Modify Velleman Kit - Transistor Assisited Ignition, kit no. K2543

[spec]

I am a neophyte, so any specifics on the test?

I.e. is this correct; I attach battery leads to the + and - terminals on the coil, with the resistor in series, and measure how hot the coil gets.

Over what time period?

Yes, that would be a test to see how hot the coil gets. I would advise staring with a high value resistor, as in post #?, and see if the coil gets hot. If not, move on to the next lower resistor.

I would say that the surface of the coil should get no hotter than 70 deg C.

If the coil quickly heats up to 70 Deg C and stays there that is OK. Then leave the coil connected for about 30 minutes checking the coil surface temperature every 10 minutes or so.

Once you find the resistor value where the coil quickly heats to 70 Deg C and stays there over about 30 minutes let us know the value of the final resistor.

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[sign216]

Holy (*^%^& 30 minutes sounds like a long time.
I mean, the dwell is just a fraction of a second, right?

I'm working on getting an appropriate resistor. Most of the automotive ballast resistors are too few ohms.
I'll visit an electronics store later.

 

[spec]

Holy (*^%^& 30 minutes sounds like a long time.
I mean, the dwell is just a fraction of a second, right?

Quite right about the dwell being a fraction of a second, but there are many fractions of a second in a second and even more in 30 minutes. Think of drops of water falling into a glass.

I'm working on getting an appropriate resistor. Most of the automotive ballast resistors are too few ohms.
I'll visit an electronics store later.

It is best to order power resistors from the net- much cheaper and wider choice.

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[spec]

I meant to say a while back that it should be possible to attach a large heatsink to the coil to increase the power handling of the coil.

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[sign216]

I meant to say a while back that it should be possible to attach a large heatsink to the coil to increase the power handling of the coil.

spec

Interesting idea. Let me what the tests bring about. I'm stopping at a Radio Shack tonight to see if they have any suitable wire-wound resistors.
I know I can get them cheaper on the internet, but I want to keep my local electronics store in business, before they all disappear.

 

[sign216]

I tested the coil with wire-wound ceramic resistors (1 ohm each) on the 6v 11amp/hr battery to see how hot things would get.
Room temp was 18 C (65 F). After an hour;

2 ohm resistance
coil = 27 C (80F) resistors = 104 C (220 F)

1 ohm resistance
coil = 41 C (105 F) resistor = 188 C (370 F)


At the end the battery was left with approx. 5.9 volts or 30% charge.
I didn't test it with no resistors because I was fearful of how hot the resistors were getting. What's a safe operating temp for those?
Any thoughts?

 

[spec]

I tested the coil with wire-wound ceramic resistors (1 ohm each) on the 6v 11amp/hr battery to see how hot things would get.
Room temp was 18 C (65 F). After an hour;

2 ohm resistance
coil = 27 C (80F) resistors = 104 C (220 F)

1 ohm resistance
coil = 41 C (105 F) resistor = 188 C (370 F)


At the end the battery was left with approx. 5.9 volts or 30% charge.
I didn't test it with no resistors because I was fearful of how hot the resistors were getting. What's a safe operating temp for those?
Any thoughts?

Hi Sign,

You have been busy and some nicely presented data.

Don't worry a tad about the resistor temperature- that does not come into the equation. It is only the coil that counts.

It is very encouraging that with a 1 Ohm resistor (total resistance 1.5 Ohms and thus coil current 4A) that the coil surface temperature only reached 41 Deg C.

So, my advice would be to go with a 1 Ohm resistor.

What are you planning on doing next?

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[sign216]

I'm planning on putting this coil in with a switch; the 1 ohm resistor is out of circuit when starting, back in circuit when running. Sort of like the carburetor choke.
That should give good results for both starting and running.

But I've got to ask about the resistor. It was too hot to touch. At 188 C (370 F) it's not going to present an issue to itself, or other components?
Should I add a heatsink to it?
While taking measurements a wire dragged across it and melted right through the insulation.

 

[spec]

I'm planning on putting this coil in with a switch; the 1 ohm resistor is out of circuit when starting, back in circuit when running. Sort of like the carburetor choke.
That should give good results for both starting and running.

I would not advise doing that. You will over-stress the coil and it is not necessary. I recon the coil will give you good starting with the 1 Ohm resistor in circuit. Don't forget that it is a high performance coil.

But I've got to ask about the resistor. It was too hot to touch. At 188 C (370 F) it's not going to present an issue to itself, or other components?
Should I add a heatsink to it?
While taking measurements a wire dragged across it and melted right through the insulation.

Yes I think I mentioned before that the resistor will require a heatsink

The resistor will be dissipating around 12W and without heat sinking it will get red hot.

What sort of resistor are you using. I would recommend a 50W minimum bolt-down resistor on a heatsink, as I described before. The heatsink should bolt to a cool metal part of the bike for added heat sinking. If you aim for a maximum surface temperature of no more than 80 deg C that should be good for reliability.

When I asked what you are going to do next I was asking about how you are going to test the coil providing the spark for the engine.

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[alec_t]

The resistor will be dissipating around 12W

At what duty cycle? (I haven't checked all the posts to see if this has been mentioned).

 

[spec]

At what duty cycle? (I haven't checked all the posts to see if this has been mentioned).

Because the dwell is so long with a Kettering ignition system, transistor aided or not, the duty cycle can be taken as a 100% for worst case calculations/testing.

Also, when there is no current being provided by the switch (contact breaker) the coil will still be dissipating power as it generates the spark.

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[sign216]

A 50w resistor? How about if I just use a standard automobile ballast resistor. They are readily available and should be up for more current than this little bike puts out.

