Ferrofluid for hub cooling? BS or real?

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rg12   10 kW

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Ferrofluid for hub cooling? BS or real?

Post by rg12 » Feb 01 2018 11:20am

Hey Guys,

Was just told by a friend that it works wonders but since it sounds too good to be true, I wanted to check here with the experts.

So, first of all, they claim that it helps conduct the heat through the air gap that is about 1mm wide between the stator and the magnets which sounds logical.
BUT, they also say that you should add about 8ml to a huge 5kw QS205 hub motor and I was wondering how is it possible the 8ml will fill that gap? are they counting on the fact that maybe if it spins fast that the fluid is pushed to a single point and then maybe fills the gap but only at a certain point and because of rotation it is spreading the heat or something?
Doesn't sound convincing to me...
Mongoose EC-D 2007 (18" motocross wheels), 21s 10Ah LiPo, Greentime 72V 110A Controller (soldered shunt), 9kg Hub Motor

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Re: Ferrofluid for hub cooling? BS or real?

Post by amberwolf » Feb 01 2018 1:12pm

Why not read the various threads about it, with their real-world testing, here on ES?

The first stuff is probably in the Definitive Tests thread about hubmotor heating and cooling, easy to find, by Justin LE.

Then there's other stuff by various members, in their build threads or specific threads about it.

Then you'll know what it can do.

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Re: Ferrofluid for hub cooling? BS or real?

Post by cal3thousand » Feb 01 2018 1:42pm

rg12 wrote:
Feb 01 2018 11:20am
Hey Guys,

Was just told by a friend that it works wonders but since it sounds too good to be true, I wanted to check here with the experts.

So, first of all, they claim that it helps conduct the heat through the air gap that is about 1mm wide between the stator and the magnets which sounds logical.
BUT, they also say that you should add about 8ml to a huge 5kw QS205 hub motor and I was wondering how is it possible the 8ml will fill that gap? are they counting on the fact that maybe if it spins fast that the fluid is pushed to a single point and then maybe fills the gap but only at a certain point and because of rotation it is spreading the heat or something?
Doesn't sound convincing to me...
The principal at hand is that gases conduct heat very poorly compared to liquids. It creates a channel for the heat to bridge across the air gap.
Get a Cycle Analyst and a Multimeter, you're still a noob if you don't have at least one of each.

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Re: Ferrofluid for hub cooling? BS or real?

Post by teklektik » Feb 01 2018 2:22pm

rg12 wrote:
Feb 01 2018 11:20am

So, first of all, they claim...
Doesn't sound convincing to me...
"They" is Justin who owns Endless Sphere.

There's no mystery here - you just need to sniff around the web a bit...

If you read the thread mentioned above, you will find careful wind tunnel tests documenting the research into FF effects.
OR
Try Googling 'Statorade" which will bring you to this: http://www.ebikes.ca/product-info/statorade.html
Visit Grin Technologies at www.ebikes.ca
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Re: Ferrofluid for hub cooling? BS or real?

Post by rg12 » Feb 01 2018 2:35pm

cal3thousand wrote:
Feb 01 2018 1:42pm
rg12 wrote:
Feb 01 2018 11:20am
Hey Guys,

Was just told by a friend that it works wonders but since it sounds too good to be true, I wanted to check here with the experts.

So, first of all, they claim that it helps conduct the heat through the air gap that is about 1mm wide between the stator and the magnets which sounds logical.
BUT, they also say that you should add about 8ml to a huge 5kw QS205 hub motor and I was wondering how is it possible the 8ml will fill that gap? are they counting on the fact that maybe if it spins fast that the fluid is pushed to a single point and then maybe fills the gap but only at a certain point and because of rotation it is spreading the heat or something?
Doesn't sound convincing to me...
The principal at hand is that gases conduct heat very poorly compared to liquids. It creates a channel for the heat to bridge across the air gap.
Yes, that I can understand but what nobody talks about is the amount of liquid actually added to the hub.
I've seen a youtube video where they add it to an open hub and put a drop of liquid between each magnet and the magnetic fluid spreads across that line.
It looks so little and so thin that you will need so much of it to really fill the gap.
So my question is, if you fill the gap with magnetic liquid, how can 8ml fill a gap of about 1mm all around the hub?
It just doesn't add up.

EDIT: Just read some on the ebikes.ca website and I understand they did test by adding 1ml each time.
I don't argue with the results and it's amazing that it works with such a small amount but it's weird to me that the amount that doesn't fill the gap (or doesn't seem like it) will work but I guess it does so I will try it myself on a 3kw hub.

