Beginners Guide to Processing 18650 Cells | Cell Database


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Nano help...
#21
Same issue with them. They ref to ground. I have bunch of them here to and that was my first thought too... But perhaps works if you isolate somehow?
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#22
I think you guys are over thinking this. If you plan to have a nano ($2) per cell, that's quite expensive to having monitoring for your whole system.

Why not use something that's already been built for just that purpose and only costs about $10 and can monitor the whole string 'and' communicates via I2C?
http://www.ti.com/product/bq76940

The whole family line of the bq769x0 can do varying series configurations
BQ76920 3 - 5 cells
BQ76930 6 - 10 cells
BQ76940 9 - 15 cells

Protection Feature(s):
- Over-current in Discharge (OCD)
- Over-voltage (OV)
- Short-circuit Discharge (SCD)
- Under-voltage (UV)
Special Features
- Cell Balancing
- Coulomb counter (integrating current sense)
- Integrated ADC
- LDO
- Low-Side NCH CHG/DSG FET Drive
- Requires separate MCU (that's what the nano or other chip is for)
- Temperature sense

I understand that whole DIY aspect of things and love it. But at some point, there is diminishing returns and better to get the right tool for the job. The nanos are great for some things. But I dont think they are great for a cell-by-cell monitoring. The TI chip can do more than just monitor the cells, it can actually do the balancing, shut the system off, coulomb counter (amps in vs amps out). And if you pair it with the other TI chip (http://www.ti.com/product/bq78350-r1), it can get even smarter.
Proceed with caution. Knowledge is Power! Literally! Cool 
Knowledge is Power; Absolute Knowledge is Absolutely Shocking!
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#23
(08-24-2017, 06:17 PM)Korishan Wrote: I think you guys are over thinking this.  If you plan to have a nano ($2) per cell, that's quite expensive to having monitoring for your whole system.

Why not use something that's already been built for just that purpose and only costs about $10 and can monitor the whole string 'and' communicates via I2C?
http://www.ti.com/product/bq76940

The whole family line of the bq769x0 can do varying series configurations
BQ76920 3 - 5 cells
BQ76930 6 - 10 cells
BQ76940 9 - 15 cells

Protection Feature(s):
- Over-current in Discharge (OCD)
- Over-voltage (OV)
- Short-circuit Discharge (SCD)
- Under-voltage (UV)
Special Features
- Cell Balancing
- Coulomb counter (integrating current sense)
- Integrated ADC
- LDO
- Low-Side NCH CHG/DSG FET Drive
- Requires separate MCU (that's what the nano or other chip is for)
- Temperature sense

I understand that whole DIY aspect of things and love it. But at some point, there is diminishing returns and better to get the right tool for the job. The nanos are great for some things. But I dont think they are great for a cell-by-cell monitoring. The TI chip can do more than just monitor the cells, it can actually do the balancing, shut the system off, coulomb counter (amps in vs amps out). And if you pair it with the other TI chip (http://www.ti.com/product/bq78350-r1), it can get even smarter.

Yep, have seen those, but the point is also to limit the wiring between the packs, with one "device" on a pack and only communication between the devices... i have stop thinking about this since i have found Batrium....
But over thinking it? hmmmmmmmm, you may be right... lets think a bit about that.... Big Grin
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#24
hahah, yes, let's think Tongue

Well, the wiring is limited. You'd only have 1 wire per cell +1, temp probes (i think 2, so that's 4 wires max) most of the other stuff is internal. The communication between boards would be I2C, so that's only 2 wires and then there's the Pos/Neg, another 2 wires.

But, there'd only be 4 wires coming from the series string/bms board. If you have 10 strings in a pack, then 2 of the wires is just making a short jog from one string to the next (<2"?). Coming from the whole pack there'd only be 4 wires. And Batrium has more than that, doesn't it? The longmon is a 3 (?) wire connector I think. But even then, they are small and twisted together. So I don't think wires would be an issue, really.
Proceed with caution. Knowledge is Power! Literally! Cool 
Knowledge is Power; Absolute Knowledge is Absolutely Shocking!
Dollar Shave Club. Best Razor I've ever used
Certified 18650 Cell Reclamation Technician
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#25
Right, only one issue, ( damn, i am thinking again Smile ) the power wires, those are tricky.... they going to be relative long, so they need fusing.... make things a bit complicated....
I am talking about a string of ie 14x 80p...
If we are talking about 1 pack of ie 14s10p at 48v, then you are right, that is the BQ76940 's job, and ignore everything i was thinking above... Wink
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#26
You can power the boards with the cells in the pack. I probably would take the grand total of the pack to power the IC's. That way they will still function even if it shuts one of the strings down.
Proceed with caution. Knowledge is Power! Literally! Cool 
Knowledge is Power; Absolute Knowledge is Absolutely Shocking!
Dollar Shave Club. Best Razor I've ever used
Certified 18650 Cell Reclamation Technician
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#27
(08-24-2017, 10:48 AM)daromer Wrote: 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?

You can slave/master Arduinos. Its easy and effective. Less processing load too. Then you also have heaps of other analogue inputs. Temp sensing, voltage monitoring, and current monitoring. Nanos are cheap, especially if  you buy in bulk without bootloader installed.
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#28
Where are you getting arduinos w/o bootloaders installed? How much? Or even clones or non-duinos (same proc, but not made by them)
Proceed with caution. Knowledge is Power! Literally! Cool 
Knowledge is Power; Absolute Knowledge is Absolutely Shocking!
Dollar Shave Club. Best Razor I've ever used
Certified 18650 Cell Reclamation Technician
Reply
#29
(08-25-2017, 01:37 AM)Korishan Wrote: Where are you getting arduinos w/o bootloaders installed? How much?  Or even clones or non-duinos (same proc, but not made by them)

Looks like that seller got kicked off eBay. Probably due to bad feedback, he did say there was no boot loader. Bummer that.
These are relatively cheap. Watch out you will need a USB to Serial driver for CH340G . Its cheaper than the one that uses the Atmega chipset for USB to serial.
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#30
(08-24-2017, 09:07 AM)watts-on Wrote: Now, if you could invent a voltage subtracter that would be awesome!

Those exists :-)

But I can't find the exact ones. Instead you could wire a reference regulator to subtract a reference voltage. but it will require a series of these. Nad you´d still need to have a divider-network so you can meassure the totalt pack span:

http://www.linear.com/product/LT1236
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