How to excite 24v secondary alternator

[Streetcar]

I have a 24V secondary alternator on an engine which isn't giving any output. I think its because there is no excitation input for the field coil and I need to figure out how to get an excitation supply to get the alternator outputting current.

The engine has 12v wiring and has its own 12v alternator so I cant do the normal thing and use the ignition circuit (different voltage).

The 24v alternator had an external regulator which previously supplied the excitation input. But this has packed up and I need to revert to the alternator's internal regulator to get me up and running.

The question is: Under these circumstances how do you normally supply excitation to a secondary alternator which operates at different voltage?

The 24v alternator is a Paris Rhone N-type with a D+ terminal for excitation supply.

[Wotname]

Assuming your 24V alternator still has the internal regulator fitted, then just take 24V from the 24V battery(ies) via a relay to the D+ terminal. The relay(12V) is operated by the ignition switch. The external regulator is most likely to have a ignition already wired to it and if so, this can be used to power the relay. It is also most likely to have a 24V wire for the excitation aspects so this can also be reused.

However I would expect the internal regulator has been removed (or disconnected) when the external regulator was fitted.

What is the make and model of the external regulator?

[Streetcar]

The external regulator is an Adverc 24v N-type. The internal regulator is still connected and works (I took the alternator off and benchtested it running on the internal regulator - runs at 27.8v).

It seems like the Adverc is designed to allow the internal regulator to take over as a backup... providing there's some way of exciting the field coil.

The relay option sounds sensible, as does the reuse of the wiring. However there is no ignition connection that I can find from the Adverc regulator so i might need to put one in.

[Wotname]

Originally Posted by Streetcar

The external regulator is an Adverc 24v N-type. The internal regulator is still connected and works (I took the alternator off and benchtested it running on the internal regulator - runs at 27.8v).

It seems like the Adverc is designed to allow the internal regulator to take over as a backup... providing there's some way of exciting the field coil.

The relay option sounds sensible, as does the reuse of the wiring. However there is no ignition connection that I can find from the Adverc regulator so i might need to put one in.

A relay may already be fitted as I would expect there was some way of interrupting the field supply anytime the engine is off. See if you can hunt it down!

I will try to find a Adverc manual later.

[billgewater]

Most 12 V systems have a small filament bulb in the D+ circuit from the ignition start switch. These are usually two or three watt bulbs. (which switch off when the alternator fires up.) However, the DC resistance of these bulbs CAN be important. (Not highly likely.)
I think the advice you have been given is excellent, but there may be a similar issue related to the D+ circuit suggestions for the equivalent 24 V system.
It is beginning to look as though you need the wiring for a parallel system (That does not include a switch to the starter solenoid!)
As the man says "When all else fails, consult the handbook."

[Fuss]

There will be a 12v relay switching a 24v wire to the external regulator, you need to find this.

[Streetcar]

Originally Posted by billgewater

Most 12 V systems have a small filament bulb in the D+ circuit from the ignition start switch. These are usually two or three watt bulbs. (which switch off when the alternator fires up.) However, the DC resistance of these bulbs CAN be important. (Not highly likely.)
I think the advice you have been given is excellent, but there may be a similar issue related to the D+ circuit suggestions for the equivalent 24 V system.
It is beginning to look as though you need the wiring for a parallel system (That does not include a switch to the starter solenoid!)
As the man says "When all else fails, consult the handbook."

Yes, I get your point about the resistance of the bulb in the exciter D+ supply. Nowhere have I seen a wiring diagram without the bulb... and I've also read somewhere that there can be unintended consequences if the resistance is bypassed.

I will put an external regulator back in when I get a chance but to get me out of trouble I have put in a temporary connection from D+ via 24w bulb and manual switch to the 24v battery + post. This works, although now that I have the alternator producing again the residual magnetism in the rotor does the job (with a rev up on the engine).

Good advice all round. Thanks.

[smac999]

It’s very rare to have an alt with both an external reg input. And internal reg. Both available. If it was. There would need to be a manual switch over somehow. Both can not be powered together.

If the alt is setup for external reg. And it no longer works. Replace the external reg. Balmar makes a 24v one.

If you have put power direct into the external field input. Yiu will have no voltage control. It will just climb.

[Streetcar]

Originally Posted by smac999

It’s very rare to have an alt with both an external reg input. And internal reg. Both available. If it was. There would need to be a manual switch over somehow. Both can not be powered together.

If the alt is setup for external reg. And it no longer works. Replace the external reg. Balmar makes a 24v one.

If you have put power direct into the external field input. Yiu will have no voltage control. It will just climb.

The Adverc regulator is designed to revert to internal regulator in the event of a failure. You just unplug the Adverc - I've attached the instructions.

I will of course put a new external regulator in when I have a chance - although I don't think Balmar make regulators for N type so would require some rewiring of the alternator.

I don't think that the exciter current to D+ continuously feeds the field winding - only at start up to my knowledge, after that the exciter voltage should balance the B+ voltage and so not supply any further current to the field. Voltage control is on the negative side for an N type. Happy to be corrected on this...

[Wotname]

Originally Posted by Streetcar

.........

I don't think that the exciter current to D+ continuously feeds the field winding - only at start up to my knowledge, after that the exciter voltage should balance the B+ voltage and so not supply any further current to the field. Voltage control is on the negative side for an N type. Happy to be corrected on this...

Yes, this is usually the case. Once the alternator reaches it's "Rise Speed", it becomes self exciting. The field potential is supplied by the field diodes i.e. rectified from the stator AC field.
The N type internal regulator effectively opens and closes the negative side of the field circuit thus maintaining the required target voltage of the output.