Permanent Magnet Servo Motors

[Ekimdaed]

I'm new to the forum. I work at an industrial robot refurbishing company. We currently have a bunch of permanent magnet servo motors from the robots sitting around. I was wondering if these three phase motor would be any good in generating electricity with wind or water. If so would someone please be kind enough to help me? I started reading some information about generators but most of them have been smaller models. To give an example one of the motors I have specs are: Output 2.1kWCont. Volt 186V Amp(~) 7.4 A Freq. 133Hz Speed 2000 min. All of them vary depending on size and make. Any knowledge would be helpful.

Thanks for your time and patience,
Ekim

[artv]

Hi EK,....First of all I have very little to no knowledge of these things ,but am trying to learn, "2000 min" does that mean a minimum of 2000 rpm before it starts to produce?? Also 133Hz that's fast......maybe if it was put in hurricane winds it might work, I don't know..
Would like to get my hands on some of those motors though,....sorry for the lack of help......artv

[Flux]

The example you quoted gives 186v at 2000 rpm. At 200rpm it would give a bit under 18v. This would probably be a bit slow for a 12v wind turbine but could work with suitable blades. it would be a good match for 24v with a prop about 6ft diameter.

The thing you have to remember is that the current will still be limited to a bit over 7A. The power out is reduced directly in relation to the speed so you loose your 2kW rating and end up nearer 200W ( probably push it to a bit over 300W for wind use).

For hydro you can maintain the higher rating but you will have to get your 180v dc down to battery volts so once again you may have to adopt the simple option of running it at low speed and accept a reduction in output if you don't want to use an expensive controller.

The fact that a frequency is given leads me to believe that these are ac machines with a brushless conversion to dc servos. If you have the control head you can probably use it as it is but otherwise you can just use a rectifier when running it as a generator.

You probably have the basis of a nice generator for a smallish 24v wind turbine as long as there are no big mechanical issues, servos normally have a decent size shaft and excellent bearings. I suspect it will be fine.

[Bub73]

 I've found that some servos will give close to their rated amperage per phase when rectified to DC.
I have a 9amp 200 volt Fanuc on the test stand now that has shown 25 amps DC @ 12v+ in wind gust up to 20mph using 6 footers.
 I'll try to get a pic or 2 up this evening as they are on my other computer.

Bob

[Bub73]

Sorry its a a 9amp 165 volt Fanuc ,

Here are some pics we took while testing. Hope they showup.........

Bob

[Bub73]

One more, a shot of the blades;

Thanks to forum members for getting me this far..

Bob

[artv]

Hi Bud73,....It says on the name plate 9 amps,...So by putting out over 25amps are you in danger of burning the windings up??
Flux you said,.. "200rpm would give ~18V a bit slow for a 12V turbine,..a good match for 24V"......So at 300rpm ~27V so better suited for 24V since 300rpm is quite easy to achieve??...........600rpm ~54V better for 48V??.....and regardless of which choice, is it still only limited to ~ 7amps??
Ek...sorry for all the questions in your thread....I hope you don't mind.....artv

[Bub73]

HI  Ekimdaed,  artv,

 I've found that some servos will give close to their rated [STALL] amperage per phase when running as an alternator, sometimes more other times less.
 They are very well built and robust and so far on the test stand the Fanuc hasn't got very warm.
When I get it up on my tower in cleaner air this could change; we will just have to see.

97fishmt has made some very good post on using servos ; perhaps he will comment here an set me straight on what to expect for safe max output.

Sorry Ekimdaed, I didn't mean to hijack your thread; just seems like we may have very similar servos........

Bob

[97fishmt]

What I look for these day's are the newer models,  they are more compact and not near as heavy as the motors that don't have the neo's in them.
My experience with the motors I find may be different than what others are finding.  But I have found the motors rated at 200 volt and 1500 rpm to be an excellent
12 volt charger with a 6' prop.  The different manufacturers do have different ways of rating their motors.  I have studied many motor spec sheets and I think every motor
I have got my hands on has a different max amp rating,  not the continuous or stall rating.  Some are 3 times, some 4 to 5 times,  so they are made very well.
Continuous duty for one of these motors would be in a hot warehouse being used to power a welding robot.   All those letters and numbers in the model number
have a meaning in how the motor was made.  You really need to go to the manufactures web site to figure out what it is saying.  A custom winding,  higher insulation
value for the winding, neo magnets, a brake all kinds of stuff.  Not to go into it more we had a good discussion about the ratings and using them as generators on the
back shed web site.  I'm not looking to promote that site or anything just this site is more geared for the axial flux machine.

