How To Ice Up Your Motor? (Cooling Ideas)

[safe]

If you are squeemish about drilling holes, you'll need a high-pressure high-volume blower/sucker like a mini supercharger or shop-vac.

It's the "Conventional Wisdom" that says that...

That's why I'm asking questions. (I just watched a show about Socrates... so I know I'm getting myself into trouble every time I ask a question ) The problem is that as you increase the power of the blower to higher and higher levels in order to push more air through the microscopic sized motor you waste more and more energy. If you just relax and realize that a fixed amount is going to get through at a fixed PSI rating then you can think in terms of:

"How to I achieve the minimum for the least energy cost?"

...once you start to think in those terms it changes things.

Remember... I'm not talking about a large sized motor, but a small one.

It would be interesting to actually measure how much real world airflow is passing through using a blower. What percentage makes it through?

10%?

40%?

65%?

If the airspeed starts out as (say) 50 mph inside the blower at what exit speed does the air exit the motor?

5 mph?

15 mph?

25 mph?

Efficiency in the motor is defined as:

Efficiency = Power Output / Power Input

So by extension the efficiency of the blower is:

Efficiency = Air Flow Output / Air Flow Input

...how much actually gets through?

 

[safe]

A Followup Question...

What is the heat transfer rate of the air in the motor?

If the air were to pass through at really high speed then the air might not rise that much in temperature as it passed through. If the rate were too low or none at all then the air temperature would go sky high. It seems to me that a moderate air flow would probably extract a respectable percentage of the heat that is possible to be extracted.

We might be chasing an illusion...

Excessive airflow might only add another 10% - 25% above ADEQUATE airflow.

Most things in the real world tend to have limits to them where when you push things outside those limits you tend to see declining returns. Maybe the goal is just to get the air to recirculate and not STAGNATE inside the motor. A motor that has no air circulating would likely not have any incentive to move the air in any direction and so the only heat exchange would be by radiant heating.

I have a feeling that 75% or more of the cooling potential comes about at very low PSI levels (like 1 PSI) and very moderate air flow rates. If you can get the air to recycle once every 10-20 seconds that should do it.

 

[vanilla ice]

Get a 80 gallon 160psi compressor and setup one of those dyno things next to it. Get a regulator and raise in 1psi increments, dyno your bike's setup on the dyno until you get one of those nice graphs, temp vs. psi vs. amps vs. time. Or something. I'd wager going from 1 to 160psi going to be more than 10% to 25% of the temp diff as from 0 to 1psi. Still gotta be a decreasing returns curve, but can't be that drastic.

 

[safe]

This chart is made with data that is NOT based on any actual measurement, so it might be totally wrong, however, this is how I would guess that air cooling would work. When there is no airflow your motor rises to the heat level that radiant heat alone can handle. (your motor cools whether you do anything or not just because of the difference between motor temp and outside temp) Once you begin to pass air through the motor the air picks up and transports out the heat at a rate that is proportional to the pressure since that is the ultimate limit on the airflow. However at some point the rate is "good enough" to lower the motor temp down to a level that matches the surrounding air. (or gets closer and closer but never touches) There would clearly be a point of diminishing returns with increasing airflow.

Of course the counter argument is that you could increase your starting baseline more (like start at an initial temp of 200 degrees (F)) and then when you apply the extra airflow it has more work to do and so it makes more sense.

Basically if you increased your heating by 50% then you would want to do something that could cut that heating INCREASE by some amount. Unless you use an intercooler and DROP the air temperature BEFORE you pass it through the motor it's going to hit the wall pretty quickly.

Assume that the surrounding air is at about 75 degrees (F).

Since I'm looking to implement Armature (Motor) Current Limiting on my motors the heat production would be a true constant. As long as the air flow rate was "adequate" to cover the heat I don't see the need to press for any more. A small 1 PSI device should work...

 

[safe]

A Better Idea?

What about a small refrigeration unit?

Vector VEC224M-WM Mini Fridge for Vehicles is the answer to eating healthy while traveling
Thermoelectric cooler/warmer design
Cools down to 40 degrees F below ambient temperature
Warms to 120 degrees F
6-liter capacity; holds eight cans and up to 32 oz. bottles
Compact and lightweight
Rests on vehicle floor or seat for easy access
Runs from 12-volt DC accessory outlet of your vehicle
Also uses 120-volt AC household outlet with AC/DC converter (included)

http://www.walmart.com/catalog/product.do?product_id=3584908

$37.84

Then take it apart and only use the core components...

