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

Discussion in 'Electronic Projects Design/Ideas/Reviews' started by sign216, Jan 12, 2017.

  1. sign216

    sign216 Member

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    I'd like to modify Velleman's transistor assisted ignition kit, so that it can be used with a modern high performance ignition coil. This would put 8.6 amps to the kit's transistors (2N2219A and TIP162 or BU319P). Can these transistors take it?

    The kit is designed for an induction ignition coil for breaker points, approx. 1.5 to 3.0 ohms, which limits current to 4 amps.
    12v / 3 ohms = 4 amps
    The 4 amps limit is for the breaker points, which erode under higher amperage.

    The transistor kit makes the breaker points a mere switch, with the transistor handling the real load. With the points gone, I can use a modern high performance coil (0.7 ohms). A high performance coil gives more spark to the spark plug, a real benefit. But then the kit is taking over it's 4 amps design.

    My vehicle is an antique motorcycle with a 6v system, so the kit would get 8.6 amps instead of 4 amps.
    6v / 07. ohms = 8.6 amps

    On the Velleman forum a company representative replied to this question some time ago. They said two things;
    1. The kit has a max input of 4amps. This limit is controlled by the transistor rating.
    2. The kit was designed 30 yrs ago by a man who's no longer present, so they can't answer many technical questions.

    Can the kit's transistors (2N2219A and TIP162 or BU319P) handle 8.6 amps?

    Joe
     

    Attached Files:

  2. spec

    spec Well-Known Member Most Helpful Member

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    Hi Sign,

    Your opening post is one of the best I have seen- full of the important information which makes answers much easier for us.:cool:

    After an initial look-see, I would say that it is possible to modify the Velleman ignition system to handle the later high current, high performance coils.

    It is getting late here, but I will investigate further tomorrow.

    I'm sure other ETO members will also have some ideas.:)

    spec
     
  3. Pommie

    Pommie Well-Known Member Most Helpful Member

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    Welcome, ST make a few darlingtons that could be used. The BU931 is almost designed for your application and available in TO-247.

    Mike.
     
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  4. dave

    Dave New Member

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  5. MikeMl

    MikeMl Well-Known Member Most Helpful Member

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    Wishful thinking? Do you have any real evidence that this is so?
    If a spark is enough to ignite the fuel-air mixture in an IC engine, why is a bigger spark better?
     
  6. spec

    spec Well-Known Member Most Helpful Member

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    Hi Sign,

    In addition to the power Darlington transistor, you also ask if the circuit in general, and specifically the 2N2219A would be up to the job. The answer is yes from a reliability point-of-view. Your main concern is obviously reliability, but there is another aspect: will the Velleman K2543 be able to drive the new coil to its full potential. Two areas which need analysis are:

    (1) The two 150V catching Zener diodes may limit the output voltage from the high performance coil.
    (2) The driver circuit may not be capable of providing sufficient voltage and current to drive a more rugged replacement output transistor. In general, higher-power Darlington transistors have lower current gains and the more current that a Darlington transistor conducts, the more base voltage it needs and, by definition, the current will be around twice the deign specification of 4A anyway.

    None of this should be a show stopper, but as a result on an analysis more modifications may be necessary to realise the potential improvement of the new coil.

    spec
     
  7. dr pepper

    dr pepper Well-Known Member

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    Beware of one thing, modern ignition coils tend to be constant energy, the on time is fixed (to that of what it would be at max revs), if you were to use one of these on an older points type ignition you run the risk of saturating the coil, which would significantly increase current draw possibly burning out the coil.
     
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  8. spec

    spec Well-Known Member Most Helpful Member

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    Hmm- an excellent observation.:cool:

    spec
     
  9. sign216

    sign216 Member

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    Spec - thanks for the kind words on my initial post. You also pointed out that the Zener diodes and the driver circuit may end up limiting ouput. That analysis is beyond me (which I why I posted), but I'm happy to swap the kit's components for higher capacity ones if this board recommends it.

    Mike - thank you finding a suitable replacement transistor, BU931. It looks much better than the one that came with the kit.

    MikeMi - You correctly opined that "more spark" at the sparkplug doesn't do anything. Just need enough spark to bridge the plug's gap, and that gives ignition. You're right, but this is an antique kick-start motorcycle. Extra capacity allows for ignition even under poor conditions; fouled plug, drained battery, eroded points, wet wires, etc. Don't want to be stuck on some lonely road.

    Dr Pepper - You pointed out that modern coils are constant energy, with an "on time" equal to max rpms, and I could end up burning out the coil. This is beyond my expertise, but I think I'm safe, in that this is a small 350cc motorcycle, and aftermarket performance coils are usually designed for larger bikes or cars. My bike has a 6v 60 watts magneto and a 9amp-hr 6volt battery, and an aftermarket coil should be safe w the limited system. But this raises another question; is it possible that the system won't adequately charge a larger performance coil?

