internal resistor in coil question

In the old, conventional distributor/breaker point systems, how does the
internal coil resistor let full voltage go through for starting, and then
drop it down for running? Is it a temperature driven thing (i.e., as the
resistor warms up, the resistance drops)?

And how does it work with the external resistor? Is there a separate leg on
one position of the starter switch that flows direct to the coil for
starting, then switches to the resistor for running?

Just curious.

"RB" > wrote in message
.. .
> In the old, conventional distributor/breaker point systems, how does the
> internal coil resistor let full voltage go through for starting, and then
> drop it down for running? Is it a temperature driven thing (i.e., as the
> resistor warms up, the resistance drops)?
>

what internal coil resistor?

> And how does it work with the external resistor? Is there a separate leg
on
> one position of the starter switch that flows direct to the coil for
> starting, then switches to the resistor for running?
>

That is how all the older resistance wire circuits I've seen work.

Ted

"RB" > wrote in message
.. .
> In the old, conventional distributor/breaker point systems, how does the
> internal coil resistor let full voltage go through for starting, and then
> drop it down for running? Is it a temperature driven thing (i.e., as the
> resistor warms up, the resistance drops)?
>
> And how does it work with the external resistor? Is there a separate leg
> on
> one position of the starter switch that flows direct to the coil for
> starting, then switches to the resistor for running?
>
> Just curious.
>
>

The ignition switch applies power to the resistor in the "ON" position.
Further rotation applies power to the "START" contact, which applies power
directly to the coil and the starter relay. This effective bridges the
resistor during the few seconds of START mode, while the starter motor is
drawing such a heavy current that system voltage drops considerably. This is
all done to help give you a good, hot spark even during cranking.

I have never seen an "internal" resistor. Since the resistor usually has to
drop about 6 volts while supplying about 2 amps of average current, the
resistor will dissipate about 12 watts. Run resistors often look like a
little ceramic brick, and are often mounted to the firewall to help
dissipate the excess heat.

The resistance element is often something like nichrome wire, like in your
toaster. It actually has a small positive temperature coefficient; that is,
resistance goes up with temperature.

Ed

To answer your original question, there obviously is no provision for
12volt bypass for starting in an internally resisted coil. And for you
other guys up there, I don't know how common they are or for how many
years they were produced or by whom but, yes, there is such a thing as
an internally resisted coil in which no external resister is required.
Good luck.

On Sat, 25 Dec 2004, RB wrote:

> In the old, conventional distributor/breaker point systems, how does the
> internal coil resistor let full voltage go through for starting, and
> then drop it down for running?

It doesn't, per se.

> as the resistor warms up, the resistance drops)?

Other way round. As the resistor heats up, its resistance *increases*,
which reduces voltage to the coil, which causes the coil to run cooler,
which reduces the resistor temperature, which increases voltage to the
coil, which causes the coil to run hotter...and thus the coil temperature
is controlled to prevent coil damage while providing the hottest spark
possible. These internal-resistor setups give shorter breaker point life
than systems with external coil resistors.

> And how does it work with the external resistor? Is there a separate
> leg on one position of the starter switch that flows direct to the coil
> for starting, then switches to the resistor for running?

Yes. The resistor bypass terminal may be on the starter switch, on the
starter relay, or on the starter solenoid.

DS

I think the "internal resistor" coils have an extra reactance coil
in them that offers little resistance when cranking, but after start
the pulsating field creates inductive resistance that limits the
current flow. All coils will have some reactance, of course, but the
internally-ballasted type will have much more.

Dan

}}} Other way round. As the resistor heats up, its resistance *increases*,
which reduces voltage to the coil, which causes the coil to run cooler,
which reduces the resistor temperature, which increases voltage to the
coil, which causes the coil to run hotter... {{{

Of course! My mistake. Should have caught that. Thanks.

pater wrote:
> To answer your original question, there obviously is no provision for
> 12volt bypass for starting in an internally resisted coil. And for
you
> other guys up there, I don't know how common they are or for how many
> years they were produced or by whom but, yes, there is such a thing
as
> an internally resisted coil in which no external resister is
required.
> Good luck.

These coil were (are) used on a lot of industrial applications, such as
tractors or forklifts. A full 12 volts is on the + side of the coil at
all times, whether it is starting or running. I'm trying to recall a
part
number on the top of my head. I think it is Stardard ignition products
#12 or #15. Something like that anyway.

the reason for the resistor is to shorten the time for a full buildup of
the magnetic field (current )
in the inductor. (coil).
the resistor limits the current in the coil to a liveable value while
increasing the rate of buildup
of the current in the coil.
this gives the capability for a full output at higher engine speeds.
the coils are still about the same as a six volt coil but the resistor
prevents overheating
and failure.
sammmm



"RB" > wrote in message
...
> }}} Other way round. As the resistor heats up, its resistance
*increases*,
> which reduces voltage to the coil, which causes the coil to run cooler,
> which reduces the resistor temperature, which increases voltage to the
> coil, which causes the coil to run hotter... {{{
>
> Of course! My mistake. Should have caught that. Thanks.
>
>