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 bitch 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(?)

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.


The whole story:

Five years ago my alternator failed. The rotor had shorted -
resistance of the coil would vary from point five to five ohms - five
ohms is supposed to be typical. Replacement rotor $350 . . . with no
guarantee that it wouldn't fail like the original in two years . . .

The regulator is the common type usually used with excited field
alternators - a two transistor circuit that pumps voltage to the coil
when the battery drops below the set point. The voltage that goes to
the rotor (rotating field) is derived from an extra three diodes on
the positive of the six diode, three phase rectifier - so it is
isolated from the battery.

One effect of using extra diodes is that when the output of the
alternator drops (when the field is shorted, for instance) the
excitation current is also lower - doesn't do much to charge the
battery, but it doesn't kill the battery in an effort to excite a
shorted field, and doesn't kill the regulator pass transistor. A good
design . . .

The original coil failed because the enamel on the magnet wire and or
varnish holding it together failed (probably because of heat or
vibration - at least that's what the wire looked like). It was a self
supporting coil - made in a mold and had no bobbin.

I didn't have the stuff to make a self supporting coil so I made a
bobbin out of very thin two sided epoxy pcb material, and insulated
the inside with pieces of thin Mylar plastic. Wound a layer - painted
it with epoxy and built up the entire coil that way. It lasted 5
years and then failed because the lead wires to the coil opened - The
wires were in a sleeve of Teflon spaghetti and probably opened due to
metal fatigue - that's what the ends looked like - when you bend a
wire back and forth until it breaks. I repaired one open to the
finish end and it worked for a few weeks and then the start end also
opened. The coil is pretty much a goner now - the clear epoxy shows
the wire to be in excellent shape - no charring like the OEM part.

I want to wind another coil but would like to avoid using a bobbin
since that took me over a day to construct with hand tools, and the
bobbin didn't survive pulling apart the pole pieces.

So I found some wire wrap wire with "Tefzel" insulation and wound a
coil with that on the mandrel that supported my original bobbin. I
secured it into a toroid shape using nylon lacing cord. Fits the pole
pieces and looks like it will work. Plan B was to serve leads to it
made of fine braid - to avoid metal fatigue and sleeve it in cambric
spaghetti then dip it in vinyl ester resin, epoxy that assembly into
the pole pieces and reassemble the rotor.

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.

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

On Sat, 08 Jul 2006 17:28:29 GMT, Rich Grise
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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On 2006-07-08, default 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.

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 bitch 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.

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?

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

jasen wrote:
On 2006-07-08, default 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 bitch 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

Vaughn wrote:

jasen wrote:
On 2006-07-08, default 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 bitch 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

"Michael A. Terrell" wrote in
:
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!

default 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.

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.

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 bitch 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.

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

jasen wrote in
:

On 2006-07-08, default 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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On Sun, 9 Jul 2006 09:59:37 +0200, "Ban" 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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On Sun, 09 Jul 2006 04:35:44 -0500, me 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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On Sat, 08 Jul 2006 23:04:48 -0000, jasen wrote:


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.

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.

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.

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

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.

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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On Sun, 09 Jul 2006 02:10:07 GMT, Vaughn
wrote:


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.

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.

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.

Vaughn

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On Sun, 09 Jul 2006 04:17:35 -0000, Jim Land
wrote:

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!

Oh, I don't know . . . where's your sense of adventure man?

All engineering is a matter of compromise. You assume the factory got
it right

- the original lasted 2 years my first repair lasted 5. It would
still be working if I'd thought to serve some stranded wire to the
start and finish ends and not used Teflon tubing to support the wire.

There are some alternators that last until the brushes die from wear
or the diodes rust through - this alternator has a very high, well
documented, rotor failure rate. I'm assuming the factory did not get
it right.

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.

The power dissipation goes down as the wire gets thinner, lower
current producing the same ampere turns in the same available space
assuming the voltage stays constant - higher efficiency.

I'm committing two sins here - going down in wire diameter and
increasing insulation thickness - fewer turns of thinner wire.
Conductivity may be better because it looks like silver plating on the
wire. I wish I'd measured the 1,000 foot reel before I started using
it . . . but I bought it for Tesla coils not alternator rotors.

The downside of using very thin wire is it is more likely to break
under stress, physical or thermal cycling. At some point wire
insulation may take up more room than wire itself with very thin wire
gauges - but within the practical range of several gauges it shouldn't
matter all that much. Theoretically.

I would expect the output to go up slightly with thinner wire due to
an increase in efficiency but don't expect it to be enough to be worth
changing to a different gauge. I'm just trying to save a buck on
wire cost.

