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induction motor as generator

Posted: Thu Jul 03, 2008 9:12 pm
by social misfit
has anyone ever tried it and if so what were the results.

Posted: Fri Jul 04, 2008 7:08 am
by microman
Only accidentally, and the sustained high voltage with no load blew up the capacitors! But in principle it can be done.

Posted: Fri Jul 04, 2008 7:29 am
by NickJ
Induction motors can make good or bad generators depending on application. They are great for constant speed applications without major overloads and were used in many of the older "big white" wind turbines as a running motor will generate if overrun (hence easy regenerative braking in EVs with AC motors). They don't make good gennys for variable speed applications such as small wind.

As per the previous post the major problem is that if wired for self excitation with capacitors the voltages can be horrendous due to resonant effects (it is quite possible to achieve 1000v or more if you get it wrong) however there are ways...see "motors as generators for micro-hydro power" IT publications which is great on the subject (see ... 15bc429c10).

hope this helps :)


Posted: Fri Jul 04, 2008 10:04 am
by 2e0bax
Yes i have here ... motor.html it gave a constant charge into 100ah of around 1 amp but would give more if the blades were better. sean

Posted: Fri Jul 04, 2008 10:38 am
by NickJ
ah! but now its no longer an induction motor its a PM alternator :)
This will of course work as a generator for small wind and is the basic idea behind most turbines up to 15kW. The problem with an actual induction motor is that it has a very limited speed voltage range due to the the large variation in inductive reactance in the rotor with speed/excitation, hence my comments above.

They work well on hydro, no PMs needed.


re induction motor as generator

Posted: Fri Jul 04, 2008 10:52 am
by social misfit
i tried it yesterday on a 1 hp three phase motor,using three 40 micro farad capacitors and got 230 volts per phase,going to see what the frequency is today.
and all things being equal will drive it off a suffolk colt lawn mower engine,which produces one to one and a half hp,then to use an alternative fuel, thus making it cheap to run,thats the theory anyway. :D

Posted: Fri Jul 04, 2008 11:42 am
by NickJ
without wanting to teach anyone to suck eggs :D if the the motor is 2 pole (will haver a plate rating of approx 2800 rpm) it will need to be driven at 3000 a to get 50 hz (50hz=50rps=3000rpm) for the 4 pole motor (nominal speed on the plate 1440 rpm ish) then 1500rpm for generator.

The plate speed is lower because of slip.

The induction motor is an amazing machine and the physics/maths behind it are super. The explanation for its function and properties will send most people to sleep within minutes! :D


Posted: Fri Jul 04, 2008 10:14 pm
by ChrisB
I'm still awake at the moment :wink:


Posted: Wed Jul 09, 2008 3:54 pm
by bobc
I know the Nuvinci CVT are being sold into windmill applications - seems like a good idea.
Actually the slip principle works in generation too, so to get 50Hz out of the induction motor as a 'generator' you have to put more than 1500/3000 revs in.
We use this principle to make cheap regenerating load banks for drives testing at work. Optimising blade pitch and CVT ratio sounds like a jolly set of sums....!!

re induction motor as generator

Posted: Wed Aug 27, 2008 11:24 am
by social misfit
tried a smaller one using a 1/3 hp motor and got 300 watts out of it :D driven by a butane/propane fuelled lawn mower engine