Posted by Don Young on June 13, 2009, 9:39 pm
>>
>> >>
>> >>
>> >>
>> >>
>> >>
>> >>
>> >>
>> >> >> > Anyone happen to know if the poles on a single phase alternator
>> >> >> > field
>> >> > coil
>> >> >> > (rotor) are opposite such as they are on a 3-phase alternator? I
>> >> > applied
>> >> >> > *some* voltage to it but don't know how much is OK and don't want
> to
>> >> > burn
>> >> >> > it
>> >> >> > out but it seems, so far, that the poles are the same on both
> sides
>> >> > (i.e.
>> >> >> > N
>> >> >> > and N and not N on one side and S on the other). Also, would the
>> >> >> > field
>> >> >> > coil
>> >> >> > be getting 120 volts on a 120/240 volt generator? I have this
> idea
>> >> >> > but
>> >> >> > before I waste my time I need to find out why it won't work ;-)
>> >>
>> >> >> There should be one N and one S if it only has two poles. If more
>> >> >> than
>> >> >> that, it should alternate N, S, N, S and so on. The voltage
>> >> >> applied
>> >> >> to
>> >> > the
>> >> >> field winding is seldom anywhere near the same as the output
>> >> >> voltage
>> >> >> and
>> >> >> it's always DC. (although once in a while the rectifier is mounted
>> >> >> right
>> >> > on
>> >> >> the rotor so you can apply AC to the rotor's slip rings).
>> >>
>> >> >> Typical car alternator uses DC on the field winding, applied via
>> >> >> two
>> >> >> slip
>> >> >> rings. Although it is only one coil, the metal pieces on each side
>> >> >> have
>> >> >> inter-woven fingers so that alternating 'fingers' are opposite
>> >> >> polarity
>> >> > (N,
>> >> >> S, N, S as I mentioned above). One alternator has as many as 28
>> >> >> 'fingers'
>> >> >> so that's 14 N poles and 14 S poles, interwoven.
>> >>
>> >> >> Surprisingly, a rotor for a three-phase machine and a single-phase
>> >> >> machine
>> >> >> have the same number of poles and winding. The only difference
>> >> >> between
>> >> >> three-phase and single-phase is in the stator (armature) winding,
> not
>> >> >> the
>> >> >> rotor (field) winding.
>> >>
>> >> >> daestrom
>> >>
>> >> > What I have in mind is to use a field coil from a single-phase
>> >> > alternator
>> >> > to
>> >> > produce three-phase (or more) power by winding three coils (or six
>> >> > perhaps)
>> >> > for a new stator. This particular field coil has a tapered mount so
> it
>> >> > would be direct-drive. It has slip rings so I could apply the
>> >> > excitation
>> >> > current directly and control it for the desired output. That all
>> >> > depends
>> >> > upon whether or not the coils are still OK. The generator I saved
>> >> > it
>> >> > from
>> >> > had a melted stator but the field coils appear to be OK but I'm not
>> >> > sure
>> >> > if
>> >> > it's one coil wound on two poles or two seperate coils.
>> >>
>> >> It may be either. The important question is just how many magnetic
> poles
>> >> it
>> >> has. If it has one N and one S, it is a two-pole rotor. Two N's and
> two
>> >> S's means four pole and so on. Call this number N. It must be an
>> >> even
>> >> number or you've got a consequent pole issue and I really, REALLY
>> >> doubt
>> >> that
>> >> for an alternator rotor.
>> >>
>> >> If you want to wind a three-phase stator, you need 3*N number of coil
>> >> groups
>> >> (we call them pole-phase groups). Then the next thing to do is then
>> >> count
>> >> the slots in your stator (call it S) and hope that it is divisible by
>> >> 3*N.
>> >> If it is evenly divisible by 3*N then you are almost ready. You need
> to
>> >> figure out how wide to make your coils (the coil pitch).
>> >>
>> >> Commercial machines we would put all the coils in with the leads
>> >> extending
>> >> out one end. The first few you leave one side of the coils 'up' out
>> >> of
>> >> the
>> >> slot until you work your way around the stator. Put one side of each
>> >> coil
>> >> in the 'bottom' of a slot and move on. After you've put in one coil
>> >> pitch
>> >> worth, you can put one side in the bottom of the next slow and the
> other
>> >> side in the 'top' of the first slot you started with, on top of the
> first
>> >> coil you laid.
