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Author Topic: Mnemonic (any excuse)  (Read 768 times)

Jonty

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Mnemonic (any excuse)
« on: September 07, 2009, 10:33:36 PM »

  I've just taken apart a defunct 24 hour timer in case it contained anything of use. The fault was mechanical, not electrical. It has a crude little field wound motor and many tiny gears. This is a mains device with a dropper resistor which, if I remember correctly my

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has a value of 47k ohms. How much will this reduce the voltage? I've tried it on 12 volts, and it just twitches a bit. Lots and lots of very fine copper windings, so I suppose I can try unravelling some until it does work.
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Mi Amigo

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Re: Mnemonic (any excuse)
« Reply #1 on: September 07, 2009, 11:03:23 PM »

For 12v operation try replacing the 47K with something aroung 2K3 to 2K4.

It may need 12 AC volts, can't really tell without seeing it.

Good luck
 Neil
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Jonty

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Re: Mnemonic (any excuse)
« Reply #2 on: September 07, 2009, 11:17:17 PM »

  Hadn't thought about AC. Could be interesting in a model boat!
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malcolmfrary

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Re: Mnemonic (any excuse)
« Reply #3 on: September 08, 2009, 02:47:20 PM »

Works out at about 5mA.  Measure the resistance of the motor, and that should tell you what voltage to offer it.  There wont be a lot of power there.
Does it appear to have brushes and a commutator as well as the field winding?  If so, it will have been intended to run in one direction only (sensible for a timer).  If the rotating bit is a magnet, then its an AC only motor, and will need some electronicery to drive it.  This is very logical for a timer - such a motor will be locked to mains frequency and be relatively unaffected by voltage making timing accurate.
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stallspeed

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Re: Mnemonic (any excuse)
« Reply #4 on: September 08, 2009, 03:28:42 PM »

It is a synchronous AC motor.It keeps time on your clock because mains voltage is at 50Hz.
As you can see from a mechanical arrangement within the timer,the motors has to be nudged to run in the correct direction.

Mains voltage ones can be run by CMOS oscillator/dividers for precision timed radars.
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