Using a Digital Panel Meter (DPM) to monitor the 12 V battery system in a vehicle (car, truck, boat motorcycle, etc.)

I get a fair number of questions from customers concerning how to connect a digital panel meter (DPM) to measure the 12 V electrical system in a vehicle. I have prepared this drawing showing the required connections along with a parts list indicating Circuit Specialists part numbers that are required to perform this operation.

Since the power for the DPM is to be derived from the same electrical system that is being monitored, this will require a DPM that uses a COMMON GND system. These include the PM-1029B and the PM-128E and PM-128E-BACKLIT. Other models with a common ground connection will also work but require additional components so I prefer the three models listed above.

All of the common ground units require 5 V power to operate the digital panel meter so some method of reducing the 12 V from the vehicle’s electrical system is required. I recommend using a 5 V regulator (such as the 78L05 or 7805) along with a small capacitor (such as 21ET100 ceramic disc) to supply the required power to the DPM.

The attached drawing shows the connections for the PM-1029B DPM and is similar to the PM-128E connections but there are differences in the jumper settings for each meter. If using the PM-128E (or PM-128E-BACKLIT) DPM, the DC and the J1 and J2 jumpers must be set correctly.

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