Author Topic: Making your own ignition system when you have too... CDI  (Read 11884 times)

0 Members and 1 Guest are viewing this topic.

Offline oztules

  • Moderator
  • Hero Member
  • *****
  • Posts: 1177
  • Karma: +105/-8
  • Village idiot
Making your own ignition system when you have too... CDI
« on: February 25, 2012, 02:39:53 am »
Part of remote living I think is beating the elements, and the things that crop from them.... sometimes they are just a nuisance, and some times the trials are almost life and death.... this story falls into the latter category.... very serious.

One of the important things of course is muscle relaxants, and free radical potions designed to help lower your cholesterol.... you know what I'm talking about of course.....WINE.... acres and acres of it.

There is a small winery near Whitemark, that produces red and pinot and chardonnay.

You cant do this unless you have grapes.... bigger and juicier the better. But this year we had unseasonal warm humid periods and this of course fosters fungal growth. Downy mildew to be more precise..... so what you say.....

Well the spray unit that does this important job, started to run for short periods, and then stop... cool down and then start again... then it was erratic. It had no markings of what kind of engine it was, but it was an industrial 2 stroke... we think a solo.

Long and the short of it was it needed a new electronic ignition system, but we couldn't get one for a start, and time was important. Waiting for a unit from Europe was problematic... the grapes would suffer.... and then I would suffer.

It was a simple CDI, with a single pickup, a black box and coil pack combined, and a spark plug. There were a couple of ducati cdi units on the island, but they all required a 2 coil system..... so I decided to make my own from the ground up type of thing.

The outline was straightforward.

On the rising wave form from the one coil, we would store the output in a capacitor, and when the waveform changed direction... at a point of our choosing, we discharge it into a coil... and make a spark... simple...particularly if you say it quickly.

The scr needs to be sensitive gate, as the currents are small at startup. The first thing was to steal the battery charging coil from under the flywheel, and use that as our CDI charge coil. This unit has no battery anyway.. or lights etc. It is superfluous to requirements.

I unwound the few hundred turns of thick wire, and rewound over a thousand turns of fine wire from a microwave secondary.... and it looks like this:
612-0

Being symmetrical, we can turn it over if the pulse is negative going from the start. We want the positive waveform to charge the cap BEFORE we discharge it with the negative wavefront.

Now that was the easy part, the next bit is the circuit... which as usual now it is all over, I don't have the scribble bits that I transfer into Protel pcb maker, but it looks like this, and if you want you can draw the circuit.
621-1
CLICK TO GET A BETTER VIEW

Next was a coil from a car down at the tip (dump), and presto, a complete CDI ignition system, which if you had to, could make any single cylinder engine run at a pinch... Briggs, Honda whatever. It may be the thing that will help you out of a hole... water pump or whatever. Because I have used too much capacitor (space was not at a premium) the darn thing starts at about half a rope pull. It is way better than the original... you  just have to look at the rope, and it starts almost. ;D

The coil primary hooks onto  to where it is marked (pins 46 and 47 note polarity), the coils secondary is earthed (usually body of coil). The coil input  (primary)goes to the input pads (pins 49 and 50)...... and the HV secondary out goes to the sparkplug....simple stuff indeed.


In my case, as I have saved the vineyard.... you can guess what I'll be doing when they ripen..... picking, processing.... and drinking last years vintage as we bottle it.....



Hic... Hic


.....................oztules
Flinders Island...... Australia

Offline artv

  • Jr. Member
  • **
  • Posts: 47
  • Karma: +1/-1
  • No Personal Text Set by User
Re: Making your own ignition system when you have too... CDI
« Reply #1 on: February 25, 2012, 05:49:39 pm »
Hi  Oztules,....this thread is completely over my head but am very interested in the part about storing the postive part of the ac.
You can build a circut that can do this???
I would be very interested it getting one of these, would gladley pay for it.

Oh and thank goodness you saved the grapes ;D........artv

Offline oztules

  • Moderator
  • Hero Member
  • *****
  • Posts: 1177
  • Karma: +105/-8
  • Village idiot
Re: Making your own ignition system when you have too... CDI
« Reply #2 on: February 25, 2012, 06:29:30 pm »
If you look at the board, you can see how this is done. When the positive wave arrives at pad 50 it goes through the diode going to pads 2.

So we store the charge, when pad 50 becomes negative, pad 49 becomes positive, ad we take that through a different diode and feed it to the gate of the scr through a zener via a small filtering circuit

This triggers the SCR and it shorts pad 92 to 93 which places the caps directly across the primary of the ignition coil.

I don't think this will be useful for what your thinking about.

However, I will do an article on real low impedance electric fences shortly ( not the toy high impedance ones with an ignition coil), and this is very much the same, kind of storage discharge cycle, but with more control.
You may find you can use that technology much easier to store charge and discharge your energy.

This charge and discharge will give you a massive increase in instantaneous power for a given energy... but it will not give you more power over time... it will be less... unless you can use it to match the load better, and that may be of benefit... but only with a stalling prop... not on a bench test I wouldn't think. Your losses because of the larger  currents involved will be worse as well.

I don't think you want or could use one of these for windmill work.. at all.



.....................oztules
Flinders Island...... Australia

Offline Norm

  • Sr. Member
  • ****
  • Posts: 475
  • Karma: +26/-0
  • Today is the day you worried about yesterday.
Re: Making your own ignition system when you have too... CDI
« Reply #3 on: February 26, 2012, 07:35:32 am »
I had a LawnBoy mower once ....wouldn't start because of no
ignition.....solid state ....sensor to tell it when to fire.
Even sensed when the motor had started (signals arriving quicker)
and electronically advanced the spark.

I concluded that moisture had gotten into the coil, so I left it out
in the sun for a day.....sure enough that fixed it .....temporarily,
but the next week it wouldn't start.
I repeated the fix but the second time, I sprayed it with clear lacquer
a couple of times and then it started every time.

Could have just got a new coil....but $60-$75.....No WAY !
Norm.

Offline oztules

  • Moderator
  • Hero Member
  • *****
  • Posts: 1177
  • Karma: +105/-8
  • Village idiot
Re: Making your own ignition system when you have too... CDI
« Reply #4 on: February 26, 2012, 01:58:33 pm »
Over here when I was still playing in industry.... we had to pay silly amounts for a cdi coil assy for Honda and Briggs and Tecumseh... $170 and upwards... You blokes are spoilt.

I like the evil simplicity of the fix though Norm.

I had hoped that maybe this article would demystify these things to most folks. They are simply simple things, over priced to hell because no-one knows what's inside them..... and easy to make in a pinch. (thinking Ghurd on a lake with a chinese outboard could use one of these)

You can make them better than the original, with more punch,and easier starting.... seemed like a good idea at the time. :o



.................oztules

Flinders Island...... Australia

Offline Norm

  • Sr. Member
  • ****
  • Posts: 475
  • Karma: +26/-0
  • Today is the day you worried about yesterday.
Re: Making your own ignition system when you have too... CDI
« Reply #5 on: February 26, 2012, 04:12:15 pm »
I used to work mostly on Briggs....the ones with points never worried
about the coils...they could be rusted and the segments spread apart
and they would still work points would be pitted and I'd just file them.
 ....of course if it was a tune-up for a customer they'd get new points
and a plug.
 You can make them better than the original, with more punch,and easier starting.... seemed like a good idea at the time.[/
and it is a good idea.
Norm.