Gents,

I done cleaning my F32 and making sure all tight.
While at it, I went deeper into the Q-Diode How It works ?

What is Q-Diode found in W212 with B03 Start-Stop using baby 12Ah battery at the trunk ?

Q-Diode is actually a small module which behaves like a relay and also like a diode which is a one way valve for electric current.






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Left iimage is my F32, on my car. Right image is from youtube.



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Since this Q-diode is an electronic circuit and semi-conductor in a package this is a module and not a simple solid state relay.
The ground wire pin 2 must always be connected to ground* ( *in case of bad contact ) as negative return power, the pin 1 is the command from Front SAM.
The positive power for the the Q-Diode management is from the B1 terminal ( KL30Z ) and/or from the Load terminal (KL30) which will have an alternator
and baby battery 12Ah Start Stop. B1 is battery positive terminal at F32. This is direct cable from battery positive post, only for F32 and nothing else.



If pin 1 command has no signal or power from N10/1 , Q-Diode behave like a normally closed relay of mechanical type and current from alternator can flow and charge battery while
also serving all the loads, main battery current can also flow to all loads when needed. Bi-directional or two way current flow allowed.

If pin 1 command has signal or power from N10/1, current won’t be allowed to flow from LOAD ( KZ30 ) to B1 (KL30Z) so no charging of battery by alternator can happen,
but current is still allowed to travel from B1 to LOAD. So this is why the name Q-Diode, the device acts as one way electrical valve aka Diode.

This Q-Diode is for Start Stop only actually, but for those who killed the Start-Stop, a defective Q-Diode or even loosing the pin 2 ground wire
connection will cause trouble for the electrical system and massive voltage drop will occur at even less than 1 amp load. Current flow is from B1 to LOAD.
If a mechanical relay of NORMALLY CLOSED type, its negative is for the coil only the 85/86 and loosing it does not matter at all to the contacts 30/87


As to why if pin 1 has signal or power from N10/1, current won’t be allowed to flow from LOAD ( KZ30 ) to B1 (KL30Z), is because this mode
is the ENGINE KILL mode in Start-Stop operation and comfort device electrical need is provided by the Main Battery and 12Ah Baby Start-Stop battery which is at the LOAD side bus bar…..
however, when engine crank-to-start and massive power is required, the blocking of current flow from LOAD to B1 will protect comfort devices from low voltage while cranking
because 12Ah Baby Start-Stop will not contribute its power for engine crank-to-start, because the Q-Diode will block the current flow .


The starter motor is directly wired to battery positive with a pyro-fuse and not from F32 Prefuse block, thus starter motor is not at LOAD zone, it is at its own zone which we can call B1 zone.
V19 below is the Q-Diode.


LEGEND:
M1 = Starter Motor. , G1 = 80-90Ah Main Battery. , F63 = Pyro Fuse ================================== G2 = Alternator , 12Ah Battery is for Start-stop, also called G1/13



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WHAT IF SCENARIO


01. If Q-Diode lost its ground wire pin 2. Status : Engine is running.
Charging from alternator to main battery won’t happen <---- BASED ON HEALTHY Q-DIODE with ground cable removed to simulate a fault.
Alternator will handle the load required by the car, thus driver may not realized battery is not charging. <-- Engine/alternator is running, simulated

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02. 01. If Q-Diode lost its ground wire pin 2. Status : Engine is OFF
The Q-Diode will allow current from main battery to flow to LOAD, but the voltage drop is massive at even low 1 amps load.
The car will behave like having a very low battery voltage condition for comfort devices.... but engine crank-to-start is very OK, this then may confuse owner
* Remember starter motor current does not go thru Q-Diode.


Test data as follows :
Battery voltage using power supply set at 12.79V, with zero load, voltage already down to 12.55V
Battery voltage using power supply set at 12.79V, with 15mA buzzer load, voltage down to 12.30V
Battery voltage using power supply set at 12.79V, with 0.36A 5 watts bulb at 4.6 watts running, voltage down to 12.15V
Battery voltage using power supply set at 12.79V, with 0.72A 10 watts bulb at 9.2 watts running, voltage down to 12.07V
END OF TEST

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03. What If Q-Diode goes bad………….. sorry no such test made


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Images of the TEST


OUTPUT means LOAD



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Battery voltage using power supply set at 12.79V, with zero load, voltage already down to 12.55V



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Battery voltage using power supply set at 12.79V, with 0.36A 5 watts bulb at 4.6 watts running, voltage down to 12.15V





Q-Diode tested , using Diode Test Mode in DMM, its pin 2 ground and pin 1 command is disconnected. B1 Battery terminal to MR8 alternator terminal.




