DIY Lithium Battery Balancer and monitoring (BMS)

Tags: #<Tag:0x00007f1be6da36e0> #<Tag:0x00007f1be6da3528>

(Vela Nautica) #731

Hi Dirk,

I had an other look at the cell module code and it looks to me as I told you before. The controller calculates the average cellvoltage and sends a bypass command to these cellmodules that are higher than the average above all.
The bypass time in the cellmodules is not limited by a timeframe. It bypasses for about 30sec and then pauses to get a cell voltage reading. Now a decision is made, if the cell voltage under the bypassvoltage when the balancing was enabled bypass process it finished and the balancing is switched off. Is the cellvoltage still above the bypassvoltage the balancing goes on and next check is in 30sec.

If I am wrong with that Stuart might help me out?

My cell modules behave according to this pattern. I use the original cell firmware from Stuart.
I do not use the original Stuart firmware for the diyBMS controller as I work with an ESP32.
At this time my firmware will probably not work with your setup bcs I adapted it for LiFePo and 8 cells. I need to go through my software and check if I can relaese it to your system.

What exactly is going on with your cellvoltage when you activate balancing?
Considder your chargers or loads my influence the balancing process while they change the voltage measured at the cells.

I would suggest you turn of chargers and loads, write down all cellvoltages and activate balancing. Now have a close look how the cell voltages change and when the cell modules stop balancing what is indicated with the blue LED´s.

I did similar to your setup, I placed 1.8 Ohms as load resistor for the bypass. As I work with LiFePo cells my nominal cell voltage is a bit lower than yours with max 3.65 V.
The resulting bypass current is very similar to yours with 2.027 A and my 10W resistors get quite hot, about 80 to 100 degree C. But it works.


(Adam Hepp) #732


Do you have an aliexpress wishlist for V3.0?

(stuart) #733

Thats correct.

Even for VERY LARGE battery banks - you won’t need massive amounts of current bypass (low resistor values) if the packs are constructed correctly, they will only need balancing infrequently (monthly or less) - and even then the cells should be no more than a few 0.1V out of balance.

(stuart) #734

Thats the reason why the thermistor was on the board - to monitor the resistor temperature and shut off in case of over temp - although most people seem to want to use this to monitor the cell pack temp instead!

(Vela Nautica) #735


I came about PCA9601D Dual bidirectional bus buffer for the guys who run into i2c noise.

I will try that driver and increase the distance from controller to slaves.

How about that? Does anybody mind about adding it? :sunglasses:


(Brett) #736

what would be coursing esp8266 to drop and not reset which the moduls still think there is wireless communication?

(stuart) #737

This is probably the wrong solution - if you are suffering from i2c interference, the DIYBMS is probably not for you. This is why the commercial solutions use CAN BUS or similar to avoid such problems.

DIYBMS could be changed to use CAN BUS however this then drives the price per unit up to that similar to commercial units so there is little point!

(Raccoon ) #738

Hi everyone, i have some little issues ordering the last piece of electronics, they all have this -ND at the end, and thus i’m not quite sure if these are the one i should buy. Because opening the file on kidcad, i don’t see those -ND at the end, could anyone confirm me please?

SE30AFG-M3/6A Diode




Thermistor 10K

Also, im unable to see anywhere MC36228 1.5A 8V PPTC 154C, it’s like this component doesn’t exist :confused:

I was trying to guess that may be this would work instead

PTC RESET FUSE 8V 1.5A 1206 ???

Thanks a lot for your precious help :wink:

(Bill Thomson) #739

Hi Raccon,

I’ve adjusted your user account. You can post more than two links now.


Bill - Moderator

(Brett) #740


SE30AFG-M3/6A Diode

(Raccoon ) #741

Thanks a lot brett, but i would have liked to know if the one im about to order from my links would work as i can’t really afford buying from different places, the shipping cost and custom can be very expensive. I would just need a YES or NO whether these are the right component to buy :wink:

Thanks you :wink:

(Brett) #742

Most of will my items i got from Alibaba but Rsonline i got items from as well there world wide mite have a wearhouse near you. They adjust cost to cover shipping. Ebay mostly have free shipping but take a long time to come.

(Brett) #743

Hi stuart
Iv rebuilt one of my modules that not getting i2c communication from but still programs the attiny.
But when i plug module into power there still nothing.
Ran a mulitmeter over the board over every component all values are the same as working modules.
So im stumped why this module not running still even after putting everything on a new board.

(Dirk Walde) #744

Check REG710NA Connect (output 4+6 (+/-) = 3,3V) (~~3,1-3,3v OK)
also had defective solder joints with short circuit.
I have not seen synonymous with a magnifying glass, since the short-circuit was under the part. :zipper_mouth_face:

Brett: Do not you have a hot air station or a simple hot air blow dryer
:wink: I have only blue LED´s on the Moduls

I can adjust in my multimeter continuity examination (BZ), so I found the short circuit for me was 4,5,6 the problem.

There should not be any connection between the contacts according to the schematics.

Update 09.12.2018

Hi Brett I hope the tips could help you

I will do some DiyBMS modules now have 30 boards (16 already finished).

(Brett) #745

Hi Dirk

Thanks for that ill have to order more REG710NA-3.3 and try replacing it may have damaged it when i was hand soldering with solder paste,
pack voltage 3.957v Pins 4 voltage 3.274v green attivity light flickers. pin 6 3.276v
As for the reason my system been dropping out is because of a module having issues not taking commands wirelessly and i think its to do with the thermistor.

The module seams to think the voltage is higher than set and burns off then re-assesses the voltage then dropped out, got me beat why its doing it since taken that module out system running good no ESP drop

(Raccoon ) #746

ok thanks, i was asking to make sure all the components on my list are the good ones coz im really unsure about how to pick them. So if its ok, i will go ahead and buy them all :slight_smile:

Btw, this post is getting so huge, i wish we could have some kind of subforum with sections like : Parts needed and advises / Programming BMS / Compatible boards* / First run setup / Debugging issue

(*)- For ex, i have only esp32, wemos esp8266 and raspeberry pi, still not sure if its enough to run the whole setup, i think i can program the attiny thanks to raspberry, but for running the bms software on esp32 or esp8266 board, not sure :confused: all i know is that wemos d1 mini works thanks to Adam Welch’s awesome youtube videos

(Dirk Walde) #747

You need a Programmer for the attiny85 = AVR or an Arduino Board

(Raccoon ) #748

i was hoping rpi would do according this video:

or this

(Robert Wall) #749

You can of course create those as new threads and make reference to this one. But to go through this thread, at 738 posts, and separate those into threads from your list would be a huge undertaking. Then what about posts that relate to more than one subject on your list?

(Raccoon ) #750

Hi Robert, i was just trying to split informations into categories as we are reaching the level “big data” thread :joy: soon we will need a cluster to dig informations :stuck_out_tongue_winking_eye:

Ok that was for the kidding part, just that we have so much info into such an “unstructured data” block (one single thread) that i think we are loosing the informations itself. Don’t have perfect solution, but it was just an attempt to may be start ordering it somehow ;). I could help in the matter if needed, and if ppl think we should do it :slight_smile: