Reversed Battery Polarity

[b:0f7236b2c5]{unnecessary but amusing preamble}[/b:0f7236b2c5] This all started when the steering on my TO20 locked up. Following some good advice gained here, I jacked up the front end and determined that the problem was not in the front end. So I disassembled the steering housing, which required disassembling a lot of other stuff.

Unfortunately the steering wheel itself was frozen tight to the shaft, and I didn't have a gear puller that fit. So I cut the thing off! And ordered a new one. I found a rusted and locked upper steering shaft bearing, so I ordered the steering bearing kit. With all that replaced, the steering worked beautifully.

Unfortunately, though, while I was testing the steering, I noticed that the right front wheel was turning badly. So I disassembled that and found yet another rusted-out bearing. I ordered the bearing replacement kit. Meanwhile, I tried to remove the old bearing races from the axle. I sprinkled WD-40 like holy water. I finally got them off with a new gear puller I purchase just for this task. Even then, I had to grind special slots in the gear puller so that it could fit into the tight space.

But I could not remove the old bearing races inside the hub. There are slots for using a screwdriver to pound them out, but I didn't want to risk damaging something I might never get out. So I just cleaned them and left them in place -- they were in good shape.

After packing the whole thing with handfuls of grease, I got it all assembled and spinning beautifully.

So I fired up the engine -- but it wouldn't start. It cranked just fine, but no spark. Lots of testing with a meter accomplished nothing. But somehow, after all the fiddling around, it started! Problem solved! Not quite. It turns out that somewhere in the system is an intermittent connection. The wiring is definitely original equipment -- some of the wires had cloth insulation!

Removing the wiring harness was easy right up to the point where I reached the voltage regulator. The wires are secured with screws that face the rear of the engine, with maybe two inches of space. Do you have any 2" screwdrivers? I don't. So I had to remove the entire voltage regulator, which was made difficult by the blockage from the oil filter and the choke and throttle lines. But I somehow got it out. And that's when I figured out that there were two major problems with the electrical system.
[b:0f7236b2c5]{end of unnecessary but amusing preamble}[/b:0f7236b2c5]

First, the polarity on my TO20 is reversed. It is specified as positive ground, but my TO20 definitely has a negative ground. Now, this should not be a big deal because all the electrical equipment works with current flowing in either direction -- except for the generator, but that's easily solved by simply reversing its connections. And in fact the tractor has worked fine for years. This leads to my first question:

[b:0f7236b2c5]Is there any good reason why the TO20 must have a positive ground?[/b:0f7236b2c5]

I also discovered that the voltage regulator was dead and that its output had simply been disconnected. No wonder battery life seemed short on this tractor. I'm ordering a new voltage regulator, but I really need to get this tractor running, so I am tempted to just bypass the voltage regulator for now. In a week or two, I'll be able to replace it. So my second question is:
[b:0f7236b2c5]
Are there any hidden gotchas to running without the voltage regulator for a week or two, other than slightly reducing battery life?[/b:0f7236b2c5]

Thanks for any help.
 
#1 WD40 is a poor at best lube for freeing things up. WD stands for water displacement and the 40 is the number of formulas they tried before they got it right.

As for no voltage regulator well if the generator is not hooked up it will run on the battery and run just fine till the battery is discharged enough not to give it spark but will work just fine for days weeks or years as long as you keep the battery charged up. My 841S Ford had a bad charging system on it for years till the bearing went out and I had to replace the alternator. I just charged the battery when it was to low to start it
 
#1 WD40 is a poor at best lube for freeing things up. WD stands for water displacement and the 40 is the number of formulas they tried before they got it right.

#2 As for no voltage regulator well if the generator is not hooked up it will run on the battery and run just fine till the battery is discharged enough not to give it spark but will work just fine for days weeks or years as long as you keep the battery charged up. My 841S Ford had a bad charging system on it for years till the bearing went out and I had to replace the alternator. I just charged the battery when it was to low to start it
 
OK, thanks. It's back to Liquid Wrench. For some reason I had always thought of WD-40 as a replacement for Liquid Wrench, so thanks for setting me straight.