>> >>
>> >> After you have them all installed and wedged suitably tight in the
> slots,
>> >> you figure out how many coils connect together to form one phase
>> >> group.
>> >> If
>> >> you have a nice even stator, it comes out to S/(3*N). So a 72 slot
>> >> stator,
>> >> for a four pole machine, you have 72/(3*4) = 6 coils that you connect
>> >> together into one phase group. When you're done with that step you
>> >> should
>> >> have 3*N (in my example 12) phase groups.
>> >>
>> >> Count off by 3 to see which ones are the same phase. If you imagine
> the
>> >> rotor in the middle of the stator and one pole directly over one phase
>> >> group, the other poles of the rotor will be directly over the other
> phase
>> >> groups of the same phase.
>> >>
>> >> Connecting the individual phase groups together into each of the
>> >> phases
>> >> is
>> >> not hard, but it's much easier to show with a diagram than to explain
> in
>> >> words. But basically you can connect them either in series (more
>> >> voltage)
>> >> or parallel (more available current).
>> >>
>> >> BUt considering this is a seat-of-the-pants design, you might be best
> off
>> >> by
>> >> insulating the leads and assembling it first one time, spin it up and
> see
>> >> how much voltage you get from one phase group. Then you can get an
> idea
>> >> what it's capable of.
>> >>
>> >> If you want more current per coil but don't want to buy wire that is
>> >> double
>> >> in size, you can use an old trick we used of winding your coils
>> >> 'two-in-hand'. Simply use two strands of the same size wire and wind
>> >> both
>> >> strands at the same time making half as many turns. You'll get half
> the
>> >> voltage but by soldering the two strands together at each end you get
>> >> double
>> >> the cross-section.
>> >>
>> >> > Like I said I tried
>> >> > applying some DC voltage and didn't get any definate answers but I
> did
>> >> > get
>> >> > quite a zap when I disconnected the DC source so something is still
>> >> > working.
>> >>
>> >> Big coil around iron is a great inductor :-)
>> >>
>> >> > All I would need to do is to make a brush holder, mount the
> non-engine
>> >> > end
>> >> > in a bearing, and one way or another position the stator coils
>> >> > around
>> >> > it.
>> >> > And rectify it, of course. Since there is some residual magnetism
>> >> > in
>> >> > the
>> >> > field coil I think it will self-excite just like my Delco car
>> >> > alternator
>> >> > does. But I don't know how much DC voltage it will need to excite
> and
>> >> > end
>> >> > up producing, say, 80 volts at 3600 rpm, but I think that will be
>> >> > controlled by the number of turns on the stator coils.
>> >>
>> >> The first thing you want to figure out is what is the max DC current
> you
>> >> can
>> >> push through the rotor. Take a look at the wire size to get an idea.
>> >> Then
>> >> start out with your trials using only about 25% of what you think the
> max
>> >> is. This would be about the 'no-load field amps' operating point.
>> >>
>> >> As the load is applied to an AC alternator, the DC field current has
>> >> to
>> >> be
>> >> increased quite a bit to keep the voltage constant.
>> >>
>> >> > To answer Jim
>> >> > Wilkins the coil was originally for a single-phase, 120/240 3600 rpm
>> >> > generator but I would be running it at 3600 maximum and slowing down
>> >> > the
>> >> > engine to control my output voltage (and adjusting the field current
> as
>> >> > needed too). Before I get started I just want to be pretty sure of
>> >> > what I
>> >> > have to work with. It sounds like, from what everyone said, that
>> >> > the
>> >> > pole
>> >> > should be correct for my purposes. :-D
>> >>
>> >> Okay, if it originally was 3600 rpm for 60Hz, then it is definitely a
>> >> 2-pole
>> >> rotor. So for three-phase you'll need six pole-phase groups.
>> >>
>> >> daestrom
>> >
>> > It's fifty years since they made any sort of electrical machine to
>> > thes principles. They were old fashioned when I was an apprentice. At
>> > one time you could get them rewound, there were little motor rewind
>> > shops in every town. Not any more. the stator is put in an autoclave,
>> > a vacuum puled and epoxy resin srayed on. Then the vacuum is released
>> > and it is baked. Stands the heat, mechanical forces and vibration
>> > better than rewindable types.
