questions on internal resistance

[azazzera]

i have been reading up on ingnition systems and following the conversations on the hot coils. my question is wouldnt a high internal resistance produce heat in the coil. would it be more helpful to provide most if not all resistance external. how do you controle voltage to the coil other than resistance. i guess im still getting this all straight in my head. thanks. also ive seen coils with fins to disapate heat. would that help or is it all about limiting the build up of voltage in primary.

[ndutton]

Good question. Your reasoning would be correct if internal coil resistance was achieved by using the same type of resistor . . . . .

. . . . . but it isn't.

The external ballast resistor heats up by design taking advantage of the resistor's properties in relation to heat - - - serious heat in this case. What follows is not from me but paraphrased from an online source. Parenthetical notes are mine:

The ballast resistor (the type we've been recommending for external supplemental resistance) is a temperature sensitive, variable resistance unit. A ballast resistor is designed to heat up at low engine speed as more current attempts to flow through the coil (energy duration in terms of dwell and RPM related time). As it heats up its resistance value increases causing lower voltage to pass into the coil. As engine speed increases the duration of current flow lessens. This causes a lowering of temperature. As the temperature drops so does the resistance allowing the voltage to the coil to increase. At high speed when a hotter spark is needed the coil receives greater voltage input.

The ballast resistor is a coil of nickel-chrome or nichrome wire. The nichrome wire`s variable resistance properties tend to increase or decrease the voltage in direct proportion to the heat of the wire.

[romantic comedy]

Neil, that is what I had always thought. Hence the name ballast resister. It is a variable resister, that provides stability.

[hanleyclifford]

Originally Posted by romantic comedy

Neil, that is what I had always thought. Hence the name ballast resister. It is a variable resister, that provides stability.

I have mine running thru 3 paths on the resistor block so voltage variation is minimal.http://www.moyermarine.com/forums/at...8&d=1331592235

[romantic comedy]

Hanley, do you ever get to SW Florida? I gotta see this boat.

Are you adding the resistors in series?

[hanleyclifford]

Originally Posted by romantic comedy

Hanley, do you ever get to SW Florida? I gotta see this boat.

Are you adding the resistors in series?

The array has 3 parallel switched paths; each path has a 1 ohm block and a 10 watt light in series. I sure do want to get back to Florida. Right now I'm sorta living aboard in Wickford and the harbor is plumb froze. Edit:http://www.wickfordyc.org/

[azazzera]

I always appreciate the response to my questions. I however feel that its at times one step forward and two steps back in regards to my understanding of the physics of it all. my studies continue. I suppose i have to ask the proper questions to "the google" I have stumbled on to the "hot spark" site and at first glance they seem to be quite explicit about using the proper resistance in your coil. they explain very clearly that if not enough resistance is used with ei coils will be fried.. I would like to hear from people that have used there product.

anyway, thanks for the continuing education. until next question.

[ndutton]

It turns out I decided to give the HotSpark EI a try on my spare engine coupled with a Moyer 4.3Ω coil and no supplemental resistor. I haven't run the engine enough since completing the rebuild to offer a useful report. All I can say right now is it starts easily without the 'R' terminal bypass and runs smoothly.

I know of one other forum member using the HotSpark. So far so good.

[HalcyonS]

I came across this product in a reference by Neil, while researching points issues (as one does). Its been a longtime now - any updates on your test engine with Hotspark, Neil, or anyone else?

[hanleyclifford]

how does the coil achieve it's internal resistance?

[hanleyclifford]

Here's a little picture I found at Google (the sum of human knowledge). We know how we measure for ohms across the terminals. So the question again, how does the coil develop it's internal resistance?

[joe_db]

The wire in the coil has resistance. There is a LOT of wire in there and it is thin. You can measure it with an ohmmeter. Coils are usually sold with a stated resistance. You can buy 3 ohm coils, 4 ohm coils, 0.6 ohm coils, etc. etc.
When the coil resistance is less than desired, we add ballast resistors...or buy a lot of coils

Originally Posted by hanleyclifford

Here's a little picture I found at Google (the sum of human knowledge). We know how we measure for ohms across the terminals. So the question again, how does the coil develop it's internal resistance?

