Phil :
The voltage at the alternator should be exactly the same as at the battery
(at idle). It sounds almost like someone has wired the alternator up to
the cutout relay for the generator, which is not correct. The alternator
output should go to the ammeter (if you have one) and then directly to the
battery. (Essentially, the diodes in the alternator serve the purpose of
the old cutout relay, which was not to regulate current but to prevent it
flowing backwards through the generator with the engine off.) Another
possibility is that you have a high resistance connection somewhere in this
circuit. With the engine off, you should be able to measure less than 1
ohm from the alternator output terminal to the battery. (The actual value
should be under 0.01 ohm, but most meters won't read this accurately.)
If you do have the alternator output connected to the cutout relay, there
is also a good chance that the alternator diodes are damaged.
It's not unusual for mechanical tachs to read high. However, I would start
with finding out why you see a different voltage at the alternator than at
the battery. As I said, they should be connected together with a fairly
short circuit of heavy gauge wire.
The control box shouldn't be doing anything, unless it was changed along
with the switch from generator to alternator. Since the requirements are
very different, it seems unlikely that a generator box would be useful with
an alternator. Many people use alternators with internal regulators, and
just leave the old control box for appearance's sake.
Randall
On Wednesday, March 24, 1999 1:20 AM, Phil Ryan [SMTP:pryan@itdesign.ie]
wrote:
>
> Hello,
> Just wondering if someone could shed some light on my problem.... I
>had
> my ailing generator in my Spitfire Mk 3 replaced with a non-Lucas
> alternator just before Christmas. The Idle on the car up until recently
> was about 1200rpm, which I knew was too high, but there was a good few
> other things to do to the car before tuning it properly. The other week,
> for starters, I altered the slow idle down to around 800-900 rpm. Made
the
> whole thing a lot quieter, but now when the car is idling (no other
> electrics on) the ignition light dimly glows, occasionally up to full
> brightness. I measured the voltage at the battery, 11.9 volts. I
measured
> the alternator and it was 14.4 volts. I thought maybe the control box
was
> dodgy. When I opened it up though it was gleaming. Looks brand new but
> the cover is old. Not sure how to test this little baby with all those
> wires coming out of the bottom. I wonder if the idle that I have set
from
> the tacho is wrong (ie too low), can those guages measure incorrectly?
> Maybe the control box is cutting out supply back to the battery to stop
> overcharging. The ignition light does go off when I increase the rpm's.
> This is probably a simple one, but I'm not sure what that control box
> does....
>
> Cheers,
> Phil
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