Go Back   The Ford Barn > General Discussion > Model A (1928-31)

Sponsored Links (Register now to hide all advertisements)

Reply
 
Thread Tools Display Modes
Old 08-14-2020, 01:48 PM   #1
30 Closed Cab PU
Senior Member
 
Join Date: Aug 2018
Location: Wisconsin
Posts: 2,294
Default Pertonix Coil Performance

Am starting a new string on an old subject. Performance of the Pertronix Coil. This has been a subject for a long time, with Purdy leading the charge (pun intended). I have been thinking about it again due to this string. https://www.fordbarn.com/forum/showthread.php?t=285559 starting with post 16

Since starting the hobby in 2011 and knowing nothing about the A, have been led astray many times, especially in the beginning. And sometimes causing me a lot of grief/wasted time. Mostly because I was not aware of the Model A forums and was not a member of a Club. So I tend to be very skeptical of things I do not understand, and typically do not blindly accept what I am told.

I have always believed Purdy's claims, but have remained skeptical since I could not grasp how this coil is an improvement. I think I've had an "Aha" moment . So would like Purdy's and others opinions of what I think I know.

A Spark happens when voltage across a gap reaches the air impedance to jump the gaps and ionizes whats between the air gaps (in an A rotor and Spark plug gaps). Once the air ionizes it reduces the impedance in the gap to almost 0, and the Spark continues until the energy across the gap is depleted.

So in the case of the Pertronix, as long as there is enough points closed time so it can reach full capacity, it stores more energy than a standard coil. Then across a close to short when the air is ionized it can supply more current in the spark, which creates a more intense higher energy spark. The limiting factors for current/hotter intensity are - the coil wire impedance , the cap button to rotor connection impedance, and Pertronix secondary impedance and other design considerations. Spark plug leads are solid straps, impedance is 0.

A possible down side to this is an increase wear on the gaps components due to the higher current sparking.

A thing I missed previously is Purdy has increased the gaps. I'm not sure what this does for the quality of the Spark. Possibly Increasing the gap increases the time the coil has to store energy, so insures the coil takes a full charge in its coils? If too much, would the coil heat up?

Sorry for being so long/wordy, trying to be thorough.




So, comments?
30 Closed Cab PU is offline   Reply With Quote
Old 08-14-2020, 02:57 PM   #2
Patrick L.
Senior Member
 
Patrick L.'s Avatar
 
Join Date: May 2010
Location: Upstate NY and western Florida
Posts: 5,895
Default Re: Pertonix Coil Performance

Point gap affects coil saturation time.

It takes just so much voltage to jump a [ sparkler/rotor] gap. The wider the gap the more voltage it takes. More voltage than what is needed is not necessary, its just nice to have if it is needed.
Patrick L. is offline   Reply With Quote
Sponsored Links (Register now to hide all advertisements)
Old 08-14-2020, 03:38 PM   #3
Purdy Swoft
Senior Member
 
Purdy Swoft's Avatar
 
Join Date: May 2010
Location: Alabama
Posts: 8,046
Default Re: Pertonix Coil Performance

When the spark jumps a gap , the spark will get hotter to a point . Its sort of like holding the plug wire a small distance from the spark plug to help cause a wet or fouled spark plug to spark .
Purdy Swoft is offline   Reply With Quote
Old 08-14-2020, 03:53 PM   #4
Jack Shaft
Senior Member
 
Join Date: Dec 2019
Posts: 704
Default Re: Pertonix Coil Performance

A coil builds voltage when the points are closed,this is called dwell,the time the coil 'soaks'and builds voltage to its rated value.this voltage is discharged when the points open,sending this "charge" to the spark plug.Any gaps jumped reduces this voltage,you cannot build voltage using discharge,only during the soak time the points are closed.
Jack Shaft is offline   Reply With Quote
Old 08-14-2020, 04:19 PM   #5
30 Closed Cab PU
Senior Member
 
Join Date: Aug 2018
Location: Wisconsin
Posts: 2,294
Default Re: Pertonix Coil Performance

Quote:
Originally Posted by Jack Shaft View Post
A coil builds voltage when the points are closed,this is called dwell,the time the coil 'soaks'and builds voltage to its rated value.this voltage is discharged when the points open,sending this "charge" to the spark plug.Any gaps jumped reduces this voltage,you cannot build voltage using discharge,only during the soak time the points are closed.

My understanding is that the rated value above is either 6 v or 12 v dependent on the battery voltage. As you indicate the high voltage is generated when the points open, and this voltage is limited to the voltage required to start the spark. The high voltage is limited by the gaps at the rotor and spark plugs. Once the gaps are sparking the coil secondary is basically shorted to ground since the ionization in the spark basically a short. So the coil does not reach it max high voltage max. rating.

