Battery Monitoring

[J_Mack58]

I built a 14S32P battery pack with no BMS. Even though I know better I been usinging it daily and so far so good but I dont feel good.. So now I am making a effort to put a BMS to my little beast. After pricing the BMS's and reading reviews that the cheap ones from overseas may not be doing anything I set out to just monitor my 448 batteries with an Arduino and some and analog multiplexing boards. After wiring two of the 14S's I looked ahead and said "Crap this going to be a lot of wires". Here is my question, if I'm only monitoring to catch when something is going wrong can I monitor two cells at a time? In my perfect world two cells will be 7.7 volts because I only charge the 14s to 54 volts hoping each cell charges to 3.85v

No such a thing as a stupid question?
Give me this chance and I'll prove you wrong.

 

[OffGridInTheCity]

>can I monitor two cells at a time?
The problem is that 1 cell can drop low enough to push the other cell above 4.2v and create risk of fire.

I've read that individual cells in series (to make a battery) can even go negative voltage (another risk of fire) but yet the overall battery will continue to produce voltage/current.

>Even though I know better I been usinging it daily
I'm with you - I ran my powerwall the 1st 6 months with no BMS, measuring the cells in my 7s battery each morning. But after I got a BMS I was surprised to find that some of my cells were going down to low 2v (damage!) and then popping backup to 3.3v when the load was removed - so the 7am measurement showing 3.1v to 3.3v low (seemingly OK) was not giving the whole picture.

BMS is needed - you'll get there

 

[daromer]

A cheap bms can be found for 20USD and upwards. To skip out on it is not worth it. Your house is worth more than that!

You say 14s32p. Thats just 1 BMS needed and nothing more. Pay up a bit more and get one for 50-100USD atleast.

 

[Redpacket]

Depending on your cell arrangement, it's not that many wires, typically only 15 or so?
You have each 32p section in parallel right? Each of these sections only needs one or two wires depending on the BMS.

 

[ajw22]

After pricing the BMS's and reading reviews that the cheap ones from overseas may not be doing anything

The outrageously are cheap ones are of course made outrageously cheaply

I use $50 ones from a manufacturer that has some history and reasonable reviews/reputation, and it's been working great. Just stay well below their stated maximum current ratings for extra safety. Mine are rated 60A, but my system is fused at just 30Amps.

My exact models seems to have been discontinued, but this is a very similar newer model:

6.51US $ 12% OFF|14s Li Ion 58.8v Smart Bms With 30a Or 60a Constant Current Rs485 Uart Communication Software Bms - Integrated Circuits - AliExpress

Smarter Shopping, Better Living! Aliexpress.com

www.aliexpress.com

[...] an Arduino and some and analog multiplexing boards.

I'd love to see your circuit design! I thought of some ways to do it, but the parts costs + time was just not worth it, if a proven design and finished product could be had for just $50.

 

[daromer]

And for 50 bucks you can today get DIYBMS if you are ok with just some minor soldering. Then you can easily expand with more modules later on. If thats your limit that is

 

[floydR]

I can see why you said " After wiring two of the 14S's I looked ahead and said "Crap this going to be a lot of wires" as your 14s1p are in pvc pipes x 32 If they were 32p in each pvc pipe then connected in series that would cut down the wires to 15 wires instead of 210 wires. if I understand correctly.
later floyd