Cold motors put out MORE POWER! (efficiently, too)

[Matt Gruber]

Anybody know how much more? I've never seen a chart on that.

 

[Leeps]

http://www.johnsonelectric.com/product/product_sheet/fect_sheet.php?ProdID=80--A
Thats a link to one of those little can motors they use in cordless drills, theres a little slide bar at the bottom to adjust voltage and temperature. Thats the closest i could find to an answer for your question.
Joe

 

[Matt Gruber]

i get a blank grey screen. could be my webtv.
thanks for looking. How much gain, say at 50F?

 

[Leeps]

The graph is hard to read so ill just do the peaks on the curves.
-30C
peak efficiency 80%
peak rpm 17000
peak current 200 amps
peak power 1050 watts
25C
peak efficiency 75%
peak rpm 18000
peak current 165 amps
peak power 820 watts
80C
peak efficiency 70%
peak rpm 19000 rpm
peak current 140 amps
peak power 675 watts

give or take a little bit on all the numbers, theres only 4 ticks per axis

Joe

 

[Matt Gruber]

thanks!
i mention this because we may need to go up a VERY steep driveway sometimes, and if the motor is cool-warm, it can put out better than expected.

 

[fechter]

That's interesting...
I suppose the copper's resistance increases with temperature somewhat.
Possibly the brushes too.

Perhaps I should try liquid nitrogen injection instead of forced-air

I actually did think of something like this before. For electric drag racers, they could carry a tank of liquid CO2 (easier to handle than LN2) and spray it through the motor prior to launch to chill the armature and commutator down to whatever CO2 temperature is, something like -88F.
The thermal mass of the cold parts will take longer to heat up to the melting point. If you kept the CO2 flowing, it might stay cold.

I'm not sure what CO2 or nitrogen would do in the presence of the arc from a commutator.

 

[xyster]

I'm not sure what CO2 or nitrogen would do in the presence of the arc from a commutator.

I believe CO2 as a carbon compound is already fully oxidized, and the nitrogen inert, so go for it fechter! And if it blows up, well that's how we remember our mistakes best anyway, right? Oh, there might be a small risk of creating hydrogen cyanide HCN.
http://en.wikipedia.org/wiki/Hydrogen_cyanide
wouldn't worry about it though...

 

[Matt Gruber]

that's quite a difference
675 to 1050 watts! hot vs. cold
thats +55%

racers could use a QUICK CHANGE snap in motor mount, and keep it in the freezer before a record run.

i bet 20 yrs from now ebikes will come with a thermistor triggered amp limiter circuit. a gradual reduction of max amps as it heats up.

 

[TylerDurden]

That's interesting...
I suppose the copper's resistance increases with temperature somewhat.
Possibly the brushes too.

Copper's conductivity diminishes significantly with rise in temperature. Something like 40% with a 100 deg. C rise.

I can't recall where I looked that up. A fat electronics catalog somwwhere?

(I had a VW Rabbit where the starter was located close to the exhaust... bad design.)


It may be helpful to note that superconductors for mag-lev applications and high efficiency generators are often cooled by liquid nitrogen. (I Don't recall where I read that either.)


:?

 

[fechter]

i bet 20 yrs from now ebikes will come with a thermistor triggered amp limiter circuit. a gradual reduction of max amps as it heats up.

That's one of the features of my "ideal controller". Lots of them have a thermostatic switch that just cuts off when it gets above a certain temperature. Not good in traffic. It would be fairly easy to have a thermistor burried in the windings on a brushless motor to gradually back off the current limit when it gets hot.
For brushed motors it's a bit trickier, but they do make cool infrared non-contact thermometers that could be aimed at the commutator or armature for a good temp reading.

 

[Toorbough ULL-Zeveigh]

For brushed motors it's a bit trickier, but they do make cool infrared non-contact thermometers that could be aimed at the commutator or armature for a good temp reading.

And you thought clamp on ammeters were bulky!

 

[safe]

Gas engines get really hot also and they use a radiator with water and that special coolant. I could imagine that some sort of radiator (micro sized) could be set up so that the heat collection tubes actually were built into the electric motor itself so that you didn't have to "blow" air through it, but could instead pump coolant through it. For the small amount of energy of a "coolant pump" and a radiator you would get some really impressive cooling. (it would also not make noise)

You could actually incorporate the pump for the coolant into the motor too, so that it's always cooling itself. The only negative with that is that at LOW rpms you really want the most cooling and that would be when the pump was pumping the least coolant. So maybe an external pump isn't such a bad idea. Maybe even vary the speed of the pump depending on the temperature?

