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32 Gtr Battery Voltage Fluctuating... Help

nuci_gtr

By nuci_gtr,
in General Maintenance

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nuci_gtr Enthusiast

nuci_gtr

Posted
Posted

Hey all,

I've been having some alternator and battery issues with my gtr lately. So a few weeks back voltage gauge was starting to show low voltages, worked out it was a bad alternator. Managed to find a second hand one that had been reconditioned in the last few year, had it bench tested and everything was fine. Had it fitted to the car and was all good.

A couple of days later I started the car and saw the battery gauge fluctuating, noticed the headlights fluctuating slightly in brightness as the gauge fluctuated.

So I tested the battery with a multimeter, and voltage is fluctuating between about 14.5 and 15.5 volts. Just constantly going up and down. Battery is brand new too.

Any idea what it could be? Bad earth maybe? Car drives totally normal but voltage fluctuates both at idle and while driving, same amount at low and high rpm. I'm normally pretty handy with mechanical stuff but electrics give me the shits. Any help would be appreciated.

Cheers, Dan.

  • 2 weeks later...
MozzMann Enthusiast

MozzMann

Posted
Posted

Voltage is fine although on the borderline high 14-14.5 is the norm engine running but I have seen excursions as high as 18 .

Step 1 In my fault finding would be to make absolutely sure your battery terminals are clean and that you have a good unit

Step 2 Check and clean the battery terminals and preferably put it on a charger for 24 Hrs at a 2-4 amp trickle , leave it for 12 Hrs and then subject it to a decent drain with a Battery tester. To eliminate this as a potential issue
(I have seen near new batteries fail simply due to an internal failure ) after all they are mass produced and your likely to get a dud every now and then.

Step 3

(A) Ensure you have a good solid ground strap from the Battery to the Engine and 2 A solid strap from the Battery to the Chassis,
(B) Also check the ground from the instrument panel gauge cluster as this can be a potential issue as well.

This should eliminate you battery and potential current flow and earth issues

A cheaper solution may have been assuming the field windings in your old Alternator were OK would have been to replace the Regulator in the Alternator and possibly have solved your issue with a bit of work and logical fault tracing.

Alternately replace the entire unit with NEW from a good supplier like Repco or AutoPro etc so you have a some warantee and or return policy if this is not a solution.

Let us know how you get on .

MozzMann Enthusiast

MozzMann

Posted
Posted

89Cal Please read my comment re 18 V again ( I did not say this was normal - I said I have seen voltages that high and with and AC component as well (Data logger told the story) )

In a modern Vehicle these days the nominal Voltage is around the 13.8-14.2 range with the engine running and the Alternator charging as I previously stated and up to 14.5 and higher but 15Vdc is on the high side and needs to be addressed,

At rest voltage (Engine Off) should be in the order of 11-12.5 over night.

As I said I have seen voltage excursions as high as 18 V DC without damage but that was years ago before CAN BUS systems and other integrated electronics came along and that is NOT a good situation at all.
If you look at the stampings on a lot of Alternator's their NO LOAD rating is often 18 V but under normal regulated delivery load they drop to 14 or so. 15 V is high yes as I said BUT this condition could well be the result of poor earth and connectivity causing the float voltage to read high with a multimeter but the actual voltage due to resistances within the electrical system are likely lower, a stuffed regulator will not limit the voltage and depending on the Alternator may be dumping 15V unregulated into the system and thus the problems that Dan is encountering Voltage is one thing but Current flow is another.

It needs attending too by a good Auto Electrician of that there is no doubt.

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