I just got home from a road trip, and had some problems with the AC/battery/alternator. I don't really know which is the culprit, but hopefully somebody will have some incite.

I drove about 6 hours the first day, blasting AC with no problem, 2 hours the second...again, no problems. After the 3rd day (another 6 hours) the car wouldn't start, or even turn over after we stopped for lunch. I got a jump, and it worked fine. When I got to my destination, it did the same (wouldn't start).

At that time, I whipped the old multimeter. The battery was sitting just below 13V without the engine running. I started it (with a jump) and it was sitting right around 14V. I turned the headlights, radio, and AC on, the battery leads read about 12.75V. Turned it off again and the battery recovered. I drove around for about 10 minutes without any electronics, and it was able to start on it's own power again.

I drove around for several days, without the AC, the car started every time with no problem. On the way home, I turned the AC off about 10 miles before our lunch destination, hoping the battery would charge enough to start...no luck there. After lunch, we did a push start and went our way, blasting the AC again. When I got home, I hooked up my battery charger, but it showed a full charge after 5ish minutes.

The battery is about 5 months old, but I'm not discounting that could be the problem. I am guessing it's the alternator loosing it's ability to output over the years. Any ideas?

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My Primary Driver - '85 300CD - 4-speed conversion, 2.47 rear, lowered, euro headlights, rebuilding (not restoring so much)

Wife's - '08 Saab Sportcombi Aero

Riding a '03 Yamaha Warrior

If the battery got overcharged as it could during the long trip, it could have lost over 70% of its capacity. I just read an intersting article about this happening. The battery heats up to 130 degrees and then starts accepting way too much current. The temp then goes to about 160 degrees and poof you loose more than 1/2 the battery. I would take it in to AutoZone or Sears and let them put a load teat on it. I would also check the regulator to make sure it is not putting out too much voltage.

The idea that it went from dead to full charge in 5 minutes is making me think that it overheated.

If you could rig up a temporary voltage meter so that you can watch it while you drive that should tell you a lot as well.

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"I have no convictions ... I blow with the wind, and the prevailing wind happens to be from Vichy"

Current
Monika '74 450 SL
BrownHilda '79 280SL
FoxyCleopatra '99 Chevy Suburban
Scarlett 2014 Jeep Cherokee
Krystal 2004 Volvo S60
Gone
'74 Jeep CJ5
'97 Jeep ZJ Laredo
Rudolf ‘86 300SDL
Bruno '81 300SD
Fritzi '84 BMW
'92 Subaru
'96 Impala SS
'71 Buick GS conv
'67 GTO conv
'63 Corvair conv
'57 Nomad

I picked one of these up for marine use,Then discovered the Sonar screen
can be configured to show a constant voltage readout as part of the display.

They are available at AutoZone about $12.00.
It plugs into your cigarette lighter socket and you can view the alternator
output voltage as you drive.

If your Alternator is consistently putting out 14+ volts DC with no loads it's OK.
If however it's putting out over 15 volts you may be in LUVMBdiesel's cooked
battery zone.

Attached Thumbnails

 

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'84 300SD sold
124.128

Kind of makes sense. Would it then be able to regulate it's charge after it cooled? What's the chances it's just a bad battery? I would assume so since it doesn't happen to everybody.

The main reason I was thinking of the alternator is because of the low voltage reading with all the electronics on with the engine running. That's still throwing me off...I'll try that test again in the morning with a cold car. How much current should the AC use anyway?

__________________
My Primary Driver - '85 300CD - 4-speed conversion, 2.47 rear, lowered, euro headlights, rebuilding (not restoring so much)

Wife's - '08 Saab Sportcombi Aero

Riding a '03 Yamaha Warrior

I'll put a new cig lighter and try this too.

__________________
My Primary Driver - '85 300CD - 4-speed conversion, 2.47 rear, lowered, euro headlights, rebuilding (not restoring so much)

Wife's - '08 Saab Sportcombi Aero

Riding a '03 Yamaha Warrior

5 month old battery should still be under full replacement warranty. Take it back and try another one. I think it could be a defect in the new battery.

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Charles
1983 300D, bought new, 215k+ miles, donated to Purple Hearts veterans charity but I have parts for sale: http://www.peachparts.com/shopforum/showthread.php?t=296386

I am going to take the battery in today. I forgot my warranty paperwork yesterday, and am getting really tired of push starting when the car is warm. I still think that's the problem, but I did find something else interesting.

I rigged up my multimeter to the wiring originally used for the cig lighter. When driving, I see around 13V, and when idle, it goes down to about 12V. This sounds a little low to me, is it?

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My Primary Driver - '85 300CD - 4-speed conversion, 2.47 rear, lowered, euro headlights, rebuilding (not restoring so much)

Wife's - '08 Saab Sportcombi Aero

Riding a '03 Yamaha Warrior

I think you joined my electrical PITA Club. Just had my 4th alternator installed this morning. Once again everything is fine, for now. Can't find the reason it stops charging. Good luck with your car.



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1984 MB 300 SD Turbo

I went through months of troubleshooting and different alternators. It all boiled down to a bad belt. Proper tensioning of a new belt solved the problem.

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Kevin

1978 300D
1979 240D

hmm, interesting. I am wanting to put my stereo in the car in the near future, so I think I am going to put the Saab 115 amp in once I can find one.

I did take the car out for a bit earlier with NO electronics going, the output stayed around 13.8V. When I turn the lights, or the AC, or a few other accessories, it drops to 12-13V, depending.

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My Primary Driver - '85 300CD - 4-speed conversion, 2.47 rear, lowered, euro headlights, rebuilding (not restoring so much)

Wife's - '08 Saab Sportcombi Aero

Riding a '03 Yamaha Warrior

Usually alt load testing is at 2000 rpm engine speed.

A faulty voltage regulator can cause this as can worn out brushes or a grooved stator on the alt.

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RRGrassi


70's Southern Pacific #5608 Fairmont A-4 MOW car

13 VW JSW 2.0 TDI 193K, Tuned with DPF and EGR Delete.

91 W124 300D Turbo replaced, Pressure W/G actuator installed. 210K

90 Dodge D250 5.9 Cummins/5 speed. 400K

Well, I took the car in to get the battery tested, and of course, it worked just fine. I messed with it for like 40 minutes and couldn't get it to replicate the problems I have been having. Maybe I'll just have to wait until the next time I have to push-start.

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My Primary Driver - '85 300CD - 4-speed conversion, 2.47 rear, lowered, euro headlights, rebuilding (not restoring so much)

Wife's - '08 Saab Sportcombi Aero

Riding a '03 Yamaha Warrior

Output on my two 123's is over 14 volts at idle. It's not charging.

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Kevin

1978 300D
1979 240D