How To Ice Up Your Motor? (Cooling Ideas)

[safe]

I've got two motors. One is a 1200 Watt @ 48 Volt and the other is a 750 Watt @ 36 Volt. The 750 has a really cool "geardown" that would allow me to directly connect my motor to my rear wheel using a normal bicycle chain rather than a scooter chain.

The 1200 Watt @ 48 Volts would give me an unbelievable top speed of about 55 mph. The 750 Watt @ 36 Volts would give me so much range that I don't know what to do with (like two hours worth) but at 36 Volts it's down about 10 mph verses the 1200 on the top end.

My question is this:

If I run the 750 Watt motor at 48 Volts rather than 36 Volts AND bump up the current from 40 Amps to 50 Amps how long is this thing going to last? What tends to break first?

It would be nice to be testing two bikes side by side and just swap the battery pack between them. I have a feeling that eventually I'm going to give up on the "little" 750 in favor of the 1200 because my calculations show that the "ideal" motor is more like a 2000 Watt which is then run at lower current to get better efficiency. Eventually I'll probably go with a PMG132 when I feel like spending $600+ for a motor. (the motor above cost me only $50)

Past Horror Stories?

 

[Lessss]

From what I've been told the motor will work but if it is over amped or over volted too much then the motor will generate alot of HEAT. If too much heat is generated it will burn off the protective coating on the windings electrically isolating each winding from the others. The windings will then beome ONE windings, or short out entirely. Since more windings means a greater electromagnetic field, then ONE winding means a weaker field. It may be so weak as to be unable to turn the motor at all let alone under a load.

At least that is my understanding. So if you fear you may be over volting or amping the motor then use forced air to cool it. Chilled air would be better, I THINK.

The real question is at what temperature will the windings fail.


Why not just exchange the sprockets on the motors? That way you can use the motor you want with the chain you want.

The thought also occurs that if you are creative enough you could hook both motors to the same chain and use the motor you needed at the moment, high speed or low.

 

[safe]

Why not just exchange the sprockets on the motors?

That was the reason I bought the two of them in the first place. My plan was to swap the "geardown" from the 750 over to the 1200. When I got the two motors and took them apart I realized that the shafts are incompatible. Not only that, but since I sent this picture to the people at TNC Scooters they said they would not accept a return on it. (since it was opened, which is reasonable)

It's a nice motor... I'm just not sure how to use it... maybe it would be fun to just see how long it would work before it blows up?

This is an excellent situation to have "Boost Control". By limiting the amount of time that I have the "boost" on full I can keep the motor temperature down and prevent a meltdown. (and get improved range)

 

[fechter]

There's a lot of ways a motor can fail, and I think I've found allmost all of those. I don't have any experience with that particular gear motor, but the 1200w one is fairly common. When I ran 48v at 50amp into a 500w Vego motor, the commutator segments would come unglued and lift up. They could take a good 10-15 second blast of 60 amps with no problem, but if you stayed on it for 30 seconds or more, they would be on the verge of failing. Normal riding would give a burst on acceleration, but then drop down to around 30 amps when cruising. I put a lot of miles one by being careful.
Once the commutator segment comes off, it's pretty much toast.

The Rad2go motors that are very similar to your 1200w would typically have the wires melt off the brush holders. This was easy to fix.

Forced air cooling will aproximately double the continuous rating.

Over volting/amping a motor will drastically shorten the brush life. Brushes are cheap, but sometimes hard to find.

 

[Lessss]

Ah I see the shaft size of the sprockets (the one on the end of the non stepped down motor and the sprocket on the offset step down) are different sizes. Those were what I was talking about exchanging. Oh well.

What you need to do is pick up a properly sized sprocket. I have the same situation with my MY1020 900W. Sprocket is not for bicycle chain.

Thank Elmweaver for the links
http://www.electricscooterparts.com/sprockets.html
http://www.monsterscooterparts.com/sprockets1.html
http://www.scooterparts4less.com/all_electric_scooter_parts.htm

I ordered a sprocket. Hopefully it'll be here this week coming (hoping monday). I'll post if it's the proper size for my chain here http://endless-sphere.com/forums/viewtopic.php?t=66 when I get it.

