How do I power 12v electronics off a 12v battery that is under charge?

ms334 Registered Users Posts: 10 ✭✭
I want to power a few electronics (Linksys Router, Raspberry Pi 4B, 2.4ghz wifi amplifier) off a 12v deep cycle battery. The battery will be charged by a Morningstar Duo PWM charge controller and 3 100w Windy Nation solar panels. I guess I'm worried about the electronics receiving too high a voltage when the battery is being charged. Is there something I can add to isolate the electronics from the high voltage of the battery charging?

This is for a solar powered robot that I can log in to from 1000 miles away and drive around, etc. 

The batteries I'm using are Deka 8A22NFs. I will be using 4 batteries total. 1 to power the wheels and 3 to power the Raspberry Pi, router, wifi amplifier, iPhone (4g connection in case wifi stops working) and a camera. I'm using the Morninstar Duo since it can power two battery circuits separately and the motors cause a voltage drop. So I am keeping those separate from the electronics. 


  • BB.
    BB. Super Moderators, Administrators Posts: 33,402 admin
    With DC to DC converters, there are several major types. One is Buck Mode--Always take higher voltage and down convert to lower voltage.

    Boost always takes lower voltage and converts to higher voltage.

    When you want 13.8 (variable) to 13.8 volts, then you want a Buck Boost converter... It has both sections in the switching power supply, and can take a wide range of input voltages around your 13.8 volts output setpoint (as an example). Besides Amazon, eBay and other places have lots of options out there.:

    [2-Pack] Adjustable DC-DC Buck Boost Converter Automatic Wide Voltage Regulator XL6009 DC to DC 5-32 V to 1.25-35 V Voltage Module

    WHDTS DC Buck Boost Power Supply Module DC 5V-30V to DC 0.6V-30V 35W 4A CVCC Adjustable Automatic Step UP Down Voltage Converter LCD Display

    On ebay, search for buck boost converter... But be careful, some say step-down buck boost, or step-up buck boost converter... The couple I checked, appeared to NOT be buck boost, but just buck OR boost.

    For a 12 volt battery bank (Lead Acid), you want something that works from ~10.5 to 16+ volts and outputs 13.8 volts (or whatever you choose).

    Don't get a really large converter--They are like AC inverters, they have a certain amount of Tare Loss (switching losses, even with no loads)--So you don't want 10 Watts "standby" power consumption on a 5 Watt output supply (again, just a made up example).

    You could, for example, have a small unit to power the electronics, and a separate converter with remote on/off for operating the drive wheels and other high drain devices.

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • ms334
    ms334 Registered Users Posts: 10 ✭✭
    Thanks, I searched a lot on ebay and found one that will work. I wish I had thought about it this before, I would have bought a charge controller with a built in load terminal. The smallest 8V-40V to 12V converter I could find was 36W. So I guess I need to figure out a way to turn the Pi, router, amplifier, and camera on remotely, only when I'm using them. I really don't want to buy 3 more deep cycle batteries. 
  • Photowhit
    Photowhit Solar Expert Posts: 6,001 ✭✭✭✭✭
    I've used a simple voltage regulator for USB output of solar panel, worked great on a pick Nokia N800.

    Most of those things would be under 10 watts, I would think they would work for them if you are worried. I thought the 'Pi' had a rather large acceptable input voltage, but it's been years since I looked at them... 

    Something like this, just lose the extra voltage as heat, may require a heat sink;

    LM340T-12NOPB - Linear Voltage Regulators Fixed 75V To 35V In 12V And 1A Out TO-220-3
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former, 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
    - Assorted other systems, pieces and to many panels in the closet to not do more projects.