Author Topic: Automotive alternator to PM alternator  (Read 21315 times)

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rustkolector

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Automotive alternator to PM alternator
« on: April 21, 2014, 05:20:06 PM »
Hi,
I am the model engine builder guy that sought help here a few years ago on a scale model engine slow speed electric plant. The 1:10 scale 1906 vintage stationary gas engine runs a 6" dia. alternator built from a ceiling fan motor. Thanks to ghurd and others here it was a success. It puts out plenty of power at 600 RPM. A video of it can be seen here: http://www.youtube.com/watch?v=a5yUtb7baOk

I am back to another engine alternator project this time using a smaller 4" dia. automotive alternator stator and I am shooting for 18-24vac output no load at 400 RPM. This stator is wound 3 phase using fairly large wire with the coils wound serpentine. The stator has 36 stator teeth and each coil spans three teeth. My first question is how many electrical poles does this stator have? Is it 6 or 12? I assume it is 6, but I don't understand the technical aspects of the serpentine winding.  If it is 6 poles, my magnets will have to span 3 teeth making cogging a real issue. I was able to skew my magnets in the alternator project above to minimize the cogging by spanning two stator teeth. Spanning three teeth on a 1" deep stator is more difficult. Is skewing the magnets the best way of minimizing cogging for a stator this size? What is the ideal number of magnetic rotor poles? I am sure I will have to rewind this stator with more turns of smaller wire, but the cogging issue is my main concern at present.

My electrical load will be 15-25 watts at 12vdc using a rectifier and external regulator. Any help or recommendations would be greatly appreciated.

Jeff

joestue

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Re: Automotive alternator to PM alternator
« Reply #1 on: April 21, 2014, 08:38:28 PM »
12 poles. use this link for more alternative winding ideas: https://www.emetor.com/edit/windings/

any particular reason why you want to use a automotive alternator stator?
do you intend to keep the rotor or start over?

rustkolector

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Re: Automotive alternator to PM alternator
« Reply #2 on: April 21, 2014, 10:09:36 PM »
joestue,
I have been looking for a high pole count stator for my low speed requirement in approx. the 4" dia. size. Anything larger in diameter will not work for this project. I need 12vdc under load from this system at approximately 400 RPM. I am not fixed on this stator, but it looked promising to me when I found it. I do not have the original rotor, but intended to make my own rotor anyway. My thought was to rewind this stator it for higher voltage, though I have not done any rewinding, but this one looked manageable for me. If you can suggest a more suitable stator for my application, or a stator that would not need to be rewound I would welcome any suggestions. Thanks for your reply.

Jeff

Flux

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Re: Automotive alternator to PM alternator
« Reply #3 on: April 23, 2014, 11:11:59 AM »
The original rotor would have been a claw type with 6 claws each side and a wound field coil between them.

If you had the original claws you could have fitted a ring magnet in place of the wound field. As you don't have the claws and they are difficult to make then you can build up a rotor with neo magnets stuck on.

As the original winding will be no use you have the option of keeping to 12 pole and copying the original winding with more turns or you can make it 4 or 6 pole, possibly the 6 pole may be easier to find magnets for.

The stator has to be wound for the same number of poles as the rotor so you can't copy the original winding if you use other than 12 poles.

A typical car alternator with full wound field generates 12v at something over 1000 rpm. On the basis that your permanent magnet may not equal the full wound field you are looking at wire about 1/4 the csa of the original with about 4 times the turns if you copy the original 12 pole.

For 4 or 6 pole the wire size will be similar and the number of total turns per phase similar but you should do a single coil test winding if your speed and volts are critical.

For hand winding I suspect that individual coils will be easier than the serpentine winding which more suits machine winding.

With decent magnets the 25w should be no problem.

Flux

rustkolector

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Re: Automotive alternator to PM alternator
« Reply #4 on: April 28, 2014, 10:05:39 PM »
Flux, Thanks. That is all good information that I will keep in mind. The stator I have presently measures 3.935" OD and is the ideal size. It is a small tractor alternator stator, I believe made by Denso. For now, I think I am going to look for the same, or similar sized stator in a 28v winding. I am assuming the output would be somewhat higher than a 12v stator. Then I'll build a rotor and experiment with some good neo magnets to see what output vs RPM I can get. I am not optimistic that it will give me a usable 12v output, but it may be enough for my purposes. If not, then I will attempt a rewind. If so, I will definitely be back to this forum. Thanks again.

