# Battery Consumption

#### moonloopsun

Joined Aug 16, 2020
17
Hi guys,
I am new here and still not an engineer and have not much knowledge in Battery / electricity but have a major project I am working on and would be very happy to get some answers..

I am trying to build a machine that is using a spin motor that work periodically in set times (650 spins a day: 10 turn per minute than a few minutes rest) by a simple electric circuit.
The manufacture of the motor sent me these consumption values: Voltage: 3 - 12VDC, Current @ maximum efficiency: 0.17A. On the machines provided power supply I have the follow values: 3v / 1.2A

They also claim that when it is operated by strong 2 x AA batteries it will be able to work for around 8-9 weeks (defined amount of movements periodically in a day - around 650 turns total).
I try to find a way to operate the machine longer without any need to change the batteries every second month.
I try to look at a solution of connecting a 40000mAh portable usb power bank to it through a 'step down voltage device' that will provide it the right amount of Voltage and Ampere.
Like this one:

https://www.amazon.de/gp/product/B07WJ82KPF/ref=ppx_yo_dt_b_asin_image_o00_s00?ie=UTF8&psc=1

My questions are:
Is it true that in these settings with a 40000mAh power bank, the machine will be able to run 20 times longer than when it will when running on 2x AA 2000mAh batteries ?
Is it safe to have the machine connected to such a power bank constantly and have it stored in a close place ?

Thanks a lot for your time !

#### jpanhalt

Joined Jan 18, 2008
11,087
Welcome to AAC.

There are almost no specifications for that charger; however, charging a depleted 40 Ah battery from a USB 1 or 2 port will take a long time.

As for your calculation, yes, a 40 Ah battery should be able to run a device 20x longer than a 2 Ah supply. However depth of discharge and discharge rate may affect the observed result.

#### moonloopsun

Joined Aug 16, 2020
17
So you think that it is safe to connect this kind of power bank to the machine i built and let it run for months inside a closed cabin?
Will the usb power supply won't get into sleep mode after a while while getting the low consumption request from the usb step down dc ?

#### moonloopsun

Joined Aug 16, 2020
17
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

#### jpanhalt

Joined Jan 18, 2008
11,087
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?

#### moonloopsun

Joined Aug 16, 2020
17
I am not sure how much current it takes while not running but i guess not much as nothing is actually happening while it's 'asleep', it runs all in all about 70 minutes a day.

Is it a good idea to try to run it with a usb power bank with a usb step down device, or would you recommend to built a power supply with a few 18650 lithium batteries and a dc-dc voltage step down ?

#### jpanhalt

Joined Jan 18, 2008
11,087
It uses 1.4 Ah /day @3 V. (1.2 A X 1.166 hours/day = 1.4 Ah/day).

A 2000 mAh battery will run it for about 1-1/2 days only. Two such batteries in parallel, about 3 days. Your 40 Ah power wall will power it a maximum of 28 to 29 days; however, you probably do not want to exhaust the batteries completely. Those are elapsed days, not actual tie running.

Something that draws that much current will be difficult to supply for long periods on battery power only. It is probably not practical to expect 6 months of unattended, non-recharged operation.

Have you considered a solar recharger?

#### KeithWalker

Joined Jul 10, 2017
2,616
The power bank will do the job so why go to the trouble of assembling exactly the same thing from scratch?
Regards,
Keith.

#### moonloopsun

Joined Aug 16, 2020
17
Thanks Keith,
I am just wondering if the power bank won't turn off when the device is in sleep mode / after a few minutes of usage because of low consumption.. Do you have any experience with it ?

#### moonloopsun

Joined Aug 16, 2020
17
It uses 1.4 Ah /day @3 V. (1.2 A X 1.166 hours/day = 1.4 Ah/day).

A 2000 mAh battery will run it for about 1-1/2 days only. Two such batteries in parallel, about 3 days. Your 40 Ah power wall will power it a maximum of 28 to 29 days; however, you probably do not want to exhaust the batteries completely. Those are elapsed days, not actual tie running.

Something that draws that much current will be difficult to supply for long periods on battery power only. It is probably not practical to expect 6 months of unattended, non-recharged operation.

Have you considered a solar recharger?
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 ?

#### BobTPH

Joined Jun 5, 2013
6,076
A powerbank steps up the voltage from 3.7V to 5V, and they rate the capacity in terms of the 3.7V battery, not the 5V output.

On your use scenario, you then step this down to 3V. Each conversion is maybe 80% efficient, so combined is 64%.

The effective capacity can then be calculated at 3.7/3.0 x 40000 x 0.64 or 31500 mAH.

Two D cells would give you 24000 maH.

As for the usage, 65 minutes at 170 mA mean 184 mAH per day or 171 days on the powerbank or 129 days on two D cells or 22 days on 2 AAs.

Edited to add: Yes, those powerbanks typically turn off if the current falls below a limit, so it might not work at all.

Bob

#### jpanhalt

Joined Jan 18, 2008
11,087
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 ?
Then the numbers you provided are not right. Just to double check, I understood that the unit runs 70 minutes total out of a 24-hour day, and while running, it consumes 1.2 A continuously. That is 1.4 Ah/day.