I've decided to go ahead with the rewiring without the new voltage regulator. I'll keep the generator out of the system and just recharge every day.

Thanks much!
 
My self I do not use WD40 or Liquid wrench or even PB Blaster I use ATF in a pumper oil can and it does as good if not a better job then any thing else at half the price
 
1) A Generator can work at EITHER polarity if its Polarized correctly.

2) Many Voltage Regulators are designed for use EITHER at POS or NEG ground so you want one to match your tractor ground.

3) If you by pass the VR altogether by dead grounding the Gennys FLD post (NOT wire to FLD on VR) that calls for MAX charge which may overcharge your battery eventually but can charge the battery in the meantime. Keep an eye on electrolyte level to avoid it going too low.

John T
 
I'm assuming his is still 6 volt, and you intend to keep it original.

For a 6 volt system to work, everything needs to be right. A good battery, large, size 0 or bigger cables, healthy starter, tuned engine, and a well functioning charging system.

You can get by running it without a charging system. Just charge the battery well between uses. I would not bypass the regulator. That could overheat the generator and over charge the battery, and run the battery down when stopped.

Sounds like a complete rewire will be in order. The wiring is so simple on those, just as well build it your self.

You said something about reversing the wiring on the generator? That is not correct. The wiring stays the same, just be sure to polarize the generator before starting it with the new regulator.

The only other thing that needs to be checked is the coil polarity. With a positive ground system, the + terminal goes to the distributor, the - terminal to the ignition switch.
 
Yes, I am going to retain the 6V system, and yes, I am simply rewiring everything. At the very least, I can replace all that cracked electrical tape with shrink wrap tubing.

I will also return it to a positive ground, as it should be. I looked up how to polarize the generator in a post made here 13 years ago. Seems easy enough, but I'd like to take the time to understand what's going on before I do it. In all honesty, I cannot understand why ground polarity should make any difference. I'll be reading up on it.

Thanks for the help.
 
Oh, one other thing: why should coil polarity matter? So long as current flows through the coil to the points and then to ground, it really shouldn't matter which way it's flowing. Have I misunderstood something important?
 
Coil polarity matters, not because of the coil but because of the spark plugs.

Plugs are most efficient when they "spit" the spark from center electrode to ground tab, rather than if they "suck" the spark from the ground tab to center electrode.

When coil post (+ or -) to side of distributor and to ground through the points matches the grounded post of the battery, the output polarity of the coil will cause the plug to "spit" the spark. Coil post reversed from battery polarity will cause plug to "suck" the spark.

The coil doesn't care.

The engine will run either way but is theoretically more efficient if wired with proper polarity.

Other than being original, there is nothing sacred about it being positive ground. If properly configured it will work equally well either ground polarity.
 
Ah, yes, I never thought of the spark process at the microscopic level. Yes, of course it will be easier if the electrons are coming out of the carbon tip instead of the metal tab.

Thanks for pointing that out. I have already started building the wiring harness, using black wires for negative and red wires for positive -- which IS ground. Maybe that's why the tractor was painted red in the first place. ????
 
Ah, yes, I never thought of the spark process at the microscopic level. Yes, of course it will be easier if the electrons are coming out of the carbon tip instead of the metal tab.

Thanks for pointing that out. I have already started building the wiring harness, using black wires for negative and red wires for positive -- which IS ground. Maybe that's why the tractor was painted red in the first place. ;-)
 
The way the coil is hooked up matter because if it is hooked up backwards the spark jumps backwards and it is not as strong as it is if it jumps the correct way
 
However YES coil polarity does matter. If its NEG ground the coils - wires to distributor but if its POS ground the coils + wires to distributor. It will still run reversed but its more efficient of correct.

John T
 
(quoted from post at 20:07:54 05/28/17) Ah, yes, I never thought of the spark process at the microscopic level. Yes, of course it will be easier if the electrons are coming out of the carbon tip instead of the metal tab.

Thanks for pointing that out. I have already started building the wiring harness, using black wires for negative and red wires for positive -- which IS ground. Maybe that's why the tractor was painted red in the first place. ????
t is not carbon. The reason is temperature.....electrons leave a hot metal electrode better than a cold one, but neither you or your engine will ever now the difference! Some engines have some cylinders firing + and others firing -.
 
