BMS Test Circuit - Page 1
Forum section: electronics / beginners

author: jerryk
author_rank: Regular Contributor
timestamp: October 19, 2021, 08:47:24 pm
content: I am trying to make a test circuit that behaves just like a series battery pack so I can test the functionality of various bms systems. I made this simple series voltage divider and it sort of works. The obvious problem is that if I change the voltage of any cell it also changes the voltage of all other cells and I have to rebalance all of the pots so as to have only one cell out of balance.My goal is to be able to have a test circuit that have like a 4S battery pack and be able to manipulate the voltage of each test cell independently. Also I want to power the circuit with one voltage source. Any ideas on how to make such a circuit?Jerry

author: Terry Bites
author_rank: Super Contributor
timestamp: October 20, 2021, 08:17:24 am
content: Have a look at this single cell emulator for some inspriation.https://www.maximintegrated.com/en/design/technical-documents/app-notes/4/4721.htmlI'm not sure I understand but:https://www.designworldonline.com/understanding-battery-simulators/So essentally a stack of isolated programable CV /CS regulators. That s headache.

author: jerryk
author_rank: Regular Contributor
timestamp: October 20, 2021, 06:04:01 pm
content: I definitely overstated what I'm looking for in my first post. I'm not really looking for something that will sink current mainly because of the added complexity and cost.Here is a circuit that I found yesterday that might approximate what I'm wanting to make using output of LM317's in series. I was hoping I could use my Rigol 832 power supply as the power source but I kept running into the issue of a common ground and with my limited understanding just kept running into dead ends.The circuit below looks like it might do with some modification to get the output voltages in line with a typical lithium cell. I'm not sure if this can be powered with a common ac source for the four LM317 circuits. Again I would like to power it with a single DC supply and skip the 4 rectifiers but I don't know if that can be done.I appreciate the input.Jerry

author: jerryk
author_rank: Regular Contributor
timestamp: January 27, 2022, 05:39:50 pm
content: I did find a circuit that seems to do what I was looking for. The solution was provided in this thread on another forum.https://electronics.stackexchange.com/questions/596782/split-one-dc-supply-into-4-independent-dc-suppliesI am trying to add individual volt readings per simulated battery cell using these cheapo led meters.https://www.amazon.com/gp/product/B08HQDH24Q/ref=ppx_yo_dt_b_asin_title_o08_s00?ie=UTF8&th=1They work fine if I use the two wire configuration taped into the series connections (as per attached circuit photo) however the minimum voltage is too high (3V or so). To get lower readings I need to use the three wire connections in the attached photo and provide each led meter with a separate minimum 4V supply. The problem is that the grounds for each led meter are different.Is anyone familiar with these little meters and how I would go about providing a separate power supply of 4V so the meters will be able read voltages to lower limit of the TLV431?Jerry