[hanleyclifford]

Originally Posted by joe_db

The wire in the coil has resistance. There is a LOT of wire in there and it is thin. You can measure it with an ohmmeter. Coils are usually sold with a stated resistance. You can buy 3 ohm coils, 4 ohm coils, 0.6 ohm coils, etc. etc.
When the coil resistance is less than desired, we add ballast resistors...or buy a lot of coils

A lot of Truth there. But the question then becomes, how is the means of resistance inside the coil different from the means of the external resistor? Do not both generate heat?

[joe_db]

Yes they both do generate heat. The coils heat up when used from current flow as well as being bolted to a hot engine.

Originally Posted by hanleyclifford

A lot of Truth there. But the question then becomes, how is the means of resistance inside the coil different from the means of the external resistor? Do not both generate heat?

[hanleyclifford]

Originally Posted by joe_db

Yes they both do generate heat. The coils heat up when used from current flow as well as being bolted to a hot engine.

That's what I thought.

[ndutton]

Originally Posted by HalcyonS

I came across this product in a reference by Neil, while researching points issues (as one does). Its been a longtime now - any updates on your test engine with Hotspark, Neil, or anyone else?

Nothing new to report here either good or bad. I don't run my spare engine much, the one with the HotSpark ignition.

About the rest of the chatter about coil heat, it may help to understand why some ignitions have (need) more resistance than others. Things to look for in your research:

• Coil heat is directly proportional to amperage x time and inversely proportional to resistance regardless of whether it's internal or external.
• The need for higher resistance systems is related to # of cylinders and engine RPM as it applies to coil saturation, the soldering iron effect.
• Unrelated to the discussion but still a factor, coil potting material affects heat.
• At a fixed voltage resistance doesn't create heat, current does. The more resistance, the less heat (see the first bullet point).

[hanleyclifford]

So would it be fair to say that, in effect, the primary windings in the coil are a "resistor"?

[ndutton]

All conductors have resistance.

[hanleyclifford]

Originally Posted by ndutton

All conductors have resistance.

Precisely. The primary windings do it with length; the ballast resistor does it with low conductivity.

[romantic comedy]

There are resistors that are wire wound. Wire wound around a non conductive core. Not all that different from the ignition coils.

[HalcyonS]

Originally Posted by hanleyclifford

Here's a little picture I found at Google (the sum of human knowledge). We know how we measure for ohms across the terminals. So the question again, how does the coil develop it's internal resistance?

In electronics, people talk about resistive loads and inductive loads. A coil is an inductor. Resistance, Inductance (or Reactance) and Impedance are all measured in ohms.
This page is explanatory
http://www.allaboutcircuits.com/text...-of-r-x-and-z/

" Resistance is essentially friction against the motion of electrons. It is present in all conductors to some extent (except superconductors!), most notably in resistors.
...

Reactance is essentially inertia against the motion of electrons. It is present anywhere electric or magnetic fields are developed in proportion to applied voltage or current,"

[HalcyonS]

Originally Posted by romantic comedy

There are resistors that are wire wound. Wire wound around a non conductive core. Not all that different from the ignition coils.

Completely different!
1, A coil is a transformer. (autoformer actually) Current in one winding induces magnetic field induces current in the secondary.
2, A wire resistor uses resistive wire. A coil uses minimally resistive - maximally conductive -wire

[HalcyonS]

Originally Posted by ndutton

All conductors have resistance.

yeah, but ... there' s reason we use copper, on alu, and not, say iron (or wood) for wiring
The wire they sell for electronic wiring is desirable because its resistance is negligible.

[JOHN COOKSON]

Originally Posted by hanleyclifford

how does the coil achieve it's internal resistance?

Well I give up. I always assumed there was a resistor in the coil since copper is a very good conductor. Maybe not?

TRUE GRIT

[HalcyonS]

Originally Posted by hanleyclifford

Here's a little picture I found at Google (the sum of human knowledge). We know how we measure for ohms across the terminals. So the question again, how does the coil develop it's internal resistance?

The bigger question is how does the coil develop high voltage output?
As I understand it, a *fluctuating*, ie AC current is needed to induce a magnetic field. And the fluctuating magnetic field induces the voltage in the secondary. The points simulate AC by regularly grounding the circuit.

This page is good:
http://mgaguru.com/mgtech/ignition/ig108.htm
note that the older MG and Morris 4 cyl engines look very like the A4.