Overcharging with new alternator

[Peksa93]

Hi

Few weeks ago I got 1998 D22 that has been parked for few years and now I'm fixing it to be roadworthy again.
Its 2.5TD 4WD so engine is TD25 I believe and cold weather model with OEM dual batteries.
Batteries were dead and where replaced with quality items.

As I started driving it I noticed all the lights and fan pulsing in 1 sec or so intervals and when I measured battery voltage it was pulsing from around 15V to over 16V.
I removed the plug from alternator and I believe I confirmed that it wast charging so that I could drive it to garage.

I checked wiring and measured voltages at the alternator plug. I found that SENSE wire fuse was blown but I believe I saw 12V from both at the start so I propably shorted it
with multimeter in current mode as I was confirming which the warning light (LAMP) pin was.

After that I bought new alternator as nothing else appeared to be wrong.
Hooked up new alternator and measured voltage. With few clicks of handthrottle it gave steady 14.2V. Perfect.

Went for longer test drive in the dark and stopped to fiddle with headlight adjustment while car was idling.
As I got on the road again battery light and some other warning light (fuel filter?) came on and I stopped.
Idle no light, revs -> warning lights came on. Measured battery voltage while reving. 17V !
I had read about battery light being capable of warning about overcharging but hadnt seen it before. Old alternator might have been too weak to trigger it.

Next I resistance measured everything I could think of. Battery to body to engine to alt.case all zeros.
I believed that I found the issue as SENSE line measures 3-5 Ohms from battery positive.
Used jumpwire to connect warning light wire to its pin and ran fused wire straight from bat.positive to alternator SENSE pin eliminatin possible loom fault.
Started car and measured around 14.9-15V at 2-3 clicks of handthrottle.

Went for test drive and was almost done with it as I revved engine a bit higher than usual and then I saw warning lights come on for a moment.
Parked, hooked up multimeter and revved the engine. over 16V and rising when RMPs got high enough. Unplugged the alternator again and drove home.

As I was driving I noticed that light did get brighter at revs and at home I measured battery voltage with alternator 2-pin plug unplugged.
It was still overcharging. Residual magnetism in coil maybe?

Any advice? I'm starting to suspect that the new alternator is also faulty. Its Hella branded one. Made in China.

PS. First post. Awesome forum you got here.
Greetings from Finland

 

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may be relevant got a little idle time, i always remove alternator and take it to auto electrician to bench test if its ok then problem is in car circuit.tell him at what revs you are having problems, also make sure you have correct size pulley,to small will cause overcharging .. having dual batteries are they connected correctly, is the isolator ok is the dual battery monitor ok . the reg may be reading incorrectly sending more voltage than it should be...
another issue is that some mod eng and elect system designed to take clutch pulley on alternator.. you may have a fixed pulley which is over running

,,,If the output voltage reading is 16 volts or higher, there's an overcharging problem. This usually indicates a bad voltage regulator.

• If voltage seems to fluctuate during your test, switch your voltmeter to the AC voltage scale and take another output voltage reading with the engine still running.
  • This time, connect your meter's red lead to the B+ terminal on the back of the alternator, and the meter's black lead to battery negative (-).
  • Usually, the presence of 0.25 AC volts means a leaking diode that requires replacing the alternator. But some manufacturers recommend replacing the alternator if 0.50 AC volts is detected.
  • However, if you have noticed engine performance issues, this might be the problem. Consult your vehicle repair manual for acceptable diode leak rate, if necessary.
  • Most replacement alternators have design and voltage output specifications meant for a specific vehicle and its requirements. Some replacement and re-manufactured alternators have much higher output ratings and designs. When the wrong alternator has been installed in a stock vehicle or if the pulley has undersized dimensions (causing extra alternator rotation), the charging supply will be higher than the demand and cause an overcharged state. High performance or racing alternators should not be installed on stock passenger vehicles.
    i have used larger out put alternator on my 1998 model nav , it hasnt caused me any problems its got air con and extra driving lights

some additional info probably not relevant
Poor battery condition and failed regulators are usually the cause of overcharging. If the regulator cannot read the electricity level in the battery, it may cause an overcharging of the alternator.


Improperly jump-starting the vehicle can send a surge through the battery that destroys one or more cells in the battery or shorts it out. This surge disrupts the wiring in the alternator, causing an overcharging condition.

 

[Peksa93]

Well new alternator turned out to be bad. Drained batteries flat one night. Measured over 2,5A draw from alternator positive.
Parts store in here is being difficult and wouldn't give any compensation before they can sent it out to be tested so I took it back out and put old one back in.
As I had old one in my hands again I noticed it missing one of those small nut at the back. Put one on there and installed it in the car and so far so good.
Problem might have been that all along or I fixed the problem when diagnosing the new alternator.