I have Tefzel insulated wire I already own . . . . Copper prices
have doubled in the last year or two. One pound was costing me $12,
one half pound now costs $35 from the same source - but in larger
quantities it has (only) doubled. I need about 12 ounces.

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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" wrote in message
...
On Sun, 9 Jul 2006 09:59:37 +0200, "Ban" 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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"Michael Kennedy" wrote in
:

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


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

default wrote:

On Sat, 08 Jul 2006 17:28:29 GMT, Rich Grise
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


--
Real Programmers Do things like this.
http://webpages.charter.net/jamie_5

default wrote:

On Sun, 09 Jul 2006 04:35:44 -0500, me 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.



--
Real Programmers Do things like this.
http://webpages.charter.net/jamie_5

Michael Kennedy wrote:

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

Hmm, 700Ft?,. bet you r only getting 10MB ?

and btw, you can get FEP motor/mag wire with
thin applied coatings on it.
tefzel, well we had experience with that, it most likely
will work how ever, if the motor burns up , toxic gas is
released..
we use that at work for products that need to be
smokeless. well it mite be Smokeless but it isn't toxless.
... if this stuff gets a little over heated you don't want to
be directly in the path of its venting area.
FEP isn't much better either actually, that is smokeless but
removes the O2 of of the air and if your a smoker! watch out.

On 2006-07-09, default wrote:
On Sat, 08 Jul 2006 23:04:48 -0000, jasen wrote:


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.

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.

All that the inductance can do is smooth out the lumps in what's already
pretty smooth.

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 -

unless there's extra turns on the output windings we're talking 1 volt
maximum above what the main output is producing.

say the thing is going all out and the main rectifier doides are dropping
1.4v (each) the extra diodes for the field aur under less extreme load
and maybe dropping 0.6V so you're only 0.8V above the voltage on the output
terminal.

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

RTV silicone may be useful to reduce movement in the wires too,
that blue stuff used for sealing tappet covers sounds suitable
(Permatex ultra blue - nuetral cure, heat, and oil resistant)

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.

Hmm, I wonder how they do that...

maybe their mail processing hardware bends the letters somewhere along the
path... or maybe there's someone who sticvks them in a microwave oven :^)

Bye.
Jasen

On 2006-07-09, default wrote:
On Sun, 09 Jul 2006 02:10:07 GMT, Vaughn
wrote:


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.

only if you can increase the voltage to compensate for the resistance
which increases twice - due to greater length and reduced cross-section
of the conductor. the extra turn compensate for only one of those increases.

annealed, and oxygen free, copper wire will have slightly loer resistance
but I don't think it'll be enough.

Bye.
Jasen

I have to point out (since I am a mechanic in an electronic newsgroup) that
you are taking the electronic approach to solving your problem. The
mechanics approach would be to adapt a longer lived, less expensive, more
popular alternator form another brand of car onto your engine.

"default" wrote in message
...
On Sun, 09 Jul 2006 04:35:44 -0500, me 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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On Mon, 10 Jul 2006 09:51:18 GMT,
wrote:

I have to point out (since I am a mechanic in an electronic newsgroup) that
you are taking the electronic approach to solving your problem. The
mechanics approach would be to adapt a longer lived, less expensive, more
popular alternator form another brand of car onto your engine.

Sure that's what a mechanic would do with a car - where one has lots
of room and can make a mount or switch pulley sizes etc to make it
work.

I, on the other hand, have a crankshaft mounted alternator that must
fit in a certain space to keep it out of the rain - and I'd much
rather put in permanent magnets and redesign the regulator than rewind
the rotor - but I don't own a metal lathe, and I'm not too sure if
wood would work - not to mention the hassle of getting the inside
taper on the rotor right with the tools I have. This seems like the
best option to me.

I have thought of just putting a sheave on the end of the crankshaft,
kludging in a mount to hold a John Deere permanent magnet alternator
out there in the elements - but there ain't no good way to do it.

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On Mon, 10 Jul 2006 07:14:13 -0000, jasen wrote:

only if you can increase the voltage to compensate for the resistance
which increases twice - due to greater length and reduced cross-section
of the conductor. the extra turn compensate for only one of those increases.

annealed, and oxygen free, copper wire will have slightly loer resistance
but I don't think it'll be enough.

Bye.
Jasen

Well I calculated for three sizes of wire, in the same physical space.
The coil resistance in going to larger gauges went from 5 ohm to 1
ohm, Power dissipation went from 28 watts to 144 watts. Magnetic
force went from 1,415 Gilbert's to 1,417 Gilbert's.

Always the chance I made a mistake somewhere.

