230V synchronous motor to generator - Page 1
Forum section: electronics / general

author: lufihengr
author_rank: Contributor
timestamp: September 17, 2023, 12:42:45 pm
content: 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 secretThere 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.

author: Benta
author_rank: Super Contributor
timestamp: September 17, 2023, 04:33:43 pm
content: Quote from: lufihengr on September 17, 2023, 12:42:45 pmOr 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!"

author: lufihengr
author_rank: Contributor
timestamp: September 17, 2023, 04:37:50 pm
content: A book? What's that?Jokes aside, maybe I do need to visit the library for once

author: Zero999
author_rank: Super Contributor
timestamp: September 17, 2023, 05:02:29 pm
content: 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.

author: lufihengr
author_rank: Contributor
timestamp: September 17, 2023, 05:27:01 pm
content: 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

author: johansen
author_rank: Super Contributor
timestamp: September 17, 2023, 06:14:17 pm
content: 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 $20I dont know how much power is wasted in cheap 5kw brushless, 3rd harmonic excited generators, as i have never found one to take apartFor 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.

author: TimFox
author_rank: Super Contributor
timestamp: September 17, 2023, 09:34:06 pm
content: 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.

author: geggi1
author_rank: Frequent Contributor
timestamp: September 18, 2023, 01:20:43 am
content: 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.