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Some of you might remember that I "installed" a USB charger with a voltmeter in my 2011 GLK. It's handy for checking my resting battery voltage, the voltage drop when starting the engine, and the running voltage.
Everything looks pretty normal for the first two - 12.2 or 12.3 volts at rest, dropping to 10-point-something when spinning the starter (at the right speed, BTW).
Thing is, sometimes when I check the voltage while driving, it'll be around 12.5 volts, and at other times it can drift as high as 14.5 volts. Just now it was reading 12.5 volts with the engine running. I turned off the A/C (hey, this is Arizona in July, so that doesn't happen often), with no change. I then flipped on the headlights, and the voltage jumped above 14 volts.
Thing is, my previous car (a 2006 BMW 530xi) had a really complicated charging system, and those voltages wouldn't seem at all odd - it really didn't try to cook the battery by subjecting it to 14+ volts all the time when running, but would make decisions on how much current (controlled by the alternator output voltage) based on history and current conditions. It apparently works, as the battery that was in the car when I bought it lasted around 9 years (2-3 is typical here).
I'm just wondering if the MB charging logic does similar things. Or the alternative is that my alternator is getting flaky.
Has anyone ever spent time monitoring their charging voltage while driving long-term?
I was having weird charging patterns and replaced my Regulator that is on the alternator, the regulator also hold the brushes , it’s one complete unit . Fcp Euro, about 110$, easy replacement . My old brushes on a 75,000m 2013 were worn below minimum specs . The new regulator evened things out. 12.5 doesn’t sound right . When was the battery tested ? How many miles ?
If voltage before first start is about 12.6 then your ok
. I don’t understand what you said voltage drop is at starting .
The voltage drop I was talking about at start was how far down the battery voltage is pulled by the load of the starter. 10.something sounds right (it's a huge load). Again, the engine was spinning at the right speed at that voltage.
Nice to know that the regulator does contain new brushes, so unless the bearings in the alternator are going south, it'll be as good as a new alternator (and a whole lot less spendy).
I did a little more research, and one of the symptoms of a regulator on the way out is that the voltage drops at idle (which mine does). I need to get this sorted quickly, and ended up just placing an order for a remanufactured OEM alternator (Bosch) from FCP Euro, so at least if it does go south I can get a new one free. I liked the idea of just swapping the regulator, but couldn't get any of the legit options delivered in time. Sigh...
Fcp is where I got mine, they do overnight, the commutator will need to be polished .my mechanic put a drill on the alternator to spin it and I used 400 sandpaper on the commutator . But I’m not sure yours is bad since you are 100% every morning and I have not checked running voltage .
I just re read your post , I should not read them at 3am and answer . 12.1 is to low.
What is voltage after sitting all night before starting ?
Is starting voltage drop 0.10v ? Or 1v?
Does it go to 12.1 when running idiling ?
12.1 is maybe 50% charge and cause for concern.
12.6 after sitting all night is charged and good.
12.3 is about 80- 85% charge and good on an older battery as my 3 yr old AGM .
Is your battery an AGM ?
the alternators are well made, just the commutator wears . The regulators last about 120,000 miles or 70,000 with a high powered amp . It’s the brushes that wear. But the electronics can fail over time.
have you charged the battery overnight with the proper charger ? AGM for an AGM battery? Have you load tested it ? New batteries can be defective . It’s good your running ok but yes it’s a good idea to know if your system is 100% or 60% and failing .
I would have opted for the regulator from FCP but need it quicker than they could deliver it (there was a delay from the order to shipment for the regulator, while the reman alternator could be shipped immediately).
My battery's resting voltage (overnight) is fine - above 12 volts, and I'm getting no signs of it having a diminished capacity. I also did check it with a battery tester not long ago, and it was fine. It's an AGM, of course.
The issue with the charging system (aka "alternator") is that it will read mid-13's to low-14's much of the time, but will then droop to 12.5, plus or minus a couple tenths, for no apparent reason.
The one mechanical thing that's left me stranded in the middle of a road trip was an alternator that failed in the middle of Nowhere, Texas... fortunately I was able to (just!!!) coast into the only rest stop for 50 miles, and get a flatbed ride to the next town, which had a hotel across the street from an auto parts place with an alternator in stock. This was on my 2004 Acura MDX, a few cars ago. I figure that it's better to just swap out the alternator at this point, since it's almost a certainty that I'd need to before I finally move onto the next car (which I figure will be well over 100,000 miles from now).
There is a hidden volt meter I tried once , it has no delay so it jumped all over the place . I will look at it again, from what I remember it jumped from 12 .?? To 14.
But 12.05 at rest is only about 50% charge. That’s a concern . I think sulfation starts at higher than 12.05, Sulfation destroys batteries fast.
i had my dash cam shorted out draining me all night.
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