Author Topic: 7.5 hp induction motor conversion single phase  (Read 12343 times)

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windy

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7.5 hp induction motor conversion single phase
« on: February 14, 2006, 04:31:38 AM »
I have an old 7.5 hp single phase 1725 rpm ac motor that burnt'd out. After pulling all of the old copper out for recycling,I started thinking if it could be used for a generator. I got that idea after seeing different articles on converting induction motors. I read a lot of posts on converting 3 phase motors but none on using single phase motors. The stator has 36 poles and I could get 12 rows of magnets around the rotor.I would rewire the stator with 36 coils in a 3 phase configuration,12 coils for each phase. I could get 60 turns of  16.5 gauge wire in each pole. Could someone suggest what would be a good starting point for the gauge of wire and number of turns that I could use for rewiring the stator? I'm thinking that I could use 15 gauge.The output voltage could be 12,or 24 volt. I would be rewinding the stator with 2 coil legs in each pole. The magnets would be 1 inch square and .250 inches thick.Or would .125 inches thick work? The rotor is 5 inches long and 5.5 inches in diameter. I would use 5 magnets across the rotor skewing each one and 12 rows around the rotor. Would this be overkill on the magnets? I also have an idea of using the start switch in the motor to switch between the star and delta winding configuration using a relay. I could reweight the centrifical switch to engage at any RPM I wanted. I'm not sure if that would work but I would try it anyway. Also, what would be a good cut-in RPM for this size generator using a 16 foot prop.

« Last Edit: February 14, 2006, 04:31:38 AM by (unknown) »
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wdyasq

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Re: 7.5 hp induction motor conversion single phase
« Reply #1 on: February 14, 2006, 05:12:07 AM »
Rather than planning the machine down to using the elecricity, I suggest getting Zubbly's writeup and going from there.  He has developed and explains methods of determining number of winds of proper size wire and cutin speed for whatever you desire.


From there you determine output.  From there comes turbine blade size.


Ron

« Last Edit: February 14, 2006, 05:12:07 AM by wdyasq »
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zubbly

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Re: 7.5 hp induction motor conversion single phase
« Reply #2 on: February 14, 2006, 05:26:17 AM »
hi Windy!


i once made a 7.5hp 12 pole conversion. it was made from a 3 phase, 4 pole motor. i made it basically for powering a 230 volt 3 phase bank of heating elements. out put driven from a large dc motor was 4700 watt @600 rpm, star configuration. no load voltage at 600 rpm was 242 volt. under the 4700 watt load, the line voltage dropped to 205 volt. i never got to fly the unit, and was sold to a client (never got any feed back if it went into service). the load test was carried out for 20 minutes, with absolutely no heating of the unit.


you can view a picture of the winding and of the rotor here.

http://www.reresource.org/User%20Pages/jam/25-Dec-2004/


i wound the stator with 2#18 magnet wires in hand (same as using 1#15),18 coils,42 turns per coil,1 coil side per coil slot, consequent pole connection, 1 star/1 delta and used N35, 1 inch diam by 1/2 inch thick round mags (48 mags, 4 per row, 12 rows). the mag rows are skewed by 10 degrees.


the rotor laminations was originally 5.458 inches in diam and 4.31 inches in length. generally for the same given hp rating, single phase stator cores are larger, but both ours are quite similar. so i think my data rewind and mag configuration will have you in the ball park.


i wrote a 3 part process (i should update it) for converting a motor to alternator. you can find it here.

http://www.reresource.org/Search/

(type in "zubbly" under internal site search and hit submit)


i would suggest you use 1 inch diam, a minimum of 3/8 inch thick (preferably 1/2 inch thick if the aluminum bars in rotor are deep enough so that the laminations don't fall apart when it is turned down in the lathe) magnets. up to you if you wish to use square or round. personally, i would use round as it is much easier to secure them to the rotor using a magnet cage. on my conversion, i used a tube made from fibre glass and also epoxy encapsulated the whole set of mags with cage. i now often use an aluminum cage and secure the mags in the cage with loctite bearing mount or thread locker (#271 or #262 is a good choice).


here is an example of a rotor conversion using an aluminum cage. it is a 3hp 4 pole conversion. 3 rows of mags are used to form each rotor pole.