>>
>> Don't understand your point. You still have to wind the thing in the
> first
>> place. How you bake it and what type of insulation you use after the
> coils
>> are in the slots is a different matter all together.
>>
>> OP wants to experiment with winding his own alternator. Not really cost
>> effective for a rewind shop, but if he wants to experiment, he has to
>> know
>> how to wind and connect the coils.
>>
>> daestrom
>>
> So far, with 12 volts attached to the rotor (field core) I have not been
> able to establish the direction of the poles or verify that it is indeed
> an
> electromagnet. I tried placing a permanant magnet on each pole and
> applying
> voltage to the slip rings and get nothing. It seem like both poles are
> either N or S based upon the attraction/repulsion of the magnet. I guess
> I
> need more volts. I think my digital multimeter is not working.
> I found some specific information on how to rewind a Delco alternator
> stator
> but the maximum wire size that will fit in there is only about #25 and it
> is
> my understanding that I will then have twice the voltage at a given rpm
> but
> I'll end up with only half the current with the small wire size. My
> making
> my own stator for the single phase rotor that I have on hand I can use
> more
> turns of bigger wire. But I'm not going to build anything until I can be
> pretty sure the field coils even work ;-)
> My ultimate goal is to come up with some kind of direct-drive alternator
> to
> charge my 48 volt battery bank using a small engine. My Delco 10SI
> alternator would be adequate with the stock stator if only I could find a
> way to drive it reliably. I figure direct-drive=no more belt problems.
> If
> I run it past about 25-30 amps the belt becomes a problem but I have
> managed
> to get about 60 amps at over 50 volts out of the thing without frying the
> diodes so the alternator is good. Maybe I should try a chain drive again
> with some better couplings.
You do not get any like pole repulsion if one magnet is a lot stronger than
the other and I think that is why you are having trouble identifying the
poles. Connect something like 1.5 volts to the slip rings and verify with a
piece of iron that the poles are magnetized. Then try another magnet or
compass to check the direction of the poles. There will probably be enough
residual magnetism to check the poles with a compass without any current at
all. Of course, if you reverse the field current you also reverse the poles.
I am no expert but the few alternator fields I have checked operated in the
12-24 volt range so it should not be necessary to apply more than 12V to get
the poles pretty strong. See if you get a little spark as you connect and
disconnect the leads.
Don Young
Posted by Ulysses on June 14, 2009, 10:44 am
> >
> >>
> >>
> >> >>
> >> >>
> >> >>
> >> >>
> >> >>
> >> >>
> >> >>
> >> >> >> > Anyone happen to know if the poles on a single phase alternator
> >> >> >> > field
> >> >> > coil
> >> >> >> > (rotor) are opposite such as they are on a 3-phase alternator?
I
> >> >> > applied
> >> >> >> > *some* voltage to it but don't know how much is OK and don't
want
> > to
> >> >> > burn
> >> >> >> > it
> >> >> >> > out but it seems, so far, that the poles are the same on both
> > sides
> >> >> > (i.e.
> >> >> >> > N
> >> >> >> > and N and not N on one side and S on the other). Also, would
the
> >> >> >> > field
> >> >> >> > coil
> >> >> >> > be getting 120 volts on a 120/240 volt generator? I have this
> > idea
> >> >> >> > but
> >> >> >> > before I waste my time I need to find out why it won't work ;-)
> >> >>
> >> >> >> There should be one N and one S if it only has two poles. If
more
> >> >> >> than
> >> >> >> that, it should alternate N, S, N, S and so on. The voltage
> >> >> >> applied
> >> >> >> to
> >> >> > the
> >> >> >> field winding is seldom anywhere near the same as the output
> >> >> >> voltage
> >> >> >> and
> >> >> >> it's always DC. (although once in a while the rectifier is
mounted
> >> >> >> right
> >> >> > on
> >> >> >> the rotor so you can apply AC to the rotor's slip rings).
