# AC Generator Design Question

Discussion in 'Electronic Basics' started by Randy Gross, Nov 1, 2003.

1. ### Randy GrossGuest

Greetings:

I've begun the construction of a small A.C. generator with 8 poles and a 3
phase stator. Instead of igniting wound poles with D.C., I've decided to
use permanent magnets. I don't know the field strengths of these magnets
but, they are Magnetron magnets 2 1/4" in diameter by 3/8" thick, not the
best but cost effective.

My problem is determining the number of turns (20 awg magnet wire) per pole
to achieve the 120vrms output. I can do this by trial but, that would mean
assemble - disassemble until I reach the goal. Each phase will be wound
with a continuous strand, not individual coils.

Does someone have a formula for calculating turns that can speed things up?
Is it 15v or is it 30v North and 30v South per set of poles?

2. ### John PopelishGuest

The open circuit voltage is proportional to the magnet field strength
, the speed and the number of turns. If the first two are fixed, the
number of turns is all that you need to find. Wind one (or a few)
turn and measure the voltage produced, then scale the winding up to
produce the desired voltage. The voltage will sag, almost linearly
with current, so you will want to produce a bit extra (or figure out
that factor with the one turn winding with a second test for short
circuit current).

3. ### Randy GrossGuest

With this plan I'd say the generator is as good as done.

Thanks John.

Randy Gross

<>...

<snip>

:
: The open circuit voltage is proportional to the magnet field strength
: , the speed and the number of turns. If the first two are fixed, the
: number of turns is all that you need to find. Wind one (or a few)
: turn and measure the voltage produced, then scale the winding up to
: produce the desired voltage. The voltage will sag, almost linearly
: with current, so you will want to produce a bit extra (or figure out
: that factor with the one turn winding with a second test for short
: circuit current).
:
: --
: John Popelish
:

4. ### Guest

The faster the coils move the more the voltage output and the more
turns you have, the more the output.

The output will "droop" when you connect the load more or less
depending on its efficiency. Trial and error is probably your best
bet.

Robin

5. ### Randy GrossGuest

Experimenting with electricity is truly fascinating. The more you learn,
the more there is. Thanks guys, I'm in a better position now to make
informed decisions.

Randy Gross

wrote in article
<>...
: > Greetings:
<snip>
: > Does someone have a formula for calculating turns that can speed things
up?
: > Is it 15v or is it 30v North and 30v South per set of poles?
:
: The faster the coils move the more the voltage output and the more
: turns you have, the more the output.
:
: The output will "droop" when you connect the load more or less
: depending on its efficiency. Trial and error is probably your best
: bet.
:
:
: Robin
: