Author Topic: Alternator voltage regulator  (Read 1521 times)

luiml73

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Alternator voltage regulator
« on: 14 November 2019, 12:11 PM »
Hi guys, my friend has a 1976 450 sel and last week it would not start. AAA came over and said the alternator was bad. We changed the alternator and today the car was dead again. Does this car have a voltage regulator and if so where is it located?

Thanks

Luis

ptashek

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Re: Alternator voltage regulator
« Reply #1 on: 14 November 2019, 12:39 PM »
The voltage regulator sits on top of the alternator housing. Before condemning the alternator, I'd check for parasitic currents draining the battery over time.

Easy to do if you have a multimeter handy.
1993 "Pearl Blue" W124 280TE
1979 "Icon Gold" W116 450SE (history, resto)

luiml73

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Re: Alternator voltage regulator
« Reply #2 on: 14 November 2019, 02:08 PM »
I dont see anythng  on top of the alternator. I guess this car doesnt use a regulator.

I have no idea what that means lol. Sorry
« Last Edit: 14 November 2019, 02:18 PM by luiml73 »

luiml73

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Re: Alternator voltage regulator
« Reply #3 on: 14 November 2019, 06:45 PM »
I will fully charge the battery then do the test with multimter te see if something isndraing the battery? I will borrow a multimeter and search on how to do the test. Thanks
« Last Edit: 14 November 2019, 07:19 PM by luiml73 »

ptashek

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Re: Alternator voltage regulator
« Reply #4 on: 15 November 2019, 01:53 AM »
This is what the regulator looks like:


To test for parasitic currents do the following:
- turn engine and ignition fully off
- remove positive terminal from battery
- switch the multimeter to amps (start with the highest setting available, ideally 20A)
- put the negative lead of the meter onto the positive battery terminal
- put the positive lead of the meter on the disconnected positive battery lead

You're basically putting the multimeter in series with the cars full electrical load at this point.

DO NOT under any circumstances turn the engine or ignition on while the meter is connected this way. Electrical fires suck.

With all lights off, doors and trunk closed, check the reading on the meter. Any reading above around 20mA (0.02A) on the W116 would suggest there's a parasitic current draw.

At this point start pulling fuses, one by one and check the reading after. Once it drops to zero, you have your culprit circuit identified. Then it's a case of checking all the things on that circuit.

If the reading is withing limits, the problem is elsewhere, and likely with the alternator after all.
1993 "Pearl Blue" W124 280TE
1979 "Icon Gold" W116 450SE (history, resto)

luiml73

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Re: Alternator voltage regulator
« Reply #5 on: 15 November 2019, 04:43 AM »
Thanks for the detailed response. I posted a puc of the enginge bay in my first post. The problem is I dont see the regulator? Are there some of 450 sel models that dont use them? Or do they all use regulators and I just need to look again?

rumb

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Re: Alternator voltage regulator
« Reply #6 on: 15 November 2019, 05:19 AM »
Make sure the electrical connections are not corroded under the battery/alt.  Give your battery a good charging.
'68 250S, '77 6.9 euro, '91 300SE, '98 SL500 '14 CLS550

UTn_boy

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Re: Alternator voltage regulator
« Reply #7 on: 15 November 2019, 02:03 PM »
Lucas, Luis, the voltage regulator is located in the BACK of the alternator housing where the wires attach.  The only part you'll see sticking out is the black and white part.  The carbon piles are hidden inside because they have to contact the commutator on the armature.  All W116 cars, and all others, have a voltage regulator.  If you bought a new alternator then it would have come with a new voltage regulator.  You really need to follow Lucas's parasitic draw testing instructions before any other determinations can be made.  Though, new and/or remanufactured alternators as of late seem to be bad out of the box, so don't rule out a bad alternator even though it's new. 
1966 250se coupe`, black/dark green leather
1970 600 midnight blue/parchment leather
1971 300sel 6.3, papyrus white/dark red leather
1973 300sel 4.5, silver blue metallic/blue leather
1976 280s astral silver/blue MB Tex
1978 450sel 6.9 Euro, Anthr/velour

ptashek

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Re: Alternator voltage regulator
« Reply #8 on: 15 November 2019, 02:39 PM »
Lucas, Luis, the voltage regulator is located in the BACK of the alternator housing where the wires attach.  The only part you'll see sticking out is the black and white part.  The carbon piles are hidden inside because they have to contact the commutator on the armature.

