Delay in alternator kicking in? Battery dies. - PeachParts Mercedes-Benz Forum

JoshMB · #1 11-27-2002, 01:38 PM

I have searched the archives, couldn't find anything.

I have a 78 240D. My battery drains every 3-4 days. There is a 3.5 milliAmp draw when the car is shut off. I assume that is the clock. When I first turn on the car, and let it idle, the voltage remains about 12.4 for 4-5 minutes. Then it climbs to 13.9-14.4 pretty quickly. Is this normal? I only have a 5 minute drive to work and maybe it is using the batttery and not charging fast enough.

Does this sound right? The alternator is a DURALAST (<1 month old). I know I should have gone with OEM, but I was suffering from a spending disability that day.

Could it be the wires inbetween the alternator and the battery? Is there a wiring set that I can just replace?

Thanks,

BTW, I replaced my old loop plugs with the fast glow from fast lane. The difference is AWESOME! Hotter glows, less smoke, and I started it at 15 degrees without plugging it in. Undreamt prior to the switch.

#2 11-27-2002, 01:54 PM

I am farily confident that a 5 minute drive to work would not lead to dead batteries as there are many people who drive a short distance to work and don't experience this problem.

I would think this may have something to do with the new alternator / voltage regulator. Have you had it tested? From your note it looks as though the alternator is putting out what it should.

How dead was the battery in the first place? If a battery gets really dead it will not take a meaningfull charge again, someone has told me something about reversing polarity?

Did you install a new battery with the new alternator??

Hope this helps,
Joel

JoshMB · #3 11-27-2002, 02:05 PM

I did have it tested at Autozone - the battery was good - and so was the alternator - except that it does have this delay in charging.

The battery is exactly 23 months old. I wish it were only the Battery, I have a 2 year free replacement warranty on it.

#4 11-27-2002, 02:16 PM

Not sure what a typical drain would be when not running, is it possible your reading is excesive?

Again, I would not think the five munites to work would be the cause.

Joel

Sorry, I suck at electrics.

dpetryk · #5 11-27-2002, 02:35 PM

Well IMHO, if it takes five minutes for the alternator to start charging and you only drive it for five minutes to work then it seems to me that you are not charging the battery during the drive and YES that will deplete the battery.

Something is wrong with the alternator. It should start producing charging current within seconds after the engine starts.

JoshMB · #6 11-27-2002, 02:41 PM

DPETRYK

That is what it seems like to me. The second logical problem is that if the voltage from the alternator is getting to the battery in five minutes, then the wires between the alternator and battery are good, no? But it is a brand new alternator and I had it tested before I left the store - no problems.

Does anyone know how a voltage reg works and if such a delay is common??

tjohn · #7 11-27-2002, 04:39 PM

I'm taking a stab in the dark here, but could the issue be that your alternator isn't putting out enough voltage to charge your battery? I've heard that some of the newer maintenance free batteries in particular need a higher voltage than the older alternators produce. I know this would not produce the delay in charging phenomenon you describe, but I wonder if maybe the folk at Autozone just misdiagnosed that??? Maybe?? Just a thought. . .

jbaj007 · #8 11-27-2002, 05:01 PM

Josh,
I had the same (similar) problem. Short trips, delayed alternator output (although I never saw 14.4 volts), dead battery every week. Assuming you checked everything with a 100% battery charge (75% is minimum for tests according to Bosch), you have a bad alternator. I replaced mine and no more midnight Sunday driveway charging for me. 4 to 5 minutes is way to long; around 10-20 seconds on a good charging system to reach 13.8 volts at ~1000 rpm.(at most)

Jim Anderson · #9 11-27-2002, 05:03 PM

Except I had a 45 minute drive to work so it was a non problem. Whats happening is your alternator isn't "starting." Alternators are esentially self starting, and yours isn't. Part of that effect is the dash "alternator" light, check that, it should come on with the ignition on and the engine off.

