Can one increase the rate of charge to the battery?

[V12]

http://www.mercedestechstore.com/pdfs/W211_technician/319%20HO%20Dual%20Battery%20(ACB%20-%20ICC)%2011-29-02.pdf

http://www.mbclub.co.uk/forums/elec...venience-functions-temporary-unavailable.html

http://www.mbclub.co.uk/forums/part...149662-211-219-small-convenience-battery.html

http://www.mbclub.co.uk/forums/elec...enience-functions-temprarily-unavailable.html

Just a few threads I quickly found, only skimmed them but should indicate the same problem.

 

[Dash1]

The main battery is weak so instead of a quick 1 minute to recharge it sufficiently to pre start condition, it's taking up to 10 minutes or so.

The system is effectively an over complicated split charge system with a fancy ecu instead of a basic relay.

I'll see if I can find the document that details how it works.

My understanding is that the aux battery won't receive charge until the control unit is satisfied with the condition of the main battery.

Hi Pitts Pilot,

As V12 has already tried to explain to you, the R230’s Dual Battery Electrical System is an extremely complicated and complex starting/charging circuit to understand. I really haven’t got the time at the moment (until the weekend anyway) to go in to all the “inn’s” and “outs” of how the system is configured and works, suffice it to say that the vehicles electrical systems demands solely relies upon the main starter battery - 12 volt 35Ah unit as additional power support in the event that the vehicles systems battery - 12 volt 70 Ah unit falls below its functional threshold voltage below 10.8 volts.

The systems battery (in the boot) only supports the main vehicles systems functionalities and plays no part whatsoever in the starting circuit other than to supply voltage to the starter solenoid only. The starter current is only supplied to the starter motor armature from the starter battery (under the bonnet).

As V12 has also pointed out, the starter battery may very well be in a low “state of charge” at the moment, therefore, being unable to give this additional support. With the engine running, the alternator charges the systems battery directly, and not the starter battery, the starter battery is only charged through a DC/DC converter within the control module at a maximum of 15 amps based upon the starter battery voltage following cranking and temperature measurements using the ambient and coolant temperature sensors over the CAN bus from the ECM

If you wish, and as a temporary measure, you could connect another battery in parallel to the starter battery (jump leads required) and leave it connected whilst you then test the system to confirm as to whether or not it is actually faulty/discharged. If everything now performs, as it should, then replace the starter battery. Also, don’t lose sight of the fact that you could very well have some additional underlying problem here and it may not be the battery at all. Have you also checked the charging rate, this should be within the region of between 13.6 volts to 14.4 volts - “off-load” - with everything turned off and the vehicle running up to 2000 rpm, the higher to the 14.4 volts the better.

Hope this info is of some help.

Best Regards,

Dash1

 

[Dieselman]

the starter battery is only charged through a DC/DC converter within the control module at a maximum of 15 amps based upon the starter battery voltage following cranking and temperature measurements using the ambient and coolant temperature sensors over the CAN bus from the ECM

You would have thought Mercedes could come up with a more elegant solution than that.
How much energy is wasted in a DC-DC converter?

 

[bolide]

The battery voltage should sit at about 12.5 Volt with no load and go to about 14.4 Volts when charging from the alternator. Anything significantly different to this would imply a problem

I think Dash1's point about an underlying problem is well made. I would expect the setup to be fine with an additional amplifier. That fact that it appears not to be might signify that the system was marginal anyway and there is an underlying fault

You could measure the charging current with a clamp meter but the charging voltage will tell you a lot. If you do test the charging current then please test to both batteries

Nick Froome

 

[Dash1]

You would have thought Mercedes could come up with a more elegant solution than that.
How much energy is wasted in a DC-DC converter?