So the rated value above is battery voltage, not the max gap voltage that the coil can jump.
30 Closed Cab PU is offline   Reply With Quote
Old 08-14-2020, 04:23 PM   #6
john in illinois
Senior Member
 
john in illinois's Avatar
 
Join Date: May 2010
Location: Illinois
Posts: 1,939
Default Re: Pertonix Coil Performance

Sponsored Links (Register now to hide all advertisements)
I do not know how a higher voltage coil affects a model A distributor. I have not tried one.

I do know that a high secondary voltage due to a hotter coil causes premature wear on rotor and cap contacts on a flathead. They were designed for a standard coil.

John
__________________
Welcome each day
john in illinois is offline   Reply With Quote
Old 08-14-2020, 04:46 PM   #7
Jack Shaft
Senior Member
 
Join Date: Dec 2019
Posts: 704
Default Re: Pertonix Coil Performance

Quote:
Originally Posted by 30 Closed Cab PU View Post
My understanding is that the rated value above is either 6 v or 12 v dependent on the battery voltage. As you indicate the high voltage is generated when the points open, and this voltage is limited to the voltage required to start the spark. The high voltage is limited by the gaps at the rotor and spark plugs. Once the gaps are sparking the coil secondary is basically shorted to ground since the ionization in the spark basically a short. So the coil does not reach it max high voltage max. rating.

So the rated value above is battery voltage, not the max gap voltage that the coil can jump.
A coil builds voltage through resistance when the points are closed and discharges when they are opened..the base charge voltage of a coil is either 6v with a 1.5 ohm resistance or 12v with a 3 ohm resistance it uses this resistance through a series of windings to create with the pertronix flame thower 40,000 v at discharge when the points open. Arc distance across a rotor /cap lowers voltage,as does a wider spark plug gap,both of theses gaps affect timing (slightly) as well...I don't quite understand your theory as described.
Jack Shaft is offline   Reply With Quote
Old 08-14-2020, 05:08 PM   #8
30 Closed Cab PU
Senior Member
 
Join Date: Aug 2018
Location: Wisconsin
Posts: 2,294
Default Re: Pertonix Coil Performance

Quote:
Originally Posted by Jack Shaft View Post
A coil builds voltage through resistance when the points are closed and discharges when they are opened..the base charge voltage of a coil is either 6v with a 1.5 ohm resistance or 12v with a 3 ohm resistance it uses this resistance through a series of windings to create with the pertronix flame thower 40,000 v at discharge when the points open. Arc distance across a rotor /cap lowers voltage,as does a wider spark plug gap,both of theses gaps affect timing (slightly) as well...I don't quite understand your theory as described.



We seem to be agreeing now. My 1st post, ignore it. I am now trying to convey that in a properly timed working A, the coil secondary does not actually generate 40,000 volts. The points and rotor are sparking before that.
30 Closed Cab PU is offline   Reply With Quote
Old 08-14-2020, 05:17 PM   #9
Jack Shaft
Senior Member
 
Join Date: Dec 2019
Posts: 704
Default Re: Pertonix Coil Performance

Quote:
Originally Posted by 30 Closed Cab PU View Post
We seem to be agreeing now. My 1st post, ignore it. I am now trying to convey that in a properly timed working A, the coil secondary does not actually generate 40,000 volts. The points and rotor are sparking before that.
Yes it does,the coils secondary develops 40k v prior to discharge..the bosch blue coil I use puts out 35v after dwell..timing does not affect coil output,nor does spark plug gap or rotor gap,the coils is charged and discharged at rated capacity for its effective life,till the windings start breaking down and the output voltage drops,this condition can be diagnosed by how hot the coil gets,old rule of thumb,if the coil is too hot to touch its done.
Jack Shaft is offline   Reply With Quote
Old 08-14-2020, 05:48 PM   #10
30 Closed Cab PU
Senior Member
 
Join Date: Aug 2018
Location: Wisconsin
Posts: 2,294
Default Re: Pertonix Coil Performance

Here is a textbook article off the internet. I am referencing the paragraph "actual coil output"


Here is the link to the info, this info.

https://www.g-wonlinetextbooks.com/a...ntals-2020/227


The entire chapter starts here
https://www.g-wonlinetextbooks.com/a...ntals-2020/223
Attached Files
File Type: pdf coil output.pdf (148.1 KB, 14 views)

Last edited by 30 Closed Cab PU; 08-14-2020 at 05:51 PM. Reason: corrected link
30 Closed Cab PU is offline   Reply With Quote
Old 08-14-2020, 06:55 PM   #11
Jack Shaft
Senior Member
 
Join Date: Dec 2019
Posts: 704
Default Re: Pertonix Coil Performance

Discharge voltage drop during transmission is real,it results in a loss of power,a stock model A ignition system has a few loss points..minor stuff compared to manual timing..
Jack Shaft is offline   Reply With Quote
Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump

Sponsored Links (Register now to hide all advertisements)


All times are GMT -5. The time now is 08:54 AM.