 

[fechter]

And you thought clamp on ammeters were bulky!

We use these ones in the hospital that they jam in your ear (or wherever). The actual sensor is very small, about the size of a dime. It's the readout and batteries that make them big.

Forced-air cooling is the most direct way to get rid of excess heat in a motor.

If you need a sealed system, then liquid cooling might be the way to go. They use it for cooling those big controllers in car-sized EV's
The motor windings could be made of micro copper tubing with water flowing inside. The power consumption of the cooling system is usually a very small percentage of the motor's.

 

[safe]

The motor windings could be made of micro copper tubing with water flowing inside.

I thought of that too, but here's a potential problem.

Is is safe to run current through a tube that carries a liquid?

What are the potential risks of electrocution?

Is coolant a natural conductor of electricity?

Also, think of how long those coil wires are... maybe that's "too much" surface area for cooling and the resultant drag might be high. (the longer the tubes the more energy required to push the coolant)

Another thing is how to get the coolant into a spinning rotor... that's a tough one.

This might be a case where "downshifitng" to save the motor makes the most sense. (there is much less heat when you run in the efficient parts of the powerband) Also using a lower current limit helps.

Air cooling is definitely the most "practical" idea...

 

[safe]

What about "Air Conditioning?"

What if you used a micro sized air conditioning unit that super cooled the air and then fed that into the motor for cooling?

You would likely have to invent such a micro sized air conditioner. You would have to think about all the complexities of heat transfer through a radiator (so you still have a radiator and coolant) but the net result is to blow the cool air against the coils rather than trying to use the coils themselves as a direct part of the coolant system.

This could work... 8)

Another advance:

There's also a potential weight savings using Freon rather than water/coolant. Freon is nearly weightless, so all you would need is the tubing and radiator, a compressor (to increase the pressure so as to increase the heat and thus radiation), an expansion valve, another cooling transfer radiator, and finally a fan to blow the air through the cooling transfer radiator into the motor. It could be pretty lightweight.

 

[safe]

How about a water cooled air conditioning unit? (you have to refill the water after it evaporates)

http://www.thinkgeek.com/homeoffice/gear/60ad/

Staying cool and comfortable has never been easier, thanks to the Desktop Personal Air Conditioner! Designed for ease of use, it utilizes frozen water to create a personal climate controlled system anyone can use! Don't let hot summer months ruin your code. Stay calm, collected & cool...

Simply fill the supplied bottle with water, freeze it, place it back in the chamber and turn the power switch on. That's it! Now you are ready to enjoy a cool, relaxing gentle breeze any time, anywhere and since it uses only natural water for cooling, the Desktop Air Conditioner is economical to use. Ideal for use wherever personal cooling is required. Requires two (2) D cell batteries. Quiet operation ideal for cubicles. DC Jack in back for use with optional adapter (sold seperately, 300mA, 3 volts).

Dimensions:Approx. 12.75"L x 6.75"W x 11.25"H.

The problem is that the direct moisture will probably produce rust in your motor... not a great thing to have happen I would think.

 

[xyster]

Matt Gruber wrote:


i bet 20 yrs from now ebikes will come with a thermistor triggered amp limiter circuit. a gradual reduction of max amps as it heats up.

That's one of the features of my "ideal controller". Lots of them have a thermostatic switch that just cuts off when it gets above a certain temperature. ...
For brushed motors it's a bit trickier...

4qd brushed controllers have the feature. Unfortunately I had to return the 48v80amp model I used for a short time on my scooter. So I didn't get to test the reciprocal heat/current limiting feature. Cold, their 80 amp models are rated for 115 amps.
The Manual:
http://robotcombat.com/images/4QD-UNI.pdf

 

[safe]

Okay now this is more like it!

Only 10 Watts of power required!

You would "recharge" the cool plate when you "recharge" the bike.

$99.95

http://www.sharperimage.com/us/en/catalog/product/sku__SI357WHT/source__10716/cm_ven__LINKSHR/cm_cat__feed/

ICEflowâ„¢ Personal Air Conditioner is a fan with an ice-cooled breeze — refreshing your personal space with a stream of air that is significantly cooler than the air around you.

A self-contained chamber of water freezes into a block of real ice after an overnight charge. Turn on the fan and its cooling breeze flows across an ice-cold chilling plate.

Cools for up to eight hours on a single 8- to 14-hour overnight charge. Choose from three fan speeds.

No need to empty and refill the water chamber. The water freezes, melts and refreezes — using Peltier Effect electronics — through thousands of daily cycles. Requires no refrigerant, Freon or window venting.

The energy-efficient ICEflow uses only 10 watts when cooling; charging/freezing requires 60 watts of power overnight.

