induction motor as generator

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social misfit
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Joined: Thu Jul 03, 2008 6:53 pm
Location: dorset

induction motor as generator

Postby social misfit » Thu Jul 03, 2008 9:12 pm

has anyone ever tried it and if so what were the results.

microman
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Location: Durham

Postby microman » Fri Jul 04, 2008 7:08 am

Only accidentally, and the sustained high voltage with no load blew up the capacitors! But in principle it can be done.

NickJ
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Joined: Thu Jun 26, 2008 12:34 pm
Location: N Wales

Postby NickJ » Fri Jul 04, 2008 7:29 am

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 http://www2.cat.org.uk/shopping/index.p ... 15bc429c10).

hope this helps :)

Nick

2e0bax
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Postby 2e0bax » Fri Jul 04, 2008 10:04 am

Yes i have here http://homepage.ntlworld.com/s.amesbury ... motor.html it gave a constant charge into 100ah of around 1 amp but would give more if the blades were better. sean

NickJ
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Joined: Thu Jun 26, 2008 12:34 pm
Location: N Wales

Postby NickJ » Fri Jul 04, 2008 10:38 am

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.

N

social misfit
Posts: 32
Joined: Thu Jul 03, 2008 6:53 pm
Location: dorset

re induction motor as generator

Postby social misfit » Fri Jul 04, 2008 10:52 am

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

NickJ
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Joined: Thu Jun 26, 2008 12:34 pm
Location: N Wales

Postby NickJ » Fri Jul 04, 2008 11:42 am

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

n

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ChrisB
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Postby ChrisB » Fri Jul 04, 2008 10:14 pm

I'm still awake at the moment :wink:

ChrisB
I reject reality and substitute my own !!!!!!

bobc
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Postby bobc » Wed Jul 09, 2008 3:54 pm

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....!!
Bob

social misfit
Posts: 32
Joined: Thu Jul 03, 2008 6:53 pm
Location: dorset

re induction motor as generator

Postby social misfit » Wed Aug 27, 2008 11:24 am

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


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