(quoted from post at 17:32:55 05/28/17) However YES coil polarity does matter. If its NEG ground the coils - wires to distributor but if its POS ground the coils + wires to distributor. It will still run reversed but its more efficient of correct.

John T

Wow, I don't understand that at all. As I understand it, the coil is just a big transformer. A pulse of 6V DC current runs through it and it generates two pulses of high voltage current -- a positive spike at the beginning of the pulse and a negative spike at the end of the pulse.

This leads to even more confusion for me. If it is generating both a positive spike and a negative spike, then the polarity shouldn't matter at all, should it? Unless perhaps the first spike needs to ionize the fuel-air mixture around the spark plug so that the second pulse can ignite it.

Even more confusion: timing is set by the OPENING of the points, which stops the pulse, which causes a positive spike...

I need to take some time to think this over.
 
It should make no difference on a cold start when the sparkplug electrodes are the same temperature, but may make a bit of difference when the engine is warm and pulling a load. The spark will jump easier when it jumps from the warmer center sparkplug electrode to the cooler side electrode.
Many two cylinder lawn mower engines fire both plugs from a single ignition coil, one plug connect to each end of the coil secondary winding , one plug firing from side electrode to center, and the other firing from center electrode to side. Works fine as long as the spark is healthy.
 
A coil uses DC voltage which cannot be transformed. Only AC voltage can be transformed to say a higher or lower voltage. A coil is just a device that with DC voltage amplifier's voltage to make a spark that is hot enough to ignite gas.
 
Let me tell you about Kettering ignition coils.

YES they function as a HV step up "transformer" (actually they are wound as an autotransformer) with the HV Secondary having many many more turns/windings then the LV Primary which is how 12 volts gets stepped up to several thousand.

With points closed the LV primary conducts current and creates a magnetic field around the LV and HV windings.

NOTE THERES NO TRANSFORMER ACTION (to step up or down voltage) IF STRAIGHT UNINTERRUPTED PURE DC IS APPLED TO A TRANSFORMER HOWEVER the points opening and closing creating 12 volts then zero acts similar to an AC input which is plus then minus. That creates an expanding then collapsing magnetic field same as applying AC would which is why it still acts as an AC Step Up Transformer even with DC applied (but interrupted by points opening) GET IT?????????

THEREFORE when the points open the magnetic field collapses (similar to how the magnetic field would act if AC was applied) and the collapsing field induces a higher voltage into the many many more turn winding of the HV secondary EVEN THOUGH DC IS APPLIED TO COILS INPUT

The HV rises at the spark plug gap and eventually arc jumps current across it in one direction of current flow.

Its easier to emit electrons off a hotter (plugs electrode tip) to a cooler (plugs ground strap) surface which is why theres a heater under the cathode in a vacuum tube WHICH IS WHY COIL POLARITY MATTERS

DISCLAIMER its IMPOSSIBLE to put in a few sentences what takes books to explain so this is just an example and NOT 100% correct so don't anyone have a calf I'm just trying to help

John T Long retired Electrical Engineer and rusty as an old nail but believe this to still be correct
 
Thanks for the many comments. Between those and some careful reconsideration, I now understand the process. I now understand the point that you fellows were making that the spark is stronger coming from the hotter surface of the core.

I also realize that the twin-spike problem that bothered me so much is resolved by noting that the second spike -- when the points close again -- is not significant because it hits when the gas-air mixture has already ignited and the piston is already on its way down.

So it's back to work getting this tractor back to a positive ground!
 
Hey you're getting there Ferguson Man, good job, but here's more info for you

The coil DOES NOT FIRE HIGH VOLTAGE WHEN THE POINTS CLOSE, ONLYYYYYYY WHEN THEY OPEN. When the points break open the coil operates off stored energy which dissipates once the plug fires, and with no more energy being inserted (points are open no more current flow) there's no more energy to fire the plug a second time. Some tractors and machinery ignition systems utilize what's called a lost or wasted spark that fires a plug on TDC of the Exhaust stroke in addition to Power/Compression, but that's NOT what my first sentence refers to.

