OT; clock running backwards?

There is a device that will do what you want with very little external circuitry.

Check out this link on mercury coulometers:

Basically, the visible gap between two columns of mercury moves proportional to the total current that has passed through the device. The direction that the gap moves depends on the polarity of the current flow.

Ron

On Wed, 30 Jan 2008 06:26:37 -0600, with neither quill nor qualm, nick hull quickly quoth:

So wire an hour meter into it and you'll have your proof.

-- My future starts when I wake up every morning... Every day I find something creative to do with my life. -- Miles Davis

If I use TWO clocks, what do I gain by having one run backwards? If they both show the same time, the duty cycle is 50%

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That would work very well BUT all that I have used moved VERY slow, so slow that movement in a couple if days would be hard to notice. I'm looking for something with a fast response, that will tell me within an hour or so if the heat pump is running continuously.

Free men own guns - www(dot)geocities(dot)com/CapitolHill/5357/

nick hull fired this volley in news:nhull- snipped-for-privacy@dialupusa.usenetserver.com:

Quite the contrary -- many older-vintage electric clocks had an electromagnetic "starter" consisting of nothing more than a pawl or segment of a pinion that engaged one gear of the train when the motor was OFF, and when the motor coil was energized, would "flip" the gear in the right direction to get the motor started, then pull out of the way, held there by magnetic force. When the motor stopped, the "starter pedal" would simply fall back down into engagement with the train.

There was no need at all to reverse anything in the clock to get it to run the other way. You simply strapped the starter out of the way, then manually flipped the train in the direction you wanted when you turned the motor on.

They used light bulbs. When the bulb went dark it meant they were in phase, and that it was safe to throw the switch. You had one generator running, and trimmed the speed of the second generator. The light would start to dim and get bright as they got close. When it was under one second per cycle, you waited for it to get dim and switched that generator onto the grid.

That depends. I've managed to make them run backwards (in college, as a prank against someone else in the dorm). The typical synchronous clock back then had the rotor and geartrain in a sealed capsule. It was mounted in a magnetic circuit frame somewhat like this:

__ __ / / \ \ +----##- / \ --------+ | ==== ===== | | +--- \ / -##-+ | | | \_\ /_/ | | | | | | | |___________________| | | 0 WWWWWWWWWWW 0 | +---------------------------+

Now -- the '< >' shape should really be curved to fit the round aluminum housing around the rotor.

The '##' is a square copper ring which surrounds the pole piece and passes through the '==' slot. It is around the upper one to the left, and the lower one to the right.

The 'WWWWWWW' is the winding (coil) which is connected to the AC power.

To reverse the clock, you have to slide each copper ring to the opposite pole piece -- or simply turn the magnetic frame over if it is symmetrical. (The '0' are the holes for screws to mount it to the rest of the clock mechanism.)

Of course, this is not very quick to do, so what I would try is to replace the square copper rings with a number of turns of enameled copper wire -- with some cardboard or plastic sleeving between it and the corners of the laminated magnetic frame so the corners don't bite through the enamel insulation. However, instead of making only two winding, make four, and set up a relay close by to short one diagonally opposite pair for forward, and the other for reverse. The number of turns needed depends on the gauge of wire. I would try to shoot for enough turns to give the coil a cross-sectional area about 20% greater than the solid copper square ring as long as the relay is close to the coils. If it is some distance away, I would go for more turns of finer wire.

You *may* have to remove power for a moment to let the clock motor stop, or you may be able to reverse on the fly. (If you try it, please post here whether you have to stop the motor for a moment to allow the reverse to operate.)

Note that if this is an alarm clock, you'll have to remove a few parts associated with the alarm, or it will lock up if it tries to go past the alarm point in reverse. A little examination should tell you what needs to be removed. If it is a wall clock which uses this style of motor, you are home free -- and have a bigger display as well. (But you may want to rig up something to count how many times the hour hand passes "12" and subtract if it does so in reverse.

Anyway -- the victim of this prank pulled the case off the clock, cut the two AC leads from the plug and reversed them in the clock, only to discover that it still ran backwards. He then ran off to get the headmaster of the school to show it to, but it was swapped back before he got back. :-)

Enjoy, DoN.

/ Yes, it has been many years since I last saw one. Given how they work, I just figured that if you could find a manufacturer, they may have one with an appropriate speed. After all, the speed will be proportional to current. Of course, so will the temperature of the device.

I do not know if it would work, but, what if you were to replace the single turn shading coil on your clock motor with several turns of smaller wire. Then add an identical coil on the other pole. Now by switching the coils with a relay, you could select the direction of rotation.