Can someone tell me what the normal running voltage on the E350. My multi meter shows12.6 when driving. Is that too low??

 

If you see 14.4 - 15,7 V when coasting or braking, everything is OK

 

Bosch has developed a variable voltage control of the alternator to "save gas"...

Any running voltage within these limits [12.6v to 14.9v] is normal by design.

Below 12.3V is a serious issue: "drained by driving" with 90Amps battery currents (aka "yoyo") - That's 1300 Watt of power roasting main AGM + ALT + PreFuse !

You can set your display to show battery sensor data while driving.

As it turns out even "normal voltage swing" disrupt CAN module networking. No voltage swing runs the GDI M276/8 engines better.


> Things you may look into....

• "battery float" (CTEK or better)
• "chassis reboot"
• "experimental ALT-LIN"

A stable 14Volts chassis voltage is proven to be as important as good fuel pressure for powertrain.

 

I've noticed a significant drop in voltage when running the A/C, it drops down to 12.8V.

 

12.8v ok, it is within control limits

Voltage is only half of the equation.
Need to see charging vs. discharging.

You can set your IC display to read both:
VOLTAGE + CURRENT: positive or negative ?

Battery current with or without A/C should hardly change: more or less couple Amps unchanged. ALT supplies 100% power, not battery.

 

My 2010 E550 has battery voltage swinging between 12.5V - 14.8V during normal driving. The highest Voltage I see is when I coast down and I think this as due to the "smart" charging system these cars have, i.e., the alternator gives more charging power when the car slows down. The alternator acts like a brake, like in the hybrid cars like Toyota Prius to charge the battery. This is not a hybrid with massive electric motors/generators but it is in that direction.

To make it short and clear, you have no problem.

 

At 15.0V or more, I will inspect, something is surely wrong.

 

above 15.0v.... barbecue modules pop when they're cooked

 

That's depends of the generation of the car. Some do like that on braking or coasting as the AGM battery can integrate short voltages spikes.

Although, the 14,4V constant voltage has nothing to do with stable CAN network ( there is no other type of CAN network - just stable, if unstable, there is no CAN transmission/) or with fuel pressure . The Voltage is PWM and everything is about the Freq of the pulses, the x.xxV are only a math Integer . Besides Voltages, there is a unique concept like "Energy". Nobody care about Voltage here.

 

Long live American Pope Leo

 

Arrie, Thanks. My e350 does the same. Nice to know not an issue. Recently replaced alternator and new H8 battery and was concerned that I have some type of a charging issue even though had no warning lights or messages. This is wife"s car and I just wanted to make sure car was good to go. She loves this car.

Again Thanks. Tom

 

Surprised Cali didn't send you over to his thread:

https://mbworld.org/forums/mercedes-...s-voltage.html

 

He forgot to : )

 

I am tolerant, not a pushy type. I went from "could not reproduce.." to easy fix!!

I recognize there's value in owning a dealer maintained car. Stock is all right for most consumers.


> VOLTAGE DOES MATTER !!
-- The ALT-LIN experimentation is an advanced procedure away from standard MB stock.

-- ALT-LIN has evidenced that multiple chassis run noticeably better with stable voltage.

-- Bosch ECU is non-compliant with Bosch voltage swings.

-- ECU tolerates unstable voltage by derating engine control. Bad from factory is sub-standard.

Stable VOLTAGE = stable PERFORMANCE.


> STARTER BATTERY:
-- Charge status of MB Battery involves more than charging the battery.
It involves battery drain.

+ battery charge
-- battery drain
= charge status


> BEST PRACTICE...
The shortcut is use a good float charger to maintain main battery else battery will get drained by chassis CAN-B.

Don't rely on engine alternator to "charge" a drained battery with it's unlimited 200A current.
Use an overnight charger, not a jump-pack!

Less problems for smart owners.