Cheap display has weird frequency count

I bought an inexpensive volt/frequency led display from eBay. On a generator, I get the proper frequency display, around 60 Hz. When I tried it on a dc to ac inverter, square wave output, I get around 120 Hz. It's a two wire device, with power and signal coming off the same wire.

What could I expect to see if a scope was connected to that inverter? The thing runs everything I've plugged into it, with a bit of noise on radios and such. Drills and things work fine. So do small induction motors.

mike

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m II
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A cloud of magic smoke. ;)

I expect that it doesn't have adequate filtering, and that there's overshoot on the inverter's output.

Cheers

Phil Hobbs

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Dr Philip C D Hobbs 
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Phil Hobbs

The inverter may not be putting out a very pure wave form. Frequency counters often expect a sine wave and will sometimes give a multiple of the actual signal. It could be trying to count the rising part of the wave and if a spike on the falling edge it may trigger on that. Some motors will run ok on power that is not near 60 hz. Try it with a simple analog clock and see if it times correctly or if it runs fast.

Reply to
Ralph Mowery

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