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TI BQ769X0 Based Monitors - Project thread
#31
Looks a lot better on the schematic design Smile

Labels make things so easy for layout and separate sections.
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#32
Just realized there's no point ordering today since it's already the weekend in china - So if anyone has anything they think I should add - or any tips on the layout of the inductor for the buck converter or anything else - nows the time.

On a separate board I'm going to make a buck upconverter to get to 24v as well as some relays for tripping breakers or Victron doodads- the works. It'll plug into the data/power connector on the main BMS board. It will be controlled via the two output lines from the MCU.

I'd prefer to use JST or other connectors on these boards - but I don't have a set of professional crimpers, and I doubt most others do either.
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#33
So I have a version of the board on my EasyEDA with on-board 200mA balancing - however, I'm basically just now learning that really, that's way too low for any powerwall application basically ever.

So in addition to that design, I'm adding one with a JST-XH connector (I know, right after I said I wouldn't) that will go to a separate board just for balancing. I'm aiming to support up to around 3A balancing on the external board, although higher currents will require active cooling.

I found out that JST-XH cables in many pin/conductor counts are readily available on amazon/ebay - so that's saving me a TON of work. I was going to go down the D-Sub road but that would have been horrible.

Tim pointed out a couple of issues with my board and has been giving me suggestions so props to him! I'm hoping to have the board finalized this week.
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#34
So I've finished the basics of the schematic for the balancing board with balancing mosfets / resistors, and an arduino nano to monitor temps.
What I'm wondering now is if it makes sense to let the TI BQ chip "control" balancing. As in, the main MCU tells the BQ chip to balance, at which point it shorts together the + and - of the cell to be balanced. The Balance board then notices this short, and turns on a mosfet to dump power thru a resistor. If I have a nano there already to monitor temps (which I thought was just a good idea), then I could have the main MCU talk to that slave and have it control balancing - this means I could give full voltage to the mosfet gate (instead of a max of 2v via the BQ chip, I could get 3.3-5v). Then I would not need a 12 conductor cable to the balance board and instead just use a 5/6 conductor cable.

I'm just wondering what is the best solution in terms of robustness and safety. The slave that controls balancing could be set to automatically turn off balancing if it loses communication with the MCU - just hoping to get people's opinions on this.
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#35
For anyone who cares, I finished the following:

BMS board with on-board 200ma balance current:
https://easyeda.com/mikethezipper/10s-ba...-balancing
BMS board with off-board balance of up to ~3A, and the balance board which was designed to support heatsinks with active cooling (think CPU cooler)
https://easyeda.com/mikethezipper/10s-ba...-balancing
and:
https://easyeda.com/mikethezipper/balance-board-5s

This is for the 6-10s version. If this sucker works out, I'll be making the 3-5s version for those with 12v systems. Since the balance boards are modular, you use one for 3-5s, and two of the same boards for the 6-10s version. As-is, though, the i2c wouldn't work for the second board since they don't share a common ground. At this point I don't really care to fix that, although this could be fixed by either making the balance board in a 10s configuration (holy expanding scope Batman!) or changing the i2c connectors to 4 conductor versions and using isolators on the balance boards.

Anyways, here are the links for your comments and suggestions:
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#36
So I guess strike one for dealing with Chinese companies (although it isn't their fault most likely). My boards and components have been sitting in US customs for the past 4 days while I'm stuck here twittlin my thumbs.
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#37
Better to be twitting them than widdling them Wink

Yeah, sometimes that stuff gets stuck for a week. I had something to get stuck in Jax for almost 2 weeks (it was "supposedly" coming from Cali, but I'm guessing not really)
Proceed with caution. Knowledge is Power! Literally! Cool 
Knowledge is Power; Absolute Knowledge is Absolutely Shocking!
Certified 18650 Cell Reclamation Technician

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#38
Ok so I finally got my boards and components in.
Initial impressions: The footprints on EasyEDA are all messed up many of these components do not match the footprint they are supposed to be per the board. I was still able to populate a board, just ticks me off.

I think I figured out a cheaper alternative to the dinkle connectors - the mystery chinese connectors look like they are made using the same molds , but they are obviously made from a cheaper plastic. however, the plating seems good.

Also, the balance board looks kinda awkward - I'm looking forward to testing this thing and seeing how hot it gets Smile I have provisions for bare resistors, resistors with a heatsink, and active cooling with a PWM fan - so this'll be fun to see if I can burn my place down.

I've looked through the balancing code in the SW and it's pretty simple and doesn't have any sort of smarts. Unfortunately, it leaves no way to just tell something to start balancing - I would need to do this manually.
I've got some coding to do so that I can trigger balancing on command for testing - so that's my next step. Hopefully by the end of this weekend I'll have the system up and running.
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#39
(02-01-2019, 08:39 AM)Mikethezipper Wrote: I'm just wondering what is the best solution in terms of robustness and safety. The slave that controls balancing could be set to automatically turn off balancing if it loses communication with the MCU - just hoping to get people's opinions on this.

If you have smart per-cell monitoring boards, you'd want the balance unit to automatically kick in even if the MCPU was off-line. This is what batrium cellmons do, they work independently unless told to do otherwise by the watchmon cpu.

In your case the sub-balance boards are simple & you'd probably want them to not attempt balancing without control or you might just end up with flat cells.
Running off solar, DIY & electronics fan :-)
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#40
Well, since this isn't per-cell monitoring like batrium, it wouldn't really help in this case. But regardless, how does a longmon for example know when to balance if the main controller is offline? It just seems like without something there to monitor everything, it could end badly...
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