 

[Lessss]

Or use a small electric compressor to compress a small amount of air (generates heat on the electric pump), release the air and pipe it into your air cooling system. Compressed air once released is very cold. thus you are pumping cold air into your motor instead or ambient temperature air.

 

[safe]

How about if you got a small tupperware container and in it you placed a couple of tubes that were large enough to be able to allow air to pass through. You then simply fill that container with water and place it into your home freezer. When youare ready to ride you connect this "cold container" to your fan that blows air into the motor. You actually "hope" to have only moderate efficiency of cold transfer because you need to pace the use of the cold with the time that you ride. Hopefully the cold stored in the container will be enought to keep the motor cool until you finish. Obviously, this doesn't work if you start and stop a lot because the ice will melt just sitting there. Insulation could slow this however...

 

[safe]

Or use a small electric compressor to compress a small amount of air (generates heat on the electric pump), release the air and pipe it into your air cooling system. Compressed air once released is very cold. thus you are pumping cold air into your motor instead or ambient temperature air.

Brilliant!

Yes, you could eliminate half of the air conditioner that way!

So all you need would be:

1. A Compressor

2. A Radiator to get rid of the heat that compression creates.

3. A Valve that restricts the air and regulates pressure. (could be static)

4. An opening that feeds directly into the motor and as the air expands it cools and blows air at the same time.

Brilliant!

Pass me a Guiness! 8)

 

[safe]

Extra Credit for anyone that knows how to run the equations of Thermodynamics so that we can calculate the amount of pressure that would be needed!

 

[safe]

Okay, so if in PV = nRT we can "factor out" as constants the V and the R we would get:

P = nT

...so if we double the number of moles of air in a compressed space that is a condensor then we get:

P = 2nT

In order to get this all to balance again we need to either reduce the temperature to one half it's Kelvin value so as to achieve the same pressure or we will have to allow the pressure to rise to twice it's initial value. Either way will work.

The real question is in calculating what happens. What percentage increase in temperature will we see? What percentage of pressure increase will we see?

I'm sure there's a table to look this up for air (I've tried to find it) and if know then we could figure out the rise in temperature and therefore the willingness of the condensor to "radiate" heat. The more "radiation" of heat we get through the condensor the more efficient the air conditioning effect and the colder the air will be when we release it into the motor and allow it to rapidly expand.

Anyone know how to calculate the "heat capacity" or "heat absorption" of air in a compressed state?

Note: An "ideal gas" would have no temperature rise (I think) and just show a pressure rise, but anyone who has ever used a bicycle pump knows that the air that comes out at pressure is hot. (you can feel the hose getting warm if you use it long enough) So air heats up when compressed. Just how much?

 

[Mathurin]

Deafscooter had posted a pic of a small scooter that was modified to pass an absurd amount of amps through some etec-ish sized motor, it had what looked like tubes for fluid cooling, and the motor was wrapped in a plastic bag. He posted it as an example of how to prevent dirt contamination of a motor (plastic bag).

 

[xyster]

Good 'ol PV=nRT, you're bringing back memories of general chemistry. All gases heat as they're compressed, cool as they're decompressed -- that's how the freon in a fridge or air conditioner works. Freon is nice and portable I think because of it's below-room temperature boiling point. Also, more of it can be used in relatively low pressure systems.

http://en.wikipedia.org/wiki/Refrigerant
The desired thermodynamic properties are a boiling point somewhat below the target temperature, a high heat of vaporization, a moderate density in liquid form, and a relatively high density in gaseous form. Since boiling point and gas density are affected by pressure, refrigerants may be made more suitable for a particular application by choice of operating pressure.

http://en.wikipedia.org/wiki/Refrigerator
"The vapor compression cycle is used in most household refrigerators. In this cycle, a circulating refrigerant such as freon enters the compressor as a vapor at its boiling point. The vapor is compressed and exits the compressor as a superheated vapor. The superheated vapor travels through part of the condenser which removes the superheat by cooling the vapor. The vapor travels through the remainder of the condenser and is condensed into a liquid at its boiling point. The saturated liquid refrigerant passes through the expansion valve (also called a throttle valve) where its pressure abruptly decreases. The decrease in pressure results in the flash evaporation and auto-refrigeration of a portion of the liquid (typically, less than half of the liquid flashes). The cold and partially vaporized refrigerant travels through the coil or tubes in the evaporator. There a fan circulates room air across the coil or tubes, and the refrigerant is totally vaporized, extracting heat from the air which is then returned to the food compartment. The refrigerant vapour returns to the compressor inlet to complete the thermodynamic cycle."