Volvo Penta D2 55A alternator problem.

[coyi]

Hi All. The problem occurs on start up. Sometimes the alternator fires up and produces a charge, sometimes not. I suspected the exciter wire as very often there was less than 12volts at the D+ terminal. So I bypassed the blue/red wire and fed D+ directly from the engine control panel. Alternator fires up every time. I took off the black connection box and discovered the magnetisation resistance had heated up the attached wires and melted their insulation. What should I do and is this resistor important.
Thanks for any advice.

 

[VicS]

Traditionally the filament type warning light provided the initial field current required to get the alternator generating. Once generating the field current is supplied by the field diodes.

LEDs now used in place of filament bulbs do not supply enough current.
The solution, in the case of VP engines, is to supply a 12v feed from the panel via the "excitation" resistor to the D+ terminal.

Without it the alternator will not start to generate.
A direct feed may be supplying to high a current but as you have discovered is a work-around fix.

IIRC the resistor is 50 ohms It should be rated at least 5 watts. Your favourite electronics component supplier will be much cheaper than VP even if the resistor is available as a spare part. I have not found it on the parts list but i found these on eBay
2 Pcs Aluminum Case Resistor 5W 50 Ohm Wirewound for LED Replacement Converter 714998018083 | eBay

 

[coyi]

A couple of photos of the offending item

Traditionally the filament type warning light provided the initial field current required to get the alternator generating. Once generating the field current is supplied by the field diodes.

LEDs now used in place of filament bulbs do not supply enough current.
The solution, in the case of VP engines, is to supply a 12v feed from the panel via the "excitation" resistor to the D+ terminal.

Without it the alternator will not start to generate.
A direct feed may be supplying to high a current but as you have discovered is a work-around fix.

IIRC the resistor is 50 ohms It should be rated at least 5 watts. Your favourite electronics component supplier will be much cheaper than VP even if the resistor is available as a spare part. I have not found it on the parts list!

Traditionally the filament type warning light provided the initial field current required to get the alternator generating. Once generating the field current is supplied by the field diodes.

LEDs now used in place of filament bulbs do not supply enough current.
The solution, in the case of VP engines, is to supply a 12v feed from the panel via the "excitation" resistor to the D+ terminal.

Without it the alternator will not start to generate.
A direct feed may be supplying to high a current but as you have discovered is a work-around fix.

IIRC the resistor is 50 ohms It should be rated at least 5 watts. Your favourite electronics component supplier will be much cheaper than VP even if the resistor is available as a spare part. I have not found it on the parts list!

Thanks a lot VicS. Thats what I thought. The ceramic resistor has 33R 5% marked on it. The D+ terminal has two wires. One (brown) going to the electronic alarm control unit which has halogen bulbs. The other (blue/red) coming from the control panel switch. The latter has the resistor. I suppose the electronic control unit isn't suitable for the excitation current. In the end I cleaned off all the burnt bits, tested the resistor which had the correct resistance and reconnected. All is well so far.

 

[VicS]

Make sure the wiring is not touching it.
Should it or could it be clipped to the box to act as a heat sink.

I'll try to remember for next time that it's only 33 ohms