R230 starter battery not charging

[zeppelin22]

Hi, I have the front starter battery not charging on SL R230, here's what I've done so far:

• Checked readings on front and rear battery, rear charging fine
• Checked and replaced 100A MIDI fuse (F52/F1) in footwell (was blown), checked 200A (F52/F2) was ok
• Taken car to local MB specialist, couldn't find any fault on STAR machine (other than MIDI fuse), reset red battery light remained off since
• Both batteries tested and working properly (starter charges normally on external battery charger)

Would appreciate any advice on this one, thanks

 

[alabbasi]

Did you put a volt meter across the terminals? If one battery charges and the other does not, I'd assume that your battery is duff or your terminals need cleaning.

 

[zeppelin22]

Did you put a volt meter across the terminals? If one battery charges and the other does not, I'd assume that your battery is duff or your terminals need cleaning.

Hi yes I did use volt meter and checked the terminals are clean on both sides

 

[alabbasi]

Hi yes I did use volt meter and checked the terminals are clean on both sides

What voltage were you getting at the meter?

 

[zeppelin22]

What voltage were you getting at the meter?

starter at 12.4V consumer at 14.1V, thanks

 

[oldguy57]

Common problem seems to be the alternator regulator. I'd try monitoring the voltage at the starter battery for a few minutes to see if there are fluctuations. Presumably the 14.1 volts was with the engine running?

 

[ChrisPDuck]

14.1V at the consumer battery suggests the alternator is working. I don't really know where the split between the charging circuits for the two batteries occurs, but I suspect there's some kind of management system that controls them separately. What I did notice when I first started investigating on my own car was that the consumer battery came up to alternator voltage almost immediately, but the starter battery took a little longer - I don't remember how much longer though. Have your readings been taken immediately after starting the engine?

I think there are a few possibilities to explain what I saw:

• The starter battery was more depleted than the consumer battery. Unlikely in your case because you've charged the starter battery separately.
• There's a management system in the car that prioritises the consumer battery, i.e. it waits for it to come up to alternator voltage before allowing the starter battery to charge.
• The split between the batteries may actually occur at the alternator's voltage regulator. I did end up changing the regulator, which fixed an intermittent charging problem I had, but I haven't checked the starter charging voltage characteristics since - I suppose it's possible the delay in the starter battery coming up was due to whatever fault I had in the regulator. But I don't really believe this is the case - I don't recall seeing two chunky wires on the back of the alternator, which would be necessary for the two batteries to be separately controlled by the regulator.

So I'd suggest, initially, check the starter battery charging voltage a few minutes after starting the engine.

 

[Deleted member 126251]

What voltage were you getting at the meter?

Only useful taking readings if the battery has not been receiving a charge for several hours. (float voltage after charging will be a high reading).

As above (chippduck ), 14.1 suggests the alternator is working. Sounds like one of the other batterys needs replacing.

Aux battery is only to keep systems operating during eco/stop-start. It is not a “consumer” battery as you’d find in boats etc.

 

[ChrisPDuck]

Only useful taking readings if the battery has not been receiving a charge for several hours. (float voltage after charging will be a high reading).

Sure - if you want to check the health* of the battery. But if you want to know what the alternator is doing, you have to measure while the engine is running.

*EDIT: Or rather, its state of charge.

 

[Deleted member 126251]

Sure - if you want to check the health* of the battery. But if you want to know what the alternator is doing, you have to measure while the engine is running.

*EDIT: Or rather, its state of charge.

HAdn’t read down to your post

 

[zeppelin22]

Only useful taking readings if the battery has not been receiving a charge for several hours. (float voltage after charging will be a high reading).

As above (chippduck ), 14.1 suggests the alternator is working. Sounds like one of the other batterys needs replacing.

Aux battery is only to keep systems operating during eco/stop-start. It is not a “consumer” battery as you’d find in boats etc.

Its an 03 model so no start/stop on this vehicle. The MB owners manual refers to it as a "battery for electrical consumers"

 

[zeppelin22]

14.1V at the consumer battery suggests the alternator is working. I don't really know where the split between the charging circuits for the two batteries occurs, but I suspect there's some kind of management system that controls them separately. What I did notice when I first started investigating on my own car was that the consumer battery came up to alternator voltage almost immediately, but the starter battery took a little longer - I don't remember how much longer though. Have your readings been taken immediately after starting the engine?

I think there are a few possibilities to explain what I saw:

• The starter battery was more depleted than the consumer battery. Unlikely in your case because you've charged the starter battery separately.
• There's a management system in the car that prioritises the consumer battery, i.e. it waits for it to come up to alternator voltage before allowing the starter battery to charge.
• The split between the batteries may actually occur at the alternator's voltage regulator. I did end up changing the regulator, which fixed an intermittent charging problem I had, but I haven't checked the starter charging voltage characteristics since - I suppose it's possible the delay in the starter battery coming up was due to whatever fault I had in the regulator. But I don't really believe this is the case - I don't recall seeing two chunky wires on the back of the alternator, which would be necessary for the two batteries to be separately controlled by the regulator.

