Hi I am making a lithum ion battery monitor and I am working out how to mesure the voltages on the battery. there are 7 cells that I need to mesure that each have a maximum voltage of 4.2 v. I have never used an auduino before and was wondering if people could help me with this. I am using an auduino pro micro and have already used 6 off the digital pins on multiplexers.
any help would be appreciated
thanks
samuel
7 cell in series?
Which multiplexer are you using.
I don't know one that can handle 7*4.2= 29.4volt.
Google "Arduino battery stack monitor" for lots of (failed) projects.
Leo..
Wouldn't it work to make one voltage divider for each + of the 7 cells? That calls for 7 analog inputs maybe by using an analog mux.
Voltage dividers on each cell node cause uneven discharge of the cells.
And measurement resolution goes down with the number of cells.
Leo..
Yes, that's correct. If it is not a long use time, low current, application this might be of less importance? OP?
While speaking, how to charge 7 cells serially connected? In case of unequal, not matched, cells some cells are in the risc of being overcharged I think. Charging would the call for splitting the pwr pack and charge them separately. What do You think ?
the project is an active balance charger I just need to mesure the battery voltages
What is "balance"?
Ugh... this is not an easy project. I've seen projects where a guy used optically isolated Attiny on each cell and sent signal back to main chip... I believe that one was a 3 or 4 cell project.
The issue with this project is the sheer number of readings as you will want a reading per cell and the accuracy of these readings which is not great with internal reference. So it's going to be a pricey and complicated project if you can figure it out.
Also due to the dangers of lithium ion it may be better to use dedicated chips that do this which are more accurate and have better voltage/current profiles of the cells instead of just a voltage reading. You may want to research lithium ion battery maintenance chips.
Railroader:
What is "balance"?
When a cell in the stack reaches max voltage (fully charged), the other cells might still need a bit more.
But current through the stack goes through every cell, so there is a risk of overcharging the already full cell(s).
A small circuit across each cell (mosfet/resistor) is activated to bypass that charge current,
preventing the full cell from overcharging (big ba-da boom).
Balance charging example circuit attached.
Leo..
Bal Charger.pdf (35.3 KB)
oh now that's pretty cool...
I have knowledge about charging stacked cells. Loook at #4.
In the world of technical terminology "balancing" was new to me. Sometimes selfmade terminology is used so I issued the question to be sure.