# Battery Consumption

#### BobTPH

Joined Jun 5, 2013
3,334
That reise that question, if i use:
1 x D cell (1.5v) with 12000mAh,
or
2 x D cells that will provide 24000mAh and step it down to 1.5v output,
will the 2 x D cells setup provide double the usage time than the 1 D cell ?
I said that wrong. To get 3V you use two D cells in series and the mAH does not add. So it would be 12000, not 24000 for two D cells in series. The motor is rated a 3-12V so it will not run on 1.5V.

You said in the original post that the manufacturer gave you a current of 0.17A at "maximum efficiencly". Maximum efficiency would be at 3V with no load. Assuming it light load, it might not be much higher than that, which is confirmed by the fact that it has run 3 weeks on two AA cells -- and not that I calculated 22 days on two AA cells at 0.17A.

Bob

Thread Starter

#### moonloopsun

Joined Aug 16, 2020
17
I said that wrong. To get 3V you use two D cells in series and the mAH does not add. So it would be 12000, not 24000 for two D cells in series. The motor is rated a 3-12V so it will not run on 1.5V.

You said in the original post that the manufacturer gave you a current of 0.17A at "maximum efficiencly". Maximum efficiency would be at 3V with no load. Assuming it light load, it might not be much higher than that, which is confirmed by the fact that it has run 3 weeks on two AA cells -- and not that I calculated 22 days on two AA cells at 0.17A.

Bob
I understand. So the highest mAh i could get from a battery in this case would be 2 x D cell (3v) which would stay at 12000 even when each one if these batteries are 12000?

i thought that if i use 2 batteries of 12000mah than i get 24000mah.
that’s incorrect?

#### sghioto

Joined Dec 31, 2017
2,363
i thought that if i use 2 batteries of 12000mah than i get 24000mah.
that’s incorrect?
In this case that is incorrect. From my calculations a pair of "D" cells should get you 100 days of use but probably a lot more if two AA batteries after 3 weeks are still running.
SG

#### WBahn

Joined Mar 31, 2012
26,398
OK, it requires 3 V at 1.2 A while running. What current does t take while not running? How many hours a day does it run?
Where does the claim that it requires 1.2 A when running come from?

The power supply is capable of delivering 1.2 A at 3 V, that does NOT mean that the motor draws that much current when it runs.

The original post indicates that the motor documentation indicates the max efficiency occurs at 170 mA. But the TS needs to measure how much current the motor is actually drawing when it is running in his application.

#### WBahn

Joined Mar 31, 2012
26,398
That's a bit weird, because i run it with 2 x AA batteries for 3 weeks now. Can be that the consumption that it written on the power supply (which i don't use) is different than the consumption of the machine ?
Almost certainly. Just because the water to your house can supply, say, 10 gallons per minute does not mean that every time you turn on a faucet you get 10 gallons per minute out of it.

The same with a power supply. The 1.2 A that it is rated for is the minimum current that the manufacturer claims that it can deliver while still holding it's voltage within specifications. It can probably deliver a bit more than that. If you connect a load that only needs 100 mA, then it will only supply 100 mA.

You really need to measure the current that your device actually consumes when running doing what you want it to do.

#### WBahn

Joined Mar 31, 2012
26,398
Thank you for your answer and for your time.

That reise that question, if i use:
1 x D cell (1.5v) with 12000mAh,
or
2 x D cells that will provide 24000mAh and step it down to 1.5v output,
will the 2 x D cells setup provide double the usage time than the 1 D cell ?

If the second scenario is right, i could theoretically create a very big power supply (6 x D cells) step it down to 1.5v, and will get 6 times the life span of 1 D cell ? (72000mAh)?
When you put cells in series the voltage adds but the capacity does not because the current is always going through both batteries at the same time, hence that current is discharging each battery at the same rate as if you only had one battery at that same current -- neither battery knows about the presence of the other.

When you put cells in parallel the voltage stays the same but the capacity doubles because the current in each is cut in half, so each battery discharges at half the rate that if would if there was just one battery at the same total current.

