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diyBMS - Stuart Pittaway/Collin Hickey Ver. 3.0
#1
I've been digging around and researching various BMS systems and have come to the conclusion that "BMS" is a catch-all term. 

Anyway, I am moving forward with the design started by Stuart and forked on Github by Colin. I considered putting this in my build thread, but thought it might better go under the BMS section as this is specific to BMS. In researching the DIY vs Batrium BMS I ended up here because it seems to be one of the most complete, but not finished, and well documented DIY designs, and I have a soft spot for the AT chipsets. I've used the ATTiny85 on projects before and can muddle my way around Arduinos pretty well. This system, as of Version 2.1/3.0 can provide cell monitoring and balancing. I am using the "smallerpcb" branch under Stuarts github for my board and the software from Collin's fork as he has implemented the balancing function and web interface.


PCB's were just ordered through www.allpcb.com which seems to be one of the commonly used board sources for others building these. Vary reasonable on prices. Others who have used them seem to have good results. 

What I really like about this approach is the cell level monitoring/balancing ability, it is developed enough to be functional, but still has room for tinkering and improvements. It is low cost, but should be more robust than the chinese (bms)protection boards. 

I think I'm as excited about getting back into this level of electronics as I am about building my powerwall.
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James 1:19-20

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#2
Did you check the prices for the pcb's on jlcpcb and pcbway? How much did they cost from allpcb?
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#3
(02-16-2019, 12:31 AM)Korishan Wrote: Did you check the prices for the pcb's on jlcpcb and pcbway? How much did they cost from allpcb?

I did check pcbway and I think they are the same company as allpcb. Their websites layout and function are almost identical. The colors are different, but that was it.

I paid $23 US shipped for 15 pieces, $1.53/board seemed quite reasonable.  Big Grin
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James 1:19-20

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#4
Good luck man, hope it works out for you. I went down a different path myself as I liked having everything on a single board (I believe the design you are using uses slave modules and a master controller if I'm not mistaken). As you work your way through it, it would be great if you can document your findings and make them public so that others can follow in your footsteps.

Can you share what your battery and use plans are? I'm curious to see how different people use differnt BMS setups. I put my balance board on a separate PCB since with the balancing currents I'm expecting from the larger packs I'm dealing with, the heat would cook the nearby components on a board like that pretty quickly. Although if you are going to be doing something that would make it pretty toasty, you could easily extend the leads for the balance resistors out and slap them onto a heatsink Smile
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#5
Working Boards V2

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#6
(02-16-2019, 03:30 AM)Mikethezipper Wrote: Good luck man, hope it works out for you.  I went down a different path myself as I liked having everything on a single board (I believe the design you are using uses slave modules and a master controller if I'm not mistaken). As you work your way through it, it would be great if you can document your findings and make them public so that others can follow in your footsteps.

You got it. That was one of the main reasons for making this a separate thread from my build. I dug through a lot to get the information thus far and still have not come across a clean, concise set information on a build. Hopefully I can provide that. As I understand it the system is slave modules controlled by a master. My feeling is that with the ATTiny85 that could be turned into a somewhat autonomous balancing slave with thermal and voltage reporting to the master. Room to play.

Quote:Mikethezipper
Can you share what your battery and use plans are? I'm curious to see how different people use differnt BMS setups.   I put my balance board on a separate PCB since with the balancing currents I'm expecting from the larger packs I'm dealing with, the heat would cook the nearby components on a board like that pretty quickly.  Although if you are going to be doing something that would make it pretty toasty, you could easily extend the leads for the balance resistors out and slap them onto a heatsink Smile

Absolutely. I am building MHF Powerwall 1 to power my small shop. I am using reclaimed 18650's and a 400 W solar array at 24 volts. My commissioning goal to turn the system on is 140 cells for a 7S20P. Once I get the system up and running on the first set of cells, I plan to continue harvesting and building packs that are 60P. Once I have enough for a balanced 7S bank I can use the other half of the boards I ordered to set it up and switch over to those, then repack the first bank into a matching 60P bank and bring it all online. That should max out the capabilities and needs for that shop, and give me what I need to know to build the bigger system for the house some day.

I like the design of the ver3.0 board because it is smaller and more compact, but as you said this can cause thermal issues with balancing. However, the smaller board footprint allows for more room to move the balancing resistor off board if needed. Or making a second board that can be mounted perpendicular to the first board. Or heat sinks like you mention. So many options...
James 1:19-20

Not all those who wander are lost - J. R. R. Tolkien
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#7
(02-16-2019, 01:47 PM)Walde Wrote: Working Boards V2


That's pretty interesting - how did you get from the raw data output of the boards to that beautiful graph? It's hard to tell from the picture, but is that an ESP8266 in the corner? 

Any chance you could share what you are doing to get that graphical output? I'm mostly done with the HW part of my project, and next will be making the interface and the programming for control etc, and that looks like you have most of it covered already Smile
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#8
That lovely graphing is where Stuart, Colin, and Adam Welch have gotten the project. They have some videos on YouTube about using it. The code is developed for the ESP8266, but word is it can be done on several Arduino boards. Probably wouldn't take much to go to Raspberry Pi either.
James 1:19-20

Not all those who wander are lost - J. R. R. Tolkien
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#9
Status Update: Boards and most components have been ordered. Currently sitting at roughly $8 US per board for 15 units. According to the emails, I should be seeing boards and some parts by the end of the week. I went with a mix of Mouser and Aliexpress for the components. I have not ordered fuses, balancing resistors, or connectors yet. I need to see what I already have on hand from previous projects in terms of wire and connectors, and I need to do the math still to properly size my resistors and BMS fuses.
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James 1:19-20

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#10
That's interesting. Have you tried easyeda / JLCPCB / LCSC ? I just put in what I hope is my final version of the board, and the all-up board cost (without labor) is about $4 per cell plus it makes is super easy to order everything through what is essentially the same company. Although I have to wonder about some of the chinese components, specifically the caps. Based on what I saw on that board, it shouldn't really be that expensive. What's the expensive part? The Attiny is like what, 1.50? the fets and other goodies should only be cents after that.

I can modify my setup for 11-15s, and the all-up cost would be around $3/cell
I'm wondering if with some tweaks that could be brought down quite a bit. Since those boards are so tiny, JLCPCB would charge around $.50 a board, and the components even with the attiny should only come out to maybe $4. At 8$ a board + the cost of a main controller ... at 14s, that's ~120 in just raw components.

I know that cost really isn't the point, I'm just starting to notice how it all adds up. Because at the end of it all, even with both of our designs, all we have is something that can measure voltages and burn off energy. It still needs extras to measure current (mine technically has it already built-in, but I have yet to test), output to charge controllers/inverters, flip relays, etc. I'm wondering if by the time we add all of that up, we end up at nearly the cost of an electrodacus or a batrium but with a tenth of the features and safety of either of those solutions Tongue I pretty much knew this going into it, but I was also hoping that thru blood and sweat we'd have a less convenient/safe DIY system in the ~100$ range. Looks like that may not be the case, but I guess $250 or so is still half the cost of a real unit.
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