Are there some kind of "side effects" doing so? I read that it can leak from the side covers and also seen a video of someone having a weird sound from his hub when it's hot using the fluid.
Are there other things like how it holds high temps over time? does it get gooey/burn/degrade somehow that will make me need to check it from time to time or do a clean?
Mongoose EC-D 2007 (18" motocross wheels), 21s 10Ah LiPo, Greentime 72V 110A Controller (soldered shunt), 9kg Hub Motor

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Re: Ferrofluid for hub cooling? BS or real?

Post by cal3thousand » Feb 01 2018 2:59pm

It's likely that the 8ml isn't going to cover every square mm of the magnets and doesn't need to. There may be something out there that's better than the current Ferrofluid because it can completely cover the magnets before it reaches the physical limitations of the fluid to cling to the surface. But for now, we know this does have a measurable effect on it.
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Re: Ferrofluid for hub cooling? BS or real?

Post by fechter » Feb 01 2018 3:28pm

It's real. Here is the thread with all the lab testing:
https://endless-sphere.com/forums/viewt ... =2&t=48753

The idea is the ferrofluid sticks to the edges of the magnets since that's where the flux is the strongest. It sweeps across the stator and transfers the heat to the magnets. You don't really want to fill the entire gap with fluid, as this will increase the drag quite a bit.

Based on carefully controlled bench tests, adding the right amount of ferrofluid can double the effective power rating of a motor without adding a significant amount of drag.

You could just use ATF or some kind of oil, but you would need a bit more to get the gap filled since it does not preferentially stick to the edges of the magnets. It can also be pretty messy. The magnets keep the ferrofluid from leaking out.
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Re: Ferrofluid for hub cooling? BS or real?

Post by brumbrum » Feb 01 2018 3:34pm

I added ff to my cromotor and on the test ride it desolved all the glue that held the magnets to the hub ring and all the magnets were moving around lol. I've had to take the whole motor apart and one by one remove the magnets, degrease and re-glue. Its a tedious process which i am only about 30% through. Not the ff fault but bad cromotor glue...Beware! :wink: .... Just Bad luck on my account but i will be using it again and i have also put on a hub-sink for maximum effect.
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Re: Ferrofluid for hub cooling? BS or real?

Post by amberwolf » Feb 02 2018 12:41am

rg12 wrote:
Feb 01 2018 2:35pm

Yes, that I can understand but what nobody talks about is the amount of liquid actually added to the hub.
Sure they do. In teh thread I recommended you look for (which Fechter linked directly), there's plenty of testing and info for at least several different types of motors.
Are there some kind of "side effects" doing so?
That's also covered in that thread.

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Re: Ferrofluid for hub cooling? BS or real?

Post by Ianhill » Feb 02 2018 2:01am

To me the design of hub motors and outrunners in general have poor thermal characteristics, poor for sinking any heat out of the stator and inevitably the magnet ring heats up and the need for massive hub fins and statorade to try and keep the rings temp below damaging the magnets, ruff ball park being very optimistic I would say 80-90c recommended 110c max and damage is occurring in field strength there on after.
I like inrunners in this respect even though pound for pound the design does not allow as much of a torque moment meaning less total power but it's spinning mass can be very little in comparison so it has a benifit of giving higher rpms reliably.
Also the magnets are internal with an air gap that does not pass heat efficenlty giving the magnets the cooler temp than the copper and stator, and with them having a good thermal path to the aluminium case that can soak the heat and vent it to air or water allowing more stable operating temp and even when pushed hard they are relatively reliable and it's normally a winding that melts from to much burst current rather than a prolonged overheat but obviously they can be broke but I just like them more I have both not really biased but would prefer a good lmx motor etc over a mxus hub.

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Re: Ferrofluid for hub cooling? BS or real?

Post by rg12 » Feb 02 2018 4:45am

amberwolf wrote:
Feb 02 2018 12:41am
rg12 wrote:
Feb 01 2018 2:35pm

Yes, that I can understand but what nobody talks about is the amount of liquid actually added to the hub.
Sure they do. In teh thread I recommended you look for (which Fechter linked directly), there's plenty of testing and info for at least several different types of motors.
Are there some kind of "side effects" doing so?
That's also covered in that thread.
I went through many videos and posts looking for the "side effects" and except for leaking and drag from adding too much I didn't find anything, so I took your advice and checked the thread by justing and found out it has almost 2000 posts so if you know any side effects that I didn't mention I would like to hear about them.

Roy
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Re: Ferrofluid for hub cooling? BS or real?

Post by Ianhill » Feb 02 2018 4:58am

From what I gather there's a small operating window in quanity amount for efficency vs heat transfer to little no noticeable effect or too much and drag is increased so ideally a temp probe needs to be used to assure there's positive cooling effect with the statorade passing the heat not just the fins cooling the magnet ring and leaving the stator hot.

