Alternator reluctant to charge

[PineappleGuy]

It is becoming increasingly difficult to persuade the ignition light to go off and the warning buzzer to stop. Revving the engine doesn’t succeed immediately like it used to. We know that the two domestic batteries are in poor condition but the starter battery is healthy. Is it likely that replacing the domestic batteries will resolve the issue (i.e. could they be hindering the alternator from getting going) or do we also have an obvious alternator problem? I believe that the belt is sufficiently tight so what other checks/measurements could be carried out before replacing the alternator (HC Cargo 111361; 14V, 67A, several years old)?

[Tracy D'arth]

Check all the connections first including the pesky multiplug and socket on the loom.  Then the brushes in the alternator.  Which battery bank is the alternator connected to primarily? Is this with a split charge relay, or a VSR or heaven forbid a diode splitter?

If the knackered cabin batteries are the first connected, try a jump lead connected from cabin batteries + to starter battery +  before you start up and see if that makes any difference.

[Tony Brooks]

So it looks like a bastardised A127 off a Nissan.

 

What state is the drive belt in and is it tight enough?

 

Has the ignition warning lamp been changed? Grain of wheat bulbs or LEDs won't energise the alternator without a parallel resistor.

 

If the warning lamp has a parallel resistor, has it broken in some way?

 

Are you sure that you are not misidentifying an oil pressure warning lamp as the charge lamp? With the lamp on and engine stopped, remove each small wire on the alternator in turn, there may only be 1 wire. It's the D+ warning lamp terminal you are looking for. If the lamp stays on, it is not a charge warning lamp unless there is a short circuit on that wire somewhere.

 

As long as the lamp is about normal brightness, I would suspect the alternator before the batteries and low alternator output would cause domestic battery failing symptoms over time.

 

 

PS just seen Tracy's post. It might be brushes, but if so the warning lamp may well not light up at all or come on intermittently. That is not to say it is not, but I suspect a diode problem more likely.

 

 

Edited September 7, 2021 by Tony Brooks

[PineappleGuy]

Thank you for the replies.

There are separate lights for ignition, oil and temperature and a buzzer covering all three. The ignition light seems to be normal brightness (the bulb hasn’t been changed) and the buzzer normal volume and both are on continuously until eventually (at the moment) they decide to go off, at which point the battery monitor rises to 13.5V which is as high as it ever gets due to the diode splitter. As a matter of interest, how much current is needed to get the alternator going?

[Tony Brooks]

58 minutes ago, PineappleGuy said:

Thank you for the replies.

There are separate lights for ignition, oil and temperature and a buzzer covering all three. The ignition light seems to be normal brightness (the bulb hasn’t been changed) and the buzzer normal volume and both are on continuously until eventually (at the moment) they decide to go off, at which point the battery monitor rises to 13.5V which is as high as it ever gets due to the diode splitter. As a matter of interest, how much current is needed to get the alternator going?

 

Very little because as soon as the there is enough magnetic field in the rotor to generate any electricity it is fed back into rotor to make more magnetic field and thus more electricity.  About 0.25 amp but that is just an informed guess, it could be lower.

 

Once the charging is sorted for goodness sake make charging easier for you and ditch the diode system. I would advise a VSR with the alternator feeding the domestic bank. You alternator should have an S terminal when paired with diode splitters and I don't think it does. An S terminal or Sense measures the charging voltage at the battery rather than the alternator output so in your case a nominal 14.4V regulator would put 14.9V at its output that would become 14.2 at the battery after the splitter. Battery sensed alternators are rare and tend to be more expensive so use an ordinary one plus VSR.

[Tracy D'arth]

Do dump that diode splitter, its sooo last century and your batteries will be much happier without it.