Alternator low voltage

[markleuty]

Hi

I have just replaced my alternator with an aftermarket version from part4engines.com because the old one wasn't charging the battery and was really badly corroded (and 19 years old).

D2-55A Engine

Problem is, the new one is also not charging and I'm wondering whether I did some really stupid when connecting it up to cause it to die.

It has 4 terminals. B+, B-, D and W. In the fitting instructions it says B+ to Battery Positive and B- to Battery negative, which I did.

On my old alternator, the W terminal had a plastic cover on it and nothing was connected to it. But in the instructions I received it said that I should connect the Tacho lead to W.

Because on the old alternator, both Tacho and Warning Lamp were connected to D, I decided to do this on the new alternator as well.

The main problem was the yellow wire (battery sensing). The yellow wire that came from inside the alternator was connected to a spade connector on the B+ terminal. So I, probably foolishly, connected the yellow wire from the battery to the B+ terminal as well.

When I started the engine, the not-charging alarm began sounding and wouldn't go away no matter now much I revved the engine. When I measured the voltage between B+ and B- I got about 12.6V. (which I think must have just been measuring the battery voltage).

Then I came to my senses and connected the yellow wire from inside the alternator directly to the yellow wire from the battery, not in contact with B+ at all.

Now when I start the engine and rev it up a bit, I'm only getting 0.2V between B+ and B-.

I have checked that the B+ has a good connection to the battery.

Have I blown the rectifier by connecting the yellow wire incorrectly, or do you have any other suggestions as to what may be wrong?

Many Thanks

Mark

[JEN-et-ROSS]

I don't think you've done anything wrong that could damage the alternator.
  The issue I see is that on your old system the 'sense' wire was connected to the B+, therefore it was 'sensing' the voltage at the the alternator and not the battery, so the voltage drop due to cabling/connection losses was not being allowed for by the alternator, so charging would be somewhat slower than it could be.
 
On your new alternator set-up, if I've read correctly, you've connected the yellow wire from the battery to the B+, (you've now got 2 wires from B+ to the battery?)
therefore the sense wire from the alternator isn't actually connected to anything?? so the alternator thinks there is totally flat battery so it pumps out all it has. OK in the short term maybe.
If the sense wire is also connected to B+, again OK in the short term (better connected to the battery +ve)

As long as the B+ & B- were always connected correctly I can't see any popped diodes.

I'd return the alternator as faulty...........I hope the above makes sense....................Bill

[Odysseus]

Some alternators (Lucas) need the stator "exciting "  at low RPM if I remember its around  1500 RPM before it supplies it's own power. It was the yellow lead that supplied this.
I am sure there will be  articals on Google YTube.

Odysseus

[SYJetzt]

check if the warning light is working. It should glow, if alt is stopped and go off, if alt revs. D needs a connection over this warning light to (B)+ to power the field of the alternator.

[JEN-et-ROSS]

Some alternators (Lucas) need the stator "exciting "  at low RPM if I remember its around  1500 RPM before it supplies it's own power. It was the yellow lead that supplied this.
I am sure there will be  articals on Google YTube.

Odysseus

On our alternator, it requires something over 1000 rpm before the rotor generates enough power to excite the stator coils into action. After which you can throttle back to tick-over and it continues to generate.
I may be wrong but I always believed the connection from the rotating rotor to the stator coils was internal, the regulator sensing when this was achieved.

If it was the sense wire that was controlling the start-up, then there's always going to be about 12.5 Volts, (more than enough to get things going) so no need to get to 1000-1500 rpm to kick-off.
 If I'm wrong then I've learnt something...............Bill

[markleuty]

Thanks for your replies...

It turns out I had wired it up wrong. There was a spare black wire, which I had assumed should be connected to the D terminal but after extensive perusing of the wiring diagram in the workshop manual, it appears that it should have been connected to the B-.

I did this, fired up the engine and whoppee, lots of happy electrons making their way to my batteries

 

[JEN-et-ROSS]

I did this, fired up the engine and whoppee, lots of happy electrons making their way to my batteries:)

Really pleased to hear it's resolved......Bill