http://www.anotherpower.com/gallery/zubbly?page=16

see pages 16 and 17


which ever magnet size you use, i would suggest you turn down the rotor the thickness of the magnets times two, plus, an extra 100 thou (.100) of an inch to acomodate the flat tops of the magnets and assure you have rotor clearance from the stator laminations. (you will read about this in the 3 part write up). your rotor diam is 5.5 inches, and if using 3/8 inch mags, i would remove .75 inch plus .100 inch. new rotor diam without mags would be 4.650 inches. if you use the aluminum cage, i would also suggest turning the rotor completely across the face including the aluminum end rings on the rotor to the one dimention. the inside bore of the cage should be that it sits snuggly, or a slight tap fit onto rotor.


getting into this size of conversion has a few other considerations. if i was to use my 7.5hp with the same winding, i would have cut in voltage at approx 60 rpm for a 24 volt battery bank. the 2#18 magnet wires that it was wound with would be a limiting factor for the current a 24 or 12 volt battery bank would demand. so using a step down transformer before rectification is an option, increasing battery bank voltage to 48 volt is another, or making the gen for a higher cut in rpm and gearing up from the prop (which would require less turns per coil, allowing you to increase magnet wire size) is another.


the prop size (just guessing) i think would have to be in the 18-20 foot diam range for direct drive. a smaller prop with gearing ratios may be an option.


it quickly becomes a can of worms and much consideration for what you wish to do with the alternator is needed.


enough said. if you need help with the coil configuration and connections please let me know and i will happily help.  :)


have fun!

zubbly

« Last Edit: February 14, 2006, 05:26:17 AM by zubbly »

vawtman

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Re: 7.5 hp induction motor conversion single phase
« Reply #3 on: February 14, 2006, 06:45:42 AM »
Zubbly.Have ever toyed around with using these has induction gens.Also when you say 3ph element bank are you talking about three single phase elements.Is star better than delta for that application.Im in the testing phase with my 5hp.
« Last Edit: February 14, 2006, 06:45:42 AM by vawtman »

SmoggyTurnip

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Re: 7.5 hp induction motor conversion single phase
« Reply #4 on: February 14, 2006, 07:35:13 AM »
Zubbly - I was looking at your pics and was

wondering what the white plastic material

that you used for yaw bearings was.


Great pics and info - you do great work.


Thanks,


Smoggy

« Last Edit: February 14, 2006, 07:35:13 AM by SmoggyTurnip »

zubbly

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Re: 7.5 hp induction motor conversion single phase
« Reply #5 on: February 14, 2006, 07:35:44 AM »
hi vawtman!


if you are speaking of using a standard 3 phase motor and overdriving it above synchronous speed and using capacitors, no i have not. sometime i may try a few to see what luck i have with it.


a 3 phase element bank is basically 3 single elements connected in either star or delta configuration. if the elements are connected in delta, each element will see 100% of the line voltage from the alternator. if the elements are connected in  star, each element will see 58% of the line voltage from the alternator.


depending what the voltage is from your alternator, it may work better with either star or delta on the alternator and star or delta on the elements. basically i would pick the highest rpm you think your alternator will safely run at, take the voltage from there, and then decide your connections.


hope that helps  :)

zubbly

« Last Edit: February 14, 2006, 07:35:44 AM by zubbly »

zubbly

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Re: 7.5 hp induction motor conversion single phase
« Reply #6 on: February 14, 2006, 07:39:23 AM »
hi smoggy!


the white plastic material is UHMW plastic. it is designed to be used as a bearing material by the manufacturer.


zubbly

« Last Edit: February 14, 2006, 07:39:23 AM by zubbly »

oztules

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Re: 7.5 hp induction motor conversion single phase
« Reply #7 on: February 14, 2006, 04:44:20 PM »
Hi Zubbly

Firstly thanks for your help on the starter motor on flinders island. it all worked perfectly.. happy little motor grader, and hope the finger has recovered as best as can be expected.


Now the trick bit, i am winding an 18 and 36 pole washing machine motor (18 first then rip apart an try 36) I believe the rotor will adjust itself to whatever no of poles i wire it for..is this so?


