Single phase induction motor run as a generator 5

[watercooled]

Hello,
I want to use a single phase motor to start a small (1.5~2kW) 100cc 4 stroke spark ignition engine and then use the engine to run the motor as a generator.
How feasible is this?
I currently dont know the starting torque required to start the small engine, but my guess is that it would be relatively large and that the motor required to start it would be mismatched size wise to the engine when running as a generator as a result, leading to lower efficency in generation or would it?

 

[itsmoked]

An induction motor needs to be hooked to a "live" power line to be able to 'add' power to a network.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[waross]

Small garden tractor engines (about 8 to 18 hp) used to use a combined starter generator. They had a heavy series field winding for starting and a shunt field for generating/battery charging
As I remember them, they were forgettable. Poor starting torque and just adequate battery charging. There was too big a compromise for either function to work well.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[Skogsgurra]

Do you have 50 or 60 Hz available when starting the engine? Induction motors need that.

Also, a single phase induction motor has a very poor starting torque. And you need torque from zero RPM. So, it is not an optimal application.

And, finally, an induction motor doesn't produce much power if it doesn't have a grid to get its magnetization from. As Keith said.

If it is about charging batteries, as Bill mentions, then the necessary external rectifier and charge regulator (no excitation winding to control) makes this an even more impractical undertaking.

Gunnar Englund

http://www.gke.org

--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[watercooled]

Thanks for the replies.

I have a 50 Hz supply to start the motor, so I do have a live line to add power to the network and that is what I am planning to do. But as Skogsgurra said the low starting torque of single phase induction motors is going to be a problem I hadn't thought about. Sounds like I will need to add a starter motor for my engine.

You would lose on the generation side too, the generator/motor would be oversized for the engine which would mean greater losses there.

Too big a comprimise for either to work well.

 

[ccjersey]

You might investigate a "clutch" arrangement where you could start the electric motor and once it is up to speed, it would perhaps have the torque to start the engine.

Some sort of belt tightening arrangement is what I had in mind, though there would certainly be other ways to do it.

Another situation that might be useful would be a diesel engine with decompression to make it easier to get it spinning.

 

[pisimatza]

I know(at my grand parents-15 years ago ) a 1 ph motor, running a circular saw. And from the network, the voltage was low (is allmost the last house from the supplying transformer). But, with a rope(motor will not start only with capacitor or with a rope )and patience, grandpa started the 1 ph motor , not on load.
And then, with a "clutch arrangement" slowly connected the motor to the saw. 50 % of the cases, the motor and the saw started, and after start there is no problem.
Clutch arrangement is like in attachement.

But please don't do like this. It is not safe! (grandpa survived WWII- it was brave ). You should not do it.
For my knowledge:
1. Electric motor speed isn't too big to start an engine.
2. For electric people: what kind of energy will produce that generator? Isn't frequency related to generator speed, you have to control engine speed continuously, to have 50(or in US -60) HZ.
Is speed(in Rotations Per Minute) = 60f/p?
How about the voltage, will that be OK?

 

[cranky108]

Induction generators require a var source, either from the line or a capacitor. The var source will determine the voltage. Not enough var support and the voltage will be low, to much and the voltage will be high. The var support required will change with the amount of generation.
The frequency output will always be less than the speed would lead you to calculate for a sync. generator.

Warning some ac motors can't be used as generators, it's just the way they were made. And some can be used as generators, but will have over heating problems because of the way they were made.

 

[watercooled]

Thanks for the responses,

The clutch arrangement is interesting, much simplier than using an extra starter motor with extra battery and all the other extra associated wiring.

Is the over heating problem coming from the extra coil needed to start induction motors? This coil would be switched out using a centripetal switch once the motor is up to speed, so I wouldn't expect heat losses there. So where is the extra heating coming from?

 

[cranky108]

I think the rotor of many induction motors is not sized for the expected current of being used as an induction generator.
You are right the extra coil for starting should be switched out.

If you will be using this induction generator off line you will need some way to build a voltage. Either you have to depend on residual magnitisum, or be able to flash a voltage in the system to develop the magnitisum.

 

[watercooled]

Thanks for the responses, Excitation of the generator is not going to be a problem.

If any one could point me towards a website or book that could provide some figures to back up the discussion around the torque of single phase induction motors at start up or the extra heat/losses that could be expected from a induction motor when used as generator that would be good.