battery light pulsing on and off - Page 2 - PeachParts Mercedes-Benz Forum

curtludwig · #16 11-21-2008, 10:24 PM

A bad battery WILL eat alternators, been there, done that...

lutzTD · #17 12-02-2008, 05:58 PM

put a brand new NAPA regulator in, now it is running 16V at the battery. I am really getting aggrevated. Is a battery issue going to allow the reg to go to 16V or did I get a bad regulator from NAPA which of course they will not refund or exchange......

79Mercy · #18 12-02-2008, 06:13 PM

why won't they exchange a part that doesn't work?

lutzTD · #19 12-02-2008, 06:18 PM

Quote:

Originally Posted by 79Mercy

why won't they exchange a part that doesn't work?

I have never had luck with electrical part exchange, I think I will go get a couple from the yard this weekend

daw_two · #20 12-02-2008, 10:12 PM

I still suspect your battery.........OR a bad ground?

Have you taken the battery out of the car and had it load tested? Be sure to compensate for the actual temperature.

lutzTD · #21 12-02-2008, 10:25 PM

Quote:

Originally Posted by daw_two

I still suspect your battery.........OR a bad ground?

Have you taken the battery out of the car and had it load tested? Be sure to compensate for the actual temperature.

I will do it tomorrow if I can. In the mean time my house thermostat decided to go out and its going to be 41 tonight. I know that doesnt sound cold to some but Im freezing

SD Blue · #22 12-02-2008, 10:31 PM

Quote:

Originally Posted by lutzTD

put a brand new NAPA regulator in, now it is running 16V at the battery. I am really getting aggrevated. Is a battery issue going to allow the reg to go to 16V or did I get a bad regulator from NAPA which of course they will not refund or exchange......

I'm thinking you have a bad diode in your alternator. Try putting your VOM in Volts AC and see if you have less than 1VAC.

lutzTD · #23 12-03-2008, 07:26 AM

Quote:

Originally Posted by SD Blue

I'm thinking you have a bad diode in your alternator. Try putting your VOM in Volts AC and see if you have less than 1VAC.

where should I measure the AC voltage? Im afraid to run the car too much because 16V might explode the battery. Can I remove the battery cables from the battery and measure it at the cables?

SD Blue · #24 12-03-2008, 11:39 AM

It needs to be across the battery just as you measured the voltage regulator DC volts. Connect the meter before start-up, while the battery is cool, and you should be able to measure within seconds after the engine is running.

A charging voltage of 16VDC will eventually boil off electrolyte but will not blow a battery in the time it takes to take your readings. That heavy duty battery can absorb a lot of energy before a 2.5 volt overcharge would cause it to heat up significantly.

lutzTD · #25 12-03-2008, 12:50 PM

Quote:

Originally Posted by SD Blue

I'm thinking you have a bad diode in your alternator. Try putting your VOM in Volts AC and see if you have less than 1VAC.

.04VAC 16.25VDC at battery at idle. Does this sound like a diode issue or should I still look at the battery?

thanx

Jeremy5848 · #26 12-03-2008, 12:59 PM

Sounds like a regulator problem to me. Your measured AC voltage is quite good – 40 millivolts is "noise," not to worry. Try another regulator, especially if you can get them cheap at a yard. As a final thought, consider picking up a complete alternator while you're in the yard.

I agree that you should not operate the car for extended periods while you have this problem. Turn on the lights if you do have to drive, it will draw off some of that excess electrical energy.

Do an experiment for us and report back: with the car idling, measure the DC voltage as before, then turn on every electrical load you can – all of the lights, the a/c system in "defrost," the rear window defroster, etc. – and see what happens to the voltage at the battery.

Jeremy

lutzTD · #27 12-03-2008, 01:08 PM

Quote:

Originally Posted by Jeremy5848

Sounds like a regulator problem to me. Your measured AC voltage is quite good – 40 millivolts is "noise," not to worry. Try another regulator, especially if you can get them cheap at a yard. As a final thought, consider picking up a complete alternator while you're in the yard.

I agree that you should not operate the car for extended periods while you have this problem. Turn on the lights if you do have to drive, it will draw off some of that excess electrical energy.

Do an experiment for us and report back: with the car idling, measure the DC voltage as before, then turn on every electrical load you can – all of the lights, the a/c system in "defrost," the rear window defroster, etc. – and see what happens to the voltage at the battery.

Jeremy

I am going to put the old regulator back in. I think the pulsing was the belt slipping. this one also pulsed until I tightened the alternator belts. I wish I had thought of this before buying a new (junk) regulator. It all started when I left the oil cap off after an oil change and drove it 30 miles. Oil everywhere. The problem started 2 days later after I had washed down the engine and underside of the hood 2 days in a row. The hood still has oil leaking out after trips on the highway.

lutzTD · #28 12-06-2008, 04:55 PM

found 2 decent Bosch regulators at the PNP, one looks brand new. Put it on the car and things are more settled but still not right.

put a meter on it. AC volts is still .04
idle volts is 13.4 DC
with load of all lights on high, fan 12.8 at idle 13.5 off idle

as far as the light at idle the battery light goes off, if a drive the off condition works up to a higher rpm over time, if I turn on the lights or run the windows or blower it gets brighter. I took the car to interstate battery and had them test the battery in the car. 12.8 volts with no load and car off. load test showed full cranking amp capacity. date code says the battery was made jan07

is there some other part in the system controlling this light? I cant see how my charging system could be any better than it is right now. Ive decided to ignore the light and check it all with a meter every once in a while but I would really like to get the light working properly

Gene Horr · #29 12-06-2008, 05:00 PM

I don't remember where I've seen it but there are cheapo voltmeters that plug into the cigarette lighter socket. Just buy one of those and keep an eye on your voltage. As long as it stays around 13.8V while you are driving everything is fine.

No alternator that I know of will keep up with a full load at idle so voltage drops while you are stopped generally aren't an issue.

lutzTD · #30 12-06-2008, 05:59 PM

Quote:

Originally Posted by Gene Horr

No alternator that I know of will keep up with a full load at idle so voltage drops while you are stopped generally aren't an issue.

my old fords give 13.5 output at idle with everything on, and never really exceed 13.5 no matter what the conditions of load or rpm. I just assumed it was the same for the merc. as this was always my homebrew alternator test on mustangs and f series trucks