Random Voltage drop

[rcnugget]

hey guys im usually pretty clued up with this kind of thing but this has me stumped.

As im driving along my battery light comes on, I have a voltage gauge installed and it drops from around 13.8 to 11.8 and stays there for 2-3 mins then goes back to 13.8.

This only started happening today so first thing I checked was the alternator output, and sure enough its reading 11.78 volts at the alternator @ 1500 rpm then randomly jumps back to 14.35 and stays there.

As im driving along with the alternator at 11.8 volts it doesnt drop at all as if the alternator has totally failed it just stays steady for a few mins ( this is with lights stereo ect on ) then goes back up ...

Ive replaced the alternator brushes about 3 months ago I havnt checked them as yet as it is too dark outside .... but it seems strange to me that it would be brushes if it goes back to normal voltage ... does a crook regulator give out these kind of problems ?

anyone have any ideas why this could be ???? its a high output item from a VT Ecotec rated at 135A

 

[VT_sleeper]

There's really on 2 things it could be if your engine is running and this happens, the alternator, or a major short somewhere, that usually ends up in smoke and burnt wire smell and then stops.

It could be the bearings are wearing out and now the brushes are only occasionally making the right contact (*wild guess*)

I would disconnect your alternator, and take it for a "short" test drive and if the problem stops, then you know what your answer is .

Failing this I would clean your battery terminals, alternator terminals, clean all the contacts on your major relays and fuses, and reconnect everything. With a wire brush this should take no longer than an hour.

Oh and its not dropping because of your 51Inch of Quad Sub woofer trying to draw large current to drive these speakers? lol

 

[rcnugget]

nah its not the stereo thats all controlled by cap's and seperate batteries it does the same when this is isolated from the stereo, I didnt change the bearings when I did the brushes but its not making any different wurring noise when the voltage drops and everything is fuse protected so I doubting a short,

I might just get a cheapo 90a alternator from the wreckers tomorrow and see what happens

 

[VrWagz1]

Could be a dodgy reg, but you should be able to get an exchange alternator for $90. Garunteed to fix our problem atleast.

 

[commsirac]

It sounds like a dodgy regulator more than anything else. 11.8V is consistent with what what the battery would drop to with the engine running and a mild load of accessories and no alternator output.
It could be a random short, though Id expect the voltage to drop much lower.

 

[rcnugget]

where can you get these exchange ? you mean rebuilt or just a wrecker swap?? im supposed to br driving to noosaville at 11am damnit trusty old commy crapping out a few hours beforehand

 

[rcnugget]

Yep it was regulator allright, went to wreckers got another one and its all good now.

I was driving the 25 km to wreckers and I lost all regulation, was kind of freaky watching the voltage gauge at 18volts @ 2500rpm lol but made it ok and everything survived

 

[Tasmaniak]

should've turned your stereo on...that should of sucked it down a little bit

 

[rcnugget]

yeah that was with stereo and lights on =/

 

[commsirac]

should've turned your stereo on...that should of sucked it down a little bit

perhaps, but a good chance of frying the stereo. If you have to drive it, put high current consuming devices like the engine(put air on) and cabin fans,rear demistor headlights etc......and maybe you wont fry the computer.