Jeff

bob g

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Re: Automotive alternator to PM alternator
« Reply #5 on: April 28, 2014, 11:01:03 PM »
fwiw

if you go as Flux suggests, that is using the clawpole rotor and replacing the field coil
with a ring magnet,

i would suggest replacing the shaft with a stainless steel shaft
reason being the original steel shaft will shunt away a significant amount of the ring magnets magnetism which lowers the available magnetism to interact with the stator.

again for what is it worth

bob g
research and development of a S195 changfa based trigenerator, modified
large frame automotive alternators for high output/high efficiency project X alternator for 24, 48 and higher voltages, and related cogen components.
www.microcogen.info and a SOMRAD member

rustkolector

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Re: Automotive alternator to PM alternator
« Reply #6 on: June 10, 2014, 08:54:09 PM »
Flux,
I'm still working on this project. I have recently found a suitable automotive alternator stator with about a 3.7" OD which fits my size requirement. I have decided to try my hand at rewinding the stator. Following your recommendation, it will be a 3 phase Wye 18 coil with 6 coils per phase. The stator has 36 slots  and I intend to use 12 magnets on an iron rotor. However if equally spaced, the center of each magnet will line up with a stator tooth, and I suspect will cause significant cogging if they are too narrow. Relative to the width of the stator teeth and slots, how wide should the pole magnets be to minimize cogging? Should skewing be used if the ideal width magnet is not available? Thanks.

Jeff

hiker

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Re: Automotive alternator to PM alternator
« Reply #7 on: June 11, 2014, 12:54:41 AM »
heres a truck alt i did a few years back..easly put out 150  watts powered by a hand drill..thats all the drill could really handle..  wired three phase..two sets of 9 coils..12 mags..used the field coil wire to make the first set of nine coils..
then just some fine plastic coated wire  for the secound set of nine.. total of 6 wires out..wired in star.. used some cheap neo mags from home depot-$3.89 for a 3 pack..they jumped up to 11 dollares for a 3 pack a few years back..now their back down.. but not at all the stores ??  as far as cogging--wasnt really a issue with the small mags i used..you could feel a slight drag when turned by hand as the mags went over the lams... good luck with yours.....
WILD in ALASKA

Flux

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Re: Automotive alternator to PM alternator
« Reply #8 on: June 11, 2014, 01:51:59 AM »
Yes skewing the magnets will reduce the cog, the alternative approach is to use non uniform spacing without skew.If you space all the magnets too close so you end up with one large gap that can work just as well, you don't get all the edges lining up and pulling at the same time.

Either method makes a fair improvement but if you get it exact you can remove cog completely. I have never been able to calculate the skew or spacing for perfect results but skewing one tooth pitch is the theoretical starting point and is usually good enough. I have only got perfect results by experiment and it is very critical.

Having said that, as long as you remove the worst of the cog it should be ok. Extreme cog will prevent starting but if it is not bad it will rock off and start up. I have found the iron loss drag to be just as bad as cog, it will turn slowly but not pick up speed until there is enough wind to get the prop out of stall enough to overcome the iron loss. Not much you can do about this so absolute perfection in removing cog is hardly worthwhile.

Flux

rustkolector

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Re: Automotive alternator to PM alternator
« Reply #9 on: July 05, 2014, 09:11:21 AM »
I have found a smaller sized (and better suited) auto alternator to use for this project. It has a 3.7 OD 36 slot stator. Unlike the previous wave wound stator I found, this one uses 12 overlapping coils per phase. It was suggested to use a 6 coil per phase winding with 12 alternating magnets for a 36 slot stator. For my use, I assume there is no real advantage to the 12 overlapping coil winding since the overlapping coils limit the winding turns that can be installed and hence the max voltage potential of the winding. My questions are:

What is the advantage of the 12 overlapping coil winding vs 6 non-overlapping coil winding?

