# DC Motor submerged in Glycol coolant



## RIPPERTON (Jan 26, 2010)

https://www.youtube.com/watch?v=koZdFxMCFJY
This is a cheap brushed dc motor that is usually found in "Barbie Cars" and the brushes are probably not graphite. The motor is capable of 12k rpm on this 30A controller but couldnt measure the rpm while it was submerged.
The Glycol is aircraft grade and was given to me by a friend who works in the RAAF as a Radar Plane technician. This stuff is used to cool the power electronics of the Radar.
I will next test a larger motor with graphite brushes maybe something like a trolling motor.


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## palmer_md (Jul 22, 2011)

When you try a larger motor, I'd be curious to see if the motor draws any additional amperage due to the liquid in the spaces between inside the motor. In other words what kind of an efficiency hit do we get when adding cooling on the DC motor.


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## RIPPERTON (Jan 26, 2010)

Yep and Im also thinking about plasma arc suppression. Will the coolant allow higher current through the brushes without flaming.
The spinning of the rotor will centrifuge any coolant out of it so you could redesign the rotor so it self pumps coolant through itself.


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## RIPPERTON (Jan 26, 2010)

Well apparently Im a little timid compared to this brit.....BOLLOCKS.
No Plasma arc suppression at 240v...damn

https://www.youtube.com/watch?v=kujrWwJfi0k


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## dcb (Dec 5, 2009)

fyi:
http://www.homebuiltrovs.com/rovforum/viewtopic.php?f=3&t=1257

" I actually tested a cheap brushed 12v dc motor running in mineral 10W-30 motor oil. 
Note that I will be using brushless motors on my rov, this was just for fun 

The result?
~40mins and it was completely dead. "

though 40 minutes might actually be good for a can motor under constant use...










hpevs uses synthetic atf fwiw.


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## dcb (Dec 5, 2009)

http://www.eng-tips.com/viewthread.cfm?qid=22278

guy mentions aquaplaning of the brushes as being a big problem 20 years ago (in a 14 year old post).


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## Karter2 (Nov 17, 2011)

But..."Will it Blend ?" 
Impressive but why didnt he have an ammeter hooked up ?
Ripptn' ...there was a guy over on ES who built a trolling motor using a Turnigy outrunner submerged on the end of a pole..completely unmodified, and unsealed
He claimed it worked fine !


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## RIPPERTON (Jan 26, 2010)

I wouldnt even need to experiment with engine oil, stupid idea. No offense
Glycol is much more feasible.
Karter, outrunner sounds like good idea even with a RC airplane prop on it would work on a Kayak.


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## dcb (Dec 5, 2009)

I'm a little confused why you are focused on brushed motors though, not sure I follow your reasoning on glycol (or what form of glycol you are using, i.e. a lot of them are a mix of ethylene or polypropylene and water http://www.electroimpulse.com/salessupp/Catalog.pdf).

Another consideration:
http://pennwell.websds.net/2012/dot/papers/T2S1O2-paper.pdf

an irregularity in the fluid filled "air gap" can create a Bernoulli effect, the motor shaft has to be stiffer than in air. Plus they completely eliminated brushed motors from consideration "for obvious reasons", whatever those are.

either way you should maybe consider a tiny dynamometer and a control motor running the same current/voltage in air to failure to get a baseline at whatever the peak continuous rating is (and other data points).


edit: this page mentions a brushed dc motor in Fluorinert. http://cce.lternet.edu/docs/bibliography/Public/0088ccelter.pdf


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## RIPPERTON (Jan 26, 2010)

Thanks for those PDF's DCB, interesting reading but is the Bernoulli effect a result of high shaft speeds (5000rpm) ?
Why dont the Deep Sea guys use large diameter motors AND pumps that spin at 200rpm. The same thing we see in wind turbines that dont have gearboxes.

