Tony :
1) The stock charging circuit wiring (at least in a TR3, TR4 should be the
same) is plenty heavy to carry anything up to 100 amps, in fact it is a
full AWG bigger than the wire in my Chevy (with a stock 80 amp alternator).
Make sure your connections are sound. (One good way to check is to feel
them after the alternator has been charging heavily for awhile. If they
are hot, then the connection is poor.)
I have been running a 63 (or more) amp Ford alternator on my TR3 for many
years, and the wires don't even get warm, even with a deeply discharged
battery.
2) It is harmful, if not downright dangerous, to disconnect a running
alternator from the battery, as I think you are proposing. In the time it
takes the regulator to shut down the magnetic field in the rotor, the
output voltage will have already risen high enough to pop the diodes. If a
human happens to be touching the wires at the time, it may pop him, too.
We are talking about potentially hundreds of volts, at 60 amps ! The
diodes will usually fail around 600 volts, but even failed diodes may not
prevent the alternator from putting out high voltage AC for awhile before
the smoke comes out.
BTW, there was a circuit popular some years ago, that would get 120 volts
DC at 30-60 amps (limited mostly by heat buildup) from a stock car
alternator. In effect, all that circuit did was to disconnect the
alternator output from the battery, and use a regulator calibrated to 120
volts instead of 12 volts (or temporarily recalibrate the existing
regulator). Before the advent of battery powered hand tools, it was quite
handy.
3) To use the stock ammeter, you should probably add a shunt across the
back of the ammeter, to keep the reading in range. This is not so much an
electrical issue (ie it won't burn up the ammeter), but an esthetic one :
it looks bad to have the needle buried on charge, and the needle may stick
or bend. I don't have the numbers handy, but I figured out shunts for TR3
and 6 earlier this year, you should be able to find them in the archives.
If you really want to isolate high charging current from the rest of the
wiring, one way would be to use a high current diode from the alternator
output to the starter solenoid. It won't conduct until the voltage across
it rises to about 0.7 volts, which isn't enough to harm the wiring, but
will bypass any excess.
Or, I can probably brew up a circuit using the old regulator, an external
relay, and a "battery isolator" to bypass the original charging circuit
when the current gets too high, but it hardly seems worth the effort.
Randall
On Wednesday, August 11, 1999 5:24 PM, Tony Rhodes
[SMTP:ARhodes@compuserve.com] wrote:
>
> I have perused the VTR maintenance page about removing a generator
> and placing an alternator. I also understand the current carrying
limitation
> of the stock wiring, and therefore the need for a heavy cable running to
> the solenoid and hence to the battery.
>
> I hate giving up the (+) side of the ammeter by hooking the alternator
> directly to the battery, but I really do not want to fry the wiring.
>
> I figured that I could install a big cut-off switch in-line with the
heavy
> cable to the solenoid so I could run the power through the stock wiring
> when the battery is not too low. I could then switch the alternator
directly
> to the battery if the car had not been run ia a while.
>
> I then thought that I'd hate to forget to throw the switch and fry the
wiring anyway.
>
> I then thought about that useless voltage regulator sitting in the engine
compartment.
> I am sure that it is possible to rig up a solenoid to do the function of
that big
> switch. It would need to come on if the current in the main wiring gets
too high.
> It then should stay on for the rest of the time the engine is running.
I.E.
> once engaged, the solenoid needs to stay on. It needs to be able to
carry
> the 60 or 90 amps that I could get out of the alternator.
>
> Anybody know of such a beast? I am not sure what such a solenoid's
> original purpose would be, but it needs to switch on a certain current,
then
> stay on.
>
> -Tony
|