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Induction for Idiots

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Mr. Arkham

New Member
I've did a somewhat thorough search but... I can't seem to find an answer that can compute for my pea brain. I'm wanting to build a generator as a side project. I was wondering if there is a formula (that I can understand) that will give me an idea how much wattage I can expect to produce.

I believe the variables involved in this equation would be:

* Strength and number of magnets
* Rotation speed
* Size and number of coils involved?

Any direction is greatly appreciated. Thanks!
 

Sceadwian

Banned
Good luck, even folks with bigger than pea brains have trouble figuring those things out =) Why try to build a generator? ANY DC electric motor can become a generator, and they're much better at it that you or I for sure. Pick a motor that uses the wattage you want to generate, figure out how to spin it fast enough with enough torque, bam, generator.
 

Mr. Arkham

New Member
I've always wanted to build one... and I always wondered what the formula is... *shrugs* Thanks for the reply though.
 

Sceadwian

Banned
Seriously, don't think about it too much. If you want to use X watts from a generator, find a motor that uses X watts and turn it's output shaft as fast as it's rated for at X watts on it's inputs will be electricity. There are equations for it, but it's all calculus WAY over my head. The physical construction itself is actually the hardest part, the closer you get the coils and magnets together the better the energy transfer.
 

MrAl

Well-Known Member
Most Helpful Member
Hi,

I cant help but agree that buying almost anything would be MUCH simpler and
faster than trying to build a practical generator at home unless you happen to
have a machine shop too.
There is much more to this than we might think at first, and part of that is
that this is a highly intricate mechanical problem as well as electrical.
Commercial generators have concave shape magnets, and convex shaped
armature laminations that match and mate to keep gap distance small. This
would be hard to do by hand.
For winding the turns you would have to use some kind of special bobbin or
else come up with something that would work like that so that the wire doesnt
contact the armature laminations directly.

The only reason people usually ever build their own generators is when they are
studying this stuff and just want something to act as a real life model to show
that it can be done, but these little things are definitely not practical in that
they are too inefficient as well as too small anyway.

I am not saying that it can not be done, just that it will be very hard to do and
unless you can get the shapes right there is a very good chance that it wont
be very efficient and you wont be happy with it for the money you have to
put out for the parts. Wire itself will run around 100 dollars if you are lucky.

The basic formula is the bigger the better. The strongest magnets you can find,
the biggest armature you can build.
 
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Sceadwian

Banned
Personally I'd just go to a junk yard and find the biggest DC motor you can get your hands on that still works.
 

MrAl

Well-Known Member
Most Helpful Member
Hi,

I think it is not too bad of an idea to use something that is already built to
make a generator, for example a car alternator. You have everything you
need right there just about so it would be fairly simple and quick.
Might have to study out the right connections, that's about it.
 

tcmtech

Banned
Most Helpful Member
I have personally favored the standard low speed permanent magnet DC motors.
They are cheap and the better ones are very rugged and reliable.
For higher power outputs look for industrial DC servo motors.
I use them and they are way beyond durable!
Industrial class or commercial class is built for 10's of thousands of hours run time at full rated loads. Plus many have overload capacities of 10x for over a minute!:)
They have almost no maintenance requirements too, brush changes and maybe a bearing every 3 - 5 years but thats it.

If you want to get away from the brushes there are the AC PM servo motors. They work just like a standard three phase motor but they have permanent magnets on the rotor. That makes them excellent low speed low frequency alternators.

Most of the industrial servos are driven from higher voltage DC sources and have their voltages rated as volts per 1000 RPM.
A 80 volt per 1000 RPM DC motor will put out 12 volts at around 150 RPM and you can pull the full rated amps at that speed and the motor will not even warm up! ;):)
 

Hero999

Banned
You'll also need to increase the speed slightly to get the same voltage at full load.

For example a 12V 3000rpm motor won't put out 12V with a load connected and spun at 3000rpm, the voltage will be slightly lower. To get 12V you'll need to increase the speed.
 
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