> >> >>
> >> >> >> Typical car alternator uses DC on the field winding, applied via
> >> >> >> two
> >> >> >> slip
> >> >> >> rings. Although it is only one coil, the metal pieces on each
side
> >> >> >> have
> >> >> >> inter-woven fingers so that alternating 'fingers' are opposite
> >> >> >> polarity
> >> >> > (N,
> >> >> >> S, N, S as I mentioned above). One alternator has as many as 28
> >> >> >> 'fingers'
> >> >> >> so that's 14 N poles and 14 S poles, interwoven.
> >> >>
> >> >> >> Surprisingly, a rotor for a three-phase machine and a
single-phase
> >> >> >> machine
> >> >> >> have the same number of poles and winding. The only difference
> >> >> >> between
> >> >> >> three-phase and single-phase is in the stator (armature) winding,
> > not
> >> >> >> the
> >> >> >> rotor (field) winding.
> >> >>
> >> >> >> daestrom
> >> >>
> >> >> > What I have in mind is to use a field coil from a single-phase
> >> >> > alternator
> >> >> > to
> >> >> > produce three-phase (or more) power by winding three coils (or six
> >> >> > perhaps)
> >> >> > for a new stator. This particular field coil has a tapered mount
so
> > it
> >> >> > would be direct-drive. It has slip rings so I could apply the
> >> >> > excitation
> >> >> > current directly and control it for the desired output. That all
> >> >> > depends
> >> >> > upon whether or not the coils are still OK. The generator I saved
> >> >> > it
> >> >> > from
> >> >> > had a melted stator but the field coils appear to be OK but I'm
not
> >> >> > sure
> >> >> > if
> >> >> > it's one coil wound on two poles or two seperate coils.
> >> >>
> >> >> It may be either. The important question is just how many magnetic
> > poles
> >> >> it
> >> >> has. If it has one N and one S, it is a two-pole rotor. Two N's
and
> > two
> >> >> S's means four pole and so on. Call this number N. It must be an
> >> >> even
> >> >> number or you've got a consequent pole issue and I really, REALLY
> >> >> doubt
> >> >> that
> >> >> for an alternator rotor.
> >> >>
> >> >> If you want to wind a three-phase stator, you need 3*N number of
coil
> >> >> groups
> >> >> (we call them pole-phase groups). Then the next thing to do is then
> >> >> count
> >> >> the slots in your stator (call it S) and hope that it is divisible
by
> >> >> 3*N.
> >> >> If it is evenly divisible by 3*N then you are almost ready. You
need
> > to
> >> >> figure out how wide to make your coils (the coil pitch).
> >> >>
> >> >> Commercial machines we would put all the coils in with the leads
> >> >> extending
> >> >> out one end. The first few you leave one side of the coils 'up' out
> >> >> of
> >> >> the
> >> >> slot until you work your way around the stator. Put one side of
each
> >> >> coil
> >> >> in the 'bottom' of a slot and move on. After you've put in one coil
> >> >> pitch
> >> >> worth, you can put one side in the bottom of the next slow and the
> > other
> >> >> side in the 'top' of the first slot you started with, on top of the
> > first
> >> >> coil you laid.
> >> >>
> >> >> After you have them all installed and wedged suitably tight in the
> > slots,
> >> >> you figure out how many coils connect together to form one phase
> >> >> group.
> >> >> If
> >> >> you have a nice even stator, it comes out to S/(3*N). So a 72 slot
> >> >> stator,
> >> >> for a four pole machine, you have 72/(3*4) = 6 coils that you
connect
> >> >> together into one phase group. When you're done with that step you
> >> >> should
> >> >> have 3*N (in my example 12) phase groups.
> >> >>
> >> >> Count off by 3 to see which ones are the same phase. If you imagine
> > the
> >> >> rotor in the middle of the stator and one pole directly over one
phase
> >> >> group, the other poles of the rotor will be directly over the other
> > phase
> >> >> groups of the same phase.
> >> >>
> >> >> Connecting the individual phase groups together into each of the
> >> >> phases
> >> >> is
> >> >> not hard, but it's much easier to show with a diagram than to
explain
> > in
> >> >> words. But basically you can connect them either in series (more
> >> >> voltage)
> >> >> or parallel (more available current).
> >> >>
> >> >> BUt considering this is a seat-of-the-pants design, you might be
best
> > off
> >> >> by
> >> >> insulating the leads and assembling it first one time, spin it up
and
> > see
> >> >> how much voltage you get from one phase group. Then you can get an
> > idea
> >> >> what it's capable of.
