Two kinds of heat

[SmoggyTurnip]

The good kind:

The bad kind:

[SmoggyTurnip]

I added some stainless steel brackets to my stator mount.

And built a test stand to alow me to connect the gennie to

the 3 point hitch of the tractor.

.

[SmoggyTurnip]

I played around with some different kinds of cooling

fins and measured the air flow.  Not very accurate but

good for comparison.  Without the cooling fins I got

.6 meters per second, with them I get 1.2 m/s

.

[SmoggyTurnip]

For my first test I connected two 5000 watt heaters in series to each phase of

my gennie for a total of 6 heating elements.  I got 9.7 amps in each phase giving

me a total of 7000 watts in my heaters.

I took no temperature measurements during this test but the water was boiling hard

in very little time - maybe 5 minutes. The stator started to smell too bad and it was obviously too much heat so I stoped the test after about 15 minutes.  I took the gennie apart and found no visible damage to the stator or rotors.

.

[SmoggyTurnip]

Next I added another 3000 watt heater to each phase to decrease the current.

Now I am getting 6.4 amps in each phase (at start of test).  I took crude temperature measurments of the stator, magnets, and the air that was comming

out of the generator.  I stoped the test every 15 minutes to take the readings.

The magnets were going to about 100 degrees, stator 170 and air was about 100.

I knew these temperture readings were not great because it took so long for the sensor to react that by the time I measured the magnets the stator would cool down.  It was taking about 5 minutes to get the temperature readings.

I got an infrared temperature sensor the next day.  I tested it by pointing it at the boiling water and it gave me a temperature reading of 212 degrees F and I did not have to wait.

Next I ran the gennie and monitored the temperature all the temperatures.

At the start of the test I was getting about 5500 watts of heat into the water.

As the temperature of the stator increased my current went down finally stabalizing

at 5000 watts into the water heater.  The magnet temperature was 100 degrees. The

air comming out of the gennie was 120 degrees and the temperature of the coils was 270 degrees.

I let the tractor run for 6 hours straight monitoring everything.  There was no smell coming from the gennie.  I did this test 2 days in a row and then took

the gennie apart to have a look at the stator and there was no visable damage.

The outside air temperature during these tests went as high as 82 degrees F during the tests.  The rpm was 350 for the whole time.  I think this will make a good water heater when the outside air temperature is 20 below zero.

I would like to find a better type of resin to use for the coils.  Does anyone know of some better type of material than polyester resin?  Has anyone ever tried ceramic materials or high temperature plastics?  

I was really surprised at the insulating properties of the polyester resin.  When the coils were 270 degrees the resin was not even warm to the touch just a few millimeters away from the coils.  This polyester resin is really the limiting factor of this generator I think.

.

[willib]

DanB did some tests on heat in coils a little while back, and the following discussions were enlightening.

as i recall polyester resin did the worst, there was talk about adding silica to the mix , to transfer the heat away from the coils.

someone will find the link for you ,

DanB decided to use a different kind of resin , i dont recall off hand what it was .

i believe epoxy did a little better than polyester resin though.

[Gary D]

Smoggy, Dan B. did a similar test with his model A.(?) a while back. His thoughts were that up on the tower, the stator will get air cooled much like turning a fan on it down on the ground. Perhaps he'll see this thread and comment/ explain better than me. There is a link on one of his wind tests somewhere in his wind pages. Hugh Piggott did a similar test also with a tractor pto, with similar results as yours, but both did it without the modern test equipment you had available.They altimately flew them with no problems till 1. Dan's got a near lightning strike killing a rectifire(with a backfeed into the stator), and 2. Hugh had a safety chain get caught up in the furling unit not allowing it to furl properly(I think).. Gary D

[Flux]

With wind power and its intermittent nature and the better cooling I think you will be able to push it to 7 kW or more.

Your continuous power rating is far worse than you will ever see with wind.

I assume you are using it for heating. With battery charging the rating would be a fraction of this with normal stall matching.

flux

[SmoggyTurnip]

Yes I kept telling myself that there would be better air flow when

the thing is in the air - but the whole front of the generator will

be blocked from the air flow so I am not really sure if this is true.

