Looking for simple and cheap 4S BMs and fuel gauge recommendations

Thread Starter

phillipsoasis

Joined Aug 22, 2022
80
I am looking for a simple 4 cell (INR-21700-P42B) battery BMS and fuel gauge solution. The batteries are in an outdoor box for powering a rocket launcher. I would like to monitor the state of the batteries remotely during launches, so some sort of interface to the Raspberry Pi on the launcher board is needed. The Pi provides a web interface for the launcher, so I could add a page that shows the state of the batteries. A LED fuel gauge on the battery board is a plus. Charging is done away from the launch site.

So far, I have found a cheap BMS from Amazon (~$10 for https://www.amazon.com/dp/B08NJTS9DV?psc=1&ref=ppx_yo2ov_dt_b_product_details) to manage the charging and balance the cells. Any recommendations for a single chip solution instead of the whole board? I think this board is the cheapest solution, as once I start adding the other support circuitry for balancing the cells (FETs etc.), it will cost more than this board when I go to JLCPCB to make the board and assemble the SMDs.

For the fuel gauge, the first idea I had was to use a couple of op-amps as voltage followers, one for each cell, appropriate resistor dividers on each output to level shift the output voltages to 0-3.3V, and a ADC on an SPI bus to measure each cell voltage. Simple, and probably not that accurate.

Then, I found the Analog Devices MAX17263, and it looks promising. Has anyone on the list used this device? Any gotchas I need to know about?

I looked through the TI chip finder (https://www.ti.com/power-management/battery-management/fuel-gauges/products.html#1152=2-4 Cells&) and most of the options require purchasing an evaluation board and Windows software to set up the chips. I don't have any Windows software - I am an open source Linux guy and I don't have a budget for an evaluation board. Many of them also use other bms related chips. I am not a battery/bms expert so I am a bit overwhelmed by all the choices and nomenclature.

I would welcome any recommendations for better/cheaper BMS and fuel gauge options.

Thanks!
 

bassbindevil

Joined Jan 23, 2014
836
That "BMS" doesn't manage charging; it only provides balancing and protects from overcharging (and over-discharging and short circuits). I doubt you can build something better for less, and you might find that identical board even cheaper on ebay or Aliexpress.

There are various chips or modules that provide the correct charging profile for a 4S lithium battery. Some are buck converters that'll run from a higher voltage, some are boost to run from 5V, some are boost/buck and very flexible. MAX745 is a buck converter that can do up to 4S; modules are available. Or, the simplest option might be an AC wall wart or power brick charger (not power supply). It should be marked lithium charger, and will usually have two-colour LED to indicated charging status.

As for monitoring, all you really need to worry about is the overall voltage. Individual cell banks should stay balanced if the cells are good.
 

OldTech

Joined Jul 24, 2009
10
I am looking for a simple 4 cell (INR-21700-P42B) battery BMS and fuel gauge solution. The batteries are in an outdoor box for powering a rocket launcher. I would like to monitor the state of the batteries remotely during launches, so some sort of interface to the Raspberry Pi on the launcher board is needed. The Pi provides a web interface for the launcher, so I could add a page that shows the state of the batteries. A LED fuel gauge on the battery board is a plus. Charging is done away from the launch site.

So far, I have found a cheap BMS from Amazon (~$10 for https://www.amazon.com/dp/B08NJTS9DV?psc=1&ref=ppx_yo2ov_dt_b_product_details) to manage the charging and balance the cells. Any recommendations for a single chip solution instead of the whole board? I think this board is the cheapest solution, as once I start adding the other support circuitry for balancing the cells (FETs etc.), it will cost more than this board when I go to JLCPCB to make the board and assemble the SMDs.

For the fuel gauge, the first idea I had was to use a couple of op-amps as voltage followers, one for each cell, appropriate resistor dividers on each output to level shift the output voltages to 0-3.3V, and a ADC on an SPI bus to measure each cell voltage. Simple, and probably not that accurate.

Then, I found the Analog Devices MAX17263, and it looks promising. Has anyone on the list used this device? Any gotchas I need to know about?

I looked through the TI chip finder (https://www.ti.com/power-management/battery-management/fuel-gauges/products.html#1152=2-4 Cells&) and most of the options require purchasing an evaluation board and Windows software to set up the chips. I don't have any Windows software - I am an open source Linux guy and I don't have a budget for an evaluation board. Many of them also use other bms related chips. I am not a battery/bms expert so I am a bit overwhelmed by all the choices and nomenclature.

I would welcome any recommendations for better/cheaper BMS and fuel gauge options.

Thanks!
You might take a look at the multi-cell, multi-chemistry charger on Amazon:
https://www.amazon.com/Battery-Char...Pk7GkXP_LDE98UIvpzbl8R6GS5U4fK2BoC2qEQAvD_BwE

Cheers,
DaveM
 
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