What's this coil for?

[chizler62]

I'm currently building a XS650 for a customer. Intent is to maintain the stock motor, electrics and carbs. The motor will be fresh.

I came across a few coils. One the offers a stock fitment for TCI models. My problem is it says it can have a possible output of 82k

What are people doing with this coil? Are your motors that worn out? 300,000 miles on a motor?
The way the TCI works my belief is it'll hot toaster the box with simple time.

What am I missing?

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[I am Carbon]

I would like to know what coil are You talking about?

 

[chizler62]

Its on Mikes.com 17-1603
loading a coil up like that is ?

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[weekendrider]

What sells them.
You can start the camp fire with a kitchen match but it is more impressive if you use a blow torch.

 

[ippytattoo]

I couldn't find anything on mikes.com and I couldn't find part# 17-1603 on mikesxs.net but if you are talking about 17-6903 Ultimate High Output Coil on mikesxs.net it say it is: Possible Output as high as 82 Kv. That just means it is capable of reaching that voltage under ideal conditions based on the primary side voltage, dwell time and current (and who knows what voltage,current or dwell time they used for their basis for those claims) not that it is the normal operating range for the coil.

Notes:

Increases in cylinder pressure and spark plug gap, as well as less than ideal mixture ratios (either too rich or too lean) will increase the voltage required to create a spark. In more simple terms, if you step on it, requirement goes up. If you increase your engine's load while towing i.e. more fuel volume enters the cylinder (upping pressure), requirement goes up. If your plugs wear and the gap burns larger, requirement also goes up. As well, any changes that you voluntarily make such as exhaust modifications, bigger carburetors or fuel injectors, camshaft changes, or upping your plug gap to get a bigger spark, all increase the firing voltage requirement.

Some Math

Having more available voltage results in more stored energy in the coil, and since physics dictates energy must be conserved in an equation, we can do some very simple math. Please bear in mind that this is an example to express the basics of the math with simple numbers and leaves out the pages of complex calculations.

Lets compare two hypothetical coils. The math was purposely kept simple for demonstration purposes.

Coil #1 produces a maximum of 50,000 volts with a current of 0.01A (10 milliamps). Total available power would work out to 500 watts (for the spark duration).

Coil #2 produces a maximum of 40,000 volts with a current of 0.01A (10 milliamps). Total available power would work out to 400 watts (for the spark duration).

If we have a condition that requires 20,000 volts to initiate a spark, with a spark current of 0.0075A (dictated by the circuit resistance - plug wires, distributor, spark plug gap and cylinder pressure) :

Coil #1 would work as follows: 500W divided by 20,000 V would equal 0.025A which is 2.5 times the current of the secondary spark since maximum output voltage is not required.

Coil #2 would work as follows: 400W divided by 20,000 V would equal 0.020A which is 2 times the current of the secondary spark since maximum output voltage is not required.

Now for spark duration (we are almost done), our conditions that required 20,000 volts to initialize a spark also dictate that the spark current would be 0.0075A for the particular situation. So Coil #1 would provide 0.025A divided by 0.0075A = 3.33 times the spark duration. Coil #2 would provide 0.020A divided by 0.0075A = 2.67 times the spark duration.

Both coils satisfy the requirements of the test, however Coil #1 produces more spark duration. Since a mixture burns in a cylinder, a longer duration spark does two things. It ensures ignition of the fuel mixture and, as the mixture swirls in the cylinder, the spark can be igniting a larger portion of the mixture helping ensure more complete combustion. With high energy ignitions, it is not uncommon to be able to increase your spark plug gap a little to get a larger spark for even better combustion. Aside from ensuring combustion, a good ignition system can improve efficiency by releasing the most energy from the fuel charge and leaving very little to go out in the exhaust.

Of course just picking a coil or ignition system that advertises high voltage is half the battle. If the system has less output current than your present system it may not perform any better. A good parameter to look for is maximum available output power/spark.

Notes taken from http://www.auroraelectronics.com/ignition_systems_-_basics_to_high performance.htm

 

[chizler62]

That applies to a CDI system where there isn't any harm to storing excess voltage. HEAT. The TCI system holds the voltage? At least till the box burns up!

I'm to believe that my own XS750 ported etc theoretically needs when new 30k to operate properly.
so what are XS owners doing that 82k is needed vs the longevity of their TCI box?