So I'd suggest, initially, check the starter battery charging voltage a few minutes after starting the engine.

Thanks Chris, I did consider the alternator issue (attached the wiring diagram), the split in charge circuit does not occur at the alternator regulator but at BCM module (N82/1) via K57 relay. Dilemma is;

• The blown MIDI fuse F52/F1 explains circuit was initially broken however I have replaced it
• If K57 relay is faulty that should flag fault on instrument cluster?
• If the BCM is faulty should flag red battery light on instrument cluster?
• If the BCM is prioritising the consumer battery then why and can it be reset?

I've had a look at the BCM and no signs of burn out like on YouTube etc How to replace an R230 BCM (Battery Control Module) | SL55 Build pt 15 - YouTube

 

[ChrisPDuck]

That's a useful diagram, thank you.

So I wonder what conditions have to be met for relay K57 to close.

Is it just a conventional split charge relay, like you might see in a camper van for instance, such that it only needs to see some alternator output for it to close? In my camper van, the voltage on the alternator exciter wire (which is used to extinguish the battery light on the dash) is also used to close the split charge relay - it means the batteries are separated when the engine is off, but connected when it's running. I realise the system probably won't be that simple in your car, but maybe there's a signal wire that would do the same job in the BCM as the exciter wire (i.e. to confirm that the alternator is running), and maybe that wire has broken or is making a bad contact. If you can see the back of the alternator, you could check for such a wire.

Or are there some 'smarts' inside N82/1 that check for other conditions, in addition to sensing some output from the alternator? Maybe the consumer battery has to get up to a certain voltage before the relay closes. I'm only speculating about 'priority', but this could be where the 'priority' of the consumer battery over the starter battery might be applied, and I'd doubt you can change that. But if the BCM needs to see a certain voltage at the consumer battery, I can't help thinking 14.1V is a fraction low - mine is nearer 14.5V I think - and maybe it's not passing the required threshold. Again, just thinking out loud. But if this IS the issue, and assuming your consumer battery is in good shape and is fairly well charged, then the slightly low 14.1V could be due to the voltage regulator.

Just to confirm - are you saying that you never see a charging voltage on the starter battery, no matter how long you leave the engine running? Does your starter battery eventually go flat - is that what alerted you to the issue?

*EDIT: If the relay DOES require a certain voltage on the consumer battery, that makes the system more similar to a VSR (voltage sensing relay) that some people use in a camper van for a split charge system.

*EDIT2: The wiring diagram does in fact show that the consumer battery has priority - it is permanently connected to the alternator, and the starter is connected in by the relay, according to whatever conditions the BCM applies. This is the other way round compared to most camper vans for instance, where the starter is prioritised over camping consumers, on the basis that most people would prefer to be able to drive home!

 

[zeppelin22]

That's a useful diagram, thank you.

So I wonder what conditions have to be met for relay K57 to close.

Is it just a conventional split charge relay, like you might see in a camper van for instance, such that it only needs to see some alternator output for it to close? In my camper van, the voltage on the alternator exciter wire (which is used to extinguish the battery light on the dash) is also used to close the split charge relay - it means the batteries are separated when the engine is off, but connected when it's running. I realise the system probably won't be that simple in your car, but maybe there's a signal wire that would do the same job in the BCM as the exciter wire (i.e. to confirm that the alternator is running), and maybe that wire has broken or is making a bad contact. If you can see the back of the alternator, you could check for such a wire.

Or are there some 'smarts' inside N82/1 that check for other conditions, in addition to sensing some output from the alternator? Maybe the consumer battery has to get up to a certain voltage before the relay closes. I'm only speculating about 'priority', but this could be where the 'priority' of the consumer battery over the starter battery might be applied, and I'd doubt you can change that. But if the BCM needs to see a certain voltage at the consumer battery, I can't help thinking 14.1V is a fraction low - mine is nearer 14.5V I think - and maybe it's not passing the required threshold. Again, just thinking out loud. But if this IS the issue, and assuming your consumer battery is in good shape and is fairly well charged, then the slightly low 14.1V could be due to the voltage regulator.

Just to confirm - are you saying that you never see a charging voltage on the starter battery, no matter how long you leave the engine running? Does your starter battery eventually go flat - is that what alerted you to the issue?

*EDIT: If the relay DOES require a certain voltage on the consumer battery, that makes the system more similar to a VSR (voltage sensing relay) that some people use in a camper van for a split charge system.

