Single coil, rotor & distributor cap system, 4 cylinder. 

Is the coil housing grounded? I always thought the coil housing was the 
return path for the secondary circuit / spark current. I know that the 
primary circuit doesn't use ground in the coil: it is grounded through the 
ignition points in the distributor (this is a 70's vintage car). 

Both the original and replacement coils do not show any continuity (lo res. 
or high res) at all to the HV output connector. 

Is the return path for the secondary circuit / HV spark through the points? 
Or...? 

Thanks.

On Sun, 18 Oct 2009 21:00:08 -0700, Paul Conners
<p...@gUSmail.com> wrote:

>Single coil, rotor & distributor cap system, 4 cylinder. 
>
>Is the coil housing grounded? I always thought the coil housing was the 
>return path for the secondary circuit / spark current. I know that the 
>primary circuit doesn't use ground in the coil: it is grounded through the 
>ignition points in the distributor (this is a 70's vintage car). 
>
>Both the original and replacement coils do not show any continuity (lo res. 
>or high res) at all to the HV output connector. 
>
>Is the return path for the secondary circuit / HV spark through the points? 
>Or...? 
>
>Thanks.


I don't think the housing is grounded.  

"Paul Conners" <p...@gUSmail.com> wrote in message 
news:0...@news.eternal-september.org...
> Single coil, rotor & distributor cap system, 4 cylinder.
>
> Is the coil housing grounded? I always thought the coil housing was the
> return path for the secondary circuit / spark current. I know that the
> primary circuit doesn't use ground in the coil: it is grounded through the
> ignition points in the distributor (this is a 70's vintage car).
>
> Both the original and replacement coils do not show any continuity (lo 
> res.
> or high res) at all to the HV output connector.
>
> Is the return path for the secondary circuit / HV spark through the 
> points?
> Or...?

The primary & the secondary share a common grounding point thru a grounding 
wire and capacitor to ground. The coil actually fires when the points open 
and the electromagnetic field collapses and induces a large voltage into the 
secondary. So, the secondary is not grounding thru the points. There's a 
ground wire from the neg. primary post, thru a capacitor (which passes AC 
current which is how the coil works. It's like a step-up transformer) to 
engine ground.

http://users.mrbean.net.au/~rover/ketterin.htm

http://www.international-auto.com/fiat-lancia-electrical-system/how-to-test-an-ignition-coil.cfm

On Oct 19, 7:23=A0am, "Steve N." <snewma...@cox.net> wrote:
> "Paul Conners" <pconner...@gUSmail.com> wrote in message
>
> news:0...@news.eternal-september.org...
>
> > Single coil, rotor & distributor cap system, 4 cylinder.
>
> > Is the coil housing grounded? I always thought the coil housing was the
> > return path for the secondary circuit / spark current. I know that the
> > primary circuit doesn't use ground in the coil: it is grounded through =
the
> > ignition points in the distributor (this is a 70's vintage car).
>
> > Both the original and replacement coils do not show any continuity (lo
> > res.
> > or high res) at all to the HV output connector.
>
> > Is the return path for the secondary circuit / HV spark through the
> > points?
> > Or...?
>
> The primary & the secondary share a common grounding point thru a groundi=
ng
> wire and capacitor to ground. The coil actually fires when the points ope=
n
> and the electromagnetic field collapses and induces a large voltage into =
the
> secondary. So, the secondary is not grounding thru the points. There's a
> ground wire from the neg. primary post, thru a capacitor (which passes AC
> current which is how the coil works. It's like a step-up transformer) to
> engine ground.
>
> http://users.mrbean.net.au/~rover/ketterin.htm
>
> http://www.international-auto.com/fiat-lancia-electrical-system/how-t...

'Old type' systems. IIRC the 'points' were between the coil primary
and ground! In other words, in operation, the points completed the
negative side of the circuit. With ignition 'on' (again IIRC) 12 volts
etc. was connected to the hot end of the coil's primary.
The points opened (or closed, can't remember which!) the magnetic
field either collapsed or or rose (can't remember which!) and the
secondary made a bl**dy big spark that was distributed by the rotor to
the appropriate spark plug!
Very simple system! If the 'points' got bad take them out and rub them
on stone/rock to smooth them up and then a week or so later replace
them or dress them up with a file! If the capacitor (condenser) went
bad you could sometimes use an old radio capacitor instead hanging it
below the distributor with wire!
No computers then. If not 'What's a computer it was some form of
'calculator' such as a circular slide rule or something!
Cheers.

terryS wrote:
> No computers then. If not 'What's a computer it was some form of
> 'calculator' such as a circular slide rule or something!
> Cheers.

Computers then were folks who sat down at adding machines or desk 
calculators (mechanical devices that not only added and subtracted, but 
could multiply) and ran long series of computations.  This terminology 
carried into the early fifties, then disappeared.