    Thanks in advance. I await your analysis,
    Joe

    [​IMG] MWdiagram1.JPG MWdiagram1.JPG
     
  10. spec

    spec Well-Known Member Most Helpful Member

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    Hi Sign,

    No problems about help.

    The characteristic of the spark can have a radical affect on engine performance, but it very much depends on the type of engine. A high capacity 'lazy' engine would normally be less affected.

    The fact that the spark is important is evidenced by the availability of high performance sports coils.

    But there is also a vast area of study of combustion in internal combustion engines, and the spark plug and spark characteristics play a big part. Some engines even have two spark plugs, not just for safety, but to improve the flame propagation and to encourage a more complete burn.

    And on some older piston aircraft you get 'mag drop' where the engine RPM drops when you turn one of the magnetos and hence plugs off. This was used as a quick and dirty test to ensure both magnetos and the other ignition components were working.

    I have designed and commissioned a number of ignition systems, and going from a traditional Kettering system to capacitor discharge, on the same automobile, brings a noticeable improvement in the torque and general running of the engine.

    There is an inherent problem with the traditional ignition system, which works by charging the coil during the dwell time (points closed) and releasing the energy as a high voltage spark when the points open.

    This works OK at low RPM, but as the RPM increases there is less and less dwell time and thus less charge in the coil and thus less spark energy. And this is made worse by points bounce which further eats into the dwell time. So at high RPM, right when you need a high energy spark, the energy in fact drops off. This is where low resistance (& inductance) coils help because they charge more quickly.

    DP raises an important point- if the coil is designed for constant energy or CD (same effect) you could well overheat the coil as DP says.
    There would be two approaches to fix this:
    (1) Convert your ignition to constant energy- this would involve fitting a timer which is not as complex as you may think.
    (2) Limit the current to the coil. This could possibly be done with a ballast resistor as is fitted to some coils.

    Of course the fact the your bike has a 6V system, rather than 12V helps a bit, but the current is still high at around 8A.

    Is it possible to get a data sheet for the new coil that you plan to use?

    I hate to say this, but for a Rolls Royce job you would be far better off going for a contactless CD ignition system (no more starting problems, no more points bounce, and no more points adjustment/replacement)

    By the way, what is the bike (Honda 250cc)?

    spec
     
    Last edited: Jan 13, 2017
  11. dr pepper

    dr pepper Well-Known Member

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    Hi again,

    Its still possible to kill a coil despite your circumstance.

    In engine speak you need a coil that will withstand the dwell angle of your ignition, or a coil that is designed to work with a points system should be fine, some electronic ignition coils will also be fine, so long as they are ok with the dwell angle of your bike.
    You can take a guess at dwell angle by fitting the points and turning the engine, dwell time is the angle the points are closed for.

    Nice looking motor, I nearly bought a matchless that looked a bit like that a while back.
    I wish vehicles these days were as simple as that electrically, they have about 15 schematics these days.
     
  12. MikeMl

    MikeMl Well-Known Member Most Helpful Member

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    Exhaustive forum thread on this topic...
     
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  13. sign216

    sign216 Member

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    Spec,
    - I'd like to use PerTronix Flame-Thrower II coil. It's data is at the bottom of this page: http://pertronix.com/catalogs/pdf/ptx/2015/ptx2015_coils.pdf
    Does this information shed any light on the coil's robustness for this?
    - CDI or other breaker-less ignition is more efficient, but I'm just looking to "enhance" the performance, without completely doing away with the stock components. A transistor-assisted ignition has an other advantage over CDI; flipping a switch you can go back to the original points set up. A real boon if the new electronics fail on the road.
    - The bike is a 1969 350cc Wards Riverside single cylinder, made by Benelli of Italy. They were sold in the USA by mail order, with the motorcycle disassembled into major components. The buyer would get a big box, and put the bike together.

    Dr Pepper,
    I checked the manuals, but no mention of dwell at all. Tonight I'll physically measure it off the breaker cam.
    And I agree, the old wire diagrams are a pleasure compared to newer vehicles.

    MikeMI,
    - That thread attacked a different problem; whether transistor-assisted ignition lived up to it's promise of a more powerful spark. Remember the hype in the 1960's and '70s, on how this new ignition add-on boosted power, fuel mileage, etc? Forum members showed with the original ignition system, the transistor assist did little to boost spark. All it did was add life to the points.

    - My question here, is how I change the kit to allow for a modern low resistance coil, and truly get a more powerful spark? I've looked at pre-made transistor amplifiers, but usually they warn off a change of coil. You are stuck. With a Velleman kit, you can upgrade components and performance (I hope).

    Joe
     
  14. spec

    spec Well-Known Member Most Helpful Member

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    Hi Sign

    Hmm, some very juicy coils in that data sheet- thanks for that.

