Alternator problems e280

FREDDEE

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Hi, this is my first time posting on any forum so you might have to bear with me, I have just got an E280(p reg) and the battery keeps going flat , I think it's the alternator that's the problem but don't want to get another and find that it's not, I currently have a C180(p reg) sat on drive with immobiliser problems, is the alternator the same and could I use that one?
Any help would be appreciated as MB's are lovely cars to drive but I am starting to get fustrated with all the niggly little faults i seem to be having.
Thanks
 

joe1972

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First thing I would do is charge the battery, measure the voltage at the battery terminals, then start the engine & measure the voltage across the battery again. It should be about 1.0-2.0volts higher reading with the engine running. If it is not, then the alternator is not doing it's job. Check connections to the battery and from the alternator before rushing out and buying a replacement alternator tho.
Alternatively, does the battery go flat after charging with the car parked up (over night for example)? Or, do you need to be out on a run for it to go flat. The former suggests a duff battery (after checking no lights left on etc), the later suggests a duff alternator.

You might also find this useful...it's more detailed than my summary;
http://www.carbasics.co.uk/How_to_test_your_alternator.htm

If you've not got a mulitmeter, try getting a battery/alternator tester. As easy to use and only normally cost a few pounds (my multimeter is tucked away 'somewhere' in the garage, so the tester I got from either wilkinsons or a pound shop, can't remember.).

good luck
 
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television

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Welcome Fred to the forum.

If the alternator was not working, the lamp would be lit in the display(might be dimly lit)

A voltmeter would be useful to confirm, as Joe said they only cost £4 The battery voltage should be 12.5 volt with engine off, and around 13.8 volt with the engine running. If 13,8 volt running then nothing wrong with the alternator.

The battery, if more than 4 years old could have a high resistance cell,, the effect is the car runs perfectly all day, but the following day it will not start. so new battery needed.

You could have a faulty ECU that is draining it and a current check would confirm that.

Could you swp the battery over from your other car to try
 

BlackC55

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How old is the battery?

When the engine is running you should get 14.4V
 
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FREDDEE

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thanks for all your suggestions and sorry it's taken so long to reply, but it turns out the alternator is fine and it's possibly alarm system that might be draining the battery ,still investigating
 

television

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thanks for all your suggestions and sorry it's taken so long to reply, but it turns out the alternator is fine and it's possibly alarm system that might be draining the battery ,still investigating

Thanks for the update it could be the alarm siren
 


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