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DIY Lithium Battery Balancer and monitoring (BMS)

Hey Bob, I’m working on the influxdb/grafana code at the moment, stuck in the airport in Paris so may as well keep myself busy :slight_smile:

I’m trying my best to keep it along the same lines as stuarts emoncms code as it’s so good so it can be configured from the web interface etc. Will hopefully manage it.

Well i may be complete… famous last words. It compiles, just not sure on the .js modifications but once i’m back in the country i’ll compile it up and see what it looks like and tweak as required but it’s looking good so far. Fingers crossed :slight_smile:

I am starting my ali orders :slight_smile: Any recommendations on the best place in the states to order the PCBs?

Ok anyone wanting to use InfluxDB my fork is working ok for me, I’ve modified Stuarts excellent code so the settings page now has settings for sending data to influxdb. I’m currently just sending voltages but shall also setup sending temps over the weekend. I’ve tried to do it as sympathetically as possible and left in the possibility to use emoncms as well. I’ve increased the reporting frequency to every 60 seconds as well so as not to flood the DB. I’ve also put in the fix which i mentioned previously regarding setClockStretchLimit being needed to be set to 1500.

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Thanks very much!

Jlcpcb.com
I ordered mine from their came to $11 usd total inc shipping for 10 boards

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Well guys i also stepped into the abyss and ordered the pcb’s !!

The thing i’m most curious about is the smd soldering. In the youtube video’s above he used a heat soldering station, i don’t have that i only got my Metcal sp200 with a small tip.
Thinking about contacting someone locally who can do it with heat (and has experience with it!!)

I think i’ll solder 2-3 first when i got everything to complete them and put them on a 3s4p 2200mAh pack to see how it works and get familiar with it!

Exciting stuff!

I went with Jman’s link and found out that ordering 2x10 is cheapest somehow. Also i got 20 dollars off shipping ??? So grand total for 20 pcs is €9.42 thats not bad at all!

Hi Joey, those are my vids. The heatgun i got was a combined unit which was pretty cheap, Stuart used the pan method as well which can work, i prefer the heatgun though. The model i got is listed further up in this thread and was recommended by Brian.

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Thanks Colin, I got a friend who works at a led billboard manufacturer. Didn’t know he could do stuff for himself but he offered to help! I’ll manage with my soldering iron he said, “Quote” If its only 1206 we’re good.

Now for ordering the rest of the components!

ok guys think im about to order an inverter for this project and use this BMS can you please confirm the BMS will talk to emoncms/mqtt

Yes the BMS will talk to emoncms.

However, just to repeat my earlier post, the BMS is work in progress. The circuit works, and the BMS will report voltage readings. Currently there is basic support for cell balancing.

Don’t use this on mega power walls expecting the reliability or features of batrium or similar!

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@stuart Why is there a double entry in the parts list?? the C1 and C2 are the same right? So 4 per board needed of 2.2uF Capacitors ?

And 3 x 2K2 resistor + 2x 47k resistor ?

I’ve been looking through what everyone is posting, but if you buy a collection book and there are only 20 in it, and you pay 9 dollars for the collection, but only 1.13 per 100 of that same value … i better buy the 1 value :stuck_out_tongue:

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I’ve tidied up the code i modified today as i’d stuck extra logging in when i was troubleshooting. I need to implement the temp logging to grafana and the bypass status for each cell.

Been wiring up my powerwall in preparation for the modules today also so should be in operation this week.

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Ok so i got a new wishlist, and i think everything is on Alie, can anyone check that i have the right components? Especially the SI2312, there is no info on that sale.

https://my.aliexpress.com/wishlist/shared.htm?groupId=100000001079545

EDIT: Is this thermistor good enough you guys think?

I ordered mine though there too. Thanks for the recommendation!

I’m new to this and trying to understand the schematic. Please forgive me if I’m missing something; I’m trying to learn.

I was wondering why the design uses the 3.3v regulator? Without it the ATTiny85 could read the battery voltage directly and after comparing it to the internal voltage reference get the batteries actual voltage regardless of the battery’s charge (voltage). The 18650’s should never go anywhere near the 5v max, and the ATTiny85 should run down to 3v without issue at 8Mhz.

I’ve never worked with the thermistor before. Does it require 3.3v to work properly?
Is it to reduce the current used by the ATTiny85 when running at 4.2v (4ma) instead of 3.3v (3ma)?

I started down this path original without the voltage regulator however the ADUM chip stops working at around 3.3v so this isn’t good!

Additionally, don’t just think of 18650 cells, this circuit could be doing other chemistry down to about 2.5v

stuart, thank you for replying.

So it’s basically down to the i2c isolator not working at lower voltages and wanting the system to be comparable with other cell chemistries other than standard lithium. That makes since.

Is there any work being done on the ESP controller board to be able to cut power to the load of the entire pack if one of the cells reports under-voltage or some other error? (Either through a relay or power mosfets.) From my current understanding the ESP only collects and reports each cell’s status.