Reverse the Test Lead,






Will continue..................

 

Thank you Surya, this is really essential to understand this well. I need to get into it deeper to understand pro/cons.

Until now... the way I understood this circuit was Batt has a "in-line handicap/bias" to always stay lower than ALT as to not contribute chassis power under normal running conditions.


I am glad to see your PreFuse looks in excellent shape.

Here a nice handy trick!!

 

More information Cali........



TEST 1 . Q-Diode test in command mode. Pin 1 get positive power/signal from Front SAM N10/1





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Note : My power supply amps reading is only good to 2 digits after decimal, so it is 1/100 and not 1/1000 milliamps resolution. But at least it has the watts reading at 0.63 watt.


At the battery, Q-Diode does not allow current to flow to battery or charge the battery, when and if Pin 1 get power/signal from Front SAM.





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Test 2 - No command for Q-Diode. Pin 1 does not get power or command from Front SAM. Q- Diode now can flow current both ways.


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Will continue.............

 

My personal take on V19 Q-Diode on my car, which I already killed the Start-Stop.....it is a liability of another electronic ON-OFF switch which can fail, while I no more have use if it.
Its failure will make my alternator to NOT ABLE to charge my battery and give so much battery voltage drop to all components when engine is not running.

I think if Q-Diode failed I would not even be able to deliver 10+ amps from battery to devices without voltage drop down to under 10V, probably....or it can be OPEN CIRCUIT.

By design it is like MOSFET, a high power switch. It is effected by heat for sure.
So aside from alternator heat soaked and reducing its power at idle RPM at night in creeping traffic, I wonder what negativity will a hot running Q-Diode will contribute.


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A failed Q-Diode is VW coasting application.
Damn video link not allowed by owner.
Go to youtube and search : q-diode coasting battery vw or

VW Golf Coasting Battery operation , the Q Diode and Fault Code P25FF00 - VOLKSWAGEN

What is Coasting Engine Kill but car is moving.....feature of VW ?
https://www.motor1.com/news/144045/v...id%20batteries.

They use Q-Diode for isolation between main battery and EXTRA Lit-ion coasting battery.
The (Lit-Ion ) battery’s role is to feed the car with the necessary electric consumer units while the coasting function is active.
There’s also a so-called “Q-diode” responsible for regulating the current flow between the newly added lithium-ion and the vehicle’s regular lead-acid batteries.


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The 6 + 1 (7th) clips you need to watch out for when trying to pry open the F32 half body/cover.
And 1 (8th) clip at the main body.




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The 7th baby size clip







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The hidden 8th big clip, at main body side and not at cover like 1 to 7th.




The interface of the clip to its lock/protrusion







At first I dare not open up the F32 casing because I am plastic clip-IDIOT and will break things for sure.
But one techy showed the clip in his youtube , albeit only 6 clips shown at cover but it was most helpful.







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What did I found when I dismantled my F32 a 100% ?
This weird whitish stuff like dry lithium grease on a few fuses. It is not corrosion .

Will continue......................

 

The whitish stuff,,,,,,,,,,, found only on 3 - 4 fuses or so.
It is not corrosion though, maybe some sort of electric paste ?....but not on all fuses ?
I don't like it.I clean them all.



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All bus bars straight or L ones are copper coated with nickle. The stud are steel, small M10 nut are steel and M13 nut are stainless steel.









The K2 relay is made by Gruner. We can buy it stand alone ....yipeeee !!!
https://xenons4u.co.uk/750h-r1a-b010...819-relay.html







Main BUS bar. Before and after cleaning, using stainless steel brush.


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Small bus bar for IG1 terminal, before & after cleaning. It has that whitish stuff....





Removing surface oxidation on the K2 terminals





Cleaning Q-diode terminals





Not only it has trace of the whitish stuff, I hate the fork shape design on 1 side of the alternator 350A fuse, smaller surface contact on the biggest fuse...duggh !!!
Why not both sides full surface contact blade




Why why ????




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The tightening torque of all M10 nuts is 8Nm +- 1Nm and the M13 is 16Nm +- 1Nm.

These all 7 brass plug is very important, it is like a super thick washer for conducting the electrical current.
This brass plug touches fuse blade or bus bar better than the stud.