A D cell typically has about five times the capacity of a similar AA cell -- let's call it four to be safe. So if you are currently using 2 AA cells in series and getting about 3 weeks of use, you can expect something like at least 12 weeks of use with 2 D cells in series, so you can probably just change the batteries with the change of each new season. If you put another pair of D cells in parallel with this (four batteries in total) you can expect somewhere around 24 weeks as a minimum (it should probably make it six months, so change the batteries on each of the equinoxes or each of the solstices).

#### jpanhalt

Joined Jan 18, 2008
11,088
It's basically a few watch winder machines that i bought and i try to rebuilt them inside a cabin without access to an electricity plug, so i want to make sure that i will not have to change the batteries every few weeks, rather every few months..
Not sure if my best power supply option will be to use a usb power bank with a usb step down device, or to built my own power source from different lithium batteries....
In the assumption that the machine takes 3Volt and 1.2A according the power supply that comes with it, (the engine inside spins 650 times a day, 10 times for each period of 1 minute straight, than a few minutes pause. And every 12 hours it will rest for 12 hours). will the power bank be really able to run the machine for 6 months ? Won't it turn off when the machine puts to sleep in between the turning cycles ?
Could you please recommend me what would be the ideal situation for this subject ?

Thanks you so much for your time
@WBahn Please try to keep up with the varied comments of this poster (troll?).

Thread Starter

#### moonloopsun

Joined Aug 16, 2020
17
When you put cells in series the voltage adds but the capacity does not because the current is always going through both batteries at the same time, hence that current is discharging each battery at the same rate as if you only had one battery at that same current -- neither battery knows about the presence of the other.

When you put cells in parallel the voltage stays the same but the capacity doubles because the current in each is cut in half, so each battery discharges at half the rate that if would if there was just one battery at the same total current.

A D cell typically has about five times the capacity of a similar AA cell -- let's call it four to be safe. So if you are currently using 2 AA cells in series and getting about 3 weeks of use, you can expect something like at least 12 weeks of use with 2 D cells in series, so you can probably just change the batteries with the change of each new season. If you put another pair of D cells in parallel with this (four batteries in total) you can expect somewhere around 24 weeks as a minimum (it should probably make it six months, so change the batteries on each of the equinoxes or each of the solstices).
That’s great to know it.
amazing. Thank you so much
is it safe to wire 2 D 1.5v batteries in series and than in parallel to another pair that connects in series? Do i need to cool it down in this case? Or it can safely stay in the closed small cabin?

#### WBahn

Joined Mar 31, 2012
26,398
That’s great to know it.
amazing. Thank you so much
is it safe to wire 2 D 1.5v batteries in series and than in parallel to another pair that connects in series? Do i need to cool it down in this case? Or it can safely stay in the closed small cabin?
Yes, it's safe to wire it up this way. No need to cool it. Would you feel the need to cool a flashlight that you left turned on in the cabin? Your watchwinders are going to generate a lot less heat than that -- the flashlight might last a few hours (days if it's an LED flashlight?) while your watchwinder will last months. Far less heat per day being dissipated.

Thread Starter

#### moonloopsun

Joined Aug 16, 2020
17
Perfect. Will 1.3mm wires Do the trick in this setup or we need thicker ones?

#### BobTPH

Joined Jun 5, 2013
3,334
1.3mm wire can carry 22A over short distances, so it is way overkill.

Standard 22ga hookup wire would be fine.

Bob

#### WBahn

Joined Mar 31, 2012
26,398
Perfect. Will 1.3mm wires Do the trick in this setup or we need thicker ones?
That's almost certainly overkill and you could get by with much smaller wire, but nothing wrong with using that size.

Thread Starter

#### moonloopsun

Joined Aug 16, 2020
17
That's almost certainly overkill and you could get by with much smaller wire, but nothing wrong with using that size.
Wonderful !

so when all will be connected, is there a simple way to check once the machine is running, how long will the batter really last with a multimeter?

is there any built in LED panel that i can install between the batteries and the machine to see how much juice is left in the batteries, And that it’s time to change them?

Thanks a lot for the kind answers and the valuable information. And sorry for the ignorance.

