to force the oil back in. If you stop with the tube pointing down, it could still drip.

[amberwolf]

Something to keep in mind for the plugs: if it doesn't completely fill the hole, at least as far as the thickness of the fluid itself (thinnest possible layer you can get of it), then you can wind up with wicking into the hole and out of the casing *because* of the plug. In cases like that, it's possible to get *less* leakage *without* a plug than with one, as long as there is no direct path for fluid to come out of the hole, if the only reason it is coming out is because some of it splatters on the part of the plug itself that protrudes away from the casing inside the motor, and then surface tension lets it crawl along the plug to the tiny space between plug and opening.

I've had this happen a fair amount with oils on various things. Not sure if it's the problem here, but it's a possibility.

[itchynackers]

I did try the no plug method. Didn't work as well as hoped. Against advice, I put the vent in perpendicular to the covers. Now I'm thinking that angling it is a better way, even though it may look a little funny. If I ever open the motor, I'll angle that vent. Hopefully that will completely stop any leakage. I'm not really worrying about it too much now since its only about 1/4 drop per trip.

Another ride in this morning:

6.5 mile ride to work:

Fluid: 300ml
Ambient: 7C
Arrival: 65.5C max
Usage: 72wh/mile

ride home:

Fluid: 300ml
Ambient: 14C
Arrival: 55C max
Usage: 47wh/mile

[itchynackers]

After being the first bike up the Pikes Peak race this year, I can attest that liquid cooling does work. I just completed my winter teardown to make a few improvements. Found out I had a detached capacitor. Who knows how long I was riding like this.

Controller:
Soldered the cap back on after hearing it rattle inside the controller. Not too bad.
Siliconed each cap for vibration resistance.
Snugged the fet screws. They were ALL loose!
Spread more thermal compound on backside of aluminum fet bar.
Installed 12v cooling fan in end cap of controller.

Motor:
Installed new Japanese bearings with thin layer of silicone sealant
Re-sealed interior axle/wire slot with silicone sealant.
Tapped hole in side cover for one way pressure valve like these...
http://www.ebay.com/itm/221106438184?ss ... 1497.l2649
Hopefully this will work a bit better than the "tiny hole" method. I will have to stop and bleed the air once I reach maximum temperature. Hopefully the motor will be in a vacuum state after cooling, which should help avoid leaking fluid.
I bolted everything back up and I'm functional, so I didn't botch the controller, woot!

After charging my 25s 12ah battery to 4.1v/cell, I get the following results:
Edit: Working on filling in the data...

ATF Fluid level Resting V Sagging V No-Load Current Wheel Speed RPM
___________________________________________________________________________
0 ml:................102.5.....102.3............1.29...........46.4.........609.5
50ml:...............102.5.....102.2............1.37...........46.4..........609.5
100ml:..............102.5.....102.1............2.16...........46.0..........604.2
150ml:..............102.5.....102.1............2.24...........45.9..........602.9
200ml:..............102.5.....102.1............2.24...........45.9..........602.9
250ml:..............102.5.....102.1............2.24...........45.9..........602.9
300ml:..............102.5.....102.1............2.24...........45.9..........602.9
350ml:..............102.5.....102.1............2.24...........45.9..........602.9
400ml:..............102.5.....102.0............2.24...........45.9..........602.9
450ml:..............102.5.....102.0............2.24...........45.9..........602.9
500ml:..............102.5.....102.0............2.24...........45.9..........602.9
550ml:..............102.5.....102.0............2.24...........45.9..........602.9
650ml:..............102.5.....102.0............2.25...........45.9..........602.9 (this is exactly half full)
700ml:..............102.5.....102.0............2.31...........45.9..........602.9
Ran out of fluid...
750ml:
800ml:
850ml:
900ml:
950ml:
1000ml:
1050ml:
1100ml:
1150ml:
1200ml:
1250ml:

I measured the total full capacity of the motor at 1300ml using water. I calculated the thermal expansion of atf3 at 0.3% per degree C, so it really doesn't expand too much even with a delta T of 100C. Its the hot air I worry about. If I don't bleed that valve properly, or didn't seal the motor properly, I may have created a pressurized, hot oil filled, spinning electric device that I'm riding at 40mph. What could happen?

[itchynackers]

These aren't the results I was expecting to see. I assumed the current required would continue to go up, but it hasn't yet. I ran out of fluid, so I'll have to get another quart.

[Alan B]

Interesting results!

[bigmoose]

Increase in current is drag. When you fill it, don't think of it as a tub being filled from the bottom up. Remember it is spinning, and the oil is "thrown" to the outer periphery by centripetal force. So when you fill it, once it is turning, it is really a ring of oil starting at the magnets and moving inwards toward the axle. The highest shear, which will be the highest drag, occurs where there is maximum velocity differential of parts. That would be right at the air gap between the magnets and the stator.

So you see the most drag right off the bat, and adding more and more oil (which should increase heat dissipation) has little or no additional drag. Usable oil level may well be set by good sealing and a usable vent system to equilibrate pressures.

[sabongi]

Since itchynackers is such a succesfull hill climber, can you talk more about this setup?

[The Stig]

Hi, I'm real interested in how this has worked out for you... I want to run a 9C (cell mans DD) for slow and fast off road use and I'm thinking of liquid cooling it. I'm also considering liquid cooling a MAC.

I skimmed the thread but i figured it would be good to have all this info for liquid cooling noobs in one place, and copy pasting it into the first post. Like:

How to seal the bearings.
How to seal the axle.
What do use for a vent: http://www.ebay.com/itm/221106438184?ss ... 1497.l2649
Any other preparations?
Maintenance?
Reliability/longevity?

[The Stig]

Ok so after reading itchy's threads, I'll give it a shot...

Guide to Liquid cooling a 9C:

1) Open motor cover.

2) epoxy spray windings. (is this necessary?)

3) Seal axle where phase wires with silicone.

4) Drill/tap hole for vent

5) seal cover with small bead of silicone. Put thread locker on screws.

6) Fill motor 1/4 to 1/3 full with synthetic ATF transmission fluid. And close vent.




I would like to propose an alternative Vent idea: a really thin breather tube that goes through the axle and then connects to an empty syringe(or something similar) on the outside. That way the syringe would open and close as air expanded in the motor from heat, but the system would still be closed and no oil would escape.