# ATO Measuring the power used by a Kundo ATO clock.

Discussion in 'Electric Horology' started by lmester, Apr 25, 2017.

1. ### lmester Registered User NAWCC Member

Dec 30, 2009
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The recent ATO thread by Les Sanders reminded me that this was on my to-do list. We all know that these ATO clocks run for a long time on a battery. They're efficient and require very little pendulum impulse to run.

I'm currently working on one of these clocks. It looks like one of the normal Kundo versions but is labeled "Seth Thomas" I expect it's just a rebranded Kundo.

I decided to try and measure how much battery power it actually takes to run the clock. With 1.5 volts applied, it takes an average power of about 53 microamps. With .95V applied (the minimum needed to run the clock) the average current dropped down to 31uA! The pendulum was actually still swinging below .95V but, no longer had a large enough amplitude to engage the pawl.

How long could the battery last?

Take 8Ah divided by 53uA and you get about 17 years of life. This is ignoring the fact that the current would slowly drop to 31uA as the battery drained.

You won't actually get 17 years from a battery. The typical shelf life for alkaline is commonly listed as 5 to 10 years depending on the temperature.

The battery self discharge rate is certainly a big part of the battery life of this clock.

The method I used:

The clock was powerd with an adjustable DC power supply. A 510 Ohm resistor was placed in series with the power supply. The power supply voltage was adjusted higher to account for the voltage drop across the resistor. The voltage drop across the resistor was measured with an oscilloscope.

With 1.5V power to the clock, the voltage drop was 125mV. With .95V applied, it was 75mV. These voltages are during the time that the coil is energized.

The voltage across the resistor was used to calculate the curent draw. (125mV/510 Ohms). About 245uA at 1.5V. The clock runs at a 1.5Hz rate (666.6ms period). The coil is energized for about 145ms per cycle. This is a duty cycle of 145ms/666.6ms (21.75%). 245uA * .2175 for an average current of 53uA. The clock will also be drawing a small amount of current when the coil isn't energized. The quiescent current. I didn't bother to measure or account for this.

I have several different makes and styles of ATO clocks. When I have nothing better to do, I'll perform this test on them and see how they compare. I also plan on doing this with quartz clocks.

On the scope screen captures, the vertical axis is 50mV per division and horozontal is 100ms per division.

2. ### KurtinSA Registered User NAWCC Member

Nov 24, 2014
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Interesting! I have this exact clock. The original battery was the long-life battery sold by Timesavers. I decided to use a battery adapter which incorporates two AA batteries. How does the use of one C sized versus two AA batteries affect these calculations?

Kurt

3. ### Tinker Dwight Registered User

Oct 11, 2010
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We are still mostly talking shelf life being the main issue.
My feelings are it is better to use a smaller battery and change more
often.
Putting two AAs in parallel can actually shorten the battery life, if the cells
are not from exactly the same process run. Slight differences in the cells
can shorten their life for such low current rates. I use single AAs and get more than
a year but for safety I change them in the fail when I change to std time.
An old leaking cell can ruin your day,
Tinker Dwight

4. ### lmester Registered User NAWCC Member

Dec 30, 2009
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A quick search shows that AA alkalines have about 2.5Ah capacity. Two in parallel would be 5Ah. As Tinker said, You're going to get a little less than double the capacity And, if the batteries are not matched, a shorter shelf life. Ignore that for now and you have 5Ah for two AA's. One C is 8Ah. So in theory, about 5/8 of the life of a single C. I'd suggest a single battery holder. AA or C is your choice. Shorter battery life versus a little higher chance of leaking on your brass. If you use a two battery holder, make sure that the cells are wired in parallel. This is NOT common for multiple battery holders. The common series two battery holder will put out 3V. Those kundo retrofit adapters are several single AA battery holders wired in parallel. A 3V series battery probably wouldn't kill the clock. The current would still be low and 3V is unlikely to break down the transistors. I still wouldn't want to risk it. Also, it would draw twice the normal current and would drain the battery faster.

My clock must be a little newer than yours. It's factory equipped with a C size holder. I have an older Kundo that used the custom rectangular battery. I've retrofitted it for use with a single C cell.

5. ### KurtinSA Registered User NAWCC Member

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6. ### lmester Registered User NAWCC Member

Dec 30, 2009
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Yes, your clock is nearly identical to mine. The cover for mine (Not shown in my pictures) is also identical. The only difference is the position of the circuit board and the type of battery it uses. You'll have no trouble dating yours. 1978

You also have the same problem as my clock. The brass coil cover is cracked. Mine is almost totally destroyed. I'm making a replacement now.

Also, with your two cell parallel AA holder you could choose to install one or two cells. Then, see how long it runs each time. It'd be interesting to see how much this changes the battery life. That would take you a few years!