Alternator or regulator

[Sunshine26]

Hi everyone!
I've gotta e class mercedes 02 plate and the lights are dimming at idle and the revs are up and down doesn't happen all the time but very annoying when it does I've been told could be voltage regulator cod got someone to plug a voltmeter on the terminals and was 13.9 is this good or bad mechanic said it was good!
Any ideas
Thanks
Frank

 

[gegs88]

You need an auto spark to load test the alternator. The alternator in essence is just a rotor and stator that makes ac voltage. The regulator converts it to dc voltage, if theres problems then its going to be the regulator but it will need checking properly. A multi meter only gives a rough guide of output voltage. You need to know the amperage as well.
Most autosparks can bench test the alternator and repair it.

 

[bob6600]

Should show around 14volts so seems ok.

I would check your earths, one has probably corroded

 

[Sunshine26]

Been on eBay looking for a regulator and they said my regulators built in to my alternator but I don't think it it so not sure!
And any ideas where the locations of the earths are so i can check em?
Thanks guys for your replys

 

[Sunshine26]

And also the digital thermometer keeps going up to 25 then dropping back down again as the as it rough idles and light dimmer

 

[frostbite]

Alternators now have the regulator built in, so DC voltage is the end product. The old dynamos used to chuck out AC and had a separate regulator to get the DC voltage. You may be able to get an exchange alternator for not too much dosh..
May be worth checking the battery (with a proper battery tester - not just a multimeter)?

 

[optimusprime]

help

Without looking at the alternator i am not 100% sure but most i have worked on the reg is replacable. For a quick job just replace regulator ,just 2 screws holding it in to the alternator. Ebay is the place do a search for one. Other way is buy carbon brushes and solder them in .

 

[Sunshine26]

Last night though it drove spot on no dimming lights or dodgy revs up and down so very Wierd indeed got in it this morning and started doing it again any ideas lol

 

[E270 Owner]

You need to "drop test" the battery and not those silly battery condition testers a proper old fashioned load tester that has a glowing metal strip and gauge to show the battery holding voltage under drop testing.

A compoetent user of a drop tester should remove the cell caps and inspect them as the test is carried out to inspect for bubbling cells etc.

And the same for the alternator it needs load testing and should be chucking out 14.5v @ 200 amps

There's a module N82 that regulates the voltage also anything under 14v isnt acceptable imho especially on a diesel in winter conditions.

 

[Merc Owner 2B]

Don't overlook the basics. Is the alternator drive belt in good order and correctly tensioned? They do tend to slip (when belt is worn) when put under heavy load during damp spells.

 

[Ted]

Just to put things right.
The regulator regulates the voltage.
The rectifier converts the a.c. generated from the stator to d.c.
Bumpy d.c. But good enough.
And dynamos put out d.c.

 

[Sunshine26]

Ok first things first get the battery tested then check earth connections then onto alternator?? Is this right

 

[Ted]

I've had an idea
First of all 13.9 is on the slightly low side of ok. Could be due to the battery being a little flat or several consumers on, but still ok enough not to cause you any issues.
Now on my car, I can get the voltage up on the dash - combination of button pushes at ignition turn on time and the display showing temp at turn on. Yours may be the same.
Use this as a general guide to your voltage and note what it drops to when the lights dim - if significant it sounds like the alternator (or reg).
Pain in the bum having to do it every time you start the car but it could be a guide.
Or you could just get the reg changed. They are cheap enough and usually the least reliable component - worth a gamble?

Did you ever get the fans working overtime/engine temp fluctuation malarkey sorted?

 

[Ted]

Oh, and to eliminate earth issues, check the cable from the battery to earth. Give it a good clean and coat with vaseline.
Now get an earth strap (heavy duty not radio suppression type) from Halfords and bolt it to a good place on the engine and wing. That should sort out any possible earth issues without having to rummage around under the engine.

 

[Sunshine26]

Ok I'm on it ted! I love my car only had it 2 weeks from going from a Vectra to this I don't wanna get outta it so wanna do my best to look after it lol no I didn't sort the temperature out its still between 40-80 never goes past 80!! And dumb question where's the battery located??
Thanks everyone for your help much appreciated!!

 

[Ted]

Pretty sure it is in the boot on them. Also pretty sure that there is another small battery up front but I don't think this will cause the problem.
P.S. Get the stat changed too! You won't regret it.

 

[Sunshine26]

What u mean by stat m8

 

[bob6600]

Thermostat is cheap as chips

Circoli Mercedes-Benz | Car Parts 4 Less UK?s No.1 Car Parts Retailer

 

[Ted]

What Bob said.

 

[Sunshine26]

Just got in it battery looks brand new and connections aswell