Confused on coil

http://www.mgcarclub.com/cny/electrical_systems.htm

Forgive us for our debate. We should have just answered your question. Now what was it again?

Paul R

What I need to confirm in my own mind, is this: I know that electrons flow from - to +, hence in a positive ground system, it seems to me that electrons build up on the point (electrode) of a spark plug, and once then reach a high enough potential, will jump to the positively charged (grounded) tang.

If the above is true, what is the benefit to a negative ground system? Seems to me that would mean that the entire frame of the tractor is teaming with free electrons looking for a place to jump to given sufficient difference in potential.

In the same vein, which way does lightening strike? If the earth (ground) is negatively charged, lightening should strike UP, right? Or is it ionization in the clouds that create the free electrons that then build up the potential to jump DOWN?

Thanks

However, with a 50:1 winding ratio, I am skeptical as to whether you can see the difference on an ohmmeter. 2% of scale if windings are same diameter (and usually they are smaller on the secondary making this measurement even harder to see). Probably one reason why they are marked.

I too appologize for complicating what looked like a simple question. However, this isn't a simple question and debate like this adds to our understanding.

For the practical, there were several references to the idea that although one way is better, either will work. So, we can debate correctness while Mack fixes his tractor.

If the coil is marked with (bat) and (dis) you need to know the +/- polarity system used in the coil. If the battery ground polarity has been reversed to negative ground, because of converting from 6 to 12 volts, then hook up the coil backwards also.

An ignition scope will tell the tale at a glance- Reversed coil polarity will give an upside down scope display.

The bottom line is to have the coil high voltage 'boil' electrons from the spark plug center electrode to the ground electrode.

Inside the coil are two windings of wire, with a common ground. Nothing is polarity sensitive. A direction the electrons are flowing across the sparkplugs doesn't matter to the gasoline.

The reason to mark one plus and one minus is to make sure the common side gets grounded by the points. If the coil were installed backward, then the high voltage winding and the low voltage winding would be in series when the spark occurred and would lessen the spark voltage with extra resistance of the low voltage winding (only a little lessened).

Therefore, if what I said is right, then for the Ford example, the plus side of the coil should always be grounded, no matter how the battery is connected, since that is really an indication of the common connection of the two windings and not a request for battery polarity.

Is this right?

But to achieve the proper polarity at the spark plug you need the + and - to match the battery polarity.

Gerald J.

So the coil CASE must be completely isolated from the windings and does not have to be "grounded" in order to function?

The current cannot be induced in the secondary windings until the magnetic field produced on the 12 volt primary is switched on/off repeatedly by the opening/closing of the points. Hence I'm back to my thought that the primary winding is electrically isolated from the coil case and the two small posts on the coil are insulated. Further evidenced by the fact that a coil wired backwards will work, albeit not as well.

If it's the secondary winding that is electrically isolated through the points (which I doubt) that little wire from the points (in the distributor) to the coil would have to be as thick and heavily insulated as the one from the top of the coil to the distributor cap. I think not.

How 'bout it ltf, is it the secondary winding (high voltage) that is case grounded to the frame? Is the primary winding, in fact, electrically isolated from ground until the points close?

Inquiring minds want to know....;-) Gadget

Also, I'm not sure I buy all the concern about whether the spark jumps from the sparkplug electrode to ground or vice versa. Don't know if you can tell, and don't know if it matters, even if you can see it.

Sounds like one of them there left handed framus wrenches.

Gerald J.

Current (electrons) flows from negative to positive, right? So, if you change the ground from postive ground to negative, would it not also follow to reason that you must also reverse the polarity of the coil in order to get the current flow in the proper direction..."according to how Mr. Kettering designed the system".

Gerald J.

Gerald J.

Dave

Ford 12 volt tractors all had the original 6 volt coil used since side distributor 8Ns. Or maybe I should say all replacement coils are the same. The 12 volt tractors had a resistance wire to cut the voltage. That wire costs around $25 from NH.

That's a pretty generic description. I'm sure ltf or someone else can provide you with more specifics, i.e. just what the voltage produced actually is...

Your battery voltage enters on one post of the coil. When the points are closed (connecting to ground) the current flows through the low side of the coil to ground. This produces a magnetic field inside the coil. When the points open it disconnects this circuit. At this point the magnetic field begins to collapse. The battery voltage is still pushing (voltage is pressure) on both the high and low side. The collapsing magnetic field allows a current flow out the high side of the coil. Due to the ratio of windings the collasping magnetic field pushs enough out to jump the gap at the spark plug.

Simplistically, the coil uses low voltage (6, 12 etc) to create a strong magnetic field in a very small space. When the points open, or the transistor switches off, the field collapses. With the primary circuit open (points open or transistor off) the magnetic energy can only return as high voltage, in the higher turns ratio secondary winding. The energy comes back with real high pressure and little substance.

A transistor can do an absolute open primary circuit cut off. A contact points system needs a capacitor to "fool" the returning energy and give the points enough time to open, so the energy isn't dissipated back into the primary.

Over on the secondary side... Pull up a technical dissertation on "cold cathode emissions", then one one on "hot cathode emissions" (Elderly ham radio operators, please jump in here).

Anyway, at the spark plug it is a smiliar deal to striking an arc with a hot welding electrode- easy to make fire. The bottom line- high voltage electrons in the spark plug behave much like people, when you're in a hellishly hot place you jump to where it's cooler. Center electrode is hot and ground electrode is cooler.

If in doubt, simply reverse the coil primary connections and see how your machine runs under a load out near it's maximum design capability. A bunch of sputtering and misfiring with even a modest load can indicate reversed coil polarity.

The internal connections of the primary and secondary windings determine how it all comes out at the spark plug. And, that's where it counts. Jest have the plug wire as negative polarity and things work out OK.

The Brits and Lucas threw tons of mud in the water, as to "electron flow" vs. "positive charge flow". Re-read the last paragraph!

All sorts of wierd engine performance problems have been traced back to, and corrected by, simply reversing the coil primary connectons. Now, you all know damn well that the shop bill write up seldom told that it took the knowledgeable local guru tune up mechanic 5 minutes to figger it out and correct the problem.

A Sun Scope demo and an eveining in a Champion Spark Plug training session would prevent this long line of discussions. Sadly, them days are part of the past.

I'll do what I can with individual e-mail help discussion on this.

Watch the future... The Model T Ford's "low tension magneto" is about to (again, 90 years later) become a tremendous automotive science technical breakthru, in the next few years. No starter motor, no alternator, all solid state controlled with stuff on the flywheel.

Get ready for my questions while overhauling my Farmall 450 hydrastic control thingee. Hank