Voltmeter Accuracy

[SkooterG]

Recently, in THIS THREAD, there has been some discussion on voltermeter readings using the Passport 8500X50 radar detector's voltmeter function. Also, the thread got into Ionbeam's apparent drop off in stator output observed by his Passport's voltmeter indications.

Well, here's some more fuel for the fire...........

Yesterday, vectervp1 came by to drop off the latest skiwi produced farkle - a metal base for the XM antennna puck. (Oooops, think I still need to pay for this little item! ) Anyways, vectervp1 had another new farkle that he had just installed - a new Datel voltmeter. He told me what the voltmeter readings had been on the ride down, and I told him they sounded low compared to what my Passport reads and what I thought was healthy.

To make a long story short, sort of, we connected my passport to his bike and compared voltage readings:

Here bike is running:

And here, engine is not running:

So, as you can see, the Passport is reading .4V higher in both cases. Sometimes, it would show .5V higher. You would have to aske vectervp1 for the details, but he mentioned that both are connected to the electrical system in about the same location.

I am assuming the Datel is more accurate. Any opinions to the contrary?

What should voltage reading be for a running engine with no additional electrical load other than normal?

My Passport reads 14.3-14.5V under normal conditions (my FJR) with engine running, vectervp1's datel was reading 13.9 pretty consistently under the same conditions (his FJR).

So, any thoughts by anybody in the know about this?

 

[TheAxeman]

Skooter,

Just an aside...not a hijack.

Does your voltage reading on the Passport jump around rapidly? The numbers run from about 13.2 to 13.9 on mine but is changing so rapidly you can barely follow it....any thoughts?

 

[ionbeam]

I jus hadz'ta know...

Tools: Afore mentioned Passport; Fluke 4 1/2 digit DMM (in calibration); substantial alligator clip lead for ground connection

Setup: DMM ground lead clipped to engine block, at a know good ground point; DMM plus lead to the front brake switch because it shares the switched ignition circuit that the Passport is connected to; Passport grounded directly to battery; Passport 4 pin connector used to supply power to the unit and the connected remote

Results:

Ignition On; Engine Off

DMM..........Passport

12.7xx..........12.7

Engine Running

DMM..........Passport

13.7xx..........13.7

=============================

The only thing I changed was to move the DMM plus lead to a rear tail light, engine running

DMM..........Passport

13.4xx..........13.7

=============================

The voltage you read on the Passport vs the Datel should be the same (well, +/- .1 volts) if they are both connected identically. Because of variations in ground quality the readings may be different. The voltage will be very dependent on where and how the voltage is tapped. The reason the tail light voltage is so low is because of the number of connectors in the circuit, wire gauge and wire length.

This gave me another chance to confirm that the switched ignition is ~.3 volts lower than battery voltage.

[Engine running] The switched ignition voltage does not drop when the Yamaha heated grips are turned on and remains fixed. Switch off the grips and turn on the PIAA 910s and the voltage immediately plummets to 13.0 with maybe 5 minutes hang time then it drops to 12.7 for a few minutes then begins the death march -- 12.4, 12.1, 11.9 and I have to turn them off PDQ. That is 11.9 per the Passport which is actually ~12.2 battery voltage. I do have to fix this before my next foray into moose country.

If you have a chance, see if you can get the Datel and Passport to share common power and common ground and see what you read. The Datel should be the very same as using a DMM. A good DMM should be make the tie breaker.

Skooter,Just an aside...not a hijack.

Does your voltage reading on the Passport jump around rapidly? The numbers run from about 13.2 to 13.9 on mine but is changing so rapidly you can barely follow it....any thoughts?

Axeman, back in the days when my Passport read like this

all the digits were stable. Now that the voltages are reading in the mid 13 volt range the least significant digit fluctuates but not as much as yours. The LSD is stable enough for me to say it is running at 13.7 or 13.2 volts with certainty and it matches what my DMM reads.

 

[ionbeam]

Wellhell, I just hooked the trusty ol' O'scope to the ignition switched power at the front brake lever and this is what I found floating on top of the 13.7 VDC:

That is supposed to be a straight line. What I saw was up to 1.5 volts of hash on top of the ignition voltage. In this picture it is .75 volts peak to peak. The garbage follows engine revs. Could be caused by a bad connection. I've verified ground so it is out of the picture. In all probability we are looking at a bad diode in the Rectifier/Regulator. I don't have time tonight to pull the panels off to troubleshoot.

