Keyne's DH Comp Build - now with liquid cooled HX35! :)

[keyne]

Trying to picture the contact area.. Is it on both sides of the stamped stator?

The contact area ends up being about 60cm^2.

The large delta T between the coolant and the windings is just due to heat getting through the winding paper and the laminations before getting to the stamped stator part. Delta T seems to be as much as 15-20deg (will check next time). But that's not so bad as 120deg should be fine as an upper winding temp (at which point the coolant would boil.)

 

[full-throttle]

Thanks keyne!

Just in case you have not seen it already, here's a video of Justin's presentation on hub motors. Weight saving talk starts @ 1:12:00
[youtube]gwlbAJLzI_w[/youtube]

 

[amberwolf]

The large delta T between the coolant and the windings is just due to heat getting through the winding paper

Do you think it would make a difference if you used a non-evaporative liquid that is thermally conductive but not electrically conductive, and wet the paper with it? Mineral oil is one thought, but there may be much better stuff?

 

[keyne]

Do you think it would make a difference if you used a non-evaporative liquid that is thermally conductive but not electrically conductive, and wet the paper with it? Mineral oil is one thought, but there may be much better stuff?

I had thought of sealing it well and flooding it with a small amount of oil to use the rotor to conduct away a bit of heat too, but I hadn't thought about how that would also help reduce the delta T - that's a good idea.

 

[amberwolf]

If you flood it, rather than just wetting the paper, make sure whatever you use is not a solvent for anythign in your CF ring's epoxy.

 

[keyne]

Does anyone have any suggestions as to what to use to improve the thermal path from the windings to the stator? I had thought of flooding the windings with sort of thermally conductive epoxy, but don't really know what to use.

I'm just trying to reduce the delta T between the windings and my cooling channel to make the cooling system more efficient, currently the delta T is about 20-25degC.

 

[full-throttle]

Epoxy mixed with magnesium oxide??

 

[teklektik]

Do you think it would make a difference if you used a non-evaporative liquid that is thermally conductive but not electrically conductive, and wet the paper with it? Mineral oil is one thought, but there may be much better stuff?

I had thought of sealing it well and flooding it with a small amount of oil to use the rotor to conduct away a bit of heat too, but I hadn't thought about how that would also help reduce the delta T - that's a good idea.

If you are going through the trouble of sealing and flooding the housing, sidestep the delta-T issue, lose the carbon channel, and just use the oil to pull the heat directly from the windings. Perhaps you can offset the pipe openings to be near the axle and outside edge - spinning the oil should move it outward so the cool oil inlet probably should be center-most. Oil cooling is well known in transformers http://en.wikipedia.org/wiki/Transformer_oil. This would probably make gear motors very happy.

 

[keyne]

I might try this stuff.
http://uk.rs-online.com/web/p/potting-compounds/0552668/

I don't like the idea of flooding it with oil.

 

[caspo6]

How about deionized (distilled, ultrapure) water? I've seen large industrial switchgear built by General Electric for a 15 kV - 23,000 HP electric drive cooled with deionized water. It is non-conductive.

I found a few references to it being corrosive to some materials, but it appears that some submersible pump manufacturers fill the motor with deionized water for cooling.

http://uk.answers.yahoo.com/question/index?qid=20080520112830AAMeyE0
http://www.lytron.com/Tools-and-Technical-Reference/Application-Notes/Deionized-Water
http://www.american-marsh.com/epg/products/pdf/iommanuals/SUBMOTORIOM.pdf

 

[keyne]

I'd rather not use anything that could potentially leak out. Something that sets on the windings and stator would be ideal - hence why I'm moving towards thermal epoxy. Water isn't actually that good in terms of thermal conductivity, though it is better than oils.

From wikipedia:


Water : 0.6 [W/(m·K)]
Alcohols and oils : 0.1 - 0.21 [W/(m·K)]
The thermal epoxy I'm thinking of using is about 1.25 [W/(m·K)]

 

[teklektik]

I had thought of sealing it well and flooding it with a small amount of oil to use the rotor to conduct away a bit of heat too, but I hadn't thought about how that would also help reduce the delta T - that's a good idea.

I'd rather not use anything that could potentially leak out. Something that sets on the windings and stator would be ideal - hence why I'm moving towards thermal epoxy. Water isn't actually that good in terms of thermal conductivity, though it is better than oils.

