I was just trying to understand. Secondary ignition voltage to the plugs on a standard distributor system is negative voltage. I checked for polarity with engine idling, put the DMM + [red] lead to the plug, just below the boot. Negative lead to the negative battery post. The voltage read a little under a volt and had the minus sign. Switch the leads and the minus sign was gone.
So the spark jumps from the plug ground terminal to the plug center terminal? And we're talking conventional flow theory?
So the voltage goes from the secondary coil, through the engine block, from ground electrode to center electrode of plug, through the plug and coil wires, back to the secondary coil? If the voltage jumps from the ground electrode to the center electrode of the plug, where does the voltage come from?
I have read the tutorials on how a transformer and ac voltage works. Negative voltage just gives me a hard time.
I have talked about this subject on other sites. I guess I just kept asking questions until the people got tired of answering. Thought I would try here. thanks
No, on a standard type single-coil with distributor system, the secondary voltage is POSITIVE relative to the block (if the coil is connected properly.
I checked
You can't read 75,000 volts with a DMM. You're lucky if you didn't blow the internals of your DMM out trying to do that, and anything it actually showed on the screen was utter meaningless garbage.
The electrons jump that way. The convention is that current flow is from positive to negative, but this was determined before it was discovered that the particles that actually flow are negatively charged- so in reality electrons always move in the opposite direction to current. So in a conventional system, current flows from the coil, through the distributor, to the center electrode of the plug, across the gap, and to the block... but ELECTRONS jump from the side electrode to the center electrode, back up the wire, and into the coil and then into the block through the coil housing.
However, when a spark occurs between two metal electrodes, not ONLY electrons move. Some metal atoms vaporize and move as well, and they move in the direction of current- opposite to the direction of the electrons. That's why the center electrode of spark plugs (on a conventional single coil system) wears away, and why "waste spark" systems that fire two plugs with one coil erode the center electrode on one spark plug and the side electrode on the other.
Negative voltage just means that the current flows the other direction. Nothing to it. But you're initial assumption about the secondary voltage being negative is incorrect.
*********This is something that has caused confusion for years. Conventional current is defined as flow of positive charge, not flow of electrons, just as you say. Mathematically, it makes no difference what you view as flowing, as long as you keep your conventions straight.
In the old Kettering systems (coil, points, etc) it was possible to get things hooked up backward and the pulse would flow in the reverse direction. It was supposed to be detectable by poorer performance, but I'm not quite sure why that was true, unless it had to do with the configuration of the electrodes at the spark gap and the likelihood that the spark can propagate easier in one direction than the other.
As I remember it, the Kettering systems were not purely a single pulse but there was a ringing or oscillating component. It doesn't make much difference, I guess, as the most of the energy was dissipated in the spark of the first pulse crest, and the ringing currents probably died pretty quickly after that.
An automotive ignition coil is an autotransformer (primary and secondary are actually sections of the same winding), and the ground for both the primary and secondary occurs a the "-" terminal on the primary side. If you reverse the primary terminals, the ground point is now in the center of the winding and things get silly. Peak magnitude voltage at the tower (spark plug connection) is reduced, and excess voltage spikes appear across the breaker points causing them to burn up faster.
That doesn't matter, or "waste spark" systems that drive one plug positive and its partner negative wouldn't work.
Modern electronically-triggered and capacitive-discharge systems "ring" too. Most of the energy is in the first half cycle, but you're right. Further proof that polarity matters relatively little as far as the spark plug itself is concerned.
No, it wouldn't make a bit of difference. GM's distributorless ignition uses 3 coils, one for each pair cylinders, 1-4, 2-5, 3-6. Current flows from the coil to plug #one, through the engine to plug #3 and back to the coil for a complete circuit.
I replied to you in another forum, I think. In the future, instead of wandering all over the place, asking a question or 2 here and a couple of more there, stick with one place. If you don't understand something ask for a clarification. Please. I am more than willing to help, but with only a partial idea of what is being asked, and not a lot of idea of your level of expertise, it is hard to tell when you are confused. You need to let the person trying to help you. Now, you do not read spark plug voltage with your DMM. Your DMM is only good to 600 volts, if it is an expensive one. Cheaper ones aren't as well protected. You run the danger of destroying it. And the meter will not be able to read that high of voltage anyway. We are talking about
40,000 to 60,000 volts. That is correct, 40 thousand to 60 thousand volts. At the spark plugs.
Now, your confusion comes in because you heard somewhere that the plugs had negative voltage in relation to the rest of the car. I attempted to explain how a coil worked and why it would appear that the voltage would be negative. Before I get into a discussion of why that happens let me describe something to you, since the whole point of confusion arose from my comment about DMM's being designed to read both positive and negative voltage. Take a good sized battey, a lantern battery will work just fine. Then take 2 high ohm, high wattage resistors. Connect one lead of each resistor to a terminal, one negative and one positive. Now connect a the remaing two leads together, and connect that to ground. Now read from the positive terminal to ground, you will get half the voltage of the battery. Leave the same probe on ground and read to the other terminal, you will get the other half, except it will read negative. That is what I was talking about. That kind of circuitry is used in electronics all the time. Being able to keep the black probe connected to the common all the time while reading voltages means that you can tell exactly what you are reading without confusion. Is that clearer now? If not, or if you are curious, go to radio shack and buy the pieces and do it your self.
It comes from the coil. It is best to forget about ground at this point. And it helps to just figure that the voltage and current is flowing from the coil to the plug, jumping to the ground.
Often times, it is easier to learn by experimenting.
I never saw any follow up questions. this is a fine place for the discussion, please keep it here and keep asking questions.
I believe I stated in my post, that I was checking polarity not voltage with the DMM. The highest dc volt setting on my low end meter is 1K volts. Still way too low for secondary ignition voltage.
My level of experience is novice. On the other sites, everybody said secondary ignition voltage was negative voltage.
I saw an article in an old Peterson basic ignition manual, it said, it takes less voltage to fire a plug negatively than it does to fire a plug positively. It also said you can check for polarity using a DMM. Positive lead to ground, negative lead to plug with engine idling, should give upscale reading, to me that means no minus sign. That is exactly what my meter showed.
The article on the transformer said, the flow in the secondary circuit is opposite to the flow in the primary circuit.
Anytime my meter shows a minus sign, that tells me the flow is opposite to how I have the leads hook-up. I guess I could be missreading.
I know I'm confused on this subject, but, at least four people on the other sites, told me that secondary ignition voltage was negative voltage, if that isn't right, I guess I'm not the only one confused.
As far as posting on other sites, I find it helpful to get as many opinions as I can. I always try to reply to every post and thank the people for talking to me. thanks
It's not "negative voltage." The high-tension secondaries of many ignition systems were GROUNDED differently than the primaries, for exactly the reason you state: less energy required to cross the gap. On electrical systems with the negative battery terminal grounded, the secondary ignition was positive ground. It mattered more years ago, with breaker point igntion systems, because they were relatively weaker at producing the high voltage required to fire the plug. Newer coils, capacitive discharge, etc. increased the voltage capacity. When I was a kid, it took something like 20 kV to fire a plug. Now, lean mixtures and much larger plug gaps can require something like three times that. In wasted-spark systems, with one discharge firing two plugs, the current flow is opposite in one plug compared to another.
Several hours later I correct myself. I meant to say Current flows from the coil to plug #1, through the engine to plug #4 back to the coil for a complete circuit.
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