Beginners Guide to Processing 18650 Cells | Cell Database


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Nano help...
#11
I understood the supply voltage part.
It was analogue reading connections that I was curious about. Unless I misunderstood, then assuming you have 10 cells in series each at 4.2V, then:

analogue input 1 will see 4.2V (fine),
analogue input 2 will see 8.4V,
analogue input 3 will see 12.6V,
etc all the way up to 42V.

The microprocessors will treat you to some magic white smoke at that voltage?
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#12
Sorry, i think I see what you mean, am I using two inputs per cell to measure the voltages? If so how do I plan to do that with just two Nanos?

I was planning to do a voltage divider network but now I'm not sure it will work, you've got me thinking here, I should have some time this afternoon to sit and try it. Maybe the voltage divider won't work...we shall see.

What ideas you got if it fails?
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#13
(08-23-2017, 04:46 PM)Inverted 18650 Wrote: Sorry, i think I see what you mean, am I using two inputs per cell to measure the voltages? If so how do I plan to do that with just two Nanos?

I was planning to do a voltage divider network but now I'm not sure it will work, you've got me thinking here, I should have some time this afternoon to sit and try it. Maybe the voltage divider won't work...we shall see.

What ideas you got if it fails?

Optocoupler? Never used one, but common place in power supplies, to separate voltage and monitor.

Mike has a thread about this topic.
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#14
Voltage divider work but as i understand it the more you divide the less resolution you will get to spare and you need to tune the division alot. I was doing that in beginning and i only got it jumping all over the place and ended up with 1 nano per 2-3 cells and those talk over optocoupled serial link.
It works fine for first 3-4-5 cells and so forth but when closing to 14th it was not very accurate. And i tried using up to 20bit AD

Optocouplers i looked at as well but for those that are linear they got expensive so it was cheaper to buy a set of nanos to do the job.
If you find any that do work that would be awesome!
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#15
(08-24-2017, 05:48 AM)daromer Wrote: Voltage divider work but as i understand it the more you divide the less resolution you will get to spare and you need to tune the division alot. I was doing that in beginning and i only got it jumping all over the place and ended up with 1 nano per 2-3 cells and those talk over optocoupled serial link.
It works fine for first 3-4-5 cells and so forth but when closing to 14th it was not very accurate. And i tried using up to 20bit AD

Optocouplers i looked at as well but for those that are linear they got expensive so it was cheaper to buy a set of nanos to do the job.
If you find any that do work that would be awesome!

Sweet. 1 nano per 1s. Then you have all the eeprom you need for data logging. Cheaper than anything else. Never thoug of it that way. Could easy get the master to alert uo of cell imbalance.
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#16
(08-23-2017, 04:46 PM)Inverted 18650 Wrote: What ideas you got if it fails?

As you and the others said, voltage dividing is probably not going to be accurate enough since, taking the 10th cell as example, if you divided 42V down to say 4.2V, then the working voltage range for that cell at the analogue input will be 4.08 to 4.2 (assuming 3 to 4.2V range for the cell itself)

So assuming the A/D is 10-bit and its range is 0-5V (haven't checked the datasheet though) then 4.08V will convert to 834 and 4.2V will convert to 859.

In other words you only have about 25 steps to represent the entire working voltage range of the cell.

Now, if you could invent a voltage subtracter that would be awesome! 

So yes, having one nano per cell is probably the way to go. Although you still need to figure out a way to get the data out of them all and into a master of some kind.

You could send serial data out from each, via an opto coupler, but then you have 10 separate serial signals, and no Arduinos have that many ports.

So if I were doing it I would probably daisy chain the nanos (again via opto coupler). So the first nano sends its reading to the second, Then second nano repeats it and add it's own and so on.

Then the final nano will output all 10 samples to be read by the master and used, displayed, whatever.
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#17
Daisy chain or just use protocol where the master calls for the slaves or a serial that works with multiple slaves like I2C or other?
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#18
Yeah, I though about I2C, but it would be more complex to implement in this scenario because the lines have to be bidirectional and operate in a tri-state way, which is non-trivial when you have to have opto couplers in line. Also each nano will have to have a unique I2C address, so you would either have to put different code in each or add a dipswitch on each to set its address.
The nice thing with the daisy chain method is that they are self addressing, so you cannot have a discrepancy between their address and the order in which you physically connect them.
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#19
True.
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#20
Why not use some of those DS2438 ? Did anyone try to use them?
I have them to test, but never got the time to...
https://datasheets.maximintegrated.com/en/ds/DS2438.pdf
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