The alternator in my 2007 S has been overcharging the battery causing intermittent no starts and some electrical glitches. At idle and with full load it registers 15.3-15.7 Volts. So the shop recommends to change the voltage regulator.

For some reason all the part suppliers in the US don't have the voltage regulator of my Bosch 150A in stock and most claim it will take several weeks to deliver since it has to be sourced from Germany.

Luckily, my friend has a spare Valeo 120A lying around and is giving it for free. In the EPC there are 2 alternators that apply, the 120A and the 150A.

Will I have problems if I downgrade my alternator to 120A? And will it bolt on straight out? My car is all stock, 2007 S Manual. So is it better to grab the 120A for free or invest $130+ for a new voltage regulator for my 150A?

Btw, why does Mini offer 2 types of alternators?

 

What should be the proper voltage output of the 150A alternator? Can 15+ volts cause intermittent hard starting (when engine is hot) and cause electrical gremlins?

 

From wiki

Open-circuit (quiescent) at full charge: 12.6 V to 12.8 V (2.10-2.13V per cell)
Open-circuit at full discharge: 11.8 V to 12.0 V
Loaded at full discharge: 10.5 V.
Continuous-preservation (float) charging: 13.4 V for gelled electrolyte; 13.5 V for AGM (absorbed glass mat) and 13.8 V for flooded cells
All voltages are at 20 °C (68 °F), and must be adjusted -0.022V/°C for temperature changes.
Float voltage recommendations vary, according to the manufacturer's recommendation.
Precise float voltage (±0.05 V) is critical to longevity; insufficient voltage (causes sulfation) which is almost as detrimental as excessive voltage (causing corrosion and electrolyte loss)
Typical (daily) charging: 14.2 V to 14.5 V (depending on manufacturer's recommendation)
Gassing threshold: 14.4 V

Can you advise the Bosch part number on the alternator as you be able to get a compatible regulator easily and they are not too expensive.

I picked up these additional tests from a ford forum but should apply to any car re method

OVER VOLTAGE TESTS
If the voltmeter reading was more than 3 volts above base voltage in the No-Load Test, proceed as follows:

1. Turn the ignition switch to the RUN position, but do not start the engine.
2. Connect the negative voltmeter lead to ground. Connect the positive voltmeter lead first to the alternator output connection at the starter solenoid or load distribution point and then to the regulator A screw head.
3. If there is greater than 0.5 volts difference between the 2 locations, service the A wiring circuit to eliminate the high resistance condition indicated by excessive voltage drop.
4. If the over voltage condition still exists, check for loose regulator and alternator grounding screws. Tighten loose regulator grounding screws to 16-24 inch lbs. (1.7-2.8 Nm).
5. If the over voltage condition still exists, connect the negative voltmeter lead to ground. Turn the ignition switch to the OFF position and connect the positive voltmeter lead first to the regulator A screw head and then to the regulator F screw head. If there are different voltage readings at the 2 screw heads, a malfunctioning regulator grounded brush lead or a grounded rotor coil is indicated; replace the regulator/brush set or the entire alternator.
6. If the same voltage reading, battery voltage, is obtained at both screw heads in Step 5, then there is no short to ground through the alternator field/brushes. Replace the regulator.

 

Do a battery only test first. I had some issue with voltage reading when my previous battery was dying of a bad cell. After going through all the trouble of first assuming it's the voltage regulator and removing the alternator (not an easy job), I found out it was the battery all along.

Check the age of the battery first, if you live in a hot area like I do, over 3 years old, just replace it. If it still young, take it out or take the whole car to some one other than the previous mechanic and do a load test on the battery only. Do it at least a few times to be sure.

 

Thanks for the replies.

I forgot to mention that the battery is 1 week old.

The Bosch part# of the alternator is 0 121 615 012

 

You will see the regulator is a Bosch part number F00M346065

http://www.woodauto.com/Unit.aspx?Ma...Ref=0121615012

Google is your friend so I am sure you should be able to source one.


I would remove the regulator and check the brushes as these are relatively easy to replace with basic soldering iron skills and cost peanuts