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Author Topic: Generator makes clocks show wrong time?  (Read 613 times)

N8FNR

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Generator makes clocks show wrong time?
« on: March 05, 2023, 09:05:29 AM »

We currently have a power outage due to a snow storm. Our backup generator fired up and keeps our furnace and fridge running along with everything else we need.
However I noticed something weird. Three of our clocks, the kitchen stove, an old digital clock and a real old wall clock are running fast. Once I noticed this I reset them all to the exact current time last night at 11:30 last night. Today I compared all of them at 11:30 AM and all are running 21 minutes fast.
The voltage is running at 115 which BTW is not uncommon during the summer when everyone has their AC on but the clocks never showed the wrong time.
What could cause these clocks to show the wrong time? If the power line frequency from the generator was not 60hz would it cause this?

73
Zack
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K7NI

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Re: Generator makes clocks show wrong time?
« Reply #1 on: March 05, 2023, 10:09:27 AM »

If you measured the frequency of the generator output, you would likely find that it is high. Many electric clocks rely on 60Hz from the power company as a time base.
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W7CXC

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Re: Generator makes clocks show wrong time?
« Reply #2 on: March 05, 2023, 10:33:13 AM »

Yup that's it. ;)
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KC6RWI

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Re: Generator makes clocks show wrong time?
« Reply #3 on: March 05, 2023, 12:51:51 PM »

Can running a fridge on more than 60 cycles damage it, thats one reason why I am reluctant to use a generator on my 10 yr old fridge.
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K9CTB

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Re: Generator makes clocks show wrong time?
« Reply #4 on: March 05, 2023, 12:58:53 PM »

That's one of the biggest bugaboos about backup and standby generators.  They are two-pole rotors that have to run at 3600 RPM to give 60 Hz.  Most single- or dual-cylinder gas engines won't provide the governor support to keep a constant 3600 RPM .... especially when the load changes.  I'm next to no help at all, but if you have to run your standby generator more than a few hours of time, make sure one of the clocks connected is a self-adjusting type that reads the satellite or WWVB.  Also, most Fluke multimeters have a frequency reading position on the mode switch.  Use it early and often. Set the no-load frequency for about 61.5Hz and that'll get you close when a load is attached.

73 de K9CTB
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N8FNR

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Thanks you all!
« Reply #5 on: March 05, 2023, 02:35:11 PM »

Thank you all for the replies!
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AF5CC

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Re: Generator makes clocks show wrong time?
« Reply #6 on: March 05, 2023, 02:37:01 PM »

I remember seeing that back at Field Day in 1982.  I was manning the novice station and brought my digital clock from home out to use for logging.  All power was provided by generators, and somehow I noticed that the clock was running slow after a while.  I assume I was wearing a watch, probably used that for logging after that.

73 John AF5CC
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WU0F

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Re: Generator makes clocks show wrong time?
« Reply #7 on: March 05, 2023, 03:27:45 PM »

For KC6RWI

A slightly higher frequency would be no problem, slightly lower could be.
Motors and transformers wound for 60 Hz don't like 50 Hz.  Check the label
on the refrigerator if it says 50/60 Hz there shouldn't be a problem.
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K4JJL

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Re: Generator makes clocks show wrong time?
« Reply #8 on: March 06, 2023, 06:15:02 AM »

Set the no-load frequency for about 61.5Hz and that'll get you close when a load is attached.

AC devices are supposed to tolerate +/- 5%.  You're good from 63 to 57 Hz.  If your no-load is 61.5 Hz, you may run under the 57 Hz lower limit under full load.
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K8AXW

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Re: Generator makes clocks show wrong time?
« Reply #9 on: March 06, 2023, 10:16:50 AM »

Zack:  Are you sure the clocks were running FAST? 

A generator must run faster than 3600  rpm to cause clocks (which uses the generator frequency as a time base) to run fast. 

Since you measured 115VAC I suspect that the meter you're using to measure the voltage is wrong or you meant the clocks were running SLOW.

You might want to invest in a meter called Kill
 A Watt Model P4400.01.  They are made by Intertek.  This little meter (which simply plugs into a 120VAC outlet or extension cord) gives a digital readout of volts, amps, watts, VA, frequency, power factor and KWH.  The accuracy is good enough for our use.  The meter can be had for less than $30.00.

I ran an old, 7 turbo-generator power plant for 22 years that didn't have sophisticated frequency control. We used two clocks.  One was on commercial power and one was on our system.  We ran the generators so that both clocks matched in time.  Sometimes we had to run slower or faster to get our clock back to the time showing on the commercial powered clock.  With the varying load of our paper mill, this was a delicate balancing act requiring almost constant attention.
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A Pessimist is Never Disappointed!

WA3SKN

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Re: Generator makes clocks show wrong time?
« Reply #10 on: March 06, 2023, 02:16:43 PM »

Many electric clocks use the 60 Hz (+/- 3%) as their reference. If the generator is off freq, the clock is off freq also.

-Mike. 
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W4JFA

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Re: Generator makes clocks show wrong time?
« Reply #11 on: March 28, 2023, 03:24:24 AM »

Zack:  Are you sure the clocks were running FAST? 

A generator must run faster than 3600  rpm to cause clocks (which uses the generator frequency as a time base) to run fast. 

Since you measured 115VAC I suspect that the meter you're using to measure the voltage is wrong or you meant the clocks were running SLOW.

You might want to invest in a meter called Kill
 A Watt Model P4400.01.  They are made by Intertek.  This little meter (which simply plugs into a 120VAC outlet or extension cord) gives a digital readout of volts, amps, watts, VA, frequency, power factor and KWH.  The accuracy is good enough for our use.  The meter can be had for less than $30.00.

I ran an old, 7 turbo-generator power plant for 22 years that didn't have sophisticated frequency control. We used two clocks.  One was on commercial power and one was on our system.  We ran the generators so that both clocks matched in time.  Sometimes we had to run slower or faster to get our clock back to the time showing on the commercial powered clock.  With the varying load of our paper mill, this was a delicate balancing act requiring almost constant attention.
Kill-A-Watt meters are extremely handy. Everyone should have one.
Bob
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