Arduino Forum

Using Arduino => Sensors => Topic started by: oshyshko on Apr 12, 2017, 01:04 am

Title: LiPo voltage alarm and measuring individual cells
Post by: oshyshko on Apr 12, 2017, 01:04 am
Hi everyone,

I am a software guy and I am working on my telemetry for my RC plane.

I want to make this, but with Arduino Pro Mini 5V/16MHz:
https://www.amazon.com/Battery-Tester-Voltage-Buzzer-Alarm/dp/B005GJCJOA

Q1. Can I just plug 8 LiPo cells (3.2-4.2V each) directly to 8 analog inputs on Arduino Pro Mini and read the signal? (while powering Arduino itself from a dedicated 5V source)

Q2. If no to the above question, what should be the circuit for this?

Thanks!
Title: Re: LiPo voltage alarm and measuring individual cells
Post by: jremington on Apr 12, 2017, 01:06 am
Q1: Yes, if each individual cell has its negative terminal connected to the Arduino ground.
Title: Re: LiPo voltage alarm and measuring individual cells
Post by: rockwallaby on Apr 12, 2017, 06:53 am
If on the other hand the LiPo cells are connected in series, which I assume you will be doing and according to that link for battery tester circuit, then you will need to measure them in a different way, using some additional hardware, such as the following, Battery Management System using LTC6802 (https://sourcelion.wordpress.com/2014/07/20/battery-management-system-ltc6802-arduino/#comments).

You need to describe better your circuit.
_____________
Paul - VK7KPA
Title: Re: LiPo voltage alarm and measuring individual cells
Post by: oshyshko on Apr 12, 2017, 11:50 pm
@rockwallaby thanks for the link

Yes, I have a typical 4-6 cell LiPo like this:
https://hobbyking.com/en_us/turnigy-5000mah-6s-40c-lipo-pack.html

All cells connected in series, the black/red output goes to an ESC.

I want to use the rainbow wires for measuring individual voltage of each cell.

Is it possible to measure the voltages with Arduino Pro Mini analog ports? (without LTC 6802-2)
Title: Re: LiPo voltage alarm and measuring individual cells
Post by: jremington on Apr 12, 2017, 11:55 pm
Quote
Is it possible to measure the voltages with Arduino Pro Mini analog ports?
Yes, but not very accurately.

You will need voltage dividers to bring each individual cell voltage level down to the 0-5V range, and each will have a large offset, depending on how many cells between it and ground.
Title: Re: LiPo voltage alarm and measuring individual cells
Post by: rockwallaby on Apr 13, 2017, 01:56 am
oshyshko, you really do need to use an interface like I linked to, something that will be able to connect and measure the six LiPo cell which are connected in series. There are other chips and other little ready made products that essentially do this and you could connect to them with an appropriate interface, such as serial or I2C or SPI, usually via an electrically isolated interface.

I do not see that it will be possible to connect the Arduino directly to the Lipo cells to be able to measure them individually.
Remember the analogue input on the Arduino is a simple single ended input and has no input front end, in terms of protection or buffering or scaling.

If you read the data sheet for the LTC6802 and family chips you will gain some insight into how they do it and why you also will not be able to do it by using the analogue input of the Arduino.
_____________
Paul - VK7KPA
Title: Re: LiPo voltage alarm and measuring individual cells
Post by: oshyshko on Apr 19, 2017, 08:51 am
Thank you, rockwallaby.