Wiring My Alternator

[BabaYaga]

What remains are two thin wires I had connected to the old alternator. They are coming from the same relay switch, but different terminals on that relay switch. One has to be ignition. What is the other? Is there any possibility the other is left over from my old external alternator regulator? What is that relay switch doing?

I have one theory: There is only one more wire, and that is ignition. However when the old external regulator was wired this wire was split, with one end going to the relay switch and the other going to the external regulator. Ironically the ignition wire is green, and so too is one of the wires coming off the relay. So, my question is this: does the ignition normally go via a relay before being connected to the alternator? If so then I think it's a case of wiring this green wire back together.

I think you will have to try and find out what is the purpose of the relay switch.
Possibly it is a paralleling relay connecting the domestic battery circuit to the starter battery circuit? Is is common to have such a relay controlled by alternator D+ (IND, ignition light, charge warning lamp etc...) I have a set up like this in my boat and it works very well.
If this is the case, the other thin wire on the relay should be connected to ground/negative, possibly to the alternator case if covenient. Normally I believe the steering current to the relay is not polarity sensitive.
The idea is that as soon as the alternator starts to put out, the polarity of the D+ changes from negative (or at least less than 12 v) to positive (12 - 14 v). This puts out the warning light and makes the relay close = both battery banks will be charged.
An external regulator would also need to have to have a connection to D+.
So to answer your question, provided the assumptions above, it is normal for the ignition to go via the relay before connecting to the alternator D+ terminal.

PS Just saw your schematic. Hard to tell without knowing what the yellow/brown picks up at the starter relay...

 

[demonboy]

Hi babayaga - I'm not sure the relay would be doing this as I used to have a 1-2-All switch wired up to switch between the batteries.

 

[the_branflake]

Thanks, Vic, you've been a great help already.

Perhaps you or someone else could help me identify the purpose of this relay switch. I suspect it may be something that's been added when the external regulator was added. I've drawn a simple schematic:

One of the terminals from the starter relay goes to this second relay. That in turn has two wires that go somewhere. I think one definitely went to the alternator but I have my suspicions that both went to the alternator. If so, what could they be?

I think that could be earthing the starter when the ignition is on not im but sure. That could be why you had the earth then going to the alternator before as its not using the block (as VicS said?). Someone will confirm.

 

[VicS]

I think that could be earthing the starter when the ignition is on not im but sure. That could be why you had the earth then going to the alternator before as its not using the block (as VicS said?). Someone will confirm.

The diagram agrees with the idea of an earthing relay and it ties in with the separate negative connection of the old alternator

The grey wire would go to battery negative, the and the green wire to the engine block or starter motor

If this going to carry starter motor current then it will be a heavy duty relay/solenoid and the green and grey wires will be heavy wires like main battery cables.

 

[demonboy]

No, they're as thin as sensing wires.

I've been looking at some photographs I took of the old alternator and I can tell you that the grey wire in my relay schematic went to the terminal as shown on these two images:

1.

2.

Also I think the green wire in the relay schematic (not the green wire pictured above) went to one of the spade terminals. In the first picture you can see the three spade terminals and I believe the green wire went to one of those.

This still leaves a spare green wire coming from somewhere too!

As I said, this relay may have been fitted for the external regulator. Possibly.

 

[VicS]

Difficult if not impossible to say esp when things have been modified in the past.

Maybe installed for field suppression during cranking ... ????? pure guess .. unlikely too.


Id suggest you forget what was there and how it was wired and concentrate on the installation of the new alternator and controller ( Sterling ??? ) how you want it.

You may have to contact Lucas for connection details of the new alternator unless you can find anything on-line.

 

[Stu Jackson]

Could someone confirm for me that it is normal to have a negative from the starter to the casing of the alternator. Cheers.

Nope, don't know. Sounds like a way to ground the alternator.

As far as positives go:

The answer to that lies in how the charging system was wired. In most cases in OEM boats, the alternator output (AO) was connected to the starter solenoid with the small wire you mentioned. Then only one large wire went to the C post of the 1-2-B switch. This wire served two purposes. Before the engine started, the selected batteries powered the wire to the starter for powering the starter, then that small wire went to the AO. Once the engine started, the large wire on the starter with the small but very short wire to the AO carried the AO BACK to the switch and charged the batteries. In most cases these days, the AO is fed directly to one of the banks (starter in the UK, house - leisure in the US), avoiding traveling through the switch, and the small wire between the AO and starter was eliminated, making the switch a battery source only switch and not a charging source switch as well.

Try this: http://c34.org/bbs/index.php/topic,4949.msg30101.html#msg30101

and

http://c34.org/bbs/index.php/topic,6604.0.html

You didn't say what kind of switching you have on your boat, so this is sort of a primer. You may know all this stuff already.