> >> >>
> >> >> If you want more current per coil but don't want to buy wire that is
> >> >> double
> >> >> in size, you can use an old trick we used of winding your coils
> >> >> 'two-in-hand'. Simply use two strands of the same size wire and
wind
> >> >> both
> >> >> strands at the same time making half as many turns. You'll get half
> > the
> >> >> voltage but by soldering the two strands together at each end you
get
> >> >> double
> >> >> the cross-section.
> >> >>
> >> >> > Like I said I tried
> >> >> > applying some DC voltage and didn't get any definate answers but I
> > did
> >> >> > get
> >> >> > quite a zap when I disconnected the DC source so something is
still
> >> >> > working.
> >> >>
> >> >> Big coil around iron is a great inductor :-)
> >> >>
> >> >> > All I would need to do is to make a brush holder, mount the
> > non-engine
> >> >> > end
> >> >> > in a bearing, and one way or another position the stator coils
> >> >> > around
> >> >> > it.
> >> >> > And rectify it, of course. Since there is some residual magnetism
> >> >> > in
> >> >> > the
> >> >> > field coil I think it will self-excite just like my Delco car
> >> >> > alternator
> >> >> > does. But I don't know how much DC voltage it will need to excite
> > and
> >> >> > end
> >> >> > up producing, say, 80 volts at 3600 rpm, but I think that will be
> >> >> > controlled by the number of turns on the stator coils.
> >> >>
> >> >> The first thing you want to figure out is what is the max DC current
> > you
> >> >> can
> >> >> push through the rotor. Take a look at the wire size to get an
idea.
> >> >> Then
> >> >> start out with your trials using only about 25% of what you think
the
> > max
> >> >> is. This would be about the 'no-load field amps' operating point.
> >> >>
> >> >> As the load is applied to an AC alternator, the DC field current has
> >> >> to
> >> >> be
> >> >> increased quite a bit to keep the voltage constant.
> >> >>
> >> >> > To answer Jim
> >> >> > Wilkins the coil was originally for a single-phase, 120/240 3600
rpm
> >> >> > generator but I would be running it at 3600 maximum and slowing
down
> >> >> > the
> >> >> > engine to control my output voltage (and adjusting the field
current
> > as
> >> >> > needed too). Before I get started I just want to be pretty sure
of
> >> >> > what I
> >> >> > have to work with. It sounds like, from what everyone said, that
> >> >> > the
> >> >> > pole
> >> >> > should be correct for my purposes. :-D
> >> >>
> >> >> Okay, if it originally was 3600 rpm for 60Hz, then it is definitely
a
> >> >> 2-pole
> >> >> rotor. So for three-phase you'll need six pole-phase groups.
> >> >>
> >> >> daestrom
> >> >
> >> > It's fifty years since they made any sort of electrical machine to
> >> > thes principles. They were old fashioned when I was an apprentice.
At
> >> > one time you could get them rewound, there were little motor rewind
> >> > shops in every town. Not any more. the stator is put in an autoclave,
> >> > a vacuum puled and epoxy resin srayed on. Then the vacuum is
released
> >> > and it is baked. Stands the heat, mechanical forces and vibration
> >> > better than rewindable types.
> >>
> >> Don't understand your point. You still have to wind the thing in the
> > first
> >> place. How you bake it and what type of insulation you use after the
> > coils
> >> are in the slots is a different matter all together.
> >>
> >> OP wants to experiment with winding his own alternator. Not really
cost
> >> effective for a rewind shop, but if he wants to experiment, he has to
> >> know
> >> how to wind and connect the coils.
> >>
> >> daestrom
> >>
> >
> > So far, with 12 volts attached to the rotor (field core) I have not been
> > able to establish the direction of the poles or verify that it is indeed
> > an
> > electromagnet. I tried placing a permanant magnet on each pole and
> > applying
> > voltage to the slip rings and get nothing. It seem like both poles are
> > either N or S based upon the attraction/repulsion of the magnet. I
guess
> > I
> > need more volts. I think my digital multimeter is not working.
