questions on internal resistance

[ndutton]

HotSpark

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]

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]

resistance and inductance

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/textbook/alternating-current/chpt-5/review-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]

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]

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]

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]

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.

[HalcyonS]

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

Regarding resistance in the coil: Single digit ohms is almost no resistance. Most resistors in electronics are measured in Kohms - 1000s of ohms. Megohms (millions) is not unusual.

[joe_db]

Ballast resistors are usually in the 0.5 to 1.5 ohm range. IIRC, the resistors I got for my coolant pumps are 1 ohm 25 watt units.

Regarding resistance in the coil: Single digit ohms is almost no resistance. Most resistors in electronics are measured in Kohms - 1000s of ohms. Megohms (millions) is not unusual.

[joe_db]

True.
Also the lower resistance coils have presumably thicker wire and less turns to give higher voltage output. The less turns in the primary, the higher the ratio to the secondary and thus higher voltage out.
What I don't know for a fact is that the difference between a 4 ohm, a 3 ohm, a 1.6 ohm, and a 0.6 ohm coil, etc. etc. are all ENTIRELY down to the amount and size of primary wire or if some of them have an internal ballast as well.
A little poking around shows this:
A 0.7 ohm coil has a turns ratio of 100:1.

http://www.summitracing.com/parts/msd-8203/overview/

A 0.6 ohm coil has a turns ratio of 108:1.

http://www.summitracing.com/parts/pnx-45011/overview/

A 3 ohm coil has a turns ratio of 50:1

http://www.summitracing.com/parts/pnx-28010/overview/

Clearly there is more wire in the 3 ohm coil (lower turns ratio = more wire on the primary side), but without sawing the thing open I cannot say 100% of the resistance increase is due to the wire. I may call a coil company and ask, now I just have to know. I think it is, but not 100% sure.

A visualization aid for those lacking EE backgrounds - A dimmer switch acts like a ballast resistor. The more resistance, the less total current, and the less heat and light coming out of the light bulb. Switching the light on and off rapidly is like the points. The more ON time vs. OFF time is the dwell. The higher the dwell, the hotter the bulb. Electronic ignition leaves the light ON more than points, so the coil gets hotter.

All conductors have resistance.

[ndutton]

Decent analogy Joe. About how different internal resistance coils are constructed, the Bosch Blue Coil #00-012US says right in its description "Stock Bosch blue coils have the 3 ohm ballast resistor INSIDE the coil" Further, here's a drawing of a vintage Autolite canister coil that should help clear up the speculation.

Is there a reason for this exercise? It seems it's headed down the path of how to build a watch when you only asked what time it was.

[hanleyclifford]

Decent analogy Joe. About how different internal resistance coils are constructed, the Bosch Blue Coil #00-012US says right in its description "Stock Bosch blue coils have the 3 ohm ballast resistor INSIDE the coil" Further, here's a drawing of a vintage Autolite canister coil that should help clear up the speculation.

Is there a reason for this exercise? It seems it's headed down the path of how to build a watch when you only asked what time it was.

Time spent on (intellectual) reconnaissance is never wasted; tell 'em, Drill Sergeant.