Need a little guidance with battery charge ICs and similar - Page 1
Forum section: electronics / projects

author: viper
author_rank: Regular Contributor
timestamp: September 21, 2025, 08:43:37 pm
content: Hoping someone with experience can point me in the right direction. Working on a battery operated device using an Li battery and primarily solar charging. Main system using an ESP32. I need both a battery temp status, but also the authority via the ESP to allow/disallow charging.What I am fighting with is the overlap of "battery monitor" ICs vs "charger ICs". I am not sure if a charger chip can do all that I need. The max charge current can be limited to 2A, battery will be 2S so I plan to use use some passive balancing either with FETs and bleed resistors, or similar.I am hoping to find ways to reduce component counts with integrated ICs, but I realize I may have to develop other circuit protections like reverse polarity, over current, etc.I'm currently looking at some charger offerings by TI, in which they have an NTC onboard with some ability to control the chip with the ESP. Typically a BMS monitors the temp, thus why I mention a bit of overlap. I wish I could make a block diagram for you guys but I'm stumped right now in what to even use.

author: RoGeorge
author_rank: Super Contributor
timestamp: September 21, 2025, 09:50:43 pm
content: Usually a Li-ion charger IC is for charging a single cell, and it doesn't keep track of the energy put in or out of the battery.If you have series cells, then the proper way would be to use a BMS dedicated IC. There are many to choose from, they can control 2...6 or more series cells, and can also act as energy meters, communicate by SMBus with a microcontroller, and so on. TI has a many BMS ICs, e.g. various models from the BQ serieshttps://www.ti.com/product-category/battery-management-ics/overview.htmlMost other IC manufacturers have their own BMS IC's, too.

author: viper
author_rank: Regular Contributor
timestamp: September 21, 2025, 10:28:41 pm
content: Quote from: RoGeorge on September 21, 2025, 09:50:43 pmThank you. If I am understanding, these 'charger ICs', when they state '2,3,4 cell', are more to do with the output voltage ranges? I don't see any mention of cell balancing and such.If I am correct, it would seem I indeed may need both a charger and BMS IC? One to strictly manage the input voltage and meter out the correct current and V? then the BMS IC would handle the other matters such as fuel gauge, current protections, balance, etc?Oh, and regarding the NTC that is provided on some of the charger ICs, I would probably disable that as we would probably do the temp work through the BMS?

author: mtwieg
author_rank: Frequent Contributor
timestamp: September 21, 2025, 11:41:36 pm
content: Sorting out a combination of parts for battery management can be a pain. IMO there are roughly three categories:1. Protection: Encompasses things like overvoltage protection, overcurrent protection, overtemperature protection, cell balancing. These are almost always integrated inside the battery itself.2. Charge controller: These set the charging current/voltage for the battery. These are external to the battery, with very few exceptions.3. Fuel gauge/Gas gauge: These monitor the battery to determine state of charge (SoC) and maybe state of health (SoH). These are usually external to the battery, perhaps part of the charger (but still a different chip from the actual charge controller chip).Depending on the manufacturer, they may use the term "BMS" to refer to one or more of these roles. The terminology is not well-defined IMO.I think there are some chips that combine multiple (maybe even all three?) roles, but there are good reasons to separate them. For example, the fuel gauge is generally an embedded processor which is highly configurable via a digital interface. The protection and charge controller, on the other hand, should generally be dumb and robust as possible.

author: viper
author_rank: Regular Contributor
timestamp: September 22, 2025, 01:19:24 am
content: Quote from: mtwieg on September 21, 2025, 11:41:36 pmI appreciate that. I have years in larger scale residential solar so the term "BMS" gets tossed, and I agree, you sort of need to understand what is under that umbrella. As for function, just think something mission critical like NASA sensor (not that extreme), but where the MCU will need to make predictive decisions based on historic battery use, temps, etc, etc. Gets more intense than I think any charger or BMS is good for. Probably most critical is we have a battery heater in which we want to soak things a bit before allowing charging. In short, full control with the MCU, not just a BMS NTC that sees the temp pop up and say "yeah, we good".I didn't realize a fuel gauge would be a separate deal. I don't honestly know other than in the solar fields, we run shunts and coulomb counting to determine SoC and Vdrop for SoH. The actual battery capacity does not need extreme accuracy other than when the SoC vs V varies about nothing between 20-90% charge, we gotta start counting watts or something. I was hoping for some magic IC potion that takes the thinking out of this.As for over current, probably just some fuse links because at the end of the day, if anything fails in the circuit, it has to be sent back to us anyway. IE, something bad happened, it's not a field repair type deal. Keep the battery from making fire and that's about the end of that.

author: mtwieg
author_rank: Frequent Contributor
timestamp: September 23, 2025, 11:23:09 am
content: Quote from: viper on September 22, 2025, 01:19:24 amI'll reiterate an old post of mine regarding my experience with a couple of these "magic" fuel gauge chips:Quote

author: viper
author_rank: Regular Contributor
timestamp: September 23, 2025, 06:34:27 pm
content: Thank you sir! How long ago was that? Ironically I had mostly firmed up a charger chip solution by TI yesterday. I would consider others but support for anything is so pathetic today that I have pretty much bumped MPS and Analog because I can't ask anyone a few basic questions.As for a 'gas gauge', if stress will really get that high, I will just find another way. A simple shunt and some calculations in the MCU will get it close enough but it's truly amazing there is this much drama with what should be main stream. I suspect the push for bigger and more is causing half baked products on the market. The nice thing with rolling your own is you know how to got built so you know how to debug it.As for solar charging, they sell these 'rare' chips with MPPT. I happen to do solar work and understand MPPT well, and seems they WAY over complicate a chip to pinch an extra 1% out, that will never even matter in a small power application. Hell, all you are effectively doing is pulling the true watts in a calculation and letting that math dictate the duty cycle of some FETs. I could nearly guess a basic algorithm and be 2x as good as fixed PWM.I'm pretty tempted to just make a data table in the MCU to define the Vmp (max power voltage) of a panel, and hunt the duty cycle to chase that voltage. It will be damn close with very little effort.