> >
> > I found some specific information on how to rewind a Delco alternator
> > stator
> > but the maximum wire size that will fit in there is only about #25 and
it
> > is
> > my understanding that I will then have twice the voltage at a given rpm
> > but
> > I'll end up with only half the current with the small wire size. My
> > making
> > my own stator for the single phase rotor that I have on hand I can use
> > more
> > turns of bigger wire. But I'm not going to build anything until I can
be
> > pretty sure the field coils even work ;-)
> >
> > My ultimate goal is to come up with some kind of direct-drive alternator
> > to
> > charge my 48 volt battery bank using a small engine. My Delco 10SI
> > alternator would be adequate with the stock stator if only I could find
a
> > way to drive it reliably. I figure direct-drive=no more belt problems.
> > If
> > I run it past about 25-30 amps the belt becomes a problem but I have
> > managed
> > to get about 60 amps at over 50 volts out of the thing without frying
the
> > diodes so the alternator is good. Maybe I should try a chain drive
again
> > with some better couplings.
> >
> >
> You do not get any like pole repulsion if one magnet is a lot stronger
than
> the other and I think that is why you are having trouble identifying the
> poles. Connect something like 1.5 volts to the slip rings and verify with
a
> piece of iron that the poles are magnetized. Then try another magnet or
> compass to check the direction of the poles. There will probably be enough
> residual magnetism to check the poles with a compass without any current
at
> all. Of course, if you reverse the field current you also reverse the
poles.
> I am no expert but the few alternator fields I have checked operated in
the
> 12-24 volt range so it should not be necessary to apply more than 12V to
get
> the poles pretty strong. See if you get a little spark as you connect and
> disconnect the leads.
> Don Young
A compass! Sheesh, my brain must be on another planet. Yes, I get a spark
when I disconnect.
Posted by Tim Jackson on June 14, 2009, 10:55 am
Ulysses wrote:
>>
>
> A compass! Sheesh, my brain must be on another planet. Yes, I get a spark
> when I disconnect.
>
>
Then it's creating a magnetic field. Where else did it get the energy
for the spark? That's all you need to know.
Tim
Posted by Jim Wilkins on June 8, 2009, 9:08 pm
> Anyone happen to know if the poles on a single phase alternator field coil
> (rotor) are opposite such as they are on a 3-phase alternator? I applied
> *some* voltage to it but don't know how much is OK and don't want to burn it
> out but it seems, so far, that the poles are the same on both sides (i.e. N
> and N and not N on one side and S on the other). Also, would the field coil
> be getting 120 volts on a 120/240 volt generator? I have this idea but
> before I waste my time I need to find out why it won't work ;-)
1800 or 3600 RPM?
jsw
XML site map
>> >>
>> >>
>> >>
>> >>
>> >>
>> >>
>> >>
>> >> >> > Anyone happen to know if the poles on a single phase alternator
>> >> >> > field
>> >> > coil
>> >> >> > (rotor) are opposite such as they are on a 3-phase alternator? I
>> >> > applied
>> >> >> > *some* voltage to it but don't know how much is OK and don't want
> to
>> >> > burn
>> >> >> > it
>> >> >> > out but it seems, so far, that the poles are the same on both
> sides
>> >> > (i.e.
>> >> >> > N
>> >> >> > and N and not N on one side and S on the other). Also, would the
>> >> >> > field
>> >> >> > coil
>> >> >> > be getting 120 volts on a 120/240 volt generator? I have this
> idea
>> >> >> > but
>> >> >> > before I waste my time I need to find out why it won't work ;-)
>> >>
>> >> >> There should be one N and one S if it only has two poles. If more
>> >> >> than
>> >> >> that, it should alternate N, S, N, S and so on. The voltage
>> >> >> applied
>> >> >> to
>> >> > the
>> >> >> field winding is seldom anywhere near the same as the output
>> >> >> voltage
>> >> >> and
>> >> >> it's always DC. (although once in a while the rectifier is mounted
>> >> >> right
>> >> > on
>> >> >> the rotor so you can apply AC to the rotor's slip rings).
>> >>
>> >> >> Typical car alternator uses DC on the field winding, applied via
>> >> >> two
>> >> >> slip
>> >> >> rings. Although it is only one coil, the metal pieces on each side
>> >> >> have
>> >> >> inter-woven fingers so that alternating 'fingers' are opposite
>> >> >> polarity
>> >> > (N,
>> >> >> S, N, S as I mentioned above). One alternator has as many as 28
>> >> >> 'fingers'
>> >> >> so that's 14 N poles and 14 S poles, interwoven.
