[AT] Well, I guess I didn't really want it to be easy

Fri Sep 29 10:17:31 PDT 2006

Wow, great explanation.  I'll have to file this away...

Rick 

-----Original Message-----
From: at-bounces at lists.antique-tractor.com
[mailto:at-bounces at lists.antique-tractor.com] On Behalf Of Dean VP
Sent: Friday, September 29, 2006 11:37 AM
To: 'Antique tractor email discussion group'
Subject: RE: [AT] Well, I guess I didn't really want it to be easy

Larry:

My choice of words at midnight could have been much better.  I won't try
to
get into the details of how a distributor vs a magneto work. But both
use
the following principles. I will use a battery based system for
simplicity.
Both the condenser capacitance and the coil inductance do work together
to
create a controlled voltage spike which in turn creates the arc (spark)
through the coil secondary across the spark plug gap when the points
open.
When the points are closed, the coil primary is essentially grounded
with 6
or 12V at the opposite end. From a battery driven system point of view
depending on the DC resistance of the coil there may be roughly 3 to 6
amps
of steady state current flowing in it. Some added resistance between the
battery supply and the coil may be installed as standard equipment.
However
when the points open both, the coil and condenser resist change. The
coil
was passing the current and now the current has no place to go, the
opening
points create a high resistance and high voltage develops. The coil
wants to
keep the current flowing and develops a very high voltage trying to keep
it
flowing. However, the condenser resisting change is now trying to keep
the
voltage at zero and starts at a low resistance until it can get charged
up
to the voltage the coil is trying to produce increasing in resistance in
the
process. The combination gives a controlled voltage rise on the primary
which produces a much higher voltage spike on the secondary which
produces
the spark across the gap of the spark plug. 

When the points open, the voltage spike across the coil is much less
than
that produced by the secondary winding. However, when the points open it
is
in essence trying to produce an open circuit so the voltage developed on
the
primary builds up across the point gap. The point gap becomes an air gap
capacitor. Depending on the condition of the points and the ambient air
purity it may try to pass current through the point gap. Points
sparking! If
the points are not opening properly, are dirty, or the gap isn't
adequate,
the voltage build up in the primary will not produce the kind of voltage
spike that is adequate to drive the secondary to produce a good clean
spark
at the plugs. The condenser being grounded and attached to the coil side
of
the points first tries to hold the voltage spike down when the points
first
open thereby reducing the current flow across the point gap as it
develops.
Later when the points are more open the condenser allows the voltage to
build up to produce the voltage spike on the primary which in turn
produces
a much higher voltage spike on the secondary producing a spark across
the
spark plug gap. Notice the gap between the points is usually quite a bit
smaller than the gap across the plug. 

So the condenser really limits the current flow across the points as the
opening resistance is increasing, thereby increasing point life and
allows
the coil to continue producing the current flow until the condenser is
fully
charged. A controlled voltage spike. 

Now the point I was really trying to make. The coil and condenser both
work
together in a dynamic non-DC voltage situation to create the spark. It's
a
voltage and current change that create the spark. Not a static
situation.
Now when one tests a condenser with a normal Volt Ohm Meter (in Ohm
Meter
mode) the kind of voltages and currents that are developed in the
magneto or
battery based distributor systems are not totally emulated. Yes, the VOM
can
be used to determine whether or not the condenser is shorted out at
whatever
the voltage supplied by the VOM is. And the condenser will start out at
low
resistance and then become very high when the leads of the VOM are first
applied if working properly. Now the voltage of the VOM is much lower
than
the voltage in actual application and also so are the currents. While
the
condenser may pass the lower voltage and current testing conditions it
may
not do so under real life (higher voltage/higher current) conditions.
That
is the only real point I am trying to make. 

