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Mystery voltage drop - Printable Version

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Mystery voltage drop - Kim - 05-08-2008

Long story but volt meter has been bouncing around a bit over last year or more. When the air is cold, ie winter, voltage shows about 13.5V always. However, when warmer, it sometimes drops mysteriously to about 12.5V and then bounces back after 1-500 minutes. Doesn't really flutter - just goes low and stays there for a while. No obvious reason so I thought it might be grounds. Took car to dealer and was told that voltage regulator was bad. It was so I replaced it and the brushes on the alternator. At first, after repair, volt meter in car showed 12V when running. Car was only making 1 amp at idle and 9 amps at speed. Left it overnight and after some magic was done to alternator now get lots of amps (I think they said 50, is that right?) but volt meter still at 12V. Supposedly everything in fine with wiring as far as firewall, suggesting something has come "loose" behind dash. Any ideas? Need to drive this car from Nova Scotia to Toronto on Sunday and am not looking for surprises. Car in shop now but needs to come out at noon tomorrow. Gauges are coming out to check.

Mystery voltage drop - flash - 05-08-2008

old wire does not transmit the same amount of current as new wire - could easily be the problem



are the readings from the dash voltmeter, or a known good meter?

Mystery voltage drop - Kim - 05-08-2008

not sure what you mean by old and new wires - no wires were replaced. Voltmeter in dash used to show 13.5V most of the time and 12.5V sometimes. Now shows 12V all the time. That is what has changed. Meter at battery showed 14.4V across terminals during charging. I think the problem is something to do with what is going to the dash, not to the actual battery / alternator circuit. Just confused that it happened all of a sudden seemingly associated with these repairs.

Mystery voltage drop - RS Barn - 05-08-2008

Kim,

There is a wire from alternator that feeds guage on dash. I'm pretty sure the wire goes to a white 2 wire connector at firewall. Could just be a bad connection/corrosion or rub on wire. We've also seen guage in dash go wacky/inconsistant

Pete

Mystery voltage drop - flash - 05-09-2008

"old" means corroded, aged, stiff, worn, etc - this is generally the condition of all original wiring



"new" means fresh, clean, flexible, etc



if your wiring is original, it is probably not up to snuff anymore - a bad connection shows up very quickly with old wiring

Mystery voltage drop - Kim - 05-09-2008

Sorry Flash, you must get tired of needing to correct us mechanically disinclined souls. I was simply confused because I didn't replace any wires.

Mystery voltage drop - flash - 05-09-2008

no worries - i tend to assume a certain accepted industry vocabulary when discussing this stuff, and forget all too often that it isn't necessarily common knowledge or obvious to everyone else



anyway, i'd be looking at connections



by the way, the alternator should put out 115 amps at full load

Mystery voltage drop - Mark - 05-09-2008

I used to have a few issues with my gauges, tried putting in an adjustable voltage regulator but it would still bounce around. When my car was up at RSbarn for my yearly boost to the Newtown, Pa economy, they installed a whole new set of "IceShark" battery cables. Since that was done all of my gauges are rock solid, which reminds me I need to turn down regulator.

Mystery voltage drop - Kim - 05-09-2008

So here is the update.



1. car is now putting out 90 amps (I have an aftermarket alternator).



2. voltage at 3000 rpm across the terminals is about 14.4 v and about 13.5 at idle.



3. oil pressure gauge still bounces (Pete, you were going to send me a picture of where it is so I could clean the connections).



4. Exciter wire (?) and adjoining wire were corroded due to coolant leak on line passing by alternator - fluid had been dripping into the alternator. Line is replaced and new wires installed today. Good news - pressure check was fine afterward so immediate concerns about head gasket might be belayed.



5. supposedly need new wiring harness from battery to alternator/starter area and new harness from battery to fuse block to instrument cluster. Guess I should plan for this.



6. Voltmeter in car shows 12.5V. Does not vary. Shows 10.5V in "on" position with no accessories running other than ignition. Across battery with car off is 12V. Is this usual?



7. problem had since I bought the car with charging circuit not kicking in until engine speed reaches about 2K is now gone. Charging starts immediately with no engine revving needed.



8. was noted by mechanic that faulty regulator might have been frequently putting out 16V, meaning that there is no "new problem" with the gauge. Maybe it has "always" been reading low.



So..



some problems that I suspected (ie coolant leak) identified and repaired.



some problems not known about (voltage regulator and brushes) fixed although I didn't know they were bad. This is good.



oil pressure gauge bouncing not addressed.



voltmeter now rock solid but low.



I am driving to Toronto on Monday so, if all is not well, I will find out about it soon enough.



Another fun day in Bugtussel!

Mystery voltage drop - xrad - 05-09-2008

These are not super accurate guages so if it is solid at 12.5 and all else checks out, I would leave it. But I know that's not your style.......





by the way, which aftermarket alternator did you have installed?

Mystery voltage drop - Kim - 05-10-2008

don't know about alternator - got it at local Nissan shop (sister is service manager). Porsche version was a bit pricey. At the time I got it there was no local dealer. That one failed in about a year so they replaced it for me. This one is the replacement version.



BTW - voltmeter is now approaching 13V. Do regulators need to "break in"?

Mystery voltage drop - xrad - 05-11-2008

Brushes need break in, voltage regulators do not.(they are high speed switching transistors)



I have used parts from these guys:

http://www.nationsautoelectric.com/regulators.html



example, for my alfa:



http://www.wai-wetherill.com/products/part...wai_num=IB353-1



You can usually rebuild these things yourself with a few tools. Hardest part is getting the case open.

Mystery voltage drop - ds968 - 04-21-2009

Same problem here, after 5 years of staying consistently at about 13 ( may be just barely under that.. say, 12.5+ ) the needle is now right on the 12 mark, while I'm driving. I noticed this for the first time on the drive back from L.A. yesterday in 100 degree heat ..about six hours with the AC continuously running, radio on, etc. But this reading was the same when I turned everything off to test and see what happens . I wonder if the heat has anything to do with it [img]style_emoticons/<#EMO_DIR#>/huh.gif[/img] but from what I'm reading between the lines on this thread it does not seem to be anything leading to impending doom, so probably ok to just leave it alone and keep an eye on it ...unless it drops another half bar to 11, or below that ?

Mystery voltage drop - Kim - 04-21-2009

There are three coolant hoses that run over top of the alternator. I had one leaking fluid onto the alternator and it destroyed the brushes and the voltage regulator. The voltage would simply fluctuate all the time. After getting an alternator rebuild, new voltage regulator, new wires between starter/alternator/battery/fuse block, rebuilding the A/C to R134 (unrelated) and then replacing the instrument gauge that houses the voltmeter and oil pressure gauge with new ones from the Fatherland (since the voltage regulator fried the two gauges) the problem was solved. So check for a coolant leak into the alternator. Any maybe look into a new voltage regulator.

Mystery voltage drop - flash - 04-21-2009

there are a number of things that can lead to voltage drops - first thing is to check with a real meter and see if it is indeed low