D2 55 alternator wiring and voltage

[elias]

Hi to all ,
I ve noticed since last service that the alternator was doing 13.5v max with 10-15amp on a low battery bank .

I saw that the little yellow cable coming out of the alternator was going again on another alternator nut.
Then I saw a yellow cable coming from the battery wrapped in tape .
When I connected them , voltage 14.4 and 20amps …
Any ideas ? Should I bridge the yellow , the nut and the battery yellow ??

[diverphil]

I think the yellow wire is for voltage signal to alternator regulator, so is controls the voltage and charge output to the battery's. we used to get trucks that needed jump start for flat batts and if you didn't leave jump pack on for a bit the alternator wouldn't kick in and so the next time they stopped they would be still flat, i.e. no alt output.(this was in times before everything was controlled by electronics). i would connect it and keep a watch on battery's for overcharging, it may have been disconnected as a temp repair for a faulty regulator at some point. how long has this been happening, how long have you had the boat. if its only been used for days out and back on mains overnight the problem of no or low charge might not have been noticed.
you may be able to find a wiring diagram on here or google.

[elias]

We got the boat like that , and I was curious why a factory cable (the yellow with the number 2 ) coming from the engine was wrapped with tape . Second day on , charges much better than before , the previous connection would make max 13.7v and in the same moment after changing the cable to the one yellow coming of battery bank would go 14v

[Jake]

This is a somewhat puzzling problem, but you seem to have a fix for it (connect the factory yellow wire again).  Is it possible that a previous owner had used an external voltage regulator and then removed it?

Jake
Bav 44

[elias]

The previous owner had the yellow female cable coming from the inside of the alternator (I guess the regulator ) to the B+ if I remember correctly and the alternator will give a voltage around 13.8 max . Now it does 14.1

[tiger79]

The previous owner had the yellow female cable coming from the inside of the alternator (I guess the regulator ) to the B+ if I remember correctly and the alternator will give a voltage around 13.8 max . Now it does 14.1

Where are you measuring the voltage?  At the alternator or at the battery?  Is there a diode splitter on the boat?

[elias]

There is , I measure negative on the engine block and positive on the input bolt (where the cable from alternator ends) on the victron diode splitter .

[tiger79]

There is , I measure negative on the engine block and positive on the input bolt (where the cable from alternator ends) on the victron diode splitter .

You should really measure the voltage at the battery terminals - that's what matters.  Depending on their design, diode splitters can cause up to 0.7v voltage drop.  Your alternator should be outputting close to 14.4v ideally.

[SYJetzt]

The yellow cable needs to be connected from the service battery +terminal to the alternator. It serves as a sensor connector to compensate the voltage drop of the diode splitter. If not connected, the alternator voltage drops and the batteries( service and starter) are not charged to the right voltage, causing premature aging of the batteries and lacking state of charge.

[elias]

Thank you guys ,
Ok works fine since I connected to the yellow of batteries I can tell the difference . 14.2 at the batteries .

[Jeffatoms]

Ironically, we too found the yellow cable disconnected last week while upgrading our alternator regulator to an external Balmar MC618.  As it was disconnected on the starboard settee (with said blue tape) and again, disconnected in the engine bay with blue tape wrap, we connected it to the new alternator regulator as a house bank voltage sensor.  Perfect!