Can one increase the rate of charge to the battery?

[Pitts Pilot]

Is there a way of increasing the charging rate to the rear battery in my SL?

And would this be a good idea anyway, given that it is a battery designed for low-mid current use, not high current use, like the front engine/starter battery? I'm thinking too much charging amperage might create too much heat, etc?

It all started less than a year ago when I had the existing MB 'stereo' stripped out and a new 'upgraded' audio system installed by Comand On Line. This transformed the In Car Audio/Nav, but the new system does draw a greater amount of power from the rear 'convenience' battery.

I find that if I make short trips around town the folding roof won't work unless the engine is running - low battery voltage. (I did renew the battery with the MB spec' one when the new system was installed, just to be thorough).

The heavy demand on the rear battery is not that surprising as I now have a 700 watt amplifier, and I listen to my music much more than I ever did before (because it sounds SO good! ).


So an upgraded audio system with an amplifier that can, in theory, draw 58 amps from the rear battery at max output (Windows shatter, in nearby houses....) does need a helping hand at the battery end of the setup.

With this in mind, I presume the MB charging unit has a fixed maximum output? So 'turning it up' probably isn't possible?

How about changing the unit for one that 'steals' some current from the front battery? (I would like to avoid upgrading the alternator!)

Has anyone else found that their modern ICE makes greater demands on their car's battery?

Thanks

Robert

 

[edstrom76]

Yoy don't say how old the car is but typical lifespan of a battery is 5-6 years. If your car is newish, an alternative to replacing your battery which wouldn't be so costly is to have a trickle charger installed. CTEK are meant to be among the best: www.ctekchargers.co.uk


This would also prevent getting caught out with a flat battery on a cold winter morning.

 

[BlackC55]

Fit a capacitor to the audio system.

 

[Dieselman]

You need an uprated alternator.

 

[grober]

Try downloading this zip file and then have a look at the electrical section/battery.

MBUSA Technical Training

Because your new amplifier setup may be making peak current demands on the convenience battery this may be enough to drop voltage sufficiently to trigger the Vehicle power supply control module (BNSG) to start switching off "non priority" consumer electronics such as the roof to protect the power supply of safety-relevant electrical consumers (e.g. electrohydraulic brake, easy-shift manual transmission etc ) and stabilizing the vehicle electrical system voltage. While the voltage drop maybe transient its enough to trigger this. Your car will have a 150 amp water cooled alternator so I doubt if charging is the problem Its more likely to be peak current demand hence Olly's [Black C55] suggestion that a capacitor IN THE POWER SUPPLY might make help smooth out these peak demands. At the heart of this is the fact that car electronics really need to move to 24volt or even 48volt systems to cope with today's higher electrical loads.

 

[BTB 500]

I find that if I make short trips around town the folding roof won't work unless the engine is running - low battery voltage.

It may be that you're supposed to have the engine running when you operate the roof anyway - what does the handbook say?

And are you sure the roof operates from the convenience battery?

If the car is used for short runs then a maintenance charger (as mentioned) would be a good idea. Car batteries are designed to be fully recharged straight away, and lifespan is shortened if they are left standing partially discharged.

My SL is kept on a maintenance charger and the battery is now 9 years old.

 

[BTB 500]

You need an uprated alternator.

That could well help if the OP does a lot of short trips with headlights, seats, HRW, etc. all on.

Charge rate is governed by the supply voltage, which is fixed (regulated). The standard alternator should easily be able to deliver the charge current resulting from that voltage to the battery - one with a higher output current rating won't deliver any more. But if a lot of electrical power is being used elsewhere at the same time (in addition to charging) then the current limit of a standard alternator can potentially be a restriction.

 

[dave e320]

+1 uprate alternator

 

[Dieselman]

With the additional 700w+ (58A) load the battery isn't being charged due to lack of current. Only a more powerful alternator can overcome that deficit.

The load is like running the starter motor on 1/3rd duty continuously. The alternator can't keep up with that.

 

[bolide]

AFAIK the charging is essentially self-regulating - the battery will charge more when the charge is low and less when it's fully-charged. That's a function of the battery

In your case you are pulling more energy out of the battery than you are putting in. There's no way round that apart from longer drives or a battery charger

A capacitor won't help as it doesn't store enough energy to change things. A bigger battery won't help much as you lack charging

I'd fit a charging socket on the car and plug a charger in when it's not in use

The actual load from the additional ICE will be pretty small on average. Your 700 Watt amp will be delivering a couple of Watts most of the time, and consuming a bit more than that.

Nick Froome

 

[BTB 500]

With the additional 700w+ (58A) load the battery isn't being charged due to lack of current. Only a more powerful alternator can overcome that deficit.

The load is like running the starter motor on 1/3rd duty continuously. The alternator can't keep up with that.

If the standard alternator is rated at 150A it's able to deliver well over 2 kW (assuming 14V).

 

[grober]

[YOUTUBE]Fv66sP9EXvQ[/YOUTUBE]

[YOUTUBE]H5MP5F-uJAw[/YOUTUBE]

ps I assume the 700 watts is not an RMS figure but rather a music power one??

 

[Dieselman]

If the standard alternator is rated at 150A it's able to deliver well over 2 kW (assuming 14V).

Is it rated at 150A?

 

[BTB 500]

Is it rated at 150A?

Grober mentioned this above. I know the 639's standard alternator is 180A, so it sounds quite feasible.

 

[Dieselman]

Grober mentioned this above. I know the 639's standard alternator is 180A, so it sounds quite feasible.

The O/p does mainly short journeys so a fair percentage of the alternator output will be taken in replenishing the starter draw.

 

[grober]

Is it rated at 150A?

Sorry I got that wrong. The 500SL has 150 watt alternator the 350 has a 180 watt alternator. ALTERNATOR ELECTRICAL EQUIPMENT AND INSTRUMENTS íà Mercedes SL 350 (230.458) | Êàòàëîã çàï÷àñòåé Mercedes, ïîäáîð àâòîçàï÷àñòåé äëÿ ëåãêîâûõ àâòîìîáèëåé Ìåðñåäåñ (ðåãèîí Åâðîïà) ïî àâòîêàòàëîãó.


ps its entirely possible of course the alternator is no longer putting out as advertised!

 

[V12]

Your upgraded sound system should draw power from your main battery.
The convenience battery just isn't man enough.

58amps is no where near enough current draw to cause you issues. I'd imagine under most circumstances you'll be using <10A.

As an example I have DLS Ultimate amps, A6 for the sub (140A) and A3 for front speakers (140A).
Although that's a potential current draw of 280A, I have no upgraded alternator and no second battery. Never had an issue.

If I played the system flat out 100% of the time then I would have big issues, but not under normal circumstances where the current draw is very small.

I recently changed my battery as a precaution as the last one was at least 5 years old and winter is coming. VARTA BATTERY H3 100AH 830A SILVER dynamic type 019 | eBay

£85 for a top quality 100A battery.

 

[GordonTarling]

Sorry I got that wrong. The 500SL has 150 watt alternator the 350 has a 180 watt alternator.

Don't think that can be right - at 12 Volts, 180W is only 15 Amps. According to Wikipedia, most cars' alternators are rated at 50 to 70 Amps.

 

[V12]

He means 150A not 150W.

Wikipedia is so outdated, or they are just referring to smart cars. 50-70A is tiny!

 

[grober]

Sorry again getting me units mixed up again. 180amps