 

[safe]

In the final analysis if there is a fairly restricted amount of air that can realistically be passed through a small motor (like about 1 PSI) and you could achieve just that amount with a fairly small air flow rate then the only place to look after that is cooling. If it were possible to find a very small 12 volt refrigeration unit that passed a small amount of air at 1 PSI it would make for the preferred cooling device. The question is finding an old "throw away" refrigerator and dismantling it to see what is inside. I'll have to keep my eyes open for "junk" to experiement with. The other issue is current drain... the ones I've seen use about 1-3 amps at 12 volts, so that's about 12-36 watts which might be worth it if the temperature is cold enough and the motor hot enough.

How much does heating decrease motor efficiency?

Increased Resistance = Resistance * ( 1 + (( Temperature - 15 (C) ) * 0.00393))

When I run that through my spreadsheet the difference in power output on my little motor is:

From (15C - 59F) to (15C - 59F) produces 0 watt loss

From (15C - 59F) to (35C - 95F) produces 58 watt loss

From (15C - 59F) to (65C - 149F) produces 131 watt loss

So it looks like using less than 50 watts if you get good cooling is a worthwhile investment and let's not forget that we are protecting our motor from failure... efficiency is one part, the other is getting high power output out of a motor with low weight. You could get the same or better performance using a heavier motor, but light weight is part of this quest. The cooling system needs to weigh a pound or two at most.

 

[TylerDurden]

Ya know... you could open yer motor and calculate the amount of space.

My guess is you have at least 3 in2^ of space around the armature to blow air through. Those little gaps add up... ask anybody who works in home-insulation.

I assume the MY1016 has ceramic mags, so there will be some good gap between them due to their height. That's a good thing... as air moves through the gaps, the armature laminations will drag it around into the spaces between the armature and the magnets.

 

[vanilla ice]

That themoelectric stuff is super inefficient. I think it'd take too many amps for something powerful enough to cool a motor. I have a few that I've played around with for cooling computer procs and video cards.

 

[fechter]

The blowers I use consume about 10w.

A Peltier effect cooler will be many times that and does not have enough heat transfer capacity.

If you could find some kind of liquid that wouldn't hurt the insides of a motor or leak out, you could circulate it through a radiator. I suppose that would cause a lot of viscous drag on the rotor. With a brushless motor, the windings could be encased in plastic and sealed to allow liquid cooling while the rotor was dry.

 

[vanilla ice]

Well hell if safe's chart is right, I'm going to stick a hose in my bicycle horn and fit a couple of check valves. Instead of squeezing it to honk, I'll squeeze when the motor is hot. This could work...

 

[safe]

A Peltier effect cooler will be many times that and does not have enough heat transfer capacity.

The electric means of cooling is not very good. What about good old fashioned "air conditioning" where the air is first compressed, cooled and then allowed to expand? Using a very small pump as the compressor you use that to compress the air into a small radiator, then (since you now have reduced the heat in that air) you release the air INSIDE the motor allowing it to expand as it's being released. That way the small opening served to add to the whole system because you WANT a small opening in order to build the pressure. You could artificially increase the pressure by reducing the entry hole and creating more back pressure which makes the radiator more efficient.

It's basically an intercooler like design.

It seems to me that if for even my small motor you have a "budget" of 50 watts to 130 watts to play with (since that's how much power you are losing already due to heating) that you could come up with a simple compressor that could pump some serious PSI. The radiator is simply something that sits between the pump and the release valve in the motor. (the entry point)

 

[safe]

PV = nRT

If you could double the pressure then the temperature should double too. So at double the pressure the radiator can more easily cool the air. The higher pressure you can get means the radiator gets hotter and hotter and cools more and more efficiently. Then when you release the compressed and cooled air through the nozzle it expands inside the motor and provides even more cooling than if you had simply forced more air through at room temperature.

See the difference?

This would actually forcibly cool the motor rather than simply helping to to return to the surrounding air temperature. You could actually sustain near ideal resistance values inside the motor if you did this well enough.

Intercoolers for electric motors... if weight is a big issue it's a way to stretch the limits of a motor well past what you would expect. (small motors running cool do the job as well as a big motor running warm)

 

[vanilla ice]

You would have to make sure the compressor doesn't draw too much power. I have a couple of those little cheap electric ones and they want more than my 5amp 12v power supply can put out. Thats nowhere close to the 120psi peak And of course as the pressure its pushing against goes up so does the amp draw. I think you would want as much psi as you get for a decent temp drop at the orifice. From first hand experience, they do melt down if left turned on continuously pushing against like 35psi for like ten minutes, unless they have a thermal shut off thing. But then they shut off.

 

[safe]

I have a couple of those little cheap electric ones and they want more than my 5amp 12v power supply can put out.