>> >>
>> >> >> Surprisingly, a rotor for a three-phase machine and a single-phase
>> >> >> machine
>> >> >> have the same number of poles and winding. The only difference
>> >> >> between
>> >> >> three-phase and single-phase is in the stator (armature) winding,
> not
>> >> >> the
>> >> >> rotor (field) winding.
>> >>
>> >> >> daestrom
>> >>
>> >> > What I have in mind is to use a field coil from a single-phase
>> >> > alternator
>> >> > to
>> >> > produce three-phase (or more) power by winding three coils (or six
>> >> > perhaps)
>> >> > for a new stator. This particular field coil has a tapered mount so
> it
>> >> > would be direct-drive. It has slip rings so I could apply the
>> >> > excitation
>> >> > current directly and control it for the desired output. That all
>> >> > depends
>> >> > upon whether or not the coils are still OK. The generator I saved
>> >> > it
>> >> > from
>> >> > had a melted stator but the field coils appear to be OK but I'm not
>> >> > sure
>> >> > if
>> >> > it's one coil wound on two poles or two seperate coils.
>> >>
>> >> It may be either. The important question is just how many magnetic
> poles
>> >> it
>> >> has. If it has one N and one S, it is a two-pole rotor. Two N's and
> two
>> >> S's means four pole and so on. Call this number N. It must be an
>> >> even
>> >> number or you've got a consequent pole issue and I really, REALLY
>> >> doubt
>> >> that
>> >> for an alternator rotor.
>> >>
>> >> If you want to wind a three-phase stator, you need 3*N number of coil
>> >> groups
>> >> (we call them pole-phase groups). Then the next thing to do is then
>> >> count
>> >> the slots in your stator (call it S) and hope that it is divisible by
>> >> 3*N.
>> >> If it is evenly divisible by 3*N then you are almost ready. You need
> to
>> >> figure out how wide to make your coils (the coil pitch).
>> >>
>> >> Commercial machines we would put all the coils in with the leads
>> >> extending
>> >> out one end. The first few you leave one side of the coils 'up' out
>> >> of
>> >> the
>> >> slot until you work your way around the stator. Put one side of each
>> >> coil
>> >> in the 'bottom' of a slot and move on. After you've put in one coil
>> >> pitch
>> >> worth, you can put one side in the bottom of the next slow and the
> other
>> >> side in the 'top' of the first slot you started with, on top of the
> first
>> >> coil you laid.
>> >>
>> >> After you have them all installed and wedged suitably tight in the
> slots,
>> >> you figure out how many coils connect together to form one phase
>> >> group.
>> >> If
>> >> you have a nice even stator, it comes out to S/(3*N). So a 72 slot
>> >> stator,
>> >> for a four pole machine, you have 72/(3*4) = 6 coils that you connect
>> >> together into one phase group. When you're done with that step you
>> >> should
>> >> have 3*N (in my example 12) phase groups.
>> >>
>> >> Count off by 3 to see which ones are the same phase. If you imagine
> the
>> >> rotor in the middle of the stator and one pole directly over one phase
>> >> group, the other poles of the rotor will be directly over the other
> phase
>> >> groups of the same phase.
>> >>
>> >> Connecting the individual phase groups together into each of the
>> >> phases
>> >> is
>> >> not hard, but it's much easier to show with a diagram than to explain
> in
>> >> words. But basically you can connect them either in series (more
>> >> voltage)
>> >> or parallel (more available current).
>> >>
>> >> BUt considering this is a seat-of-the-pants design, you might be best
> off
>> >> by
>> >> insulating the leads and assembling it first one time, spin it up and
> see
>> >> how much voltage you get from one phase group. Then you can get an
> idea
>> >> what it's capable of.
>> >>
>> >> If you want more current per coil but don't want to buy wire that is
>> >> double
>> >> in size, you can use an old trick we used of winding your coils
>> >> 'two-in-hand'. Simply use two strands of the same size wire and wind
>> >> both
>> >> strands at the same time making half as many turns. You'll get half
> the
>> >> voltage but by soldering the two strands together at each end you get
>> >> double
>> >> the cross-section.
