Alternator

[Richard71]

Hello all,

I'm looking for some advice regarding alternator wiring. The attached photo shows the two alternators I have, the one on the left is an aftermarket item and the other is my original (remanufactured) 17ACR Lucas item.

I've been running with the aftermarket alternator since putting the car back on the road, but I'd now like to fit the Lucas one for a little originality. However my Autosparks supplied wiring loom suits the aftermarket alternator, being that the plug connector has 2 wires connected to the large spades 1 x brown & 1 x brown/yellow and another brown to the spade terminal roughly circled in blue. The Lucas alternator only has the 3 spade plug connectors, ie; the blue circled connector isn't present. So my question is, can I fit the brown wire from the blue circle into the 3 spade plug and have everything work has it should? Or, should it be left disconnected?

I have wiring diagrams for various years for TR5/6 1968-75 but can's make sense of them.

 

[RobH]

Those are both Lucas-pattern alternators Richard - your old one is an A127 while the new one is an ACR type.  There are a wide variety of terminal arrangements for both types but the thin brown wire to the circled terminal is a voltage sensing wire for the regulator. That isn't necessary on the new alternator and must be insulated and left disconnected .  Insulation is important as the wire is connected direct to battery live. 

You should have a heavy brown wire ( or sometimes two)  going to the large spade terminals and a smaller yellow/brown wire going to the small spade in the group of 3.  

 

I hope you are not disappointed with the output of the new one. A127s are often higher current than standard ACRs, unless you have specified an up-rated one. 

 

 

Edited April 13 by RobH

[Richard71]

Thanks Rob for the informed reply.

So it's a straight forward swap but for thoroughly insulating the spare voltage sensing cable? I guess what got me thinking about this was (and I should have mentioned this in my original post) Autosparks supplied the new loom/harness with a spare flag terminal crimp tie-wrapped to the voltage sensing cable, as if to give me the option of inserting the cable into the plug.

I take note of your advice on current output of the ACR alternator, if it proves inadequate it's an easy enough job to swap back to the A127. I gave the ACR alternator to a Glasgow based auto electrician who reconditioned it, he says he put uprated internals in, to what extent I know not, it has a 17ACR tag on suggesting 36amp??? Did that tag come with the overhaul kit, or is it a leftover from the factory, who knows?

I'll get around to fitting it and see how it performs.

Richard.

[Andy Moltu]

The 3 pin plug output on most out alternators is meant to carry an intended maximum of 30amps to the loom. This was why alternators with significantly higher outputs such as the A127 have an additional output post to take some of the current. In theory you take this to the solenoid.

As has been mentioned already some have a terminal for directly sensing the battery voltage so the output voltage can be slightly different to that sensed by the wires going to the main loom, especially if the run to the battery is long and carrying significant current. Probably not significant on our cars where the runs of wire between battery, solenoid/starter  and alternator  are pretty short.

Additionally some have a terminal to drive an electronic tachometer, not normally relevant for TRs.

The benefits of high output alternators for our cars are limited. If it can deliver enough current to supply all the electrics, more output becomes irrelevant. Even with an electric fan, Bosch pump and heated seats the current draw is finite. Having a spare 30amps alternator capacity won’t charge the battery much quicker as the voltage is regulated.

[Richard71]

Thanks Andy, good info there.

Richard. 

[SpitFireSIX]

On 4/13/2024 at 9:53 AM, RobH said:

Those are both Lucas-pattern alternators Richard - your old one is an A127 while the new one is an ACR type.  There are a wide variety of terminal arrangements for both types but the thin brown wire to the circled terminal is a voltage sensing wire for the regulator. That isn't necessary on the new alternator and must be insulated and left disconnected .  Insulation is important as the wire is connected direct to battery live. 

You should have a heavy brown wire ( or sometimes two)  going to the large spade terminals and a smaller yellow/brown wire going to the small spade in the group of 3.  

 

I hope you are not disappointed with the output of the new one. A127s are often higher current than standard ACRs, unless you have specified an up-rated one. 

 

 

Hi RobH,

are you sure "the thin brown wire to the circled terminal is a voltage sensing wire for the regulator."?
I believe the circled terminal  is a B+ terminal.
The smaller terminal of the triple row is D+ and this is connected to the regulator?

Cheers,
Iain.

[RobH]

I can't be certain Iain as I have no information on  Autosparks intention but I think the thin wire supplied there was meant for use with an alternator which needs a battery sense connection as some early models did.  Normally the The A127 doesn't - that circled tag is connected directly to the large screw terminal next to it which is an alternative connection for the main output ( B+ ) instead of using the two big spades. The tag is usually either not used or has a suppression capacitor on it.  Certainly there is no real point in having a connection from there to the battery as it is just in parallel with the main connection.

The small terminal of the group of three is the connection for the ignition lamp, and goes to the 'triple' in the diode stack which also supplies the regulator.  That is the internal machine-sensing connection and although the voltage should be the same as B+ it is coming from a separate set of smaller rectifiers . 

 

Of course all this is really not relevant to the original question which was how to connect the new ACR type and what to do with the thin wire, so I hope it doesn't cause any confusion 

 

Edited April 19 by RobH

[Richard71]

I suppose it wouldn't do any harm to drop Autosparks an email (with photo attached) with the same query.

Richard.