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[ippytattoo]

No the ignitor box does not hold the voltage. The ignitor box only sends the primary voltage to the primary side of the coil and the flow of current through the primary side of the coil creates a magnetic field in the coil which creates the high voltage on the secondary side of the coil when it collapses. This is basic physics. The secondary voltage is controlled by these things:

1. the strength of the magnetic field in the primary side of the coil.
A. gauge of wire used in windings.
B. number of wraps in the windings.
C. electrical supply both voltage and current
2. secondary coil windings
A. gauge of wire used
B. number of wraps in the secondary coil
3. rate of decay of the primary magnetic field

The voltage that is created, in the secondary side of the coil, by the collapse of the magnetic field in the primary side of the is a type of electromagnetic induction which was "discovered" by Faraday in 1831.

I believe that your fundamental understanding of how an ignition system works is weak and/or misguided. The output voltage of the coil has little to do with the ignitor box's ability to hold voltage as you suggest and the output voltage of the coil has little to no determination on the longevity of the trigger being used whether it be points, TCI or CDI based ignitions.

side note:
You can have a situation arise where the primary side of the coil draws too much current for the specific ignition trigger being used in such a way that it would draw too much current through the ignitor and cause damage because the ignitors are designed to be able to handle a given amount of current flow. A very crude example of this type of problem based on conventional conductive materials:

You have a circuit in your house that is capable of handling a single 120watt light which is basically a very small coil of conductor when current flows though it generates heat and light (120w/120v=1a) and you change to another type of fixture that uses 3 of those same bulbs you have increased the load on that wire by three fold (3a vs. 1a) and the circuit is not designed for it. Your ultimate outcome will be the circuit (or the conductor supplying voltage to the fixture) will be compromised and will fail.

The principle is the same in regards to the power handling capabilities of the circuit of the ignition trigger as designed for our ignition systems. Just for the sake of numbers (no these are not actual amperage capacities used for anything other than an example) if the stock tci box was designed to be able to handle a current flow of 10a using the stock coil (again just for the sake of number as I do not know if there will be such a coiil as I am going to describe) with an output of 10kv with a specific gauge of wire in the primary winding and you change to a coil that has either a different gauge of wire or number of windings in the primary side (in a nut shell altering the resistance of the primary side of the coil) that will draw 30a with an output of 7kv you are going to blow the tci box because of the current flow through the tci box and not due to the change in the secondary high voltage output voltage of the coil because as you can see in the example even though the primary current increased the secondary output decreased.

 

[XSLeo]

From what I understand, in ideal conditions a plug takes around 6-8,000 volts to fire. The points coils were rated about 10,000 volts at 4000 rpms. I assume this is with a fully working charging system and good battery. Capable of keeping voltage up at around 13.8 volts.
Now lets say the conditions are not ideal, the plugs now takes 10,000 volts to fire, this is about all the coil can do. Lets say the charging system and battery are not at 100%. Lets say it can only keep 12 volts to the coil. That's a 13% drop, this should give about 13% less voltage at the plug. That leaves about 8700 volts.
Would this prevent the engine from running?
Now lets say the same conditions are the same as the second example but using a coil with 20,000 volts. The plug still needs 10,000, but even with a 13% drop in plug voltage it still has 17400 volts at the plug.
Much more than the 10,000 volt coil can ever provide.
The TCI coils I believe are around 15,000 volts. The ignitions don't care what the output voltages are, they care about input ohms. The TCI uses a 2.5 ohm primary side ohms. Using a lower ohm coil will create to high a current draw through the ignition, this can and will burn out the ignition.
These numbers may not be exactly correct but do show the trend.
Having excess voltage at the plug is a good thing. It helps engines start and run better, get a bit more power and use less fuel.
I admit Mike's Green Monster coils at 75+ or the Ultimate coil at 82+ is more than needed but it won't hurt. I believe one around 20-30,000 is good.
Leo

 

[chizler62]

LOL

Using a lower resistance coil to achieve higher output voltage passes too much current thru the TCI box.

My question is why dampen the reliability?

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[I am Carbon]

I think this is the coil that you are refering Part #17-6903 http://www.mikesxs.net/product/17-6903.html

I'm no expert in this matter but I have this very coil.
I have used it with TCI and Pamco ignitions It has workd very well for me with no problems. that's all I know about it.

 

[pamcopete]

Keep in mind that in a wasted spark system the spark plugs are effectively in series so whatever voltage you are talking about, it has to jump twice the distance of the gap on each spark plug.

