How does a rotary machine produce such a waveform? - Page 1
Forum section: electronics / general

author: G7PSK
author_rank: Super Contributor
timestamp: July 16, 2012, 12:13:44 pm
content: This is the waveform of a cheap Chinese alternator set. I am amazed that a rotary machine is able to produce a waveform with such flat sides to it, almost a trapezoid shape, i have only seen this type of waveform on electronic oscillators before I expected a bit of noise at the peaks where the AVR cuts the field or more usually on these small size machines shorts out the field when the voltage gets too high but the flat sides to the wave instead of a sine. This is something I have never seen on UK or Italian made alternators which is what I usually use.

author: SeanB
author_rank: Super Contributor
timestamp: July 16, 2012, 03:32:25 pm
content: At a wild guess if youn disconnect the AVR the output would be around 500VAC and a sine wave. Looks just like a voltage clamp that disconnects the excitation voltage.Have you tried it at full load with a resistive load like a heater or such? It might be somewhat more sine like then.

author: G7PSK
author_rank: Super Contributor
timestamp: July 16, 2012, 03:42:09 pm
content: It was about three quarter's load when I took that, all the alternators that I have looked at before had a sine wave with just the effects of the clamping showing on the peaks but this unit produces very flat sides to the wave almost approaching square wave, as I said before without the squiggles on the peaks it would be trapezoid in shape for each half wave.

author: G7PSK
author_rank: Super Contributor
timestamp: July 16, 2012, 04:23:52 pm
content: It's solved, just spoken to one of the manufactures I deal with in the UK. It is to do with the amount of skew on the stator coils or rather the lack on the cheap Chinese ones.

author: siliconmix
author_rank: Frequent Contributor
timestamp: July 19, 2012, 08:47:45 pm
content: i wonder what a "dyson motor's " waveform look's like .it's supposed to be digital ?.good vacuum's encased in shit plastic.only ever bought one.

author: G7PSK
author_rank: Super Contributor
timestamp: July 19, 2012, 09:20:50 pm
content: I have 2 Dysons there is nothing digital about them except the number of digits on the price tag both have plain old universal type motors the brushes went on one you cant even buy the brushes you have to buy the complete motor. Got 2 due to one blowing up so wife went and purchased another then I found that the other one still had a few weeks left on the warranty so I phoned Dyson's and they sent two men round to fix it they replaced the switch which had broken the lead drive belt hose and brush the one that sweeps the carpet, the motor brushes went on the new one.

author: SeanB
author_rank: Super Contributor
timestamp: July 20, 2012, 04:54:05 am
content: To be fair to Dyson the motor fan assembly is only around $25 as a spare part. I buy them for the Columbus at work, and they are tenth of the price of the OEM part, and have the same life. There are really only around 8 different motor fan units among all the cleaners, from the low end to the top of range industrial units. The only exceptions are the real cheapies that last around 20 hours of use, and the really big ones with TEFC motors that can inhale bricks.

author: siliconmix
author_rank: Frequent Contributor
timestamp: July 20, 2012, 06:56:27 am
content: Quote from: SeanB on July 20, 2012, 04:54:05 am"and the really big ones with TEFC motors that can inhale bricks." lmao

author: G7PSK
author_rank: Super Contributor
timestamp: July 20, 2012, 07:31:29 am
content: I once got asked by a large local land owner who had invested a large amount of money into a vacuum machine to have a look at what had been developed so far and advise him on its manufacture and as to whether I would manufacture it for him. He had paid a huge amount of money for his prototype that he brought along, it was powered by a twenty horse power petrol engine and had a ten inch suction hose and would pick up bricks and stones.I told him that it was dangerous as it was and I would not wish to have any thing to do with the machine as the stones and bricks that did not come out of the fans exit at 200 miles an hour exited through the 6mm thick casing of the machine like bullets.He took the machine away to do further work on it and I never heard from him again.