## How to Calculate the battery Run-time for my circuit? Moderators: adafruit_support_bill, adafruit

Please be positive and constructive with your questions and comments.

How to Calculate the battery Run-time for my circuit?

Hi,

I am a noob in batteries and circuit stuff so any help will be greatly appreciated here~

I've created a wearable led project with reference to this tutorial as attached below:

My circuit consists of the following:
- 1 x FLORA wearable electronic platform V3 and
- 13 x Flora RGB Smart NeoPixel version 2

I've got 2 battery supply to choose from:
- 3 x AAA Battery Holder with On/Off Switch and 2-Pin JST connector
- 3 x AA Battery Holder with On/Off Switch and 2-Pin JST connector

My Concerns:
- How do I calculate the battery run-time for my circuit with the 2 different Battery holders? Do AA and AAA batteries make a difference in the run-time? Is there an equation or formula I can reference?
- Would my circuit have a longer run-time if I use a 9V battery? If yes, how long would that be?
- Does Adafruit have a 9V battery holder with a JST connector?

P.S: I hope to achieve a battery run-time of at least 3 hours of continuous running and am not comfortable with using a Lithium-Ion battery.

Cheers,
Jacelyn :)
Flora NeoPixel V2.jpg (449.63 KiB) Viewed 75 times
Attachments
Flora Mainboard V3.jpg (197.37 KiB) Viewed 75 times

Jacelyn

Posts: 11
Joined: Mon Oct 01, 2018 12:48 pm

Re: How to Calculate the battery Run-time for my circuit?

- How do I calculate the battery run-time for my circuit with the 2 different Battery holders? Do AA and AAA batteries make a difference in the run-time?

Typically, AA cells have a little more than twice the capacity of AAA cells, so they should give you more than twice the run-time.
Is there an equation or formula I can reference?

Mike has an in-depth tutorial on the subject here: https://learn.adafruit.com/energy-budgets.
The basic formula is run-time = (cell capacity in mAh) / (circuit current draw in mA)

Calculating the current draw for your circuit can be a little tricky - especially with a lot of Neopixels involved. It depends largely on what kinds of light patterns you have in your program.

- Would my circuit have a longer run-time if I use a 9V battery? If yes, how long would that be? - Does Adafruit have a 9V battery holder with a JST connector?

No. 9v cells are not a good match at all for what you are doing.

P.S: I hope to achieve a battery run-time of at least 3 hours of continuous running and am not comfortable with using a Lithium-Ion battery.

Phil has an excellent tutorial on optimizing power usage for maximum run-time with Neopixel projects here:

Posts: 81328
Joined: Sat Feb 07, 2009 10:11 am

Re: How to Calculate the battery Run-time for my circuit?

Thanks for your quick reply. I've read the articles you sent me and I am overwhelmed with the information. In summary, it's kinda complicated for me to digest.

My understanding is that:
- Flora V3 requires 26mA (correct me if i am wrong)
- Each pixel draws as much as 60mA (runs at a maximum which probably won't be the case)

Total mA required for my circuit:
- 26mA + 13x60mA (assuming running at maximum) = 806mA

A typical AA battery (2500mA)
3 x AA Batteries = 7500mA

Estimated Runtime = Total no. of batteries (7500mA) / Total mA for my circuit (806mA) = 9 hours.

My concerns:
- Is this above a good estimation of my run-time? Can I total up the batteries mA together in the equation above like that?
- When you mentioned 9V battery is not a good match for my current project, Can you help to elaborate further? Is it bcos of the mA? or there is no 9v battery holder with a JST connector available on site?

Cheers,
Jacelyn

Jacelyn

Posts: 11
Joined: Mon Oct 01, 2018 12:48 pm

Re: How to Calculate the battery Run-time for my circuit?

Total mA required for my circuit:
- 26mA + 13x60mA (assuming running at maximum) = 806mA

Probably quite a bit less than that - especially for a wearable project. The "sipping power" link has a lot of good tips on getting the most our of your batteries.

A typical AA battery (2500mA)
3 x AA Batteries = 7500mA

It doesn't work that way for batteries in series. 3 cells in series has the same 2500mAh capacity - but at a higher voltage (4.5v).

- Is this above a good estimation of my run-time? Can I total up the batteries mA together in the equation above like that?

It it probably a reasonable estimate for run-time. Although the capacity is not additive, your current draw per pixel is likely to be quite a bit lower. 1/3 to 1/2 of is typical. Even lower for wearable projects.

- When you mentioned 9V battery is not a good match for my current project, Can you help to elaborate further? Is it bcos of the mA? or there is no 9v battery holder with a JST connector available on site?

Your processor runs at 3.3v. Your Neopixels would be damaged by anything higher than 5.5v. So the higher voltage does not buy you anything. In addition, the capacity of a typical 9v cell is typically only 300-400mAh. And we do not have any holders with JST connectors.

Posts: 81328
Joined: Sat Feb 07, 2009 10:11 am

Re: How to Calculate the battery Run-time for my circuit?

Thanks for your reply :) It has given me better insight.

I thought a 9V battery is compatible as I saw this "Battery: 3-9VDC" written at the back of the Flora board. See the screenshot attached. What does the "Battery: 3-9VDC" means in this case?

On another note, Is it still relatively safe to use 3 x AA or 3 x AAA batteries (4.5V higher than 3.3V) for a 3.3V processor?

To sum things up, is it correct to estimate the following below?

Estimate run-time for using a 3 x AA batteries with 13 Pixels (running at 50%):
= 2500 mAh / (26 mA + 13x30mA)
= 6 hours~

Estimate run-time for using a 3 x AAA batteries with 13 Pixels (running at 50%):
= 1200 mAh / (26 mA + 13x30mA)
= 2.8 hours~

Cheers,
Jacelyn :)
Attachments
Flora Mainboard V3 (Labelled).jpg (207.89 KiB) Viewed 60 times

Jacelyn

Posts: 11
Joined: Mon Oct 01, 2018 12:48 pm

Re: How to Calculate the battery Run-time for my circuit?

I thought a 9V battery is compatible as I saw this "Battery: 3-9VDC" written at the back of the Flora board. See the screenshot attached. What does the "Battery: 3-9VDC" means in this case?

The Flora can handle a 9v input. The Neopixels cannot.

On another note, Is it still relatively safe to use 3 x AA or 3 x AAA batteries (4.5V higher than 3.3V) for a 3.3V processor?

Yes it is safe. The Flora has a voltage regulator on the board. And regulating 4.5v down to 3.3v is a lot less stress for the regulator than regulating 9v down to 3.3v.

To sum things up, is it correct to estimate the following below?

Yes. Those look like reasonably conservative estimates.

Posts: 81328
Joined: Sat Feb 07, 2009 10:11 am

Re: How to Calculate the battery Run-time for my circuit?

Ah! Thank you so much :)

Jacelyn

Posts: 11
Joined: Mon Oct 01, 2018 12:48 pm

Please be positive and constructive with your questions and comments.