Replacement Alternator Not Charging

[mnrkks]

Hello all,

I'm looking for advice on a charging issue with my Volvo Penta MD2020 after fitting a replacement alternator (PSH 70A, eBay link below):

Lichtmaschine für Volvo Penta Marine AQ225A TAMD40A AQD41A AQ211A AQ140A AQ131 | eBay

Background: The alternator was installed and worked fine for a while, but the boat has been used only sporadically due to the season. About a week ago I tried to run the engine and now have a charging fault.

Symptoms (engine running at idle):

• Engine starts and runs normally
• Battery voltage stays at 12.5V — alternator is not charging
• Tachometer reads 0 RPM at any engine speed
• Charge warning lamp does NOT illuminate when key is turned to ON (engine off)
• All other panel lamps and instruments appear fine

Tests already done:

• Charge warning bulb removed and tested — filament is good
• Engine harness fuses checked — all intact
• 8A fuse on the yellow battery sense wire (from service battery to alternator) checked — intact, reads 13.7V at the alternator end with engine off (normal resting battery voltage)
• Voltage at alternator terminals with engine running:
  • B+ / battery: 12.5V (no charging)
  • D+: 12.7V (should rise to ~14V if charging)
  • W: 0V AC (no stator output)

My current suspicion:The fact that the charge warning lamp doesn't illuminate at key-on suggests the excitation circuit (D+) is broken somewhere between the key switch, warning lamp, and the alternator's D+ terminal. Without that initial excitation current, the alternator never begins charging — which would also explain the dead W signal and dead tach.

Before contacting the seller for warranty, is there a definitive test to prove the alternator itself is at fault vs the wiring?

Any advice appreciated before I escalate to the seller. Thanks in advance!


Onur

 

[Minerva]

If it were me, firstly I’d re-fit the old alternator and put the new one away as spares.

Once that’s done I’d look to run a Hotwire from a suitable place to the terminal that excites the alternator.

If this doesn’t go to plan and the alt goes bang. Refit the new alternator.

 

[mnrkks]

If it were me, firstly I’d re-fit the old alternator and put the new one away as spares.

Once that’s done I’d look to run a Hotwire from a suitable place to the terminal that excites the alternator.

If this doesn’t go to plan and the alt goes bang. Refit the new alternator.

I am not good at these hotwire things so no thanks

 

[Boater Sam]

There is a contradiction here.

• 8A fuse on the yellow battery sense wire (from service battery to alternator) checked — intact, reads 13.7V at the alternator end with engine off (normal resting battery voltage)

And you say that there is only 12.5v on the alternator B+. This does not add up.
13.7v is not a battery resting voltage. Is something else charging the battery?

 

[mnrkks]

13.7v is the service battery voltage. The yellow sensor wire is connected to the positive of the service battery which is charged through shore power.

 

[Boater Sam]

Disconnect the shore and try it again.

 

[Alex_Blackwood]

Hello all,

I'm looking for advice on a charging issue with my Volvo Penta MD2020 after fitting a replacement alternator (PSH 70A, eBay link below):

Lichtmaschine für Volvo Penta Marine AQ225A TAMD40A AQD41A AQ211A AQ140A AQ131 | eBay

Background: The alternator was installed and worked fine for a while, but the boat has been used only sporadically due to the season. About a week ago I tried to run the engine and now have a charging fault.

Symptoms (engine running at idle):

• Engine starts and runs normally
• Battery voltage stays at 12.5V — alternator is not charging
• Tachometer reads 0 RPM at any engine speed
• Charge warning lamp does NOT illuminate when key is turned to ON (engine off)
• All other panel lamps and instruments appear fine

Tests already done:

• Charge warning bulb removed and tested — filament is good
• Engine harness fuses checked — all intact
• 8A fuse on the yellow battery sense wire (from service battery to alternator) checked — intact, reads 13.7V at the alternator end with engine off (normal resting battery voltage)
• Voltage at alternator terminals with engine running:
  • B+ / battery: 12.5V (no charging)
  • D+: 12.7V (should rise to ~14V if charging)
  • W: 0V AC (no stator output)

My current suspicion:The fact that the charge warning lamp doesn't illuminate at key-on suggests the excitation circuit (D+) is broken somewhere between the key switch, warning lamp, and the alternator's D+ terminal. Without that initial excitation current, the alternator never begins charging — which would also explain the dead W signal and dead tach.

Before contacting the seller for warranty, is there a definitive test to prove the alternator itself is at fault vs the wiring?

Any advice appreciated before I escalate to the seller. Thanks in advance!


View attachment 210025OnurView attachment 210026View attachment 210027

The fact that the tacho is not working would suggest that the alternator is, either defective or it is not exciting, the fact there is no charge warning lamp illuminating would cause excitation failure and suggest that there is an open circuit somewhere in that line, possible between the lamp and the alternator. Can you disconnect the charge lamp connection at the alternator and with the switch on connect it to a negative and see if lamp comes on. Or use a meter, set to volts! to check between the alt. lamp connection and a negative. If the lamp lights then there is a problem within the alt. The open circuit could of course be on the input side to the lamp. A positive supply to the input side of the lamp would prove that. Again a multimeter between the input and a neg. should show 12+ volts. If all the external connections are sound then looks like a duff alt. Hope that makes sense.

 

[mnrkks]

The fact that the tacho is not working would suggest that the alternator is, either defective or it is not exciting, the fact there is no charge warning lamp illuminating would cause excitation failure and suggest that there is an open circuit somewhere in that line, possible between the lamp and the alternator. Can you disconnect the charge lamp connection at the alternator and with the switch on connect it to a negative and see if lamp comes on. Or use a meter, set to volts! to check between the alt. lamp connection and a negative. If the lamp lights then there is a problem within the alt. The open circuit could of course be on the input side to the lamp. A positive supply to the input side of the lamp would prove that. Again a multimeter between the input and a neg. should show 12+ volts. If all the external connections are sound then looks like a duff alt. Hope that makes sense.

Thank you I will check and let you know

 

[Geoff A]

You could take it to a reputable auto engineer who could bench test it. Or to an independent garage for testing.