While driving noticed DC voltage readout from VMSPC display ranges as follows:
Headlights on-Dash AC on high= 12.8-12.9 VDC
Headlights only on = 12.9-13 VDC
All off = 13.1 VDC
Is this normal? or should I be testing some things? what for example?
Chassis batteries less than 3 months old.
Fiddler, Assuming that dash gauge is accurate you should be seeing 14.1 / 14.3 with nothing drawing voltage. I suggest that you use a VOM and check voltage at batteries with engine running. And first things first, clean all battery connections while you are checking voltage.
Gary B
That all looks normal to me. Those appear to be voltages with the engine running. The voltage at the batteries will be higher.
There will always be voltage losses with a load on a battery. Longer wires cause more voltage drop. Smaller wire means more voltage drop. More load means more voltage drop. The will be voltage drop internal to the batteries as load increases. That is a separate issue from voltage drop due to discharge.
JD, You are right, my thinking was to verify that the voltages at the batteries were indicating that the alternator was working properly.
Gary B
Correct. The more amps drawn by "front of coach" accessories, the lower the voltage as read at the front of the coach.
Where is the
VMSPC getting the voltage reading? At the ECM? My VMSPC voltage reading is almost always between 12.9 to 13.4 no matter what lights, etc are on.
Mine are like Bob's but mostly 13.4 volts. I have seen 13.1 from time to time but it usually pops back up the 13.4 and I have seen 13.8 but it does not stay there long.
Clearly, the question is WHERE does the VMSPC pick up its voltage signal. If at dash, the readings would be considered normal.
If at engine or battery, there should NOT be that kind of voltage drop/fluctuation, as the alternator is sized to well-handle all the electrical loads mentioned. Only exception would be right after starting if batteries are deeply discharged.
I have recently downloaded and implemented 4.0.2. I have not driven with it yet as we are parked for a while, but it seems to have much better functionality. The Retarder gauges look much different with temp, status, and percent displayed. Other gauges, e.g. message box, tank minder, cruise status all seem better. So far I am very happy with the results.