What is the coil winding direction vs magnet orientation on the 12 coil stator?

I am confused with the beginning and ending phase wire locations. On both my stators, two ending wires are to the left and one is to the right of the common wye connection. Is there any good winding illustration that would explain these wire ending locations to this dummy?

Again, the goal here is to produce maximum voltage at 400-500 rpm. The output goal is approximately 25-30 watts at 12 volt regulated DC. (or 6 volt regulated as an option).  Thanks again for any assistance.

Jeff

Smithson

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Re: Automotive alternator to PM alternator
« Reply #10 on: July 05, 2014, 08:39:53 PM »
Hi:  One way to rewire the stator is to wind alternating direction coils.  Wind coil 1, phase 1 from slot 1 to slot 4 cw, then wind coil 2 phase 1 ccw from slot 4 (the same slot that coil 1 ended in) to slot 7, continuing all the way around the stator until the last coil ends in the same slot ( 1) that coil one started in.  As you go around you are skipping two slots for each coil.  If you use wooden dowels in slots 2 and 3, 5 and 6, etc it's helps you remember what you are doing and makes the coils uniform.  Wind phase 2 in the same way slots 2 to 5, etc skipping 2 slots and ending up in slot 2.  Then wind phase 3 in the only remaining slots.  Remember to alternate the coil winding direction.  Cw, ccw etc.
Also as you finish each phase use you thumbs to push the coil ends to the outside to get all the coils in.  But still leave room to get the case on.
Hook all 3 starts together and use the 3  finish wires as your 3 phase output.  But if when measuring the open output one phase is lower than the other two hook the starts of 1 and 3 and the finish of phase two as your star (wye) connection.

Higher frequency is better for any alternator.  Alternate the 12 magnets north south, north south etc.
Arch. Ps the magnets size should fit in the hole of a coil.  For example it should be smaller than the distance between slots 1 and 3 by half a slot.
« Last Edit: July 05, 2014, 08:47:52 PM by Smithson »

Flux

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Re: Automotive alternator to PM alternator
« Reply #11 on: July 08, 2014, 10:31:21 AM »
It really matters very little whether you use the full 12 coil per phase or use the equivalent 6 coil virtual pole arrangement.

The 12 coil winding will have half the number of turns per coil but the total number of turns per phase will be similar and will take up a similar winding space. Car alternators are a complete compromise and ease of machine winding and effective cooling come into the design. With a lot of care you may be able to get more turns in with a careful hand winding but it does require practice.

The 6 coil design will have all coils wound the same way and connected start to finish. The 12 coil version will have alternate coils reversed or flipped. If all wound all the same then they go  start- start, finish - finish etc which effectively reverses the coil polarity.

Regarding the star point, you have 3 windings displaced 120 deg electrically and the start end of each phase connected to the star point. In real life it is easier to star adjacent phases but these have a 60 deg displacement. To get the correct phasing at the output you have 3 ends starred but A and C will have the start but B phase will have the finish at the star point. This will be what you have found.

Smithson covers this point and if you end up with unbalanced line voltages it will be because you have used the 60 deg ( 6 phase) layout without reversing the B phase.

Flux

hiker

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Re: Automotive alternator to PM alternator
« Reply #12 on: July 08, 2014, 11:32:34 AM »
so its 12 pole ...should be able to hit 25-30 watt. easy with just one single phase..
just wind 12 coils single phase..with one continouse wire..first coil clockwise secound counter clockwise and so on..
leave two slots empty in the middle of each coil..with legs right next to each other[no empty slot]..
put some little round dowels in each empty slot that stick up above aways to help hold the wire in as you wind the coils..remove dowles when done..then stick some kind of thin matrial down each leg that has wire in it.. to hold the wire in ..i belive i found some thin wooden strips at a hobby store that worked great.. with a little trimming..
somthing like popsickle sticks..or anything that works..plastic strips ?
by leaving those two slots open you can really cram a lot more wire down each leg ..more turns equal higher votage.
WILD in ALASKA

