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

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Wait, wait. How can there both be inadequate power for the electrical system, but still too much for the coil? I feel betrayed.

How about if instead of the 0.6 ohm performance coil, I use the 1.5 ohm coil? Would this yield a significant gain over the stock 2.0 ohm coil?
 
I don't know why you quoted my name there. I did not write this.

https://www.electro-tech-online.com...ition-kit-no-k2543.149878/page-2#post-1284356

 
Hello Sign

sign216 said:
Wait, wait. How can there both be inadequate power for the electrical system, but still too much for the coil?
Click to expand...
Because that is exactly the position.

The only source of electrical power on the bike is the 60W generator (magneto). The battery only stores power that it gets from the generator- it does not make power. The battery is like a tank in a plumbing system that holds water but is only fed from the water main by a small pipe.

The tank will supply as much water as you like until it empties, then the only water supply will be the small flow of water from the mains pipe.

So to get back to your bike's electrical system, the generator would probably be able to supply a continuous 7A current to one of the FT coils during the day if the lights were switched off. But if the lights were switched on the generator would not be able to supply the combined current demanded by the coil and the lights, so the battery would supply the difference. And this would be fine but the battery would be discharging and it would not be long before the voltage dropped when the battery was exhausted and, at that point, the lights would dim and the spark voltage would drop, maybe sufficiently to stop the bike's engine. The lead acid battery would also be damaged because its terminal voltage would drop below the minimum specified voltage for the battery.

sign216 said:
I feel betrayed.
Click to expand...
I can't see how you can feel betrayed unless you mean disappointed. Don't take things personally.

I addressed all who have contributed to this thread, including you, because what I said has a fundamental impact on the design of your advanced ignition system.

The other members, and I, are only trying to help you get a practical working system. And that may involve some negative aspects. Otherwise, you may waste money and effort on a system that could not work.

sign216 said:
How about if instead of the 0.6 ohm performance coil, I use the 1.5 ohm coil? Would this yield a significant gain over the stock 2.0 ohm coil?
Click to expand...
If the original coil on the bike is 2 Ohms and no ballast resistor is fitted that would imply a maximum current of 7.5V/2R = 3.75A
If you fitted a FT (1.5 Ohm) performance coil that would imply a maximum current of 7.5V/1.5R = 5A which is 1.25A more. I can't say if that would be OK for the coil or OK for the bike.

But you could fit a ballast resistor of 0.5 Ohms to limit the maximum current to 3.8A like the original coil. That should be OK for the bike but I cannot say about the coil.

The Vellerman switching unit would still require a higher voltage switching element (transistor) and the the voltage of the Zener chain would still need to be increased to at least 400V to cater for the increased primary voltage produced by the FT (1.5R) performance coil.

Yes, I think you would get a considerable performance improvement, but remember that I am working with incomplete data and that is only an opinion

spec
 
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You are assuming the max voltage is 7.5V, but what is it if the Battery Bypass switch is flipped? Will that mechanical regulator maintain 7.5V when the ignition coil is driven directly by the magneto?
 
alec_t said:
You are assuming the max voltage is 7.5V, but what is it if the Battery Bypass switch is flipped? Will that mechanical regulator maintain 7.5V when the ignition coil is driven directly by the magneto?
Click to expand...
Hi Alec,

The definitive answer is that I do not know, but the bike works OK, by design, off the mag with the original coil so, with the new coil adjusted to take the same current, logic says it should be fine.

The secondary voltage may be down when running off mag, but so it would be with the original coil, but the FT coil should still produce a higher voltage, at a guess 250% higher. This is based on the assumption that the FT coils are far more magnetically efficient than the original and that the FT coil has a turns ratio of 100:1 compared to an assumed turns ratio for the old coil of 40:1 (about average for the day).

Don't get to hung up with the 7.5V. That is a worst case figure which I am assuming for the calculations. Any circuit to drive the coil will have to work from a worst case low voltage (to be defined) to the worst case high voltage- all pretty standard stuff really

By the way, the constant current approach (option #2 in post #24) is better at maintaining the coil secondary voltage as the bike voltage drops.

spec
 
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Pardon me, I didn't mean to get snippy. I'm just try to get my mind around how the bike's inadequate generator is yielding the worst of both worlds;
not enough light,
too much power for the new, improved coil.

Spec, your idea below seems the most straightforward. Your thoughts?

 
I summary,
I've got a small vintage Italian motorcycle with a 6v 60 watts magneto, 8 amp-hr battery, and battery + coil ignition.

I wanted to add a Velleman transistor assisted ignition kit, and use a high performance coil.
Initial theory is that the orig. points are the design limit; they can handle no more than 4 amps. So with the transistor acting as the current relay and taking the load off the points, I could add a high performance coil.

But I'm learning there's a second design limit; there's not enough power to handle both the lights and the improved coil.

Do I have it correctly?


Edit:
Here's some addition data on the high performance coil, from a competitor, MSD. Does the Peak Current figure help in the calculations?

Inductance 8 mH
Maximum voltage 45,000 Volts
Peak current 140 mA
Primary resistance .7 OHMs
Secondary resistance 4.5K OHMs
Spark duration 350 uS
Turns ratio 100:1
 
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You are correct that there is some limitations, like all designs.