Also, with a dual output coil, one of the spark plugs will get a positive voltage from the coil, the other spark plug will get a negative voltage. The Negative voltage is 40% more efficient than the positive voltage, so you have to have a voltage from the coil that is 40% in excess of the minimum required.

Here is a video of the 17-6903 "Ultimate" coil running on a test setup using a PAMCO and 13.5 Volts.

That's a 1" gap.

Here is the same setup but with a 6 Volt lantern battery supplyuing the power:

That's a 1/2" gap:

And that's an important consideration for using a high output coil. To ensure a healthy spark when starting.

 

[ippytattoo]

LOL

Using a lower resistance coil to achieve higher output voltage passes too much current thru the TCI box.

My question is why dampen the reliability?

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You are missing the basic principle. The secondary high voltage output can be controlled and altered independently from the resistance of the primary side of the coil.

If you are using a coil with the same primary resistance the increased secondary high voltage output has little to no effect of the ignition trigger. If you use a coil that has a lower primary resistance (which is not what you were asking about) then yes you could get into a situation where you are drawing to much current through the tci ignitor.

Your question was why use a higher output coil? And your assumption was that the tci box stored the voltage. Your question was answered and your assumption is wrong. Never once did you ask about a lower primary resistance.

 

[chizler62]

No nobody still has answered my question.

Why is a coil with 82k marketed to XS650 customers?

Yes, dwell time or rise time will require the current to the coil be readied in the.......TCI box.

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[NONclow]

It might not be ideal, but probably the same reason 1.75-2" exhausts are used, because you can!!! MORE POWER!!!! HA!...........lol

Not to mention extra revenue for the manufacturer by fitting on as many models as possible......

 

[ippytattoo]

I'm currently building a XS650 for a customer. Intent is to maintain the stock motor, electrics and carbs. The motor will be fresh.

I came across a few coils. One the offers a stock fitment for TCI models. My problem is it says it can have a possible output of 82k

What are people doing with this coil? Are your motors that worn out? 300,000 miles on a motor?
The way the TCI works my belief is it'll hot toaster the box with simple time.

What am I missing?

Posted via Mobile

That applies to a CDI system where there isn't any harm to storing excess voltage. HEAT. The TCI system holds the voltage? At least till the box burns up!

I'm to believe that my own XS750 ported etc theoretically needs when new 30k to operate properly.
so what are XS owners doing that 82k is needed vs the longevity of their TCI box?

Posted via Mobile

LOL

Using a lower resistance coil to achieve higher output voltage passes too much current thru the TCI box.

My question is why dampen the reliability?

Posted via Mobile

The way that an ignition coil is constructed you have an inner coil wrapped around an iron core which makes up the primary side of the coil. Then you have an insulator around the primary windings. Then you have the secondary windings. then you have another insulator that encompasses the whole of the ignition coil assembly.

The primary windings get power from the ignition trigger or in this case a stock yamaha xs650 TCI ignition module which creates a magnetic field which surrounds both the primary side of the coil and the secondary winding. In the case of the TCI ignition with a dual coil one end of the secondary winding attaches to each spark plug via the spark plug wires. At no time (unless you have a direct short between the primary and secondary windings which is a failed coil) will you have any direct connection between TCI ignition module and the spark plugs.

The only current that would ever be flowing through the TCI black box is the amount required by the primary windings in the coil. The manufacturers do not state what that current is but it is very easy to figure out and that is by using ohms law [ A = V ÷ R ] A (amps) = V (volts) ÷ R (Ω). For this example we will assume that battery is at 100% and maitains 13.8V through all of the applicable tests and we will assume that the coil is 2.5Ω (the same as the other replacement coil for the TCI ignition since the primary resistance for the Ultimate Coil is not listed) as is readily accepted as within specs for the TCI ignition and this coil is advertised as a replacement for the stock factory Tci ignition coils. If I remember correctly the OEM coils were 2.4Ω so will calculate both

A=13.8÷2.5 so A=5.52amps For the Ultimate coil.
A=13.8÷2.4 so A=5.75amps for the OEM coil

Now onto secondary voltage vs. longevity. As you can see above by going from the OEM coil to the Ultimate Coil there is actually a 4% drop in current flow through the TCI module. I don't remember exactly what the output for the OEM coil but I think it is in the neighborhood of 20kv. The Ultimate coil is advertised as 82kv. So as you can see through advancements in coil designs and materials there is roughly a 310% rise in secondary output while reducing primary current by 4%. So according to your theory that more current will destroy the TCI module the decrease in primary current should actually extend the life of the TCI black box.

