Questions arise from time to time about powering a data logger using a battery. What’s the necessary voltage? How long will my data logger run on battery power? A couple simple formulas will help shed some light on the subject.
Most DATAQ Instruments data acquisition products require 9 to 36VDC. Power consumption varies by model and configuration. Take for instance a DI-718B-E, loaded with eight DI-8B38 strain gage input modules. The DI-718B consumes 2.5W, while each DI-8B38 module consumes 0.75W. Totaling up the power consumed by the DI-718B and each of the modules, we get 8.5W. Now, let’s assume that we’re powering the DI-718B-E with a 12V, 40 amp-hour (Ah) car battery. It provides adequate voltage, but how long will it power the DI-718B?
To convert amp-hours to watt-hours, we’ll multiply by the battery voltage:
12V * 40 Ah = 480 watt-hours (Wh)
Now that we know the capacity of the battery is 480 watt-hours, we’ll simply divide by the total power consumption:
480 Wh / 8.5 W = 56.47 hours
Note that this is an approximation since the battery voltage does not remain constant.
Can I use a 9V transistor battery?
Once in a while a customer will ask if they can power their data acquisition product using a 9V battery. Here’s the problem; a typical 9V battery will have an amp-hour capacity right around 500mAh (0.5 Ah).
Using the formulas from our example, above:
9V * 500 mAh = 4.5 watt-hours (Wh)
With a known capacity of 4.5 watt-hours, using the same setup as our original example (a DI-718B-E populated with eight DI-8B38 modules), we get:
4.5 Wh / 8.5 W = 0.53 hours
This short operating time is further limited by the fact that the voltage will quickly fall below the 9V minimum as the battery discharges.