My late friend Duane Larson who was a Nuclear Physicist conducted an experiment on coil polarity and found if it was reverse wired voltage had to rise a few thousand volts HIGHER before the plug fired. That's a less efficient method ALTHOUH REMEMBER many Magneto ignition systems have to fire at BOTH POS and NEG but still do a good job !!!!!!!!!

Hope this helps

John T Retired Electrical Engineer
 
Dammit, I have a master's degree in physics, but I am struggling to figure out exactly what happens here -- and this is second-year physics! That was a long time ago...

When the points close, the high impedance of the coil retards the rapid increases in current, because the coil is building up a magnetic field -- the same one that drives the spark when it later collapses. This changing magnetic field imparts a voltage in the secondary coil. The one thing I am certain of is that voltage = dM/dt, where M is the strength of the magnetic field and t is the time.

So the two spikes coming out of the secondary coil should be equal but opposite in sign.

I can also testify that I have gotten myself zapped from coils on both sides: initiating the pulse or terminating it.
 
Gee, I suppose that we could settle this once and for all by holding on to the coil's output line while manually rotating the crankshaft -- but having been zapped hard by automobile coils before, I don't have the courage to try. Does anybody want to sacrifice themselves for tractor science?
 
What sacrifice it is simple to watch a spark and which way it goes wit ha spark plug or even the end of the plug wire.
 
NOT me lol I hate being shocked. I'm like Old I would use a spark plug or just an air gap to check for fire.

I wasn't aware of anything remained that needed settled?????????????? You have received good info below, but ask away if you still have questions we are glad to help.

Best wishes and God Bless

John T
 
It remains true the plug fires WHEN THE POINTS BREAK OPEN NOTTTTTTTTTTTTT WHEN THEY CLOSE. If you Google Kettering Ignition you will find a gazillion hits explaining it all and I cant explain in a paragraph here what takes books and volumes to describe. But hey I'm never too old to learn lol so if you find any info that says the coil fires when the points close PLEASE SHARE IT SO WE CAN ALL LEARN. I'm an Electrical Engineer and been here since the nineties and your the first to indicate the coil fires when the points CLOSE.

PLEASE help the rest of us if you find info to that regard I would sincerely appreciate it as I've been wrong before and maybe again after 50 years of thinking the coil fired when the points open NOT when they close GEEEEE WAS I WRONG ALL THIS TIME !!!!!!!!!

Thanks and God Bless so please help us all out, were eager to learn if we had it wrong all these years lol I will be the first to eat crow and humble pie yukkkkkk lol

Is there anyone else here who says the coil fires when the points close instead of open ????????????????

Help me out here guys, have I been wrong for fifty years grrrrrrrrrr my bad if so

PS of course if the points close but then AFTERWARDS there's even a brief current disconnection HV can appear on the coil and you could feel it BUT THATS BECAUSE THEY WERE CLOSED THEN REOPENED IE THE COIL STILL FIRES UPON REOPENING NOT CLOSING !!

Nice chatting with you Ferguson Man, please cite me some research and hard core data if you find I was wrong

John T, BSEE, JD
 
I'm not saying that the spark fires ONLY when the points close -- I'm saying that it fires BOTH when the points open AND when the points close.

But you're right -- one good experiment is worth a million speculations by an old geezer like me, so I'll go out and try it with the spark plug. I'll report back here.
 
"PS of course if the points close but then AFTERWARDS there's even a brief current disconnection HV can appear on the coil and you could feel it BUT THATS BECAUSE THEY WERE CLOSED THEN REOPENED IE THE COIL STILL FIRES UPON REOPENING NOT CLOSING !! " That John will be the reason he will report back that it shocked him when points closed........because he can't make or find that "perfect switch" that has no switch bounce. It also (due to time of coil charge) will very likely be enough to shock a human, but not enough to fire a plug.
 
Only time a coil fires is when the points are opening but never when the point close
 
I couldn't manually turn the crankshaft using the fan because the fan belt is too loose and I needed one hand to hold the test spark plug in place. I'll drag my ancient oscilloscope out there and see what it says.
 
