Installing a Trimetric Battery Monitor

The idiot light panel is almost (but not quite) worthless for monitoring the condition of your house battery or batteries.  It uses voltage levels to change the color of the lights.  You can use a volt meter to do a slightly better job, but the problem is that unless the battery is sitting with no load for a period of time, the reading will not be accurate.  And your battery always has some load unless you have disconnected it.

You can use a hydrometer and check each cell for an accurate reading, but that is a pain, and impossible if you have sealed batteries.  The easiest way to keep track is a battery monitor that does more than measure voltage.  After reading up on the options, we settled on the Trimetric.  It was said to be easier to set up and use than monitors of similar capability.

We got our Trimetric 2025RV from Randy at  Randy is very helpful answering questions and giving advice.

The Trimetric comes with a display unit, a shunt, and a very long cable.  And a lot of instructions.

The shunt looks intimidating, but it is not hard to install.  The shunt is necessary to get current readings.

The cable is long enough for the largest Class A, we just left the excess coiled up in a storage compartment.

We found the wiring diagram for the Trimetric to be rather confusing, so we later drew our own version of it to hopefully be a bit clearer than the one with the instructions:



Step 1.  Find a place near the battery to install the shunt.  Depending on the location of your battery (or batteries) this may be easy or difficult.  In our case there was room just outside the battery compartment which is a vented compartment under the driver’s side dinette seat.  We drilled two holes for the cables. 

These holes were later sealed so any battery gases would vent through the proper vents rather than into the coach.

The radio rear speaker and the propane detector are also in this area.





Step 2: The shunt is installed on the negative side of the battery.  That means that the cable (or cables) currently going to the negative terminal (or terminals) on the battery with go to one side of the shunt and you will add a new cable from the other side of the shunt to the negative post on your battery.

You will need to buy at least one additional length of battery cable to go from the negative terminal on the battery to the shunt.  If the negative cable currently going to the battery is not long enough to reach the shunt, you will need to replace it.  Various lengths of battery cables are available at auto parts stores and online.  Measure to see how much you need.  You should keep cables as short as possible.




Inside the battery compartment you can see the new cable for the shunt exiting the battery box.

You can also see the red wire from the Trimetric wiring harness attached to the positive terminal.  (See Step 4).  It is mounted to the same post as the heavy white wire providing 12 volt power used for starting the Onan generator.

This is a Group 24 deep cycle Exide battery.  It is only 80 amp hours. 






Step 3:   You will need to locate the display in some visible location.  Pick a place it will be easy to run the wiring harness to.  We mounted ours on the back of the pantry cabinet above the TV.  You will have to drill one or more holes to run the wiring harness

After adding a solar panel we put the monitor for the solar controller next to the battery monitor.  It is very interesting to see the amps generated by solar and the amount going into (or out of) the battery at the same time.







Step 4:  The diagram for the wiring is not as complicated as it first appears.   There are 4 wires – one white, one red and two black.  One end of the cable has connectors on the wires.  Remove the fuse before connecting the wires.

1.     The red wire with the fuse and the big end goes to the positive terminal of your house battery.  So it needs to go inside the battery compartment.

2.     The white wire goes to the small terminal on the side of the shunt that connects to the negative battery terminal.

3.     Both black wires go to the small terminal on the opposite side of the shunt.



Step 5:  Route the wires to the display.  This is probably the most time consuming step – depending on where you located the display.  Leave the extra wire coiled up somewhere out of sight or shorten the cable if desired.

We fished the cable up from the dinette storage compartment behind the wall panel into the pantry cabinet.





Step 6:  At the Trimetric display the terminals on the circuit board are labeled.

1.     The red wire goes to the B1+ terminal

2.     The white wire goes to the SIG terminal

3.     One black wire goes to the G1 terminal and the other goes to the G2 terminal.  It does not matter which wire goes to which terminal since they both go to the same side of the shunt

The B2+ terminal is extra – you can run a wire up to your engine compartment if you would like to monitor the voltage on your engine battery.  It will not give any other info other than voltage about this second battery




Step 7:  Check your connections and then install the fuse.  You now have to program the unit.  It needs to know your battery’s capacity and some other info in order for it to provide you with accurate information.  The basic required information is P1, P2 and P3.  P1 will be 14.4 volts (bulk charging voltage), and P3 will be the capacity of your battery in amp hours.  Ours is 80 amp hours.  If you are running two 6 volt Trojans you could be at 220 amp hours.  P2 is computed from the other numbers as the manual states.  Entering these values is a bit like figuring out how to set a new multi-function watch.  You will likely mess it up a couple of times before getting it right.

Depending on what we are doing we may leave the display on % Full or we may leave it on Amps (in or out).  You can display voltage and watts as well.

We have been very pleased with the usefulness of the Trimetric.



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