Hello DM,

I am extremely sorry for the delay in answering your post, so my apologies, it’s not always possible or indeed convenient to come on the forum during the day or whilst I am at work, I do sometimes have to wait until I get home at weekends, and even then, I don’t always find the time. Yes, I do tend to agree with you on the above, you would definitely have thought given their resources that MB would offer up something more elegant than this, however, this system is pretty much dated by comparison now compared to the SMART charging systems available today, which were available when this system was actually designed and developed. This system gets slightly more complicated than I previously mentioned, during the emergency operation, (limp home facility/loss mode) on this model of car anyway, the charging circuit for the starter battery is diverted away from the DC-DC converter and is “quick charged” for up to 5 minutes directly from the alternator via a switched relay circuit until sufficient charge is accepted by the starter battery, which is monitored by the control module. This system really is overcomplicated for its intended use, probably inherent in its design and function anyway to stop others effecting its repairs outside of the dealer network, which seems to work in their favour to some degree I suppose, unless, you understand how the system works and have the ability and skills to repair it.

Quote – “How much energy is wasted in a DC-DC converter?”

That is a very good question indeed, and as an engineer, to an engineer, I would look at that issue from a totally different perspective and then asked the question - what are the benefits in using a DC-DC converter, and do these benefits far outweigh any inefficiency. It really does depend upon which way you wish to view it and the choice of the converter that is employed within the system. In percentage terms, then the best available DC-DC converter controlled systems with fet technology processes and pulse width modulation, then, “allegedly” these systems offer up as much as a 95% efficiency, compared to the lowest figure of a really sub-standard DC-DC converter at only 65%, so at best - 5% inefficient and at worst 35% inefficient. Although Bosch manufactures this DC-DC unit, I don’t have the specific manufactures data on the exact model/specification itself as it is and forms part of the control module anyway. To give a very accurate analysis of the total power losses in the conversion process anyway, you would need to establish exactly what the power - volts x amps (watts) are on the input side and then calculate the same on the output side. The only true “manual” way to do this would be to place a voltmeter in parallel and an ammeter in series on the input side and the same set-up on the output side with an additional oscilloscope facility in-between to view the waveform patterns and measure the time frame duration. Although MB do state that charge rate can be as high as 15 amps on the output side, so it is variable and would depend upon the discharged state of the battery at the start of the charging process, and this in itself will alter following any starter cranking current draw to cranking current draw situations over different ambient temperatures anyway during winter/summer months. Typically, 120/140 in the summer and between 140/180 in the winter, neglecting any additional frictional losses on oil viscosity, transmission drag etc.

The only data that I have on this car are the wiring schematics and diagrams, which only show the control module. Inside the control module it just indicates a DC/DC conversion process, no more than that, refer to the wiring diagram which I have labelled the components on for easy identification purposes and attached below, it doesn’t stipulate which type, therefore, I can only assume it to be no better than the typical DC-DC converter of the generation as mentioned above - take you pick, input to output data, less the inefficiency in the conversion process either measured in units of percentage efficiency, inefficiency, watts or energy, it doesn’t really matter that much, you would just convert one unit to the other given the voltage/amps units to work with. Funnily enough, at one time a very long time ago now in the electronics industry, the DC-DC converter family was often thought to be the worst of any “boost” energy conversion process and was given the infamous title as the “joule” thief, not so much that today though given the modern systems “circuit-switching” technology.

If you look at the photo of the module in the pdf file that I attached below, you will see that it is quite a large unit (approx 8”x 4”x 2”) manufactured in a cast alloy case, which serves as the heatsink to dissipate any excess heat above 10 degrees centigrade. If you look at the bigger overall picture, then there is a benefit to the split charging circuit, it means that the demands placed upon the alternator only serve and has one system to look after, (unless in limp mode for up to 5 minutes where it charges both batteries) whereas, if it was a conventional charging circuit, then the alternator has two batteries to maintain and charge, therefore necessitating possibly a larger alternator with a bigger output which in effect places a greater demand on the engine itself to rotate it under extreme and demanding conditions. As you originally suggested in one of your posts - put a larger alternator on the vehicle, you could do that, but it wouldn’t serve any purpose on this particular vehicle given the layout and configuration of the system, it is still controlled, monitored and processed by the control unit. This is the only problem with “power-management” controlled systems, they can “mask” problems that really are there and “flag” faults that aren’t there.

