I used the following circuit to power and measure my pressure transmitter (4-20ma) sensor and the microcontroller, when the charger and battery are connected at the same time or when i disconnect the battery i get a fluctuating readings from the connected ADC (Arduino or Raspberrypi), i only get a stable readings when the battery is the only power source.

Uninterrupted power source

Would you please explain the possible causes of this issue, and what should i do to have uninterrupted power source without affecting the measured values.


  • \$\begingroup\$ Define Charger, CC or CV mode, ripple frequency, Battery age, ESR? ripple V. You probably need a Cap across transducer if not included. \$\endgroup\$ – Tony Stewart Sunnyskyguy EE75 Mar 17 '18 at 20:32
  • \$\begingroup\$ CV charger found here: controllers4generators.com/catalog/… , the battery is a normal 12vdc car battery. \$\endgroup\$ – Amr Sohil Mar 17 '18 at 21:37


simulate this circuit – Schematic created using CircuitLab

What kind of switch are you using that switches both charger and battery? Beware of arcs. You only need to switch the load.

  • \$\begingroup\$ I'm using a bridge to switch between the power source automatically, and to keep the battery charged. \$\endgroup\$ – Amr Sohil Mar 18 '18 at 11:46
  • \$\begingroup\$ This method I suggest is better for low ripple and automatic charging. Your method has high R from diodes thus worse voltage regulation and your failure. \$\endgroup\$ – Tony Stewart Sunnyskyguy EE75 Mar 18 '18 at 17:46
  • \$\begingroup\$ Thanks for your help, I'll try the method you suggested and feedback here \$\endgroup\$ – Amr Sohil Mar 18 '18 at 18:04
  • \$\begingroup\$ Start by adding from either side of battery one or other or both filters should work \$\endgroup\$ – Tony Stewart Sunnyskyguy EE75 Mar 18 '18 at 18:21

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