Battery Idiot lamp - PeachParts Mercedes-Benz Forum

crhenkel · #1 09-03-2010, 01:20 AM

Does anyone know if installing an LED lamp in place of the 3 watt oem bulb in the battery charge idiot lamp would cause alternator charging problems?

Some have said that if the bulb is burnt out or not the correct wattage, the charging system will not work properly.

About the time I changed all the idiot lamps in my cluster to leds that are much brighter and more vibrant colors that are easier to see during the day, I started seeing a low charging issue with my alternator in my 1986 190E 2.3-16valve
It has a volt meter and it shows as low at 9 volts at times with the blower motor on high, the radio on, the headlamps on, and the rpm up.
It has a new rebuilt alternator, voltage regulator and the cables test out good.
Driving or reving engine increases the charge some, but not much. With everything off and driving the car, I can get the volt meter to register over 12.5 volts but as soon as I turn something on, it drops like a rock. It is a 70amp alternator.

Thanks

Duner · #2 09-03-2010, 02:16 PM

Don't know about Bosch alt but old 10si Delco alt. the idiot light supplied current to excite the alt to get it to charge. With the Delco if you used too small a bulb it would not excite and not charge. I suspect that may be your problem with LED light . However you said it did charge some sometimes so that has me wondering. I would put the old bulb in and see what happens.
I have a feeling you will be back in bussiness. No guarantee tho.

macdrone · #3 09-03-2010, 03:41 PM

Id look into the regulator to your alternator. Go bad with lots of age. At 24 years I bet the contacts on it are worn. If you dont have like 13 volts when running thats probably the issue. Only a couple of screws and it comes right out.

crhenkel · #4 09-04-2010, 02:05 AM

Yep, I did think the same thing. I changed out the alternator voltage regulator just to be safe. It was not worn too bad. Put a new one in just fine, most the fight is the heat shield bolts and not the regulator bolts. Still not charging right. I get good high charge volts in park with things turned off, but as soon as the lights and ac and blower get turned on, I drop down below 10 volts. A new alt and volt regulator should be able to handle everything turned on with no problem. Not sure where my draw is yet. I am still suspecting the blower motor or the blower regulator. Also, going to take the LED bulb out of the battery idiot light tomorrow to make sure that didnt cause any issues.

mak · #5 09-04-2010, 02:21 AM

Most likely it is the very low current(.020A) flow from the LED that is not letting the alternator come up to full operating current and voltage. Installing the bulb back will bring the system to normal
mak

crhenkel · #6 09-04-2010, 11:29 AM

Ok, so for breakfast I got my coffee and my wiring diagram book and looked up the diagram for the battery charge idiot lamp. It does look like the circuit for the lamp goes from the run position of the start switch to the F1 Electrical controller to the lamp. Then from the lamp to the controller to the alternator (blue/white) wire that connects to the stator. I am reletively sure that the LED lamp that I put in place of the 2 watt OEM bulb is the problem. Everything else checks out as good, but the alternator is just not keeping up with the loads as they increase. You can watch the voltage drop like rock on the voltmeter the 16v has in the console.
SO...just because the LED bulb looks better and is easier to see in day light for easy identification of warning lamps, I am guessing it is a bad idea for the battery charging lamp. I will pull it today and replace the OEM bulb to see if I am right.
All the other warning lamps that got LED bulbs look great and are functioning fine. I can actually see them in the day light now and the high beam indicator is actually blue and vsisable in the day now. I also have very bright turn signal indicators and low fuel indicators. It is nice to have the warning lamps easy to see. I do like the LED bulbs much better, just not for the the charge lamp.

Duner · #7 09-04-2010, 01:43 PM

On a delco alt conversion one time the gen idiot lamp was too small to excite the alt and I wanted to retain the factory original light so I added another bulb in parallel . Worked fine then. I would not suggest such a solution for your car but if you really had to have your LED light that might be one way.
They are about 7 other ways to excite your alt too providing your alt is not being excited by too small a current draw from LED.

crhenkel · #8 09-04-2010, 02:03 PM

No, I am ok with putting the OEM bulb back in the warning light for the battery charge indicator. The main reason I put LED bulbs in was that all the other bulbs were the much smaller bulbs and they put out dull dim light that made the warning lights easy to miss in the day light. The LED bulbs are brighter, more colorful, and are not hot. The instrument cluster has enough problems with hot bulbs and solder joints as it is, so I figured it was an added benefit to cut down on power draw and heat. They worked great, bright and good deep color. Only catch is I didnt think that the led would cause a charging issue. I didnt notice it right away cause I drive the car infrequently and when I did, I didnt have headlamps or AC on. The day I notices it was 98 degrees F. AC on high and headlights made voltage drop so low I noticed the volt meter at 9 volts and the dash lights were dim. Figured the alt or voltage reg was bad no big deal. Voltage reg tested bad, and I replaced it, but it didnt fix the problem. Replaces alternator, volt reg still showed bad. That is when I figured it was not charging system but a power draw. Now I know the field on the alternator voltage regulator was not getting excited due to the LED bulb not providing enough resistance. Ironic, but an easy fix.
Back in with the OEM bulb, the otehr LEDS can stay.

