Alternator beta 43

[dave mackie]

Yes , the light goes out and rev counter starts to work

[Tony Brooks]

21 minutes ago, Tracy D'arth said:

Nearly.

 The ignition puts 12v on the warning lamp which earths via the non rotating alternator, it lights up and feeds energising current to the alternator.

When the alternator starts to produce charge current, the lamp is then fed 12v from the alternator and as it has 12v on both wires, there is no current flow and the lamp goes out.

 

Sorry, not if it is a six diode machine as Nn suggested, but true for a 9 diode machine.

 

For a six diode alternator. There is an extra Ign terminal that is fed from the ignition on position on the ignition switch. There is a warning lamp terminal that seems to be similar to the D+ on a 9 diode machine except it is "earthed" by an electronic switch in the alternator. This switch is on when there is voltage eon the IGN terminal. As far as I can see it is the Ign terminal that excites the alternator.

[nicknorman]

1 hour ago, dave mackie said:

Both alternators are basic stand alone systems. There's no relays. One lower amperage for starter battery and a higher amperage for the domestic batteries. The domestic side is working perfectly so I'm sure there's no relays used between the starting and domestic charging systems  . I'll get the alternator removed and checked and while it's removed it will give me better access to the distribution block wiring for  the charging/starter motor .

Actually there is a small relay within the instrument panel. It is activated when the ignition is turned on, and connects the leisure battery + to the leisure alternator D+. But this is not relevant to your problem.

4 minutes ago, Tony Brooks said:

 

Sorry, not if it is a six diode machine as Nn suggested, but true for a 9 diode machine.

 

For a six diode alternator. There is an extra Ign terminal that is fed from the ignition on position on the ignition switch. There is a warning lamp terminal that seems to be similar to the D+ on a 9 diode machine except it is "earthed" by an electronic switch in the alternator. This switch is on when there is voltage eon the IGN terminal. As far as I can see it is the Ign terminal that excites the alternator.

No I don’t think the field current doesn’t come from the IGN terminal, I’m pretty sure it comes from the B+. The IGN is just a “logic input”. I think!

[Tony Brooks]

30 minutes ago, nicknorman said:

Actually there is a small relay within the instrument panel. It is activated when the ignition is turned on, and connects the leisure battery + to the leisure alternator D+. But this is not relevant to your problem.

No I don’t think the field current doesn’t come from the IGN terminal, I’m pretty sure it comes from the B+. The IGN is just a “logic input”. I think!

 

Fair enough, I have never seen am internal circuit diagram for a six diode machine. Sir N was not very forthcoming when I asked him about it. Whatever happens it needs the Ign feed to allow it to excite.

[nicknorman]

19 minutes ago, Tony Brooks said:

 

Fair enough, I have never seen am internal circuit diagram for a six diode machine. Sir N was not very forthcoming when I asked him about it. Whatever happens it needs the Ign feed to allow it to excite.

My presumption is based on the description in the manual - leisure (9 diode) alternator is described as “machine sensed” whereas the engine alternator (6 diode) is described as “battery sensed”. Battery sensed via the IGN wire. So if the rather thin IGN a wire is to be used to measure battery voltage, you certainly wouldn’t want 4A or so of field current running from engine battery via ignition switch via fuse via thin wire back down to the engine. You would want the current in that wire to be minimal so there wasn’t any voltage drop.

[ditchcrawler]

[Tony Brooks]

But that is the diagram for a battery sensed nine diode machine, not a six diode one.

[ditchcrawler]

19 minutes ago, Tony Brooks said:

But that is the diagram for a battery sensed nine diode machine, not a six diode one.

I did wonder, but I have never seen a drawing and that was the best I could find while googling 6 diode alternator 

[nicknorman]

10 minutes ago, ditchcrawler said:

I did wonder, but I have never seen a drawing and that was the best I could find while googling 6 diode alternator 

The 6 diode machine just has the 6 main rectifier diodes. There is no internal supply for the field current, which is derived from the B+ terminal either from the battery (before and during start) or from the rectified alternator output (during normal running). All controlled by some electronics that switch off the field current completely and sends the circuitry to sleep when the IGN doesn’t have 12v. And when it does have 12v (ignition on) it sends field current and grounds the warning light circuit. Once the alternator is spinning fast enough it extinguishes the warning light. Voltage regulation depends on the voltage at B+ modified a bit by voltage on the IGN wire - hence the battery sensed bit.