*EDIT2: The wiring diagram does in fact show that the consumer battery has priority - it is permanently connected to the alternator, and the starter is connected in by the relay, according to whatever conditions the BCM applies. This is the other way round compared to most camper vans for instance, where the starter is prioritised over camping consumers, on the basis that most people would prefer to be able to drive home!

Confirmed never had charging voltage on starter. Will put consumer on charge tonight to see if threshold at 14.5V makes any difference. Will also remove/test K57 relay.

I did notice this thread ref similar issue on a W221, fault resolved with new wire into BCM W221 2008 S320 CDI Starter Battery Charge Issue URGENT HELP REQUIRED! | Electronics and Audio | MBClub UK - Bringing together Mercedes Enthusiasts

Could someone please ping @DieselBenz for me, show this thread, I can't message as a new member here, thanks

 

[ChrisPDuck]

It certainly seems as though the wire that mbenz1 was referring to in that thread could serve the same function as the exciter wire on an older dumb alternator, in that it tells the BCM that the alternator is running and then the BCM closes the relay. I can't see the equivalent wire on the circuit diagram that you posted earlier though.

I think your @Diesel Benz should have been enough to alert him (apart from the space in his username, which is why I've done it again).

 

[Diesel Benz]

I've never had any R230 and I'm not familiar with the model. It has a similar dual battery approach as the pre-facelift W221 but they are not exactly the same.

The R230 is relatively simple:


The alternator is connected to the consumer battery, protected with the 200A f2 fuse. The battery control module connects the starter battery to the consumer battery (to charge the starter battery) either by the K57 relay or the internal DC/DC converter.

The dual battery function description can be found from WIS gf54.10-p-1001r. Google finds it too.

Without proper knowledge about the R230, I feel the f1 fuse must have blown in the emergency start mode (where the K57 is exceptionally closed during starting) or after that from excess consumers (should be less likely). Once the f1 is good, it should be relatively easy to check the wiring from the starter battery to F52 and further to N82/1.

Measuring the voltage at each pin would tell if charging works but measurements need to be done when the car is known to charge the starter battery. That does not happen all the time when the engine is running. Charging stops when the starter battery SOC is good.

 

[ChrisPDuck]

That's a useful diagram and document, thank you. For completeness, are you able to explain the role of the DC/DC converter? The PDF seems to imply that the relay has sole responsibility for connecting and disconnecting the two batteries. Is the DC/DC convertor perhaps used for the 'floating operation mode' - i.e. when the starter battery is fully charged the batteries are disconnected, but the starter battery continues to receive a float charge (presumably around 13.5V)?

 

[Diesel Benz]

Unfortunately I have to count on the function description document as I'm not familiar with the model. We have many R230 experts onboard, would be nice to have some comments based on experience with this car.

The function description is actually a bit vague or confusing. It says N82/1 works on the basis of starter battery temperature and voltage which is only possible if the starter battery is not connected to the consumer battery with K57 (if K57 was closed, N82/1 would only see the alternator voltage which is the consumer battery charging voltage). The document also says the starter battery is disconnected from the consumer battery once the starter battery is fully charged. This gives the impression that K57 was always closed until when starter battery was charged. My interpretation is that this sentence only refers to the limp-home mode.

The N82/1 operating states include two where K57 is closed and neither one is normal operation. The normal mode must use the DC/DC converter to charge the starter battery when K57 is actually open. This way N82/1 can properly control starter battery charging, also taking into account the starter battery voltage separately from the consumer battery (G1).

K57 would be closed for starter battery charging only in a scenario where G1 has undervoltage and the car is not sure G1 is able to supply sufficient current for safe driving.

"Floating" mode does not seem to be any specific N82/1 operating mode as it is not included in the table with that name. Actually the normal mode is where the two batteries are "floating", not directly connected with K57 but current flow controlled "intelligently" by N82/1.

Because of the DC/DC converter with a bit unclear current characteristics, it actually gets a bit difficult to conclude a lot by simple voltage readings from different points. In normal mode we do not know which charging voltage N82/1 aims at.

 

[ChrisPDuck]

I think you're right, and I had it backwards. It seems that the relay is only closed for 'Emergency Start' and 'Limp-home mode'. At all other times the starter battery is charged via the DC/DC converter. This probably explains why my starter battery didn't start charging immediately when the engine started, and why I observed the voltage gently rising when it did so - the DC/DC converter is much more like an intelligent battery charger than a simple split charge relay. It's quite an impressive system in fact.

It also, as you say, makes it tricky for the OP to trouble-shoot. The relay seems like a bit of a red herring, and the focus should be on N82/1 and its inputs/outputs.

 

[Jobsworth]

I’ve never properly got my head around how the BCM on the r230 works. I keep a new unit on the shelf, as I have found the only sure-fire diagnosis is by substitution.