It has 36 slots. I'm going to wind a pitch of three 1-3, 3-5, 5-8 all the way around. This will leave a vacant slot inside each pole. 18 coils of 35 turns should be easy to wind and test the symmetry. What would your idea of a winding pattern for 18 and 36 pole be ? 18 coils series wound ie 18 north poles with 18 phantom south poles for 36 pole. (No start winding and single phase.)


or should i wind 36 coils 2 pitch consequent for 18 pole or... or... what do you suggest. The aim is to sucessfully test 36 pole single phase 240v 50hz .Once I get the pattern down, i'll wind for the proper voltage. for testing i'l use transformer to step down the voltage.


first test yesterday was 18 coils censequent wound 1-3, 3,5 etc, this gave me 18 poles north s n s n south etc, but motor speed was very low as if it were 36 pole??? don't know what happened here i'm about to go out and ponder it now.........oztules

« Last Edit: February 14, 2006, 04:44:20 PM by oztules »
Flinders Island Australia

vawtman

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Re: 7.5 hp induction motor conversion single phase
« Reply #8 on: February 14, 2006, 04:58:41 PM »
Zubbly I should have known the element question outcome since the elements are from 3ph sauna heater.Sorry about that.But if I could throw another question by you and maybe help Windy with his exploits.I can spin mine with 2 fingers and get 2 rotations and a stock 5hp get 8.You can feel each stator slot slightly.Is that good,bad or ugly?I tested them delta with a small drill on the gen shaft and the elements didnt seem to warm up much.The drill certainly did though.Maybe around 200rpms is as fast has it turned over.I have a 9speed drill press in the garage.My testers are at work now.What figures would you expect from a 5hp at 600rpms?The elements are 240v.Another question is if I used half the mags per pole and doubled the speed what would happen?This is fun and thanks for your reply earlier.
« Last Edit: February 14, 2006, 04:58:41 PM by vawtman »

kitno455

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Re: 7.5 hp induction motor conversion single phase
« Reply #9 on: February 14, 2006, 05:59:29 PM »
you are using caps to provide initial magnetization? what are you planning to drive this with?


allan

« Last Edit: February 14, 2006, 05:59:29 PM by kitno455 »

oztules

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Re: 7.5 hp induction motor conversion single phase
« Reply #10 on: February 14, 2006, 06:01:43 PM »
i've used the term consequent pole wrongly i think. if wound such that adjacent poles are of like polarity, ie n,n is that consequent wound?, and if adjacent poles are opposite polarity ie nsn etc is that series wound? if so above should be series wound instead of consequent


thanks .......oztules

« Last Edit: February 14, 2006, 06:01:43 PM by oztules »
Flinders Island Australia

oztules

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Re: 7.5 hp induction motor conversion single phase
« Reply #11 on: February 14, 2006, 06:27:49 PM »
hi kitno455


I think your question is addressed to me? if so, my intention is to wind an induction motor to the maximum no of poles i can, in order to get the rpm for 50 hz down as low as possible. With 36 pole,  i should be at 3000/18=167 rpm for synchronous operation with 50 hz output. This is well within reach of quite large props direct drive, however the physical winding of such a beast may not be practical, this is what i am testing. 12 pole is certainly doable, this comes to 500rpm, at the top end of decent sized props, but only 4:1 step up for more useful wind speeds. 18 pole will come in at around 330 rpm, step up is looking simpler and less difficult to achieve with homebrew gearing (timing belts, chain drive or any manner of device) I think 36 pole is out the window, but 18 pole may be achievable  I think perhaps Zubbly holds the key here, he has wound at least 12 pole that I know of, but most likely more


If we can do these pole configurations, practically, then grid connect which has thus far been too expensive (inverter), is within reach, or by using the grid as a synchroniser, we may well be able to use 240v 50hz directly fom the gennie, and take over some of the daily load of the house, without batt banks and inverters.

« Last Edit: February 14, 2006, 06:27:49 PM by oztules »
Flinders Island Australia

zubbly

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Re: 7.5 hp induction motor conversion single phase
« Reply #12 on: February 14, 2006, 07:35:15 PM »
hi vawtman!


in all my conversions, i end up with some detectable cogg, a little cogg, quite a bit of cogg.it boils down to each conversion being slightly different than the next. a lot of it may have to do if you used rectagular mags or round mags, or even how well you did a proper skew. assuming all was done perfectly, you may still have some slight cogg just for the fact that the top of the stator tooth may be slightly narrower or wider than the last conversion. and again, if everything is perfect, you still have some magnetic drag even if there is no detectable cogg. everything in a conversion is somewhat of a compromise and not sure if even a top manufacturer could make it perfect.


