Lately when I place a load on the electrical system by running the A/C and radio, I can see a drop in voltage (I have the voltmeter installed) from 14V to 12V, sometimes as low as 10V. This occurs 100% of the time when engine RPM is below 3000; it occurs about 70% of the time at 3000RPM or above. It's getting to the point where I really can't turn on the A/C unless I am at highway speed.

My guess is that this is a failure of the voltage regulator, which I assume these days is integrated into the alternator, necessitating a replacement alternator. Any thoughts here? Suggested tests I can perform?

If I do have to replace the alternator, is there a source for a high-output model?

 

I am in the process of sorting out an electrical problem with my car (battery dies overnight) and came across an easy test which may help you. If the alternator is undercharging, that problem can worsen as it gets hotter (i.e. while driving or under a load). Since it is often the diodes that fail, an easy test to check for diode failure is to use a multimeter - set it to AC (not DC) volts, and check the readings across the battery terminals. If you get a reading of 0.5V (some say 1.0V) or higher, the diodes are bad and you need a new alternator...

Melanie

 

Something is most definately wrong. Take it to a specialist in automotive electrical systems.

 

I have the same problem, but when I jumped it , I had no power steering. Any thoughts?

 

bad alternator?

 

How about the Crank Pulley? I keep forgetting this when Trouble Shooting the Charging System.. When the Crank Pulley starts to fail the outer ring slips on the inner and when under load from the Alternator and will not spin the Alternator fast enough.

EDIT: And of course if the crank pulley is fine, then more than likely your alternator is failing. Back in the day I used to rebuild them, well going back to Generators and Voltage Regulators, then in some cases even alternators, replacing brushes and even a diode or two. But now from a shop perspective, unless you are working on an item that is so rare you will either have to mortgage your house to afford the replacement part, or even the part just isn't available for replacement rebuilding a mass produced alternator just doesn't pay off. The OEM MINI compact Alternator generally sales for about $716.00 but can be found for as low as $278.00 or so and the OEM Voltage Regulator as a replacement part is around $122.00 but can be found for as low as $120.00. So it pays to just replace the assembly, do it once... and...

Best of luck.

Motor on!

 

Anyone find a definitive answer to this issue? I am experiencing the exact same issue as the OP. 14.0 volts at Idle but drops to 12.3 and sometimes down to 11.8 when the AC is on. I only run the AC at highway speeds and even then it's only 13.5 volts. I know it's not the crank pulley because I replaced it with an ATI unit back in May.

 

13.5 volts on the highway is fine....even with full load...
As an alternator ages/wears, the brushes wear...and the max output drops...
What you are seeing is 100% normal...IMO you are chasing a ghost (car hypochondriac?!, naww, just kidding!) Drive your car and enjoy it. When the alternator become MUCH weaker, you may need to replace it...but it sounds like it is doing fine.
Remember, an alternator output varies with rpm...and often much of its output might be going to the PS pump, recharging the battery, the cabin fan, radiator fan, lights, etc...most cars need the battery to even out the voltage since VERY few cars can run 100% of all loads possible solely off the alternator... No need too..the battery is a great storage device....the car just needs to handle the base loads...and the peak loads can get the extra boost from the battery...

 

This is not normal, something is definitely wrong with the charging system, I'm just wanted to know if anyone has determine if it's the brushes or the voltage regulator. Last summer, my voltage never dropped below 13.5 volts sitting Idle with the AC on. With the way the car is acting right now, I'm surprised it hasn't died on me yet sitting in traffic.

 

See above EDIT:

I had a MINI Alternator die on me when driving, the first real signs I was in trouble was the voltmeter was dropping down below 12 volts, then on occasion it would just drop out to 0 volts and the dash would go wacky as the needles would bounce from extreme to extreme and every warning light would flash and the LCDs would go dark. But I had several hours of highway driving to go before I could stop, and since I had just enough power in the battery (I would end up replacing it as well) to keep the car running I was able to make it to my destination, when I turned off the car... that was it.

Replacing the Alternator can be a DIY job, should only take about 2.5 hours if you have the tools and have never done it before, but you have taken the front of the car off for other maintenance reasons.

I will add as yet another alternative to buying new, is buying a used unit from a Auto Recycle Center (Junk Yard, Breaker), you could possible find one for as low as $100.00 from a low mileage vehicle.

Best of luck.

Motor on!

 

Here is a great DIY for the alternator. Check it out as it also provides a lot of great information about it and failures. Alternator options here too if needed.