Simon,
I do agree that in the case with only the field wire connected that the
voltage regulator may raise the voltage to the field to the point of burning
out the field windings.
Regards,
Phil
-----Original Message-----
From: Simon Favre [mailto:simon@mondes.com]
Sent: Tuesday, October 31, 2000 2:21 PM
To: Jack W. Drews
Cc: vintage-race@autox.team.net
Subject: Re: generator / alternator question
See below. You should have started the question by mentioning the
cutoff switch.
"Jack W. Drews" wrote:
> I'd appreciate some input and education regarding generators vs.
> alternators, and damage that can be caused by turning them without them
> being hooked up. Three questions:
>
> If a ONE-WIRE alternator is spun without being hooked up, my
> understanding is that no damage will occur. True or false?
If it's only got one wire, and that's not hooked up, there is no
damage, because the field was never energized. A one-wire alternator
has an integral regulator, so even if you switch out the main battery
cable while it's running, the regulator should keep it under control.
It will keep generating voltage while turning, if it was energized
before being cut out. Are the secondary contacts on the cutoff switch
rated for the same current as the alternator output? If not, you have
a problem. The cutoff switch needs to kill all power to the rest of
car, so you can't have any power drain between the switch and the
battery. If you can't kill the alternator output with the switch, then
you can't have the power drain between the switch and the alternator
either.
> If a generator is spun with the fields energized but the armature not
> hooked up, my understanding is that it will damage the generator. True
> or false?
The only way to do this is to first start the car normally, then pull
the main battery cable at the generator. If the regulator is not sensing
any output from the generator, then yes, you will eventually burn out
the field winding. To kill a generator, you typically only need to break
the field connection.
> If a generator is spun with neither fields nor armature hooked up, my
> understanding is that no damage will occur. True or false?
Nothing hooked up, nothing carrying current, means no damage.
> --asking this in relation to master switch hookup, and the difficulty
> I've experienced trying to use the expensive six-contact master shutoff
> switch in cars with one-wire alternators.
Since a one-wire alternator has an integral voltage regulator, you have
no access to the internal connections to the field. I doubt the fancy
cutoff switch can perform its function in that case. In the case of a
generator, the field terminal needs to go floating on switch disconnect.
In some alternator circuits, the field needs to be grounded, in others
you might need to disconnect it. Note also that in an alternator, the
field winding is actually on the rotor. The stator has the diode chassis
which provides the output.
In a one-wire alternator, I believe the brush assembly is part of the
regulator. That's what might make this real tough to do. One possibility
is to modify the regulator/brush assembly so that the brush that normally
goes to ground is floating unless the main switch is in the ON position.
You would have to insulate the mounting screw from the terminal and bring
a wire from that terminal to the switch. You might also be able to do
this with two wires spliced into a cut in one of the brush leads. If you
cut either brush out of the circuit, you got no juice.
Simon
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