if you can turn your shaft in the completed conversion with just 2 fingers, consider that excellent!  if you have one that requires a good full hand grip to turn it, it will still produce well but will need a larger prop and you will just miss out a little more on the low wind end. once rotation starts, it is easily maintained by the prop.


testing a conversion with a load will require a considerably strong drive mechanism. i think you mean you tested a 5hp conversion with a small hand drill. forget it, it does not have enough power. when i tested my 7.5hp conversion, it was driven with a 5hp dc motor and tripped the breaker after 600 rpm and 4700 watt load was exceeded. (the breakers may have been small or week), but also, 4700 watt is a 6.3hp load. i tested most of my conversions in a 2hp lathe, and the lathe does not have enough power to drive a 1.5hp conversion past 300 rpm with a battery bank connected to it. i am basically just saying that it takes plenty of power to mechanically drive a large conversion for testing. a rule of thumb may be that you need as much hp to drive it as the original rating of the motor before conversion. one more note: i have had my 1.5hp 12 pole conversion do 2kw on more than one occasion, which is more than 2.6hp output. so, you may actually need more hp than original rating in some cases to be able to fully test a conversion under load.


as you said, your small drill got hot and elements hardly got warm. monitor your voltage output and the current the elements are drawing and you will se that you did have a sigificant load on your drill. i expect your drill press will also have a difficult time to drive a 5hp conversion to any great extent.


as far as your question for 1/2 the mags and double the speed, i am not sure. i always put in the mags to the max. with half the mags i suspect your voltage output would be close to half, and doubling the speed would come back with more output, but not sure how much. using only half mags would certainly give you a unit of robust construction with limited output.  all depends on what you want from it.


zubbly

« Last Edit: February 14, 2006, 07:35:15 PM by zubbly »

zubbly

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Re: 7.5 hp induction motor conversion single phase
« Reply #13 on: February 14, 2006, 08:04:14 PM »
hi oztules!


i am a little baffled as to what exactly you wish to do. are you going to have a permanent magnet rotor?, or just use a single phase winding and drive above synchronous  attached to the grid. i am not sure. please explain a little more if you could.


a consequent pole winding (phantom pole) produces 2 poles per coil group (usually associated with a 3 phase winding)


a series pole winding, produces 1 pole per coil group.


often for multiple pole windings (up to approx 12 pole) there usually is not a problem with the rotor. it depends on the stator slot/rotor bar combination. i am not sure, but trying to acheive that many poles in a 36 slot stator, runs a good chance of producing rotor problems. i have not wound any single phase stators with a high pole count, but a high pole count in 3 phase motors can cause one or more of three possible rotor problems. cogging, cusp, or severe electrical noise.


zubbly

« Last Edit: February 14, 2006, 08:04:14 PM by zubbly »

windy

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Re: 7.5 hp induction motor conversion single phase
« Reply #14 on: February 14, 2006, 08:24:48 PM »
Zubby


Thanks for the reply!


I was thinking of using the generator to heat water,so the information you gave me will be a great help. This is my first attempt at building a generator so I'll need as much help as possible. One question that I have is,I thought that the number of coils should be the same as the number of magnet rows.You have 18 coils and 12 rows of magnets. Is this correct?


Do you wind the coils on a coil winder and then install into the slots or do you wire directly into the slots? How do you hold the coils in the slots.Do you use varnish that was used originally,or can I use an epoxy.


I'm not sure how to wire the coils so I'll need help with that.


I have a 7 foot diameter 6 blade aluminum blade from a cooling radiator for a large generator that I was thinking of using for my prop.I can make it a 3 blade if it needs to be.I had it hooked to a tractor and had it turning at over 1000 rpm so I know it wouldn't fly apart. We seldom get 50 mph winds so I was wondering if I would need to turn the generator out of the wind if the prop is heavy enough.Could gear rotor down at the prop to charge batteries, or gear up to heat water. All just ideas!


Thanks again!

windy  

« Last Edit: February 14, 2006, 08:24:48 PM by windy »
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oztules

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Re: 7.5 hp induction motor conversion single phase
« Reply #15 on: February 14, 2006, 10:01:54 PM »
 hello from below


quoting your good self: "i am a little baffled as to what exactly you wish to do. are you going to have a permanent magnet rotor?, or just use a single phase winding and drive above synchronous  attached to the grid. i am not sure. please explain a little more if you could."