[Gary D]

The link to one of Dan B's test, if it works, must sometime learn to cut and paste...

http://www.otherpower.com/dynotest.html

[SmoggyTurnip]

Yes I was thinking the same. I checked the weather data for my area.

We have a total of 270 hours per year of winds 28mph or higher.

And each year we have a sustained period of 23 hours of 28 mph or higher.

So this thing should be putting out maximum power for more than 5 or 6 hours

at a time several times a year.

I did a little checking about air temperature vs altitude and all

I could find is that the temperature drops .3 degrees F for each

100 ft in altitude.  But this was from info going up to 30000 ft.

I think it may be more in the first 100 ft.  Anyone know any more about this?

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[SamoaPower]

Well done SmoggyTurnip! It's great to see some real tests done on what I consider to be the biggest problem with the axial flux alternator.

I particularly like your application of forced air via the magnet rotors. Unfortunately, because of your resin cast rotors, the air flow through the gap is quite linited but it's the right idea. Think what it might be without the resin between the magnets.

I don't think my one-man crusade against casting stators (and rotors) has made many converts. I guess the common-sense reasoning doesn't get through to many. The main issue is that for good cooling, you need to expose as much of the coil surface to moving air as possible. That's why casting is contra-indicated.

Many thanks for the supporting data.

[Gary D]

Depending on your furling wind speed(tail weight), the stator will see more airflow as the blades start to turn away from the wind... Just a thought from the cheap seats here... Gary D.

[Slingshot]

Smoggy,

How did you use the IR sensor to separately measure the coil and resin temps?  I thought IR sensors only measured surface temperature, versus something like buried coils.

[SmoggyTurnip]

I measured the surface temperature of the part of the coil

that was comes out past the rotors. And for the magnets I

actually measured the temperature of the steel behind the

magnets - assuming that after everything reached equalibrium

that the magnets and steel would be the same.  But now that

you made me think about it I guess that the magnets would

be quite a bit hotter than the back of the steel.  Hmmm well

I guess they didn't get too hot cause they still work.  

.

[Nando]

Smoggy:

Have you taken the generator output voltage versus RPM ?

Have taken the winding Phase resistance ?.

Can you as well supply the resistor values used for each case ?.

Supply the info and we may be able to calculate the generator dissipation for each test.

As well, the proper loading for the generator can be designed for optimum power harvesting .

What are your overall use for this mill ?.

Can you connect directly with me, my address is in the heading, do correct for @ and . for proper connection

Nando

[kitno455]

can we please do this here in the open so that everyone can learn?

allan

[Grant MacLeod]

How do you mount the magnets on the rotors is you don't cast them?  Just glue them on?

Same question on the coils.  How do you mount them on the stator body?

Grant MacLeod

[dinges]

Hear hear.

[SmoggyTurnip]

Here here here

[shmuu102]

check out this thesis on cooling axial flux stators..

http://www.ee.kth.se/php/modules/publications/reports/2005/IR-EE-EME_2005_012.pdf

i have been tossing around trying something similar, but with all the airflow up there, expcially when the heat is at its greatest, a passive system would seem like a more eligant design..

[Ungrounded Lightning Rod]

Look up "lapse rate".

It's different depending on whether the air is dry or wet (condensing), because of the heat released when the water vapor condenses.

I think the lapse rate of an ideal gas is proportinal only to the strength of gravity.  Dry air is VERY close to an ideal gas, and the earth's gravity strength doesn't change much in the range between sea level and the peak of Mt. Everest.

[TomW]

Oh, yeah! I am with you guys. The whole point here is to get the info out to the widest audience possible.

Again, just one mans opinion.

Cheers.

TomW

[Ungrounded Lightning Rod]

I don't know how S.P. would do it, but if I ever make a radial-flux machine I intend to try casting only the straight sections between the magnets, leaving the looping sections exposed to lose heat.

