Battery not being charged - PeachParts Mercedes-Benz Forum

subman60 · #1 06-01-2012, 05:50 PM

The battery on my 82 240D is not being charged by the alternator. Took the alternator off to be rebuilt. Shop called me back it's ok. Owner of the shop told me to put it back on and check voltage at the leads going into the alternator. He said two leads should have battery voltage all the time the other when the key is switched on. I have battery voltage at the two but the other one registers just over 2 volts with key in on position. Started the car to check voltage going to battery started out at 14.2 volts then went right down to 12.7 then 12.4. Battery is very low now will hardly turn over the car. If it's not the alternator and the battery has checked good at two places what else do I need to look for?

Air&Road · #2 06-01-2012, 05:58 PM

Sounds like you have a bad connection, probably at the alternator. I have had the terminals get loose from the wire on the alternator connector. If they're loose you can tighten them with pliers.

Next time, don't pull the alternator off to have it tested. If you're not making that 14 Volts or so at the battery, simply pull the two screws at the connector on the alternator and lift out the voltage regulator from the alternator. The brushes are in this. If they are worn and the groove in the alternator sliprings is about an 1/8" or less deep, then replace the regulator. This will work a large percentage of the time.

In this case I really think you have a flaky connection and it is likely at the alternator.

Hope this helps.

subman60 · #3 06-01-2012, 06:10 PM

Thanks, I'll pull the wires off the back and check them out. I had two different shops check the charging system before pulling the alternator, I hate pulling anything if I don't have to. The alternator is a NAPA rebuilt that the PO put on it. Will the original Bosch unit be a better choice?

Markp · #4 06-01-2012, 07:09 PM

I'd say a reman bosch would be better then Napa, but if it tests OK no reason to replace it.

Like Larry said, its a bad connection or the reg/brushes need to be replaced.

Did you check the engine to chasis ground?

subman60 · #5 06-01-2012, 07:49 PM

No I didn"t, I'll check that also

jay_bob · #6 06-01-2012, 08:32 PM

Check your charging indicator on the dash, it is part of the regulator circuit. Without the bulb in circuit the regulator has no power. If the regulator and field do not get power, the alternator will not produce electricity.

Seems kind of weird, you need to give the alternator some electricity to have it produce but that is exactly how it works. The small energy input from the field combined with the rotational energy from the pulley (less the losses) creates the output energy.

The big generators I work with are exactly the same (2.5 MW) except the field exciter gets its power from a small permanent magnet generator on the end of the main shaft. To sync the generator to the bus we alter the voltage by biasing the field excitiation. Zero excitation on the field means no output voltage.

(and we have to match frequency and phase angle too, much easier with the modern computer controlled direct injection engines)

These get driven by 16 cylinder diesel engines larger than my entire car. And of course there are no diodes, we are making lots of three phase to keep those servers running and cooled when the power company can't.

Diesel911 · #7 06-01-2012, 09:32 PM

Quote:

Originally Posted by subman60

The battery on my 82 240D is not being charged by the alternator. Took the alternator off to be rebuilt. Shop called me back it's ok. Owner of the shop told me to put it back on and check voltage at the leads going into the alternator. He said two leads should have battery voltage all the time the other when the key is switched on. I have battery voltage at the two but the other one registers just over 2 volts with key in on position. Started the car to check voltage going to battery started out at 14.2 volts then went right down to 12.7 then 12.4. Battery is very low now will hardly turn over the car. If it's not the alternator and the battery has checked good at two places what else do I need to look for?

What the Guy said about the Connector is true. The 2 large slots go to the 2 fat red wires and always have Battery Voltage.

The single Short Slot goes to the skinny Blue Wire that goes to the Charging Lamp in the Instrument Cluster.

When the key is on it should have slightly less than Battery Voltages. I mean within several 10ths of a Volt less.

In another thread some one mentioned cleaning the Terminal Block Connections.
If you are careful you can pry open the Alternator Connector.

subman60 · #8 06-06-2012, 11:53 AM

Got it working. I couldn't find anything wrong so drove the car to the alternator and starter place. He asked me to pull the alternator and he would look at it again. Turned out the regulator was going bad.

vstech · #9 06-06-2012, 01:22 PM

Quote:

Originally Posted by jay_bob

Check your charging indicator on the dash, it is part of the regulator circuit. Without the bulb in circuit the regulator has no power. If the regulator and field do not get power, the alternator will not produce electricity.

Seems kind of weird, you need to give the alternator some electricity to have it produce but that is exactly how it works. The small energy input from the field combined with the rotational energy from the pulley (less the losses) creates the output energy.

The big generators I work with are exactly the same (2.5 MW) except the field exciter gets its power from a small permanent magnet generator on the end of the main shaft. To sync the generator to the bus we alter the voltage by biasing the field excitiation. Zero excitation on the field means no output voltage.

(and we have to match frequency and phase angle too, much easier with the modern computer controlled direct injection engines)

These get driven by 16 cylinder diesel engines larger than my entire car. And of course there are no diodes, we are making lots of three phase to keep those servers running and cooled when the power company can't.

...
ok, I had NO idea you did this stuff...

you HAVE to take pictures of this equipment, and most importantly, the engine that drives it!!!!!

MAKE A NEW THREAD!

jay_bob · #10 06-06-2012, 07:41 PM

Sorry photos and cameras strictly banned at my customer sites.

If I got caught taking pictures I would be fired and or arrested.

Some places make me leave my cell phone at the security desk because it has a camera.

If you are curious what these guys look like search for one of the major manufacturers
Cummins, Caterpillar, Kohler, MTU/Detroit Diesel

jay_bob · #11 06-08-2012, 12:37 PM

Quote:

Originally Posted by subman60

Got it working. I couldn't find anything wrong so drove the car to the alternator and starter place. He asked me to pull the alternator and he would look at it again. Turned out the regulator was going bad.

Yep just as I suspected.

No regulator = no field excitation = no electricity.

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