"just use a single phase winding and drive above synchronous  attached to the grid." This is the application i have in mind, or even stand alone...ie asynchronous single phase on its own.


The big question is can it be done.. or how can it be done. Assuming no rotor problems what would the winding pattern look like ie slot pitch and coil numbers. can't help but feel i'm up the big creek without locomotion, but nothing to loose. The more poles I can get, the less steep any gearing would have to be 18 pole would be nice, 36 pole would be nicer. How far can we take this do you think?


.........oztules

« Last Edit: February 14, 2006, 10:01:54 PM by oztules »
Flinders Island Australia

hvirtane

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Re: 7.5 hp induction motor conversion single phase
« Reply #16 on: February 15, 2006, 03:43:33 AM »
Yes 12 poles is certainly doable

as grid connected. I've got one

small washing machine motor 12

pole. But I did not manage

to get it working as a stand alone.

It might be only because of

wrong size capacitors, but it

might be something else, too.

For some time I haven't had

any time to work with it.


I've been thinking about

big induction machines as rewound

with many poles. But do you think

that it would work with the

original rotor? What about

converting the rotor to have

more rods?


- Hannu

« Last Edit: February 15, 2006, 03:43:33 AM by hvirtane »

hvirtane

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Re: 7.5 hp induction motor conversion single phase
« Reply #17 on: February 15, 2006, 03:54:14 AM »
I've seen one 8 kW induction three phase engine

as converted into PMG.


The rotor was made of ordinary steel,

the shaft made of stainless.


Magnets were not put on the surface,

but in slots like in the picture below.

The magnets are suitable small square pieces

in rows in the grooves.


The performance is good, cogging is low.





- Hannu

« Last Edit: February 15, 2006, 03:54:14 AM by hvirtane »

oztules

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Re: 7.5 hp induction motor conversion single phase
« Reply #18 on: February 15, 2006, 04:28:43 AM »
Hi Hannu.


Your twelve pole will run as an altenator.

Run it up to synchronous speed with your cap. If no voltage, then put 12v batt on run field for a sec. This should give you some remnant magnetism to work with. If still no good, it will require a larger kick start. One way is to run it on grid with motor on as well, then simply remove grid. Still need cap for ongoing generation. I believe that the rotor will have enough rods to auto track up to 12 pole. try this


http://www.qsl.net/ns8o/Induction_Generator.html


http://www.windpower.org/en/tour/wtrb/async.htm


good reading for your questions.


.......oztules

« Last Edit: February 15, 2006, 04:28:43 AM by oztules »
Flinders Island Australia

zubbly

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Re: 7.5 hp induction motor conversion single phase
« Reply #19 on: February 15, 2006, 05:10:56 AM »
hi windy,


the rotor does have 12 poles and the stator also is 12 poles. the stator is wound with 18 coils (6 per phase) and connected consequent pole (consequent pole produces 2 poles per coil group). it also can be wound with 12 coils per phase. with 12 coils per phase, it will have 2 coil sides per slot, with consequent pole, it will have 1 coil side per slot.


the coils were wound on a coil form, then inserted into the slots. the slots first have new slot insulation made and inserted, then the coils, then what is called a "wedge" also of an insulating material is inserted to hold the coils in place. after connecting and shaping, the stator is then dipped in an electrical varnish and baked at 300 degree F for approx 3-4 hours.  other types of varnish can be substituted.


your 7 foot diam truck blades will not begin to power a 7.5hp conversion. i have an 8 foot prop on a 1.5hp conversion which stalls badly unless connection is changed over to delta. i think you should be considering a minimum of an 18 foot prop to start with for the 7.5 conversion. depending on your type of wind conditions, you may get away with a slightly small prop or have to use a much larger prop.


to get the most out of your conversion for higher voltage water heating or lower voltage battery charging, you could have multiple circuits built in with many additional lead wires brought out for selecting the best connection/voltage curve for what you need. for a 12 pole winding, you have the possibility to have 1,2,3,6, or 12 circuit star/delta if you wish.


zubbly

« Last Edit: February 15, 2006, 05:10:56 AM by zubbly »

hvirtane

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Re: 7.5 hp induction motor conversion single phase
« Reply #20 on: February 15, 2006, 05:38:09 AM »
I've tried all that kickstarting

already many times. But I think

that my capacitor was simply

much too big. (About ten times

actually.)


