How To Ice Up Your Motor? (Cooling Ideas)

[safe]

PUSH OR PULL?

Another question is whether to "push" air into the motor or to "pull" air out of it. One possible advantage of a "pull" approach is that you would be "pulling" warmer air. Now let's think about the physics for a second, which type of air is easier to move, hot or cold? My guess is hot because it's going to be thinner and so you would be "assisting" hot air in moving from a hot and compressed state to a cool state. Hot air expands by nature, so I would figure that the "pull" would be better.

Thoughts?

One other thing is that the outside colder air might be providing more "inertia" than the hot inside motor air so one would want to get that figured out. Maybe thinner air is less able to be moved because the fan relies on "inertia" to generate it's movement? Does thinner air effectively lower the efficiency of a fan?

What comes to mind is that "compressions equals more heat". So in order to compress air INTO a place that is hot you are adding to the heat because you are increasing the pressure. By "pulling" from a contained space that is already expanding due to heat you are working in parallel with what the air already wants to do.

 

[safe]

0.32 in H2O won't cut it unless you have about a 2" diameter hole through your motor. The space between the armature and the magnets is pretty small, so you need a lot more pressure.

I don't think that ANY fan is going to go above about one P.S.I. (most are about half) and I notice that the fans you listed above have no rating of their pressures. How do you know (what leads you to believe) that they support higher pressure?

 

[Leeps]

It is generally accepted that a centrifugal blower can generate higher pressure than an axial fan. Not to say there arent axial fans that generate more than the blower. As far as push or pull its definetely push. You want the fan blades to be acting on dense air so that they can "bite" into it so to speak. Think of a propeller on an airplane and a prop on a boat, the boat prop can transmit more energy to the water with a smaller prop because its moving in a thicker fluid than the airplane propeller.
In general i would be looking for a centrifugal blower type fan because you have a greater chance of getting a higher pressure fan because of design. And if for no other reason its easier to fabricate a duct going to the motor.
Joe

 

[safe]

As far as push or pull its definetely push. You want the fan blades to be acting on dense air so that they can "bite" into it so to speak. Think of a propeller on an airplane and a prop on a boat, the boat prop can transmit more energy to the water with a smaller prop because its moving in a thicker fluid than the airplane propeller.

I agree with you about viscosity and propeller size. The thicker the material being moved the less propeller needed. But the other angle is the "air conditioning" angle of compressing and expanding air and how it relates to limited spaces. (like the insides of a motor)

Think of an airplane jet engine. It has an inlet that takes in cool air and a fan on that end with a shaft that runs to the rear where the hot air escapes. The "pull" of the front blades is more than the rear because they reshape them and resize them to match the heat effects.

So it's not just about compressing air. It's also the differential between the inside engine air temperature verses the outside air temperature. It's very possible that both sides of the equation "balance out" and either way "push" or "pull" is the same. (that has a "laws of physics" ring to it)

P.S: No matter what fan choice you make they just don't go above one P.S.I. no matter what you do. It seems to be a limit that you can't exceed unless you get into extreme rpms and other forces of physics of air momentum take over. (like in a turbo where they hit speeds of 100,000 to 200,000 rpm)

 

[Leeps]

I dont quite follow with the jet engine example.
The way i visualize a propellor is as a screw working in a fluid. Being that the screw (propellor) cant move forward or backwards the fluid its working on is moving. The pressure is formed by the reduction in space as the blade moves in an arc.
\ imagine the slash moving to the right doesnt seem like theres a reduction in space, there isnt the only thing that's making the air compress is its own inertia keeping it there. Since the pressure is at an angle there are two components two it, one to the left and one pointed down. The one pointed down has an opposite and equal reaction thats the thrust of the propellor and the resulting usuable air pressure blowing the air into your motor. The other pointed to the left is the torque load apparent on the motor spinning the fan.
Since the density of the fluid is directly related to the pumping ability of the fan and the hot air is less dense, well you see where im going. There is also the possibility that blade shape can very well be optimized for pushing or pulling, this would pretty much make the decision for you.

The centrifugal blower (these include turbos) use a different effect, they use centrifugal force(effect) to rotate and sling the air out the blower housing. This can create much greater pressure than an axial fan set up, at a loss of total airflow. This shows when you look at the applications of centrifugal blowers and axial fans. Axial fans are usually 'lofty' in nature desk fans, ceiling fans, computer cooling, general moving air around the room stuff. Centrifugal blowers are usually used when the air goes through a pipe to get to the destination. Actual pressure im not sure of but 1 psi does seem like a good estimate.

Joe

 

[safe]

The centrifugal blower (these include turbos) use a different effect, they use centrifugal force(effect) to rotate and sling the air out the blower housing. This can create much greater pressure than an axial fan set up, at a loss of total airflow.

