Cheap display has weird frequency count

[m II]

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



--
It is hard enough to remember my opinions, without also remembering my
reasons for them!

Friedrich Nietzsche

 

[Phil Hobbs]

On 06/23/2017 01:30 PM, m II wrote:

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

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


--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510

hobbs at electrooptical dot net
http://electrooptical.net

 

[Ralph Mowery]

In article <oijj12$jid$1@dont-email.me>, C@in.the.hat says...

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.

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.