In Finland it has been a quite

common knowledge how to run

induction engines as stand alone

generators using capacitors,

but it took some time

to find the knowledge

about the size of the capacitors  

as needed.


(By the way I found in an old

textbook for engineers a

text telling that 'induction engines

cannot run as stand alone generators'.

That cleared to me, why so many

self made men knew about induction

engines as stand alone generators,

but normally engineers were ignorant

of that possibility.)


I've been too busy with other things

to continue testing. I had to take

down my test bench also. The test

bench was consisting of an exactly

similar engine driving the generator

engine via a belt. I tried to rise

the speed of the generator side by

lying in the groove of v-belt pulley

of the engine side some rope.

Another possibility is that it

was still driving the generator a bit

too slowly. I will come back to

test again after some days.


My idea was to use that engine

as the generator of a very

small wind machine. The engine

as a motor is only 50 watts

with 400 RPM. It is a variable

speed dish washing machine engine,

with much more power at higher speeds.


- Hannu

« Last Edit: February 15, 2006, 05:38:09 AM by hvirtane »

Flux

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Re: 7.5 hp induction motor conversion single phase
« Reply #21 on: February 15, 2006, 06:12:18 AM »
Oztules I hope you can find this, sometimes replies don't end up where I expect them.

The more poles in an induction generator the less effective they are although they still work. Larger grid tie machines usually don't go beyond 6 poles, but once they are committed to a gearbox they choose efficient generators, if you can manage without the gearbox you may choose more poles but I think you will have very poor results beyond 8. The other snag is that single phase induction generators are very poor in relation to 3 phase. Whilst I think you may actually get a 36 pole single phase machine to work, it will be extremely poor and never worth the effort, but don't let me put you off.

Flux
« Last Edit: February 15, 2006, 06:12:18 AM by Flux »

vawtman

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Re: 7.5 hp induction motor conversion single phase
« Reply #22 on: February 15, 2006, 07:27:33 AM »
Hi Zubbly,One of the reasons I asked about fewer mags was would it be possible to make Windys 7.5 act like a heavy duty 1hp?What do you think about mounting a flywheel to the motor shaft to help with stall.I know hes oversized for his prop and I might be also.Like him I just had a motor to play with.I can see my playing days arent over yet.Thanks.
« Last Edit: February 15, 2006, 07:27:33 AM by vawtman »

kitno455

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Re: 7.5 hp induction motor conversion single phase
« Reply #23 on: February 15, 2006, 07:28:18 AM »
zubbly- can you explain the reasons you chose to use an 18 coil phantom-pole winding in three phase, instead of the 36 coil series winding? easier to make, but does it give a difference in output?


allan

« Last Edit: February 15, 2006, 07:28:18 AM by kitno455 »

zubbly

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Re: 7.5 hp induction motor conversion single phase
« Reply #24 on: February 15, 2006, 02:34:56 PM »
high vawtman!


if the donor motor is burnt, or already stripped, and you wish to use less magnets to get a heavier duty machine, i would go one step further and remove a large portion of the laminations. if you have 2 inch length in magnet, and 5 inch length in laminations, i would remove 3 inches of the laminations. this way the mags would be totally focused on the matched laminations, but i think more importantly you would greatly reduce the amount of copper required for the coils and much less resistance.


i think i read in the past in other posts, where a few people had tried using flywheels for various reasons. i think the mutual opinion in the end was that there was little gained.


zubbly

« Last Edit: February 15, 2006, 02:34:56 PM by zubbly »

zubbly

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Re: 7.5 hp induction motor conversion single phase
« Reply #25 on: February 15, 2006, 02:45:37 PM »
hi kitno455.


a few reasons. only half the coils to make and you work that stator slot just once.


               to do  a proper winding with 36 coils, where 2 coil sides lie in the same slot, it is always better to have a seperator insulative strip between the 2 coils. this strip takes up valuable room that could otherwise allow you to use larger magnet wire to better handle the current.


               in this case, there is absolutely no difference in performance if the same coil span is maintained. it was wound with a coil span of 1-4. to use 36 coils would have required 1/2 the turns of the 18 coil winding per coil. in the end, you have the same effective turns per phase.


zubbly

« Last Edit: February 15, 2006, 02:45:37 PM by zubbly »

zubbly

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Re: 7.5 hp induction motor conversion single phase
« Reply #26 on: February 15, 2006, 03:02:30 PM »
hi oztules.


