From what I can see, voltage goes down to 12.4V but with small current signaling ALT still online but draining slightly ie. not too good + not too bad.

Power would be much better if voltage was above battery resting at or above 12.6V and never below that (12.4V!is technically a drain).

> TEST DRIVE CONDITIONS :
Try to drive for 20mn on a straight road without A/C and NO headlight... this will show resulting voltage control: too low vs. ok ?

Let's see if voltage goes much lower with high load current out of battery.
That would then qualify as "drained by driving".

 

I'll do this test as soon as I can. I have a question: could the alternator be faulty?

 

Clearly NOT a faulty ALT.

The chassis voltage is remotely controlled outside of the ALT not internally like in the old days.

During the float cycle, the voltage is remotely controlled by the REAR-SAM according to the computed load SAM senses.

Your test drive is important to evaluate what needs fixing. Right now it looks like a bad dirty GND is causing voltage drop where measured.
Hopefully you don't see the combination of low voltage and high drain out of battery.

Your ALT IS 100% OK despite remotely controlled voltage issue. R-SAM > CGW > ECU > ALT.
This system is built without any way to pin-point what part is disfunctioning quietly.

 

@CaliBenzDriver , do you mind explaining more on the float mode?

As winter fast approaches the finish line, I am almost ready take the vehicle out of hibernation.

I used to daily drive this car even in winter ever since I bought it new but things changed this year (well, last year so this winter).

As a result I purchased a trickle charger/battery maintainer today.

The car has been in hibernation since about 6 months ago unplugged no battery maintainer as I was out of country and car started up fine today except for a few things such as blindspot in-op but after an hour drive it was back to the condition same as 6 months ago.

Revisiting this topic because of CTEK and float mode.

Just a few quick questions:

For float-mode it is stage 7 on the CTEK MXS 5.0, I have it set to Car mode and AGM mode. It says float mode takes 10 days?

Is it fine if I unplug it in the middle of float mode (so stage 7) instead of waiting 10 days for it to reach stage 8?

What does float mode do again?

Is it better to let float mode happen even if I need to say interrupt and unplug it before the 10 days up (examples such as power outage) or just great weather and want to take it for a spin? Why does float-mode (stage 7) take this long, 10 days though?

Or is it better to not start float at all knowing I can't leave it plugged in for 10 days non stop?

Thanks!

 

Yes ALT-LIN has been unplugged and stayed unplugged. The amp is at 2.9-3.3 after the drive.

 

I happen to have two main/starter batteries (two of the same batteries, not two batteries in the car) and keep one as a spare. Sometimes the electronics will act up and I will switch the batteries. The process leaves the car unconnected for about 30-40 minutes. I disconnect the aux battery when I do this. The battery out of the car is hooked up to a battery maintainer (usually a CTEK MXS 5.0) so that it is always fresh and fully charged should I need it. The CTEK maintainer does reach Stage 7 after a few days. I never counted, so it may be 10 days.

Please note that the CTEK trickle chargers are rated at 4.3A. If you do any load intensive diagnostics, such as running the Compression Test (comparative), the 4.3A may not be sufficient. (The conditions for running the Compression Test requires a battery maintainer to ensure there is sufficient voltage. Otherwise the test will not run.) I also have so other Smart Chargers rated at 20A for those purposes, to include any control module programming.

 

I’m sure Cali will point out that switching batteries with the car unpowered for that long, effectively reboots the chassis.

 

Much obliged! Is this the original battery you have in your vehicle maintained by CTEK when not in use? Curious, I am still on my original battery on a 2017 model year vehicle and it is still going strong, sadly the inactivity this winter and last year might had caused some damage, hopefully CTEK will help out.

 

Yes, my original battery. I will send a picture later.

 

 

A good first step is to read the CTEK manual.
Lead-acid battery charging can involve release of dangerous hydrogen gas. Beware of non-Mercedes batteries that are not properly vented out ("Sport vehicle AUX"!)

The manual explains the various steps the smart logic goes through as follow:


Lead-acid AGM charger steps

Simply put the CTEK matches the charge current based on increasing battery voltage. Charging stores power using the lead-acid chemistry similar to a huge "capacitor".


mode steps details... Voltage vs. Current
During charge the Voltage goes up and the current comes down.