 

[safe]

What you need to do is pick up a properly sized sprocket.

The "geardown" 750 motor has a weird size. No one sells sprockets for them. (I checked with TNC Scooters) I've got a welding torch and could grind and weld anything if necessary. But the larger question was whether I can run all that extra power and not blow the motor up. The answer seems to be "forced air cooling".

So I'm thinking of a computer fan which runs on 12 Volts DC and I would make some sort of "ram air intake manifold" to channel the air inside the motor:

I'm definitely going to run one bike with the 1200 Watt motor, that's for sure and there are already go-kart chains that are perfect for that. (size #35 chain rather than the smaller #25 scooter chains) But I was also planning to run a second bike in parallel so that I could be testing different ideas on each as I went along. The idea was to create a "platform" which had a standardized frame and then have component parts like the motor assembly, seat mountings, battery, etc... that could be put together in different ways. I want it to be flexible on the options rather than be stuck with just one configuration. (it doesn't take any more work to do it the right way)

So if on one bike the engine blows up that's okay, I'll just swap in something new...

 

[Lessss]

I tried that too. I found the wires and connectors weren't very weather resistant.
Go big on the blower and split the output between cooling the motor and controller.

Try a car blower instead, they are also 12V

This is the one in my bike

Horn is at the bottom, blower is in the center left, controller is at the top angling down to the center. The Mosfet(and buzz bar) are on the bottom of the controller which is sitting in the blower so they get the maximum cooling. The screw on the bottom right is what attaches the blower to the bike frame. The left side has a screw and X set of bars the attach it to the plastic shell. The blower is too big to fit it in any other way.

 

[safe]

Try a car blower instead, they are also 12V

Wow, that's a SERIOUS blower. Do you know how much current that draws? Do you have a link to one and a range of prices?

I agree with you, a good blower could force air into the motor and significantly cool it and allow you to run "insane" power through a tiny little motor. You have to admit that this sort of stuff is rather funny when the real way to solve the problem is to use a larger motor than can handle the larger load. Of course, LEGALITY being what it is, you can normally squeeze a "tricked out" small motor past inspection easier than a grossly oversized motor that is detuned. So there is some method to all this madness...

 

[Lessss]

It's a $3.00 blower I picked up at a $1.00 type store. The left side screw hole was broke so could no longer be mounted in a car properly. I didn't need that hole however.

I hooked it up to my lights. I turn the lights on the blower comes on. No idea on the power draw. It shouldn't be much.

 

[safe]

Very cool.... um I mean "cooling"... oh whatever...

http://www.electricsupercharger.com

For those into ridiculous cooling potential...

They claim an actual 1 P.S.I. of pressure... :wink:

 

[fechter]

I've found that a centrifugal blower works much better than an axial fan. Fans generally can't produce enough pressure to get a good airflow through a motor. Ram air from a scoop doesn't do it either.

The motor has a ring of 1/2" holes around both ends. There's a plastic cup taped over the brush end to feed air to all the holes. The blower is connected to the cup with a large diameter flexible tube.
It would be better to connect the blower direclty to the cup.

Here's one that Scott MacGreggor did and the Nidec blower on my Zappy:

 

[safe]

I've found that a centrifugal blower works much better than an axial fan. Fans generally can't produce enough pressure to get a good airflow through a motor. Ram air from a scoop doesn't do it either.

A fan does work if you have adequate speed and the tolerances are very tight. Most fans that run at lower speeds can't produce even 1 P.S.I. of pressure. You have to distinguish between air volume and air pressure. Many blowers have high volume, but next to no pressure. When you have a restricted space (bad airflow like you would expect in a cramped motor) all the volume in the world won't do much good because it simply backs up into the blower and you get little actual airflow.

Basically you need something that produces REAL pressure. Something like a piston driven pump guarantees that air will flow through because there is no other way for it to escape. It's all the same problems that people with fast cars deal with using a Turbocharger. In order to get a Turbocharger to create real pressure you need unbelievably high rpms and since getting up to speed means conquering the inertia of the turbine you get "turbo lag". Which is why Superchargers are very popular since they are driven off of the motor itself and they simply ram the air directly into the pistons. Superchargers use a "roots" style pump which is able to produce higher pressures than any fan can do.

