Inverters cause time shift

[iFred]

This week I hooked up all of my lights and digital clocks to my inverters and APC units and was sort of amazed to find that all my digital clocks are showing times that are 3-5 hours out. For example if it was 1pm real time, the clocks running on the inverters and APCs would show something like 3 or 5 oclock. Very interesting!

Modified sine waves are not good for digital clocks! has anyone else had this problem?

[Victor]

This is a common problem with MSW. The clocks see 4 zero crossings/cycle insted of two because of the deadband.

Victor

[TomW]

Guys;

Correct me if I am wrong, but aren't digital clocks run from a crystal for the timebase and use all DC voltages internally?

Motor driven clocks would obviously be affected by ac frequency / waveform variations but once rectified to DC for use in the digital clock that would seem to not be a factor?

Kind of confused here since a crystal theoretically produces a constant frequency under varying conditions.

My one digital clock that is on an APC has not varied on time for like 2 years so I wonder about why yours does, fred? Maybe there is some other factor at work here? Just thoughts from here.

Cheers.

TomW

[Victor]

"Correct me if I am wrong, but aren't digital clocks run from a crystal for the timebase and use all DC voltages internally?"

 I think some of the cheaper clocks use the power line freq. for timing.

The syncronous motor clocks will run fine on MSW becouse its not the frequincy that is the problem it is the wave shape that tricks the digital into running at twice the speed. The clock may not run exactly twice as fast though because it probably runs correctly some of the time.

 Just unplug the clocks. That way they give the exact time twice a day.

Victor

[baggo]

5kw is correct in saying that some of the cheaper clocks use the line frequency as the timebase for the clock and the MSW will cause problems with these. Also the cheaper MSW inverters are not Xtal controlled and the output frequency can vary by + or - 1Hz (or maybe more) which could give nearly half an hour error in every 24.

John

[Wolvenar]

I remember old heathkit clocks using the 60hz as a reference, but since those long past days, I'd be surprised to see a clock that is not crystal controlled, the cost differences are insignificant.

 I would be lead to believe however that cheaper clocks circuitry may be affected by the high frequencies or harmonics of invertors, in similar ways that RF devices like HAM radios will mess with a cheap digital clock

Besides when you look at these clocks in a different light, they aren't much worth having in a RE system or battery backed one, they are quite inefficient compared to battery operated ones. Battery operated ones are immune to power troubles, and you could use rechargable batts in them , which you could swap with the batts in a solar charged yard accent light.

[Ungrounded Lightning Rod]

Correct me if I am wrong, but aren't digital clocks run from a crystal for the timebase and use all DC voltages internally?

Virtually all line-powered clocks use the line frequency as a time base, not a crystal oscilator.

This is because even, say, an error of 50 PPM (i.e. a moderatly GOOD crystal oscilator) will gain or lose 4 1/3 seconds per day.  Customers would complain and pitch it out.

Meanwhile, the power company adjusts the line frequency continuously so that a synchronous motor attached to a clock face by a gear train will hold against the national bureau of standards timebase within a small fraction of a second as long as it is powered continuously.

Indeed:  Using power to distribute accurate time to cheap synchronous-motor clocks was one of the original selling points for AC, and planned before the sale of the first hookup (if I recall my history correctly).

If you want to power a clock off an inverter (which has rotten regulation as a timepiece even if it IS sine wave) and have it keep accurate time, get one of the "atomic clocks" - actually a crystal-oscilator clock with a radio that updates it from one of the WWV broadcasts.

[Ungrounded Lightning Rod]

Indeed:  Using power to distribute accurate time to cheap synchronous-motor clocks was one of the original selling points for AC, and planned before the sale of the first hookup (if I recall my history correctly).

Indeed:  In the early days, one local power company that wasn't yet grid-connected had a half-hourish outage.  So they decided to do the town a favor and run a little fast until the clocks were back to keepting correct time.

Of course the townsfolk reset all their clocks, and were really confused and annoyed when they gained another half-hour over the next day.  So nobody tried that again.

(Now with the national grid it's not practical any more, anyhow, since everybody's on the same timebase in order to stay hooked up.)

I wonder if any commercial inverters have a reference clock input?  Or if you could convince a grid-tie design to sync to a reference but not power from it?

[iFred]

Well, this is really weird then, cause my phone which has a digital lcd display and has like every known function to man a phone could have has also a clock with the built in functions, well I accidently hooked up the wall wort for it to the inverter and it's clock is also off, so somethings up, not sure what. The wall worts convert ac to dc at like 12 vdc, so it must contain a crystal and yet it's out as well... Go figure...

[Victor]

Are you sure the wall wart's output is DC some are low voltage AC.

Victor

[Ozwald D]

My pulse-mig welder foibles almost any digital equipment that's placed within about a 20ft radius when I'm welding. I guess it's some kind of emp effect because of the high-power dc square-wave. I have one radio that has MP3 CDR playback and it always goes haywire. But, if I'm playing a regular CD there's no problem.

You might have one device in there somewhere that's putting out a really noisy square-wave and it's scrambling the digital stuff a bit, extra signals popping around inside the clocks and stuff.