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On 2006-07-10, default wrote:
On Mon, 10 Jul 2006 07:14:13 -0000, jasen wrote:

only if you can increase the voltage to compensate for the resistance
which increases twice - due to greater length and reduced cross-section
of the conductor. the extra turn compensate for only one of those increases.

Well I calculated for three sizes of wire, in the same physical space.
The coil resistance in going to larger gauges went from 5 ohm to 1
ohm, Power dissipation went from 28 watts to 144 watts. Magnetic
force went from 1,415 Gilbert's to 1,417 Gilbert's.

Always the chance I made a mistake somewhere.

I think so... if you show your working I might be able to spot it.

Bye.
Jasen

On Tue, 11 Jul 2006 06:41:08 -0000, jasen wrote:

On 2006-07-10, default wrote:
On Mon, 10 Jul 2006 07:14:13 -0000, jasen wrote:

only if you can increase the voltage to compensate for the resistance
which increases twice - due to greater length and reduced cross-section
of the conductor. the extra turn compensate for only one of those increases.

Well I calculated for three sizes of wire, in the same physical space.
The coil resistance in going to larger gauges went from 5 ohm to 1
ohm, Power dissipation went from 28 watts to 144 watts. Magnetic
force went from 1,415 Gilbert's to 1,417 Gilbert's.

Always the chance I made a mistake somewhere.

I think so... if you show your working I might be able to spot it.

Bye.
Jasen

I don't have my data - it was from the original winding five years
ago. The formula to get from ampere turns to Gilbert's is simple
(current *number of turns*1.257).

If my memory serves, I used something like the number of turns that
could fit in a cross sectional area times the mean length per turn to
get wire length and resistance, from a 1914 book on solenoid
construction . . . .

But logically I see your point and it seems likely I went wrong
somewhere in there . . . For the sake of argument:

If each turn of wire has one ohm resistance, and I have a four turn
coil and 8 volts to drive it I have a current of 2 amps and 8 ampere
turns dissipating 16 watts total.

If I halve the diameter of the wire the cross section drops by a
factor of four so the resistance should increase by a factor of four.
So now I have 16 turns fitting where 4 where, and the resistance is 64
ohms. Four times the turns, with four times the resistance per turn.
With the same 8 volt supply that's 0.125 amps for 2 ampere turns
dissipating 1 watt.

Conclusion: I was full of **** to state that wire size didn't matter.

Efficiency: To produce the same 8 ampere turns with a 1/2 size wire
will take only 4 watts - so it becomes four times more efficient to
decrease the wire size by one half (keeping the volume the same), or I
could produce 32 amp/turns of field strength for the same 16 watts
that produced 8 A/T with larger wire. (if the volume were to
increase)

Practically speaking there's something like a theoretical increase of
7% or so when wires lay in the interstices created by the layer below.
Increase the turns by a factor of four and that 7% becomes significant
too.

See any flaws in the logic?

I'm glad we had this chat.

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default wrote:

But logically I see your point and it seems likely I went wrong
somewhere in there . . . For the sake of argument:

If each turn of wire has one ohm resistance, and I have a four turn
coil and 8 volts to drive it I have a current of 2 amps and 8 ampere
turns dissipating 16 watts total.

If I halve the diameter of the wire the cross section drops by a
factor of four so the resistance should increase by a factor of four.
So now I have 16 turns fitting where 4 where, and the resistance is 64
ohms. Four times the turns, with four times the resistance per turn.
With the same 8 volt supply that's 0.125 amps for 2 ampere turns
dissipating 1 watt.

Conclusion: I was full of **** to state that wire size didn't matter.

Efficiency: To produce the same 8 ampere turns with a 1/2 size wire
will take only 4 watts - so it becomes four times more efficient to
decrease the wire size by one half (keeping the volume the same), or I
could produce 32 amp/turns of field strength for the same 16 watts
that produced 8 A/T with larger wire. (if the volume were to
increase)

Huh? It comes out exactly the same either way:

8V, 4 ohm, 4T = 16W, 8A-T
32V, 64 ohm, 16T = 16W, 8A-T

The only issues as far as efficiency goes are the insulation thickness
as a percentage of the winding, and the wasted space due to the imperfect
packing between the wires. You can write equations for each, and calculate
the best wire size for an 8A-T coil, if you want.

-Chuck

On Tue, 11 Jul 2006 15:36:47 -0400, Chuck Harris
wrote:

Efficiency: To produce the same 8 ampere turns with a 1/2 size wire
will take only 4 watts - so it becomes four times more efficient to
decrease the wire size by one half (keeping the volume the same), or I
could produce 32 amp/turns of field strength for the same 16 watts
that produced 8 A/T with larger wire. (if the volume were to
increase)

Huh? It comes out exactly the same either way:

8V, 4 ohm, 4T = 16W, 8A-T
32V, 64 ohm, 16T = 16W, 8A-T

The only issues as far as efficiency goes are the insulation thickness
as a percentage of the winding, and the wasted space due to the imperfect
packing between the wires. You can write equations for each, and calculate
the best wire size for an 8A-T coil, if you want.

