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diyBMS - Stuart Pittaway/Collin Hickey Ver. 3.0
#11
(02-21-2019, 12:56 AM)Mikethezipper Wrote: 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. 

Quote: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 [Image: 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.  
Big Grin
Wolf likes this post
James 1:19-20

Not all those who wander are lost - J. R. R. Tolkien
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#12
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
Church1182 likes this post
If 18 X 650 = 2200+mAh then we have power! 
May all your Cells have an IR of 75mΩ or less Smile
Last count as of 3/23/2019
Total Number of Cells           3743
Cells  >80% of Capacity        2445
Cells <80% of Capacity         1265
Cells ≥2200mAh & ≥ 80%     1709
Google Drive for info https://drive.google.com/drive/folders/1...sp=sharing
Not your average Wolf       
            Cool



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#13
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 Smile

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 Smile But that never stops me, I just forge ahead.
Church1182 likes this post
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#14
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.
Wolf likes this post
James 1:19-20

Not all those who wander are lost - J. R. R. Tolkien
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