Voltmeter accuracy

[Rich]

How many of us owners know whether our car's voltmeter is accurate? I didn't until recently.

I ran a simple test to find out.

With engine idling I added various accessory loads to get the dash voltmeter where I wanted it and ran a remote voltage check.
When ours is reading dead on 13V as in photo below I get a reading of 14.0V with the remote meter probing between the (+) jump terminal in the engine bay and the (-) engine valve cover.
Remote readings made with two different digital volt ohm meters reported same 14.0V.

So in this particular DeLorean ~13V indicated on the dash is actually ~14V. Now I know.

31347

Not trying to start a thread about what is a normal voltage, only about instrument accuracy. Your D's voltmeter accuracy may be different.

[Jonathan]

I like it.

Gauge calibrations that is. Makes troubleshooting from one car to another a bit different, eh? I think I'll try this little test out myself on my own car. Temperature would be another good one to test if a simple way to do so could be found.

I've often thought of how well calibrated my torque wrench really is. I have a big and a small wrench and the large one I do the wheel lug nuts with. The DeLorean is 60 ft lb and my Pontiac is 125 ft lb. But after owning the wrench for five years or so, how accurate is it still? Is 60 ft lb really around 59 or 61? Or 50 and 70? I would guess it's still reasonably close, but I can't say with any valid certainty.

I remember some ISO9001 training years ago talking about calibrating your measurement tools and systems. Even something as trivial as a tape measure, since the little metal end can get loose over time with the rivet or whatever and might throw off the measurement by a millimeter or so. Not the biggest deal if you're hanging picture frames but could be more important if you're building a fence or deck or whatever.

They tend to say that anything you are measuring something with should be calibrated regularly, but so few things really are. Even simple things in your home like the water meter, thermostat, power setting on your microwave, etc. Many of them don't matter much, but some do. Look no further than how much gas is needed to fill your tank in the warm summer months and then compare it to the cold winter months. The tank stayed the same size, but how much gas going out the pump is measured with something that's calibrated to temperature. Never seems to come out in my favor though!! Good call on doing this on your volt gauge.

[DMCMW Dave]

Clean the contacts on fuse #5 and try it again. I've seen that fuse cause a 1-2 volt drop if the contacts are grey!

[Dangermouse]

Of course this begs the question - how do you know your remote voltmeter was correct at 14v?

Unless it was recently calibrated against a known voltage source, you really don't know.

Logic would lead you to believe that a modern microprocessor controlled meter must be better than an old analog one. But is it?

Yes, this is just a devils advocate type question, but as Confusious say: Man with one watch always knows the exact time; Man with two watches is never sure.

:)

[Kukem]

Clean the contacts on fuse #5 and try it again. I've seen that fuse cause a 1-2 volt drop if the contacts are grey!

You're not lying! This was part of my issue with my low voltage earlier on. Cleaned all the grounds and fuse 5 (which was very grey) and it jumped from slightly above 8 to above 13.

[Bitsyncmaster]

Another problem is the gauge uses a ground wire that also conducts the fuel pump current. That can cause the gauge to read about 0.3 volts lower. Now was the gauge calibrated with that voltage drop in mind.....I think not.

What I had done was connect the inertia switch ground to a new frame ground wire and that did bump the gauge reading up.

I now run the fuel pump to frame ground and use the inertia switch to disconnect the battery power.

[Rich]

Thanks for getting a good check-up chat going, gang.

Good to know about the fuse, Dave. I sanded, then wirebrushed fuse #5 for a re-test, then reinserted it a few times. Had last cleaned all the fuses about 3yrs ago.

Results: No change. 13V on dash voltmeter = 14.0V on the same two VOMs I used before. Good to be sure about that, though.

Yes, both of the voltmeters that gave me the readings in these tests are uncalibrated, at least to any extent known to me. One of them is a pro-grade Fluke. The other one isn't.

Not that I plan to take either step but if I wanted to drill deeper then it could be done with a calibrated VOM reading across the dash voltmeter terminals or as close as I could get to them.



How many of us owners know whether our car's voltmeter is accurate? I didn't until recently.

I ran a simple test to find out.

With engine idling I added various accessory loads to get the dash voltmeter where I wanted it and ran a remote voltage check.
When ours is reading dead on 13V as in photo below I get a reading of 14.0V with the remote meter probing between the (+) jump terminal in the engine bay and the (-) engine valve cover.
Remote readings made with two different digital volt ohm meters reported same 14.0V.

So in this particular DeLorean ~13V indicated on the dash is actually ~14V. Now I know.

[DMCMW Dave]

There's a reason you don't see voltmeters in cars any more. How many average drivers know what's good or bad?

[AugustneverEnds]

There's a reason you don't see voltmeters in cars any more. How many average drivers know what's good or bad?

