# Convert Generator to DC motor?



## GeeDub (Jun 25, 2008)

I saw an FAQ on a website describing a generator as a DC motor that runs backwards.
Is this true? 
Can you change a DC motor to a Generator and vice versa without much labor?


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## ga2500ev (Apr 20, 2008)

GeeDub said:


> I saw an FAQ on a website describing a generator as a DC motor that runs backwards.
> Is this true?


Not even backwards. Pretty much spinning a DC motor will cause it to generate power.

The only issue is the fact that many motors are not permanent magnet motors, but instead are wired as series or shunt would motors. With these you have to generate a magnetic field in the field coils in order for the motor/generator to generate power.


> Can you change a DC motor to a Generator and vice versa without much labor?


If you lookup the concept of regenerative braking, you will see that it's essentially using a motor/generator to give motive force by applying power and recovering electrical power when braking. The only labor that's involved is having the controller generate the magnetic field as I described above. 

Hope this helps,

ga2500ev


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## major (Apr 4, 2008)

GeeDub said:


> Can you change a DC motor to a Generator and vice versa without much labor?


Hey GeeDub,

Without much labor? Depends. Basically all motors can run as generators, and all generators can run as motors.......if properly excited. And the proper excitation can be difficult in some cases. Take your car alternator. It is a generator. You can make it run as a motor, but you have to replace the rectifier with an inverter, add a shaft position sensor and excite the field properly. Some guys have actually done it. But it is a lot of work, more than justified for the result in my opinion.

Take a commutator PM motor. Easy to run as a generator. But a series wound DC motor. Yeah, it can do as a generator. But series generators are not stable. So it will give you big headaches to run as a generator. You can do it, but it takes special control (or excitation).

Hope that helps.

major


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## jamzky (Jul 4, 2008)

Conversions of motor-generators may be used for various conversions including the alternating current (AC) to direct current (DC), DC to AC, DC at one voltage to DC at another voltage and AC at one frequency to AC at another harmonically-related frequency. 

You can check the DC motor specifications here: coolmagnetman.com/magdcmot.htm. Following autopartswarehouse conversion basic steps won't take much labor.


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## tom_k (Jul 5, 2008)

*TO Jamzsky - Re: Convert Generator to DC motor?*

Jamzky;

I tried to follow the link for conversion to autopartswarehouse for conversion steps, but couldn't locate it.

Do you have a direct link to the page perhaps?

Thanks!

Tom


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## Dennis (Feb 25, 2008)

It is possible to run a field wound motor as a generator without an external excitation source by using the fact that some residual magnetism in the iron can be "amplified" by feedback action which is accomplished by hooking the armature circuit to the field circuit in a shunt wound motor for example. This small generated current will flow into the field coils increasing the magnetic field and therefore more current will flow from the armature circuit into the field coils and so on....


The downside? Well the RPM/volt constant is terrible so the speed would be high. However the load voltage characteristic of this generator is perfect for charging lead acid batteries. But like I said it's not very useful in EV applications due to the speed requirement..So the best option is to run a shunt wound motor with an external excitation source if you want to use the DC motor as a generator. The series wound motor though, just forget about it, not worth the trouble....


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