Alternator problem

[Dr Bob]

6 hours ago, Tony Brooks said:

The Lucas test card for 9 diode alternators says that to test at the D+ terminal you disconnect it and measure the voltage at end of the D+ cable with the ignition switch on - expect battery voltage.

 

A quick and dirty test is to earth the D+ wire/terminal at the alternator end with the switch on and see if the waning lamp bulb lights. If yes its a faulty alternator (brushes), if no it a bow bulb or a wiring fault/relay fault in the case of many domestic alternators.

 

However Nick is correct as long as you have a few volts but less than battery voltage at D+ with the ignition on that circuit should be OK.

 

Personally I tend to use the second test above because its quick, easy and needs no meter. the meter comes out later.

Thanks Tony. All understood.

Chris, the new owner, will be back on the boat in a couple of weeks so will troubleshoot it then. I will make sure he has all this info...which should make the job easier.

[Dr Bob]

On 08/06/2020 at 09:36, Tony Brooks said:

The Lucas test card for 9 diode alternators says that to test at the D+ terminal you disconnect it and measure the voltage at end of the D+ cable with the ignition switch on - expect battery voltage.

 

A quick and dirty test is to earth the D+ wire/terminal at the alternator end with the switch on and see if the waning lamp bulb lights. If yes its a faulty alternator (brushes), if no it a bow bulb or a wiring fault/relay fault in the case of many domestic alternators.

 

However Nick is correct as long as you have a few volts but less than battery voltage at D+ with the ignition on that circuit should be OK.

 

Personally I tend to use the second test above because its quick, easy and needs no meter. the meter comes out later.

Tony, Chris the new owner is on board today and has done all of the above.

All connectors cleaned and secure. 2V to the D+ terminal when connected and and 13V when the D+ wire is disconnnected.

Earthing the D+ wire sees the warning light going from off to on.

That suggests the ignition circuit to the domestic alternator is fine.....but no output from the Alternator when the engine is running.

Chris is currently checking that the AtoB is working by routing the engine start alternator through it, but it sounds like there may be an issue with the alternator.

Any suggestions on how to check the alternator output other than just putting the multimeter across the output terminal and ground?

[Sir Nibble]

On 07/06/2020 at 15:26, WotEver said:

It should be labelled Ind or D+ (or, rarely, WL)

 

Cheers,
Tony

DIN terminal designation is 61 and American machines it may be L, I or 1.

[Tony Brooks]

51 minutes ago, Dr Bob said:

Tony, Chris the new owner is on board today and has done all of the above.

All connectors cleaned and secure. 2V to the D+ terminal when connected and and 13V when the D+ wire is disconnnected.

Earthing the D+ wire sees the warning light going from off to on.

That suggests the ignition circuit to the domestic alternator is fine.....but no output from the Alternator when the engine is running.

Chris is currently checking that the AtoB is working by routing the engine start alternator through it, but it sounds like there may be an issue with the alternator.

Any suggestions on how to check the alternator output other than just putting the multimeter across the output terminal and ground?

 

Yes. Throw the A to B away

 

Seriously and from memory. The A to B has two sets of thick cables (I think its just the positives). One from the alternator and one to the battery. Take one cable off the A to B and connect on the other terminal so you have two cable son one stud. That bypasses the A to B so if the alternator then charges it the A to B, if it does not then its probably the alternator but might still be a cabling fault.

 

Personally, if the main charging lead runs through the idiot multi-plug I would run a completely new one without such a plug.  Given the result of the test then if it still did not charge a faulty alternator is almost certain.

[WotEver]

1 hour ago, Sir Nibble said:

DIN terminal designation is 61 and American machines it may be L, I or 1.

That’s what I love about standards, there are so many to choose from. 

[nicknorman]

3 hours ago, Dr Bob said:

Tony, Chris the new owner is on board today and has done all of the above.

All connectors cleaned and secure. 2V to the D+ terminal when connected and and 13V when the D+ wire is disconnnected.

Earthing the D+ wire sees the warning light going from off to on.

That suggests the ignition circuit to the domestic alternator is fine.....but no output from the Alternator when the engine is running.

Chris is currently checking that the AtoB is working by routing the engine start alternator through it, but it sounds like there may be an issue with the alternator.

Any suggestions on how to check the alternator output other than just putting the multimeter across the output terminal and ground?

Why not just check the voltage at the B+ input to the A2B with the engine running? If the alternator is working it will be 14.4 or thereabouts. It it isn’t working it will be battery voltage (12.7 or whatever).

 

If he gets 14.4v at the A2B input then check the A2B output. If it is ~12.7v the A2B is knackered. If it is 14.4v or whatever, there is a disconnect somewhere between the batteries and the A2B.

[Dr Bob]

3 hours ago, Tony Brooks said:

 

Yes. Throw the A to B away

 

Seriously and from memory. The A to B has two sets of thick cables (I think its just the positives). One from the alternator and one to the battery. Take one cable off the A to B and connect on the other terminal so you have two cable son one stud. That bypasses the A to B so if the alternator then charges it the A to B, if it does not then its probably the alternator but might still be a cabling fault.

 

Personally, if the main charging lead runs through the idiot multi-plug I would run a completely new one without such a plug.  Given the result of the test then if it still did not charge a faulty alternator is almost certain.

Thanks Tony.

We isolated the AtoB (before you told us to throw it away) and everything was fine, except the low volatge (13.9V - which is why it has an  AtoB) from the domestic alternator. So the AtoB is faulty. Everything therefore OK now. Problem solved.....apart from 13.9v being too  low. The AtoB has worked well for 3 years. It was the 'perfect' solution for the Li batteries!

[WotEver]

47 minutes ago, Dr Bob said:

It was the 'perfect' solution for the Li batteries!

Except for the blowing-up bit, you mean?

[Tony Brooks]

44 minutes ago, Dr Bob said:

Thanks Tony.

We isolated the AtoB (before you told us to throw it away) and everything was fine, except the low volatge (13.9V - which is why it has an  AtoB) from the domestic alternator. So the AtoB is faulty. Everything therefore OK now. Problem solved.....apart from 13.9v being too  low. The AtoB has worked well for 3 years. It was the 'perfect' solution for the Li batteries!

 

Yes I can see it would do well for Li but unless that is a strange and rare alternator I think i would have fitted a new 14.4V regulator or a new alternator is a regulator was not available. I wonder if that alternator has had a diode open circuit for some time because that can give a low charging voltage but still charger.