You can bet your booties that this is the source of the flickering least significant digit. If you have an audio hook-up you are looking at the devil that buzzes incessantly in your ears.

 

[RonBB]

From the DMM vs the Passport voltages it appears that your readings at the taillight are similar to mine. My Passport is wired through a J & M CB which receives it's voltage via the tail light circuit. The hash riding on the DC voltage very well may be due to the ignitors for the sparkplugs. I can't read the frequency of the hash from the posting-It may very well be the norm for the circuit with all working as designed. I'm not sure that a 0.4 Volt difference is significant as long as one knows the norm for their particular bike & reading location. In other words - know the voltage where the downward spiral starts & stay above it. The voltage also appears to vary depending on the need to charge the battery as well. Thanks for the info & best of luck. Ron

 

[twowheelnut]

Jeezums, Ionbeam! That's some impressive testing/reporting you did. Word! :good:

But... Does it really matter which voltage is shown or what the actual voltage is? Why can't you use one as a baseline figure and go from there? And does it matter a hoot if neither has been calibrated?

 

[antvq]

Are you sure that's not TWN's EGT taken while reading this month's issue of American Gerbil?

 

[ionbeam]

Why can't you use one as a baseline figure and go from there? And does it matter a hoot if neither has been calibrated

Sorry for the following, it is not only taken directly from the source, but the source is Skoot:

[Relevance]To make a long story short, sort of, we connected my passport to his bike and compared voltage readings.....So, as you can see, the Passport is reading .4V higher in both cases. Sometimes, it would show .5V higher. You would have to aske vectervp1 for the details, but he mentioned that both are connected to the electrical system in about the same location.[/Relevance]

We have our **** in a knot over .1-.2 volts. In this case being off .100 - .200 is actually meaningful. In terms of being calibrated, it is like your torque wrench being off by 'only' 10 lbs/ft. Glad you are at 14.3 nominal.

Love the ride videos. Happy that you don't have electrical noise in your audio system.

Some of us have to supply fodder for sustaining these threads :yahoo: :lol: :lol:

Edited to include what got my attention:

turn on the PIAA 910s and the voltage immediately plummets to 13.0 with in maybe 5 minutes hang time then it drops to 12.7 for a few minutes then begins the death march -- 12.4, 12.1, 11.9 and I have to turn them off PDQ. That is 11.9

At this point (11.9 volts) a calibration error may make the difference between restarting or a fire.

 

[twowheelnut]

Oh. Well, ok, then...

 

[FJRandy]

Skooter, the difference you're getting is between a direct connection to the battery vs, an ignition fed 12v lead.

Last year I did the Fluke DMM vs. Datel test. I thought the Datel was going south. Turned out to be a bad ground connection. Datel now reads 13.7-13.8 consistantly through the windshield retract wire which is ignition fed. It's exacly .4 less than the battery charging voltage. My bike looked like a science project as I rode around town watching both meters. I had the Fluke connected to the battery, and left the Datel wired into ign with the repaired ground wire. ALL readings between batt and ign feed never changed from a .4v difference.

So now I just add the 4 tenths when I look at the Datel

 

[krashdragon]

Skooter, the difference you're getting is between a direct connection to the battery vs, an ignition fed 12v lead.
Last year I did the Fluke DMM vs. Datel test. I thought the Datel was going south. Turned out to be a bad ground connection. Datel now reads 13.7-13.8 consistantly through the windshield retract wire which is ignition fed. It's exacly .4 less than the battery charging voltage. My bike looked like a science project as I rode around town watching both meters. I had the Fluke connected to the battery, and left the Datel wired into ign with the repaired ground wire. ALL readings between batt and ign feed never changed from a .4v difference.

So now I just add the 4 tenths when I look at the Datel

I dont' have any problem... I cant' find the voltmeter reading on my new Escort! ... and there's already a teeny digital voltmeter installed on my bike....

Now, as for accuracy, oh well.... I'll get around to checking it someday...

mary

 

[PerfectBlueride]

Just mount it and wire it directly to the battery post then you know you are getting an acurate measurement, unless it's faulty. no complicated math equations while riding please :lol:

daylight

night light

No more stickin calibrating