 

[demonboy]

Hi Stu,

Thanks for this and also for the links too. I have to say I am really struggling here, if only because I cannot source a diagram for a suggested ignition circuit. I have four books on boat electronics in front of me and none really explain the basics of a starter circuit. Perhaps you or someone else could help explain to me the following:

If I no longer have the connection between the starter solenoid and the alternator, how does the alternator start?

I assume there is current going to the starter as soon as I turn on my isolation switch, but what then?

What is the starter relay switch actually doing? Is it just starting the solenoid or is it also talking to the alternator?

The problem I'm having is that all schematics I've studied just show an alternator connected directly to the battery. What I need to understand is what is wired from the ignition switch to the engine dash (tacho, temp etc), from there to the starter relay, from the relay to the solenoid and from the solenoid and starter relay to the alternator.

 

[Playtime]

What I need to understand is what is wired from the ignition switch to the engine dash (tacho, temp etc), from there to the starter relay, from the relay to the solenoid and from the solenoid and starter relay to the alternator.

What engine is it and do you have any circuit diagrams that you could upload?

It is normal for the 'ignition' switch to operate one or more relays. On some Volvo set-ups for instance, there are 3 relays. The first is operated when the ignition switch is turned to 'on' and connects an earth to the engine block (so that the glow plugs have a return path; the block is electrically isolated when the switch is off.

The second relay operates the glow plugs and third is for the starter circuit.

Modern alternators 'self excite' and therefore do not need any 12V 'kick' to get them going. As soon as they start to rotate they will start generating.

 

[demonboy]

Indeed, I have three relays: Glow plugs, Starter and the other one. But then there is that fourth one that is completely throwing me.

I do not have a circuit diagram for my Perkins Prima M60 though a cursory Google came up with this book that has a standard Perkins starter circuit pictured. Unfortunately I can't really read the writing as it's a preview and neither is it available as an e-book.

However I found a similar thread on Cruisers Forum and came across this.

Annoyingly I still can't read it!

 

[Playtime]

I can't say what the 4th relay was doing without more info and/or a circuit diagram. I would be very tempted to remove the 4th relay, wire the new alternator up as already suggested and see if it all works.

However, if you are unsure about what you are doing I would call in a competent electrician.

 

[Stu Jackson]

If I no longer have the connection between the starter solenoid and the alternator, how does the alternator start?

I assume there is current going to the starter as soon as I turn on my isolation switch, but what then?

What is the starter relay switch actually doing? Is it just starting the solenoid or is it also talking to the alternator?

The alternator starts when the crankshaft turns the pulley, and the alternator output goes to battery bank (or in the old days through the switch). The ignition switch provides power to the alternator and the regulator adjusts the output voltage.

The wire from the C post of the switch determines which battery provides the power TO the starter.

Don't know about the relays. Mine are all hard wired. The only relay we have is a solenoid I installed for the glow plugs.

 

[demonboy]

I understand that the crankshaft turns the pulley, but what is the power the ignition switch is supplying to the alternator doing?

I have managed to get hold of a schematic and it seems as if there are only three relays in the circuit. However I don't know what the 15amp switch is doing or where that is. Would that be the solenoid above the starter motor?

 

[demonboy]

wire the new alternator up as already suggested and see if it all works.

However, if you are unsure about what you are doing I would call in a competent electrician.

Of course I would do this! However I do not know how to wire up an alternator within the context of my start circuit, hence my OP, and I am in south India so finding a competent marine electrician is impossible, again hence my OP!

 

[Playtime]

However I don't know what the 15amp switch is doing or where that is. Would that be the solenoid above the starter motor?

You are correct - the "15A switch" (BTW I think that may be the pin number) is the starter solenoid.

The wiring diagram you have now supplied is exactly as I would expect, with 3 relays. As suggested above, I would remove the 4th relay and wire in the new alternator exactly as shown in the circuit diagram.

I understand that you don't have access to a competent electrician so, before you start, ensure that you have a very clear idea of what you are doing. If still in doubt, come back on here.

Good luck.

 

[demonboy]

I like your signature. I might change mine to 'Love sailing, hate starter circuit wiring'

Thanks for the pointer. I have just found continuity between the starter relay and that fourth relay so, as you say, I'm whipping it out.

Alternator man is coming on Wednesday, which is as close as I'll get to a half decent electrician. He knows what he is doing on car circuits at least. We have a third person who can translate if need be but that circuit diagram is a god-send.

 

[Playtime]

Alternator man is coming on Wednesday, which is as close as I'll get to a half decent electrician. He knows what he is doing on car circuits at least. We have a third person who can translate if need be but that circuit diagram is a god-send.

Good luck. Let us know how it goes.

 

[demonboy]

Cheers, I'll keep you posted. This project's been a bit of a steep one but there's light at the end of the tunnel.

No wait, that's the ignition light