if you are up to an experiment, you can try this to get your 36 poles. not sure how performance will be, or whether the rotor will accept and work the 36 poles.


lets try a wave winding. it will look like a snake, but give you the 36 pole you wish.


start in slot #1, pull the wire back through slot #2, go up slot #3, come back through slot #4, go back up #5, come back through #6. continue this until you come back through slot #36.


you now have a complete wave winding with 18 coils that will produce 36 poles. it is only a one turn winding, so to get the number of turns per coil that you want, come out of slot #36 and go back into slot #1 and continue this process until you reach the desired turns you wish. continuing till you have 10 turns per coil and then testing should give you sufficient test readings to calculate the number of turns you actually need.


lol! its up to you.  have fun!

zubbly

« Last Edit: February 15, 2006, 03:02:30 PM by zubbly »

oztules

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Re: 7.5 hp induction motor conversion single phase
« Reply #27 on: February 15, 2006, 07:28:01 PM »
thanks zubbly,

an excellent reply, and as you know (going cold turkey into a starter motor rewind with none of the right gear), i'm just stupid enough to give it a burl. Will get onto it very soon. It's been good fishin weather over here and my dog feels that we should be down the beach (about 900 meters away). (she insists on eating the salmon on the spot, and so very keen on getting down there almost every day). will keep you posted re the results. The 18 pole one worked, but seemed to run at two speeds. If i gently spin  started it, it ran at around 160 rpm, or if i spun it faster it ran more comfortably at 320. both situations were fairly lossy. will battle on. i've taken note of Jerry's blind enthusasim and figure life is more fun to live if you appreciate the journey more than the destination.

Thanks again..........oztules
« Last Edit: February 15, 2006, 07:28:01 PM by oztules »
Flinders Island Australia

oztules

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Re: 7.5 hp induction motor conversion single phase
« Reply #28 on: February 15, 2006, 07:49:54 PM »
thanks flux......A sensible caution indeed.


I can't help but feel you are correct. I feel that i will require more wire in the stator than will physically fit, and that the rotor poles will not be structured to respond to the complex and numerous fields that are going to exist in this configuration. The fact that 12 pole single phase washing machine motors do work, and work well, would imply that even though the efficiencies will be lower than higher speed low pole count motors would be, they work well enough that motor manufacturers make them.


 This very point is why I feel I will in all likleyhood FAIL. If Zubbly hasn't come across more than 12 pole in his career, then there are only three reasons I can think off .



  1. just doesn't work due to pole face interferance ie too many poles in too small an area which stops the flux from being usefully directed at the rotor and cogs or eddies to death.
  2. Does work but just too lossy to be of any practical use.
  3. too expensive to manufacture because of monster amount of copper being packed into too small a space. A quick calculation from rosenberg electric motor repair makes the total wind around 5000 turns for the motor.  How can one possibly get any useable power out of that? ( maybe thats really point 2 in disguise)


I don't know, but I would like to physically see it anyway.


In the remote possibility that i can get one to work , lossy as it will be, efficiency is not of prime consideration, as the power source is free. However that being said, the less efficient, the more heat ....... may find the motor dribbling down through the cracks in the bench...

There's fun and failure aplenty here.

eyes partially open.......oztules

« Last Edit: February 15, 2006, 07:49:54 PM by oztules »
Flinders Island Australia

Jerry

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Re: 7.5 hp induction motor conversion single phase
« Reply #29 on: February 15, 2006, 10:05:24 PM »
Hi Zubbly.


Higher voltage in delta confuses me I thought star wasc higher voltage?


Another thing puzels me.


I was just looking through an electric motor catalog. There are some 1 HP 120 volt motors that draw around 12 amps some as high as 14 amps some as low as 10 amps.


I also looked at 1 HP 3 phase motors. Most of these list 208-230v/460v.


Most of those list around 3.8 amps at 230 v.


I would asume since they stated 3.8 amps at 230v there saying each phases uses 3.8 amps.


This would be a total of 11.4 amps at 230v. or 3.8 ampsX 230v= 874 watts X 3 = a total of 2622 watts.


The single phase motor uses 12 amps at 120 volt = 1440 watts. Why is the 3 phase concidered more eficient?


                      JK TAS Jerry

« Last Edit: February 15, 2006, 10:05:24 PM by Jerry »