I am set for the switch to put the resistor in or out of the starting circuit, as that can really enhance a problem start. For a little extra wiring it is a genuine improvement to a problem start situation.

As for testing the system, um...en empirical test is difficult. I usually just connect a spark plug outside, and see if there's spark when kicked. I must admit, there was spark even with the old battery and the old coil, so this new system should give me added capacity for when things go wrong. I imagine I could test it with a modern "resistor plug" and an in-line spark tester (which I have) but these aren't very sophisticated.

 

[spec]

A 50w resistor? How about if I just use a standard automobile ballast resistor. They are readily available and should be up for more current than this little bike puts out.

You need a resistor as I described. 12W is 12W.

I am set for the switch to put the resistor in or out of the starting circuit, as that can really enhance a problem start. For a little extra wiring it is a genuine improvement to a problem start situation.

You will be in danger of over stressing the coil voltage, current, and power.

As for testing the system, um...en empirical test is difficult. I usually just connect a spark plug outside, and see if there's spark when kicked. I must admit, there was spark even with the old battery and the old coil, so this new system should give me added capacity for when things go wrong. I imagine I could test it with a modern "resistor plug" and an in-line spark tester (which I have) but these aren't very sophisticated.

I meant test the coil on the bike running the engine. As I said before, I would advise using the points without the Vellerman unit- don't forget the capacitor across the points.

Of course, I can only advise. At the end of the day it is obviously up to you which way you want to go.

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[sign216]

You need a resistor as I described. 12W is 12W.

Okay, I'll get a 1 ohm 50w resistor and work-up a heat sink. Are pre-made heat sinks commonly available for these resistors?

You will be in danger of over stressing the coil voltage, current, and power.

You misunderstand; the resistor will be out of circuit only for the initial kick-start. Once the engine catches I'll switch the resistor back in. This is done with some cars; the ballast resistor is out of circuit as long as the starter solenoid is in action. I.e. as long as the starter switch is depressed.

I meant test the coil on the bike running the engine. As I said before, I would advise using the points without the Vellerman unit- don't forget the capacitor across the points.

Of course, I can only advise. At the end of the day it is obviously up to you which way you want to go.

spec

The bike's not running (yet), but I can test it by connecting the elements and using an inline spark tester to see the quality of the spark. We just got a foot of snow here in Massachusetts, USA, so it'll be a month or two before this hits the road. Before I started, I had fair spark with the the 10 yr old orig. battery and the tiny orig. coil, so this should be a real step up.

About the Vellerman transistor ignition unit, I recognize that this is separate discussion from using a high performance coil, but I'd still like to add it at a later date. Reportedly it extends point life almost indefinitely, and no longer requires the 5k mile adjustment that normal points have. This is a benefit because the points are hard to reach on this machine, requiring removal of some items before you even reach the engine cover.
Your thoughts on the Vellerman unit as a stand alone device?

 

[sign216]

I tested the very small, original 50 yr old coil (approx. 2k ohm resistance) against the modern large high performance coil (approx. 0.6k ohm). To "stress" the system I used a resistor spark plug that adds 5k ohm resistance, and I also increased the plug gap to 0.06" (1.5 mm). Normally the plug gap is 0.026" (0.66 mm) so the increased plug gap + 5k ohms should be a stringent test. To measure the spark I used an in-line spark viewer, and also just viewed the plug raw, outside the engine, to see the actual spark.

And...I couldn't see a difference between the two coils. Both produced decent sparks, and I couldn't tell if one was weaker than the other.
On the good side, if the coils are firing with a resistor plug and crazy gap of 0.06" (1.5 mm), then they should fire with no problem in real life.

This is an instance where better equipment is needed. My eye cannot tell the difference between a 40k spark, and a 25k spark, if both are jumping the plug gap. Don't get me wrong, I've seen weak sparks before. And strong sparks. It's just that in this example I couldn't see a difference.
I don't know what to say. There should have been a huge difference. My un-calibrated eyes just couldn't see it.

It's also possible that a different part of the system is limiting performance, so that the coils are not the deciding factor. Something like the small 6v battery, or the incredibly thin orig. wiring of the bike, etc.

 

[shortbus=]

Maybe increase the gap in known increments until it fails to jump the gap. That should give a functional proof of whether one coil is stronger than the other. Shouldn't it? Just a shade tree, no instrument way of measuring.

 

[sign216]

Shortbus,
That's a good idea to compare the different coils. Th plug gap is already unrealistically large. The bike's normal is 0.026" (0.66 mm). Max gap on cars, with a high performance coil, is approx. 0.045" (1.15 mm).

I wish I knew more about the relationship between voltage and jumping the gap. As the gap widens, does the necessary voltage increase linearly?

 

[shortbus=]

Don't know if the relationship linear. But it does take a higher voltage to jump a bigger gap. Just be sure when putting the plug in the engine to reset to the recommended gap. The increased compression internally makes the spark harder to jump the gap. There's a term for the gap to voltage but can't seem to recall it right now. Old age and a couple of strokes do that to you.

 

[dr pepper]

Increasing the gap of a plug increases the flash over voltage, however it doesnt necessarily increase the spark energy, esp with a different coil.
The coil charges during the dwell time and discharges during the flat topped burn time of the plug as seen on a crypton or sun machine, you can have lower energy at a higher voltage. The brightness of the spark changes visibly when the spark energy changes, so long as the coil doesnt saturate you can increase the spark energy by increasing the dwell time, or of course changing the coil for a lower inductance one with a bigger core.

At one time 80's I think, 'plasma' spark systems were popular, these basically put the vehicle battery inline with the spark voltage, and you ended up with blinding sparks, they quickly went out of fashion, probably because plugs burned up fast.

 

[Crosserke]

Interesting toppic.
Has there been any progress in this project?