OpenEnergyMonitor Community

DIY Lithium Battery Balancer and monitoring (BMS)

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!


@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.

EDIT: Is this thermistor good enough you guys think?,searchweb201602_1_10152_10151_10065_10344_10068_10342_10343_5722611_10340_10341_10697_10696_5722911_5722811_10084_5722711_10083_10618_10304_10307_10301_10059_10534_308_100031_10103_441_10624_10623_10622_10621_10620_5723011_5722511,searchweb201603_25,ppcSwitch_5&algo_expid=d0199ad5-a06f-429c-a096-467e805389d1-7&algo_pvid=d0199ad5-a06f-429c-a096-467e805389d1&transAbTest=ae803_1&priceBeautifyAB=0

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.

How has your setup been performing Stuart?

I’m in Portugal at the moment so will let you know when I’m home!

Enjoy :slight_smile:

Finished my first hand soldered board. Waitng for the programming adaptor to arrive…

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Looks good, I hand solders my first one too. I had mine installed for about a week. They initially started great but then I started getting more and more false figures till all but one wasn’t working. Going to look at the code modifications to see if I’ve broken anything. I need to double check the validation code as the rogue readings are getting through to grafana which shouldn’t be happening.

Hi everyone,

I’ve been following along for the past few weeks and have been working on a parts list this weekend. I have published my current working list here. I have found everyone on Mouser and Element14 and prices are in Australian dollars.

During my search for parts I noticed a slightly cheaper I2C isolator and wondered whether the Texas Instruments ISO154x-Q1 isolator (ISO1540QDRQ1) would work as alternative to the ADUM1250ARZ. From my very limited understanding they do look similar, and have the same pin layouts and dimensions. Thoughts?

Hi Jesse C, Your list is handy if you want it fast but …some items are expensive over there!!! Take a look at my list above on Aliexpress the Adums are 1/3th of the price!!

Which 50w resistors are you guys using?