No amps from alternator!!

[boatbuilder]

Here is the set up, gardner 6lw, alternator supplying cav regulator 406c . 24v+ from terminal B+ to split diode and onto 2 battery banks, no volts or amps to be seen on insts and tacho not working.
However before putting split diode, there was a 123 switch and everything was perfect ,50amps and 29volts, and all insts working.
I have a suspicion that the diode is stopping the alternator from seeing the batteries and there fore not being exited.
By the way the no charge light is on but only weakly and does not go out, there is another bulb in parralel to this that used to light up, as I presume as a load, but now that doesent light up either.
I don't think that the usual answers will work as this is a 30 year old set up with a control box the size of a brick. Perhaps one of the older (like me) and wiser (unlike me) members have a clue.

 

[Brian_Moffat]

Boatbuilder from brian

1. measure the D+ (exiciter) at the alternator - I suspect you haven't got any (may be marked as 61) because you have a dim lamp (Charge Warning) the voltage should be the same as Batts +ve (IGN ON - Engine OFF i.e. not spinning - and please don't tell me that you are spinning the engine!)

2. the circuit is ( + to - ) Batts / IGN switch in / IGN switch position 2 / IGN WNG LT / ALTernator D+ (Exciter coil) / Ground - the light goes out ONLY when the alternator produces current at the output which results in a back electromotive force inducing a reverse voltage in the exciter coil which causes a positive voltage to appear at the un-grounded terminal of the coil ( + batt volts / bulb / + alternator volts = no current through the bulb so it don't light up does it?)

3. lose that other lamp in a hurry - one of them is correct - the other should be deep-sixed.

4. situation complicated by external CAV regulator but treat the CAV as if it was integral to the alternator - you haven't touched it - so it is not part of the fault.

5. wiring problem from original 123 switch - the IGN feed wire has been removed from the 123 select and fitted to the INPUT of the split diode? - there should only be one wire (the 6 or 10 mm charging cable FROM the alternator to this connection.

6. it is not the diode that is causing the problem - but where the wires were put after the diode was installed. This is an install problem.

7. further problem on board is indicated by the fact that you have a weak / dim glowing ALT WNG LT - you have a leakage from another circuit which has previously been masked - this you will have to eradicate before you attempt the (for you) apparent main problem.

8. the second lamp (3 above) is not a "load" it is either a historical legacy of some long-gone equipment or it is a 'cock-up' by some well-meaning but utterly incompetent 'electrocutionist'

9. solve the apparently 'minor' (7 above) problem first - otherwise you're going to be chasing your tail up your posterior.
Get that IGN dead 'dead' when it's supposed to be and don't take NO for an answer.

10. then you can look at what the IGN wiring should actually be.

!!. a 30-year-old-boat? I would expect lots of 'orrible surprises!

12. don't know what you are referring to as the 'control box' - Engine Management? Electrical Switch Panel? Everything? so can't help you there.

13. only other thing I can think of is that if you have a CAV regulator (external) you have a Lucas alternator - now no longer supported.

14. Hmm! have a look at the regulator - move the link to position 'H'

15 the obvious is to go over all the wiring again (you did take notes of the original wiring AND number them so that you restore to original if something goes 'orribly wrong - didn't you?) and check it.

regards

brian