Thanks JMOR, yep perhaps a solid state electronic ignition might reduce the chances of less then perfect switching???

Regardless, as you well know, even if there's point bounce, its still when the points REOPEN the coil fires NOT when they close.

Oh well I tried my best to help

John T
 
AMEN RICH, seems you and I "usually" agree but NOT always. No one is perfect including meeeeee for darn sure. If were wrong then all the engineers and designers and technicians and auto makers and books and designer Kettering for like a hundred years all got it wrong also, ya reckon?????????

John T
 
OK, I've figured it out. First, the experimental results confirm exactly what you guys have been saying all along: no spark on making contact, yes spark on breaking contact.

I was insisting that Faraday's Law has not been repealed -- so, what gives? The trick is that I forgot about that capacitor. Yes, its primary function is to prevent arcing across the points, but it ALSO has the effect of absorbing the initial onrush of current when the points make contact. That slows down the rate of change in the flux, which reduces the voltage output of the secondary coil.

In other words, the DC pulse going through primary coil is NOT a simple rectangular pulse with instantaneous step up at the beginning of the pulse and instantaneous step down at the end of the pulse. Instead, it has asymptotic curves at each end, but the two curves are NOT mirror images of each other, so we don't get symmetric output. The rising pulse is concave up but the falling pulse is concave down.

Ta-da! I have theoretically proven what all of you knew long ago! Isn't physics just peachy-keen?

And thanks for all the help. It's been fun. But now, believe it or not, the internal starter switch is misbehaving. Here we go again...
 
(quoted from post at 16:39:17 05/29/17) OK, I've figured it out. First, the experimental results confirm exactly what you guys have been saying all along: no spark on making contact, yes spark on breaking contact.

I was insisting that Faraday's Law has not been repealed -- so, what gives? The trick is that I forgot about that capacitor. Yes, its primary function is to prevent arcing across the points, but it ALSO has the effect of absorbing the initial onrush of current when the points make contact. That slows down the rate of change in the flux, which reduces the voltage output of the secondary coil.

In other words, the DC pulse going through primary coil is NOT a simple rectangular pulse with instantaneous step up at the beginning of the pulse and instantaneous step down at the end of the pulse. Instead, it has asymptotic curves at each end, but the two curves are NOT mirror images of each other, so we don't get symmetric output. The rising pulse is concave up but the falling pulse is concave down.

Ta-da! I have theoretically proven what all of you knew long ago! Isn't physics just peachy-keen?

And thanks for all the help. It's been fun. But now, believe it or not, the internal starter switch is misbehaving. Here we go again...
hat?? "but it ALSO has the effect of absorbing the initial onrush of current when the points make contact." Just exactly how is that going to happen?, seeing as how the capacitor is shorted out by the closed points?

What causes the exponential current rise upon points closing is the L/R ratio. No C in circuit when points close.
 
Well i can say this for sure I have yet to get shocked when I close points but boy oh boy it sure does not feel good when you open the points
 
You have to remember a coil or transformer works different on DC then it does on AC so things do different things
 
Youre gonna get it Ferguson Man, HANG IN THERE

JMOR IS CORRECT

When the points are closed that creates a dead short across the condenser in parallel with it WELL DUH

HOWEVER when they first break OPEN THEN THERES THAT INRUSH (stored coil inductor energy) and it would create a small arc across the points and cause premature carbon and arcing and pitting BUT FOR the discharged condenser sitting there in parallel acting like a big empty electron bank just waiting to fill with electrons so it absorbs some of the energy and charges up. At time T = 0+ a condensor is (until it charges up) like a short circuit to DC but once charged it acts like an open no longer accepting electrons cuz its full.

Hope this helps

John T Retired Electrical Engineer
 
Youre gonna get it Ferguson Man, HANG IN THERE

JMOR IS CORRECT

When the points are closed that creates a dead short across the condenser in parallel with it WELL DUH

HOWEVER when they first break OPEN THEN THERES THAT INRUSH (stored coil inductor energy) and it would create a small arc across the points and cause premature carbon and arcing and pitting BUT FOR the discharged condenser sitting there in parallel acting like a big empty electron bank just waiting to fill with electrons so it absorbs some of the energy and charges up. At time T = 0+ a condensor is (until it charges up) like a short circuit to DC but once charged it acts like an open no longer accepting electrons cuz its full.