Actually, with some ignitions of the Kettering type (coil and breaker 
points) the vacuum lines had both advance and retard functions, and 
could be considered almost a "fluidic" computer.  Much more involved was 
the fully evolved fluidic computing going on inside a carburetor in the 
sixties and later.  Marvels of non-electronic computing.

"Steve N." <s...@cox.net> wrote in message 
news:SdWCm.31895$y...@newsfe05.iad...
>
> "Paul Conners" <p...@gUSmail.com> wrote in message 
> news:0...@news.eternal-september.org...
>> Single coil, rotor & distributor cap system, 4 cylinder.
>>
>> Is the coil housing grounded? I always thought the coil housing was the
>> return path for the secondary circuit / spark current. I know that the
>> primary circuit doesn't use ground in the coil: it is grounded through 
>> the
>> ignition points in the distributor (this is a 70's vintage car).
>>
>> Both the original and replacement coils do not show any continuity (lo 
>> res.
>> or high res) at all to the HV output connector.
>>
>> Is the return path for the secondary circuit / HV spark through the 
>> points?
>> Or...?
>
> The primary & the secondary share a common grounding point thru a 
> grounding wire and capacitor to ground. The coil actually fires when the 
> points open and the electromagnetic field collapses and induces a large 
> voltage into the secondary. So, the secondary is not grounding thru the 
> points. There's a ground wire from the neg. primary post, thru a capacitor 
> (which passes AC current which is how the coil works. It's like a step-up 
> transformer) to engine ground.

Right.  The secondary voltage relies on a ringing (AC) voltage which is 
generated
by the collapse of the magnetic field, inducing currennt via a series tuned 
circuit, IIRC. 

> The primary & the secondary share a common grounding point thru a grounding 
> wire and capacitor to ground. The coil actually fires when the points open 
> and the electromagnetic field collapses and induces a large voltage into the 
> secondary. So, the secondary is not grounding thru the points. There's a 
> ground wire from the neg. primary post, thru a capacitor (which passes AC 
> current which is how the coil works. It's like a step-up transformer) to 
> engine ground.

In order to test the coil in place (without a point set), there must be a 
capacitor from coil (-) to ground, yes? And then ground the (-) terminal and 
release. Spark should be seen? 

Thanks.

"Paul Conners" <p...@gUSmail.com> wrote in message 
news:0...@news.eternal-september.org...
>> The primary & the secondary share a common grounding point thru a 
>> grounding
>> wire and capacitor to ground. The coil actually fires when the points 
>> open
>> and the electromagnetic field collapses and induces a large voltage into 
>> the
>> secondary. So, the secondary is not grounding thru the points. There's a
>> ground wire from the neg. primary post, thru a capacitor (which passes AC
>> current which is how the coil works. It's like a step-up transformer) to
>> engine ground.
>
> In order to test the coil in place (without a point set), there must be a
> capacitor from coil (-) to ground, yes? And then ground the (-) terminal 
> and
> release. Spark should be seen?
>
> Thanks.

There will be already be a capacitor, usually inside the distributor, or 
maybe
external to it.  You should be sure that capacitor is good before you make 
any
judgements on such a test.

Then when you ground the (-) terminal, the primary coil will charge, and
when you release the ground the field will decay and you should get a spark
from the HV tower of the coil to ground.

> There will be already be a capacitor, usually inside the distributor, or 
> maybr external to it.  You should be sure that capacitor is good before you 
make 
> any judgements on such a test.

What is the value of such a cap, uF & V?

> Then when you ground the (-) terminal, the primary coil will charge, and
> when you release the ground the field will decay and you should get a spark
> from the HV tower of the coil to ground.

Thanks.

Paul Conners wrote:
> Single coil, rotor & distributor cap system, 4 cylinder. 
> 
> Is the coil housing grounded? I always thought the coil housing was the 
> return path for the secondary circuit / spark current. I know that the 
> primary circuit doesn't use ground in the coil: it is grounded through the 
> ignition points in the distributor (this is a 70's vintage car). 
> 
> Both the original and replacement coils do not show any continuity (lo res. 
> or high res) at all to the HV output connector. 
> 
> Is the return path for the secondary circuit / HV spark through the points? 
> Or...? 
> 
> Thanks.
> 

Both windings in the coil ground through the negative terminal.

You should find conductivity from the + terminal to the - Terminal. And
from the high voltage terminal to the - terminal.

The positive terminal on the coil goes to the battery (through a switch
or relay usually) On most vehicles this voltage is NOT 12 volts, it is
stepped down through the ballast resistor or through resistance wire so
that 6 volts gets to the coil.

The - side gets connected to the points. You will usually see a
capacitor on the coil, it is there to stop radio noise and voltage
spikes from going into the wiring.
On the points you will see another one. It's purpose is to damp the
electric pulse and keep the points from arcing.

This all supposes the old style can coils.
Most of the new high voltage coils DO ground through the coil frame.

-- 
Steve W.