    The coil resistance of the Flame Thrower II is 0.6 Ohms, and the bike's voltage, when the alternator is running, would be around 7.5V, perhaps higher.

    That means that the maximum current in the coil primary would be 7.5V/0.6 = 12.5A

    The power dissipation in the coil primary would thus be, 7.5v * 12.5A = 93.75W

    This is too much heat for comfort, but even if the coil will stand that heating, it is highly undesirable from a reliability point of view.

    This high current would also load the bikes alternator excessively

    So the conclusion is that your Vellerman K2543 will need a timer to generate a constant dwell.

    In addition, the the coil's turns ratio is 100:1 which, with a 45KV output, means a primary voltage of 45KV/100 = 450V, but a 600V minimum output transistor would be advisable.

    With a fixed dwell the transistor current may not be too high- I haven't worked it out yet
    You could have both CDI and conventional ignition and change over just the same. :cool:
    Thanks for info. A 125cc Benelli was one of the first bikes I rode in the 1960s- one of our biker gang had one. I had a 250 Matchless G2.:)

    (1) Change the output transistor for a more powerful version with a much higher voltage capability and current capability. A MOSFET or IGBT may be suitable rather than a Darlington BJT.
    (2) Increase the Zenner voltage chain to 450V total, or use another voltage catching approach
    (3) Add a fixed dwell timer (LM555 for example)

    And that is all there is to it: nice big fat spark giving good performance and easy starting, no stress on the output transistor, low current drain on the bike alternator/battery, and high reliability (famous last words).:D

    spec
     
    Last edited: Jan 13, 2017
  15. sign216

    sign216 Member

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    Spec,

    A Matchless G2 250, I am jealous. That's coveted over here in the US. Vintage British bikes have a strong following, although your non-system of Whitworth/English/Metric bolts back then is tough to swallow.

    I like your ideas on the ignition system, but I'm a babe-in-the-woods, and don't know how to incorporate them into the kit.
    When you get a moment, could you guide me?

    Joe
     
  16. spec

    spec Well-Known Member Most Helpful Member

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    Hy Sign,

    I think my bike had every thread imaginable: Whitworth, BSF, AF BA.

    Yes, old Brit bikes are worth a fortune here too. But I remember the time, in the 1970s, when you couldn't give Brit bikes away.

    I sold my G2 for about £165UK in today's money and all the aluminum parts were hand polished too.:)

    At the same time you could get a nice Truimph Thunderbird 650cc for £950KUK equivalent.
    Don't worry about that. It can all be sorted.

    I presume you are OK with soldering and that kind of stuff.

    spec
     
    Last edited: Jan 14, 2017
  17. spec

    spec Well-Known Member Most Helpful Member

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    I have just had a look at providing a fixed dwell period and it is a bit more complicated than I first imagined, but nothing that Les or one of the other ETO boffins can't sort.:cool:

    spec
     
  18. sign216

    sign216 Member

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    Soldering is no problem, but I'd like to avoid building a NASA style circuit board.
    Is there another way of protecting the coil from overheating?

    I'm still surprised this is an issue. Remember how inadequate the generators are on these old bikes? The lights go dim at idle.


    Not that it matters, but the original coil is 2.0 and 6.8k ohms for the two internal spools.
     
  19. spec

    spec Well-Known Member Most Helpful Member

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    Good :)
    There may be: I am thinking about it.

    Yes, I remember well. Not only dim lights on tick-over but boiled batteries and blown light bulbs at high speed (82.5MPH). There was a whacking great Zener diode under the seat. The adverts for the bike made a big thing of this new 'Zener technology'.:D I remember being well impressed at the time.


    Hmm that would be 7.5/2 = 3.75A which is 3.75 * 7.5V = 28W (about normal I would say)

    I don't think you could rely on the bike voltage sagging to protect the coil, but may be possible.

    Of course the thing to do, would be to contact the manufacturer of the new coil and ask about your proposal, or at least get the maximum power rating for the coil.

    If push comes to shove, we can always put a power resistor (1 Ohm) in series with the coil primary.

    spec
     
    Last edited: Jan 13, 2017
  20. spec

    spec Well-Known Member Most Helpful Member

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  21. spec

    spec Well-Known Member Most Helpful Member

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    Hi Sign,

    I think there is a fairly simple way to use the Flame Thrower II 45KV (0.6 Ohms) coil with a modified Vellerman ignition switch, but I suspect that the Fire Thrower 40KV (1.5 Ohms) would be a better choice. 40KV would still be vastly higher than the standard coil on your bike, so you should still get the same benefits.

    With the Flame Thrower 40KV the mods to the Vellerman ignition switch would be pretty straight-forward.

    If you do want to go with the Flame Thrower II 45KV (0.6 Ohms) just say and I will post a suitable circuit.

    spec
     
    Last edited: Jan 14, 2017

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