Those guys with the "mini" electric supercharger are capitalizing on the fact that electric motors can be spun at unbelievably high speeds pretty easily. So if they claim 1 P.S.I. that's pretty impressive for a non-roots style pump. (nothing like the 5-10 P.S.I. you can get with a Supercharger though)

 

[Leeps]

a centrifugal turbo can get a 3 to 3.5 for 1 pressure ratio from input to output. 3.5 atmospheres on the output (assuming no pressure drop from the airfilter) gives you 14.7*3.5=51 psi. The only thing with the turbos though is that you have to be already flowing a decent bit of air otherwise the air sets up a resonance in the tube going to the intake manifold. The resonance is enough to break turbine blades if it gets bad enough, usually it just beats the bearings to death. The roots blowers just blow hot air at those pressures.
Sorry i had to, i used to be into v8's and muscle cars.

Joe

 

[safe]

The roots blowers just blow hot air at those pressures.

That's why they use intercoolers to lower the air temperature.

My point is that if you want real pressure you need to be serious about it and not just use a big fan and pray that it works.

 

[Lessss]

The motors we are talking about are also pretty small unless you are talking electric cars. So simply large volume should be sufficient as the air will easily push through the motor. Granted that is a large assumption.

 

[Leeps]

Less your right that we are talking small motors with relatively low heat loss (well compared to electric cars like you said). There are a couple things to look at though. The total thermal resistance, which is high since its a small motor with a small surface area. Then the temperature difference between the air and the motor. Then the thermal inertia of the air which depends on humidity and density (temperature and barometric pressure).
The air will take on thermal energy based on the thermal resistance and difference in temperature. The rate of temperature rise depends on thermal inertia. As the temperature of the air rises it will take on less heat because the difference in temperature is less and thus the motor will heat up in order to dissipate its heat and maintain this temperature gradient. The fan serves two purposes one is to get rid of this hot air and replace it with fresh cool air, the second is to keep moving air in the system so that you can never get a layer of stagnent warm air (convection currents usually keeps this from happening but it depends on the shape of the object and its enclosure).

And safe im sorry but take a look at some compressor maps from the bigger turbos, they can make more pressure with better efficiency than a roots blower(no praying required :wink: ). They have two major limitations that is the turbo lag and the fact that they have to be flowing a significant amount of air to be stable at higher pressures. Other than that they will pump just as much pressure 30 psi is easily done with 70 % efficiency. Most roots blowers are already at 50% efficiency at 15 psi. Or another way to put it the guys that do tractor pulls usually have one turbo blowing into a second turbo and get some 70 or so psi out of em. No roots blowers there, and you could run air tools on the pressure coming out of the turbos. The srew type superchargers though are closer to turbo efficiency they can get up to 70% or so (note its not a roots lobed rotor design) but the peak efficiencys still go to the turbos.

Joe

 

[safe]

...take a look at some compressor maps from the bigger turbos, they can make more pressure with better efficiency than a roots blower(no praying required :wink:

There's no debate that a turbo can produce enormous pressure (and therefore horsepower) but there are other issues that come up when you get into that level in the gasoline world. All those differences in pressure have to adapt to air conditions (like you mentioned) and you end up needing some fancy computerization to pull it off.

If my memory serves me right in F1 car racing they have now banned the use of turbos because only a few teams got it working in a "stratusphere" of performance all their own. The winner of the races was becoming whoever could pour the most money into research.

But all that aside....

In order to get more than 1 P.S.I of "boost pressure" from an "air compressing device" you need to choose between one of two options:

1. Very high fan speeds so that the air velocity (it's momentum) is high enough that it can't simply leak out as back pressure. (air is a little like electricity flow... it seeks the path of least resistance)

2. Some type of mechanical "pump" that contains and transfers air from one chamber to another. Examples are the "roots" style or a "piston pump" style.

Here's an idea...

What about trying a very small pump?

