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Help, any gurus with alternator experience or knowledge?
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Rich Grise
electronics forum Guru


Joined: 24 Mar 2005
Posts: 3971

PostPosted: Sat Jul 08, 2006 5:28 pm    Post subject: Re: Help, any gurus with alternator experience or knowledge? Reply with quote

On Sat, 08 Jul 2006 10:23:58 -0400, default wrote:

Quote:
The quandary

I'm rewinding an automobile style alternator rotor. I want to use
some "Tefzel" insulated wire I have on hand, instead of magnet wire, I
have to special order. I wound a test coil and it fits and looks like
it will work.

My concern is that I have no idea how much current it takes to excite
the field and if the potting compound will survive the heat. The
Tefzel coil has the same DCR (5 ohms) as the original magnet wire, but
it is two gauges thinner (went from 22 AWG to 24 AWG). So I would
assume that it will dissipate more power to achieve the same ampere
turns in the field.

I can't test it very well without potting the coil and epoxying it
into the pole pieces, mounting it to the engine, etc. - and if it
turns out to be bad, it is a real b***h to pull apart and do over with
different wire.

Could you temporarily stick it in place with hot glue, just for testing
purposes? Hot glue should just be able to just peel right off between
tests and so on.

Good Luck!
Rich
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default
electronics forum Guru Wannabe


Joined: 03 May 2005
Posts: 175

PostPosted: Sat Jul 08, 2006 6:22 pm    Post subject: Re: Help, any gurus with alternator experience or knowledge? Reply with quote

On Sat, 08 Jul 2006 17:28:29 GMT, Rich Grise <richgrise@example.net>
wrote:

Quote:
Could you temporarily stick it in place with hot glue, just for testing
purposes? Hot glue should just be able to just peel right off between
tests and so on.

Probably long enough to start the engine and measure the current. I
was sort of hoping to get it to work without a test except perhaps a
coil alone - with a fixed dissipation.

Even the hot melt adhesive isn't a pleasant idea - run long enough to
get real data and I'd probably have the adhesive slinging off into the
stator or space between the rotor and stator - too risky to chance
that - adhesive being ground up would take out the brushes - unlike
auto alternators, this one has axial slip rings - any bit of epoxy etc
that comes off eats the brushes.


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jasen
electronics forum Guru Wannabe


Joined: 18 Jun 2006
Posts: 204

PostPosted: Sat Jul 08, 2006 11:04 pm    Post subject: Re: Help, any gurus with alternator experience or knowledge? Reply with quote

On 2006-07-08, default <none@nobody.net> wrote:
Quote:
The quandary

I'm rewinding an automobile style alternator rotor. I want to use
some "Tefzel" insulated wire I have on hand, instead of magnet wire, I
have to special order. I wound a test coil and it fits and looks like
it will work.

My concern is that I have no idea how much current it takes to excite
the field and if the potting compound will survive the heat. The
Tefzel coil has the same DCR (5 ohms) as the original magnet wire, but
it is two gauges thinner (went from 22 AWG to 24 AWG). So I would
assume that it will dissipate more power to achieve the same ampere
turns in the field.

I'm no guru but:

if the wire is thinner, but the coil the same dimension then you
theoretically have more turns - this means for the same current you have
more magnetic field.

if the coil is the same resistance as the old one then you will have the
same max current, and the same worst-case resistive heating as the old coil.

if the conductor is thinner but the insulated wire is thicker you have fewer
turns and threfore a less-effective altenator.

Quote:
I can't test it very well without potting the coil and epoxying it
into the pole pieces, mounting it to the engine, etc. - and if it
turns out to be bad, it is a real b***h to pull apart and do over with
different wire.

I figure the excitation power probably drops with speed of rotation -
alternator voltage output tracks speed so it should need less
excitation as speed increases - and the frequency goes up so inductive
reactance also increases(?)

the coil is fed DC, inductance doesn't enter into it.