Stud is locked by the plastic molding of the fuse main body.
And a B1 bus bar ( jumper bus bar ) is placed on top of stud and then Q-Diode sat on top of bus bar.
Observe the flat touch surface of stud hex head round thingy, that is all the surface area of the stud when touching the bus bar



Contact surface area of stud to bus bar, I marked in red







The tightening of B1 stud + Q-Diode terminal blade+ jumper bus bar only takes place when B1 battery cable installed properly at 16Nm +- 1Nm because the brass plug made it possible for compression.




Compared to the the friction forced fit stud on a bus bar , which the stud will carry current well aside from the bus bar it self.





All these studs are loosely-touching the fuse terminal/blade, until each and every nut on the cable end compressed each brass plug and tighten everything properly.
What I am saying is, this design carry more risk of overheating when the nut is loose than say all the ground stud type design on our car metal body.




Our ground stud is a beautiful design.
Welded permanent on the car metal, has round contact surface area A and the stud B itself is a full current capable conductor.





Typical dumb-azz stupid design found on Ford, Toyota and most other cars using female thread welded on a painted steel plate.
Even assuming the female thread is free of paint, the current carrying surface area is only the female thread, it is small and difficult to clean.






The same as the latest Land Cruiser 300. This is a 2024 model year.
They made a U plate on the firewall metal with 2 nuts welded on it. The u plate is painted, but the female thread of the nuts is not... still the total surface area is small and how the hell to clean a small
female thread effectively ?






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The single fuses, except the 350A is called MIDI type : https://www.littelfuse.com/assetdocs...7-bebc2d4a94f5

The dimension is standard if MIDI. Easy to get.


The special 3 blades-in-1 and 4 blades-in-1 , sorry I do not know who sell those stand alone.






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Did I screw up during this F32 teardown ?
Well yes and no.

1st screw up is me wrong stacking of the 3 blades-in-1 and it made the blade for the connector i3 angled up.
Sorry, oily trace on camera lens.




Should be like this :




The stacking from bottom to top should be :
1st - Main Bus Bar
2nd - 4-blades-in-1 fuse set the yellow one and then....
3rd - 3-blades-in-1 fuse set the black one.






I screwed up by placing 3-blades-in-1 fuse set as second layer....LOL



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I messed around with the main bus bar installed and removed and torqued all M10 and M13 nuts like 5-6 times.
I discovered a weakness on the main bus bar.

This part of the bus bar in red circle will turn clockwise a bit when torqued to 8Nm a few times.
Copper is soft, the material of the main bus bar. The cut is so much, leaving behind only small copper left.
This thinnest section of the main bus bar A in red for 80A fuse. NOTE : I instead use the un-use 100A fuse as emergency.


B in green/cyan is what I should have inserted into that gap with screw driver or something to stiffen up and prevent this part of the bus-bar from deforming a tiny bit clockwise rotation.

Left image is before the thin joint section of bus bar got distorted.



That 100A fuse is emergency substitute for the 80A fuse which its housing locking tab got broken and fuse got twisted and broke its thin burn element.



So this fuse integrity or strength comes from the white plastic cover holding basically two blades together.
C is the thin burn element of 80A value, bridging between two separate blades.
A, 4 of them holes are to be locked by B, also 4 of them, like rivet. One of the A hole simply broke because the bus bar drag it clockwise when torqued.
I heard the plastic cracking sound.


I will be ordering LittelFuse brand, locally I can get it ..... as heavy equipment uses these MIDI type.
They look stronger for their overall mechanical design.



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For the time being I will be using the 100A fuse in lieu of 80A for MR3 terminal which is for ELECTRIC POWER STEERING.

• When the 80A fuse arrive , I will modify my main bus bar by soldering (yelllow dot simulated ) some 2.5mm solid copper wire at two spots, to stiffen up the weak section.

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Attached the K2 Relay data sheet.

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Thank you very kindly Mstr Surya for your grand-tour of F32.


We see how opportunities are setup with each connection style.
It seems that F32 can work really well as long as contacts stay non-oxidized and not over-heated.
The part mfg uses a silicon paste as a oxide protection. However we both do not trust dielectric to help better contacts. The grease paste stays around longer than any type of oil can (deox liquid).
The issue is insulation properties... I am not a heavy gauge power specialist - I know there must be a brst practice to help connexions without hurting them. This is what F32 needs as a preventative maintenance against roasting downfall.

something along those lines ....

