Battery charging

[Matt45]

Done a bit of looking through the posts but can't find a ref to this so thought I'd let you all know as it's winter.

Had a poor battery recently due to the car being prepped and all the toys being tested and used etc. Sorted it out by a trickle charger and some miles but:

When I asked the local stealer if the battery was OK etc and about warranty claims they advised me that if I wanted to charge the battery faster I should put a drain in the electrics like the lights or something. They said by putting the lights on the alternator recognised the load and increased the charge rate. Sounded a bit odd at first but more than one dealer has told me the same thing. They tell me they leave their cars running on the fore-court with the headlights on to give the batteries some juice. They charge faster with a load, so, perhaps give your car a chance this winter by running in daylight with the lamps on.

Anyone else heard of this?

Matt

 

[television]

Done a bit of looking through the posts but can't find a ref to this so thought I'd let you all know as it's winter.

Had a poor battery recently due to the car being prepped and all the toys being tested and used etc. Sorted it out by a trickle charger and some miles but:

When I asked the local stealer if the battery was OK etc and about warranty claims they advised me that if I wanted to charge the battery faster I should put a drain in the electrics like the lights or something. They said by putting the lights on the alternator recognised the load and increased the charge rate. Sounded a bit odd at first but more than one dealer has told me the same thing. They tell me they leave their cars running on the fore-court with the headlights on to give the batteries some juice. They charge faster with a load, so, perhaps give your car a chance this winter by running in daylight with the lamps on.

Anyone else heard of this?

Matt

For a start alternators are not designed for charging flat batteries, secondly the max voltage that the alternator gives is 13.8 volt, so what ever you turn off or on you cannot charge at more than the 2 volts difference. the lights are a load, but the battery is not seen as such, if putting the lights on raises the voltage then the charge rate will also increase in proportion.

Still not a good way for the problem

 

[Matt45]

You're right, but the battery wasn't flat, just in need of some decent charge. I was getting the usual 'convenience functions unavailable' warning. I was advised to either run it for an hour or so or put it on charge, so I chose the later. It's been fine ever since.

 

[fredfloggle]

Done a bit of looking through the posts but can't find a ref to this so thought I'd let you all know as it's winter.

Had a poor battery recently due to the car being prepped and all the toys being tested and used etc. Sorted it out by a trickle charger and some miles but:

When I asked the local stealer if the battery was OK etc and about warranty claims they advised me that if I wanted to charge the battery faster I should put a drain in the electrics like the lights or something. They said by putting the lights on the alternator recognised the load and increased the charge rate. Sounded a bit odd at first but more than one dealer has told me the same thing. They tell me they leave their cars running on the fore-court with the headlights on to give the batteries some juice. They charge faster with a load, so, perhaps give your car a chance this winter by running in daylight with the lamps on.

Anyone else heard of this?

Matt

There are two sorts of alternators - machine sensing and battery sensing .

A machine sensing device will maintain 13.8->14.2 volts at the rectifier and doesn't care what the battery gets out of that .

A battery sensing device has a sensor wire that goes separately to the battery and the alternator modulates its rectifier to the actual voltage at the battery posts so that volt drops are not important.

Remember that a fully charged battery will show 13.8 Volts for a short period only the float charge soon dissipates and the battery drops back to 12.7 volts - the effect of leaving the lights on is to encourage a lazy battery to drop back to its nominal voltage .

Remember that the alternator is not really suitable for fully charging a battery because all automotive batteries are charged so as to avoid excessive heating and loss of water from the electrolyte.

Of course the alternator is more than happy to kick out high currents to feed accessories, but this current is useless unless there is a PD between the alternator and the battery .

Stick a meter across the battery while it is being charged , then switch the lights on - it will answer your own question .

Cars with twin batteries also suffer from volt drop across the diodes , all the more reason why the batteries never get charged much more than 65%, and if you check , I bet your alternator kicks out more than 13.8 volts , Just checked mine and it is at about 14.4 Volts.

 

[Matt45]

Thanks, I'm impressed.

 

[fredfloggle]

I did a job years ago for Holland and Holland , charging their truck batteries for the clay traps - with good equipment to get 85% capacity is not too much problem but to get the last little bit is very much a dark art and takes a lot of work to achieve.

 

[Matt45]

The charger I used to top up the rear battery was only a cheap one I borrowed, but in a couple of hours I had it showing fully charged and it's been fine ever since. The front battery has always been good and MB tested both for me when the problem occurred and told me they were both in good condition. Better still they tell me they are both warranty items and so if I have any more probs thay will exchange them for me. Rather pleased that they are both fine though regardless of the replacement offer. I think the rear one got used alot when the car was in the show room - the roof was always going up and down to show customers but without getting a good run to put back the juice.

 

[television]

Just adding while on this subject, all of the above on charging current is part of the voltage, and you cant have one part without the other, they also work hand in hand.
When the battery is hooked up to the car, there are these days wake up circuits and these are always live.

