voltage regulator possible problem

[mauro12]

Hello guys, today I decided to check my battery with a tester to see if the alternator was working. The voltage of the battery was 12.8 volt , fully charged . When I turned on the engine , the current was jumping from 13.8 to 15.2 and was not stable , maybe for 1 second but after was jumping again. I believe the alternator is overcharging the battery and my thoughts is about a possible malfunctioning of the voltage regulator or probably a bad battery too . I want to clarify that I've never had any problems with the battery or any red light in the dash and I have been having this battery for more than 6 years. What do you suggest me to do ? I read that the best option is to buy a new Beru regulator but the main website of spare parts from mercedes here in Europe do not sell this brand but another brand called Hella , made in china .
Having said that  I've also realized that the Beru regulator part 0 190 005 024 ( correct for pagodas )was also very common for Italian motorbike like Guzzi and old alfa Romeo. Due to the fact that the part number is the same , do you think is actually the same item in size and characteristics?
thank you

[mdsalemi]

Hoping others tell you their results.

With everything off, my battery (two years old) measures 12.44 V.

When I start the engine, and running at idle (750 RPM) the battery reads a rock-steady 12.15; no fluctuations.

As I increase the RPM, the voltage will increase. By 2000 RPM it’s up past 14 V. Steady RPM is steady voltage reading.

[mauro12]

Hi mike , I suppose that at idle your alternator should give at least 13.5 or 14v , otherwise during heavy traffic stop and go you could risk to absorb too much current from the battery . That’s my idea , correct me if I’m wrong .

[mdsalemi]

Hi mike , I suppose that at idle your alternator should give at least 13.5 or 14v , otherwise during heavy traffic stop and go you could risk to absorb too much current from the battery . That’s my idea , correct me if I’m wrong .

I think you are probably correct. My battery voltage is reading correctly, and when running (above idle) the alternator seems to be putting out proper voltage. However as you suspect I think I should be seeing a higher voltage, say 14V even at idle.

An older car like the Pagoda can run without a battery once started. But, it should be charging a bit at idle, and my situation indicates I'm probably NOT charging the battery at idle.

I've had no apparent charging system issues with this situation, so it just gets added to the list of things to check.

Anyone else care to share your readings?

[BobH]

Hello both, my car's readings:

Battery with ignition/engine off - 12.6V
At tick over/idle 750 RPM- 12.8V
Revs anything over 1000 RPM - 13.8V fluctuates very slightly, but steadies at 13.8V

The car gets used a couple of times a week, but not long journeys and i've never had a battery problem (that's the kiss of death!) battery is probably 4 or 5 years old

Just compared it to my 2003 Landrover diesel, gets used even less, so battery is never fully charged

Engine off - 13V
Throughout rev range - 14.2V steady

[mauro12]

I guess the biggest problem you can face is if you have a/c on . During stop and go traffic can take your battery down .
After I shut off the engine the battery has 13.2/.4 volts but after few seconds it goes back to 12.8.

[BobH]

Might be worth checking the belt tension, perhaps it slips at low revs?

[Kevkeller]

Mike after you rev the engine and the voltage increases if you let it idle again does the voltage drop back to the 12.15 volts?
With some of my cars and boats the alternator had to reach a certain rpm/voltage before it would start charging.  After reaching that the voltage would remain higher even when the engines went to idle again.

[mauro12]

What is the lowest acceptable voltage with everything turned on ? Radio , fan blower , lights or ac . I tested mine and it shows around 13volts under load  . As soon as I accelerate and reach 2000rpm I have 14.5volts .
How difficult is to repair or overhaul the 35 amp alternator ? Is it a job for every mechanic ?
Is always difficult to check if the problem
Is on the voltage regulator or the alternator.  I realized that my current is not stable but fluctuates a bit . No symptoms at all but it is just what the multimeter shows.
Any experience with made in China voltage regulator ? Is better to prefer the old bosch or beru ? Thank you

[rwmastel]

Is always difficult to check if the problem is on the voltage regulator or the alternator.

Mauro,
Do some searches on our forum.  I know testing of regulators has been discussed.

[mauro12]

Hi guys , this morning I’ve replaced the voltage regulator and the problem of dim red light went away. I installed the beru regulator .
The voltage at idle is 14.2v and under maximum load at idle is 13.7.
I was wondering if there is a way to test the old one or maybe repair it . I know is very expensive compared to the 20€ beru.
How about the quality of beru regulator? Have you had any trouble?
Thanks

[WRe]

I was wondering if there is a way to test the old one or maybe repair it .

See https://www.sl113.org/wiki/Electrical/Alternator

[paddockman]

I had an issue with the charging light coming on. Tested the battery 12.6v static then 17v+ with the engine running. Regulator! After some searching on here I located a BERU replacement. With the new Regulator, the Battery is perfect 14.4v running so the BERU is regulating but - the Red light is still illuminated (dim) at idle and throughout the range with an electrical load on. My car is a 230sl - Is the BERU acceptable with the older system e.g 35 amp - I have read the 250 and 280sl have 55 amp and some stockist at saying the BERU is not ok with the 230. I'd really be thankful for some guidance.

[BobH]

Hello, as i understand, the Beru should work with all alternators that have the external regulator, others may know different

I wonder if you have a leaky diode in the alternator, which could possibly have been the cause of the original regulator failing

There's a good test procedure in the manual

https://www.sl113.org/wiki/Electrical/Alternator

[mauro12]

I put the new regulator and the voltage is stable . No red light anymore . Anyway the light was only visible at night with everything on ( fan , radio etc) . I don’t know if it’s a faulty diode or was the regulator itself. For sure the voltage was not stable . I had 16 volts and more . What do you think ?
If the voltage regulator fails , the car will just quit ?

[pede754]

I have had two new regulators which sadly seem to be from the same cheap Chinese source. Mine have both flashed the ignition light when running and had voltage spike upto 17.4 volts at the same time.

[mauro12]

Mine is from beru and cost only 20€. I’ve always wondered if the regulator fails , what is the first symptom? From Kent bergsma of mercedesource he says that the engine quits . Is it true ?