Author Topic: 230V synchronous motor to generator  (Read 973 times)

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Offline lufihengrTopic starter

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230V synchronous motor to generator
« on: September 17, 2023, 12:42:45 pm »
So I have been trying to figure out how to use a 230V synchronous motor as a generator.

Is it correct that it will output 230VAC at any RPM? Do I need anything except a way to spin it at 50Hz?

I have been trying to figure this out, but it seems it’s almost a trade secret :D

There are some kind of excitation control boards as spare parts for gensets, but unclear if it is necessary.

It needs excitation of some sort of course.
 

Offline Benta

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Re: 230V synchronous motor to generator
« Reply #1 on: September 17, 2023, 04:33:43 pm »
I have been trying to figure this out, but it seems it’s almost a trade secret :D
Or a rethink from "I can probably find everything I need for free on the web" to "Perhaps I need to buy a good book here. Darn!"
 

Offline lufihengrTopic starter

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Re: 230V synchronous motor to generator
« Reply #2 on: September 17, 2023, 04:37:50 pm »
A book? What's that?  :o

Jokes aside, maybe I do need to visit the library for once
 

Offline Zero999

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Re: 230V synchronous motor to generator
« Reply #3 on: September 17, 2023, 05:02:29 pm »
The motor will have a certain V/Hz characteristic. In other word, you're mistaken. The motor's shaft needs to be rotated at the rated speed to give 230V out and even then, the voltage will probably drop when loaded. If this is unacceptable, then add more turns to the motor or use a transformer to increase the voltage.
 

Offline lufihengrTopic starter

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Re: 230V synchronous motor to generator
« Reply #4 on: September 17, 2023, 05:27:01 pm »
I see, so for 230V output, I need to spin it at the rated speed. More amps out = more torque in.

Now the question is with an externally excited motor/generator, how/what to use to control the exciter current
 

Offline johansen

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Re: 230V synchronous motor to generator
« Reply #5 on: September 17, 2023, 06:14:17 pm »
I was confused for a long time on the excition problem until i found out that even gigawatt sized generators have 30% regulation under load.

Cheap generators achieve regulation by saturation. They waste 600 watts in the rotor and stator at no load on a brushed, 5 to 6kw 3600 rpm gen head.

You can buy an avr on ebay for $20

I dont know how much power is wasted in cheap 5kw brushless, 3rd harmonic excited generators, as i have never found one to take apart

For what its worth i removed 3 pounds of copper from a single phase 5kw generator and put 5 pounds back in. Made a nice 10 pitch, 24 slot, 2 pole 3 phase winding, very nice sine wave output.
« Last Edit: September 17, 2023, 06:17:37 pm by johansen »
 
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Offline TimFox

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Re: 230V synchronous motor to generator
« Reply #6 on: September 17, 2023, 09:34:06 pm »
In general, the output voltage of a rotating generator (with given windings, etc.) is proportional to the field strength and the rotational speed, and the torque required for rotation is proportional to the load current.
For different types of generator, the analysis of the fields, etc. can be complicated and a function of construction type.
 
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Offline geggi1

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Re: 230V synchronous motor to generator
« Reply #7 on: September 18, 2023, 01:20:43 am »
Assuming your motor has sliprings.
You will need a voltage regulator (AVR) to controll the magnetizing.
The AVR must be capable of delivering enough current at the correct voltage to get your 230V. This voltage and current can normaly be fond on the dataplate or in the datasheet of the motor.
The RPM is the same as what the motor is suppose to run when it is used as a motor at 50Hz.

The power source for the generator must take in to account the internal loss of the motor. This is found on the dataplate or the datasheet of the motor.

If voltage regulation is less critical you can have an ajustable power supply for magnetizing. Just set the voltage at a wanted level and tune it a bit if required.
« Last Edit: September 18, 2023, 04:43:47 am by geggi1 »
 
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