Electromechanical Appliance Timers

I've gotten curious about the accuracy or not of these. I am speaking of the motor-driven timers with a 24-hour dial on the front.

Obviously not something someone would use where precision is required so this is purely an academic question.

I was under the impression that these were driven by tiny sync motors and therefore as accurate as the power line frequency just like a traditional electric wall clock. Not easy to set precisely but should repeat nearly to the second day after day. Or so I thought.

Recently, using a timer on Christmas lights, I noticed variation as much as a minute. But that was a newer timer and I don't know what kind of motor it has. I know on the older ones, the motor rotor could randomly start in either direction but there was device in gear train that would kick it to reverse if it happened to start by running in reverse. Doesn't that sound like a sync motor?

So for a few days I've been running a little experiment. I have a number of timers of various vintages. I ran each to where it just kicked on then unplugged it. I put the group on a couple of outlet strips and powered them at the same time, each hooked to an indicator lamp. At the expected time each night I put a smartphone running an NTP-connected clock app nearby and video the scene with another phone so as to produce a record of when each turned on. I was expecting them to switch on a few seconds before the designated time (based on how many seconds elapsed during the setup adjustment between the timer triggering and my unplugging it) but the variation has been much greater, nearly a minute early on one but generally all over the map and different each night and not in unison as though the power line frequency* had varied. Maybe this is from mechanical variations from the switch part of the timer snapping over. Or maybe they are not sync motors after all.

  • I think the utilities used to make up for lost or gained time keeping it

variation I see though it could be some of it.

Again, there is no practical point to this; a digital timer can be used where precision is needed. I am just curious.

Reply to
Steve Kraus
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These devices usually run on a cartridge motor, often paired with a non-syn chronized motor if any torque is really needed. The synchron more-or-less g overns the standard motor - within very broad limits. As you note, these ar e not designed to be precision devices as there is really nothing to be gai ned on a cheap timer that gets reset every so often. But any load on the mo tor for these devices will definitely slow things down until it re-aligns.

If it is a purely cartridge-driven device - a regular electric clock for in stance, there is a very short gear train of lightweight gears and a soft-sw itch for the alarm function, if any.

More-so, tariffs now are far less stringent on AC frequency, as you noted. Keep in mind that it is no longer a small, happy family of large utilities, but a much broader family of small generators, many using very small solid

-state grid-tie inverters that may be very precise in frequency regulation

- but may not be instantly synchronized to the grid when they come on-line. And solar micro-converters are nightmares as not only do they need to alig n to the grid, but to each other as each comes and goes on and off-line. Th e process is very nearly instantaneous, and the are not supposed to tie unt il properly synched - except...

Peter Wieck Melrose Park, PA

Reply to
pfjw

If they are only a minute off, or even 5 minutes, you're doing good. They are not meant for precision.

Reply to
oldschool

I'm not familiar with the term "cartridge motor."

Here is a photo of one type of timer motor. I was under the impression, perhaps wrongly, that this is a sync motor. This one does start either way and there's a thing in the gear train to jam it and cause it to reverse if it starts up in reverse.

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If this is in fact a sync motor then the variation I see must just be something with the actual switch mechanism and how it snaps over each time.

snipped-for-privacy@aol.com wrote:

Reply to
Steve Kraus

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This is a cartridge motor with the gear-train included. They come in many variation, including a double-layer device for additional torque. They are usually about 40mm across, but can be smaller/larger.

Peter Wieck Melrose Park, PA

Reply to
pfjw

IT TOOK SITRE MAGANA ABOUT FIVE MINUTES TO CUT HIS HAMSTER UP WITH A PAIR OF SCISSORS.

Reply to
Steve & Lynn

" snipped-for-privacy@aol.com" wrote in

So that *is* a sync motor?

I need to go to Goodwill or someplace and find a sync motor clock with a second hand and see how much variation it has (no switch mechanism friction to overcome) against an accurate reference like an NTP server as that would tell me how the power line is varying these days. That may be part of it.

Reply to
Steve Kraus

Four of five timers were trending the same way suggesting power line frequency.

From 2/20 to 2/21 to 2/22:

Timer B1 got 47 seconds later then 38 seconds earlier.

Timer B2 got 55 seconds later then 58 seconds earlier.

Timer C1 got 41 seconds later then 32 seconds earlier.

Timer C2 got 82 seconds later then 39 seconds earlier.

Timer D1 got 10 seconds earlier then 14 seconds later.

The B's are nearly identical to the one whose motor I showed. The C's I've never had open. The D's I've looked at but have no clue if it's a sync motor or not. If not, it's kind of funny as that one seems to hew most closely to the expected turn-on time.

Getting a vintage electric wall clock off eBay. Will set it accurately to an NTP server and then watch it for subsequent variations. Inexpensive way to look at this and then ultimately a useful device.

Reply to
Steve Kraus

o
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Years ago I designed and built a nixie clock with digital TTL counters usin g mains frequency as timing source. Here in Spain the typical variation I s ee is between 1 and 10 seconds per day and within some days I've seen it go as far as 30-40 seconds, then slowly correct back. That has been always th e behaviour of that clock from 2007 to now. At long term time keeping is go od.

I've found this website clock

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a good time reference, I suc cessfully calibrated a quartz clock with adjustable trimmer in a few days c hecking once per day and it kept perfectly aligned for a month. My previous attempts with some cheap DCF77 radio controlled clocks failed, apparently they randomly added or removed a few seconds on each sync.

Reply to
Jeroni Paul

I just had an idea. I have a UPS sitting around out of service as the batteries went dead and even with good batteries I don't know how long it would run even at very low load. I don't know how precise it is though when I looked at it on a scope it was a nice sine wave and looked stable in frequency compared to the mains. I could rig a 24VDC supply and use the output of the UPS to run my group of timers that I am testing. If the UPS has an accurate output then the timers should be accurate as well. If the UPS is fast or slow then at least the timers will get ahead or behind the same amount each day, not varying like I have observed. Hopefully it would be stable at whatever frequency it is and not go up and down.

Jer>

Reply to
Steve Kraus

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