From wikipedia:

Water : 0.6 [W/(m•K)]
Alcohols and oils : 0.1 - 0.21 [W/(m•K)]
The thermal epoxy I'm thinking of using is about 1.25 [W/(m•K)]

The desire to avoid leakage is certainly valid and a good enough reason in its own right to avoid flooding the motor body - I wouldn't have suggested it if you had not already volunteered it as a solution you were considering.

As far as the thermal conductivity is concerned, the figures you quote are for static heat propagation and are not directly applicable to situations with circulating coolants where specific heat is the primary characteristic in play. Beyond that and regardless of any Wpedia spec, you are already successfully water cooling and are currently battling the thermal barrier of the conduction necessary to get the heat from the windings to the coolant (your delta-T is measured across this barrier). Adding epoxy may reduce the thermal barrier in that its thermal conductivity is better than air, but it cannot be as effective as eliminating the barrier (heat conduction path) by allowing direct contact of the coolant with the windings.

I think if you are embracing a specific design and want to pursue the epoxy, then you should do so if for no other reason than 'just because'. There are reasons to shy away from flooding the motor, but the Wpedia thermal conductivity argument doesn't seem to be one of them.

 

[keyne]

I had thought of sealing it well and flooding it with a small amount of oil to use the rotor to conduct away a bit of heat too, but I hadn't thought about how that would also help reduce the delta T - that's a good idea.

I'd rather not use anything that could potentially leak out. Something that sets on the windings and stator would be ideal - hence why I'm moving towards thermal epoxy. Water isn't actually that good in terms of thermal conductivity, though it is better than oils.

From wikipedia:

Water : 0.6 [W/(m•K)]
Alcohols and oils : 0.1 - 0.21 [W/(m•K)]
The thermal epoxy I'm thinking of using is about 1.25 [W/(m•K)]

The desire to avoid leakage is certainly valid and a good enough reason in its own right to avoid flooding the motor body - I wouldn't have suggested it if you had not already volunteered it as a solution you were considering.

As far as the thermal conductivity is concerned, the figures you quote are for static heat propagation and are not directly applicable to situations with circulating coolants where specific heat is the primary characteristic in play. Beyond that and regardless of any Wpedia spec, you are already successfully water cooling and are currently battling the thermal barrier of the conduction necessary to get the heat from the windings to the coolant (your delta-T is measured across this barrier). Adding epoxy may reduce the thermal barrier in that its thermal conductivity is better than air, but it cannot be as effective as eliminating the barrier (heat conduction path) by allowing direct contact of the coolant with the windings.

I think if you are embracing a specific design and want to pursue the epoxy, then you should do so if for no other reason than 'just because'. There are reasons to shy away from flooding the motor, but the Wpedia thermal conductivity argument doesn't seem to be one of them.

I agree. I guess what I'm asking now is if anyone knows of something that would work in a similar way to the thermal epoxy, but conduct even better?

 

[teklektik]

I guess what I'm asking now is if anyone knows of something that would work in a similar way to the thermal epoxy, but conduct even better?

I believe the epoxy will be beneficial but that you need to somehow impregnate the windings to replace the air in the inter-wire gaps with a solid material (cured epoxy) possessing a higher thermal conductivity. I'm thinking this is going to minimally require a vacuum chamber to expand the trapped air into bubbles that will rise out of the liquid epoxy (I have seen this done in casting) but this is just a guess. Cheap vacuum pumps and small chambers are to be had on eBay if this is really the path needed - dunno...

I ran across this which sounds like where you are heading, but I couldn't find the referenced paper with a casual Google search:
http://www.finishing.com/419/43.shtml:

Furthermore, if you want to further improve heat transfer within the motor then you pot the stator winding using a thermally conductive epoxy instead of the traditional "varnish" still used in most AC induction, stepper, and low performance BLDC motors. 15-years ago I began potting BLDC stators using a thermally conductive epoxy and this is becoming standard in high performance BLDC motors since the improvement in heat transfer is 40-50% higher compared to using a varnish! If you want to read more about potting then obtain a copy of my paper I presented at the 2006 SMMA Fall Conference in Saint Louis MO, "How to Increase a Motor's Continuous Torque Output and Power Density by Potting its Stator With Thermally Conductive Epoxy".

In addition, I have published companion papers in two different motor industry trade magazines, Sept. 1, 2009 issue of "Energy Efficiency & Technology" and Aug 1, 2009 issue of "Motion Systems Design (MSD).