Quote:
So, I'm thinking worst case is probably close to idle speed. To
further complicate that idea, excitation also has to track speed to
some extent, since it is derived from an extra set of diodes from the
rectifier - lower speed means less current/voltage to work with.

those diodes don't give a greatly elevated voltage, they're mainly to
provide a way to power the generator warning light.

Quote:
I tried powering the coil with a dc supply and pushed 2.5 amps through
it for 3 hours - no idea how hot the coil was, but the area between
the coil and pole pieces was 70 degrees F over ambient - around 150 F.
On the engine, it is driven directly off the crankshaft and probably
has an ambient of closer to 170 F - enclosed with no ventilation just
conduction and radiation cooling, and whatever air the rotor itself
stirs up.

your altenator doesn't vent slots or a fan behind the pulley?

Quote:
The whole story:


Plan A is to laboriously construct a new bobbin (1+ day of effort) and
order the right gauge wire and do the wind - epoxy routine, then serve
leads made of braid instead of wiring directly to the slip rings. A
lot of work.

maybe you can epoxy in screw terminals this time incase the leads fail.

maybe you could use old CD-Roms (the shiny can be removed using a metal pot
scourer) for the ends of the bobbin and a dowel (or threaded rod?) wrapped
in paper and cling-wrap for the centre?

hmm, if I could fix a 3-jaw chuck to the back of a sewing machine that'd
make a good tool start for winding magnet coils

--

Bye.
Jasen
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Vaughn
electronics forum beginner


Joined: 13 May 2005
Posts: 7

PostPosted: Sun Jul 09, 2006 2:10 am    Post subject: Re: Help, any gurus with alternator experience or knowledge? Reply with quote

jasen wrote:
Quote:
On 2006-07-08, default <none@nobody.net> wrote:

The quandary

I'm rewinding an automobile style alternator rotor. I want to use
some "Tefzel" insulated wire I have on hand, instead of magnet wire, I
have to special order. I wound a test coil and it fits and looks like
it will work.

My concern is that I have no idea how much current it takes to excite
the field and if the potting compound will survive the heat. The
Tefzel coil has the same DCR (5 ohms) as the original magnet wire, but
it is two gauges thinner (went from 22 AWG to 24 AWG). So I would
assume that it will dissipate more power to achieve the same ampere
turns in the field.


I'm no guru but:

if the wire is thinner, but the coil the same dimension then you
theoretically have more turns - this means for the same current you have
more magnetic field.

if the coil is the same resistance as the old one then you will have the
same max current, and the same worst-case resistive heating as the old coil.

if the conductor is thinner but the insulated wire is thicker you have fewer
turns and threfore a less-effective altenator.

Again no guru, but from what I remember of winding my own transformers,

more coil turns equals greater voltage, so this alternator MAY produce a
greater voltage for a given rotational speed.

Quote:

I can't test it very well without potting the coil and epoxying it
into the pole pieces, mounting it to the engine, etc. - and if it
turns out to be bad, it is a real b***h to pull apart and do over with
different wire.

I figure the excitation power probably drops with speed of rotation -
alternator voltage output tracks speed so it should need less
excitation as speed increases - and the frequency goes up so inductive
reactance also increases(?)


the coil is fed DC, inductance doesn't enter into it.


So, I'm thinking worst case is probably close to idle speed. To
further complicate that idea, excitation also has to track speed to
some extent, since it is derived from an extra set of diodes from the
rectifier - lower speed means less current/voltage to work with.


those diodes don't give a greatly elevated voltage, they're mainly to
provide a way to power the generator warning light.

But as the Alternator produces an Alternating current, don't they also
work as a Bridge Rectifier?

Like I said NO GURU, but its my pennys worth ;-)

Best of luck with the build

Vaughn
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Michael A. Terrell
electronics forum Guru


Joined: 24 Mar 2005
Posts: 2291

PostPosted: Sun Jul 09, 2006 3:21 am    Post subject: Re: Help, any gurus with alternator experience or knowledge? Reply with quote

Vaughn wrote:
Quote:

jasen wrote:
On 2006-07-08, default <none@nobody.net> wrote:

The quandary

I'm rewinding an automobile style alternator rotor. I want to use
some "Tefzel" insulated wire I have on hand, instead of magnet wire, I
have to special order. I wound a test coil and it fits and looks like
it will work.

