Servo motor as wind generator

[GAC]

Can anyone advice me is this servomotor good as a wind generator? I can easely spin it by hand and get 1,5 Amps.

Thanks!

[fungus]

Should be pretty nice for a few hundred watts of power; it'll cut in at approximately 200-250rpm; it sounds like a nice match for a 4-6ft prop; the servos have nice heavy shafts and bearings so are pretty nice for wind gens.

[wooferhound]

How many volts at 1.5 amps ?

Which one of those readings is the RPM ?

[GAC]

RPM is N and it equals 4400 min-1. Voltage at 1,5 A was probably zero because it was short circuited by Ampmeter. Winding connection was star.

Shaft is 18mm thick.

What do I need to tell you so you can tell me exact diameter of the prop?

[fungus]

Could you try spinning it at a known speed and see what voltage you get? Also; is it much harder to turn with it short circuited?

[GAC]

Yes it is harder to turn it short-circuited. But this is three phase motor so I could put Amp only between two phases so probably it would be harder to turn when it's completely loaded!

Tomorrow I'll try to spin it at constant speed and will post the results.

[scorman]

PM 3 phase servo motors (like the ones we are planning to install) are great as a generator.

We have several of the AB1326AB-B515E which are rated at 3000rpm

lot of generic info here:

http://support.elmark.com.pl/rockwell/Literatura/1326a-2_9.pdf

...but nobody says you can't load it to full power capability at 1000rpm (150v at 5.5amps x 3 legs = 2.5KW)...these have extra heavy windings so that they can be totally stalled (zero rpm) and draw about 2x+ nominal current in those windings when run as a servo motor..only limitation to use as a generator is if the permanent magnets don't have enough flux to produce juice at a particular rpm and load resistor...bench test it to find out

Servos are unique in that they are specifically designed to function at varible frequency from 0 -> 250hz w/o cogging ...typical efficiency is about 85% , but the key spec which you would need to look up for your brand unit is the winding resistance for each leg .. ours are about 3.3 ohms.

Quick calc ...a 1.8KW/230v water heating calrod element is by definition 29 ohms.

Run it at only 150v/5a and you get 775 watts x 3legs = 2.3KW generator

you'll have plenty of overspeed capability in both the load resistors and the windings,

just get the gearing at the best ratio to get 1000rpm at furling.

note that the winding resistance is very much smaller than the load resistor = goodness

Stew Corman from sunny Endicott

[97fishmt]

  Hey, I have not posted much in a long time, but I wanted

to comment on what has been working for me for about 7 years.

I've found the brushless servo motors to be an excellent starting

point for a wind turbine. They are a sealed unit with heavy windings

and bearings. All you need to do is make a mount and put a rotor

on it. The trick is to match the rotor to the power curve of the

out put. They work very well if you match voltage and RPM to the

system voltage. I have found that just by omitting a zero or halving

in the name plate ratings has gotten me producing power and I think

it is pretty close. For example 280v @ 4400RPM = 28v @ 440RPM or

14v @ 220RPM. The amps are going to be a given for this is the size

of wire in the windings. Once the turbine comes up to battery voltage

it will put out the name plate amperage.

  So ideally you want to find one that will fit your systems voltage

and current requirements.  I would think the more amps the better

and the right cut in speed for a particular rotor diameter, smaller

faster, larger slower. I am using a 12hp motor rated

at 144V @ 2000RPM and 65AMPs. I see 14v at, I think 200RPM and some

times over 70AMPs with some strong gusts into a 12v battery. I have

some 400v units I am going to start experimenting with soon. I just

really need to get my rohn tower up. Cool have fun and make it work!!

 

[GAC]

Finally testing results.

First picture is my setup for measuring: one motor connected to generator. Inductive switch which gives one pulse per shaft revolution, instrument that counts pulses and displays frequency. True RPM is than frequency multiplied by 60. Generator is connected is star connection (I think so because only 3 wires are coming out of it) and it has 6 diodes as rectifier.

Table below gives resultant current (Ic) charging 12V battery. Uc is induced voltage without load.

First I need to know is this good way to find out true RPM of generators shaft or my math is bad?

If firs is OK than is this generator worth making the blades or should I trove it away?

And at last if first two are OK where to look for blade calculations (diameter and ...)?

[GAC]

Any suggestions?

[ghurd]

It's not much power even when the open volts are high.  The winding resistance is high.

I would try "Jerry Rigged". If you can find the star connection point, cut it, add 3 wires, making 3 separate phases.

Each phase gets its own bridge.  Parallel the bridges to the battery. The resistance is reduced.

The cut it will raise to about 375 RPM, but when it cuts in the amps will climb a lot faster.  

I would expect at about 550 RPMs the output will pass the way it's connected now, maybe around 630 RPMs the output would about double to 4.85A. Guessing.

I'm not much good with blades, but I would guess ~36" could be a nice match.

Some people use this,

http://www.alton-moore.net/wind_calculations.html

G-

[SparWeb]

Before going too far with your tests, I think you should look at the state of the battery you used.  Was it mostly discharged or mostly charged?  That would affect the current you measured.

[GAC]

Sorry I didn't complete the table above, line Ubat is missing. But battery was almost full because as I remember at 3 A current battery voltage was around 13,7V and fast rising. I couldn't spin generator for long at that speed because my setup for spinning was very poor and I didn't want something to break.

How does this affect current measurements?

Thanks!

[SparWeb]

Sorry - I was away and couldn't get a response back to you sooner.

I made the same mistake earlier in the year when I tested my alternator into a 3/4 charged battery.

When the battery is full, it doesn't accept a charging current.  That's an over-simplification, but it's close to the truth.  Another way to picture it is to put a resistor in the place of a battery.  

If you conducted your test into a resistor with a high value, the resistance would prevent much current from flowing, hence you would collect very little power.

If you used a low value resistor for your test, then the current would be higher, though if the resistance was too low, the power collected might drop again.

A fully charged battery is like the high-value resistor.  It won't let as much current flow as it would if it was nearly empty.  So start testing into a nearly discharged battery, and repeat the test after it's half-charged, then again when it's fully charged.  You will then learn how the alternator loads the power source (windmill blades) depending on the battery's state of charge.

Your tests are educational, but they will be most useful only if your are prepared to pursue the mathematics to the full extent of sizing the propeller for you before you make it.  I love that stuff, but it ain't everyone's cup of tea.  You've proven that your genernator works.  The motor you started with was only rated for 4 Amps, anyway.