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Re: Ignition Polarity

Posted: Tue Feb 10, 2015 11:26 am
by tornitore45
...that was to power the P 47 Thunderbolt
I can believe that.
The Sparking distance has a nonlinear dependence on the gas pressure.
At High pressure like in an engine the spark voltage is much higher than at atmospheric pressure,
it follow that at low pressure, high altitude the sparking occurs at lover voltage.
The trend does not continues, in high vacuum the sparking threshold rises again because there is not enough ionization until the the electrons are extracted from the metal electrodes which take a stronger field.

Re: Ignition Polarity

Posted: Tue Feb 10, 2015 11:05 pm
by golfpin
Thanks Ronm, trying to get my head around this one, I presume the Mack trucks were fitted with alternators? If they were then it blows my assumption that if you run an alternator, the system has to
be Neg ground. Am a little out of my depth here, anyone perhaps clarify this please.

Mauro, thanks for that input, was running on fading 70.345 memory, very articulate reply sure you arn,t the Bsc elec we were looking for for answers?

Cheers Golfpin

Re: Ignition Polarity

Posted: Tue Feb 10, 2015 11:42 pm
by ronm
Some big truck alternators are ungrounded, i.e. they have a positive post & a negative. Either post can be grounded. Some are 24V also...

Re: Ignition Polarity

Posted: Wed Feb 11, 2015 4:22 am
by ken572
(ALL) Who might be interested. :D

Prestolite/Leece Neville

Alternators and Starters

FREE Training Manuals and More,

Under Support. (Pdf Format)

(Very Interesting) (Enjoy) 8)

http://www.prestolite.com/index-na.php

Ken. :)

Re: Ignition Polarity

Posted: Wed Feb 11, 2015 6:36 am
by tornitore45
Golfpin I am an electrical engineer, worked mostly in, low power, power supply design for the electronic industry.
My original post show I have little knowledge of the automotive technology.
This thread has dig up some interest topics.

Re: Ignition Polarity

Posted: Thu Feb 12, 2015 7:34 pm
by ken572

Re: Ignition Polarity

Posted: Fri Feb 13, 2015 8:54 am
by golfpin
Thanks Mauro, mind you, a wasn,t bad guess on my part, thanks for putting up with some perhaps inane questions and answers.

Ken thank you for all those links etc went onto that Prestolite site and just drooled but with the US $ being at now nearly 12.5 to the Rand, used to be on par, and 99 % of stuff coming from China need I say more.
Thanks to all for the contact,
Cheers Golfpin

Re: Ignition Polarity

Posted: Sat Apr 08, 2017 8:32 pm
by Herb Kephart
Month old subject here, but I just joined and am reading a lot of things of interest to me at the site

What I used to hear, back when dragster people and the like were the only ones looking for that last little bit that they could get out of an engine, was that the center electrode of the plug, being red hot, it was easier for electrons to flow if the center electrode was positive, and the colder plug shell was negative. Had to do mostly due to the red hot condition (think of an old glass radio tube) than anything, Seriously doubt that a hit and miss engine plug center electrode ever gets there, unless it was working at 110%.

Herb Kephart

Re: Ignition Polarity

Posted: Mon Apr 10, 2017 1:02 am
by BigDumbDinosaur
Herb Kephart wrote:Month old subject here...
Month old? Actually several years old. :D
What I used to hear, back when dragster people and the like were the only ones looking for that last little bit that they could get out of an engine, was that the center electrode of the plug, being red hot, it was easier for electrons to flow if the center electrode was positive, and the colder plug shell was negative. Had to do mostly due to the red hot condition (think of an old glass radio tube) than anything,
It was a baseless assumption. Electron flow in a vacuum tube is due to thermionic emission. Thermionic emission occurs at relatively low temperatures and voltages, and is a phenomenon of black body radiation.

Electron flow across spark plug electrodes is caused by high voltage breakdown of the air charge in the cylinder. The result is an arc of extremely high temperature. The high voltage used in internal combustion ignition systems is necessary due to the cylinder pressure at the end of compression, which causes the breakdown voltage to be substantially elevated over what it would be at normal atmospheric pressure.

Re: Ignition Polarity

Posted: Mon Apr 10, 2017 6:55 am
by tornitore45
To recap what BigDumbDynosaur said
in Vacuum tubes electrons are "boiling" away from the filament "willingly" under the impulse of thermal agitations.
In Compression Chambers electrons must be extricated by means of high voltage against their bonding to the electrode metal.

Given that corrosion always happens at the positive terminal, this seems the motivation to choose negative polarity at the plugs.

On the other hand, corrosion is not an issue in automotive power distribution since small wires are never used.
Corrosion is an issue for buried conductors (and Pipes) aggravated by the existence of ground currents, hence the practice of biasing them negative. Same for the old Telephone Central Offices using small wires and designed to last 50 years.