My concern is that I have no idea how much current it takes to excite
the field and if the potting compound will survive the heat. The
Tefzel coil has the same DCR (5 ohms) as the original magnet wire, but
it is two gauges thinner (went from 22 AWG to 24 AWG). So I would
assume that it will dissipate more power to achieve the same ampere
turns in the field.


I'm no guru but:

if the wire is thinner, but the coil the same dimension then you
theoretically have more turns - this means for the same current you have
more magnetic field.

if the coil is the same resistance as the old one then you will have the
same max current, and the same worst-case resistive heating as the old coil.

if the conductor is thinner but the insulated wire is thicker you have fewer
turns and threfore a less-effective altenator.

Again no guru, but from what I remember of winding my own transformers,
more coil turns equals greater voltage, so this alternator MAY produce a
greater voltage for a given rotational speed.


I can't test it very well without potting the coil and epoxying it
into the pole pieces, mounting it to the engine, etc. - and if it
turns out to be bad, it is a real b***h to pull apart and do over with
different wire.

I figure the excitation power probably drops with speed of rotation -
alternator voltage output tracks speed so it should need less
excitation as speed increases - and the frequency goes up so inductive
reactance also increases(?)


the coil is fed DC, inductance doesn't enter into it.


So, I'm thinking worst case is probably close to idle speed. To
further complicate that idea, excitation also has to track speed to
some extent, since it is derived from an extra set of diodes from the
rectifier - lower speed means less current/voltage to work with.


those diodes don't give a greatly elevated voltage, they're mainly to
provide a way to power the generator warning light.

But as the Alternator produces an Alternating current, don't they also
work as a Bridge Rectifier?

Like I said NO GURU, but its my pennys worth ;-)

Best of luck with the build

Vaughn


Automotive alternators are usually three phase with six diodes. this
helps reduce the ripple current in the charging system, and reduces
filtering requirements for the electronics.


--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida
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Jim Land
electronics forum beginner


Joined: 06 Jun 2006
Posts: 46

PostPosted: Sun Jul 09, 2006 4:17 am    Post subject: Re: Help, any gurus with alternator experience or knowledge? Reply with quote

"Michael A. Terrell" <mike.terrell@earthlink.net> wrote in
news:44B0762F.D55C6DC6@earthlink.net:
Quote:
I'm rewinding an automobile style alternator rotor. I want to use
some "Tefzel" insulated wire I have on hand, instead of magnet wire,
I have to special order. I wound a test coil and it fits and looks
like it will work.


My concern is that I have no idea how much current it takes to
excite the field and if the potting compound will survive the heat.
The Tefzel coil has the same DCR (5 ohms) as the original magnet
wire, but it is two gauges thinner (went from 22 AWG to 24 AWG).
So I would assume that it will dissipate more power to achieve the
same ampere turns in the field.

Anytime you rewind a motor or alternator, you want to use the same gauge

wire. Your alternator was designed with 22 AWG, for the number of
turns, the dc resistance, the current through it, the power dissipation,
and the space available. If it would work just as well with 24 AWG,
they would have used 24 AWG originally. If you're going to all the
trouble of winding these coils, placing them, and wiring them up, you
might as well use the right size wire to start with!
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Ban
electronics forum Guru


Joined: 04 May 2005
Posts: 466

PostPosted: Sun Jul 09, 2006 7:59 am    Post subject: Re: Help, any gurus with alternator experience or knowledge? Reply with quote

default wrote:
Quote:
The quandary

I'm rewinding an automobile style alternator rotor. I want to use
some "Tefzel" insulated wire I have on hand, instead of magnet wire, I
have to special order. I wound a test coil and it fits and looks like
it will work.