To summarize (only my view though):
(1) The bike generator will only supply a maximum of 7.5V/2R= 3.75A which relates to a 2R coil
(2) We do not know how much current either the FT(1.5R) or FT2(0.6R) needs for an effective charge (my unsubstantiated opinion is that both would acquire a full or adequate charge at 3.75A
(3) The Vellerman unmodified will provide 3.75A but it will not handle the increased voltage from the FT (1.5R) (400V) and definitely the not the FT2 (0.6) (450V)

The solution (only my view again):
(1) Whichever FF, add a ballast resistor to make the primary circuit a total of 2R
(2) Find a Darlington transistor that will handle about 15A or over and 500V or over, ideally 600V.
(3) Fit the replacement Darlington transistor.
(4) Increase the Zener chain voltage to 400V (FF) or 450V (FF2) by adding extra Zener diodes to the chain.

And, in essence that is the job done.

The only problem is that I cannot find a suitable Darlington- somebody else might though.

spec
 
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Spec,
Thanks for figuring out the circuit. Is there an alternate way, that doesn't require the unattainable component?
 
sign216 said:
Spec,
Thanks for figuring out the circuit. Is there an alternate way, that doesn't require the unattainable component?
Click to expand...
Sign, yes there is.

Although I could not find a higher voltage Darlington, I did say that I have found a load of NMOSFETs, but this will require some changes to the Vellerman.

But nothing horrific or expensive. If you like I will post an outline schematic showing the circuit so that you can get an idea of what is involved.

spec
 

Please do. The cost isn't the issue. It just that as things get bigger and more involved, there's more points for failure.

Can you show me what modifications the Vellerman needs?
 
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If it were 20 degrees I think you'd be ok, but if your talking 30 then at idle when the on period for the coil is longest it might well overheat.
This is why points ignition coils usually have a higher resistance.

If your thinking of designing/building some electronics then maybe you could consider constant on time for the coil, its tricky to do in software.
 
I'm trying to figure out the purpose of D1, D2 in the Vellerman circuit. Blocking massive negative spikes on the 6V rail? If so, the SMPS is going to need some serious protection.
 
Yes, agree- that is why the current is limited. The answer as to whether the coils will be happy dissipating 30W (360 deg dwell) will come from the manufacturer.

The coils that I have messed with will take 30W without objecting and remember that, when an 8 or 12 cylinder engine is running at maximum RPM, the coil is being fired with little time to cool off between sparks and when the coil is delivering a spark it is subject to heating from the pulse it generates and the power demanded by the plug when it arks over.

For my money the best approach would be CDI and with a switching element that can be controlled off, BJT, MOSFET, IGBT, GTO thyristor, it would be relatively straight forward.

CDI would give the best spark and lowest coil dissipation coupled with lowest current drain on the bike generator (magneto). It is a win, win ,win approach.

spec
 
alec_t said:
I'm trying to figure out the purpose of D1, D2 in the Vellerman circuit. Blocking massive negative spikes on the 6V rail? If so, the SMPS is going to need some serious protection.
Click to expand...

I am fairly certain the two diodes, coupled with the VBE of the 2N2222 driver transistor give around 1.8V stand-off voltage to prevent false trigging from contact bounce and any hash around the input. A Schmitt trigger monostable timer would be much better.

By the way in case anyone is wondering about the low value pull-up resistors connected to the points, they provide the cleaning current for the points.

I did a CD ignition for someone who thought they knew better and replaced the low value resistors with a 1K Ohm resistor. He then complained that the engine misfired at time and that the CD ignition I had done was no good. I won't tell you what I said after a long investigation to find the problem.

spec
 
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Below is a list of likely candidates for the high-voltage, power NMOSFET in the ignition system of post #53

spec

​
 
Spec,
Thank you for that. Let me chew on that in comparison to the Velleman diagram, to make sure I understand everything.
About the two Ebay units, one looks like a voltage "step up" and the other down. Are they possibilities for the SMPS module at the top of the diagram?
Can I trust buying modules off Ebay?

The list of NMOFSETs, they are for the element between R9 and R10?

I've started a service ticket communication for the coil specs, with the coil manufacturer, and will let you know their reply.
 
Hi Post

sign216 said:
Spec,
Thank you for that. Let me chew on that in comparison to the Velleman diagram, to make sure I understand everything.
Click to expand...
No sweat.

There is not a big difference between the schematic of post #53 and the original Vellerman circuit although I have used a slightly different layout to clarify the operation of the circuit.
sign216 said:
About the two Ebay units, one looks like a voltage "step up" and the other down. Are they possibilities for the SMPS module at the top of the diagram?
Click to expand...
Yes, but remember that the schematic of post #53 is only an outline to establish feasibility and give you an idea of the extent of the work involved and the cost. It is definitely not a circuit to build at the moment.

The power modules input the varying voltage from your bike's battery/generator (magneto) and output a constant stabilized 12V power line.
sign216 said:
Can I trust buying modules off Ebay?
Click to expand...
Yes, I use them all the time. But once again, those power modules are just examples. You can procure the final modules from any source you like- the choice is endless. Besides, the power module is not doing much. Also the guts of many modules are similar, if not identical, to the eBay modules.

I have an encapsulated metal-can power module in mind, but but did not have time to find it last night.

sign216 said:
The list of NMOFSETs, they are for the element between R9 and R10?
Click to expand...
Yes, the list of potential MOSFETs, in post #58, are contenders for Q2 in the schematic of post #53. But once again, remember that, although I have done an initial analysis of the NMOSFETs, I have not done a detailed analysis.

There are other candidate NMOSFETs too.
sign216 said:
I've started a service ticket communication for the coil specs, with the coil manufacturer, and will let you know their reply.
Click to expand...
Excellent. Lets hope we get a positive response from the FT manufacturer.

spec
 
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