diyBMS - Stuart Pittaway/Collin Hickey Ver. 3.0

Church1182

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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.

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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.
 
Did you check the prices for the pcb's on jlcpcb and pcbway? How much did they cost from allpcb?
 
Korishan said:
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. :D
 
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 :)
 
Mikethezipper said:
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.

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:)

Absolutely. I am building MHF Powerwall 1to 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...
 
Walde said:
Working Boards V2


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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 :)
 
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.
 
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.
 
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 :p 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.
 
Mikethezipper said:
Have you tried easyeda / JLCPCB / LCSC ? ... What's the expensive part? The Attiny is like what, 1.50? the fets and other goodies should only be cents after that.

I have not tried them yet, but I am adding it to my sources list. I have used Mouser, Digi-Key, and Newark/Farnell for various components over the years. They all seem pretty competitive price wise. I know I can use other sources and get parts A LOT cheaper, but then again they are cheaper parts. For this project I wanted to get some of the parts sooner than a slow boat from China. In terms of cost, the ADUM1250, ATTiny85, REG710NA-3.3, and thermistor of all things, are the most expensive components. From Mouser the ADUM1250 is $5.55. On AliExpress I was able to order 20 for $20.03 shipped. Mouser actually had better prices on ATTiny85 chips than I could find on eBay or AliExpress. From what I've seen, and what even Stuart says, these can be assembled for under $5/board if you take a little time to source parts and are willing to wait on that slow boat. Personally, for what this system should be able to do I felt like up to $10/board was reasonable considering a Longmon is roughly $17 and does essentially the same thing. Monitors the cell, burns off energy when necessary, and reports to the controller. That sounds about right. Typically the markup on something like this is 100%. Take what it cost in parts and double that, that's your retail price.

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.png
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.

Where the real challenge comes in is that main controller/monitor. The programming and design of that will make or break your setup. I think the safety aspect really depends on the user and what they set the limits at. The hardware is, relatively speaking, easy enough to figure out. Programming that includes the appropriate safety cutoffs is essential. In another forum I was basically told that because my project was DIY and not built by a company it would be inherently dangerous.
:dodgy:
I've seen a lot of stuff made by companies that I would not consider inherently safe, so saying that something is safe just because a company built it is ignorant in my opinion. Perhaps willful ignorance.If you are operating within the design specifications of the components you are using and ensure you have safety features, like fuses, breakers, voltage cutoffs, etc, how would it not be inherently safe? But I digress.

I'm confident that I can build a system that will provide the same level of functionality as the Batrium system for a fraction of the cost. Perhaps it doesn't have the polish of the Batrium setup, then again it might. Just depends on how far down the programming rabbit hole I want to go.
:D
 
Church1182.
I am looking forward to what you will come up with!

Just remember most notable discoveries were not made with a loud announcement of"EUREKA"
but more of a subdued mutter of "That's Strange"

Wolf
 
Yeah that ADUM1250 chip is pretty interesting - I should totally use that sucker on the balance boards I have - the i2c isn't properly isolated on my boards. I wanted to, but I just got too tired/lazy and just ordered the boards instead :)

At the price you got them, ~$1 each, I really have to wonder if those are real chips - or if they fell off a truck haha. That's sooo much cheaper than any real supplier... I mean, even with lcsc, I feel like they are using totally unfair chinese special pricing. Like they buy them by the truckload and offer them at below MSRP - which they are even doing with their pcb prices. JLC PCB offers pcbs for cheaper than just the price of the copper on the boards. $2 for ten boards lol

I wasn't saying that because something is made by an individual it is inherently worse than what a company makes - far from it. What I was trying to say is that the battrium and electrodacus systems are systems that represent probably a thousand hours worth of work by industry experts - they are well designed, well thought out, and because they've been used by soo many people, they have had the time to iron out many kinks. So I believe they are safer because they've had the time to incorporate those failsafes that hobbyists think about, but don't usually have the time to implement. I know in the projects I do (since I'm not paid) I usually run out of steam once I finish, but before I incorporate many of the ideas I have. The issues aren't what normally happens - but the corner cases. Like, what if the overvoltage is supposed to trip, but it doesn't? Do either of our systems have built-in failsafes? I know mine doesn't. I don't know what sort of extra safety doodads the "pro" systems have, but I would at least hope that for the price they have lots of testing. I have seen plenty of professional products that are less safe than DIY solutions - however I suspect that both the systems I mentioned are way better than what I do.
I'm not an EE, I'm not a programmer - so really just about anything out there is better than what I do :) But that never stops me, I just forge ahead.
 
Welp, on to Plan B for at least some of the components. According to the tracking number my ADUM1250 chip order was canceled by the shipper. They claim the carrier lost it. So not sure how that will play out, but I found 10 on eBay for a little more than what they were on AliExpress, so I'll roll the dice on those. LCSC was out of stock for that one. If eBay falls through I may have to break down and order some through Mouser or Newark.

On a positive note, 80 LiitoKala 26-FM batteries were delivered today. Be interesting to see how those test out on the ol'Opus. They should almost match the batteries I already have and be enough to start assembling packs. Hopefully I'll have BMS modules ready to attach and test by the time that's done.
 
Keep us updated David.
I haven't posted in a while, but my BMS is still in development. I'm updating the design of the BMS board now. What would be nice to see is the firmware/SW you end up using. I managed to get the BMS itself to stream it's info to influxDB/Grafana/NodeRED so at least it looks pretty. But my balance board design really needed some overhauling.
 
Mikethezipper said:
Keep us updated David.
I haven't posted in a while, but my BMS is still in development. I'm updating the design of the BMS board now. What would be nice to see is the firmware/SW you end up using. I managed to get the BMS itself to stream it's info to influxDB/Grafana/NodeRED so at least it looks pretty. But my balance board design really needed some overhauling.

Interested in your project Mike. As you have suggested I am also more interested in a single board type design ... though I do really like the Stuart/Adam/Colin design.

Do you have schematics or BOM list? Is your's going to be open source?

Thanks for the work!
 
derekisastro said:
Mikethezipper said:
Keep us updated David.
I haven't posted in a while, but my BMS is still in development. I'm updating the design of the BMS board now. What would be nice to see is the firmware/SW you end up using. I managed to get the BMS itself to stream it's info to influxDB/Grafana/NodeRED so at least it looks pretty. But my balance board design really needed some overhauling.

Interested in your project Mike. As you have suggested I am also more interested in a single board type design ... though I do really like the Stuart/Adam/Colin design.

Do you have schematics or BOM list? Is your's going to be open source?

Thanks for the work!

Lol, I have a thread for my project on here, just search for my screen name. All schematics, bom, code, etc is open. I'm currently working on an AC/Heating/Fridge &inverter controller that will utilize most of the same technology, but at much lower risk for testing. I'm most of the way done on that. Once I finish, I'll be moving back onto the BMS project.
Be aware that the most recent version I have shared has ... issues that I have since resolved. It takes too much time to upload everything every time I make a change so I'm only uploading now when I'm closer to being done.
 
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