My concern is that I have no idea how much current it takes to excite
the field and if the potting compound will survive the heat. The
Tefzel coil has the same DCR (5 ohms) as the original magnet wire, but
it is two gauges thinner (went from 22 AWG to 24 AWG). So I would
assume that it will dissipate more power to achieve the same ampere
turns in the field.

When your wire is thinner but has the same resistance, it will be

shorter(40%) and hence the field will be weaker, probably less than half. It
also means it will heat up much more for 2 reasons: The diameter is smaller
and the insulation is much thicker, so the heat cannot be transferred to the
metal or air so easily, builds up in the center and can blow up the sleeve
of epoxy. Another remark: how well do you think your insulation is sticking
to *any* glue? An additional property of PTFE is its tendency to "flow"
aggravated by vibration, temperature and pressure, all of which are present
in your application.

Quote:
I can't test it very well without potting the coil and epoxying it
into the pole pieces, mounting it to the engine, etc. - and if it
turns out to be bad, it is a real b***h to pull apart and do over with
different wire.

I figure the excitation power probably drops with speed of rotation -
alternator voltage output tracks speed so it should need less
excitation as speed increases - and the frequency goes up so inductive
reactance also increases(?)

Back EMF increases linearly with speed, but since you have less windings,

the current will be higher.

Quote:
So, I'm thinking worst case is probably close to idle speed. To
further complicate that idea, excitation also has to track speed to
some extent, since it is derived from an extra set of diodes from the
rectifier - lower speed means less current/voltage to work with.

I tried powering the coil with a dc supply and pushed 2.5 amps through
it for 3 hours - no idea how hot the coil was, but the area between
the coil and pole pieces was 70 degrees F over ambient - around 150 F.
On the engine, it is driven directly off the crankshaft and probably
has an ambient of closer to 170 F - enclosed with no ventilation just
conduction and radiation cooling, and whatever air the rotor itself
stirs up.

I can do some empirical testing with a sacrificial coil when the vinyl
ester resin gets here.

Anyone with experience/ideas in rewinding rotors and do you think this
should work? Smaller gauge wire - same DCR, but lower ampere turns
and consequently more power used to cause more heat and excite the
field..

The potting resin is supposed to be good for ~240 F so I might be
pushing the limit there.


forget about the tefzel for this app and get the right magnet wire suitable
for high temp.
--
ciao Ban
Apricale, Italy
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me
electronics forum addict


Joined: 05 May 2005
Posts: 73

PostPosted: Sun Jul 09, 2006 9:35 am    Post subject: Re: Help, any gurus with alternator experience or knowledge? Reply with quote

jasen <jasen@free.net.nz> wrote in
news:42b3.44b03a10.45758@clunker.homenet:

Quote:
On 2006-07-08, default <none@nobody.net> wrote:
The quandary

I'm rewinding an automobile style alternator rotor. I want to use
some "Tefzel" insulated wire I have on hand, instead of magnet wire,
I have to special order. I wound a test coil and it fits and looks
like it will work.

My concern is that I have no idea how much current it takes to excite
the field and if the potting compound will survive the heat. The
Tefzel coil has the same DCR (5 ohms) as the original magnet wire,
but it is two gauges thinner (went from 22 AWG to 24 AWG). So I
would assume that it will dissipate more power to achieve the same
ampere turns in the field.


Quit bloody wating your time(and likely effort) and get one at a salvage
yard...

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default
electronics forum Guru Wannabe


Joined: 03 May 2005
Posts: 175

PostPosted: Sun Jul 09, 2006 2:35 pm    Post subject: Re: Help, any gurus with alternator experience or knowledge? Reply with quote

On Sun, 9 Jul 2006 09:59:37 +0200, "Ban" <bansuri@masterweb.it> wrote:

Quote:
default wrote:
The quandary


When your wire is thinner but has the same resistance, it will be
shorter(40%) and hence the field will be weaker, probably less than half. It
also means it will heat up much more for 2 reasons: The diameter is smaller
and the insulation is much thicker, so the heat cannot be transferred to the
metal or air so easily, builds up in the center and can blow up the sleeve
of epoxy. Another remark: how well do you think your insulation is sticking
to *any* glue? An additional property of PTFE is its tendency to "flow"
aggravated by vibration, temperature and pressure, all of which are present
in your application.

