# Single Phase Field Coil Question - Page 3

Posted by Tim Jackson on June 13, 2009, 9:13 am

Ulysses wrote:

>>> 3 phase alternator but couldn't find

I mean the power you want it to dissipate, eg 5% of that.  The general
ohms-law formula can be written as P = V**2/R, so what I wrote,
V = sqrt(P*R), is the way of getting calculating the voltage given the
power and resistance.  You can measure the resistance and you can choose
the power.  So the voltage you need to get your chosen field power is
what you calculate.  What I am suggesting is you won't go far wrong if
you choose a field power of about 5% of the rated output power (and
calculate a voltage from that).

Tim

Posted by Ulysses on June 13, 2009, 3:46 pm

alternator.

original

OK, thanks :-D

Posted by harry on June 12, 2009, 6:52 pm

It's fifty years since they made any sort of electrical machine to
thes principles.  They were old fashioned when I was an apprentice. At
one time you could get them rewound, there were little motor rewind
shops in every town. Not any more. the stator is put in an autoclave,
a vacuum puled and epoxy resin srayed on. Then  the vacuum is released
and it is baked.  Stands the heat, mechanical forces and vibration
better than rewindable types.

Posted by daestrom on June 12, 2009, 9:09 pm

Don't understand your point.  You still have to wind the thing in the first
place.  How you bake it and what type of insulation you use after the coils
are in the slots is a different matter all together.

OP wants to experiment with winding his own alternator.  Not really cost
effective for a rewind shop, but if he wants to experiment, he has to know
how to wind and connect the coils.

daestrom

Posted by Ulysses on June 12, 2009, 11:10 pm

non-engine

So far, with 12 volts attached to the rotor (field core) I have not been
able to establish the direction of the poles or verify that it is indeed an
electromagnet.  I tried placing a permanant magnet on each pole and applying
voltage to the slip rings and get nothing.  It seem like both poles are
either N or S based upon the attraction/repulsion of the magnet.  I guess I
need more volts.  I think my digital multimeter is not working.

I found some specific information on how to rewind a Delco alternator stator
but the maximum wire size that will fit in there is only about #25 and it is
my understanding that I will then have twice the voltage at a given rpm but
I'll end up with only half the current with the small wire size.  My making
my own stator for the single phase rotor that I have on hand I can use more
turns of bigger wire.  But I'm not going to build anything until I can be
pretty sure the field coils even work ;-)

My ultimate goal is to come up with some kind of direct-drive alternator to
charge my 48 volt battery bank using a small engine.  My Delco 10SI
alternator would be adequate with the stock stator if only I could find a
way to drive it reliably.  I figure direct-drive=no more belt problems.  If
I run it past about 25-30 amps the belt becomes a problem but I have managed
to get about 60 amps at over 50 volts out of the thing without frying the
diodes so the alternator is good.  Maybe I should try a chain drive again
with some better couplings.