I agree with you on this point. The centrifugal blower is better than the regular fan at creating pressure in many cases. The pressure ratings are often published, so you just compare one verses the other based on that. Higher rpms in a fan can achieve the same pressure as lower speeds on a centrifugal blower.

My point was a different one based on different ideas.

Hot air expands... so without any fans involved there will be a natural tendency for anything that is hot to expand out of it's container and try to go "up" like a hot air balloon. My thought is that when you force air INTO a contained space that already has air that is trying to escape and go upwards you might be working against it to some degree. By "pulling" the hot air outwards you are doing what the air wants to do already... it wants to dissapate heat... and exit the contained space. Not only that but the act of compressing ALWAYS means MORE heat produced. At one P.S.I. I'm sure it's no big deal, but I just thought I'd mention it. By creating a "vacuum" you have already lowered the pressure and temperature by a small amount within the contained space of the motor. It's like "air conditioning" your motor verses "heating" it while forcing air through it. If I were to guess I'd say that the "pull" approach would probably cool the motor by 5% more at the very most, it's a small difference.

It's a simple experiment. Take the fan and try it both ways. Compare and see if there is a difference. All you have to do is reverse the direction of the motor if it's a simple fan. The centrifugal blower all of a sudden is not going to be working correctly, so it's not really a "fair" test for it.

Think of the intercoolers...

The idea with them is to cool the "compressed air" before it enters the "contained space" of the piston chamber. Our "contained space" is the motor shell and we have the luxury of choosing to "push" or "pull". The gasoline engine designers DON'T have the same options we do.

Imagine a weird gasoline powered turbo which somehow "sucked" the contents of the pistons rather than "pushed" air in. You would get an automatic "vacuum" and a lowering of temperature inside the piston chamber.

In the old two-stroke days those "fat pipes" they use were done because they realized that if you "tune" your exhaust so that a pulse bounces back to the exhaust chamber at exactly the right moment you can create a "pressure wall" that holds the pressures inside the piston for a brief moment longer. You can then retime everything to match and get more power. You just have to think of the entire process and not just one side of it.

Tuned "header pipes" operate on a similiar principle in the four stroke area, but I think the pulse is timed so that it's a "vacuum" instead and helps to "suck" the spent fuel out of the piston chamber.

 

[Leeps]

Yes creating a vacuum would lower the temperature of the air. However this is a one time event. Imagine if you will the moment you turn the fan on you might have a couple degree(maybe a fraction of a degree?) drop in temperature. Now you have a constant pressure in the motor what have you gained? The total air must pass through the same holes with the same pressure differential, there is no more pressure change. The total amount of air in the motor(in moles) has been reduced meaning that a greater volume of air must now pass through the motor due to the reduced pressure(and thus reduced mol/L). And the fan is working with less dense air. Note that these are all minor effects just as minor as the temperature drop that you would have gained in the first place.
Joe

 

[safe]

The decline in air volume because the air is thinner might equal the temperature advantages. (the slight "vacuum" should be constant in a "pull" setup and a slight pressure gain in a "push" setup it seems to me based on how air flows) All in all there is probably little difference either way. It would be an interesting idea to test if someone chooses to use a simple fan over a centrifugal blower.

I've got a situation where one side of my "geardown" motor is currently closed... no vents at all... so I'm going to need to drill holes to get some air to pass through it. On the "normal" side it has holes radiating about the center of the motor. If a fan was placed so that the 4"-5" fan blades fit snugly against the motor, then it would "push" or "pull" right through those little holes. (no ackward corners to force the air to wiggle around)

So it would be easy to test that situation and come up with some kind of result. (which would probably be inconclusive anyway)

If the speed can be increased as the air flows through then you would expect a "vacuum" situation and better cooling. I'm just not sure if it matters whether you are "pushing" through a "contained space" or "pulling". In any compression situation the "compressing" side gets hotter and the "decompressing" side gets cooler so if the "compressing" side is getting hotter and it runs smack up into some already hot air... well I don't know.... maybe I'm simply full of "hot air" at this point?

If atmospehric pressure at sea level is roughly 15 P.S.I. then as long as your "boost" intentions are less that 15 P.S.I. then a "vacuum" approach would work. To go beyond 15 P.S.I. you would need to do a "push". So my guess is that for less than one P.S.I. fans that "pull" would not run into pressure limitations at all.

 

[fechter]

At the kind of pressure differences you get with a fan or centrifugal blower, I don't think you could measure the change in temperature. It would take a lot of power to create a significant cooling or heating effect by compression.

