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  #31  
Old 09-14-2020, 12:12 PM
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The voltage regulator has temperature compensation so you might see 14 volts on a hot day as the internal resistance of the battery gets higher and higher voltage is needed to achieve a full charge. This is all assuming voltages accurately measured at the battery NOT the OBC or scan tool. I would say the OP has his problem fixed and shouldn't be looking further unless it's just to learn more.
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  #32  
Old 09-14-2020, 12:16 PM
jac jac is offline
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Hi gents, thanks for the observations. I am learning from you all.

I saw the 13.4 when I first turned on the car and as it idled for a few seconds. That's all I had observed. But now that you guys informed me that 13.4 is on the low end, I have taken the time to observe it further.

So, my observations are:
  • Voltage: starts at 13.4 after about 3 seconds from cold start, and while in Park for at least first 30 seconds (not sure if it climbs or stays there if it stays in park for a while)
  • Voltage: 13.4 while reversing from park
  • Voltage: 13.6/13.7 while driving at around 20 miles per hour
  • Voltage: 13.7 while driving at higher speeds than 20 miles/hr

The alternator is a new Bosch 140 amp unit. Well, it is supposed to be new, at least according to FCP Euro. But I am not certain because the box is a retail Bosch box nicely sealed, but the unit has a Bosch sticker, but the plastic part says Valeo... I am reaching out to FCP Euro to check.

Thanks!
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  #33  
Old 09-14-2020, 01:10 PM
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Which is exactly inline with expectations. Also good on the 140 Bosch. Same I did. I picked Bosch over Valeo as the VR is 1/3 the price.

I did get a lifetime warranty with O'Reilly but I might be stuck in a town without an O'Reilly at some point and it'd be a great perk to have a $35 fix one day vs $250.
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  #34  
Old 09-14-2020, 01:19 PM
jac jac is offline
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Ah... Yeah, it is a remanufactured one... It did look really nicely cleaned up though, even the coil windings. Hopefully it lasts. :-)
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  #35  
Old 09-14-2020, 01:53 PM
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Quote:
Originally Posted by jac View Post
Hi gents, thanks for the observations. I am learning from you all.

I saw the 13.4 when I first turned on the car and as it idled for a few seconds. That's all I had observed. But now that you guys informed me that 13.4 is on the low end, I have taken the time to observe it further.

So, my observations are:
  • Voltage: starts at 13.4 after about 3 seconds from cold start, and while in Park for at least first 30 seconds (not sure if it climbs or stays there if it stays in park for a while)
  • Voltage: 13.4 while reversing from park
  • Voltage: 13.6/13.7 while driving at around 20 miles per hour
  • Voltage: 13.7 while driving at higher speeds than 20 miles/hr

The alternator is a new Bosch 140 amp unit. Well, it is supposed to be new, at least according to FCP Euro. But I am not certain because the box is a retail Bosch box nicely sealed, but the unit has a Bosch sticker, but the plastic part says Valeo... I am reaching out to FCP Euro to check.

Thanks!
Wow, that's a shocker on the Bosch / Valeo hybrid you've got. Let us know what the answer is. Am sure it's OK, but still weird.

On the voltage, as was said earlier, it matters where you measure it. A voltmeter measuring at the B+ jump port in the engine bay will give you pretty close to exact alternator B+ voltage.

Measure anywhere other than that point, and voltage will be lower. I think I remember noticing the built-in high cluster internal test showing consistently up to half a volt lower than the true alternator voltage.

You'd get similar results if using one of those voltage gauges that plug into the 12V outlet.

The electronics like to have regulated voltage, and generally regulating voltage (for stability and control) means reducing it a little.

My guess is that things are fine with the new alternator, and that you have solved your problem. But it is a little concerning that the store did not confirm your old alternator as bad. Those tests are always a little suspect. It could be that you have an intermittent problem - diode conducting or not, for example - that somehow temporarily fixed itself during the removal, disassembly and reassembly.
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  #36  
Old 09-14-2020, 03:28 PM
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The usual suspect of bad alternator is the combination of loss of spring pressure on the brush and enough debris or enamel buildup on the slip ring. Just a good bump the right way and you can probably get another 1000 miles.

When I removed mine I discovered it failed from brush dust buildup it just needed a cleaning. However I already bought the new one so I'm keeping the old one as an emergency spare I do have two e53.

Anybody within a couple hours drive of me could take advantage of the spare should it come in helpful.
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