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Re: TR6 - Alternator Output

To: Bud_Rolofson@nps.gov, triumphs@Autox.Team.Net
Subject: Re: TR6 - Alternator Output
From: DANMAS@aol.com
Date: Tue, 6 Oct 1998 21:19:37 EDT
In a message dated 98-10-06 13:34:26 EDT, Bud_Rolofson@nps.gov writes:

> Put a voltmeter on the plus lead of the coil, and to see what the voltage 
> read
>  with all the above electrical devices turned on.  According to Dan If it's 
> the
>  alternator that's the problem, you should see a fairly large voltage drop. 
> I
>  didn't see a large drop...the voltmeter still read 12 volts. 

Bud,

It is normal for the smaller, underpowered, alternator on a TR6 to experience
a small voltage drop with all loads on. Try a voltage reading with all loads
off (rpm above 1500). If the voltage stays around 14 volts, you are OK. There
is quite a bit of variation in alternator output voltage from one unit to
another, but theoretically, they all should produce 14.6 volts under light
load.

When the alternator is loaded so high as to drop the voltage to the battery
level, what you are doing then is drawing power from the battery.
Theoretically, a good battery should produce 12. 6 volts. If for example, it
takes 30 amps to bring the alternator voltage down the battery voltage, and
you have applied a 35 amp load, the extra 5 amps will come from the battery.

Check the voltage again with no loads, and if it is around 14 volts or more,
then no reason to worry. If it is less than 13 volts, then you may want to
consider getting the alternator repaired or replaced. In between, it's a
judgement call.

That is one of the advantages of the larger GM unit. Even though the Lucas has
sufficieant capacity, when fully loaded the voltage goes down, causing a
corresponding reduction in light output, etc. The 55 amp GM will provide the
typical TR6 load and still maintain voltage.

I bought three GM units in the last year or so, from two different stores, and
they all three had the 7127 model number, so I assumed that must be a
universal number. Evidently not. Anyway, the model you want is called a
"Delcotron SI", and was used on GM cars from the eary '70s till the mid '80s.
They are almost universally used in Street Rod applications, so if you can
find a store that caters to that crowd, you should have no problem getting the
right one.

I can get them locally for about $24 -$30 dollars, plus a $15 core charge, so
if you can't get what you want in your area, I can get you one and ship it to
you. They are fairly light, so shipping costs should be small. They can be
sent UPS or USPS. 

Hope this helps.

Dan Masters,
Alcoa, TN

'71 TR6---------3000mile/year driver, fully restored
'71 TR6---------undergoing full restoration and Ford 5.0 V8 insertion - see:
                    http://www.sky.net/~boballen/mg/Masters/index.html
'74 MGBGT---3000mile/year driver, original condition - slated for a V8 soon
'68 MGBGT---organ donor for the '74

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