You would have to be selective with your compressor motor seeking out the most efficient one you could find. (like with everything else) I've seen some of the compressors out there claiming that they use about 12V - 2 amps at full load. So that's somewhere around 24 watts.... which is HALF to a QUARTER of the budget that we're working with.

Don't forget.... you have up to 130 watts to play with in order to bring down the motor temp to equal room temperature. That's how much of a loss you currently absorb when the heat inside the motor rises to near failure levels. (a really hot motor I figure to be about 150 (F) degrees)

 

[safe]

Why Not Use The Chain?

Here's an idea that takes this a step further...

You place what is essentially a chain tensioner on the chain coming off of the motor. However, this isn't an ordinary chain tensioner because it's actually the compressor shaft.

You have now eliminated:

1. The need for additional batteries.

2. Concerns about switching the compressor on or off, since the compressor works whenever the motor works.

3. Difficulties in finding high efficiency small compressor motors.

All you do is take the compressor output and pass it through a radiator which cools the compressed air. The nozzle that limits the airflow into the motor could even be adjustable like a paint sprayer nozzle, so you could even have adjustable levels of cooling based on how much pressure you are willing to build. This could allow you to compensate for a 95 degree summer day verses a 65 degree fall day. In the fall you would open the nozzle and let room temperature air into the motor. In the summer you restrict the air and force it to be compressed highly and cooled. (adding to the motor load, but in the summer it's worth it) So your amount of cooling would be adjustable based on "boost pressure". :wink:

This solution uses NO electronics.

In the picture (of a compressor that costs $12) imagine removing the electric motor and just using the compressor part. This particular compressor can produce pressure as high as 250 PSI. The volume of air would be small, but the air would be very cold.

I know on my bike that in the summer the heat really builds up in my motor, but now, when the temp is only 70 degrees, (soon to be 25 degrees) my motor no longer even overheats even if I try. So getting the air temperature that the motor "sees" down to lower than the outside air temp could be the equivalent of "super cooling" the motor.

Note: I've just been browsing the computer cooling websites and they have all kinds of radical stuff these days... about the right size too. 8)

 

[safe]

My motor has a rated heat level of only 71 watts. You can figure this out by just reverse calculating the value from the rated speed. At the standard level of peak power at 30 amps the peak heat level is 183 watts. So that's the range that the motor normally operates within, somewhere between 71 watts and 183 watts (of heat) depending on load. This can actually get worse in certain circumstances (high load, low rpm) but for my geared bikes this doesn't ever have to happen, so I can exclude this as a problem. Armature (Motor) Current Limiting forcibly removes this as an issue. (something I plan to do)

All that said...

What I see by calculating the heat charactoristics of my motor with increasing current is that until you get up to about 50 amps the rate of power growth is about the same as the rate of heat growth. So let's do a quick calculation on this:

Let's look at 50 amps.

Heat - 508 watts
Power - 1176 watts

If we compare that to our "baseline" of 30 amps. (overvolted motor! 8) )

Heat - 183 watts
Power - 799 watts

The net increase in power is 325 watts.
The net increase in heat is 377 watts.

So the question becomes:

"How much power might I need to pull out of the drivetrain in order to power a compressor pump to cool the motor down?"

...if I could use 100 watts to cool the motor down then I've made a 225 watt profit. Unless the compressor sucks as much as 325 watts (which is extreme) the net gain will make the extra power worthwhile.

And don't forget I'm starting with a 350 watt motor...

 

[safe]

Relative Rates

The rate at which the power increases with amps is different than the rate at which heat increases with amps. If we start with our baseline value of 30 amps and compare that to the other amp rates we get the chart below.

It's a little bit esoteric, but what it's showing me is that at 55 amps the rate of growth of the power declines to such a degree that you are now suffering unacceptable efficiency losses. So there is an upper limit to this possible forced cooling "intercooler" solution. After a certain point the heat is building so fast and with no real power to show for it so that more current is a total waste.

The theoretical maximum limit of "good power" would be about 55 amps for this motor. This means that you are getting 1250 watts out of a 350 watt motor... assuming you can cool it. It's the cooling issue that limits the ability to do this. So an "intercooler" could make this little motor radically exceed it's baseline.

 

[vanilla ice]

I like the chain driven compressor idea. Do it. I'll do mine with the blower. We'll contrast and compare.

 

[safe]

I like the chain driven compressor idea. Do it. I'll do mine with the blower. We'll contrast and compare.