Mr GOLD

specs

👍

there's one best way and many bad ways to help this... I duno


This F32 PreFuse must stay reliable to prevent drop-voltage penalties.

 

As you so expertly pointed out...

partial connection


reduced contact area

This split-fork contact surface is not built to help extended survival. Good until oxidized.

It's kinda good because everything is NOT undersized to fail at 50kMi.

The busbars are beefy, the main 200A duty fuse is rated at 350A... there's room for overload!

We've got : copper, bras, stainless, nickel ...

 

Its a mix salad

I have the De-Oxit the concentrated one without propellant .
I did use it on my front SAM connectors but not for this F32.
The De-Oxit also helped my decade resistance box to be normalize, its kept too long and its giving like 30 ish Ohms on its rotating contacts due to copper oxidation.

 

It's kinda what I understand... Deoxit contacts becomes high service maintenance.
One had the cleaner and no protection
the other one had protection and no cleaner
what do they think we want: more frequent headaches or less??


either or but not both... can't get peace


chart explains the details

The GOLD DeOx does not add any gold, it only cleans it. Gold metal does not oxidize thus its reliable.

Then silver paste maybe interesting...
more so than a black-carbon grease.

 

@S-Prihadi
I'm in the process of tracing power on a 2014 SL and came across your post. Some very interesting info here, but I wanted to make one clarification about V19. The circuitry you described appears identical to what I'm seeing on the SL so I think it applies to your car as well.

After studying the schematics here's what I found:

V19 - ECO start/stop function diode: this is a solid state relay as described. However, it is not intended to control charging. It works in conjunction with another SS relay for ECO start/stop, which is:
K114 - ECO start/stop additional battery relay. This relay controls whether the aux battery is connected or isolated. It's isolated by default.

During an ECO engine restart, V19 is commanded open. This isolates the main battery from all loads except the starter.
and K114 is commanded closed. This connects the aux battery to all consumer loads in place of the main battery.
Once the engine starts the relays are returned to their default states, which isolates the aux battery and reconnects main battery to all consumer loads.

K114 is also closed whenever the SAM decides the aux battery needs charging. This puts the aux battery in parallel with the main battery during the charging period since V19 also remains in its default closed state.

Hope you solved your problem!

 

I don't have any problem with my F32, I just enjoy tearing it apart.
Yes, V19 Q-Diode is not charge controller, but since all current from alternator have to pass thru it and if you read well my 1st post to 4th post,
you would understand my statement by my 4th post :



See what I mean, Q-Diode is another device which will eventually fail.
For me who has disabled start stop many years ago and have removed the trunk 12Ah battery and render the K114 useless, Q-Diode is a potential liability.
I tricked the car computer into believing there is a 12Ah battery at the trunk

 

Perhaps you can by-pass that MOSFET "Q-diode junction" since you no longer have AUX Batt. Is there anything left that needs switching?

Diodes are really rugged semi-conductors. They can literally last for ever, unaltered like new.

The proven way to destroy a diode in a split second is with a spike gretter than specifications. A surge of reverse voltage or forward current.
Heat is normally not a direct concern unless marginal conditions are present: 90Amp yo-yo currents.

Its always true that less parts have less chance of failure ... can we simplify out K114?

 

I'm curious if you've ever torn open a V19? I ask because a solid state device usually has a small voltage drop across it. I'm not seeing any, which leaves me wondering if there's actually a relay in there?

 

Nope, never tear open V-19 Q-Diode, I do not have a spare or a defective one for experiment and it is 100% epoxy casting.

It has small controller chip inside it, thus it can fail.
I probably can not bypass it because the Front SAM N10/1 controlling module which communicate with V19 would detect the hack.

The VW/Audi link I posted which uses the same Q-Diode in a bit of different application, which is for coasting, shows Q-Diode seems to fail when old enough or probaby the inrush current higher in VW/Audi application.
If Q-Diode is working well, its voltage drop is ultra low, it is an excellent product I must admit.

I have something similar to Q-Diode on my boat as part of charge controller. 3 alternators from 3 engines managing and charging 4 battery banks, it goes thru 2 of charge controllers similar
to Q-Diode in design, very low voltage drop, approx 20 millivolts only at rated load.

 

OK, no need to tear open V19. Did a bit of research. A normally closed solid state relay would use a depletion mode MOSFET for switching. These are normally conducting until a control current is applied. When conducting they have a very low voltage drop, like a mechanical relay.