Then the effect of the magnets adhesive failing with oil contamination is another risk that on an expensive motor kinda defeats the point when its destroyed it with no heat at all.

But there's good reviews out there and they claim life cycle of over two years without top up, then there's pics of it leaking out at high rpm so to me it's a suck it and see venture at your own risk you play the I know best game and need to make sure you have the technical knowledge to make it perform as intended.

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Re: Ferrofluid for hub cooling? BS or real?

Post by spinningmagnets » Feb 02 2018 9:23am

I read that it can leak from the side covers
I'm not saying that FF is good or bad, but...I have it in a 1500W 35mm Edge hub and it hasn't leaked at all in the past year or so.

As to FF dissolving the glue that holds the magnets onto the rotor...there are several varieties of FF, they are not all chemically the same. The glue that is used to hold the magnets onto the rotor will also vary in their chemistries.

The majority by far (>99%) of FF users have not had that problem, but...it would be useful to find out which chemistry of FF and glue do not work well together. If anyone finds out this info, please post it on the FF thread...

actually...I AM saying FF is good.

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Re: Ferrofluid for hub cooling? BS or real?

Post by rg12 » Feb 02 2018 11:21am

spinningmagnets wrote:
Feb 02 2018 9:23am
I read that it can leak from the side covers
I'm not saying that FF is good or bad, but...I have it in a 1500W 35mm Edge hub and it hasn't leaked at all in the past year or so.

As to FF dissolving the glue that holds the magnets onto the rotor...there are several varieties of FF, they are not all chemically the same. The glue that is used to hold the magnets onto the rotor will also vary in their chemistries.

The majority by far (>99%) of FF users have not had that problem, but...it would be useful to find out which chemistry of FF and glue do not work well together. If anyone finds out this info, please post it on the FF thread...
I think it may be easier to find out about the glue types since you can ask for your hub supplier to send you some magnet glue (got it from mine, it's green...) but FF chemistry I believe is more complex to find out...
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Re: Ferrofluid for hub cooling? BS or real?

Post by fechter » Feb 02 2018 4:20pm

rg12 wrote:
Feb 02 2018 11:21am

I think it may be easier to find out about the glue types since you can ask for your hub supplier to send you some magnet glue (got it from mine, it's green...) but FF chemistry I believe is more complex to find out...
There are several flavors, but the stuff Grin sells is based on "synthetic hydrocarbon" according to the Ferrotec web site. Basically like synthetic motor oil. I think it's called APG1110. Ferrotec can tell you exactly what the composition is.

Normally, epoxy is very resistant to oil.

I've had FF in my A2B Metro hub motor for almost 2 years and no issues. Not a drop of leakage.
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Re: Ferrofluid for hub cooling? BS or real?

Post by brumbrum » Feb 03 2018 3:24am

Apologies if i put the cat amongst the pigeons concerning bad glue, not my intention. I have also heard of other people with same version cromotor as mine where magnets came loose and they were NOT using ff.
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Re: Ferrofluid for hub cooling? BS or real?

Post by liveforphysics » Feb 03 2018 4:03am

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Re: Ferrofluid for hub cooling? BS or real?

Post by Toorbough ULL-Zeveigh » Feb 18 2018 1:08pm

liveforphysics wrote:
Sep 21 2012 4:20pm
Dextron FTW
https://endless-sphere.com/forums/viewt ... on#p641118

soo FTT now?

howz bout iff either's good then do both must be better.
FTW squared n'est-ce pas?

what happens if you mix the two?
concerned lemmings gotz 2no.
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Re: Ferrofluid for hub cooling? BS or real?

Post by brumbrum » Feb 18 2018 2:05pm

‘Real’ statorade + hubsink has made a massive temperature difference to my cromotor. I went on a two hour ride yesterday to give my rebuilt Cro with newly added belt and braces cooling a good shake down and I never at any point saw over 57oC. I normally see 100+ as the heat just builds and runs away. It has been a real eye opener for my overheating hub.
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Re: Ferrofluid for hub cooling? BS or real?

Post by fechter » Feb 19 2018 3:33pm

Toorbough ULL-Zeveigh wrote:
Feb 18 2018 1:08pm

howz bout iff either's good then do both must be better.
FTW squared n'est-ce pas?

what happens if you mix the two?
concerned lemmings gotz 2no.
touch o' da spring fever
Probably a bad idea. The oil bases may not be compatible and the surfactant in the FF might not like it and cause all the iron particles to settle out. ATF doesn't work well at the very low fill levels that FF does. 10cc of ATF isn't likely to work nearly as well as 10cc of FF.
If you add more volume, then it probably wouldn't make sense to use FF at all, just use ATF and have a higher drag.
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Re: Ferrofluid for hub cooling? BS or real?