#### sghioto

Joined Dec 31, 2017
2,363
so when all will be connected, is there a simple way to check once the machine is running, how long will the batter really last with a multimeter?
You can monitor the battery voltage with the meter. When the voltage drops to certain level say 2.75 volts replace the batteries.
SG

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#### WBahn

Joined Mar 31, 2012
26,398
Wonderful !

so when all will be connected, is there a simple way to check once the machine is running, how long will the batter really last with a multimeter?

is there any built in LED panel that i can install between the batteries and the machine to see how much juice is left in the batteries, And that it’s time to change them?

Thanks a lot for the kind answers and the valuable information. And sorry for the ignorance.
I wouldn't put anything on there that will draw any power from the battery continuously, otherwise you'll likely find that your monitoring circuit is dictating the battery life.

One thing you could do would be to lower the battery voltage (using a series resistor, if necessary) until the machine stops working. Let's stay that that happens at about 2.6 V. Then come up a bit and make a criterion of something like 2.7 V. But I wouldn't set the threshold below about 2.4 V as battery life drops pretty fast below that. Then when you are there, just measure the voltage and change if needed.

The thing to keep in mind is that you need to pick a decision threshold that will let the system continue to run until the next time you go there if the decision happens to be not to replace them.

I'd recommend placing a log sheet near the batteries and measure the voltage every time you are there and record the date/time. Then let the system fail and see what the plot looks like.

Also, keep in mind that temperature has quite an effect on batteries. Is this cabin going to be getting below freezing? If so, there are other things to consider.

Thread Starter

#### moonloopsun

Joined Aug 16, 2020
17
I wouldn't put anything on there that will draw any power from the battery continuously, otherwise you'll likely find that your monitoring circuit is dictating the battery life.

One thing you could do would be to lower the battery voltage (using a series resistor, if necessary) until the machine stops working. Let's stay that that happens at about 2.6 V. Then come up a bit and make a criterion of something like 2.7 V. But I wouldn't set the threshold below about 2.4 V as battery life drops pretty fast below that. Then when you are there, just measure the voltage and change if needed.

The thing to keep in mind is that you need to pick a decision threshold that will let the system continue to run until the next time you go there if the decision happens to be not to replace them.

I'd recommend placing a log sheet near the batteries and measure the voltage every time you are there and record the date/time. Then let the system fail and see what the plot looks like.

Also, keep in mind that temperature has quite an effect on batteries. Is this cabin going to be getting below freezing? If so, there are other things to consider.
Thanks a lot
The temperature is ok. It’s inside a room.
do you think that if such a small LED device will empty the battery fast?

Pack of 5 Mini DC Digital Voltmeter 0.28 Inch Two-Wire 2.5 V - 30 V Mini LED Digital DC Voltmeter Display Voltage Tester (Red) https://www.amazon.de/dp/B084VKD55P/ref=cm_sw_r_cp_api_i_gKIoFbZJXF1AN

what about one of those push switched with LED?

EEEKit Push Button Switch https://www.amazon.de/dp/B07QGBJ2X3/ref=cm_sw_r_cp_api_i_3LIoFbZMSHJNG

#### WBahn

Joined Mar 31, 2012
26,398
Thanks a lot
The temperature is ok. It’s inside a room.
do you think that if such a small LED device will empty the battery fast?

Pack of 5 Mini DC Digital Voltmeter 0.28 Inch Two-Wire 2.5 V - 30 V Mini LED Digital DC Voltmeter Display Voltage Tester (Red) https://www.amazon.de/dp/B084VKD55P/ref=cm_sw_r_cp_api_i_gKIoFbZJXF1AN

what about one of those push switched with LED?

EEEKit Push Button Switch https://www.amazon.de/dp/B07QGBJ2X3/ref=cm_sw_r_cp_api_i_3LIoFbZMSHJNG
Are these going to be on continuously? If so, what is the purpose since, presumably, the reason that you want the machine in the first place is because no one is around to wind the clocks, which means no one will be around to look at the LEDs.

If they are only going to be on momentarily when you check the system, then it's a non-issue.

Thread Starter

#### moonloopsun

Joined Aug 16, 2020
17
thanks. You are right.
is there any on/off switch button you recommend to use that has a light indicator when the circuit actually work but wouldn’t consume too much of my battery power? All i could find us for 12v and not for 3v.

Or better to have an on/off switch and separately connect a little led indicator light to make sure that the battery still provide current?