#### BobTPH

Joined Jun 5, 2013
6,076
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 ?
The rating of a power supply is how much current it can provide, not how much any use of it will consume. The manufacturer stated that its run current is 170mA. It needs a bigger power supply because a motor takes a lot more current when starting and when under a heavy load.

Bob

#### moonloopsun

Joined Aug 16, 2020
17
Then the numbers you provided are not right. Just to double check, I understood that the unit runs 70 minutes total out of a 24-hour day, and while running, it consumes 1.2 A continuously. That is 1.4 Ah/day.
It runs 70 minutes a day, but i don't know how much it really consume, i know that on the power supply it is written 1.2A
Is there a way to find it out ?

#### jpanhalt

Joined Jan 18, 2008
11,087
You would need a current meter. If the power supply is rated at 1.2 A and it doesn't get hot, then likely the device is using considerably less. Let's just guess it's 200 mA. 1.2 A/0.2 A =6 , so multiply all the times calculated by 6. Now your 40 Ah battery bank seems more reasonable. I would still consider a small solar cell.

Something like this from Amazon in 3S2P configuration (requires photo 6 cells instead of the 5 for that price) will give 6 V at 320 mA. That would almost be enough to charge a lithium back-up battery during the day. Nine of those photoelectric cells could make a 3S3P which would work well with any of the single-cell chargers available. Many of those chargers will work when the cell being charged is under load too.

There are lots of possibilities with that approach. BTW, it is nice to see someone interested in old time pieces. You are aware that in a small cabin, they will probably all synchronize, right?

#### moonloopsun

Joined Aug 16, 2020
17
You would need a current meter. If the power supply is rated at 1.2 A and it doesn't get hot, then likely the device is using considerably less. Let's just guess it's 200 mA. 1.2 A/0.2 A =6 , so multiply all the times calculated by 6. Now your 40 Ah battery bank seems more reasonable. I would still consider a small solar cell.

Something like this from Amazon in 3S2P configuration (requires photo 6 cells instead of the 5 for that price) will give 6 V at 320 mA. That would almost be enough to charge a lithium back-up battery during the day. Nine of those photoelectric cells could make a 3S3P which would work well with any of the single-cell chargers available. Many of those chargers will work when the cell being charged is under load too.

There are lots of possibilities with that approach. BTW, it is nice to see someone interested in old time pieces. You are aware that in a small cabin, they will probably all synchronize, right?
Thanks a lot for the answer.
The problem is that i can't take any cables our of the cabin.. otherwise, i wouldve used the dc power supply which i received with the machine....
Do you think that i would get better results with a few d-cell batteries and a volt step down ?
Than with the power bank idea ? - i don't even know if in the power bank scenario the power bank wouldn't turned off when the device is in sleep mode...

#### moonloopsun

Joined Aug 16, 2020
17
Thanks a lot for the answer.
The problem is that i can't take any cables our of the cabin.. otherwise, i wouldve used the dc power supply which i received with the machine....
Do you think that i would get better results with a few d-cell batteries and a volt step down ?
Than with the power bank idea ? - i don't even know if in the power bank scenario the power bank wouldn't turned off when the device is in sleep mode...
You are aware that in a small cabin, they will probably all synchronize, right?

What do you mean with it ? It's super interesting..

#### moonloopsun

Joined Aug 16, 2020
17
A powerbank steps up the voltage from 3.7V to 5V, and they rate the capacity in terms of the 3.7V battery, not the 5V output.

On your use scenario, you then step this down to 3V. Each conversion is maybe 80% efficient, so combined is 64%.

The effective capacity can then be calculated at 3.7/3.0 x 40000 x 0.64 or 31500 mAH.

Two D cells would give you 24000 maH.

As for the usage, 65 minutes at 170 mA mean 184 mAH per day or 171 days on the powerbank or 129 days on two D cells or 22 days on 2 AAs.

Edited to add: Yes, those powerbanks typically turn off if the current falls below a limit, so it might not work at all.

Bob

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)?

#### sghioto

Joined Dec 31, 2017
3,689
That's a bit weird, because i run it with 2 x AA batteries for 3 weeks now.
AA alkaline batteries are typically rated at 2500maH on low current drain. If you are getting 21 days of use out of two AA batteries I calculate the current draw of the machine at 102ma.
70 minutes = 1.17 hours per day
1.17 hr X 21 days = 24.5 hours Total
2500 / 24.5 = 102ma
SG
EDIT: based on the above calculations that's 119maH per day.

Last edited:

#### jpanhalt

Joined Jan 18, 2008
11,087
You are aware that in a small cabin, they will probably all synchronize, right?

What do you mean with it ? It's super interesting..
Here's an article about such synchronization in pendulum clocks: https://physicsworld.com/a/the-secret-of-the-synchronized-pendulums/ I am not sure, but I thought it also applied to large watches and such with hairsprings and escapements (mechanical oscillators) on the same table/wall. Couldn't download this reference: https://arxiv.org/abs/1805.06647 but did find a neat demo of pendulum synchronization: https://demoweb.physics.ucla.edu/content/160-spontaneous-synchronization It's at the bottom of the page.