Glad to see you still at it Bub73,  I'm still at it also,  I've only put 4 motors up so far, many tested on the bench.  The amp rating I was referring to can sometimes be found
on a spec sheet for a particular motor.  It would be for absolute max amps the winding could handle.  I don't know if it works like you explained but the rated amps per phase
after rectified and combined, for 3 times the name plate amperage. Sounds like a safe way to rate one of these motors.  I did finally take off my original motor this year to just try something new.
The old motor is still just fine after  10 years or so.  I picked up another Rohn 45g on craigslist to even have more fun.

Mike

[Bub73]

 Good to see you still at it also Mike.
 The summer was to hot for us to get much done outside but we hope to get a couple flying this fall.

 Bob

[birdhouse]

hey all-
i've built a mill from a fanuc servo.  it's specs are 140v 20a 2000rpm.

have it set up with a 24v battery bank with 8.5' diameter blades.

these motors don't always follow the rules as far as V/rpm breakdowns.  it's kinda an unknown until you test it on the bench. 

just got home from my ranch this evening, and when i left, it was putting out a record output of 500watts!  no idea on wind speed because i have no logging, but the winds didn't seem terribly strong. 

yesterday, i was running the inverter powering a stereo receiver, lights, ect.  and i happened to wake up at 1AM last night, and the batteries were on float from the servo-mill!  made me stoked! 

anyways, the specds on that servo in the pics sound perfect for a 24v system! 

run with it!

adam

[Ekimdaed]

Thank you all for the info. I'm going to tear down the motor this evening and get it ready for a bench test. No worries about the string going in different directions. All questions and info are welcome. I'm very new to windmill generators.

Ekim

[dave ames]

Hi Ekimdaed,

A note of caution..others may have more on this..

We want to be carefull on how far we disassemble that servo. We have seen reports of them loosing some of their power producing abilities if the magnetic circuit is broken by removing the rotor even for a short time?

cheers, dave

..And welcome aboard!

[birdhouse]

dave is very correct.  DO NOT remove the magnet rotor from the windings/core.  you WILL lose magnetic flux. 

i'm not quite sure why you're talking of a motor teardown for a bench test?? 

i could understand if the servo has a built in brake, but still, try to remove the brake without pulling the rotor from the windings.  most motors this is possible, but might take elbow grease, and thought. 

adam

[Ekimdaed]

It has a brake on it and needs to be taken apart to get the pads out. Thanks for the heads up I'll try not to pull it all the way out. If I screw this one up I literally have tons of these motors. I'd like to see how much energy they produce and the next step is going to be find a few forklift batteries for storage. As soon as I get this prepped and bench tested I'll be sure to post my findings. Thanks for the support and understanding everyone.

[12AX7]

I have read many times about the magnets loosing power when the rotors are removed,  however I have not observed this to be true.  I found an old Kollmorgen in the junk, it's rotor had been removed.  I took the parts home and it sat on a shelve for almost a year before I put it back together.
Once it was together it spun freely by hand,  shorting any two leads makes it very difficult to turn,  short all three and it's almost impossible to turn.
Turning the shaft by hand and touching any of the main power leads together and you'll get a small spark.

Granted,  I have no way to compare it to "before" but I can't imagine that were would have been a major difference.

I've also taken apart a couple of AB servos and haven't noticed any difference between "before and after"  (using the shorted leads method).
I have also taken apart an Emerson servo and had the same out come.

I've taken apart more than a dozen (junked) servos and each one of them had the magnets on a magnetic rotor (keeper) and I still don't understand why or how these magnets would lose their magnetism,  whether the rotors are removed for moments, hours, or weeks.

Now for my disclaimer!!    I have never taken apart a servo, with out trashing the encoder/tach/reslover.   Thus never verified it's level of performance after it's been dis and re- assembled.   Maybe the magnets did lose something,  but I doubt it was a whole lot.

I would NEVER suggest taking apart a WORKING servo motor,  unless it's your intention to "trash" the "servo" part of the motor.

Again,  I've seen many posts saying that removing the rotors will permanently damage the magnets So I guess it must be true,  but I haven't been able to verify this.
I do believe that taking most any servo motor apart (with out the proper tools/calibrations) will permanently wreck it's ability to perform as a SERVO MOTOR (but not necessarily it's ability to act as an alternator),  and often have wondered if this is why people say that the magnets will lose power.

[RP]

A simple way to compare magnet strength on brush motors is by comparing unloaded rpm on a fixed voltage before and after a disassembly.  The stronger the magnet, the higher back EMF and the slower the unloaded rpm.

PM motors can be damaged by over current demagnetizing the fields and this test is used to detect it.  Basically if the unloaded speed goes up, the magnets have weakened.