Practically battery is ready when it reaches the Step-7. Charging mode is stopped to switch over the voltage maintenance.

The charging cycle is quicker when the battery is in good internal shape and not too discharged.


> CTEK "AGM" Setting...
The only confusing CTEK setting is the AGM Mode. This mode is beneficial to rebalance deep cycled AGM batteries.
Should we use it?? Yes but when battery is out of circuit with Neg. (-) disconnected from the car else prefer non-AGM mode while the main AGM is normally connected to the car.


> The CTEK Magic...
What's great about CTEK and perhaps NOCO & other chargers is that it lowers the battery internal resistance.

- A - In the fully charged top-shape condition battery acts as an electronic capacitor that absorbs the riples of electrical noise.

- B - With low-resistance the battery heats up much less under high current loads.

- C - With lower resistance battery absorbs charge more quickly. It also packs a better punch to crank starter.


Battery condition can be precisely measured with a battery tester.
The long story short is you really don't need a batter tester because CTEK charger has one built-in to guide its automatic steps.

Ultimately what kills even the best AGM battery is loss of plates capacity. CTEK can't prevent that on a 10Yr old battery... twice the normal battery lifespan!

 

Yes, I did read the manual first thing before plugging it in hence why I know about the 10 day as mentioned.

My question is very simple : ) I just want to know if I should keep it for 10 days so it reaches step 8 since you recommended the floating process (and first thing I heard about it was from you) last year. In that case, is it better to have the float process completed (so a full 10 days)? Will there be harm in starting the flow process and ending it early (like 5 days in) as in would it had been better if I unplugged it before the flow process has started being a better option than interrupting it in 5 days? So stop at day 0.

 

I was under possibly the wrong impression Step-7 was inactive.
It does show a reduction of current to zero under constant float voltage.

Steps 7 + 8 are referenced as "maintenance".

Battery is ready as it reaches green step-7.
Beyond that you can keep the charger plugged for as many month you want under trickle maintenance mode.

Typically I try to connect my CTEK overnight twice a month (non-AGM mode or AGM with "reboot" AUX out) despite running ALT-LIN stable voltage... This benefits point to how these cars are REALLY VOLTAGE SENSITIVE!!

MB chassis like what CTEK does:


not placebo effect

There is an interesting root cause that needs to be uncovered right there.

Something about :

• Prefuse power distribution
• Undersized resistive wiring harness
• marginal connections drop voltage
• ECU specific circuits: coils + piezo...
• .??.

Enjoy CTEK power until we can find out exactly what is so voltage sensitive.

 

 

As promised, here are pics of my apparently 10-year old Mercedes battery connected to my CTEK charger. This is out of the car.

 

That is textbook perfect use case of CTEK trickle charger function.

 

hm.. really curious to see someone else 1st time experience with CTEK to compare before/after, if its matched with the above statement I might give a shot for CTEK hahaha

 

do you mean CTEK vs other brand tenders or putting the car on a tender when not driving in general?

 

I don't think charger brand mater so much. Noco and clones are a copy of patented CTEK smart chargers.

All they do is top off the battery really precisely to lower the internal resistance.

The uncommon magic is that our MB GDI chassis are seriously sensitive to the battery condition.


> TEST CASE :
Compare a CTEK (or equal) float charged main battery preferably (not mandatory) recent AGM and using ALT-LIN for stable voltage.

You then may notice what has been referenced couple times by different ppl.

-- ALT-LIN 14.15Volts helps but does not solve this.

-- Newer battery better than older one but does not solve this.

I don't yet understand exactly the role battery condition play. A fully charged battery is still less than steady ALT-LIN voltage besides its internal resistance is lower.
That means it is not battery voltage that chassis is sensitive to while powered by fixed 14.1V ALT output.

A few car components are able to interact better under optimal conditions. Let's not ask why we consistently get handed all the short sticks.


### I left "Rebooting" out of that mix. It too helps by way of CGW networking.

### Similarly "ALT-LIN" is nice but you can get evidence "Batt. float-magic" without having 14.1V. In fact without ALT-LIN the difference is more pronounced but last only few days.


