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Chris Miller
Grand Master
Username: cjm51213

Post Number: 330
Registered: 5-2013
Posted on Friday, 06 February, 2015 - 07:14 am:   Edit PostDelete PostView Post/Check IP

Hi Folks,

My horn on my '72 stops working about half the time, and this is a result of low voltage. I am unfamiliar enough with the system that debugging will be error-prone and upgrading is probably less of a problem. I'm thinking it is probably a lot easier to install a contemporary alternator and then by-pass the existing external Lucas voltage regulator. A modern alternator will have an integral voltage regulator and rectifying diodes.

Assuming this is true, is there a known contemporary alternator replacement, probably GM, part number? What are the characteristics I need in my replacement, or will all contemporaries generate the same voltage at different current levels? Is there any problem installing an alternator that generates more current than the stock unit?

Thanks for the help,

Chris.
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Jan Forrest
Grand Master
Username: got_one

Post Number: 759
Registered: 1-2008
Posted on Friday, 06 February, 2015 - 07:56 pm:   Edit PostDelete PostView Post/Check IP

I've not availed myself of their services, but this site appears to have every RR/B alternator variant known to man.

And they're damned inexpensive!
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Chris Miller
Grand Master
Username: cjm51213

Post Number: 331
Registered: 5-2013
Posted on Saturday, 07 February, 2015 - 02:24 am:   Edit PostDelete PostView Post/Check IP

Seriously? 220 Amps? OMG, what would require that kind of current?
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Brian Vogel
Grand Master
Username: guyslp

Post Number: 1196
Registered: 6-2009
Posted on Saturday, 07 February, 2015 - 03:55 am:   Edit PostDelete PostView Post/Check IP

Chris, that single alternator is meant for the new Phantom. Given the amount of electrical equipment in these behemoths I'll bet they need every bit of that uumph. (And the price on that one is anything but inexpensive.)
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Chris Miller
Grand Master
Username: cjm51213

Post Number: 332
Registered: 5-2013
Posted on Saturday, 07 February, 2015 - 04:01 am:   Edit PostDelete PostView Post/Check IP

Hi Brian,

Whew! I was looking through various after-market alternators, and 170 Amps was the maximum I found, and they warned of improvements to the 12-volt battery lead -- larger than 4-gauge. So, that raises the question, what is the minimum required current output of a '72 shadow alternator? Can I live with 40? Do I need 80? 120?

Thanks for the help,

Chris.
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Geoff Wootton
Grand Master
Username: dounraey

Post Number: 632
Registered: 5-2012
Posted on Saturday, 07 February, 2015 - 05:08 am:   Edit PostDelete PostView Post/Check IP

Hi Chris

Why not disconnect the alternator and put an ammeter in series with the main battery terminal. Turn all the electrics on and that is your answer. It would be interesting to know the actual figure.

Geoff
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Geoff Wootton
Grand Master
Username: dounraey

Post Number: 633
Registered: 5-2012
Posted on Saturday, 07 February, 2015 - 05:22 am:   Edit PostDelete PostView Post/Check IP

Chris

At 3000 rpm under full load (all electrical items turned on) a reading from an ammeter in series with the positive terminal of the alternator should give 53 amps - page M26 of the SY1 manual.

Geoff
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Chris Miller
Grand Master
Username: cjm51213

Post Number: 333
Registered: 5-2013
Posted on Saturday, 07 February, 2015 - 05:25 am:   Edit PostDelete PostView Post/Check IP

Hi Geoff,

That's a pretty good idea. I think my most capable meter, HP 974, is only good to 10 Amps, and that's not good enough. I need to borrow a more capable meter...

I can turn on the ventilation fan, the rear window defrost, the radio and the lights, but I need someone to run the windows up and down and click the central locking system on and off. I need to borrow some kids...
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Geoff Wootton
Grand Master
Username: dounraey

Post Number: 634
Registered: 5-2012
Posted on Saturday, 07 February, 2015 - 05:27 am:   Edit PostDelete PostView Post/Check IP

Chris

Another point to remember is to make sure the alternator is rated at about twice the expected max load. Otherwise it will be running at full output whenever all or most of the electrics are on.

Geoff

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