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clock movement battery

crutschow

May 7, 2021
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Was hoping I could install one and leave it in there indefinitely and have it be just used for when the power goes out.
Then I think my suggestion of using a 1.5V alkaline while applying 1.5V to it through a 1kΩ resistor should keep it going indefinitely.
 

notny41

Apr 24, 2023
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ramussons the capacitor idea is intriguing. How long of a power outage do you think that setup might keep the clock going for?​


Ok thanks to everyone for cluing me in on the Schottky diodes. I went ahead and ordered some 1N5817 diodes, hopefully those would be a sufficient type for this application.

In the meantime, I decided to do a little experiment. I connected an alkaline AA battery in parallel with the output of the buck converter, which is also connected to the clock battery contacts. Before doing this I measured the battery voltage and it was exactly 1.487 volts. I also measured the output of the buck converter which was powering the clock and it came in at 1.6 volts. I figured this was close enough and maybe it would even charge up the battery a little bit.

After connecting the battery in parallel I came back after about 30 minutes to find something very surprising. I connected my meter to everything and to my astonishment it read 1.95 volts. I didn't expect anything above 1.6 volts. So then I disconnected the battery and measured it. It was at 1.73 volts and gradually decreasing. The buck converter still measured 1.6 volts with the battery disconnected.

I went back and measured the battery again after a few hours and it stabilized at 1.567 volts.

Something strange was happening when I had the battery connected in parallel without any diodes. When the diodes get here, I'll try putting them in so that no electricity can flow from the buck converter to the battery and so no electricity can flow from the battery to the buck converter.

Just thought that was very strange how the voltage increased to more than either of the power supply sources when in parallel....
 

crutschow

May 7, 2021
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Just thought that was very strange how the voltage increased to more than either of the power supply sources when in parallel....
Yes, that is strange.

Try connecting the converter to the battery with a 1 megohm resistor across the battery
It may be the converter needs a small load to properly regulate.

Don't understand why you used a buck regulator here as, at that low output current its quiescent current likely makes it less efficient then a simple linear regulator.
The linear regulator also would not go above its set voltage, even with no load.
 

notny41

Apr 24, 2023
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It's been my experience with linear regulators that they put out quite a bit of heat when you are trying to drop voltage significantly. Also I would probably need to find one that outputs 1.5volts. I'm assuming you are talking about the 3 connector things that look like you would attach them to a heat-sink.

With this buck converter, it is tiny, it doesn't put out any heat, and it's adjustable with a tiny pot for the output voltage you want. I wouldn't think you'd need a load for it to properly regulate since a multimeter doesn't put much of a load on it when you measure voltage coming off it with nothing else connected, right?
 

crutschow

May 7, 2021
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It's been my experience with linear regulators that they put out quite a bit of heat when you are trying to drop voltage significantly.
True for high current loads, but here you are only outputting microamps, so the power loss would be insignificant (which equals the regulator voltage drop times the current), and no heatsink would be required.
I wouldn't think you'd need a load for it to properly regulate since a multimeter doesn't put much of a load on it when you measure voltage coming off it with nothing else connected, right?
But perhaps it needs a tiny load comparable to the multimeter, which is why I suggested adding the 1 megohm resistor across the battery.
 

notny41

Apr 24, 2023
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I think I'm going to shelf it til the diodes get here and then I'll post my findings then. Thanks for all of the help everyone!
 
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