[AT] AT Digest, Vol 28, Issue 7

Wed May 13 04:58:59 PDT 2020

Glad you mentioned resonance, Carl.  This is the next level of the
discussion that I purposely avoided in my previous comments.   With points
open, it's a LRC circuit.  L is the inductance of the coil primary; R is
the small resistance of the primary; and C of course is the capacitance of
the condenser.  At initial points opening (only open a tiny amount thus
far) a voltage spike comes out of the primary and is absorbed by the
condenser.  This discharges back thru the coil primary in a "ringing" or
resonance fashion, and some energy is dissipated by the resistance.  The
"ringing" reverses again, several times, with an exponentially decreasing
amplitude as energy is dissipated.  It happens (or should happen, if the
circuit is properly balanced, as you mentioned) very rapidly.  The points
re-closing will dead-short the condenser but by now there's very little
energy left to be dissipated.

I have some neat oscilloscope plots of this phenomenon somewhere... oh,
just realized where they are:  in the instruction manual for an old Snap-on
"Counsellor" oscilloscope from the 1980's.  It happens to be at work right
now.  I wonder if I can remember to scan some and send them along.

What is really fascinating is that the points-and-condenser ignition was
developed, as far as I know, before the invention of the oscilloscope.
Early electrical engineers had a strong intuition for analog circuits.

SO

On Tue, May 12, 2020 at 7:19 PM <szabelski at wildblue.net> wrote:

> I agree that the condenser is wired across the points, and it helps
> prevent burning of the contacts by helping to suppress the arc when the
> points open. But a condenser can only store so much energy and must be
> discharged at some point, it can’t absorb energy forever. The condenser has
> to be discharged before the next opening of the points or it can’t absorb
> any more energy and help suppress the arc.  It becomes discharged when the
> points close again. That is also when the plug is firing, so that stored
> energy goes into the spark. The condenser and coil also form a resonant
> circuit which is what is needed to try to have a stable system since the
> energy from the coil rises and falls as the energy is created and released.
>
> That is why there are as many different condensers available ,as there are
> cools. You need one that properly works with the coil to absorb the level
> of energy developed by the coil. If it can’t absorb enough, points burn.
> You also don’t have a properly balanced resonant circuit.
>
> Carl
> ----- Original Message -----
> From: Stephen Offiler <soffiler at gmail.com>
> To: Antique Tractor Email Discussion Group <at at lists.antique-tractor.com>
> Sent: Tue, 12 May 2020 10:04:58 -0400 (EDT)
> Subject: Re: [AT] AT Digest, Vol 28, Issue 7
>
> Condenser function:  it connects across the points, aka in parallel.
> Points are used to switch current through the coil primary.  Coil primary
> functions like a big inductor - it  stores  energy in a magnetic field, and
> it uses that field to supply energy to oppose any change in current.  It
> can't win, because the energy gets depleted, but it does try. As the points
> open, that implies a sudden change in current from the steady DC value to
> zero.  Inductance responds by trying to keep that current flowing.  It
> "piles up" electrons at the opening points which elevates the voltage
> there.  It would certainly arc, if the condenser wasn't there.  The
> condenser charges up and gives that voltage (that pile of electrons) a
> place to go, thus suppressing the arc and extending the life of the points
> substantially.
>
> SO
>
>
> On Tue, May 12, 2020 at 9:49 AM <szabelski at wildblue.net> wrote:
>
> > Steve,
> >
> > The condenser is actually a capacitor, originally called a condenser
> > (probably because a charge condensed internally) and later called a
> > capacitor. There should be no continuity between the condenser case and
> the
> > pigtail wire. A capacitor is made of two thin sheets of metal that hold a
> > charge until there is a short between the case and the pigtail. The two
> > thin plates are separated by a thin medium that allows the charge to
> build
> > up to a specified amount. The purpose of the condenser is to store extra
> > energy and give you that little “extra kick” when discharged.
> >
> > As I said in an earlier post, it is difficult to check a condenser, it
> > takes special equipment. Even if it passes, there is no guarantee how
> long
> > it will last since the medium that separates the two plates can fail and
> > allow a short between the two plates. The best thing is to try a
> different
> > condenser. It just has to be one with the same capacity to store the
> > required charge.
> >
> > Carl
> >
> >
> > ----- Original Message -----
> > From: STEVE ALLEN <steveallen855 at centurytel.net>
> > To: at at lists.antique-tractor.com
> > Sent: Mon, 11 May 2020 17:39:06 -0400 (EDT)
> > Subject: Re: [AT] AT Digest, Vol 28, Issue 7
> >
> >
> > ----- Original Message -----
> > Message: 7
> > Date: Sun, 10 May 2020 19:53:23 -0500
> > From: Phil Auten <pga2 at basicisp.net>
> > To: at at lists.antique-tractor.com
> > Subject: Re: [AT] Project Updates '49 A, '51 A, and '47 B (STEVE
> >         ALLEN)
> > Message-ID: <168f1f90-8d7a-1eef-e95e-28fb0fa7e41b at basicisp.net>
> > Content-Type: text/plain; charset=utf-8; format=flowed
> >
> > '49A - If your points are clean and reading .5 ohms when closed and .7
> > ohms with cardboard separating the points, your points are shorted. With
> > the cardboard in, they should read an open circuit, and .5 ohms when
> > closed says your contacts aren't making contact well. If you took those
> > measurements with the points installed, disconnect them and retest. If
> > the points read 0.0 ohms closed and open circuit with the cardboard in,
> > then the problem is elsewhere.
> > '49 A: I forgot to mention, if the points measure correctly outside the
> > distributor you may have a bad coil.
> >
> > Phil in TX
> >
> > Phil,
> >
> > Remember that the points set in a Wico X mag is two separate pieces.  If
> I
> > take them off, I can screw them back together and check for continuity,
> > BUT:  while mounted in the mag,
> > the fixed one is in contact with the case of the mag, and the other, the
> > one that moves, is in contact with the terminal of the condenser.  Now,
> let
> > me speculate here:
> > the terminal in the condenser does not touch the case of the condenser,
> > right?  So, the two points should not have continuity because the one is
> > connected to the terminal
> > and the other is "connected" (through the case) to the mag case.  UNLESS
> > there is continuity inside the condenser.  I do not understand condensers
> > well at all,
> > but *SHOULD there be continuity between the case of the condenser and the
> > terminal of the condenser*?
> > If not, that may well be my problem (per Cecil).  I will investigate
> > tonight.
> >
> > BTW, I know that the shaft is turning and that the points are opening and
> > closing:  I have verified that much by turning the crank.
> >
> > The "original" Steve Allen
> > Who is avoiding the local Menards
> >
> >
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