A trick I did was after everything warmed up a little reving the engine up. That helped it "start" sooner.

dpetryk · #10 11-27-2002, 06:32 PM

Jim is right about the alternator light. If its bad, then the alternator will not start generating output. Good diagnosis Jim.

JoshMB · #11 11-27-2002, 10:36 PM

Hmm. The diagnosis of the alternator not "starting" sound like that could be it. But my light on the lower left hand side of the dash comes on when I set it on "glow." At least I think it is the alternator light. It looks like a little battery. That it what was showing when I had a bad alternator -- that light came on while driving. It is lit when I take the key out of the ignition and let it "diesel down" for a shut off.

Any other reason that the alternator would not "start"?

Thanks for the help.

josh

Mike Murrell · #12 11-28-2002, 12:12 AM

Autozone should change the name of their "DuraLast" products to "QuicklyGone".

I went thru this with an American car about 15 yrs. ago. I forget how many times I pulled the thing off and went back for another.

Autozone's price is appealing; their quality is a whole 'nuther thing.

Bite the bullet and get a Bosch reman for your MB or a brand new one. Anything will be better than the crap Autozone sells.

My 2 cents.

dpetryk · #13 11-28-2002, 10:12 AM

Try another alternator regardless of the fact that the one you have now tests "good".

JRBrown · #14 11-28-2002, 11:35 AM

JoshMB,

Bear with me as I lead into my point by way of example.

Over the years with Bosch Alternators I have noticed that they can fail to charge (worn out brushes on the voltage regulator) without illuminating the Light in the cockpit. So in my 1981 Volvo I installed a Voltmeter gauge. After start, the needle always went to 13-14 volts (where it should be for a charging condition).

At 175k miles, the factory Bosch alternator failed. As this was a daily rusty driver, I purchased an Autozone Duralast alternator for my Volvo. They are "cheap". And that is probably the operative word.

Mine exhibits the same behavior your's does. After start it shows about 12-12.5 volts (no charging). If I pop the throttle above 2000 rpm the voltage gauge shows that it is now charging. You may want to try the same thing. However, since I don't know how many rpm the alterantor is at with 2000 rpm at the crank, your rpm may be higher or lower to get it to charge.

I'm going to make a guess here. The Duralast design probably had cost as the top priority. That includes the regulator. The regulator provides an excitation function that gets the juice flowing. Mine requires more rpm to get going than does the OEM speced Bosch. I've test my theory on my three other Bosch based systems. After start, with no increase in rpm, there is charging voltage.

If the battery isn't being charged, then your running off the battery and it can not self charge just sitting there.

Please let us know if my experiences are yours too.

JRBrown · #15 11-28-2002, 11:36 AM

JoshMB,

Bear with me as I lead into my point by way of example.

Over the years with Bosch Alternators I have noticed that they can fail to charge (worn out brushes on the voltage regulator) without illuminating the Light in the cockpit. So in my 1981 Volvo I installed a Voltmeter gauge. After start, the needle always went to 13-14 volts (where it should be for a charging condition).

At 175k miles, the factory Bosch alternator failed. As this was a daily rusty driver, I purchased a Duralast alternator for my Volvo. They are "cheap". And that is probably the operative word.

Mine exhibits the same behavior your does. After start it shows about 12-12.5 volts (no charging). If I pop the throttle above 2000 rpm the voltage gauge shows that it is nwo charging. You may want to try the same thing. However, since I don't know how many rpm the alterantor is at with 2000 rpm at the crank, your rpm may be higher or lower to get it to charge.

I'm going to make a guess here. The Duralast design probably had cost as the top priority. That includes the regulator. The regulator provides an excitation function that gets the juice flowing. Mine requires more rpm to get going than does the OEM speced Bosch. I've test my theory on my three other Basch based systems. After start, with no increase in rpm, there is charging voltage.

If the battery isn't being charged, then your running off the battery and it can not self charge just sitting there.

Please let us know if my experiences are yours too.