 

[safe]

At the kind of pressure differences you get with a fan or centrifugal blower, I don't think you could measure the change in temperature. It would take a lot of power to create a significant cooling or heating effect by compression.

Given that any boost that an electric motor blower can create is one P.S.I. or less (seems to be the case) then what other conditions might determine the effectiveness of a cooling system?

Size of holes into the motor?

Angle that the air is entering the motor?

"Push" or "Pull" probably does not make a big difference.

Has anyone tried to radically open up the ventalation in order to make airflow better? Big Holes?

 

[Leeps]

Read my last post about what the purpose of the fan is in the first place. If the air leaving the motor is cool then the fan is doing its job. The only optimization you can hope for after this is even air flow in the motor, as in no stagnant pockets of air.

Joe

 

[safe]

If the air leaving the motor is cool then the fan is doing its job. The only optimization you can hope for after this is even air flow in the motor, as in no stagnant pockets of air.

True. If I understand your "input output balance" train of thought what jumps to my mind is that the limit of airflow is probably based on the small gaps between the rotors and the inner wall of the motor. It's through these little gaps that air must flow. The external holes to get into the motor simply need to be "adequate" to not clog the system. The "weakest link" in the compression scheme is the motor itself.

Here's a test:

Take a motor and using a known air pressure (like from an air pump or something that measures precisely volume and pressure) force that through the motor and simply find out what the "air pressure and volume" rating is for the motor. From that you could then select the appropriate fan or blower for the job. Since the limit of pressure would be one P.S.I. all you need to do is look for:

"How much air volume flows through the motor at one P.S.I.?"

You can then select the electric fan/blower that satisfies the volume condition and yet doesn't surpass it. You then would know that you would have the smallest fan/blower to do the job. And the cool thing is that once that air volume "number" is known for a "fact" then if it gets passed around people will know exactly the size to buy for a specific motor. (and my guess is that all the Unite motors will have similiar air volume "numbers")

 

[Leeps]

In hindsight my thing about stagnant pockets of air applies to air cooling in general, the armature in a motor makes a good blender.
Testing the airflow capabilities of a motor does seem to be a thorough way of doing it. I cant really think of an easy(nor cheap) way to regulate one psi at a high volume and then measure the volume of air passing through. Most regular pneumatic regulators have a decent pressure drop when moving large quantities of air. Measuring the airflow is another can of worms altogether, perhaps the MAF meter from a small european car, would be able to measure low enough for these airflows im not sure. If you can find a way i would love to see the data.
Then again people have already proven that the large computer sized blowers work well enough for our use.
http://www.reliance.com/prodserv/motgen/c7090/ Heres a link that i got from the original VisforV forum about brush life, slightly off topic to our conversation but i think you would be interested in it. It goes on about humidity in the air being necessary for proper brush functioning. Taking it a little further it seems plausible that adding a humidification system (wet sponge i suppose) to air cooling would do wonders for cooling the motor, if not for better brush conductivity evaporative cooling should have some effect. I think reid tried this with his unite motor.
Joe

 

[Mathurin]

I have tried both blowing and sucking with the fan(s) on various computer heatsinks, pushing came ahead marginally better.

 

[fechter]

I've found it works best having the air blow in on the brush end of the motor to maximize cooling on the commutator and brushes. The air comes out the other end pretty hot after a hard run.

There's not much space between the armature and the magnets. The gap between magnets is bigger, but you really don't want to try enlarging it.
Just make all the other holes bigger than the path around the armature.

I used 7/8" tubing on one end and eight 1/2" holes around the shaft just to give you an idea.

 

[safe]

I've found it works best having the air blow in on the brush end of the motor to maximize cooling on the commutator and brushes.

That's a very good point. The main things to "save" are the brushes. Having the coolest air hit the brushes first does the most good where you need it most. (this seems like an "absolute truth" that the air flow ALWAYS needs to enter the brush side and exit out the other)

And the flip side, if you were to be "fair" in testing "push" and "pull" you would need to do a "push" INTO the brush side and a "pull" OUT of the OPPOSITE side to get the cool air running into the brushes for an accurate comparison. (this is assuming that the heat related power losses are most noticeble when the brushes are overheated)

So there might be some issues of "false results" in previous experiments if that wasn't taken into consideration.

It still seems like "pull" would work better because it's effectively acting like a jet engine "pulling" the hot air out as exhaust at the tail end of a contained space. My "gut" tells me that hot air wants to exit and the best thing would be to "assist" that process. Hmmmmm...

What about two "undersized" (computer) fans, one on each end?

But then it's just getting overly complicated...

 

[fechter]

Whether pushing or pulling, the air flow and cooling won't be noticeably different at the kind of pressures the blower runs at.

