> First off, thanks to everyone who responded to my request for
> help last week on installing the alternator into my TR4A. It's
> in, and it works!!!
Congratulations !
> I don't know if this is quirky or not but two observations on the
> conversion. The first is that there seems to be a minimum
> "cut-in" time for current to start moving. It takes a few moments
> for the red light to extingush and the ammeter to go positive. Is
> this strange?
Many American alternators rely on the current passed through the 'ignition'
lamp to 'start' the alternator. With my Ford unit and only the original
lamp, I found I had to rev to about 3K to get the alternator going. Adding
a 10 ohm, 5 watt resistor across the lamp solved the problem, now the light
goes out as soon as the engine fires off. Having the resistor also means
that the alternator will not be disabled if the light burns out.
> Second is that the 63 amp alternator pegs the ammeter when the
> engine starts. If the battery is low could any damage be caused,
> or should I go to the "heavy-duty" wiring that Dan suggests? I
> don't want my new harness fried.
IMO, no, it won't hurt anything, although the ammeter needle may take a
beating from being repeatedly slammed into the peg. The electrical
'mechanism' inside the ammeter is just a loop of fairly heavy gauge wire, it
should have no trouble with 63 amps.
> The downside to the heavy-duty wiring is that the alternator
> output is connected directly to the battery, so you can't see the
> charging, only discharging.
_Very_ distasteful, IMO. In fact, what you see isn't necessarily charging,
so the ammeter can read substantial charge while the battery is running down
! There are some alternatives, one is to run new "heavy duty" wires to/from
the ammeter. Another is to switch to a voltmeter. I don't know of one that
will look "at home" with the other instruments, but the original ammeter is
a standard size, there are many voltmeters (including most 2" aftermarket
units) that will fit in the hole. The later TR6 voltmeter will also fit.
> But, I've read somewhere that
> shunting the ammeter with a parallel resistor (a high wattage
> one) would effectively could make the ammeter read 1/2. I prefer
> this approach. Has anybody done this? And, will the wiring
> harness take the possible 63 amps for short periods?
I don't know that the TR4A is the same, but on the TR2/3 the relevant brown
wires are plenty large enough to handle 63 amps indefinitely. The quick
connects used on later cars may be a problem, but the wires will handle it.
I didn't try reusing the yellow wire that originally went to the generator,
it's probably too small.
I believe I was the author of the 'shunt' idea, I've been using it on my
TR3As for almost 30 years now. It works quite well. However, you don't
want a 'resistor', just a short length of wire. All wire has some
resistance, and the resistance required for the shunt is very low. Because
the resistance is so low, it doesn't dissipate much power.
On my current daily driver, the shunt is three strands of steel "handy wire"
(or baling wire if you're from the Midwest <g>), just long enough to reach
from one ammeter terminal to the other. Don't recall what size offhand,
probably around 20 AWG.
>From a post I made a few years back :
TR3 : 1.2 milliohms 3.5" 16 AWG copper makes a 50% shunt
However, it's likely there is some variation from ammeter to ammeter.
Another approach (the one I used) is to pull the ammeter out of the dash,
leaving it connected. Turn on the headlights briefly, and note the ammeter
reading. Then add a trial shunt, and try the headlights again. About 1/2
is a good target (resulting in an ammeter that reads 60-0-60). The shorter
the shunt wire, the lower the ammeter will read.
Randall
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