Voltage read out

jjoerger · Dec 2, 2011

Normally our digital voltage read out stays at 13.9 while driving and 14.1 while idling.
The last two days the voltage has dropped as low as 12.8 while running and seems to fluctuate from 13.7 down to 13.2 a lot. At idle it stays at 14 to 14.1.
All batteries tested good. The alternator is showing 14 volts at idle.
The only thing that has been changed is a different type of qualcomm was installed.
Would the QC be pulling it down that much?
Or should I be looking at the alternator suspecting the voltage regulator?

greg334 · Dec 2, 2011

Depends on who installed the QC unit. I wouldn't think that QC unit pulls 100 amps.

BUT with that said, I am thinking the alternator is starting to fail. It may be getting warm for it and because of that, there is an internal problem where the regulator is not working right.

I have the same issue with mine right now, I am going to pull it to have it rebuilt (replacing the regulator) because when it was about 60 a few weeks ago, I had a 20 amp load on the system while driving and the voltage was about 13.3. When it cooled down, it went up to 14.2.

jjoerger · Dec 2, 2011

The QC is the Omnitracks used by Landstar.
I thought about the alternator getting hot, but as soon as we stop it jumps right back up to 14 volts.
I am at home, so tomorrow morning I am going to pull the fuses on the power wires for the QC and take it for a drive to see if anything changes.

greg334 · Dec 2, 2011

I understand what you are saying but see here is the point, the load doesn't vary with the engine speed, but the voltage does internally so the alternator regulator varies the voltage to the field windings to maintain the right voltage going out of it for any given engine speed. Speeding it up with the same voltage on the field windings will send the voltage way way up (maybe 100 volts) if the regulator is "stuck" so this is why I'm thinking my regulator is going bad, my voltage will drop while going the same speed and go up when I'm idling.

teamjdw · Dec 2, 2011

Check ground wires,check wire to ECM,I had this problem with our m2 freight liner. The wire to the ECM was loose.

comet_4298 · Dec 2, 2011

check belt 1st, might be a loose.

jjoerger · Dec 2, 2011

teamjdw said:
Check ground wires,check wire to ECM,I had this problem with our m2 freight liner. The wire to the ECM was loose.

Good suggestion. I wonder if the QC installer knocked something loose?

zorry · Dec 3, 2011

Clean ground wires to frame.

jjoerger · Dec 3, 2011

This morning I took it for a 10 mile ride down I 75.
Before leaving I pulled the fuses from the QC. The readout stayed between 13.8 and 13.9.
I pulled into a parking lot and put the fuses back in for the QC and drove 10 miles back home. The readout stayed between 13.8 and 13.9.
The only thing I did was clean the battery terminals when I had them off to test the batteries.
My thinking is that the voltage regulator was malfunctioning and that maybe didn't drive it long enough to get it hot.
Any other suggestions would be appreciated.

bubblehead · Dec 3, 2011

jjoerger said:
Normally our digital voltage read out stays at 13.9 while driving and 14.1 while idling.
The last two days the voltage has dropped as low as 12.8 while running and seems to fluctuate from 13.7 down to 13.2 a lot. At idle it stays at 14 to 14.1.
All batteries tested good. The alternator is showing 14 volts at idle.
The only thing that has been changed is a different type of qualcomm was installed.
Would the QC be pulling it down that much?
Or should I be looking at the alternator suspecting the voltage regulator?

Same problem with my truck. Removed and cleaned all battery terminals and cables and ground connections and we are back at 13.9-14.1