I hope you find the attached pdf file and electrical schematic diagram below on the R230 charging circuit/system beneficial and informative, I would assume that someone such as yourself would appreciate and express an interest in this anyway, however, Pitts Pilot may also find it of some benefit. Your thoughts and observations after reading the attached material would be interesting to know though, I hope its of some use to you. To the OP, I am extremely sorry for digressing slightly away from your issue at the moment, but I like to try and answer any question as and when I can.

Best Regards,

Dash1

 

[Dash1]

Attached Links.


http://www.mercedestechstore.com/pdfs/507%20Systems%20I/507%20HO%20R230%20Dual%20Battery%20System%20%2011-28-02.pdf

 

[V12]

That's a great document. I had presumed the system was identical to that in the W211.

 

[ivan1983]

I think the problem may be the way the system is wired.

In my old car the amps and head unit were able to draw a max of about 110A, and my alternator was only rated at 90A, but these systems very rarely draw close to maximum current for more than a short period of time unless you are listening to continuous bass lines. If crawling in first with no throttle the extra alternator load would appreciably slow the car on heavy bass lines but I never had any battery issues.

It may have already been mentioned but why dont you re wire the amp to run off the main battery.
In reality the battery is effectively a charge store/smoothing unit and the alternator is your power source. It seems that the split charge system is limiting the current available to the secondary battery which is flattening your battery as it cant keep up with the amps demands and also means that your amp is not as "punchy" as it could be.

The stock alternator if functioning correctly is more than adequate for a system much more demanding than this.

You should not replace the front battery with a deep cycle battery as they are not designed for the massive current draw of starting an engine, they are designed for situations where the batery is cycled from full to empty which would kill a normal car battery very quickly.

 

[Pitts Pilot]

I think the problem may be the way the system is wired..... It may have already been mentioned but why don’t you re wire the amp to run off the main battery.

I am coming to think this is the way to go.

However, why do Comand On Line, a very professional firm who specialise in ICE for Mercedes, wire the amp to the rear convenience battery? Perhaps Richard or Rob could explain? There is bound to be a good reason.

The rewire would involve some considerable upheaval; seats out, centre console taken apart, etc. The cost would be interesting!

 

[Pitts Pilot]

Your thoughts and observations after reading the attached material would be interesting to know though, I hope its of some use to you. To the OP, I am extremely sorry for digressing slightly away from your issue at the moment, but I like to try and answer any question as and when I can.

Thank you for the explanation which I found very helpful
I had no idea that MB had a charging and battery monitoring system that rivals the one on the Space Shuttle. Is such complication really necessary I wonder?

The .pdf is surprisingly clear and straightforward to understand, and I’m not a MB technician.

One thing did catch my eye was the sophisticated battery tester. I have put a mere multimeter on both batteries and they seem to be charging OK. I get 14.4 volts across the engine battery when ticking over, so the alternator is clearly functioning OK.

However, % of life and internal resistance are two things I would be interested to know.

Both batteries have spent some time recently on my Optimate 4 battery conditioner, but there is no way of really knowing how they are performing under load.

One of the ‘emergency’ things the System clicks into is to allow the roof to close only. I currently have this situation, ie. I need the engine running to open it, but I can close it without the engine – a safe guard built in to the Charging System that I spotted on the .pdf.

Is a Battery Analyser something that folk tend to own, or should I just take the car to a garage that has one?
The .pdf shows a Midtronics MCR 717, but this may be out of date. I found this for £99, (there aremany others). It might be worth the investment if you have an SL with a complicated charging system?

http://www.tantronics.co.uk/acatalog/Ring_RBA600_12V_Digital_Battery_Analyser.html#abac_2drng_2drba600

Of course, for the same money I could replace the engine battery, I suspect, and that would probably solve my wows for now!

Thanks again for the time and effort in explaining things

Cheers,
Robert