Kienzle Automatic, solenoid flaky

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Unheard
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Kienzle Automatic, solenoid flaky

Since you’re a buch of talentent, highly clever boys and girls:

I have an AA battery driven watch with a solenoid that sometimes refuses to work. I understand this is a common mechanical problem with solenoids. A contact is closed, the coil gets current, emptying the battery.

My idea was to give the switch signal signal to a MCU which itself kicks the solenoid once, then measures current. If contact is still closed (kicking hasn’t worked), it repeats this procedure. Problem is voltage. I have an Arduino nano, but only 1,5V at most. Soooo … any idea for an analog circuit which is able to do this? I mean, a really simple one.

I don’t feel like repairing this clockwork again. I did once and it was really complicated. Replacing the solenoid requires finding a replacement in the first place, but also to have all required tools.

Thanks for reading :-).

Edited by: Unheard on 09/16/2020 - 05:43
kennybobby
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Do you have a schematic of the solenoid circuit? Need a bit more information to know what is needed.

What drives or causes the contacts to close? Is there a freewheeling diode or some other snubber device to dissipate the solenoid coil energy when the contacts open? If not then the contacts are likely frosted over or welded shut, damaged by arcing. What is the rating of the solenoid coil, how much voltage and current is required to engage the contacts, and at what voltage do they release, etc.?

Did you inspect and clean the battery terminals, especially the negative side—that is where the alkaleak AA batteries will spill their guts and cause corrosion and a high resistance junction that no longer can supply the necessary current.

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Unheard
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Yes, the negative terminal had to be cleaned. I did it only on the inside, so it still looks messy. But resistance is very low.

When the mass driving the unruh spring runs down, it closes the contact and the solenoid kicks it up again. It is really simple. No semiconductor components visible.

kennybobby
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Oh it sounds like the contact has welded shut. Likely the cell voltage got too low to provide enough kick power to throw the weight, so the contacts remained closed with current flowing = small welder.

Or there is too much friction in the mechanical path for the weight and it won’t slide easily.?

i suppose you tried testing with a power supply or a higher voltage cell in order to give a little extra “kick” current to the coil in order to move the weight off of the contacts? if so and the circuit is still closed, then indeed the contact points have welded or corroded shut, and will require mechanical manipulation to separate, clean and burnish if possible for re-use.

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Unheard
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Yes, maybe the core rod tilts sometimes. Most of the time, it works, and the click sounds right. Therefor I thought about multiple impulses. Something like a charging element (capacitor) that triggers repeatedly an impuls, discharges itself and recharges again. But I’m terrible at electronics.