Is this harmonic distortion (AC generator output) - Page 1
Forum section: electronics / projects

author: aquaaddict
author_rank: Contributor
timestamp: November 03, 2016, 12:05:01 am
content: HiThis is the output from a 5KW generator running with no load, its a 15 year old high end marine unit not a cheapo portable, but I was dissapointed to see the poor quality of the output:Does this look like harmonic distortion (its traditional stator based unit not digital inverter) or do you think it is caused by somthing else? If it is harmonic distortion I presume not much can be done about it?(Apologies if its not 'electronics' related enough question but there is such a great variety of related knowledge on this forum. I did ask the manufacturer but they just refer me to a dealer, and the dealers just want to come and service the engine side of it without appearing to have any true understanding of the electrical side)Thanks Anthony

author: danadak
author_rank: Super Contributor
timestamp: November 03, 2016, 02:09:44 am
content: Use scope cursors to measure ripple frequency, then youwill know if its harmonically related.Is the scope picture taken with unloaded mains ? If not isolateone at a time to eliminate load related issues.Regards, Dana.

author: AlfBaz
author_rank: Super Contributor
timestamp: November 03, 2016, 02:36:34 am
content: If it's an alternator does the rotor have slip rings(2 off) or does it have a separate exciter bolted on the back of it?If it's the latter the ac generated by the exciter's armature will be AC that is then rectified by and passed through or along the shaft to the alternators rotor. You may have a blown diode in the rectifier

author: singapol
author_rank: Frequent Contributor
timestamp: November 03, 2016, 02:53:32 am
content: The info is on the scope screen. Timebase is 2msec. One cycle of waveform occupy 10 divisions.10X2msec. = 50hz. There are 2 humps in per square graticule...One hump is 1/2 of 2msec. = 1 devide by 1msec.=1000hz. ..rough calculation.I would check the bridge diode rectifier first then the capacitors but be careful this is 5KW power supply. wear safet glasses if you have them. BTW what do you want to do with such a big power supply?

author: cvanc
author_rank: Frequent Contributor
timestamp: November 03, 2016, 03:00:31 am
content: Does the waveform "calm down" with a load applied to the generator?(obscure generator testing tip: Go to your kitchen and get the toaster! Makes a nice ~1 kilowatt load LOL)

author: johansen
author_rank: Super Contributor
timestamp: November 03, 2016, 06:51:35 am
content: you have 24 slots on your stator.. unless its 4 poles, and then you have 48.it will all go away if you put a 20-60uF capacitor across the 240v output of your generator.a 5kw generator will have about a 10vac increase in its no load output voltage with a 60uF cap across its 240v output.if you want to improve the voltage regulation of your system, add capacitors at each load sized for the load. for example a refrigerator might only be 100 watts but it could draw 3 amps of reactive current, so the voltage drops even though the load isn't that much. keep in mind though that capacitors and switches don't go together. NTC resistors are your friend here... don't go overboard with the capacitors, and don't use them to compensate for resistive loads, no point in doing that.