In other words reverse the psychology from "high volume low pressure" to "low volume high pressure". More like a bicycle pump. (maybe an electric bicycle pump?) Since most of the electric motors we use have a steel tube as their shell you could seal off all but a small hole in each side and pump this high pressure air through a small hole. The effect is that it reduces the size of the hardware needed and makes the airflow more certain. (this one claims a weight of 1.55 lbs)

http://www.amazon.com/Schwinn-SW74180-Electric-Bike-Pump/dp/B000DZF6X8

And heck, you could even fill up your tires!

Also, in looking at that picture I don't think you would need the gauge, or the large (and heavy) pressure chamber. All that you would need is the pump mechanism which looks to be the finned circular shape to the left. You could probably get the weight down to a half of a pound. The air volume becomes the only real question mark, if the volume is TOO LOW then the ability to create pressure loses importance because the air is leaking out of the other side of the motor faster than the air is being forced into it. The best thing to do is to test the pump beforehand and simply feel how much airflow passes through the pump without resistance. If it's just a trickle then it wouldn't work, but another brand MIGHT work, so you would need to try them out for size.

In a "perfect world" you would hook up an electric motor to a dyno and run high power through it while incrementally increasing the forced air through it for cooling. You then graph the "sweet spot" where the maximum benefit is achieved and then select the appropriate pump size for the need. (my "hunch" is that there are diminishing returns on air pressure above a certain cooling level) Without a "lab" we are forced into "trial and error" which eventually gets you there.... just more slowly....

 

[fechter]

I've done a fair amount of flow testing with blowing air through motors. The Nidec and Rotron blowers I used only draw about 0.25 amps at 24v. And they were less than $10.
The tire pump draws about 10 amps. I would guess the 1psi electric turbo draws quite a bit of power also.

Think of a hair dryer. It has to dissipate over 1000w of heat and uses a small centrifugal blower. In fact, many hair dryers use a 12v motor to run the blower and you could rewire one to use for motor cooling.

 

[knightmb]

My question is, are all of these motors designed for long term use? I know they work great for a few minutes, but what about a couple of hours everyday from riding around?

 

[fechter]

The Nidec and Rotron blowers I showed on my scooters are both brushless and made for continuous operation. I've seen some similar blowers made for CPU cooling.

 

[safe]

If you do a search for "electric air pump" you can find dozens and dozens of products out there for less than $20. It just seems a question of reviewing products to find the "Best of the Bunch". And you (Fechter) are right that the current draw is very important. I've got a "DustBuster" that produces some great airflow, but I suspect it draws a good amount of current.

What we need is an "electric air pump" shootout to see which is best. (we all need to subscribe to "Electric Air Pump Magazine" and read their reviews... as if there were such a thing! )

 

[knightmb]

The Nidec and Rotron blowers I showed on my scooters are both brushless and made for continuous operation. I've seen some similar blowers made for CPU cooling.

That's good. I saw some earlier post with using air pumps, I can tell you those things wouldn't last long in extended use. They usually already have warnings on them against using it for too long on tires that are too big. Mainly because they over-heat and melt the pump causing all the air to come rushing back out of the tire, LOL.

 

[fechter]

Here's what I would recommend:

http://www.allelectronics.com/cgi-bin/item/CF-228/220/24_VDC_BLOWER,_95MM_.html
$ 7.50 each

or

http://www.allelectronics.com/cgi-bin/item/CF-270/220/12_VDC_97_MM_CENTRIFUGAL_BLOWER_.html
$5.50 each

 

[safe]

There are a lot of options to choose from that's for sure. This one has very impressive air volume numbers:

Operating Voltage: 48 Volts
Voltage Range: 24 - 55.2 Volts
Power Supply: 16.8 Watts
Line Current: 0.35 Amps
Locked Rotor Current 0.35 Amps
Nominal Speed: 3000 RPM
Dimensions: 4.7 x 4.7 x 1.5 in
Weight 9.4 oz
Max Airflow @ 0 in H2O 128.0 CFM
Max Pressure @ 0 CFM 0.320 in H2O
Noise 40.8 dBA

...and since it runs at 48 Volts I could probably run off the power going to the motor itself. (with some sort of resistor I would guess)

 

[fechter]

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.