Hope this helps

John T Retired Electrical Engineer
 
(quoted from post at 14:56:50 05/29/17)
What?? "but it ALSO has the effect of absorbing the initial onrush of current when the points make contact." Just exactly how is that going to happen?, seeing as how the capacitor is shorted out by the closed points?

What causes the exponential current rise upon points closing is the L/R ratio. No C in circuit when points close.

OK, I sat down with pencil and paper, drawing the circuit diagram, and managed only to come up with screwy results.

There's clearly a problem here: Faraday's Law says that the EMF is proportional to the rate of change of the magnetic flux. It applies regardless of whether the rate of change is positive or negative. So we should expect that the spark on closing the points should be identical -- but of reversed polarity -- to the spark when the points open.

The only thing violating the symmetry of the situation is the capacitor.

Let's work backwards. We KNOW that the spark on closing the points is much less than the spark when opening the points. Why does that happen? Why aren't the two sparks equal and opposite in polarity?
 
(quoted from post at 19:10:02 05/29/17)
(quoted from post at 14:56:50 05/29/17)
What?? "but it ALSO has the effect of absorbing the initial onrush of current when the points make contact." Just exactly how is that going to happen?, seeing as how the capacitor is shorted out by the closed points?

What causes the exponential current rise upon points closing is the L/R ratio. No C in circuit when points close.

OK, I sat down with pencil and paper, drawing the circuit diagram, and managed only to come up with screwy results.

There's clearly a problem here: Faraday's Law says that the EMF is proportional to the rate of change of the magnetic flux. It applies regardless of whether the rate of change is positive or negative. So we should expect that the spark on closing the points should be identical -- but of reversed polarity -- to the spark when the points open.

The only thing violating the symmetry of the situation is the capacitor.

Let's work backwards. We KNOW that the spark on closing the points is much less than the spark when opening the points. Why does that happen? Why aren't the two sparks equal and opposite in polarity?
ecause the rate of change on closing & opening is NOT the same. Relatively slow on closing, for the reason that I have already explained, the L/R ratio. Rather instantaneous upon opening, as the R is momentarily absent.
 
Wow Ferguson Man you're really getting into this lol Now that I have you convinced the coil fires ONLY when the points OPEN NOT when they CLOSE, lets move on to the small sparkys that happen across the points when they OPEN and when they CLOSE.

When the points are closed the condensor is discharged and a short circuit exists across the condenser.........When the points open the stored coil energy arc jumps some current across the points (little sparky 1 direction 1) and the rest of the energy goes into charging up the condenser.........When the points reclose the condensors stored energy arc jumps some current (little sparky 2 reverse direction 2) across them in order to discharges the condenser.

IFFFFFFFFFFF the condenser capacitance is properly matched to the coils inductance (matched LC Circuit) the current and sparky 1 is the same as the current and sparky 2 BUT IN THE OPPOSITE DIRECTION.......

IFFFFFFFFFFFFF the condenser is sized to match the coil the points will wear the same on both surfaces with no mound build up on one side and no pit on the opposite side. If the condenser isn't matched properly the points will develop a mound on one side and pit on the other.

BUT DONT TAKE JUST MY WORD FOR IT heres a copy taken form a Delco Remy Instruction book PLUS a picture that describes the same

Ignition system condensers vary in capacitance from about .15 mfd to about .35 mfd, depending upon application.
They can be tested for value with a cap checker.

Some parts catalogs list values vs. part numbers/applications, and if you have a service manual for a specific application it MAY give the cap value required.

If the wrong value is used for a given application, moveable or stationary breaker point pitting MAY occur.

"Contact pitting results from an out of balance condition in the system which causes the transfer of tungsten from one point to the other so that a tip builds up on one point and a pit on the other. The direction in which the tungsten is transferred gives an indication for correcting the situation. If the tungsten transfers from the negative to the positive point increase the capacity of the condenser, If the transfer is from the positive to negative point, reduce condenser capacity."

