c220 cdi, w203, 2002, high voltage on battery

mb_fan

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Hi,
I have high voltage on battery checked by an analog meter at a garage, and the guy said the alternator is responsible. there were no numbers on the meter just red and green areas and the pointer went in red.

Is it confirmed to be alternator or is there any other device like a regulator that might be at fault?

its a 190Amp watercooled alternator, I recently had it replaced as the other one died mechanically.so still in waranty.

If I drive the car will it affect anything?
There is a battery light that comes up in the dash if I go over 80mph.

please help?
 

Cole@MBS

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It sounds like its overcharging, wouldnt like any thing over 14.50 volts as control units start to fry on the 203.s could just be a regulator?

Welcome to the forums
 
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mb_fan

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if regulator?

Hi thankyou,

If its regulator, where is it located?
If its inside the alternator then can i get to it without taking the alternator out of the engine?

If its located in a fuse box somewhere in the engine ?

If I can get to it then I can replace the diodes without taking it out as its a big job with this watercooled unit.
 

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Its on the rear of the alternator held in with 2 screws, i have always removed them to change due to the lack of space!!
 
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mb_fan

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from where to get hold of the regulator or diodes?
 

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I do not quite follow this,,the battery will hold the voltage down to a certain level,, The bit with the meter just going blank shows the the meter was set on the wrong range, had the next range been used the actual voltage could have been read out.

OK the lamp comes on at 80,,so the reg is at fault, so do change it
 
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mb_fan

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Hi, thnkyou for your help.
The meter he had was from stone ages. It had a switch for 12V of 24V.
Then on the dial it had green and red shaded areas.
The pointer moved to red on the far right side which meant that it was higher voltage than needed.

I think its overcharging the battery. guess its the regulator diodes.
just need to know where to get hold of them...may be farnell, and can i do it with the alternator still in?
if anyone has done it out there?
 

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Rappey69

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Wouldnt it be wise to actually check the charging voltage with a accurate multimeter before doing anything else?
 

television

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Wouldnt it be wise to actually check the charging voltage with a accurate multimeter before doing anything else?

Well to be truthful yes and why not,,someone who does not understand electrics can be a real pain, and do more harm than good
 
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mb_fan

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checking voltage at battery

Yes, I am going to check the actuall battery voltage with a proper meter tonight.

with the car in idle
and with car at high revs.

just to make sure its the same.

Because the dash light only comes on when I go over 80mph.

will post results.
 
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mb_fan

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will check tonight and post results.
 

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absolutely the voltage needs checking as a first measure. sometimes it is slightly higher than the 14.5v maximum in normal operation. to my knowledge the regulator/rectifier is not replaceable with two screws on this w/c alternator. if the batt light comes on at speed then ideally a voltage test needs doing at this speed. sounds like either an alternator fault or front sam, as this signals the batt light on w203s and controls charging to some extent.
 
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mb_fan

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I checked the voltage on the battery:

normal idle= 14.35 to 14.4V
higher rev = 14.65V

is this normal?
 

television

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Thats fine,,, its on its upper limits but many are, so happy motoring
 
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mb_fan

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thankyou very much to all of you for all your help on this.
 

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agree with television, not unusual voltage.
 

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Well to be truthful yes and why not,,someone who does not understand electrics can be a real pain, and do more harm than good

But, there's no suggestion that whoever tested the car didn't know about electrics - they simply used a bespoke tool, an analogue meter with colour shading on the dial instead of voltages to indicate pass / fail. It's a perfectly reasonable way to test, I have a very similarly marked meter, although it also has the voltage marked on it (as well as acceptable cranking voltages marked in red and green for various different sizes of battery). Using a moving coil meter can be advantageous sometimes where a voltage is varying - on a DVM*, you just see some fairly randomly updated numbers, where on the analogue gauge, you can see the needle swaying, and get an idea what's going on.

* unless you have a posh one which also has a bargraph

Where I do differ from whoever tested the car originally is that the voltage reported is a bit marginal, and I would probably have backed up the test by using a DVM too.
 
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