There are other considerations. There's a bunch of carbon dust that exits the motor and it would be better if it didn't deposit on the blower blades.
Also consider where the inlet is. You don't want any debris to enter the inlet. On my Vego, the blower is located inside the battery box, where it's pretty clean. The exhaust is on the side of the motor, where there's tons of road spray and dirt thrown up by the rear wheel. The air flow keeps crap out of the motor. A fine mesh screen on the inlet and outlet might be a good idea just to keep the big chunks out.

 

[safe]

There are other considerations. There's a bunch of carbon dust that exits the motor and it would be better if it didn't deposit on the blower blades.

Another good point.

I'm satisfied. The best approach seems to be a centrifugal blower forcing air into the brush side of the motor.

 

[mr.electric]

My 60v currie with blower. I actually switched this blower for a cool clear cased blower. You can see the impeller spinning. This scooter was sold and I forgot to take a final photo with the clear blower installed. It worked great.

 

[mr.electric]

Here is a picture of the clear cased blower. I did not read the description carefully when I bought this item. This blower has no front cover and is designed to be mounted to a flat surface. I ended up fabricating a front cover plate from plexiglass and gluing it in place. I made the hole in the front cover for intake air the same diameter as the inner edges of the impeller blades.

 

[lemmiwinks]

Interesting discussion. I'm in the process of converting a motorcycle to electric (OT I know, sorry) and for a proof of concept as much as budgetary constraints, I will be using a 1.6Kw rated series wound motor. The catch is the 1.6Kw rating is intermittent :| so it will certainly need forced air cooling.

The motor is about 6.5" in diameter and around about 10" in length. The plan is to overvolt it slightly to 48V (up from 36V) and hook it up to the el cheapo Chinese 100A continuous/150A peak controller I got. Is it the considered opinion of the brains trust (in particular Mr fechter) that this:
http://preview.tinyurl.com/y5ezwe
blower will cut the mustard? I don't envisage run times greater than 20 minutes to 1/2 an hour with my proposed batteries anyway and current load will fall away rapidy once rolling.

The specs of the blower are:

97mm x 94mm 12V DC Blower Fan Ball Bearing - 2 wire

Air Volume: 0.74 (m3/min), 26(CFM)
Noise: 51dB(A)
Input: 10.32 Watts
Size: 97 x 94 x 33mm
Voltage: 12VDC
Impeller: Plastic, fibreglass filled
Housing: Plastic, fibreglass filled
Bearing System: Ball
Speed: 3,600 RPM
Current: 860mA
Static pressure: 1.00 (Inch - H2O)
Flylead connection

 

[fechter]

lemmiwinks, nice to see you here.
That's a big motor! We're talking golf car motor size. The blower in the catalog looks good. That's a big blower, but a good match for that motor.

I'm not so sure how happy the cheap controller will be. You might consider inspecting the insides of the controller before hooking it up to look for weak spots and poor workmanship. If it blows up, I guess it was cheap. Any refurbished Curtis controllers down there?

It is possible to take even a poorly designed controller and rework it into something that will compete with a much more expensive model. Some simple mods can greatly improve reliability.

Post pics!

 

[lemmiwinks]

Hi fechter, thanks, and thanks for the reply. It is a pretty big motor, but then again the price was right too, about $200 which fits pretty well into the "budget" such as it is. The motor I'm using is apparently out of those tugs used for dragging aeroplanes around. I don't know how big we're talking here, I suspect much smaller than 747's but I would guess bigger than Cessnas. I've since bought another motor from a forklift, rated 2.4Kw on 24V but I'm not taking delivery for a while.

Series wound motors supposedly produce the most torque for a given current so I'm hopeful this will work out well, but wont cry if it doesn't. The goal is to build something better (in terms of perfomance if not appearance) than the EVT scooter. Target is 25km range at 100kph, pretty ambitious but you gotta dream.

At this stage the cheap controller (found here: http://www.evparts.com/shopping/product_details.php?id=262&product_id=4106)
is just for proof of concept testing. It makes a horrible hub as mentioned on the website, but it was literally the cheapest semi-high current controller I could find. When I get more work done on it, if I can go up and down the driveway successfully then I'll look into getting a real controller :wink:

I don't have any pics of the conversion yet (it ain't pretty trust me) though I have the motor and gearbox (yes, gearbox!) mounted and connected together. So here's a photo of the armature after we machined the commutator (no, actually this photo is before we machined the commutator):

 

[Lessss]

PICS PICS PICS

 

[lemmiwinks]

PICS PICS PICS

At this stage, I don't have any with me of the conversion, but I'll stop hijacking this thread and start a new thread in the "E-vehicles General Discussion" section later 8)