Voltage Regulator

[Superman]

My digital VOM is telling me that system voltage with my car running can vary as much as .7 or .8 volts, with no reason. Sometimes voltage is fairly steady, fluctuating only .1 or .2 volts. Other times the fluctuations are wider, as reported above. The digital meter just gives me snapshots at about .5 to 1.0 second intervals. Each snapshot can be anywhere in the range. For example one voltage reading might be 14.85 volts, and the next one, less than a second later might be 14.2 volts. Usually the fluctuations are not that wide, typically they are in the .1 to .2 neighborhood.

Should voltage fluctuate like this? Would this be causing my headlight brightness fluctuations? If I had an analog meter, I could watch the needle and the headlights at the same time. I once said "goodbye and good riddance" to analog meters, but now I'd like to have one again.

[vesnyder]

I just ordered a digital volt meter that I will install in my Pcar so I will be able to tell if mine varies that much!

[L Sjoberg]

The voltage regulator is what caused more or less the same headlight problem with my SC. Also caused the interior lights to dim and brighten (if that's a word), as well as the ever popular jumpy tach. Less than a volt difference doesn't sound that bad, though, at least to me as a total layperson. When the VR went bad on my 914 the fluctation was more like 2 or 3 volts...

[Superman]

Thanks, Lee. Vance, a digital readout will do a poor job of showing you voltage fluctuations. All in all, I'd probably prefer an analog meter as a permanent addition to my onboard instruments. I envy Leland, with his voltmeter and cylinder head temp guage improvement. Those are exactly the two meters I would like to have.

[RoninLB]

Super...I use a dual CHT gauge. The temporary volt meter is above it. I use cylinders 2 & 5 for CHT with the probe that replaces the spark plug gasket....Ron

[vesnyder]

Here is what I am going to install ...

http://www.lascarelectronics.com/data/pdf/EMV%201200.pdf

Can I just monitor the voltage at the cigarette lighter, or should I monitor it at the battery?

[Superman]

You can monitor the voltage anywhere there is no resistor or resistance. The ignition switch is a nice place and there are convenient ground connections on the way.

[john walker's workshop]

snapon sells a digital readout, adjustable advance timing light. anybody who uses one would never know exactly where their timing was set, because the readout is forever changing. i had one for a week and gave it back. long live analog meters!

[Early_S_Man]

There are several issues that have been raised so far in this thread, and all are important in a general way ... to the real world situation of trying to monitor the health of a car's electrical system! An analogy would be looking at the heart rythm on an EKG machine or monitor ... the 'normal' signal has variations, but the difficulty is knowing what to look for, and being able to recognize when the signal presents with BOTH normal and abnormal characteristics.

Most built-in and aftermarket analog Voltmeters (like the VDO 'Cockpit' Voltmeter Leland is installing) for use in monitoring auto electrical systems are highly damped ... for a reason! Just the type of behavior that JW described is normal, and variations of 0.2 V to 0.4 V on a continuous basis need to be dampened so that the needle isn't jumping all of the time. At a threshold above the 0.5 V to 0.8 V level, the needle does need to show some activity, and the electrical system does need to be assessed for potential problems, just as Jim is trying to do.

The real question here is whether or not the VR will continue to be erratic, or will it settle down, or perhaps get even worse, and how soon ... or when it will fail? Metrology questions I can answer, but my crystal ball got backordered a few years ago ... never to be delivered!

The problem with that Lascar Voltmeter is that its' 0.2 Volt uncertainty/error potential means it isn't any better than an analog meter, but if you like to watch 'jumpy' digital readouts ... feel free to partake!

If it was me, I would put a scope on the power bus and see how the Voltage varies with changing rpms vs steady, constant rpms at idle, 2000 rpm, 3000 rpm, 4000 rpm. I have a programmable lab grade Fluke digital Voltmeter that can take 1500 readings per second and can average anywhere from 2 to 1024 readings, and log them to a computer file ... a five-minute session's data plotted on a graph might make the decision easy to make! And, I would probably order another VR and change it out.

Something like this would sure come in handy to evaluate this particular problem, too:

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=1719955685

[Superman]

Here's my level of sophistication: I'll get ahold of an analog voltmeter that is "jumpy," (not damped I guess), hook it up somewhere in the system, and see if the needle wiggles a lot. Warren is WAY past me again, particularly on electrical stuff.

[304065]

Super:

How's the battery in your digital meter? Mine was all over the place until I changed it. I have one of those Radio Schack $65 specials.

Which now refuses to measure resistance, and there is a faint smell of burnt insulation coming from the inside. Perhaps I shouldn't have lent it out.

Warren, I have long admired the products of the John Fluke company (of Everett, WA). Is there a particular model you recommend, that is a balance between price and performance? How about the 180 series?

[Superman]

There's no question that I'm going crazy. I could've swore that someone had posted some good information in this recent thread. Someone told of a washer or something that was not making good contact inside the alternator, causing symptoms similar to mine. Anyone remember that? I hope I didn't hallucinate a post.

[Zendalar]

I came up upon an idea of installing a big capasitor parallel to car battery. Like the one they use with big amplifiers. This would make the electricity..more stable.

[RoninLB]

Zen...it's easy to have "clean" output voltage. Smooth, filtered, constant voltage..and the unit is adjustable from 13.5v - 16.25v...and the unit has auto shutdown at 17.5v, that may save your DME & CDI/don't know...I run 14.7v

Super...IMO, if I thought my volt. reg. was flakey I'd change it and use "flakey" as a necessary spare for big rides...they may be about $60...changeig "flakey" is easy

cramer...I use the Fluke model 78 Automotive Meter...great options and it's good for 10a current measurement...not cheap, but I'd price around for a good price and investigate the options that are an easy plug in so you place one order. It is a dig. readout

Personally, I don't like no stinken digital dash gauges. I want to scan gauges quickly, and it's easier for my little fuel burner between the ears to register the angle of the dangle than to prossess a numerical numero......Ron

[Superman]

Okay, I'm still going crazy but I did locate the remark I was recalling. It was in an e-mail from jdub. Hooray for functional sanity.

[RoninLB]

Well Super..what's the story on "functional sanity" ??? I need all the help I can get..does it have to do w/slip rings???...Ron