Post by liveforphysics » Feb 21 2018 3:31am

ATF escapes the motor much faster and adds more drag, but performs similarly at the right fill level. It can be awful to keep oil contained if it foams, so racing ATF that uses no detergents and has bubble popping additives.

FF and hubsinks together is about the continous power capability of having 2 motors.
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Re: Ferrofluid for hub cooling? BS or real?

Post by Chalo » Feb 21 2018 3:47am

If the motor runs too hot, it's too small or you're demanding too much power from it. This isn't rocket science; we've had boringly reliable electric motors for more than a century. Use enough motor for the job and you'll have no problem.
This is to express my gratitude to Justin of Grin Technologies for his extraordinary measures to save this forum for the benefit of all.

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Re: Ferrofluid for hub cooling? BS or real?

Post by Buk___ » Feb 21 2018 7:16am

Chalo wrote:
Feb 21 2018 3:47am
If the motor runs too hot, it's too small or you're demanding too much power from it. This isn't rocket science; we've had boringly reliable electric motors for more than a century. Use enough motor for the job and you'll have no problem.
We've had boringly reliable -- but horribly inefficient -- 500ci shopping cars for decades too.

More motor means more of the heavy stuff -- copper, magnets, casing -- so more weight. More weight needs more battery. More battery means more weight; needs more battery ... Better make the motor more efficient; so generate less heat to need to dispose of.

When run in their optimum operating range BLDCs can be ~97% efficient. Trouble is, that invariably means at highish speed, but the greatest requirement is for acceleration/torque from low speeds. That's where the heat is generated.

Rather than throw mass/size/energy at the problem, throw some engineering at it. Keeping a motor at optimum operating speed across a wide range of road speeds is a solved problem. The gearbox.

But gearboxes are complicated -- giving many extra points of failure -- and either heavy and strong, or lightweight and fragile. But there is a better way; an electric IVT.

Two 100mm x 20mm (Qute class) rotor/stators combined in a single hub with a planetary differential.

2 x 20mm rotor/stators, 36mm for gears (for the human), 10mm for disk, leaves a 49mm budget for 2 hub casings, and 2 planet carrier webs, and 3 widths of gears. So:

Code: Select all

 1 * 36mm gearset
 1 * 10mm disk
 2 * 20mm stator/rotor
 3 * 10mm planet gears
 4 *  3mm hub sides/planet webs
 6 x 1mm interstigials.
     ------
135-134 1mm spare :)
A start up, the two motors turn in opposite directions -- bike remains stationary, as power is applied, one motor slows down causing forward motion. As that motor reduces to 0 rpm, the other remains running at its highest optimally efficient rpm. The first motor now reverses direction and moves up to half the speed of the first whilst the first reduces to half its previous speed, forward speed remains unchanged, now both motors increase in concert and the road speed increases to double that achieved by the first motor once both reach their highest optimal rpm with half the load each, so less power needed than 1 motor at the same loading.

Doable today. A 4kg class 5/6in motor with ~2kw of power and 100N of torque. All whilst running at best efficiency.

If only I still had access to a well equipped workshop and some spare cash :)

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Re: Ferrofluid for hub cooling? BS or real?

Post by brumbrum » Feb 21 2018 8:59am

I dont think ff and hubsinks make motors more efficient, they just help dissipate the wasted heat, so things in the motor dont get cooked :D
My NYX and cromotor build
viewtopic.php?f=6&t=74615
My LMX 161 dirt bike build
viewtopic.php?f=6&t=94074

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Re: Ferrofluid for hub cooling? BS or real?

Post by Chalo » Feb 21 2018 2:48pm

brumbrum wrote:
Feb 21 2018 8:59am
I dont think ff and hubsinks make motors more efficient, they just help dissipate the wasted heat, so things in the motor dont get cooked :D
Exactly. And the motor represents the smallest source of weight savings and practically no size savings compared to every other part of the system.

The most power efficient motors both now and back when I started messing around with these things are still the big slow direct drive hubs, once you factor in efficiency losses due to reduction gearing. In a 150kg gross weight vehicle, the weight penalty of those is something like 2% of the total compared to most of the lightest alternatives. And even that difference only comes into play when accelerating or climbing.

The fact that ferrofluid cooling and supplementary heat sinks seem to appeal to the same folks who use heavy draggy wheels/tires and heavy energy-wasting suspension instead of lighter and more efficient alternatives tells us what this stuff is really about: fetishism. It's hot rodding for the sake of hot rodding, like putting a big turbo on a little economy car engine, or overclocking and water cooling an outdated CPU.
This is to express my gratitude to Justin of Grin Technologies for his extraordinary measures to save this forum for the benefit of all.

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