Thanks, you've given me some ideas.


I kinda lied about the resistance - my repair to the original
measures 4.5 ohms and the Tefzel coil measures 3.8 . Turns out my DVM
isn't great in the low ohms range - two different days and two
different readings.

The Tefzel wire does have what appears to be a silver plating if that
is enough to enter into it. What I can do is measure the thickness of
the ETFE and compare that to an enamel wire table and see how many
turns should fit in the same cross sectional area and pin down the
turns difference with some accuracy. My repair winding was relatively
sloppy and wasn't "perfect lay" by any means.

PTFE FEP PFA are in the same class when it comes to physical
properties ETFE is Tefzel and is in a different class - twice the
tensile strength, 20% harder, better compressive strength, similar
flexural strength. Lower temperature rating for the physical
properties than FEP (260 C) types but good to 155 degrees C.


Quote:

Back EMF increases linearly with speed, but since you have less windings,
the current will be higher.

Back EMF in the excited field rotor? I didn't know there was any.

I'm not convinced current will be higher - the excitation current is
directly derived from the alternator output - it isn't fixed - it
doesn't come from the battery. A shorted or nearly shorted rotor is
less effective for output at the same rotational speed so it has less
voltage to send to the rotor - that's the reason for an extra three
diodes on the regulator - not for the warning light as one poster
suggested (it has no warning light). There is a fixed dropping
resistor that provides a tickle of current from the battery to get
things started.
Quote:

So, I'm thinking worst case is probably close to idle speed. To
further complicate that idea, excitation also has to track speed to
some extent, since it is derived from an extra set of diodes from the
rectifier - lower speed means less current/voltage to work with.

forget about the tefzel for this app and get the right magnet wire suitable
for high temp.

Price of magnet wire in small quantities has quadrupled in the last
year and doubled in large quantities - place I bought one pound from
for $12 now wants $35 for a half pound (8 ounces) and I need about 12
ounces. At that rate it would probably be cheaper to buy a 6 pound
reel of the stuff.

Yeah - you're right to point out ETFE won't stick to epoxy, to work it
has to penetrate between the wires - I'm using vinyl ester resin,
similar to polyester resin (water thin compared to epoxy and good
wetting properties) higher temperature rating than epoxy. I'll use
epoxy to hold the coil in place or thickened vinyl ester resin for
that.

Blow it apart due to thermal expansion? That should be no problem to
discover with empirical testing - vinyl ester resin sets up hard -
but it isn't glass hard - just hard compared to unfilled epoxy. The
coil will always have some air trapped in the center of the windings
unless I can figure out how to turn my mandrel into a mold (I'm
working on that now)

Buying wire is always an option - but I'll kick this around some more
before I give up. I have two weeks to get it working.

Thanks for the reply.

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default
electronics forum Guru Wannabe


Joined: 03 May 2005
Posts: 175

PostPosted: Sun Jul 09, 2006 3:38 pm    Post subject: Re: Help, any gurus with alternator experience or knowledge? Reply with quote

On Sat, 08 Jul 2006 23:04:48 -0000, jasen <jasen@free.net.nz> wrote:

Quote:

I'm no guru but:

if the wire is thinner, but the coil the same dimension then you
theoretically have more turns - this means for the same current you have
more magnetic field.

if the coil is the same resistance as the old one then you will have the
same max current, and the same worst-case resistive heating as the old coil.

if the conductor is thinner but the insulated wire is thicker you have fewer
turns and threfore a less-effective altenator.

