AC current.

May 5, 2020 | 07:12 PM

James Hewitt

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S320CDi

AC current.

At idle engine there is AC current at the battery terminals, is this normal?
I am getting approx V 3.2 AC being produced by the alternator.

May 5, 2020 | 07:59 PM

kraut56

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From: Montreal, Quebec

2009 E350 4M Avantgarde;mistress 2002 S600; wife 2014 C300 4M

How do you measure this?
Alternators produce AC current, that is rectified with diodes.
A bad diode can produce excess ripple, but you need some know-how to detect that.

May 5, 2020 | 08:12 PM

James Hewitt

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S320CDi

Quote:

Originally Posted by James Hewitt

At idle engine there is AC current at the battery terminals, is this normal?
I am getting approx V 3.2 AC being produced by the alternator.

Reading is done with a multimeter at the battery terminals with the engine running.

May 5, 2020 | 08:14 PM

James Hewitt

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S320CDi

Reading is with a multimeter at the battery terminals with the engine running.

May 5, 2020 | 10:07 PM

kraut56

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From: Montreal, Quebec

2009 E350 4M Avantgarde;mistress 2002 S600; wife 2014 C300 4M

What's the problem?
You measure at the Battery DC, not AC.
Is it charging properly?

May 5, 2020 | 10:52 PM

James Hewitt

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S320CDi

There AC and DC current at the battery terminals.
The battery charges but after a short while the HID headlights starts to flicker and there is interference in the radio.
The battery looses charge overninght.

Last edited by James Hewitt; May 5, 2020 at 11:38 PM.

May 6, 2020 | 07:23 AM

joseluu

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W221 S500 2010

The condition of that alternator does not sound good to me. Maybe the regulator is gone.

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May 6, 2020 | 07:57 PM

kraut56

Super Member

Joined: Sep 2012

Posts: 690

Likes: 76

From: Montreal, Quebec

2009 E350 4M Avantgarde;mistress 2002 S600; wife 2014 C300 4M

Quote:

Originally Posted by wallyp

Sounds like a shorted diode.

Most auto parts stores are able to test an alternator.

Fully agree!
One way to check, after the car is completely is cold, to have the charger connected, and access the alternator and touch it.
With a shorted diode(s) it will be warmer than ambient.

May 9, 2020 | 06:13 PM

#10

kraut56

Super Member

Joined: Sep 2012

Posts: 690

Likes: 76

From: Montreal, Quebec

2009 E350 4M Avantgarde;mistress 2002 S600; wife 2014 C300 4M

Soooo.... how about an update????

May 10, 2020 | 08:40 AM

#11

Kebowers47

Senior Member

Joined: Apr 2019

Posts: 428

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From: Houston

001 s600, 94 sl600

Dear Mr Hewitt--one of the 'unwritten rules' of Forums like this one, it to follow-up and let the others know the results of their attempts to help you, even if you don't do anything. 'Belonging' takes some 'effort' , and to not respond is unfair.