Multiple batteries with fuel gauge and BQ24195

I have connected 3 batteries (Panasonic NCR18650) in parallel to the LiPo+ pin on my electron. Everything works fine except the reading from fuel gauge is very inaccurate. When i connect an external power supply (12v connected to Vin) the red indicator led is light up and SoC reading increases from for example 10% to 60% but when i disconnect the power supply it goes back to 20%. My questions are now:

  1. Do i have to change something in the fuel gauge to make it work? (Restart when power source is detected?)
  2. I read the BQ24195 is only for single cell. Does it matter when the batteries are in parallel?

Thank you very much in advance!

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How much current is the Electron pulling from your 12v power supply when charging the battery bank?

The SOC reading will jump up like you see if the battery voltage rises quickly because the SOC reading is based on Voltage. When you stop charging the battery voltage settles out, and the SOC reading will drop down to a real level. After a few cycles, the SOC should be more stable and predictable.

Make sure your battery connections are with properly sized wiring and have good reliable connections to prevent voltage spikes and sags during operation since this will help to avoid large jumps in SOC.

Connecting multiple batteries in parallel is perfectly fine. Ideally make sure your battery pack has a Protection PCB to prevent the cells from overcharge, over-discharge, and short circuits, the batteries that come with the Electron have this protection circuit built in.

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You still need to be very careful connecting batteries in parallel, as a bad battery could cause the others to dump their charge into the bad one, damaging them, or worse! So RWB is correct, ideally use only batteries with Protection built in, or a single battery, as I believe the Electron and Power Shield charging circuits are “smart” (should not allow over charge/discharge, etc).

Thanks for that hint! As far as i understood it the problem is that the 12V power supply rises the battery voltage and therefore the SoC is wrong. The cause of this problem is maybe the wire thickness. I made a standard PCB with 12mil traces for the batteries. I think thats properly sized? Otherwise i don´t really have ideas how to takle this problem.

The batteries have some kind of protection circuit integrated. I hope thats enough? Link to battery info

Thank you really much for your help!

Hi @marcusone,

I have my concerns over using 2 x 7.4v li-po batteries connected in a parallel circuit. The batteries were all fully charged to 8.4v with individual diodes connected to each battery. I am worried that the batteries may wear out and burst into flames as li-po batteries are too volatile. Is there any possibility where the batteries may be damaged or the diodes not being able to prevent a reverse flow in current. Below is the circuit diagram for the batteries.

You should have a battery protection circuit on each dual cell 7.4v packs to prevent over current, over and under voltage at a minimum.

The diodes are not really adequate in my opinion if the dual packs do not have any other protections.

Just get a single battery large enough to do the job if possible to avoid cell imbalance issues over time.

Hi @RWB

Thanks for the reminder :grinning:. The li-po batteries have a built in circuit protection. I have to add in a second battery to remedy the short battery lifespan temporarily while waiting for new batteries to arrive. Is the above circuitry enough to prevent any mishaps when used in conjunction with the built-in circuit protection in the battery? I need to run it for at least 3 months.

Thanks

If the built-in circuit protection is proper then yes I see no problems with your schematic.

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