No one is advocating using a lower primary resistance (which is what is advertised) to increase secondary output voltage and once again based on your conclusions about higher current draw being detrimental to the TCI module then the Ultimate Coil should actually increase reliability and not dampen the reliability.

As you can see in my first post there are actually measurable and definable performance benefits in both spark intensity and duration by going to a coil with the ability to generate a higher secondary output voltage (expressed as kv or kilavolts or thousands of volts) that go beyond tired old motors.

Why are 82kv coils being marketed to xs650 owners? Why is there so much chrome being marketed at Harley owners? They are both marketed for a couple of reasons. One is to make the owners believe that by adding either of these types of products to their machine they will get some kind of perceived improvement in either performance or style whether real or imagined. And the other is so that the manufacturers and retailers can make some money providing these types of products.

I hope I have now answered all of the posted questions.


P.S. I almost forgot, what are we doing with the Ultimate Coil? We are lighting an air fuel mixture (if the engine is tuned properly) that is present in the cylinders of our 360* parallel twin motors if we are still talking about a motor that is running the stock TCI ignition.

 

[mrriggs]

82kv is a meaningless number. The voltage is determined by the weakest component in the ignition system, which hopefully is the spark plug.

A ignition coil is a big inductor. Inductors are like electric flywheels. When current is put into the primary of the coil, the coil adds resistance to try and keep the current low. Eventually, the current will build up which the coil stores as energy. When primary current is interrupted the coil will add voltage to try and keep the current going. The voltage will continue to rise until there is a current path for the stored energy. The coil doesn't care where the energy goes. Whatever "shorts out" first will determine how high the voltage rises and where the energy will be dissipated.

A spark plug will not require 82kv to fire. If it did, the spark plug wires would be unable to supply that much voltage. The spark would jump through the insulation on the spark plug wires before jumping across the spark plug gap.

OK, assume you had some 1/2" thick spark plug wires that could handle that much voltage and the coil is rated for 82kv so surely it wouldn't short out internally. What about the primary side?

If the coil has a 100:1 turns ratio then the primary voltage will rise to 820 volts in order for the secondary to reach 82kv. The wire you used to hook the coil to the ignition module is likely rated for 600 volts. So, unless you upgrade the primary wiring, your 82kv coil is limited to 60kv.

Sadly though, the ignition module itself is going to hold you back more than the wiring. The power transistor used to switch the primary current can be damaged from high voltage so there is a diode protection across it, typically around 400 volts. That means the secondary voltage would be limited to 40kv with a 100:1 coil.

The good news is that the spark plug is going to "short out" well before any of these other components. If the spark plug fires at 10kv then the primary is only rising to 100 volts, well within the breakdown voltage of all the other components.

 

[pamcopete]

mrriggs,

Well, the IGBT transistor I use has a built in zener that back feeds the gate (turns the transistor on) when the collector voltage reaches 400 Volts. The primary voltage always goes to 400 Volts with this arrangement and is not dependent on the voltage at which the spark plugs gap is bridged. This same arrangement means that the primary voltage will be clamped to 400 volts and not be able to rise to the 820 Volts in your example, so we have to assume that the winding ratio is different.

I think you forgot about the secondary resistance. Remember that the secondary winding resistance is typically 10 K to 15 KOhms and even with the spark plug shorted, the collapsing field will induce current into the winding of the secondary which will dissipate that energy in the secondary resistance, which is not zero ohms.

 

[retiredgentleman]

ippytattoo;

"A=13.8÷2.5 so A=5.52amps For the Ultimate coil.
A=13.8÷2.4 so A=5.75amps for the OEM coil"

Don't forget that the ignitions don't have 100% duty cycle, or 360 degree dwell angle as its called. I've measured the TCI primary current @ 0.5 amps, which works out to about 32 degrees of dwell.

chizler62 seems to be concerned that the TCI boxes would burn up from the large amount of heat, but 0.5 amps is actually quite low. I'd say the TCI circuit was well designed, and if they are failing now its only because of old age and vibration, not from large current flow to the coil primary.

 

[chizler62]

Makes sense if you're using a bipolar transistor.

But, What if you, as in my case, just bolt it on with a stock TCI system?

And yeah, I should explain myself better. HOLD isn't really the proper term

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[ippytattoo]

RG, good to know about the 32* of dwell angle. I was just using the basic formulas to show that the Ultimate coil really isn't much different in amperage draw when compared to an OEM coil since chizler is worried about burning up the TCI due to a higher secondary output voltage.