Matching Blades to Alternator

[valterra]

I know from reading the experts' advice that you need to match your blades to your alternator.  My question is how you figure this out in short order.

My motor conversion is all complete.  I just need to build (or buy) blades and mount it on to my tower.  (I need to devise a tilt-up, but that is another story).  But I don't know what size of blades I need.  I am thinking between approx 7 and 10 feet based upon some very preliminary tests.

I know a guy who runs a machine shop who would probably let me hook my motor up to his lathe.  I am thinking that I should wire my bridges up to a battery, test various speedsand record the results.

Right now I have it wired High Volt Jerry which reaches 12voc at approximately 180 rpm.  Hooking it up to my electric drill with the (in)famous duct tape method, I can get 60voc AC on each coil at some unknown speed.  (helpful, ay?)  It will light up an  incandescent bulb.  

Wired High Volt Jerry, I believe I was able to put about 5.5A into my battery before I stopped for fear of burning out my nice drill.

If any of that information is helpful, great.  I suspect that it may not be.

Proper test results should reveal "cutin" RPM and then I need to match that RPM to a chosen windspeed?  Part of that equation is the TSR or the built or bought blades.  For example, if I want a blade that spins 180rpm in 10mph wind, it might be 10 foot diameter.  If I want it to turn 180rpm in 20mph wind, the blades would be much larger.

Is that all I need?  I can post RPM and VOC using different wirings.  Then I can also post RPM , Voltage, and Amperage into a battery.  Would that be enough info for you guys to tel me what size blade would be best?

I want to know in advance so I don't waste the guy's time or yours.

Thanks!

[Jerry]

Hi valtera.

Can you give a complete description of your motor conversion?

Things like phase count, rpm, voltage, amperage, magnet count size & shape ECT also?

This will help to know what to expect for power and help to determin blade size.

                      JK TAS Jerry

[ghurd]

This one isn't blue, is it?

Blue never works as well.

LOL

G-

[valterra]

Jerry - here is part 1 of the project:

http://www.fieldlines.com/story/2008/5/22/2002/75469

Part 2:

http://www.fieldlines.com/story/2008/6/6/05848/70393

I don't know that I have more information than that.  4 magnets, 6 coil pairs.

GHurd - if the Blue ones don't work, can't I simply paint this one another color?  Would latex paint act as an insulator and trap the electricity inside?    :-)

[zap]

hehehehe

Now I know why I've been having so many problems! Time to toss Ohm's law out the window!

[Flux]

You may have trouble using 12v with a motor conversion. A cut in of 150 rpm would be typical of a 10ft machine but unless this is a really big motor it will not handle 10ft blades.

If you can lathe test it you may get a better idea of what it will do. You can do a couple of points open circuit and measure the dc voltage after a bridge. No need to do more than 2 points. We already have 12v at 150 rpm, that tells us everything but in real life it is good to have another point as a check for errors.

A couple of points loaded into a battery would be useful, ideally one near cut in and one well up the speed range.

The open circuit voltage with speed will be linear, the load curves may not be and a significant number of points to give a proper curve would be good. Unless you can maintain the battery voltage fairly constant the curve may not mean a great lot.

The most useful thing for matching the blades would be an input power curve while charging the battery. To do this you would need to mount the shaft in the chuck and support the back end on a centre so that the stator is free to rotate ( over a limited range at least). You then need to measure torque on the stator with a spring balance at a known radius. From torque and speed you calculate input power and that is the bit that needs matching to the prop.

Unless you can reconnect for a lower voltage I think you will be heading for a 24v machine.

Flux

[Jerry]

I'm short of time here to read all the links. However in a breif scan of the links and responces I think you said your using curved magnets. What are the dementions of those magnets?

I convert 1 hp single phase 120 volt motors. There stock wireing lends real well to 12v and 24 volt use after mods.

3 phase motors stock wireing works real well to 24 volt use.

I use my 49" tip to tip blades with good results on both 1hp single ph. and 3 ph.

MY single phase conversions actully become 2 phase PMAs.

Since you have 6 seperat coil sets available and are "Jerry Rigging" it I would gues its best suited for  24 volt use. This would be the lower voltage configuration. For 48 volt use wire it in the high volt configuration.

4ft to 5ft high TSR blade should work well depending on your available wind.

I'm hopeing to wind tunnel test a 1hp conversion within the next mounth.

                           JK TAS Jerry

[valterra]

Jerry - I was eyeballing a set of 5 or 5.5 foot TSR 8ish blades already.  I just didn't know if by using such "small" blades if I was robbing myself of the opportunity to extract some real power from this motor.

Flux - I know what you mean about whether or not it will support the larger blades.  It isn't  small like my AMETEK, but there is only so much weight one can expect to mount on a 7/8 inch spindle.