Richard Welch Jr
Consulting Engineer - Oakdale, Minnesota USA

 

[keyne]

I've spent quite a few hours working on the bike recently and made up a carbon fiber motor side panel on the freewheel side. It was mainly to see where I can save weight. It turned out pretty well - annoyingly I'd run out of twill carbon for the outside, so it doesn't look as cool as it could. It's almost 300g lighter than the stock panel, and hopefully will reduce motor hum a bit too - rather than ringing, it just makes a dull 'thock' noise when you tap it . I'll post a photo when it's daylight. I'll make up the disc side too when I get some time - hopefully a similar saving to be made there.

 

[kfong]

Modding the motor plates with CF sounds like a great idea for saving weight, but sounds bad for heat dissipation. I will be courios on how it holds up.

 

[Alan B]

But this motor is liquid cooled.

 

[keyne]

Modding the motor plates with CF sounds like a great idea for saving weight, but sounds bad for heat dissipation. I will be courios on how it holds up.

I guess someone didn't read the thread title :wink: Carbon fiber side panels would be a bad idea for stock hub motors which have a bad thermal path for cooling.

Here's a picture:

Larger version here:
View attachment 1

 

[Sacman]

Sounds cool.
Yes show some pics please.

Edit: Ahhh... thanks. Very nice!!! But yes it would hamper motor cooling since it doen't conduct the heat to the outside as well as the original covers.

I'm curious about how do you kept the steel threaded collar (for the freewheel) perpendicularly aligned to the face of your side cover so it doesn't wobble. I guess also applies to the axle bearing to the other side cover you'll be making.

 

[grizmoblust]

How does one simply build radiator cool motor?

 

[sn0wchyld]

hey mate
any updates on this one? how's it running/holding up? Did you get the CF in?

Love to see some more vids, I miss the nz countryside.

 

[keyne]

Yeah I should really post some updates:

Not a lot of riding in the last couple of months, I managed to kill a cell group a while ago though lack of battery management during discharge. It happened to coincide with buying a house that needed a bit of work and somehow the kitchen got higher priority than the garage so I didn't fix it until recently (thanks to full throttle with his plastic ruler trick for separating lipo packs). Now my garage is finally in a state I can work in I hope to get everything up and running again soon.

The carbon fiber motor panels have been removed because there is just the tiniest bit of slop (my molds were't made on a lathe) which I found always ended up with the stator rubbing on the rotor at some point during a bumpy ride. I'll make some new ones with nice molds once my new lathe is set up.

It's turned very wintery here recently so I'm going to try a metal studded rear tyre with a ski up front and see how that goes should make for some interesting vids.

Just this morning I'm building a roll-able scissor-lift stand for the bike to make it easier to work on and have installed a sealed regen switch on the front brake. I can't think of a time when I use the front brake and don't want regen (maybe if I wanted to do a burn-out?), but to allow wheelie control I didn't put one on the back brake.

 

[sn0wchyld]

......
View attachment 7
1x 12v solar water pump - pc cooling pumps have great specs but are usually only rated to 65degC, this one is rated to 110degC. With the whole system hooked up I get a flow rate of about 1.7L per min with water, a bit less with the 33% antifreeze I use.
For those who don't know, antifreeze is also antiboil, so the 33% coolent I'm using is good from -15 to 105 degC. It also stops corrosion which is pretty important given how the cooling tubes work in the motor.
...
gotta go...

hey mate
can I ask where you got the pump (and the rest of the cooling gear, for that matter)?

Yeah I should really post some updates:.....
Just this morning I'm building a roll-able scissor-lift stand for the bike to make it easier to work on and have installed a sealed regen switch on the front brake. I can't think of a time when I use the front brake and don't want regen (maybe if I wanted to do a burn-out?), but to allow wheelie control I didn't put one on the back brake.

damn... thats a good idea. ive got my switch on the left (rear) break, but really it'd be better off on the right, as with a left hand throttle I too have trouble with wheely control. Hell... I could even just have 2 switches...
whats the weight looking like now? any more ideas for jenny craig?

 

[keyne]

The pump was from ebay - (just search for 12v water pump), the rest of the cooling stuff was from frozencpu.com

In terms of the weight, it's a bit under 40kg. There's not much unsprung weight that I can take off without changing to a different motor, using narrower tyres or dropping the derailleur. There is a lot of sprung weight to be lost, but I'd be better off with a different frame. So I'm going to just use it for a while and see how the current configuration holds up.

 

[mikebikerad]

radiator! DH team e-bike owners are definitely wooping the stealth owners with build like this