You are forgetting the extra diodes in the regulator - they provide

the current to the field rotor - not the battery. The warning light
on automobiles serves two functions - it provides the "tickle" of a
few hundred milliamps get things started as well as indicate that the
alternator is working. Some autos won't charge the battery at all
when the warning light burns out. My system has no warning light just
a small resistor to start things off.
Quote:

the coil is fed DC, inductance doesn't enter into it.

Fed pulsating DC albeit three phase rectified DC, inductance may be a

factor. I don't know. Right now it is an unknown variable - when I
switch on a load the voltage drops for ~100+ milliseconds and
overshoots again when I switch it off - if the regulation were better
I'd say inductance didn't matter.
Quote:

those diodes don't give a greatly elevated voltage, they're mainly to
provide a way to power the generator warning light.
I disagree there -

your altenator doesn't vent slots or a fan behind the pulley?
No fan, no pulley, driven - bolted directly to the crankshaft. No

venting what so ever - no way for rain to get in. Conduction and
radiation and convection around the cast aluminum cover.

Quote:
maybe you can epoxy in screw terminals this time incase the leads fail.

That's a good idea. screw terminals of brass tabs imbedded in the

epoxy to solder to

Quote:
maybe you could use old CD-Roms (the shiny can be removed using a metal pot
scourer) for the ends of the bobbin and a dowel (or threaded rod?) wrapped
in paper and cling-wrap for the centre?

Here if I send a mini CD through the mail in a regular envelope - it
comes back with the shiny side in the bottom of the envelope - Have to
see how the post office does that - no scouring necessary, perfectly
transparent.
Quote:

hmm, if I could fix a 3-jaw chuck to the back of a sewing machine that'd
make a good tool start for winding magnet coils

Actually I have a crude coil winder. I have a large tape recorder,
reel drive, DC, permanent magnet, motor. It has a taper on the end
of its 2" long shaft. To the end of the motor I can bang on a block
of wood and turn it down with a chisel and rasp to any diameter from
1/2" to 5" I already built a three part mandrel to wind the coil out
of wood - the tricky part is figuring out how to get some plastic on
there that will act as a mold release and mold a self supporting coil.

The coil winder was made for winding long Tesla coils and I did use it
for a large induction coil. Works very well with an adjustable DC
supply to power it. Crank up enough voltage to pull wire from a
supply reel and guide it on by hand. Lower the voltage to keep
tension on it to paint with varnish, epoxy, or to get a beer. Paint a
Tesla coil with epoxy and set it to rotate slowly while it cures and
it is possible to get a really smooth finish.

The winding lathe has a tail stock made from a carriage bolt and is
threaded through a long nut mounted in blocks of wood - for Tesla
coils - short coils go on the mandrels mounted to the motor shaft and
turned to diameter.

I have some of those mini CDR discs and they are the ideal diameter
for side plates (have to bore out the center to about 1-5/8") I don't
know that I'd trust the poly carbonate plastic at those temperatures
for a permanent bobbin - a tin can lid would make better sense there.

I'm toying with the idea of using a couple of polyethylene recyclable
lids like one sees on re closable food cans to make temporary side
plates. Coat them will silicone wax and epoxy the coil together and
then remove it from the mold. The spindle (hub/center) could be
wrapped with Teflon pipe joint tape and making the side plates
undersize and sliding it over the tape may give a liquid tight seal to
make a self-supporting coil. Then that coil could be further
insulated with tape or dipping in resin.


Thanks for the reply - more ideas to think about

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default
electronics forum Guru Wannabe


Joined: 03 May 2005
Posts: 175

PostPosted: Sun Jul 09, 2006 3:56 pm    Post subject: Re: Help, any gurus with alternator experience or knowledge? Reply with quote

On Sun, 09 Jul 2006 02:10:07 GMT, Vaughn <vaughn.lucock@ntlworld.com>
wrote:


Quote:
Again no guru, but from what I remember of winding my own transformers,
more coil turns equals greater voltage, so this alternator MAY produce a
greater voltage for a given rotational speed.