Absolutely correct, it's in the back of the housing when mounted on the car :)
Bottom-left corner, when looking from the front of the car.
1993 "Pearl Blue" W124 280TE
1979 "Icon Gold" W116 450SE (history, resto)

luiml73

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Re: Alternator voltage regulator
« Reply #9 on: 15 November 2019, 04:04 PM »
Thanks for the help guys. I will try and work.on the car on Tuesday

luiml73

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Re: Alternator voltage regulator
« Reply #10 on: 19 November 2019, 07:36 AM »
Lucas, Luis, the voltage regulator is located in the BACK of the alternator housing where the wires attach.  The only part you'll see sticking out is the black and white part.  The carbon piles are hidden inside because they have to contact the commutator on the armature.  All W116 cars, and all others, have a voltage regulator.  If you bought a new alternator then it would have come with a new voltage regulator.  You really need to follow Lucas's parasitic draw testing instructions before any other determinations can be made.  Though, new and/or remanufactured alternators as of late seem to be bad out of the box, so don't rule out a bad alternator even though it's new.

Tested the Alt at Advance Auto and they said its not charing  12.13v

« Last Edit: 20 November 2019, 09:43 AM by luiml73 »

luiml73

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Re: Alternator voltage regulator
« Reply #11 on: 19 November 2019, 08:50 AM »
I just noticed the Battery light is not comong on in the instrument panel when i turn they key. Could this be the problem?

PS: Are these the bulbs?

Thanks
« Last Edit: 19 November 2019, 10:29 AM by luiml73 »

UTn_boy

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Re: Alternator voltage regulator
« Reply #12 on: 20 November 2019, 06:40 PM »
No, the lack of the battery light bulb being burned out or not present won't cause the alternator not to charge.  You have issues elsewhere.  I'd start by cleaning all of the connections at the 3 terminal phenolic junction block mounted under the battery frame.  If after you do that and renew the bulb and the bulb still doesn't light then you'll probably have an actual wiring issue and/or a bad alternator.  I know it's new, but these days brand new has no merit.  I'd also take the alternator off of the engine and have it tested at some place like Advance Auto or the like.  At least then you could rule the alternator out at that point. 

As far as your indicator bulb goes, the one you posted a picture of is not the correct one.  Those are for the instrument lighting and center console lighting. Research Mercedes part number N072601-012240.  That is the one you'd need for the indicator lights in the instrument cluster. 
1966 250se coupe`, black/dark green leather
1970 600 midnight blue/parchment leather
1971 300sel 6.3, papyrus white/dark red leather
1973 300sel 4.5, silver blue metallic/blue leather
1976 280s astral silver/blue MB Tex
1978 450sel 6.9 Euro, Anthr/velour

PosedgeClk

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Re: Alternator voltage regulator
« Reply #13 on: 21 November 2019, 10:42 AM »
DO NOT under any circumstances turn the engine or ignition on while the meter is connected this way. Electrical fires suck.
FYI, you aren't going to start a fire this way. Ammeters have fuses. If you exceed 10 or 20 amps, it's going to blow which will render the ammeter portion of the multimeter useless until the unit is disassembled and the fuse is replaced.
1979 450SEL 6.9

ptashek

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Re: Alternator voltage regulator
« Reply #14 on: 21 November 2019, 12:38 PM »
Yes, good multimeters will have a fuse, or a couple. But it's false to assume all do, and I'd rather play it safe and warn about the risk.
1993 "Pearl Blue" W124 280TE
1979 "Icon Gold" W116 450SE (history, resto)