hiker

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Re: Automotive alternator to PM alternator
« Reply #13 on: July 08, 2014, 11:50:44 AM »
dam after looking at my files..i found i could only get nine coils in that space..with two empty slots..
heres one i did three phase..all coils wound same dir. wire three coils each phase..then out to rects..  still should be able to hit your 25-30 watts easy..with just nine coils 3 phase...
WILD in ALASKA

rustkolector

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Re: Automotive alternator to PM alternator
« Reply #14 on: July 13, 2014, 12:30:19 PM »
Smithson, Flux, and Hiker,
I have been away for a bit. Thanks for all your help. My questions are all pretty much answered and thanks to you guys, I believe I have it figured out now. Can't thank you enough. The power end of this little project is about half done. I think I will take a break from machining and get started on the generator end now.

Jeff

hiker

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Re: Automotive alternator to PM alternator
« Reply #15 on: July 13, 2014, 08:59:29 PM »
wire those nine coils  star...will work just fine with 12 mags [poles]
if you want you could even fill in the other slots [another set of nine]..just make sure you leave enough room to fill them in..then you would have six wires output..if you wire each set of nine in star..
break those nine coils into three sets of 3 coils-same with other set of 9 coils..hope this dosent confuse you to much.
oh yeah...rectifie each set of nine..then parelle the output of both sets...
WILD in ALASKA

rustkolector

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Re: Automotive alternator to PM alternator
« Reply #16 on: July 29, 2014, 10:19:08 AM »
OK, I am ready to build the rotor to test the original alternator winding. Couple more questions. My slot width is .076" and tooth width is .166". Each coil spans 4 slots. Stator inside diameter is 2.75".  I am skewing the magnets approx. 11.5 degrees according to Peter Dingemans nice cogging reduction techniques writeup. Zubbly shows skewed magnets residing completely within the coil winding in one of his illustrations. I was planning on using one .25" x .25" x 1.0" N52 neo bar magnet per pole. Using two of these magnets overlaps the inside of the coils about 15-20%. One magnet has room to spare. Most projects I see here use multiple round disk magnets per pole and all of the skewing techniques seem to be based on using round magnets. Relative to potential output and anti-cogging skewing, does one magnet shape perform better than the other? What would be the best magnet size and shape?

Jeff

joestue

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Re: Automotive alternator to PM alternator
« Reply #17 on: July 29, 2014, 11:33:29 AM »
i would try 1/8th inch thick magnets.

1 inch wide magnets can get you an 8 pole machine if you have one magnet per pole.

one magnet per pair of poles means you only need 6 magnets for a 12 pole machine and there is nothing wrong with that.
even better would be to try and find some .75 inch wide magnets.

rustkolector

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Re: Automotive alternator to PM alternator
« Reply #18 on: July 29, 2014, 06:35:56 PM »
Joestue,
The 36 slot stator will be wound 3 phase, 6 pole, wye. The rotor will be 12 pole. The bar magnets I am looking at are 1" long to match the stator length with a 1/4" square cross section. Skewed 11.5 degrees, and using one magnet per pole, this skewed magnet will fit within the winding coil inner diameter like Zubbly shows in his illustration. Question is, what size magnet and magnet configuration relative to the winding coil inside diameter, gives the best voltage output. Also keeping in mind that the magnet(s) will be skewed by the helix method to reduce cogging. I am unsure just how skewing affects the magnetic strength if it is larger or smaller than the pole coil ID. 

Jeff

Flux

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Re: Automotive alternator to PM alternator
« Reply #19 on: July 30, 2014, 12:44:46 AM »
To use a 12 pole rotor, the stator also needs to be wound 12 pole.

You can do this with 12 coils per phase (36 total) or you can do it with 6 coils per phase as a virtual pole winding, is that what you were meaning by 6 pole. If you are following Zubbly's ideas it will likely be the 6 coil per phase (18 coil ) layout.

Within moderation the skew makes little difference to the voltage. If the magnets are longer than the core then base your skew on the core length. I seem to remember this is engine driven so cog may not be an issue at all, unlike wind where it affects start up.

