That's true, but you are saying it a little backwards. The less amperage draw at the coil will mean higher voltage after the resistor.
Things to remember about voltage and current... Voltage won't kill you... Static electricity from scuffing your feet across a carpet can hit 4000 volts really easily. Current is what will kill you. Ten amps of current through your body will make you very dead.
I didn't post anything in this thread to bust Dave's (or anyone else's) balls. I like to make people think about how stuff works.
Sorry I wasn't more clear, after the resistor or at the coil... you will have more current with more volts R=E/I... so at .5ohm=6v/12a or 9v/18a...
One of the examples I have had some success with, when training the youngsters about this...
Voltage is the road....
Amperage is the trucks hauling stuff on the road...
Resistance is the traffic devices slowing down the road...
To do a certain amount of work, like hauling 1000 dump trucks of fill to a new housing development, you will need a good road to work efficiently. A small road (low volts) will allow less trucks to travel (less amps). Too many stop signs will restrict the flow even if it's a big paved 4 lane (ohms, or resistance).
This example is my own invention, I welcome the membership to pick it apart and help me improve. The reason I tend to use this, the youngsters have all heard examples about water flow and hoses and still sometimes struggle with the concepts. It gets really bad when gravity is thought to play a role.
I have had a number of apprentices in the past and I was often one of the guys the shop would defer to when dealing with electrical/electronics issues. I spent a long evening once while at the introductory training for MB helping a room full of techs, some with over a decade in the dealer, who were cramming for an pass/fail test on basic electricity... the instructor thanked me at the end, as it was his first fully successful class.
Suffice it to say I have trained a lot of technicians in these concepts, and I always am looking for better ways to connect the dots when explaining this stuff.
Those numbers may be true. When a 6volt system is starting it is maybe 5 at best so in the dead of winter you want that coil to light a fuel air mixture at barely half of its designed voltage?
The ballast resistor is bypassed while cranking sending full battery voltage to coil which when cranking on a 12 volts system which usually drops below 10 volts right in the designed voltage for the coil.
@Big John I should not have said Dammit stop, should have said ahhh yes, no I did not think you were breaking balls just sorry I did not think to help explain correctly.
Sorry Dave... I was smiling as I typed it.
BTW 6v cars didn't need a ballast for 6v coils, 12v coils don't need a ballast for 12v cars. The ballast is used to let a coil rated for 6v (around 9v running) to survive in a 12v car and the starting circuit bypass is used to allow full voltage or close to it during cranking.
Did I say it better that time?
The coil is in fact a transformer, a coil wound inside a coil such that an alternating voltage on one coil, the primary, will induce a voltage on the other, secondary, coil. If the primary and secondary coils have the same number of windings, the input and out voltages will be the same. If the the primary has say 50 wraps and the secondary has say 1000 wraps, the ratio is 1:20. So 12V AC in would produce 240V out. (actually a little less due to transformer efficency) Notice all the voltages must be alternating or rapidly switched off and on. Notice also no mention of current because current does pass through a transformer.
So how does this transformer do it's thing? A current passing through a wire creates a mild magnetic field, wind the around a piece of iron to make coil and you have an electromagnet. Now wind a second wire on top of your first coil and you have a transformer. Why, because current flowing through a wire creates a magnetic field and as that field builds the field cuts through the secondary coil and induces a voltage. This secondary voltage works across the secondary load to create current, ie I=V/R.
We often explain the coil is a step up transformer, I generally try not to get super specific when I explain it, because the youngsters I deal with have been taught about the winding ratios before... and that knowledge won't directly be a part of their troubleshooting.
I highlighted a part of your statement, and left the following paragraph which I think makes your information match up with that I have given. I do explain, when appropriate, that there is a relationship between the current given the coil and the current it produces. Current (amperage) is the part of the electricity that can hurt (kill) a person and milliamps can stop a heart. Current is also the part that causes the fuel to catch fire, so weak volts would cause weak amps (most testing is done in volts), which causes a weak flame front during propagation... in other words, it's all related. This is particularly important when discussing newer cars which often have current limiting circuitry for the ignition coils.
I also explain a Tesla coil at the mall won't hurt you because of super low current, and it won't make cylinders catch fire either.
OK, no problem...
I'm assuming that you mean the electronic ignition, so here's what I understand.
The first production electronic ignitions had a double ballast resistor.... actually two resistors housed in the same white ceramic. One resistor had 1.2 ohms resistance and the other 5 ohms.
When you twisted the key to start, the current flowed through the 1.2 ohm resistor. After the car started, and you released the key, the current flowed through the 5 ohm side.
This was the earlier version and is known as the "five pin" because of the five connections on the ignition box.
I'm not sure when or where it happened, but a "four pin" version of the ignition box came into play later on. This box used a single 1.2 ohm ballast resistor and the start position bypassed the resistor. Release the key back to "run" and the current flows through the ballast resistor.
I have no idea why the early one was designed like that just as I have no idea what (other than less pins) was changed in the later box. We're beyond my knowledge.
FWIW, the whole system seems pretty flexible. My car was wired by a PO for a five pin box with a dual ballast resistor, and the box was a four pin. It still ran fine.... I switched some wires around and it's wired correctly now.
I've also seen a lot of cars wired incorrectly using the four pin box with both positions (start and run) of the ignition switches running through the 1.2 resistor. They seem to start and run OK, although they are also used when the weather is nice etc. There's a few incorrect wiring diagrams floating around on the internet that have brought this about.
Then I've seen cars that are wired using the four pin that have bypassed the resistor all together. The resistor is still there... bolted to the firewall and there are wires going to it... but it's not wired right and they seem to have issues with failing coils that just can't be explained. If you ever see a coil mounted to a fenderwell because "it gets too hot and fails when it's mounted to the engine", chances are strong it's wired this way.
The failure you are describing is because the coil is running too close to 12v... the coil can survive like that for short periods, but will over heat and fail prematurely if run that way continuously.
I ran a job for Westinghouse in Quebec. We were working inside a switch yard where the feed lines were 750KV from Labrador. The electric fields were intense and everything metal had to tied to the yard ground plain. Switch yards are gravel resting on a copper grid with tie points everywhere. A favorite trick for new guys, we would tell them about grounding and we would suggest they park their car just inside the fence. Most didn't ground the car because, after all, it's insulated on it's rubber wheels. Come quitting time everyone waited for the poor guy to touch his car. I don't know, maybe that's how the taser got invented.
On another job, this time in the turbine and generator division, a 4' diameter electro magnet is hung from a gantry crane and used to pickup large sheets of steel. It used 36V DC, direct current to generate a strong enough field to lift major weight. Any way, one day they had a big sheet of 3/4" plate up about 5 feet and the magnet lost power. The sheet didn't hit anyone but it did a lot of damage on the floor. The operator, figured he could fix it, since it was only 36V. He climbed on top and used his crescent wrench to pull one of the power cables to clean the contact. Well the magnet was energized and the magnetic field was fully developed. When he pulled the cable, the field collapsed and produced a huge back voltage. Before anyone could do anything he was literally fried like a piece of bacon.
Moral, HV AC with throw you across the room, but DC with lock our muscles and very likely kill you. My rule, don't mess with big DC and keep one hand in your pocket when working with AC.
You just summed up my biggest fear of hybrid and electric vehicles... once you cross around 40v... the human body is at risk. With hundreds of DC volts available, I wouldn't refuse to work on the stuff, but I would be very conscious of safety practices and proper repair techniques. I have a big distrust of community gloves too...
