12v battery monitor

  • Hi, I'm using WebThings on a RPI with mobile net to monitor some Zigbee sensors in my sailboat for the winter.

    Would be really nice to monitor the 12v battery - any tips to solve it? In an easy way 🙂

    Thanks, Trond

  • I am monitoring a RV's 12VDC battery system. The Zigbee analog pins will accept a max of 1.2VDC on the analog pins, so I used a 10K Ohm Precision Cermet Potentiometer Trim-pot Trimmer Pot - 10K Ohm which can be ordered on Amazon. One side of the pot I wired to the negative battery terminal and the other side of the pot to the 12VDC battery terminal. The center pin, PRIOR to connecting to any of the ZigBee Analog pins, must be calibrated to read a max of 1.2VDC.

    I let my battery discharge overnight and I then connected the battery charger to battery the next morning. The charging voltage was 14.3VDC and I then adjusted the pot center pin output to 1.1 VDC. I left a little buffer zone by not adjusting to the maximum 1.2VDC. Use 14.3 as your batteries max voltage when doing the program calculation.

    Now you will need to configure one of the Zigbee's ANALOG pins (AD0/AD3) as Analog. After you complete the configuration you can connect the pot's center tap to the Analog pin you selected.

    Should work fine. Have fun.

    You could use 2 resistors (voltage divider) instead of the pot, but I find it easier using the pot adjusting screw to get to the desired voltage and I ordered a bunch of them to use on other projects.

    Simple Voltage Divider Circuit.jpg

  • Here is a picture of my battery-backup board that has 2 supply sources, a 12VDC battery circuit (2 6VDC 260Ahr in series... overkill, I know, but recycled them from my RV) and a 12VDC output from a 110VAC>>12VDC power supply. When the 110VAC power is lost, there is uninterrupted 12VDC that is supplied by the 12 battery (thanks to the 2 capacitors). There are 3 10K pots on the board I designed . The battery backup board supplies power to my Energy Management System (BrulTech GEM/DashBox) that monitors my energy usage and stores the data on a memory card. It also will provide battery backup for my Home Automation System (Universal Devices ISY994 and Polisy). It also provides power to a WiFi Router that supplies Internet connectivity (when there is AC power for the ISP modem).

    The WiFi router's DHCP provides IP addresses and allows the ISY to keep talking with my DashBox in the event of a 110VAC power outage. This setup prevents both systems from having to reboot every time that there is a power interruption, which happens once every few weeks.... what a pain.

    Battery Backup Circuit Board.JPG

  • @trond-arntzen I just use a voltage divider with 1Megaohm and around 82K resistor for measuring my solar charged battery.

    @Mustang65 That ups board looks good. I could do with something similar as a battery backup for my raspberry pi's. Of course they would need a 12V to 5V conversion.

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