I know Id rather concentrate on Brushless motors but atm Im working on an EBay level where most of the cheap stuff is brushed DC.
Im working on a propulsion system for a Kayak but cant use a trolling motor because its too heavy and increases the draft too much so Im trying to adapt a axial flow pump. The cheapest flow per dollar unit is a 235lpm 12v bilge pump for $60 that has a duty cycle. If I fill its motor case with Glycol I can make it a continuous motor. Cost is about $120 for 1000lpm

http://www.ebay.com.au/itm/131771199571?_trksid=p2055119.m1438.l2649&ssPageName=STRK:MEBIDX:IT

Either that or its 2 davies craig 150lpm units for $460 that I can overvolt for 250lpm per unit. The Davies Craig units are DC motors cooled by the pump flow.

http://www.ebay.com.au/itm/151449553831?_trksid=p2055119.m1438.l2649&ssPageName=STRK:MEBIDX:IT


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## dougingraham (Jul 26, 2011)

No idea what the RC car guys use today but I was developing a controller for the brushed motors used in the early 1990's and attended a few races. There was a kind of event where for your entry fee you were given the motor you had to use for the race. The idea was to put everyone on an even playing field. The surprising thing to me was everyone grabbed a battery pack and went to the bathroom where they would hook up the motor to the battery and dip the motor into the toilet. In less than a minute the brushes would be fully seated and ready to go. The water would wash away the film from the brushes and cause quick wear of the brush face. This would allow the seated brush to carry more current than the two points of contact of the V cut on the original brush face.

Pure water is a decent insulator so it would not be a problem for electrical conduction but a water glycol mix I would guess would be a conductor of electricity. Tap water is usually pure enough that you don't get a lot of conduction at the 7.2 volt pack voltages used. But toilet water? Really?


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## Karter2 (Nov 17, 2011)

Ripp'tn
You may be aware, but there is a whole forum section devoted to EV watercraft, electric trolling motors, EV drives for canoes and kayaks, jet powered surfboards etc etc...over on ES
https://endless-sphere.com/forums/viewtopic.php?f=39&t=41960
Also in their motor section is a long thread on oil filled motors etc with guys testing everything from water, mineral oil, veg oil, ferrofluids, even coconut oil !
There may be some useful tips there.


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## bigmotherwhale (Apr 15, 2011)

it sounds like a terrible idea to me, the coolant in the gap between the stator and the rotor will will cause huge amounts of drag and heat up very quickly, and +1 all things bad thats has been said about the brushes... whats the advantage?


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## Karter2 (Nov 17, 2011)

bigmotherwhale said:


> ... whats the advantage?


 Liquids are much better at transfering heat than gases.
Pick the right situation , and it can be a huge advantage.
Probably not ideal for a 25,000rpm brushed motor, but a <1k rpm brushless outrunner, being used as a submerged trolling motor, may well benefit.


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## bigmotherwhale (Apr 15, 2011)

I can understand using a ferrofluid for high torque and good heat transfer in brushless motors but that's a different kettle of fish. 

My opinion is using liquids on a Brushed DC motor will never work, or wont work for long...and will offer no advantages over high flow air cooling. 

liquids act as lubricants and brushes rely on contact 

the viscosity of the fluid will cause more drag and therefore produce heat

your best bet would be to liquid cool the stator and air cool the rotor - whats done already.


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## RIPPERTON (Jan 26, 2010)

A few further tests and not really good news. There is a lot more drag but zero heat in the immersed motor. At high rpm (full throttle) there was an increase in battery side current from 1.1A dry to 7A wet. At low rpm 0.7 dry up to 1.4A wet but this afternoon I ran the motor immersed for over an hour.
The controller was behaving strangely too, one of its mosfets was getting hot when the motor was immersed. Heres a few shots from my favorite new toy, the SEEK thermal camera.
Controller with motor dry. can see 3 of the 6 heatsinks.



Controller with motor immersed.



Motor dry running at full throttle.


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## dcb (Dec 5, 2009)

those seeks are sweet! you gotta play with the focus ring though.

5x more current draw without any external load might not be too significant, not if it can carry more current.


I expect your controller needs help, it would do that if you loaded the dry motor as well.

edit: you might need a thermistor on the motor to see how hard you are pushing it heat wise when it is in a bath, unfortunately.

A small-ish prop (depending on motor size) in more glycol would probably suffice for a wet/dry load. horizontal vs vertical basically. of course proper prop selection is a whole nuther set of iterations.


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