This information was taken from a Delco Remy electrical equipment book.


Sooooooooo hope you understand it now, at least this is how Delco Remy explains it and I happen to agree.

John T BSEE, JD Retired Electrical Engineer
a161350.jpg
 
You ask "Why aren't the two sparks equal and opposite in polarity?"

ANSWER IS THEY ARE ifffffffff the condensor is sized to match the coil, see my post above with Delco Remy literature and picture to prove it, IE dont take my word for it, see what Delco Remy says and I happen to agree with them

I'm talking about the little sparky across the points now remember. It remains true the COIL ONLY fires when points OPEN not when they CLOSE

John T
 
My problem isn't believing you, it's understanding why you're right. But you did explain a detail that I have long wondered about: how do they figure the ideal capacitance for the capacitor? Your answer makes perfect sense to me.

I am still struggling to understand the asymmetry between the two events. First, at one point you seemed to be saying the the electrical characteristics of closing contact are different from those of opening contact. That one flew right over my head. The best I can figure is that opening contact is hard-driven by the cam, whereas the closing contact is soft-driven by a spring and therefore permits the possibility of contact bounce. But if that were the case, then why wouldn't we get a spark identical to the contact-breaking spark? Is it because there isn't enough time to build up enough energy in the coil?

Or perhaps the closing process is simply not as fast as the opening process. The opening is driven by a cam -- no variability there. But the closing might be slower than the opening because the spring isn't strong enough to push the point closed quickly. This would be similar to valve float in an engine that is running too fast.

I have been poring over web pages explaining transformers and coils, going through the equations (oh, my aching head!) and trying to understand why there's an asymmetry. A purely theoretical approach just doesn't answer the problem. I keep coming back to the electrical characteristics of the points opening and closing, or perhaps the capacitor.
 
(quoted from post at 22:47:06 05/29/17) My problem isn't believing you, it's understanding why you're right. But you did explain a detail that I have long wondered about: how do they figure the ideal capacitance for the capacitor? Your answer makes perfect sense to me.

I am still struggling to understand the asymmetry between the two events. First, at one point you seemed to be saying the the electrical characteristics of closing contact are different from those of opening contact. That one flew right over my head. The best I can figure is that opening contact is hard-driven by the cam, whereas the closing contact is soft-driven by a spring and therefore permits the possibility of contact bounce. But if that were the case, then why wouldn't we get a spark identical to the contact-breaking spark? Is it because there isn't enough time to build up enough energy in the coil?

Or perhaps the closing process is simply not as fast as the opening process. The opening is driven by a cam -- no variability there. But the closing might be slower than the opening because the spring isn't strong enough to push the point closed quickly. This would be similar to valve float in an engine that is running too fast.

I have been poring over web pages explaining transformers and coils, going through the equations (oh, my aching head!) and trying to understand why there's an asymmetry. A purely theoretical approach just doesn't answer the problem. I keep coming back to the electrical characteristics of the points opening and closing, or perhaps the capacitor.
e -read what I already said. Still valid.
 
It really has nothing to do with how the points open or close, it's due to the fact that the magnetic field in the coil is slow to build, but very fast to collapse. Just the nature of the beast.
 
Think about it, how the speed that the magnetic field cuts across the coil windings determines the voltage.
That's why the 6 or 12V going into the coil to build that field, creates as much as a 300 volt spike in the primary winding when it collapses.
 
Good Ferguson man, you're just gonna have to do some in depth research and study up on this. No one here including me can explain in a paragraph what takes books and volumes and a lot of study to understand, it just cant be done on here what may take people months or years to fully comprehend.

Hope you find your answers, it should be a fun and rewarding experience but its getting to be a bit much to cover on here, were boring the non electrical people to tears lol but hey we try to help the best we can.

God Bless and guide you in your search

John T
 
When the points close, the expanding field is cut by the windings and that produces a current that is opposite the input from the battery. That is why it takes longer & won't show much in the secondary. When the points open the collapse is at the speed of light. Or close to it as it produces many sparks that we see as one.
 
