battery alternator failure mystery - PeachParts Mercedes-Benz Forum

coleman kelly · #1 08-23-2003, 01:11 PM

is anyone available for coaching tis afternoon over the phone?
I hve repaces my battery and alternator 1500 miles ago and now they are both cook again? 11.8 volts on the battery after overnithgt 1.5 amp charge and the alt is putting out nada.
What cooked what? Hunting down bad conections and such as per the threads I have found, but still haven't found the phantom.
thanks for the help.

P.E.Haiges · #2 08-23-2003, 09:42 PM

Kelly,

Disconnect one terminal from battery and charge the battery.

Then reconnect battery and see if the starter will crank the engine.

If the battery was good enough to crank the engine do the next test below. If the battery will not crank th engine, the battery is probably NG. Replace the battery and see if that solves problem.

You will need an ammeter for this test: Turn everything off and disconnect one battery terminal. Setthe ammeter to the highest range and connect the ammeter between the battery terminal and the battery cable. There should not be more than 50 ma current flow. If more than 50 ma, do next test.

If there is more, start removing fuses until the current drops to almost zero. That is the circuit tha is drawing the current.

Let me know your results.

P E H

coleman kelly · #3 08-23-2003, 10:44 PM

PEH
thanks for the response. The battery turned up god. Fresh charge. Turns out a 2 amp charge may take several days? News to me, I thought overnight was sufficient. Anyway it's fully chaarged now and I have new alternator in. I upgraded to a Bosch reman.
Haven't started or tried to start the vehicle yet. Should I try to run down the original culprit before starting? Can I cook anything? I don't think so as long as battery is charged. My brother says I may have simply bougt a bad alt. off the shelf, Test said bad diode.
I am going to clean up both the ends of the frame to engine grond straps that is the last of the connections I can think of.

If I do do this test you speak of one question. Why would I look for the currect(if over 50 ma) to drop to zero and not back to 50 ish?
Also, are there fuses besides the ones in the box that I should check? I see some inline ones around.
thanks for your help. WIll know more in a.m. coleman

P.E.Haiges · #4 08-24-2003, 11:46 AM

Kelly,

What model car are you talking about?

If you remove a fuse and the current drops to almost nothing, it should go back to the original when the fuse is replaced, I.E. 50ish.

The fuse removal test is to find a circuit that is running down your battery when the car is not being used. If the problem is a bad alternator, you won't have to do this test.

Yes, it will take more than 24 hours to fully charge a battery at 1.5 amps.

P E H

diesel don · #5 08-24-2003, 09:13 PM

Have you checked the voltage regulator that tracks on the diodes? It may be toast. I've experienced bad VR's more that bad Alts.

Don

coleman kelly · #6 09-08-2003, 11:08 PM

Well, Of course I can never be sure, but I think I may have gotten a bad unit right off the shelf. I had the replacement bench tested(was in the car for about a week) and it came up witha bad diode) I'll never really know if it was bad off the shelf or something about my wiring ate it up, the new one is doing well charging at 13.5 after approx 2k miles.
I continue to have a crazy tach needle with the headlights on, testimony to a bad dash ground I have read. Only thing that may be related as far as I can tell. thanks.

#7 09-09-2003, 06:51 AM

It probably was a bad unit, I've had it happen many times with aftermarket alternators. If they make it past the first week, they might be ok for a month or so. To be honest they are junk. I always try to stick with a reman done by the manufacturer of the alternator. I think when an aftermarket company rebuilds them they just clean them up and make them work, not worrying whether they'll last or not.

Just my 2 cents!

Brandon