As far as how it is wired... no wires have been soldered.  I used High Volt Jerry because it got my the most obvious results on my voltmeter.  If I am looking for 12v then do you mean to rewire for a low volt Jerry or a traditional wiring scheme (Cant remember off hand if it is star or delta that everyone hates, but I would certainly look it up before I started twisting wires together again).

As I understand Stall, trying to pump too many volts into batteries presents a much stronger workload on the blades.  If the wind is stong enough you could break through it.  But more likely it is best to pump, say 5 amps into a 24v bank instead of 10 amps into a 12v bank.

I will conform where necessary to the nature of the machine.  I am not going to stubbornly attempt to defy physics.  However, I would like to do whatever is necessary to stay at 12V.  I have no 24 (or 36 or 48) volt equipment or inverters at this point.

[ghurd]

It seems to me changing the wiring to Low Volt Jerry Rig would take the 12V cut-in up to 390 RPM, and cut the coil resistance in half.

Seems more reasonable for 12V.

G-

[valterra]

Stupid Question Time.

Changing from HVJ to LVJ (that sounds fancier than I suspect Jerry would like) would essentially double the cutin, from what you said.

In that case, we are simply sliding the voltage scale in relation to the RPM.  I hope that made sense.

What other relationships  change in that situation?

For example, would a LVJ wiring actually create HALF the power as well?  Or are we trading volts for amps and the wattage remains the same?

[Flux]

This is a bit complex. If you use the hvJ connection you will be able to use larger blades and extract more power in light winds. I doubt that you could control that alternator safely with a 10ft prop unless you were very careful indeed with the furling.

Changing to LVJ will give the alternator  a lower resistance and you will be able to get far more power from it but the snag is that you will need a far smaller prop to get the speed up.

Do you want modest power in reasonably low winds or do you want very high power in high winds and very little in low winds, that is the choice you have to make.

You know your wind area better than the rest of us. If I thought you could safely load the 10ft prop and manage to get it to furl without running away then it may be your best choice but you may be very limited in the maximum power ( don't know until you do more tests.)

If you go for something like a 5ft prop you probably will see very little below 10 mph but you may manage quite high power levels in winds over 30 mph.

I am inclined to suspect at this stage that your best prop size would be 7 to 8ft but you probably will not get a good match with the existing windings. It may be that a good compromise would be 8ft but with a lower tsr ( 5-6).

Without more load tests it is just guesswork.

Flux

[ghurd]

Open Voltage would be a bit under half at the same RPM.

Sort of trading volts for amps. I don't think watts will graph the same.  Might stall without good planning?

G-

[valterra]

Okay guys.  I sent a letter to the guy I know who has a lathe.  Fingers crossed.

Any specific RPMs to test?  Seems to me that hooking it to the lathe / changing the wiring is the hardest part of the test.  Otherwise, just set the lathe and write down the number.

I was thinking 150, 300, 600, 900(?) because they are nice round numbers.  Absolutely no other reason, so if something else is better, please let me know.  900 probably doesn't even matter?  I'd hate to see 10' blades spinning 900 rpm.  RUN!!!!!!

And then with a battery - test the output for a few seconds and note the battery voltage and incoming amperage?  Then stop, and put a load on the battery to return it to its "pre-test" voltage?  Do this a few times at different RPMS?  I've been told to only let it run for a few seconds, which makes sense.  If you change the battery voltage any significant amount, then the numbers will get all mixed up.

But test the battery at the same RPMs as the OC tests?

Thanks for all the help guys.

[Flux]

Yes that makes sense but you will have to take the lathe speeds as they come unless it is a modern one with variable speed drive. The old gearbox units usually had some irrational speeds.

Don't start with a fully charged battery,the volts rise rapidly as it reaches gassing point. For low currents the volts will not move much if you are quick with the readings. For higher currents try to leave the load on and if it is somewhere near the charging current the volts will stay fairly constant.

Flux

[valterra]

Thanks Flux.  I am trying to meet up with him tomorrow.  He said he can dial it in to the single digit RPM.  Like 300, 301, 302, etc.

He doesn't want to take up up much over 300 due to the way it has to be mounted and shimmed into the lathe.  At least on the battery portion of the test.

[valterra]

I've asked before, but don't think anyone told me.  Do short-circuit CURRENT testing results mean anything?  This one is approx 4.5A at approx 120RPM.  Very unscientific test method.

[valterra]

I have some numbers.  Battery numbers are preliminary - all figures approximate, but done to the best of my non-scientific ability.

I will post them as a new journal entry - 1HP 3P Motor Conversion Part IV

Here is a link:

http://www.fieldlines.com/story/2008/11/10/211911/74

THANK YOU EVERYONE WHO CONTINUES TO GIVE ME ADVICE.

[Jerry]

In my opinion short circut test are dumb. Its like driving a car into a brick wall to see how fast it can go with a very heavy load.

                          JK TAS Jerry