>>>> Got to do hands-on testing...
This is aiming towards being undersized ECU harness noisy drop-voltage helped by battery noise cleaning abilities.
Target is strong reliable performance regardless of basic voltage or battery condition.

Next Mod: smooth out moody powertrain electronics the way that runs best.

 

Over the weekend I got a chance to test drive my experimental solution.

my F32 Prefuse distribution


Charge circuit floating low current by itself

-- Right away tranny is noticeably more snappy and very easy to kickdown.

-- Also electric steering assist noticeably gets much lighter when car when car fully stops.

-- Engine throttle is very direct... "pressure sensitive" from 900Rpm. Its easy to see that injectors coils are up to something better. Absolutely zero pinging now thanks to proper ignition TDC advance.

-- Pre-mapped coolant temp mgt seems to be responding differently undergoing changes.

All that under 150Mi only: that is unusually good with the same "unchanged 14.15V".
Powertrain is indeed responding to bypass strap only (no floating, no reset, no reboot, no fresh oil).

Only a single change: THIS IS IT!
With or without the strap battery read exactly the same voltage.
IB goes lower.


experimental bypass: Power supplied by dual paths to main bar.

F32 prefuse ALT path is dropping voltage. Chassis super sensitive to its power supply.

I have improved the ALT power supply path to the prefuse distribution bar where floated battery was shown to make a difference...
Based on all the clues it had to be dropping between ALT and batt... I then considered all the components and came up with a quick test step.


> TEST OUTCOME MEANINGS...
Today is is an intermediate test step not a final fix.

-- Prefuse needs prestine condition to super flow power. Prefuse bypass test should be part of 50kMi tune-up.

-- Downstream circuits are proven poorly filtered sensitive to stock glitches. How to best fix that simply ??
Everything with a coil is affected/benefits:

1. cops voltage = timings
2. injectors opening = A/F Mixture!
3. valve-body solenoids = pressure
4. VVT Solenoids = cam positions
5. ABS/ESP solenoids = brake valves

-- I doubt stock variable voltage (12.6 to 14.9V) goes un-noticed by ECU/TCU. I'll stick with ALT-LIN for now!

-- How many other places occur drop-voltage penalties through marginal circuits (F-SAM + R-SAM)??
Need to trace VIP power supply path.


> MISC...
-- My engine bay has never been washed down. Car is garaged in dry California ie.prefuse internal oxydation should not be significant. Imagine how many GDI ppl are impacted by that !!

Cars with Bosch variable voltage should not be that sensitive to power supply.

Chassis with rear batteries BENEFITS THIS PWR MOD many folds because long lines are guaranteed to drop float benefits to zero.

Even I don't know how to diagnose this issue. Reduced performance?


> NEXT...
-- Enjoy driving 500 to 1000 Mi to see how everything adapts to best behaviors.

-- Clean the prefuse module oxidized tinned junctions (Not with DeOx).

-- I wonder what if we could play with "Farad voltage converter" module NOT to backup ISP but to clean up VIP power feed ??

-- Try to capture measures of strap current and voltage riples.

 

Thanks Cali

On the other hand car is done float charging (10 days after reaching step 7, now at step 8 and done).
Picture 1 this morning so 9.9 days after step 7 started.
Picture 2 is now so 10+ days after step 7 started. Altogether is 11ish days from step 0.

 

Very nice No7 float step!

Now you have couple days to enjoy best electrical supply. Pretty simple right ?
You can float at will & pleasure every other day -

Notice that even LED HL are brighter based on 12.5v battery condition.

I'm going to look at the various heavy circuit loads tied to Prefuse so I can bettter understand power distribution vs. VIP vs. voltage drop.

 

The brighter image is probably my camera 😅

 

Yes the brightness was my camera, I use a samsung phone and I did a manual exposure adjustment so the light is dimmer than the numbers otherwise the light makes the numbers illegible.

 

(not the CTEK LED Bar... lol )

LED Headlights driving Hwy at night beam further & whiter vs. regular stock without batt float.