To those who use the Passport to monitor voltage..

[dshepp806]

For years now, I have been making use of my Passport's voltmeter function (while unit is plugged in at cig lighter. I always checked the actual cig lighter potential (at it's socket, with a Fluke VOM) and compared that to the actual battery post measurements (with the Fluke) to establish any voltage loss between these t points (cig lighter socket's always been at 0.1 VDC lower than the battery terminal potential).

This config has saved me a few years back, alerting me to two intermittent voltage spikes (via the unit's alarm), ultimately ending in an alternator and VR replacement (removed the ORIGINAL 1989 alt/VR, BTW).

Recently, I noticed that the Passport would read 14.4 VDC (or, generally higher than it used to)...not having had any alarms, nor time to investigate,..I would engage a few circuits to get that voltage down a bit.......after looking into this just now, I've dicovered that the Passport's Voltmeter function is now reading in error,..to the degree of 0.4 - 0.5 VDC !!!!!!!! All measurements verified with 2 Fluke VOMs.....at 2000 RPM, the battery posts read 13.7-13.8 VDC, while the cig lighter socket reads 13.6 - 13.7 VDC (all on the Flukes).

Just an FYI for those trusting their radar detectors to provide accurate measurements to the driver. Mine, obviously, has an issue, as of now.

I think I'm gonna' go ahead and get that clock out of there and install a voltmeter (maybe a combinational gauge...)

AGAIN,..just an FYI.

BEST to all!

Doyle

[Joe Bob]

Don't know about Passport but Valentine is really good about fixing little problems for free or a nominal charge.

As to dumping the clock, I did and put in a dual volt and head temp gauge. Wesstach did it for me....they are an aircraft gauge manufacturer.

[doug_porsche]

That matches my unit from new. My in dash stereo can read voltage.

Stereo reads 13.6ish
Escort reads 14.4is

I figure, like a tire pressure gauge, its not the exact number, but the trend of the number.

[wwest]

Passport may not be an error reading. Passport may be reading absolute PEAK voltage while the Fluke reading will be the DC "offset" plus the AVERAGE of the ripple content riding on top of the DC offset.

The "spread" between the 2 is telling you that that the PWM regulator control of the Alternator rotor current has a WIDE variation. As long as the alternator is not working too hard to maintain the battery and system voltage at ~13.55 the ripple content will be at a minimum and the fluke and Passport readings will be closer to equal.

Additionally, the ripple content will increase as you more the measuring point toward the rear of the car, closer to the alternator and away from the battery ripple "sink".

[dshepp806]

As mentioned, this change was recent so I assume it to be error. I used the same meter(s) that I always use (the flukes are true RMS meters). Voltages were once very close to each other (Flukes and Passport). Maybe I need to break out my O-scope and have a look at the ripple?...As well as true peak voltage.

It's already around the 13.5-13.7 VDC range (the minimum ripple content-as you put it), yet the D.C. voltage readings are out,...I'll have a look at the scope to see what's there...I think all is fine, and that the Passport is off. I think I may take it inside to the shoppe and hook it a labgrade power supply (very clean DC) and see what the Passport reads versus the true RMS Fluke meters......I bet I find a 0.4 volt difference (still).

We shall see........

Don't mind making relative measurements,..say,... on a dipstick, but do desire absolutes when it comes to voltage(s).

Thanks for the replies.

Doyle