# A generator head question



## akseminole (Jan 5, 2014)

I have a question which the search function named google has been giving me the wrong answer to repeatedly.

My question is; can a generator head be used as a traction motor?

I ask because large gen sets come up on Craigslist fairly frequently where the engine is often questionable. 

It is my (perhaps flawed) understanding that a generator head unit is an electric motor being spun by an engine to produce electricity, to my logic it seems that if you applied electricity to the generator head that it should spin and generate force.. 
I do realize that it was not built with the intention of being used as a motor and so probably would not be efficient in that use. I don't know if gen set heads are durable enough to provide torque with intent to move a car. But they are built to be spun By a 5-100 hp gas or Diesel engine at a fairly constant rate and so should be able to withstand a given amount of torque, etc..

Anyway. I've been reading this forum since around late November and this is my first post. I have never done a car conversion though I have been somewhat idly considering doing one to either my 71 bronco or 77 CJ5. But that's a different post for a different thread.

Thank you for your replies and if this was covered somewhere else on the forum, I apologize. I did a search that had similar results to google which were basically the failed "can I do perpetual motion by spinning a generator with an electric motor to power my ev" thought experiment. Blech, how do so many people ask That question??


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## dougingraham (Jul 26, 2011)

akseminole said:


> My question is; can a generator head be used as a traction motor?


Maybe is the answer. Motors and generators share a lot in common but there are differences as well. There are lots of different kinds of motors and lots of different kinds of generators. Depending on the design it may not be practical to generate the waveforms necessary to spin a particular kind of generator. Even a 10kw generator turned around to become a motor is not going to be able to drive much of a vehicle. Probably something like a small motorcycle. This would be on the order of around 10hp continuous output after accounting for losses. A 100kw generator would similarly be able to do 100hp continuous.

If you want to have an easy conversion this is probably not a path you want to pursue.


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## akseminole (Jan 5, 2014)

Thank you for the response.

The generator question was more on the order of a random idea that popped into my head than a genuine interest in using it as a drive motor. I just couldn't find an answer to my question on google. 

No matter how I worded the question, google could only find answers to the question; can you use a motor to run a generator to run the motor or similar nonsense to that. I don't need google to understand why that Won't work and I wish google had the answer to why so many people are convinced that it Can. 


My main reasoning is that I've seen used 100-200kw ac generators with questionable engines on Craigslist in the 4-5k range. They may run or they may take work.. But they are definitely a giant electric motor... 

But I agree, it's not within my skill level of tinkering.


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## dougingraham (Jul 26, 2011)

akseminole said:


> No matter how I worded the question, google could only find answers to the question; can you use a motor to run a generator to run the motor or similar nonsense to that. I don't need google to understand why that Won't work and I wish google had the answer to why so many people are convinced that it Can.


Oh, Oh! I know this one. It is because they are not educated. It appears you can get out of taking physics courses in high school these days. And the internet appears to give credence to opinion without penalty.



akseminole said:


> My main reasoning is that I've seen used 100-200kw ac generators with questionable engines on Craigslist in the 4-5k range. They may run or they may take work.. But they are definitely a giant electric motor...


If you were going to do this what you would look for would be a generator that could handle around 30kw continuous. This would have the potential to operate in an EV at power levels of 150kw for short periods and the continuous rating would be adequate for highway travel.


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## Duncan (Dec 8, 2008)

Hi Akseminole

To try and answer your question 
Any motor can be used as a generator and any generator can be used as a motor

Can - not should or can be used easily

Motors/Generators come in a number of different forms
In my low level of understanding you can split this into two
Motors/generators with commutators
Motors/generators without commutators

If your motor/generator has a big beefy commutator it can be used with an easily affordable controller

If not then it will need an expensive controller that has to be custom matched to the motor/generator

Most Gen sets use AC motor/generators - and it is difficult to use them as a motor,


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