Good electric conductors are good thermal conductors (because the electrons carry heat, too).  Leaving a third or more of the length of the wire exposed (to the passing wind, too), once or twice per turn, should drastically improve cooling even of the imbedded portion of the wire.

An open question is how to bind it against vibration from the magnetic-pinch forces without excessively insulating the exposed portion or retarding the airflow through it.  I'm leaning toward using copper strip rather than wire.

[Ungrounded Lightning Rod]

(A dot of silicone goop near the center of the loop, to damp the major vibrational modes, might do the job.)

[DanB]

In my test actually the polyester held up to the heat a bit better.  Now I'm using vinyl ester though which is supposed to be much better than polyester.  It also seems harder/less flexible.

Talc helps some to dissapate heat through resin - I noticed the same thing, you can burn yourself quickly right over the coils but 1/4" away the resin is fairly cool.  It does a poor job of moving heat...  but - I think it can work fine.  

[RP]

Bear in mind that IR thermometers vary the indicated reading depending on the emissivity of the surface being measured.  A flat black surface has a high emissivity and will read about 93-97% of the actual temperature of the metal.  A shiny chrome surface will read less than 50% of the actual temperature.

I'm concerned tha the actual temperature of the rotors and stator may be significantly higher than you are reading.  This may also be contributing to the difference in readings over the copper in the stator as opposed to the resin.

Consider painting a small flat black area on the rotor and stator and then repeating your tests.

Oh, BTW:  The operators manual may address this with other suggestions to get more accurate readings.

[willib]

i'm not sure electrons carry heat

dont they cause heat by bumping into atoms

look up super conductors , the reason they superconduct is there is a clear path to flow,with nothing to bump into, no resistance

[SamoaPower]

See:

http://www.fieldlines.com/story/2006/3/27/212954/042

[Ungrounded Lightning Rod]

i'm not sure electrons carry heat. dont they cause heat by bumping into atoms

Both.

They carry heat.  (That's how peltier cells work.)  And they transform electrical power into heat by first being accellerated by it then bumping into things and changing their own momentum to vibration of their surroundings.

look up super conductors , the reason they superconduct is there is a clear path to flow,with nothing to bump into, no resistance

Actually it's because the electrons pair up and the pair (which, as a partnership, has integer spin and thus isn't subject to the pauli exclusion principle) can go whizzing through the surrounding matrix tunneling through some of the things the component electrons would otherwise would bonked off from due to not being able to overlap with it.  It's the sourrounding material that creates the conditions that let the electrons pair up and maintain the pairing (which is why electrons don't superconduct except in particular materials and conditions.)  Too much vibration (heat) also breaks up the conditions that let the electrons pair (which is why superconductors have to be cold - and HOW cold depends on how well the create pairing conditions and thus how much disturbance it takes to break up the pairs.)

(Or at least that's how I THINK it works.  I gave up on really understanding quantum mechanics decades ago.)

[willib]

I was going to add , that i thought it was the right number of electrons in the outer shell of the compound , that while being frozen , just bumpd electrons along the path from one compound to the next

pauli exclusion principle i havnt heard that in a long time , cant believe i've forgotten what it was...

of course i could look it up , but like you said ,it's been decades,and who cares anyway , i'm not sure i understood it when i was taking it

[SmoggyTurnip]

Yes - I didn't really mean for the temperature readings to be taken to be very accurate.  The main thing I was looking for was a stable temperature.  I wanted to keep an eye on things and see if the temperature was going to continue going up.  I did take a long time to reach equilibrium (2 1/2 hours) but I think that was partly due to the increasing temperature of the surounding air because of the 5 gallons of water boiling and also because of the outside air temperature increasing as the day went on.  So the temperature readings are most likely inaccurate but the wires didn't melt, the magnets didn't lose ther magnitism, and the resin didn't distort.  So what ever the final temperature was it was winthin the limits.

[SmoggyTurnip]

Interesting article about cooling axial flux motors.  The big difference between cooling a motor and a generator is that the motor may produce alot of heat at low rpm if it is producing alot of torque so it can't rely on an attached fan for airflow but a generator produces less heat at low rpms so it may be an easier problem to deal with.

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