Flux


joestue

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Re: Automotive alternator to PM alternator
« Reply #20 on: July 30, 2014, 08:11:40 AM »
Try 1 bar magnet per pole, so that's 12 magnets, 1/8th inch thick, 1 inch long, and half inch wide. skew it as much as what you need to get the cogging torque out.
6 coils *can* equal 12 poles so I understand what you're saying.

79 cents each here http://www.magnet4less.com/product_info.php?cPath=5&products_id=36&osCsid=fe8821d2c2de9c447a1f5490242d89d1

i would venture to say a 1 by .25 by .25 magnet is just about useless... yes if you can skiew it so most of the magnetic flux is evenly dropped across 2 stator teeth.. it might work but you would need a large air gap.

Flux

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Re: Automotive alternator to PM alternator
« Reply #21 on: July 30, 2014, 08:57:25 AM »
I haven't drawn this out but based on 2.75" diameter this gives a circumference of 8.64" Assuming pole arc is 2/3 of pole pitch that gives a pole arc of 5.75". Divided by 12 gives .479".

I am in agreement with joestue that the 1/2" wide magnets would be much better but I don't think you will be struggling for output so the 1/4" magnets may be ok.

Flux

hiker

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Re: Automotive alternator to PM alternator
« Reply #22 on: July 30, 2014, 11:33:55 AM »
if its going on a engine..why worry about cogging..might use a small amount of skew..the less skew the higher the output..
car alts are not skewed !
WILD in ALASKA

Smithson

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Re: Automotive alternator to PM alternator
« Reply #23 on: July 30, 2014, 08:01:34 PM »
Hi:  If you have  found a new alternator does this one have the rotor with it?  Are you going to mount the magnets to the claws or make a whole new rotor?  To me it seems like a whole lot of trouble.  Does this rotor have 14 claws (poles) like some GM Delco alternators.  Someone mentioned that  automotive alternators were hard to turn down.  I think Ed Lents on Windstuffnow.com.

I think Flux made the best  suggestion when he said to use a ring magnet where the field is wound.  Arch

rustkolector

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Re: Automotive alternator to PM alternator
« Reply #24 on: July 31, 2014, 10:53:38 AM »
Yes, this latest alternator is complete with a 12 claw wound rotor. I will be making a new rotor. The reason is, this is not a wind turbine alternator. The final alternator, if it works to expectations, will go behind a 1/8th scale model internal combustion engine patterned after a 1910 vintage 2 cylinder gas engine. Model engine building is my hobby. The only thing to be reused with be the auto alternator stator which will be rewound for higher voltage. The claw type rotor would not look right on the model. The alternator will be built to look like a vintage DC generator or AC alternator of the 1910 period.

I was going to use .25" x .25" x 1.0" bar magnets for the rotor, but I think I will go with the Joestue's recommended .50" wide bar magnet. Skewed 10-11 degrees the .50"magnets will just fit. The thinner .50" wide magnets have the same gauss rating and fit the inside of the coil better. Two .25" wide magnets side by side would be too difficult to mess with, but I find a lot of other uses for them.  I am assuming here that the gauss rating is the best way to determine magnetic flux strength for power generation. I am primarily after voltage as my load requirement will only be 25-50 watts, if that. If you have any other magnet recommendations for max field flux I am still open. Haven't ordered the magnets yet.

My skewing and cogging concerns are for noise. The first PM alternator I built has a distinct and audible "hum" that I am hoping to reduce in this version. 

Jeff

Flux

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Re: Automotive alternator to PM alternator
« Reply #25 on: July 31, 2014, 11:03:12 AM »
Yes it is common for alternators and even dynamos to whine or hum, dynamos were often skewed to keep this within reason.

A really badly cogging car alternator conversion could be quite noisy, Nominal skewing to take the worst of it out should

Flux

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Re: Automotive alternator to PM alternator
« Reply #26 on: July 31, 2014, 11:09:48 AM »
Hit a wrong key somewhere and posted before I finished, I suspect there is an edit thing somewhere if I could only find it.

Meant to say , Nominal skewing to take the worst out should remove the worst of the noise, without having to do an exact skew that is more needed for wind.

I suggest you make the rotor then do a test coil to get the voltage you want, perhaps winding one phase with a few turns per coil.

Flux