headlights draining battery 1963 190D fintail - PeachParts Mercedes-Benz Forum

mirce · #1 12-13-2013, 12:57 PM

Hi, there this is my first post.

I have a 1963 190D fintail with a really frustrating issue. every time i run my headlights the battery drains very quickly. nothing else seems to drain the battery just the headlights. i have a retrofitted 3 wire GM alternator. I just had a new carrier for it machined and replaced the fan belt.

I replaced the battery a few days ago and the voltage regulator yesterday. I couldn't find any bare wires that might be grounding out.

If anyone has any suggestions they would be much appreciated thank you.

vstech · #2 12-13-2013, 01:30 PM

so, you have a GM alternator, AND the stock voltage regulator?

mirce · #3 12-13-2013, 01:32 PM

No it is a GM voltage regulator. It was a direct replacement for the one the was in place before.

SD Blue · #4 12-13-2013, 01:46 PM

Basically, it sounds like a minimally charging scenario. First suspects would be loose belt, and voltage regulation but it's going to be easier to determine the problem if you can provide us with some voltage measurements across the battery. ( Engine OFF, Engine RUNNING, and Both DC and AC measurements. )

Low DC = Voltage Regulator
High AC, and DC = Alternator Diodes

mirce · #5 12-13-2013, 01:53 PM

I'm actually going to go pick up the battery from o'reillys right now. when i was measuring the voltage from the battery terminal while the car was running, it measured around 11.8DCV

mirce · #6 12-13-2013, 01:54 PM

The belt is brand new and has good tension.

RavenTBK · #7 12-13-2013, 03:12 PM

Quote:

Originally Posted by mirce

I'm actually going to go pick up the battery from o'reillys right now. when i was measuring the voltage from the battery terminal while the car was running, it measured around 11.8DCV

I guess thats lights off?

If so, that says alternator issue. Did you bump the throttle a bit to see if it rises?

mirce · #8 12-13-2013, 10:03 PM

Alternator tested fine, so i took it apart and the brush was broken on it. Thought this could be causing my problem. New GM alternator was $50 but didnt fit the mounts so i will have to modified the housing and talked the guy there into letting me still have the warranty even if it was modified. the voltage read at 12.1-12.2DC ~26AC when the car is idling with the ignition on. Different accessories drop the voltage in small increments. Once i turn on the headlights the voltage trickles down slowly.

SD Blue · #9 12-14-2013, 12:24 PM

Quote:

Originally Posted by mirce

Alternator tested fine, so i took it apart and the brush was broken on it. Thought this could be causing my problem. New GM alternator was $50 but didnt fit the mounts so i will have to modified the housing and talked the guy there into letting me still have the warranty even if it was modified. the voltage read at 12.1-12.2DC ~26AC when the car is idling with the ignition on. Different accessories drop the voltage in small increments. Once i turn on the headlights the voltage trickles down slowly.

From your voltage readings, it points to bad rectifier diodes or poor grounding. A reading of 26Vac is entirely too high. It should be much less than 1Vac. If you have a bad rectifier diode it can take out voltage regulators, over and over. Also, check your battery-chassis ground and especially the chassis-engine ground.

mirce · #10 12-13-2013, 10:04 PM

Quote:

Originally Posted by RavenTBK

I guess thats lights off?

If so, that says alternator issue. Did you bump the throttle a bit to see if it rises?

nothing happens when i move the throttle.

sixto · #11 12-13-2013, 02:30 PM

Is the crank pulley diameter comparable with a GM engine's?

Sixto
87 300D

mirce · #12 12-13-2013, 02:31 PM

I'm not sure but i know that it was working fine before

SD Blue · #13 12-13-2013, 08:17 PM

With your setup, is the voltage regulator mounted on the alternator or somewhere else, such as a fenderwell?

Besides the voltage regulator, which should be producing about 13Vdc across the battery, you could have a grounding problem. It may be the grounding of the voltage regulator to the alternator housing. I'll have to do some digging to see if we can find out how the alternator gets its excitation as well.

mirce · #14 12-13-2013, 10:05 PM

Quote:

Originally Posted by SD Blue

With your setup, is the voltage regulator mounted on the alternator or somewhere else, such as a fenderwell?

Besides the voltage regulator, which should be producing about 13Vdc across the battery, you could have a grounding problem. It may be the grounding of the voltage regulator to the alternator housing. I'll have to do some digging to see if we can find out how the alternator gets its excitation as well.

The voltage regulator is mounted to the firewall. when the voltage regulator is bypassed the results do not change.

RavenTBK · #15 12-14-2013, 11:08 AM

12.2 with no accessories on is still too low. So, since increasing the throttle (to say 2000 rpm...not just a hair above idle) does not increase the output voltage, that leaves the external voltage regulator (if you have one..kind of confusing when I reread the above..standard run of the mill GM 3 or 1 wire alts are internally regulated), wiring harness (highly unlikely as voltage should rise just the same), or alternator failure in itself. There are no other physical parts in the system. Unless the battery gets nice and warm indicating a shorted plate thats simply eating the alternators output.

I ask you to increase the throttle to verify its not a pulley issue...ala speed differential between crank and alternator. Most alts are set up around 1.25:1, 1.25 turns alt for every crank turn. Swapping in a GM alternator into your MBZ might end up with a different ratio. Gotta remember most gassers idle near 1000rpm, not at the 650-750 our diesels do. Increasing the throttle would spin the alternator up into its peak range, and if the voltage rises with no accessories on, changing the pulley size is the correct solution.

Just for my knowledge, I assume by 3 wire, you refer to having a B+ post, and a "T" shaped connector on it? Give me a part number if you've got one.

If the alternator is indeed what I think it is, it is internally regulated, and if you have an external regulator too, thats the first problem. Remove it.

As a functional example:
At idle, with my 3-wire 100amp GM installed in my Subaru, voltage rests comfortably at 13.3 with no accessories on. Turning absolutely everything on, including my 700watts of lights, blower, and such, voltage drops near 12.0 at idle, but will slowly drop lower as all the accessories are drawing more than the alternator can produce at idle to maintain a stable voltage (Kind of like what you're describing!). Bumping the throttle peaks it back to 13.4 at 2000 rpm, outputting roughly 85 of its 100amp capacity. I had to change my pulley to keep the alternator from overspeed and keep it in the peak generating range over my Subaru's RPM range.