I wind transformers too. If one winds the stator (non movable outside

part on my alternator) with more turns, the voltage will increase for
the same rotational speed.

We are talking about a DC electromagnet here - the rotating field --
magnetizing a hunk of cast iron (pole pieces). I ran some calculations
on wire size and cross sectional area of the coil. All things being
equal - same magnet wire insulation - the resistance goes up (as wire
gets thinner) the current goes down (greater resistance) but the
magnetic field strength stays the same if the cross section (filled
with wire) stays the same.

I'm contemplating changing the size of the insulation with a (possibly
silver plated) copper wire and increasing insulation thickness and
decreasing wire diameter two gauges - that's what gives me pause.

Quote:
But as the Alternator produces an Alternating current, don't they also
work as a Bridge Rectifier?

Three phase delta connected output that goes to six diodes for primary
rectification and three additional (smaller) diodes to provide field
excitation independent of the battery.
Quote:

Like I said NO GURU, but its my pennys worth ;-)

Best of luck with the build

Thanks - I enjoy tinkering with it - but don't want to get stuck

hundreds of miles from home with no way to repair it.

Quote:
Vaughn

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Jamie
electronics forum Guru


Joined: 24 Mar 2005
Posts: 597

PostPosted: Sun Jul 09, 2006 7:44 pm    Post subject: Re: Help, any gurus with alternator experience or knowledge? Reply with quote

default wrote:

Quote:
On Sat, 08 Jul 2006 17:28:29 GMT, Rich Grise <richgrise@example.net
wrote:


Could you temporarily stick it in place with hot glue, just for testing
purposes? Hot glue should just be able to just peel right off between
tests and so on.


Probably long enough to start the engine and measure the current. I
was sort of hoping to get it to work without a test except perhaps a
coil alone - with a fixed dissipation.

Even the hot melt adhesive isn't a pleasant idea - run long enough to
get real data and I'd probably have the adhesive slinging off into the
stator or space between the rotor and stator - too risky to chance
that - adhesive being ground up would take out the brushes - unlike
auto alternators, this one has axial slip rings - any bit of epoxy etc
that comes off eats the brushes.


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Lacquer



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Jamie
electronics forum Guru


Joined: 24 Mar 2005
Posts: 597

PostPosted: Sun Jul 09, 2006 7:44 pm    Post subject: Re: Help, any gurus with alternator experience or knowledge? Reply with quote

default wrote:

Quote:
On Sun, 09 Jul 2006 04:35:44 -0500, me <me@here.net> wrote:


Quit bloody wating your time(and likely effort) and get one at a salvage
yard...


Would that it was that simple. These things are scarcer than hen's
teeth, and all have a reputation for failing as originally made.

There is some emotional satisfaction to be derived from solving
problems.

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when we send out motors for repair we also request them to use teflon

instead of the various ranges of enamel's they have out there.
in one location we use AC motors as tension units, they don't last
long when running at the max with out proper ventilation and cool air
going across the unit. so we started to have these units repaired with
teflon and they have been great ever since with the exceptional bearing
blow out now and then which we can fix our self's.



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Michael Kennedy
electronics forum Guru


Joined: 11 Jun 2005
Posts: 401

PostPosted: Sun Jul 09, 2006 9:10 pm    Post subject: Re: Help, any gurus with alternator experience or knowledge? Reply with quote

I have no experience wiring motors but, it sounds like you think your wire
will work and you don't want to hear that it won't... It probably will
work.. All you can do is try it and see.. That is the only way to get a
definative answer.. I had a similar problem, well similar with everone
telling me that it wouldnt work. I was going to try to run ethernet over
700ft of cat5 wire. Everyone said it wouldn't work, but I tried anyway and
it worked just fine, with the exception of lightning..

Anyway my point is just do it and see if it works, it probably will...