compress ignite · #9 09-04-2010, 02:18 PM

The reason you have to add a RESISTOR to Brake,Tail,Turn,Etc.that are LED lights is the lack of Measurable Resistance,which the "Lamp Out" relay determines is "No Filament" OR "Bad Bulb".

[Comparative Analogy ABOVE]

The Alternator's Excitation Circuitry "Sees" not enough RESISTANCE in the LED.
AND as a result produces LESS energy (Electricity).

DISCLAIMER:

Not a suggestion !
BUT,
'Could it be possible that a resistor of the Exact Same Resistance DIFFERENCE
between the O.E. (Osram) Incandescent and the LED when added to your LED
Illumination would allow the Excitation Circuitry to function properly?

(I almost hesitate to proffer this idea,knowing the superlative group of
"McGiver-ists" inhabiting this forum...
I will not be surprised to hear of someone enabling their Dash Reostat [Dimmer] for "Adjustable" control-able power output from their Alternator.)

crhenkel · #10 09-04-2010, 02:29 PM

Ya, I agree, an inline resistor or load to bring the resistance back up to the correct amount would likely work. I just am not that dedicated to the LED. I just wanted them to be bright and a good color and I got that in all the others. Plus the battery charge lamp is a 2 watt ( I think) and not the tiny wheat bulb that the rest are, so, it is actually bright enough, it just got the LED treatment since I was doing them. It will come out and the OEM bulb back in and all will be fine.

crhenkel · #11 09-04-2010, 03:41 PM

OK, so now I am irritated...Pulled the instument cluster only to find out that I put an LED bulb in every lamp EXCEPT the Battery Charge warning lamp! I must have decided that the larger style bulb was putting out pleanty of light as it was or since it was a different style bulb (194 wedge style) I might not have ordered the LED for it. Regardless, I found an OEM type bulb in the lamp holder! Not good for my theory.
SO, anyone know exactly what the wattage for this mystery bulb in the charge indicator lamp? I do not know what it is supposed to by from the factory and I want this to be right to eliminate this as a possibility.
I have 2 watt, 3 watt, 4 watt and 5 watt bulbs to choose from.
They all fit the holder. I thought it was the 2 watt.
IF I put a brighter higher wattage bulb in the resistance should go down making the field less likely to work properly? I am guessing the range to get it to work is pretty decent but I am not sure. Any help is appreciated at this point.
Right now I have 13.8volts charge on the volt meter in park with AC off and headlamps off. It starts to go south as I turn things on and up and arrives at about 9.8 volts with AC on high and headlamps on. The voltage also drops by 1.5 to 2.5 volts when I put the car in drive. I am noticing a possible correlation with the aux fan gong on and off with the AC cycle.

Grrrrr!

compress ignite · #12 09-04-2010, 04:17 PM

according to the EPC.

crhenkel · #13 09-04-2010, 05:44 PM

3 watt bulb, same as the lighting bulbs...thanks...I have those available. I'll go put one in....
So, no luck. Bulb is in fine and voltage still drops like a stone. I followed the instrument cluster charge indicator light wiring to the terminal block (X4/10) in front of the battery in the passenger side fender well. Contact 61. It has voltage on it of about 13.95v then it starts dropping when the loads are put on it. Just continues to drop as loads stay on. When loads are turned off ( ac, lights. radio) the voltage on contact 61 starts to rise again. It goes directly to the smaller gauge wire that goes to the electrical plug on the back of the alternator then to the alternator voltage modulator field.

Any one know if the voltage modulator for the 16v is the same as the 8v? I would guess it is the same.

lkchris · #14 09-05-2010, 11:58 AM

Yes, the LED will cause problems. Alternator requires current flowing through the bulb filament to excite it to start working.

crhenkel · #15 09-05-2010, 02:02 PM

Quote:

Originally Posted by lkchris

Yes, the LED will cause problems. Alternator requires current flowing through the bulb filament to excite it to start working.

I now see the error of my ways. I took out the LED bulb and replaced it with the 3 watt OEM bulb. It seeemd to help a bit, but it is not fixing all the problem. I am starting to suspect the wiring from the alt to the battery harness, gonna test it this afternoon. It has a lot of corrosion on it and the connecting plug at the alt looks like it needs cleaned.