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Cheesy
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Unusual Amount of Frequency Output

02/23/2019 6:58 AM

I have auxiliary windings in a welding generator machine. When running the voltage output is 220 vac @ 1500 rpm. Why is it when i measure the frequency i get a reading of 38 khz which is confusing. Looking for clarity on the reason why
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redfred
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#1

Re: Unusual Amount of Frequency Output

02/23/2019 8:43 AM

There's usually only a few reasons why test equipment produce baffling data.

  • The test equipment is not working properly.
  • The test equipment works properly but is reporting data not properly understood by the user.

I suspect the trigger level of your frequency counter needs to get above the noise.

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SolarEagle
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#2

Re: Unusual Amount of Frequency Output

02/23/2019 10:59 AM

38khz or 38hz? my wag's....If it's 38hz, I would verify the rpm is correct, it could be running slow....If it's 38khz it's either something is creating crazy harmonics or your frequency counter is set wrong or is malfunctioning...

The speed of alternator is determined by the below formula,

Ns=120*f/P

Where,

Ns=synchronos speed

f=frequency (50 hz in India /60 hz for EU)

P=NO. Of poles of synchronous generator.

Now generally say speed is determined as below,

If generator is 4 Pole machine than,

Ns=120*50/4= 1500 rpm.

It means that generator has to be rotated at 1500 rpm to get 50 hz frequency.

So at 1140 rpm you would get 38hz...

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SolarEagle
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#4
In reply to #2

Re: Unusual Amount of Frequency Output

02/23/2019 11:16 AM

You need one of these....

https://www.amazon.com/KEYSIGHT-U1242B-Handheld-Digital-Multimeter/dp/B00XNXB6FY

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#6
In reply to #2

Re: Unusual Amount of Frequency Output

02/24/2019 11:02 AM

Sounds like you hit the nail on the head.either his rpm indicator is wrong or his frequency meter is wrong.

I would bet on the RPM meter being the culprit.

If it is bad,a cheap work-around would be to use the frequency meter to adjust the rpm on the motor,via the governor adjustment.

Utilites use RPM to adjust their generator speed.(or used to anyway,I've been out of the loop for many years). May be solid state by now for all I know.

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#3

Re: Unusual Amount of Frequency Output

02/23/2019 11:08 AM

Put an oscilloscope on it to see what's coming out. There's no point in flying blind with just a frequency counter.

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#5

Re: Unusual Amount of Frequency Output

02/23/2019 1:49 PM

That’s twice the top end of human hearing and will be sending all dogs inside 150m radius around the twist. Unlikely or what?

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#7

Re: Unusual Amount of Frequency Output

02/24/2019 3:58 PM

A frequency counter can read wrong if the input voltage is too low or if it is too high. Try changing the sensitivity. You should have the same reading over a fairly wide range of input levels.

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#8

Re: Unusual Amount of Frequency Output

02/24/2019 10:29 PM

38 khz? Does this machine have HF noncontact start for TIG? If so perhaps you ar registering some harmonic of that HF.

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PWSlack
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#9

Re: Unusual Amount of Frequency Output

02/25/2019 9:45 AM

What did the <...welding generator machine...>'s manufacturer say during the telephone calls on this topic?

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#10

Re: Unusual Amount of Frequency Output

02/25/2019 3:25 PM

Along with all of the other replies regarding what the mfr. says and powers of ten, TIG welders now operate between 20 Hz and 400 Hz. So, what does the manual say it is supposed to be? TIG welders often have a foot pedal to change frequency while you weld. This is for better puddle control.

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