Hello,
I have a remote application that needs to run on a battery (XBee radio and a sensor plus CMOS IC)
The XBee runs nicely on 3.0-V and the sensor/CMOS also runs on 3.0-V
The XBee is an end device and sleeps for 5-minutes, or is woken by a pulse from the sensor.
Two 'C' cells (3.0-V) are looking like lasting for a year at least.
I want to put another sensor on that will need at least 4.5-V, at low power consumption.
Is there anything inherently wrong with having a stack of three cells (4.5-V), taking 3.0-V at the two cell junction and 4.5-V at the three cell junction.
It sounds too easy. I wanted to avoid regulators.

 

You can do that but the two cells that are providing current to everything will obviously go dead before the third cell that's only powering the 4.5V load.
Depending upon the relative current draw, you might be able to use a smaller battery (such as an AA) for the third cell, if you like.

 

Hello,
I have a remote application that needs to run on a battery (XBee radio and a sensor plus CMOS IC)
The XBee runs nicely on 3.0-V and the sensor/CMOS also runs on 3.0-V
The XBee is an end device and sleeps for 5-minutes, or is woken by a pulse from the sensor.
Two 'C' cells (3.0-V) are looking like lasting for a year at least.
I want to put another sensor on that will need at least 4.5-V, at low power consumption.
Is there anything inherently wrong with having a stack of three cells (4.5-V), taking 3.0-V at the two cell junction and 4.5-V at the three cell junction.
It sounds too easy. I wanted to avoid regulators.

It was very common practice in the early days of radio! Go for it!

 

Thanks all
I do remember the EverReady valve radio battieries that supplied the HT and LT voltages - 150-V HT comes to mind.
If you go into the theoretical side and start to try to calculate the currents flowing through the various cells, it starts to get complicated.
Sometimes the best approach is to just try it. Everything I am using, the XBee, the Hall sensor, the temperature sensor and the CMOS are working well, below the recommended limits. The various voltages can be monitored via the XBee. The possibility of different mAhr capacities will be looked at. What I did notice was that the two 'C' cell voltage dropped from 3.1-V to 2.97-V quite quickly, but has stayed at 2.96 to 2.97-V for months. For information, the Hall sensor is an SMD Infineon low power device and is being used to monitor a water meter.