If a single coil will give me two ampere turns with 1 watt of
dissipation won't four parallel coils give me the equivalent of 8
ampere turns at 4 watts dissipation? All running at 8 volts in
parallel.

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default wrote:
On Tue, 11 Jul 2006 15:36:47 -0400, Chuck Harris
wrote:

Efficiency: To produce the same 8 ampere turns with a 1/2 size wire
will take only 4 watts - so it becomes four times more efficient to
decrease the wire size by one half (keeping the volume the same), or I
could produce 32 amp/turns of field strength for the same 16 watts
that produced 8 A/T with larger wire. (if the volume were to
increase)
Huh? It comes out exactly the same either way:

8V, 4 ohm, 4T = 16W, 8A-T
32V, 64 ohm, 16T = 16W, 8A-T

The only issues as far as efficiency goes are the insulation thickness
as a percentage of the winding, and the wasted space due to the imperfect
packing between the wires. You can write equations for each, and calculate
the best wire size for an 8A-T coil, if you want.

If a single coil will give me two ampere turns with 1 watt of
dissipation won't four parallel coils give me the equivalent of 8
ampere turns at 4 watts dissipation? All running at 8 volts in
parallel.

Of course, but you will have twice as much wire volume as the original
coil.

TANFL!

-Chuck

Please cut to one newsgroup forum, you're cross posting to many
newgroups. Thanks.

Reason those wires breaking off is that crankshaft have firing
impulses on the crank, even with flywheel and damper crankshaft still
vibrate in rotation plane. Whack whack whack, those poor wires from
the winding to the slip rings vibrating like twanged bow string and
evenually come apart.

Is the winding throughly SECURE? Also you may want to redesign the
eyelets to be MORE close to the winding. Always fabric sleeve these
flying wires and use cotton twine wetted with varnish and bed it then
lay the wires across it and bury the wires with more twine. Let set.
This is what old school motors were done this way to stop wires from
vibrating.

Especially look at the old vacuum motors, They had to be built to
survive 10,000 rpm from dead stop, same with engine starters.

Cheers, Wizard

On Wed, 12 Jul 2006 12:53:08 GMT, (Jason D.) wrote:

Please cut to one newsgroup forum, you're cross posting to many
newgroups. Thanks.
Yeah was hoping to find a person who's done a rewind himself. The
repair group is too busy, figured I'd drop off the screen in a day or
two.

Reason those wires breaking off is that crankshaft have firing
impulses on the crank, even with flywheel and damper crankshaft still
vibrate in rotation plane. Whack whack whack, those poor wires from
the winding to the slip rings vibrating like twanged bow string and
evenually come apart.

My latest plan is to try a self-supporting coil. I found some 22
gauge wire I could afford. Rather than make a bobbin, I put some
polyethylene facings to my mandrel and plan to spray it with silicone
as a mold release agent. I'm serving some small braided wire to the
ends of the magnet wire and bringing those up through fabric sleeves
and anchoring the ends in wraps of cotton twine.

Is the winding throughly SECURE? Also you may want to redesign the
eyelets to be MORE close to the winding. Always fabric sleeve these
flying wires and use cotton twine wetted with varnish and bed it then
lay the wires across it and bury the wires with more twine. Let set.
This is what old school motors were done this way to stop wires from
vibrating.

I'm using the same epoxy that worked last time for this winding. The
stuff I ordered didn't get here and won't until Friday. I may still
do a second coil with vinyl ester resin since I have more than enough
wire now.

There's no doubt the wire and sleeves I used were anchored well enough
the last time - but I think it was a mistake to use Teflon sleeves -
the wire had about .5 millimeter of play in the sleeve and it was 1.5
centimeters long embedded in epoxy - but epoxy can't penetrate the
sleeve.

Fabric sleeve (called spaghetti in the repair trade here) has been
supplanted with Teflon and heat-shrink tubing. I have some Military
type, small diameter (2.5mm), silver plated coaxial cable with a
fabric braid. Probably used for airframe applications from sensors to
cockpit. I'm using the braid and fabric and discarding the Teflon
center conductor.


Especially look at the old vacuum motors, They had to be built to
survive 10,000 rpm from dead stop, same with engine starters.

Cheers, Wizard


Thanks for the ideas

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