>> >>
>> >> > Like I said I tried
>> >> > applying some DC voltage and didn't get any definate answers but I
> did
>> >> > get
>> >> > quite a zap when I disconnected the DC source so something is still
>> >> > working.
>> >>
>> >> Big coil around iron is a great inductor :-)
>> >>
>> >> > All I would need to do is to make a brush holder, mount the
> non-engine
>> >> > end
>> >> > in a bearing, and one way or another position the stator coils
>> >> > around
>> >> > it.
>> >> > And rectify it, of course. Since there is some residual magnetism
>> >> > in
>> >> > the
>> >> > field coil I think it will self-excite just like my Delco car
>> >> > alternator
>> >> > does. But I don't know how much DC voltage it will need to excite
> and
>> >> > end
>> >> > up producing, say, 80 volts at 3600 rpm, but I think that will be
>> >> > controlled by the number of turns on the stator coils.
>> >>
>> >> The first thing you want to figure out is what is the max DC current
> you
>> >> can
>> >> push through the rotor. Take a look at the wire size to get an idea.
>> >> Then
>> >> start out with your trials using only about 25% of what you think the
> max
>> >> is. This would be about the 'no-load field amps' operating point.
>> >>
>> >> As the load is applied to an AC alternator, the DC field current has
>> >> to
>> >> be
>> >> increased quite a bit to keep the voltage constant.
>> >>
>> >> > To answer Jim
>> >> > Wilkins the coil was originally for a single-phase, 120/240 3600 rpm
>> >> > generator but I would be running it at 3600 maximum and slowing down
>> >> > the
>> >> > engine to control my output voltage (and adjusting the field current
> as
>> >> > needed too). Before I get started I just want to be pretty sure of
>> >> > what I
>> >> > have to work with. It sounds like, from what everyone said, that
>> >> > the
>> >> > pole
>> >> > should be correct for my purposes. :-D
>> >>
>> >> Okay, if it originally was 3600 rpm for 60Hz, then it is definitely a
>> >> 2-pole
>> >> rotor. So for three-phase you'll need six pole-phase groups.
>> >>
>> >> daestrom
>> >
>> > It's fifty years since they made any sort of electrical machine to
>> > thes principles. They were old fashioned when I was an apprentice. At
>> > one time you could get them rewound, there were little motor rewind
>> > shops in every town. Not any more. the stator is put in an autoclave,
>> > a vacuum puled and epoxy resin srayed on. Then the vacuum is released
>> > and it is baked. Stands the heat, mechanical forces and vibration
>> > better than rewindable types.
>>
>> Don't understand your point. You still have to wind the thing in the
> first
>> place. How you bake it and what type of insulation you use after the
> coils
>> are in the slots is a different matter all together.
>>
>> OP wants to experiment with winding his own alternator. Not really cost
>> effective for a rewind shop, but if he wants to experiment, he has to
>> know
>> how to wind and connect the coils.
>>
>> daestrom
>>
> So far, with 12 volts attached to the rotor (field core) I have not been
> able to establish the direction of the poles or verify that it is indeed
> an
> electromagnet. I tried placing a permanant magnet on each pole and
> applying
> voltage to the slip rings and get nothing. It seem like both poles are
> either N or S based upon the attraction/repulsion of the magnet. I guess
> I
> need more volts. I think my digital multimeter is not working.
> I found some specific information on how to rewind a Delco alternator
> stator
> but the maximum wire size that will fit in there is only about #25 and it
> is
> my understanding that I will then have twice the voltage at a given rpm
> but
> I'll end up with only half the current with the small wire size. My
> making
> my own stator for the single phase rotor that I have on hand I can use
> more
> turns of bigger wire. But I'm not going to build anything until I can be
> pretty sure the field coils even work ;-)
> My ultimate goal is to come up with some kind of direct-drive alternator
> to
> charge my 48 volt battery bank using a small engine. My Delco 10SI
> alternator would be adequate with the stock stator if only I could find a
> way to drive it reliably. I figure direct-drive=no more belt problems.
> If
> I run it past about 25-30 amps the belt becomes a problem but I have
> managed
> to get about 60 amps at over 50 volts out of the thing without frying the
> diodes so the alternator is good. Maybe I should try a chain drive again
> with some better couplings.