(quoted from post at 21:49:21 05/29/17) It really has nothing to do with how the points open or close, it's due to the fact that the magnetic field in the coil is slow to build, but very fast to collapse. Just the nature of the beast.

Why in the world would the magnetic field take longer to build than to collapse? What is the underlying physics of that?
 
(quoted from post at 04:52:07 05/30/17) Good Ferguson man, you're just gonna have to do some in depth research and study up on this.

Yes, I am definitely having problems getting this into my thick skull. There's no question that there is asymmetry in the phenomenon, but I will have to do more work to figure it out.

Who knew that tractors could be one of the mysteries of the universe?
 
(quoted from post at 11:29:43 05/30/17)
(quoted from post at 21:49:21 05/29/17) It really has nothing to do with how the points open or close, it's due to the fact that the magnetic field in the coil is slow to build, but very fast to collapse. Just the nature of the beast.

Why in the world would the magnetic field take longer to build than to collapse? What is the underlying physics of that?
To repeat myself, "Because the rate of change on closing & opening is NOT the same. Relatively slow on closing, for the reason that I have already explained, the L/R ratio. Rather instantaneous upon opening, as the R is momentarily absent."
i.e., the circuits are different with points closed vs points open.
Primary wave forms:

Top trace is coil primary voltage. Far left is at points opening & voltage rising to initiate the arc (ringing).
Most of the first division is duration of arc (arc sustains at lower voltage than it takes to initialize it, as once established the hot plasma is a much lower resistance for the current to flow thru than the air was at the start). Additionally, before arc established, there was zero primary current & once established, the arc current flows in the coil secondary & some voltage drop occurs in the copper of secondary winding as result of arc current).
Next ringing is at end of arc. At this point enough of the energy stored in the coil has been dumped into the arc's hot plasma that there is no longer enough remaining to sustain the arc & the arc ceases & the remaining energy is dissipated ringing back and forth between the coil & condenser until it is all turned into heat.
The next ~5 divisions show a flat, zero volt trace of dead time where points are open. All concerned take a break, pop a tab on a cool one.
Next you see a sharp rise to 12 volts as points close. At this point in the lower trace you see the current start to rise in the primary, the rate of rise, determined by the L/R time constant of the coil inductance/resistance of the circuit, toward it's final 4 amp value. During this time (dwell time), the coil primary voltage started at 12v, but as it's current increases (the energy being stored in it's magnetic field), that 12v decreased. The voltage ultimately across the coil after it is fully charges or is saturated, becomes only the voltage drop of the copper windings in the primary, in this case 6 volts at 4 amperes. This is a 6/4=1.5 ohm coil.
Next is a repeat. Points again open, next spark begins.
 
Thanks so much for that scope trace and the explanation. I now see that one mistake I was making was to think of the coil as a transformer under continuous operation. That is, I was modelling the system as identical to how a transformer with a resistive load would handle a square wave input.

Galileo once said, "You can see the workings of the entire universe in a glass of wine." And tractors, too.
 
You state that your tractor is set up negative ground. Before you get too carried away with voltage regulators and polarization, are you sure the generator has not been replaced by an alternator? Do you know the difference? Can you take a picture? What size is your battery?
 

No, I didn't know the difference, but I just looked it up. Once again, even with a master's degree in physics, the operational difference evades me. So it looks as if I have more reading to do.

By the way, I got the system up and running. The generator -- or whatever it is -- is definitely recharging the battery. I've got all new wiring in place, but I made some of the wires too long (always better to err too long than too short), so I'm going to replace some of the wires. Also, I got a bunch of 10-gauge wire with different color insulation, so I'll replace a wire or two for better color differentiation.

I found a nice explanation on this site of generator issues. I was able to determine that my device is a 3-pole device, and from that I was also able to figure out which terminal was "A" and which terminal was "F".

I realize that all the information I needed was somewhere on this site, but sometimes it's difficult coming up with the right search phrase to find it.

Now all I have to do is figure out where the last remaining loose nuts and bolts go... ;-)
 

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