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Hello all and sorry to bug everyone for basic info.
I was doing prevetative maint. when I noticed some odd charging from my alternator to battery. So i decided to replace battery and alternator just to cover my basis and not be found stuck on road.
I do have 130k miles on my 2011 C63 now, cant help it i love driving it haha.
As you can see at idle it does charge and read upper numbers for IB and VB where I would typically see the.
However once you engage Rev. Or Drive and start driving any amount of gas it drops voltage to 12.6 or 12.7 for VB and IB goes as negative as 10 and 12 amps.
Once I let off gas it will eventually hit positive amps for a second and two and then dive back down.
Now I haven't had to follow the voltages or amps on my benzs really yet, so used to a more steady 14+- volts going to battery no matter what when a cars alternator is running, always been my go to check.
It's not helping me here though, it's confusing me more than anything.
Is this normal operating? Or is there a relay or fuse i should be tracking down in the charging system?
I did try searching but couldnt find any clarifying info, closest i came was reading where if voltage drops below 12v and you have negative amps then there is an issue.
So is 12.6v steady and negative amps normal?
Thank you for any knowledge in this area.
Last edited by catmandoob; Jun 6, 2022 at 07:09 PM.
Hey hey Barry, Yes which is why I went with a new alternator while I get the service kit to rebuild my old alternator. It's a new WAI alternator with Bosch voltage regulator, it said new as opposed to a reman so I was hoping to circumvent rebuild issues right out of the gate.
The battery is an Odyssey AGM from FCP euro, both have been replaced new and fresh over past week.
Now to add some WTH is going on, I have went through 3 downstream O2's since this as well. Each one will be fine for about 5 miles and read about the 455mv range and then on next start up back down to 55mv to 65mv, but only on Bank 1. And yes, My tune has them turned off as well.
I'm getting the feeling I have some electrical gremlins running around.
But as of now, I can drive the car just fine, no technical issues aside from IB and VB being lower than supposed to, not to mention I was always taught if amps are negative then there is obvious drain and no charging of system.
Charge strategy to prolong life of the battery while also increasing efficiency. I think target is ~75% battery charge but don't quote me. It will charge while idling and during deceleration/braking and won't charge during acceleration when battery charge target is reached. I was seeing the same thing as you and then geeked out on the internet for a couple hours until I figured it out.
As some have figured out, if you bypass that BMS sensor at the battery it will function as Barry has stated above.
Appreciate the information. My search left me thinking it was going to be due to the way the charging system worked but I felt it left some holes for me to feel 100% on that plus my scanner still reads mechanical fault as it's going from charging to non charging.
It's one of the carsoft scanners though so maybe it doesnt read that correctly.
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