Bad Alternator or Headlight wiring issue? - Page 2 - PeachParts Mercedes-Benz Forum

hookedon210s · #16 07-27-2010, 07:42 PM

Quote:

80 Amp VS 70 Amp is a negligible gain

This is actually not true. One supplier I use uncovered the sordid truth that the 70amp alternator only puts out 55 amps or so at full tilt and barely keeps up with latent demand at idle. He documented this by testing several Bosch rebuilt units. He called Bosch on this and Bosch acknowledged that he was correct. Apparently the alternators are mislabeled/overrated. According to the 1991 technical data manual, on the test bench the 70 amp alternator is rated at 26 amps at 1500 rpm, both the 80 amp and 100 amp alternators are rated at 36 amps at 1500 rpm and the 110 and 120 amp alternators are rated at 60 amps at 1800 rpm. My 300TE had the factory installed 80 amp alternator with a 75 watt RMS X 4 secondary amp, 100 watt H-4 headlights, HVAC constantly turned on (Florida heat you understand) and I never had a problem with dead batteries or shortened battery life. Ps2cho, I would install whatever alternator fits your budget that you can find at a junk yard (no core) provided the alternator is at least the 80amp unit used in the later model 124 vehicles. Mark

ps2cho · #17 07-27-2010, 08:48 PM

Just got back from Autozone. They tested it and confirmed what I had been getting.

He used his tester and reported Alternator PASS. So I then turned on the lights. The tester then said Regulator FAIL. Alternator PASS.

So I'll try to dig out my old VR. I keep old items like that for this very reason. Charging the battery tonight as it is completely dead again and hopefully it is just the regulator.

If not, I'm pretty sure it is electrical-related.

Is there a way I could read the draw at the fuse for the headlights? Would that give me any indication of anything?

Side Note: Prior to this event, I have never had a dead battery and I run a 300W amplifier, new Alpine headunit, all new speakers, a 800W Sub and A/C all the time...So I don't think my amperage on the alternator is the problem here. Either way in the future I will go with the 80A unit.

400Eric · #18 07-28-2010, 02:10 AM

Quote:

Originally Posted by ps2cho

Yes I have the 70amp alternator. I'll see if I can get somewhere to load test it so I'm not chasing electrical gremlin theories I guess....

If the alternator is the issue I would like to upgrade to the 80 amp...any bigger and I think it'll steal too much hp which I lack as it is with A/C on. How much would the 80A steal from me?

Hey, What's wrong with "chasing electrical gremlin theories"?

As for your second item, the bigger alternator draws extra horsepower only when you put a high current draw on it. no current draw = no horsepower draw.
Regards, Eric

MBeige · #19 07-28-2010, 02:21 AM

Robert, what wattages are you running on your main beams? I went through the thread to check but it was not mentioned. Thought I'd throw it out there.

I really love the side profile photo of the AMG front bumper. It looks just right!

compress ignite · #20 07-28-2010, 02:39 AM

"Is there any way I could read the draw at the headlight fuse?"

(Four separate fuses for headlights: Low,R and L. High R and L.)

[It's too easy for me to measure the lights draw in total,rather than mess around with each of four fuse holders.]
[draw total for light switch in headlamps LOW 11.22 Amps
draw total for light switch in headlamps HIGH 14.35 Amps.
(Throw away a few amps for side lights and tail lights)
Standard O.E. Lighting,No Other Loads,No Phantom Draws]

(It will tell you what the headlights are pulling.)

Favorite New Diagnostic Tool (Below)
I paid about $90. USD +Shipping. [Hey,So it ain't a Fluke,But I'm not Larry Ellison]

400Eric · #21 07-28-2010, 02:43 AM

What RPM was the engine at when the Autozone guy was doing his testing? The posts about how low the amps are in the lower RPM range with the so called 70 amp alternator is very telling. Maybe that would cause the tester to indicate that the VR was amiss?
Regards, Eric

ps2cho · #22 07-28-2010, 11:21 AM

Quote:

Originally Posted by 400Eric

What RPM was the engine at when the Autozone guy was doing his testing? The posts about how low the amps are in the lower RPM range with the so called 70 amp alternator is very telling. Maybe that would cause the tester to indicate that the VR was amiss?
Regards, Eric

It was at idle 650rpm...either way I ordered a new VR as it's nice to have a spare anyhow...

ps2cho · #23 07-29-2010, 10:37 PM

It's gotta be the lights. Check this out...

With the car OFF. I turned on the lights. Starting voltage 12.51v. 5minutes later. 11.6v.

Even though the battery load tested OK, I think I'm gonna go to Costco, buy a new battery, try it and if it does not fix the issue I'll take it back. Can't hurt.

ps2cho · #24 07-30-2010, 09:38 PM

This thing is so random...

The draw seems to happening with A/C now, not lights.

At this point I am getting tired of chasing as I don't think this is electrical gremlins anymore. Battery or Alternator.
So Today:
1) I bought a new OE MB Battery. Put her in, but no change, but car starts up faster (not just due to battery being charged. She started up much faster than I have ever seen!!)

2) Bought new Bosch Voltage Regulator. No change.

---

I am now going to replace the alternator. Since I am doing it, I may as well upgrade to the 80A unit.

Does the upgrade just require a pulley swap...anything else? Is the connector the same as the 70A?
I want the most painless upgrade possible for both myself and my wallet.

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