Alternator voltage

[maxiz1]

Hello,
I just like to ask whether my car is running on the correct alternator voltage. Basically, during cold start, the instrument cluster shows 14V. After the car has been warmed up, with ambient temperature > 30degC and air conditioning, voltage dropped to approx 12.3V. The worst case is when the ambient is hot and headlights are switched on. Voltage is slightly below the 12V mid point. However I don't experience any problem driving it, rather just worried of any impending damage. Fyi, I've also replaced the carbon brushes on the alternator.

Any thoughts?

[maxiz1]

bump

[Nollywood]

Sounds like a bad voltage regulator / rectifier in the back of the alternator.

[Believer]

Voltage at the battery while running should be between 13.9 and 14.4 volts to keep it fully charged. Any less and the battery will have a shortened life.

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[seanf86]

does the needle jump when you step on the gas? my B5 does this and I just figured at idle the alternator could not keep up with demand, high blower speeds and rad fan running with headlights on is a lot of draw and if you have a stock 90A alternator at idle it won't be able to keep up, my B5S4 has a 120 amp alt and at idle with the same loads it has no issues so I figured it was just a small alt problem. When it fails replace with 120 amp alt.

[walky_talky20]

Yes. With the 90 Amp alternator and tons of stuff turned on (seat heaters, rear defroster, headlamps, blower motor, dome light, can opener, life raft, etc) it is expected for voltage to fall down to 12 or so at idle. As long as it jumps up to 14 when you rev it a bit, you're fine.

If you're doing excessive amounts of idling (ie: often go on all night "stakeouts", or otherwise creepy/stalker-ish activities where you keep the engine idling for long periods), you may want to upgrade to the 120A unit. Or switch some crap off. Or stop being such a creeper.

[maxiz1]

Thanks for all your input. It looks like my alternator has worn out I guess. My mechanic told me it's already a 120A version. I couldn't verify this via the sticker coz the part number does not match any equivalent North America or ECS parts.

The other thing I will check is the accuracy of the cluster voltmeter.

[maxiz1]

Just wanted to share. I turned out that the excessive voltage draw was caused by my old and nearly failing AC compressor. I had it replaced with a brand new one and since then it never dropped below at least 12.5V under the highest load consumption.

[maxiz1]

Ok. Another update. I finally solved the problem! It was actually due to the degradation of the positive wire from the battery to the starter and alternator. Over time, resistance built up causing high voltage drop during high current draw.

I hooked up a separate wire from the alternator positive post directly to the battery positive terminal and the voltage increased significantly. Not to the full factory spec but good enough. Now the new wire is carrying 2/3 of the current compared to the old one which is still attached.

I guess to further improve i need to renew the ground wire as well.

[Rmr1499]

If you're doing excessive amounts of idling (ie: often go on all night "stakeouts", or otherwise creepy/stalker-ish activities where you keep the engine idling for long periods), you may want to upgrade to the 120A unit. Or switch some crap off. Or stop being such a creeper.

😭😂😂😂🤣 kinda made my night there lol.

But yes I to get the funky voltage reading I’ll be driving and tit will be at like 14.2 then I’ll look again it will be 12ish area nothing has change nothing turned off. I’m going to take mine out. Shop by me rebuilds starters and alts with quality parts for $50