Since most of us may be limited to an inexpensive VOM to use for
testing, it
is a good preliminary check but all I wanted to do was expose the fact
that
incorrect results may be derived. Obviously, if the condenser always
reads a
very low resistance and never changes it is obviously bad. The rate at
which
it charges up (capacitance value) and it's resistance at high voltage is
not
really checked by the VOM. This is where one can get really mislead. If
it
isn't shorted out the VOM doesn't really tell us how good it is under
application conditions. Since we often don't have a way to check these
parameters, we just simply replace the condenser with a new one to see
if
that fixes the problem. 

Dean A. Van Peursem
Snohomish, WA 98290

"Experience is a series of non-fatal mistakes."

www.deerelegacy.com

http://members.cox.net/classicweb/email.htm

-----Original Message-----
From: at-bounces at lists.antique-tractor.com
[mailto:at-bounces at lists.antique-tractor.com] On Behalf Of Larry D. Goss
Sent: Friday, September 29, 2006 7:30 AM
To: 'Antique tractor email discussion group'
Subject: RE: [AT] Well, I guess I didn't really want it to be easy

If the only reason a condenser is in the circuitry is to keep the points
from burning, then if you take the condenser completely out, the
ignition should still work -- but it won't.  Something's wrong here.  I
was taught that the coil and condenser worked together to form an
elementary I-C (inductance-capacitance) tank circuit.  I suspect that's
still true.  It's the breakdown and discharge of the circuit that causes
the voltage spike to cause the spark.  If that wasn't so, you'd be able
to hook an ignition coil directly to a battery and get a constant arc at
the spark plug.  I think we got away from that sort of ignition system
when Ford abandoned the buzz box coil.

Larry

-----Original Message-----
From: at-bounces at lists.antique-tractor.com
[mailto:at-bounces at lists.antique-tractor.com] On Behalf Of Dean VP
Sent: Friday, September 29, 2006 2:03 AM
To: 'Antique tractor email discussion group'
Subject: RE: [AT] Well, I guess I didn't really want it to be easy

They can be tested this way but passing this test does not guarantee
performance in a real life tractor application. The voltage applied by
the
voltmeter does not duplicate the actual voltage spike which occurs when
the
points open. A basic test but one that does not really test actual
performance under real life application conditions. These test results
can
be very misleading. False negative and false positive results can occur.

Most condensers (capacitors) only fail under high voltage conditions.
The
real purpose of these condensers is to extend point life and if they
become
open they will not cause ignition failure, only if they develop a short
at
DC or under high voltage spike conditions. A typical voltmeter will not
test
properly for these specific application conditions. 

Many are replaced inappropriately when they are operating perfectly.
Very
few condensers fail in real life applications. 

Dean A. Van Peursem
Snohomish, WA 98290

"Experience is a series of non-fatal mistakes."

www.deerelegacy.com

http://members.cox.net/classicweb/email.htm

-----Original Message-----
From: at-bounces at lists.antique-tractor.com
[mailto:at-bounces at lists.antique-tractor.com] On Behalf Of Spencer Yost
Sent: Thursday, September 28, 2006 9:09 PM
To: at at lists.antique-tractor.com
Subject: Re: [AT] Well, I guess I didn't really want it to be easy

Condensers can be tested with a simple multimeter.   Place the
multimeter
on the resistance setting, the red lead on the "pigtail", the black on
the
the metal side of the condenser.   Resistance should start at some
number(where it starts is immaterial).  It will then steadily build
until
it reads infinity/pegs the meter.  Anything else and the condenser is
bad

Of course, you could replace it as part of a tune-up, but there no
reason
to replace it blindly.

Spencer Yost
Owner, ATIS
Plow the Net!
http://www.atis.net

*********** REPLY SEPARATOR  ***********

On 9/28/2006 at 8:54 PM Dean Vinson wrote:

>Or I'd have bought one that was all restored and perfect.
>
...snip...
>Rick has been patiently suggesting I replace the condenser, so that
seems
>like next on the list.  Only trouble is I can't figure out how to get
the
>
>Dean Vinson
>Dayton, Ohio
>www.vinsonfarm.net

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