- Mike

"default" <none@nobody.net> wrote in message
news:gr12b2hlbgq0aehkitucv1gkfriq3hq9o5@4ax.com...
Quote:
On Sun, 9 Jul 2006 09:59:37 +0200, "Ban" <bansuri@masterweb.it> wrote:

default wrote:
The quandary


When your wire is thinner but has the same resistance, it will be
shorter(40%) and hence the field will be weaker, probably less than half.
It
also means it will heat up much more for 2 reasons: The diameter is
smaller
and the insulation is much thicker, so the heat cannot be transferred to
the
metal or air so easily, builds up in the center and can blow up the sleeve
of epoxy. Another remark: how well do you think your insulation is
sticking
to *any* glue? An additional property of PTFE is its tendency to "flow"
aggravated by vibration, temperature and pressure, all of which are
present
in your application.

Thanks, you've given me some ideas.

I kinda lied about the resistance - my repair to the original
measures 4.5 ohms and the Tefzel coil measures 3.8 . Turns out my DVM
isn't great in the low ohms range - two different days and two
different readings.

The Tefzel wire does have what appears to be a silver plating if that
is enough to enter into it. What I can do is measure the thickness of
the ETFE and compare that to an enamel wire table and see how many
turns should fit in the same cross sectional area and pin down the
turns difference with some accuracy. My repair winding was relatively
sloppy and wasn't "perfect lay" by any means.

PTFE FEP PFA are in the same class when it comes to physical
properties ETFE is Tefzel and is in a different class - twice the
tensile strength, 20% harder, better compressive strength, similar
flexural strength. Lower temperature rating for the physical
properties than FEP (260 C) types but good to 155 degrees C.



Back EMF increases linearly with speed, but since you have less windings,
the current will be higher.

Back EMF in the excited field rotor? I didn't know there was any.

I'm not convinced current will be higher - the excitation current is
directly derived from the alternator output - it isn't fixed - it
doesn't come from the battery. A shorted or nearly shorted rotor is
less effective for output at the same rotational speed so it has less
voltage to send to the rotor - that's the reason for an extra three
diodes on the regulator - not for the warning light as one poster
suggested (it has no warning light). There is a fixed dropping
resistor that provides a tickle of current from the battery to get
things started.

So, I'm thinking worst case is probably close to idle speed. To
further complicate that idea, excitation also has to track speed to
some extent, since it is derived from an extra set of diodes from the
rectifier - lower speed means less current/voltage to work with.

forget about the tefzel for this app and get the right magnet wire
suitable
for high temp.

Price of magnet wire in small quantities has quadrupled in the last
year and doubled in large quantities - place I bought one pound from
for $12 now wants $35 for a half pound (8 ounces) and I need about 12
ounces. At that rate it would probably be cheaper to buy a 6 pound
reel of the stuff.

Yeah - you're right to point out ETFE won't stick to epoxy, to work it
has to penetrate between the wires - I'm using vinyl ester resin,
similar to polyester resin (water thin compared to epoxy and good
wetting properties) higher temperature rating than epoxy. I'll use
epoxy to hold the coil in place or thickened vinyl ester resin for
that.

Blow it apart due to thermal expansion? That should be no problem to
discover with empirical testing - vinyl ester resin sets up hard -
but it isn't glass hard - just hard compared to unfilled epoxy. The
coil will always have some air trapped in the center of the windings
unless I can figure out how to turn my mandrel into a mold (I'm
working on that now)

Buying wire is always an option - but I'll kick this around some more
before I give up. I have two weeks to get it working.

Thanks for the reply.

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Jim Land
electronics forum beginner


Joined: 06 Jun 2006
Posts: 46

PostPosted: Sun Jul 09, 2006 10:54 pm    Post subject: Re: Help, any gurus with alternator experience or knowledge? Reply with quote

"Michael Kennedy" <Mikek400@remthis.comcast.net> wrote in
news:K86dnXE_epcv7SzZnZ2dnUVZ_sWdnZ2d@comcast.com:

Quote:
it worked just fine, with the exception of lightning..


LOL! We should all be so lucky in our projects.
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