Using electric motor as a generator

[Pooh_Bear]

I have some big single phase electric motors here.
3hp 110v/220v 32 amps/16amps. 1725 RPM.
They were used to power hydraulic pumps.

I would like to convert one to a generator and run it off my PTO.

Has anyone here done this, or know how to.
How much power can I expect to get out of this.
If I could get 3000 watts I would be real happy.
I'm using a 700 watt inverter now and it almost covers everything I need.
But I have to run the tractor at full throttle.
Was also thinking of just running an alternator off the PTO.
Hook it up a to a battery and run the inverter off that.
Gear it so the tractor can run at idle up to 1/4 throttle.

I can't afford to go by a generator. Even a used one.
So I was hoping I could just build one with stuff I have.

Thanks.

Pooh Bear

 

[shawnspeed]

you can use a 3-phase electric motor to generate current with ,but,you must excite the windings first, with 110 or 220 whichever you wish to produce, then spin the motor faster than the 1725 rating to generate excess electricity. you can also modify the armature ,and imbed some rare earth magnets to excite the windings. I can look at the plans That I purchased through a small scale steam site I found,and clarify a few things if you wish....but it sounded like it was more work than it was worth... Shawn
P.S. Watts =Volts x amps......110x32=3520 Watts

 

[bill18163]

I know that if you reverse the field in a DC motor it then becomes a generator. This is how diesel electric locomotives stop a train or control their speed on a downward grade. Mechanical brakes would never stop a 100 car train traveling 70mph. But I don't know how that would work in an AC motor.

 

[michiman]

I have wondered about doing this too.

 

[Ford960]

Do these motors have brushes?

The residual magnetism in the stator will allow them to self excite and produce a small current that can be used to regulate the output. You can build a pulley system to increase the speed at a lower tractor rpm. Use a volt meter to set the require output speed and this should equal 60Hz.
And remember...PICTURES!

 

[Pooh_Bear]

What I have found on the internet seems to say you just put a capacitor across the motor leads and hit it with a short pulse of current to excite the field.
From what I know about using a 3 phase motor to generate that 3rd phase from single phase power it sounds about right.
And I understand you have to spin the motor faster than rated speed to make up for internal losses.
It may be 3520 watts but I won't get that much out of it.
I'll be happy if I get 3000 watts.

And what about frequency. It's gonna be off some. But will it hurt other motors to run with the wrong frequency. I'm thinking a weed eater and other small stuff. Maybe an electric chainsaw.

Pooh Bear

 

[dentonsisk]

I read these forums alot. As I am currently converting an old mill dam and site to hydroelectric. Lots of discussions her about alternative power.



check out the links at the bottom of the webpage.Welcome to OTHERPOWER.COM

 

[Henro]

I have some big single phase electric motors here.
3hp 110v/220v 32 amps/16amps. 1725 RPM.
They were used to power hydraulic pumps.

I would check out that site that was referred to in the post above (sorry, can't see the poster's name right now).

But I think the short answer is that you have single phase induction motors. My bet is that it is highly unlikely that you will be able to convert this type of motor into a generator that is of any practical use.

Do let us know if you find a way...

 

[Brad_Blazer]

I wish I had one of those motors for my lathe! You should consider selling the motors - you might make enough to buy a generator head e.g. the $279.99 item 45416 at HF. Interesting - when I just searched their site I noticed some turnkey pto generators. Maybe they are actually getting into farm implements.

 

[Volfandt]

If all your going to run is AC power tools that have brushes then you might try modifying a std 65 - 150 amp alternator to output around 105 - 120 VDC.
Basically all you have to do is bypass & remove the regulator and modify the brushes to where they don't use frame ground for the stators return.
I modified a 65amp Delco to run off of my WheelHorse L&G tractor and it not only powers tools and std incandescent lamps but will also weld upto 1/4" steel.
It won't run any 120VAC devices that uses transformers in their power supply's, which is the majority of consumer electronic eqt, but it will power anything that has brushes that contacts a stator or commutator which is most electric tools.

I am very curious about useing an AC motor to produce pure signwave AC but like's been mentioned, the frequency may not be the desired 60 hz we need.
Even tho I'd like to fab a genset up, I think the best bet is to find a genset with a blown engine....
Volfandt