digital clock mystery

bgowg

Member
Location
Sterling Heights,MI.
Occupation
Retired master electrician
2 digital clocks connected to same circuit in condo both clocks would sometimes gain around 15 min. almost seems like 50Hz instead of 60
 

retirede

Senior Member
Location
Illinois
50 hz clocks connected to 60 hz would consistently run fast by 20%. They would not “gain 15 minutes sometimes.”

I have a digital clock with battery backup that runs fast whenever power is lost causing it to run on the battery.
 

gar

Senior Member
211201-2115 EST

A clock that derives its timing function from the AC line frequency does not run faster at a lower frequency.

A clock that runs from a battery and uses an internal timer, like a quartz crystal, runs at a rate defined by that crystal, and is independent of line frequency. That is my kitchen clock.

My computer clocks on recent computers run on an internal clock, but are often reset or corrected from Internet links.

Clock ( timer chips ) that I have and use have a built in battery, a quartz crystal time base, that is quite accurate. If you do not reset one of these clocks, then they hold quite good accuracy over a one year period. Also their internal battery is good for about 10 years with no external power applied. And longer, if external power ( +5 V ) is present most of the time. Dallas Semiconductor is the source of these modules, an oversized dual inline integrated circuit.

bgowg I have no idea how your clocks are made, designed, and why they would behave as you describe. Get different clocks.

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Missing info..... gain 15 minutes over what period (instantly? in 24 hours?)

There was a discussion about this a while ago. IIRC one of the promising ideas was power line noise that is sufficiently strong to count a "tick" to the time-base detector. Move one to another circuit and continue to monitor both.
 

synchro

Senior Member
Location
Chicago, IL
Occupation
EE
2 digital clocks connected to same circuit in condo both clocks would sometimes gain around 15 min.
If the clocks get their timebase from the AC line, there might be noise on the branch circuit that is creating additional triggers beyond the intended ones at the zero crossings of the AC waveform. And this would effectively speed up the clock. A good quality clock would have adequate hysteresis and filtering (and possibly also a phase locked loop) to prevent such false triggering, except under relatively severe interference.

Is there any appliance being used on the circuit with the clocks such as a vacuum cleaner, blender, washer, etc.?

I just noticed that zbang mentioned noise as a possible cause as well.
 

bgowg

Member
Location
Sterling Heights,MI.
Occupation
Retired master electrician
If the clocks get their timebase from the AC line, there might be noise on the branch circuit that is creating additional triggers beyond the intended ones at the zero crossings of the AC waveform. And this would effectively speed up the clock. A good quality clock would have adequate hysteresis and filtering (and possibly also a phase locked loop) to prevent such false triggering, except under relatively severe interference.

Is there any appliance being used on the circuit with the clocks such as a vacuum cleaner, blender, washer, etc.?

I just noticed that zbang mentioned noise as a possible cause as well.
I am leaning to that option of line noise or interference the clock are 2 different vintages 1 new 1 older model ,thinking back before retirement I had a problem within a half a mile of this location with a county building computer room rooftop condensers alternating system.Several comm towers on county building would actually energize the alternating cycle relay.It was looked at because of difference in hour meters on units.I actually saw the relay energize with both units at rest.Thanks for all the feedback from everyone
 

Hv&Lv

Senior Member
Location
-
Occupation
Engineer/Technician
Arcing on the line,PLC smart meter readings, I’ve come to find out a couple of different things can cause this.
Cheap clocks usually counting a part of a wave form rather than all of it.

 
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