It's like a turbocharger in that the motor pushes the compressor (which subtracts from the motor) but you get more power (longer) by doing it. Since you could adjust the boost pressure you could crank up the pressure (increasing the drain on the motor) in the summer and lower the pressure on a cooler day. There would be some point where the increasing boost pressure produced diminishing returns.

My Armature (Motor) Current Limiting will also be adjustable so I can decide on any day what current limit to allow. It should allow me to squeeze the very last bit of power out of any weather condition. (and also allow me to choose Range or Power for that ride)

All I need is:

1. One of those $12 air compressors.

2. A small radiator... possibly one of those computer cooling ones. (still looking around for the best solution for that)

3. A nozzle that accurately limits the pressure.

4. This isn't a must, but it might be nice to have a pressure gauge so that I can know how much boost pressure I'm using. (with luck I might find a compressor that comes with one of these)

You wouldn't need to turn your motor into swiss cheese either because a single entry point would be enough to get the cooler air in and a small exit hole (maybe two) would be enough to extract the air at a moderate rate. The essential point here is that the air going in would be cooled, so you aren't in a hurry to get it out of there... you WANT it to take it's time and absorb as much heat as it can before it exits.

 

[safe]

On sale... only $10.

http://www.xoxide.com/80mmradiator.html

 

[safe]

This is specifically an AIR COOLING system while many of the others are really designed for water cooling. It would require some modifications, but you would at least know that the radiator is designed for air and not water. The fan adds a complication, but it would increase the cooling. You might be able to shape your fairing so that the radiator gets enough air just by the wind... like the motorcycles do, then you could get rid of the fan. It's less than a pound.


$27.99

http://www.xoxide.com/kingwin-rtv-9225.html

 

[fechter]

When using an air compressor as a refrigeration unit, you need to calculate the cooling capacity to see if it will work. I'm not exactly sure how to do this, but if you know the outlet temperature and the flow rate (CFM), and the heat capacity of air, you should be able to do the math.

The radiator is cute, but I bet you could just use about 3 feet of soft copper tubing to get the same results.

The centrifugal blowers I use don't have enough pressure to have a significant effect on air temperature due to compression. They do have a LOT more CFM. Again, it's possible to do the math.

 

[safe]

The radiator is cute, but I bet you could just use about 3 feet of soft copper tubing to get the same results.

Air is hesistant about transferring it's heat. It's 25 slower than water in it's ability to carry heat around. The radiator would make the rate of compressed air cooling faster and that makes a big difference when the air is decompressed inside the motor.

Basically the idea is to MOVE the cooling process from inside the motor to outside the motor. All the cooling is done in an ideal environment outside and then the results are transported inside the motor.

Doing the math is a good idea too... (I'll get to it eventually)

The one thing I do know is that efficiency RISES the higher the temperature gradient from hot to cold. So the higher the pressure the higher temperature and the more rapidly that heat transfer takes place.

It's like air conditioning (something that people in San Francisco don't need to know about) if you run the air conditioner in the morning when the air is cooler it very rapidly cools down your house. If you try to run the air conditioner during the heat of the day the efficiency drops to nothing. So the smart thing to do is run the air conditioner hard in the morning, then close all the drapes and let the heat in the house rise with the air conditioner off during the afternoon. At about 10 pm things have cooled enough to turn it back on again. By this point the heat inside had risen, but it's not that bad. (depending on your house insulation)

Basically in the heat of the day in the summer a fan blowing hot outside air into the motor doesn't do any good... you couldn't increase the airflow any more and expect to achieve anything. (the efficiency drops to nothing) You end up better off infusing cold air into the motor at a slower rate.

 

[fechter]

The "radiator" needs to have a relatively long path for the air inside. Something like the condenser from a car AC system or refrigerator would be good. I used to have a nice little one from a dehumidifier.

I still suspect that with a reasonably sized air compressor, the total cooling capacity will not be enough to dissipate the heat generated by the motor. It's sort of the same problem with the Peltier effect devices. They have a nice temperature differential, but the total BTU capacity is not enough for a motor.

 

[safe]

Look at how much of a temperature difference you get at only 20 PSI. (even 10 PSI) I don't know.... seems to me that a small stream of very cool air could achieve better results than blasting high volumes of hot air.

Don't forget that I deal with road temperatures of about 110 degrees in the summer with typical air temperatures of 95 degrees. (and high humidity) Blowing that hot air into the motor wouldn't cool it much. But if you could compress that THIN hot air and heat up the radiator (so it cools more efficiently) then you could place some really cool air into the motor.

Eventually I'll have to present the formal mathematical proof, but my intuition leads me to think that a radiator is the solution. Do the cooling in the ideal environment rather than trying to force things.