Now to increase the charge rate you have to increase the voltage, thats OK to a point where it gets dangerous as the voltage can rise beyond the safe working tolerance of the rear SAM units in the wake up circuit.
You can pretty well safely charge up to 4 amps without problem as the voltage will be around 14volt, this said the 203 cars do blow the rear SAM very easily. If some one sticks a jumper on the car, you can often expect a large bill in return.

The 230 are quite safe in this respect, except when the rear car battery goes flat.

These are whats known as AGM batteries and are dry, and can be mounted anywhere or any way up. The most important thing is the charge rate and the type of charger.
They should really be charged from flat with a constant charge rate of 10% of the battery capacity,
You cannot use an automatic charger on them, as they will shorten the life of the battery, an auto one is OK for a weekly top up, but do start the car then connect the charging leads, then plug it in,then turn off the car

 

[Matt45]

Thanks Malcolm, I'll remember that if I ever have to use a charger again. MB did try and sell me a charger [£30] and didn't mention any of the risks but then they wouldn't. I opted for a quick charge from my borrowed charger and all seems well now. I think the car just needed to be used and not fiddled with by potential buyers. There was a vacuum prob with the drivers seat on delivery and I think their messing about with it gave the battery a good caining. But now I've done plenty of stable miles, it's all as it should be.

Thanks again for the info. Matt

 

[television]

Thanks Malcolm, I'll remember that if I ever have to use a charger again. MB did try and sell me a charger [£30] and didn't mention any of the risks but then they wouldn't. I opted for a quick charge from my borrowed charger and all seems well now. I think the car just needed to be used and not fiddled with by potential buyers. There was a vacuum prob with the drivers seat on delivery and I think their messing about with it gave the battery a good caining. But now I've done plenty of stable miles, it's all as it should be.

Thanks again for the info. Matt

Dont get caught out like I was over the drivers seat, if neither seat works, tell them to turn the seats "on" there is a glitch in STAR where it say leak on drivers seat when there is not

 

[Matt45]

Originally neither seat lumbar support would inflate/deflate so got them to turn them on with a code. Then the drivers seat still wouldn't work and they found a trapped pipe so it was exchanged and all is fine now. I learnt how complicated things were on the SL when the seat air leak was causing the central locking pump to run on for about 30 seconds or more on unlock/lock. Luckily they traced the problem and got it all sorted, but I was a little concerned at first.

Something else you might be able to explain with your experience of the SL. With the wing mirror button selected to left the left wing mirror dips in reverse and returns when back in drive. If I select the right mirror and put it in reverse, should the drivers wing mirror dip also. It currently doesn't but I suspect it isn't meant to.

 

[television]

Originally neither seat lumbar support would inflate/deflate so got them to turn them on with a code. Then the drivers seat still wouldn't work and they found a trapped pipe so it was exchanged and all is fine now. I learnt how complicated things were on the SL when the seat air leak was causing the central locking pump to run on for about 30 seconds or more on unlock/lock. Luckily they traced the problem and got it all sorted, but I was a little concerned at first.

Something else you might be able to explain with your experience of the SL. With the wing mirror button selected to left the left wing mirror dips in reverse and returns when back in drive. If I select the right mirror and put it in reverse, should the drivers wing mirror dip also. It currently doesn't but I suspect it isn't meant to.

The left hand mirror only dip as long as its selected on the switch, so normal. The drivers does not dip

Yes re the seat there is a known problem where the pipe comes up into the seat and a small mod for that

 

[Ted]

While we're having an excellent tutorial on batteries/charging, heres another thing which is not often appreciated.
As a battery gets older/starts to fail, its internal impedence will go up (unless there is a short in a cell. This means that there will be less voltage supplied for a given load (usually starting).
The double whammy is that the when the reverse is true (charging) the battery will also reach the voltage at which the regulator is set more quickly, meanining thay it will take much longer to reach its already limited capacity.

So if your car is sluggish starting, AND quickly shows it is reaching 13.7-14.3 volts, you may have a battery problem.

 

[jac]

If i may ask a question here without starting a new thread. Can i charge the battery on a 2003 E500 without disconnecting it from the car and if i can what is the safest way to go about it.

Thanks jac

 

[television]

If i may ask a question here without starting a new thread. Can i charge the battery on a 2003 E500 without disconnecting it from the car and if i can what is the safest way to go about it.

Thanks jac

Do Take care with the 211, but reasonably safe at a low charge rate, this is where automatic chargers fail as they go up to max charge to find a level,and then drop down.

As above It you want to do it on the car, Start the car up (if you can) join the charger leads to the battery, then plug it in, if the indicated charge is no more than 4 amps, then you can turn the engine off.

If it is a switched charger, put it on low first, then after some hours you can turn it up providing it does not exceed 4 amps

 

[jac]

Thanks Malcolm, much appreciated.

jac