# 100V DC Generator using an Induction Motor

#### Research Survey

Joined Feb 27, 2016
16
Good day! We are trying to make a dc generator using an induction motor. Currently, the voltage generated is only at minimal i.e. around 2V. How can we increase the voltage induced without using any transformer? Thanks

#### shortbus

Joined Sep 30, 2009
9,761
You need to spin up the motor before connecting any load and you need the right capacitor(s). See the information in this link:
http://www.electricaleasy.com/2014/12/induction-generator-working.html
Did you read the link? This is how they make generated three phase from a two phase input, what is refered to as a "phase convertor". Wasn't the OP asking about making DC? Even if what was in the link worked without an AC input to the motor, the resulting output would be AC, due to the way an induction motors stators winding are made. Right?

#### AlbertHall

Joined Jun 4, 2014
12,187
Sure was. But OP also said:

How can we increase the voltage induced without using any transformer?
So clearly knows what will be generated would be AC, otherwise what use would a transformer be?
Converting AC to DC is trivial.

#### shortbus

Joined Sep 30, 2009
9,761
So clearly knows what will be generated would be AC, otherwise what use would a transformer be?
Converting AC to DC is trivial.
My thought's are he doesn't know much(yet) about electricity. The induction generator in your link still needs an AC input, and a 'prime mover' to get it past the "slip" point. If he has voltage to start with why not just use it? Must be missing something?

#### AlbertHall

Joined Jun 4, 2014
12,187
No. Induction motors (1ph or 3ph) can work as generators if you get the capacitors right. You only need to spin them up with no load so the residual magnetism can generate enough to get the field going, then you connect the load. If you overload them they will just stop generating not go up in smoke.

#### shortbus

Joined Sep 30, 2009
9,761
Please don't think I'm arguing with you, just trying to learn more about this. I've used the induction "generator" thing to make a phase convertor, before VFD's became inexpensive. Have had many 1phase motors apart to change out bearings, but never found one with a rotor that was magnetized (that was detectable)at least when it was out on the bench.
So I have been under the assumption that it would be like a car alternator, not self energizing.

Joined Jul 18, 2013
26,278
There is a book by Nigel Smith that explains how it is done for wind generators, but this motor has fallen out of favour due to the use now of P.M. in Wind farm generators.
The simple 3ph motor requires a great deal of reactive power for excitation.

Max.

#### AlbertHall

Joined Jun 4, 2014
12,187
Please don't think I'm arguing with you, just trying to learn more about this. I've used the induction "generator" thing to make a phase convertor, before VFD's became inexpensive. Have had many 1phase motors apart to change out bearings, but never found one with a rotor that was magnetized (that was detectable)at least when it was out on the bench.
So I have been under the assumption that it would be like a car alternator, not self energizing.
In days gone by cars used dynamos. The field winding of the dynamo was fed by the dynamo output, i.e. by the rotor, not by the battery. The residual magnetism in the iron core generated a very small output which fed the field which generated greater output which increased the field and so on, until it was up to full output.

I found this article detailing some some experiments with soft iron with some surprising results. Especially read section 26.
https://www.jstor.org/stable/108001?seq=8#page_scan_tab_contents

Joined Jul 18, 2013
26,278
In days gone by cars used dynamos. The field winding of the dynamo was fed by the dynamo output, i.e. by the rotor, not by the battery. The residual magnetism in the iron core generated a very small output which fed the field which generated greater output which increased the field and so on, until it was up to full output.
Self exited DC generators has virtually always been the way up to the present day, from Edison's original to present day applications such as mobile cranes using lift magnet generators.
They are generally fitted with a regulator once the field is self fed.
Max.

#### Research Survey

Joined Feb 27, 2016
16
In days gone by cars used dynamos. The field winding of the dynamo was fed by the dynamo output, i.e. by the rotor, not by the battery. The residual magnetism in the iron core generated a very small output which fed the field which generated greater output which increased the field and so on, until it was up to full output.

I found this article detailing some some experiments with soft iron with some surprising results. Especially read section 26.
https://www.jstor.org/stable/108001?seq=8#page_scan_tab_contents
i resorted to buying a dc motor , i think it is a treadmill motor, since it needs at least 50v to operate as motor rotating very slowly, there's no name plate on it, however if use a power drill to rotate the motor, it can reach up to almost 200v, didn't go further as im not sure of the sturdiness of the motor itself. Thanks sir for ur help sir.

#### Research Survey

Joined Feb 27, 2016
16
There is a book by Nigel Smith that explains how it is done for wind generators, but this motor has fallen out of favour due to the use now of P.M. in Wind farm generators.
The simple 3ph motor requires a great deal of reactive power for excitation.

Max.
thank you sir, ur help is significant sir to me