Help, any gurus with alternator experience or knowledge?

[jasen]

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

 

[Guest]

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.

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teeth, and all have a reputation for failing as originally made.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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[default]

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.

 

[default]

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.

 

[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.

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

Bye.
Jasen

 

[default]

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 shit 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.

 

[Chuck Harris]

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 shit 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

 

[default]

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.

 

[Chuck Harris]

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

 

[Jason D.]

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

 

[default]

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