'89 240DL strange charging issue

[Reverend]

I have an '89 240DL, B23F. After improper diagnostics by the shop, I have replaced the alternator to no avail to solving my charging problem.

My battery is a bit over 2 years old. I have checked cell to cell voltage and they range around 2 volt each.

With the electrical system fully intact, i.e., the battery connected, the car will charge the battery to a full 13.7 volt if no other load is running (lights, blower, etc.). Once activating any load with the car running, the battery will rapidly discharge (voltage reading from the alternator dropped to less than 10 volt over a 5 minute duration). Upon de-activating the load, the system will charge again to 13.7 volt within a reasonable amount of time. I let the car sit over night and the battery still has more than adequate power to start the car.

If I start the car and disconnect the battery, the alternator takes over and allows for the car to continue to run. Upon activating a load (or even several loads) the output of the alternator remains above 13 volt.

All grounds appear to be good and I don't suspect a short.

I realize the logical culprit would be the battery but I don't get it due to the tests I have ran on the battery. It charges fine and holds a charge.

Any thoughts?

regards

Rev

[Reverend]

Status Update

Today I have found the following:

Start the car fine with no loads on - battery VERY strong.
Check alternator voltage at 13.+ volts - battery connected
disconnect battery - Alternator reads 13.56 volts
Turn on lights - alternator reads 13.3+ volts
re-introduce the battery - alternator reads 12.5+ volts
disconnect battery - alternator reads 9,6 volts and will not recover.
turn off lights - alternator recovers to 13.56 volts

I've seen a lot of reviews but no replies.

I hope the additional info will stir some thoughts on this matter.

regards

rev

[Paul240480]

Sounds strange, to say the least!

When you say you've replaced the alternator, is a brand new unit or a second hand unit. Just wondering ir the voltage regulator on it is playing up. Maybe worth pulling out that darned regulator & checking the brushes on it.

HTH's

[Clan]

disconnecting the battery with the engine running is always warned against you may well have damaged the alternator ...

[Reverend]

Paul -

It is a new after market alternator.


Clan -

I have heard that story in the past regarding disconnecting the battery under alternator load. As there is minimal load on the alternator (the battery is up to charge) the amplitude of the PIV on the diodes should not be enough break them down, i.e. >1000 volt typ.). And if that were the case, the alternator would never recover.

But, thank you for the feedback!

[OldBlueVolvo]

With the engine running and no unnecessary loads connected, what voltage would you expect to see across the battery terminals? I would have thought that it would be around 14V. And, if you then switch on a load and the regulator is doing its job (or is able to do it), by definition it should regulate the voltage. Was the regulator replaced with the alternator? If the regulator is a separate unit (I don't think it is) then I would suspect it. Is the V-belt tensioned correctly?

[Reverend]

old blue

I would expect to see the 13.56 volt reading on the battery if fully charged as it does while waiting a reasonable amount of time (as stated with no loads, only the motor running). 14 volt or better would probably be achieved from an OEM alternator. As stated, without the battery in the system, I see ~13.5 volt at the alternator, which I feel is acceptable with a load running.

The regulator is a new integrated part with the alternator.

V-belts are tensioned correctly.

Please advise.

[Peter D]

Running with a fully charged battery 14.2 to a max of 14.75 volts. Can you explain whow come you have a 2 year old batterty that give you access to the separate cells to measure there voltage. They should all charge upto 2.2 to a max of 2.25 volts. Do not run the car without the battery, you do not risk the alternator so much but you may fry the ECU's. Check all earthing points between battery and alternator. Regards Peter

[chesters6]

a battery with a dead cell will charge to 14v on a meter (your seeing the alternators output)but it will very rapidly drop back to 10 ish with the engine off.
try turning the engine off and measuring the ampage drop by putting a meter between the pos terminal and its disconnected lead it should be very small milliamps if not theres a short to earth somewhere if its just milliamps (nothing more than the clock running) then try a substitute battery and compare to see if that battery flattens.
the voltage across the battery with engine running lamps and fan on should be 14v + if the alternators charging correctly any less the battery is dodgy or the alternator is.
the battery getting hot shows a cell is shorted somewhere ,quickly discharging shows a cell isnt charging,in the former the battery will fizz far faster than normal and the effected cell will boil of the acid making it worse.
some poorly batteries can be recovered using a smart charger which get rid of the buildup of crud on the plates that stop the battery charging correctly they cant cure buckled or broken plates though.
even the original 55amp alternator will give +14v (all lights and fan on )on a good battery ,i just replaced my brush pack which was worn out so the alternator only pumped out 13 odd volts (did it pump out or did the battery suck in who knows)

[pigfight]

i maybe stating the obvious here, but are the distilled water levels topped up in all the cells? gotta be worth a look. otherwise, could it be a relay fuse starting to fail somewhere?
i dont claim to be an expert but whenever i have similar problems to this, i try to start with the simplest (and cheapest) options first.
hope you get it sorted soon, let us know how you go.
regards,
david.