[AT] AT Digest, Vol 28, Issue 7

Wed May 13 05:35:12 PDT 2020

Thanks very much, Mark.  Regarding the Snap-on 'scope, yes, absolutely, it
was automotive-specific.  Here's a link to one for sale on eBay just to
give you an idea:

https://www.ebay.com/c/1104491855

SO

On Wed, May 13, 2020 at 8:11 AM Mark Johnson <markjohnson100 at centurylink.net>
wrote:

> Steve:
>
> Great explanation of LRC circuits...I know (or used to know) most of this,
> but your explanation is one of the best I've ever seen.
>
> I didn't know Snap-On ever sold oscilloscopes - presumably for diagnosis
> of automotive ignitions and electrical systems?
>
> With all the GHz-range clocking of modern personal computers, a knowledge
> of analog and RF is still very important. At 3 GHz, a 1-inch trace on a
> circuit board is an antenna!
>
> Mark Johnson (WB9QLR)
>
> Columbia MO
>
>
> On 5/13/2020 6:58 AM, Stephen Offiler wrote:
>
> 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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>> >
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>>
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