Very true. My truck (04 Silverado) has one but I guess in trucks they serve more of purpose since connecting a trailer or something draws power. Since getting accustomed to the D, I miss the voltmeter in my BMW! To me more info about critical vehicle functions is preferable to less

[Jonathan]

There's a reason you don't see voltmeters in cars any more. How many average drivers know what's good or bad?

Yep. This idea of people not knowing what it is that a gauge or message is telling them got me thinking about iPads...

One day in the "Offspring IT Department" as I like to call it when helping the older generation with computer problems, I was trying to get someone to update their apps on an iPad. I get the play by play of all the messages streaming by, like "initializing", "copying", "uploading" or whatever. All of it basically irrelevant when the only important message would really be one that said "finished."

I was thinking maybe if we can have a "safe mode" or "kids mode" for computers or web browsers, how about a mode for anyone out there (not just old people) that has only the information they need? Like an iPad that has only a couple buttons, like email, Facebook, Words with Friends, and off. Anything more just confuses it seems. This came to me after being asked if they should press the "F" and the "4" at the same time while trying to get them through some other computer issue.

Just a silly rant/tangent... less is more seems to be the way to go nowadays. There is a lot more to know now though, but knowing what to do with all of it is too much to ask on many subjects.

[David T]

Yep. This idea of people not knowing what it is that a gauge or message is telling them got me thinking about iPads...

One day in the "Offspring IT Department" as I like to call it when helping the older generation with computer problems, I was trying to get someone to update their apps on an iPad. I get the play by play of all the messages streaming by, like "initializing", "copying", "uploading" or whatever. All of it basically irrelevant when the only important message would really be one that said "finished."

I was thinking maybe if we can have a "safe mode" or "kids mode" for computers or web browsers, how about a mode for anyone out there (not just old people) that has only the information they need? Like an iPad that has only a couple buttons, like email, Facebook, Words with Friends, and off. Anything more just confuses it seems. This came to me after being asked if they should press the "F" and the "4" at the same time while trying to get them through some other computer issue.

Just a silly rant/tangent... less is more seems to be the way to go nowadays. There is a lot more to know now though, but knowing what to do with all of it is too much to ask on many subjects.

The gauge is really redundant anyway. There is an idiot light for the alternator. Just make sure it lights when the motor isn't running and if you ever see it lite while the motor is running it is time to fix a problem. The voltmeter, fuel gauge, and the oil pressure are not accurate in most Deloreans. You can also include the odometer. Each can be made to be more accurate, it depends on how much work and money you want to spend.

[kings1527]

I installed Hervey's double ground wire (it grounds to the frame and to the transmission, also) and it was a huge improvement in accuracy on my volt meter. In fact, the volt meter reads exactly what the multimeter reads if I check it.

[Exolis]

I believe the real reason behind the removal is Battery/Alternator related Warranty concerns. When your typical customer uses additional loads and sees the Voltage drops down, they get concerned and take it to the dealership. The dealership looks at the car and might even change the battery to keep the customer happy. The work and new battery is then billed to the OEM under Warranty. Stuff like this is why so much filtering and such is taken into consideration for Fuel Gauge (the size, radius travel, etc) because Fuel slosh can cause huge customer concerns. Coolant temp gauges in most cases is not linear, you essentially have Cold, Warming up, Running and Over Heat ranges.

[David T]

I believe the real reason behind the removal is Battery/Alternator related Warranty concerns. When your typical customer uses additional loads and sees the Voltage drops down, they get concerned and take it to the dealership. The dealership looks at the car and might even change the battery to keep the customer happy. The work and new battery is then billed to the OEM under Warranty. Stuff like this is why so much filtering and such is taken into consideration for Fuel Gauge (the size, radius travel, etc) because Fuel slosh can cause huge customer concerns. Coolant temp gauges in most cases is not linear, you essentially have Cold, Warming up, Running and Over Heat ranges.

Actually there have been studies, most drivers never even look at gauges but lights get their attention. And you are right, when they do look at the gauges they do not know how to interpret the readings anyway. On modern cars the gauges do not measure anything anymore, they are driven to certain readings by the ECU. Including the fuel gauge (to take out the fluctuations) and even the speedometer.

[Exolis]

Actually there have been studies, most drivers never even look at gauges but lights get their attention. And you are right, when they do look at the gauges they do not know how to interpret the readings anyway. On modern cars the gauges do not measure anything anymore, they are driven to certain readings by the ECU. Including the fuel gauge (to take out the fluctuations) and even the speedometer.

Right, which works out better because the signals read by ECU. Such as VDC/ABS module for Speed, sends the Speedometer data on the CAN Bus then other modules like the Meter reads that data, Airbag module will read it for it's "black box" function, Memory seats, Audio, etc.