Model engine CDI easy and cheap

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bluejets

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Model engine CDI easy and cheap.

Many years ago, I started making transistor assist ignition for model engines running rather large coils from motorcycles operating on the Kettering system (points,condensor, battery and coil).

These changed through the years as the learning curve advanced.

I built transistor assisted Kettering, hall effect, and small basic cdi units, adding microcontrollers etc. etc. all labour intensive and requiring differing levels of learning.

I saw these small motorcycle coils years ago (GY6 style) and this removed any need for building homemade coils.

GY6 is 30mm dia x 50mm long weight approx 50g.

Cheap too, a bonus at around $7.00 and the only mod was to remove the large HT lead and replace with something more scale-like but still practical.

The cable used is around 4mm diameter, rubber insulation, Belden 8899-010 Black.

These ignition coils were not designed for Kettering style so started the road to CDI.

Making one's own CDI units does work but they have limitations, namely getting enough power into the capacitor in an ever-decreasing time, increasing rpm. plus of course the time involved in building, programming etc. etc.

One's I built here were successful for single cylinder engines turning around 8,000 max. which even had electronic advance map built in to the microcontroller.

I like to build engines primarily. With electronics, if nothing is available it can be built quickly using modules. The latter is a great thing these days being cheap and relatively reliable into the bargain.

I noticed the "DC CDI units" a couple of years back. These are the type that makes use of power from a 12v battery and the high voltage energy required to charge the internal capacitor is generated within the unit. Also cost $7.00 approximately. (and that, in Aus at least, is delivery included, unbelievable really).

Small totally encased box 70 x 40 x 25mm weight around 120g (4 oz.).

I knew they were triggered by a pickup coil generating basically a sine wave (ac signal) in which the first rising wave was used (eventually) to trigger the internal SCR.

As the commercial pickup unit was LARGE for model use, I began to experiment with the use of a very small relay and modified it to give the correct trigger.

This worked a treat and even though the size was now acceptable at around 15x15x15mm, it still required some refining. That was over 1 year ago and the other day, dragged everything out once again for another "go".

Hall effect is a great thing BUT as it stands it will not trigger as required. It turns out that by adding a simple single inverter transistor circuit with a small modification to allow a "one pulse signal" was the key to the problem.

If one wants to use the old points approach, I have another add-on for that as well in the form of another single transistor and a slightly larger pc board. In this version, the points with a grounded frame as original, on opening will give the one pulse required to the CDI unit trigger input.

The last couple of weeks have been spent making the modification as simple as possible with as simple as possible parts. Strip type Veroboard seemed the logical approach and most should either have no problem working with it or at least know someone who can help.

I have also been using a hall effect module available on eBay at 5 for $3.00 approx. which saves a lot of mucking around. George has made a 3D plastic casing/mounting for the hall effect module so I imagine the files will be available if required.

Testing the unit at this stage has been done using a test bed I made up many moons ago, but final proof will be testing on an engine. George almost has a3-cylinder I.C. ready for such a test so fingers crossed. I cannot foresee any real problems given they were designed initially for the small motorcycle market.

Total cost for the complete system is around the AU$20.00 mark which is pretty good for any ignition system, let alone a CDI. I have an idea there may also be an amount of electronic advance built in to these units but only further tests will prove if this is the case.

The pre-built parts are easily obtained and cheap with the small modification pc board easy for most to build.

So, if interested, I'll post more detail in the form of a pdf file on the build. Any testing we do I can add later.
 

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bluejets

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Hi Ron,
Currently doing the write up with diagrams etc. and should be finished by the weekend.
In the meantime I'll pop some links in here to the parts currently available at what I found to be near to the lowest cost.

GY6 ignition coil
https://www.ebay.com.au/itm/Racing-Ignition-Coil-for-GY6-ATV-Go-Kart-Moped-Scooter-50CC-125CC-150CC/183109938606

4 pin DC CDI Unit ....important to note there are a few different types such as 5 pin AC but if one quotes the 4 pin DC CDI , all ok.
https://www.ebay.com.au/itm/4-Pins-DC-CDI-Ignition-Box-For-90cc-100cc-110cc-PIT-Quad-Dirt-Bike-ATV-Buggy-HT/113693555335?hash=item1a78a9fa87:g:y~QAAOSwxLVa86yR

KY-003 Hall effect module ( 5 )
https://www.ebay.com.au/itm/5PCS-KY-003-Hall-Effect-Magnetic-Sensor-Module-For-Arduino-PIC-AVR-Smart-Car-EW/264066092323?hash=item3d7b90cd23:g:s6cAAOSwutFZfua-

6 pin connector ....yes, I know I said 4 pin CDI but there ya go, 2 pins are not used and all reference is to 4 pins.
Don't have to use this as wires could be simply soldered to the CDI connector if you want to do it that way.
https://www.ebay.com.au/itm/2-9-Pin-Male-Female-Wire-Connector-Plug-Socket-Pit-Quad-Dirt-Bike-ATV-Scooter/182919740250?var=690232623303

And finally the strip veroboard to make up the small inverter board that goes between the hall module and the trigger input of the CDI unit.
https://www.ebay.com.au/itm/5x-6-5x14-5cm-Stripboard-Prototyping-uncut-pcb-platine-Single-Side-circuit-board/222747969213?hash=item33dcd046bd:g:B4UAAOSwi0xaKPaO&frcectupt=true
 

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mnay

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It looks like those are also available in the US on ebay. I would also be interested to knowing how to connect them. Seems like a very inexpensive way to build a small ignition. Would appreciate the information also.
thanks for your help.
Mike
 

bluejets

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The hall effect module as purchased will not operate the CDI Unit as is.
A small single transistor inverter/pulse board is added to make it work. (details added )
This is simple enough for most to do and building on a piece of strip veroboard I thought the easiest way to go in respect of pc boards.
I'll also include the overall circuit diagram below.
 

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Johno1958

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Thank you .This is very interesting.
John
 

bluejets

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Did the write up for the points version of the ignition , never know, could be of interest to someone. see below.

Currently doing the details on how to use the hall effect with a couple of different variations and then there will be the original inductive pickup which started all of this.
Thanks for the interest.

Cheers Jorgo

PS....forgot to mention originally, with the hall effect system, the ignition fires when the magnet approaches the hall effect.
 

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tornitore45

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The CDI for mopeds needs a bipolar trigger. The CDI give a spark when the trigger voltage goes positive but needs to see a negative voltage to arm before the next positive pulse for the next spark.
The typical Hall effect output is an open collector swinging from GND to VCC+ and repeating. Never goes negative.
A simple C-R network to differentiate the signal will remove the DC component and output bipolar pulses. That is what I have done and work fine.
Make the time constant 1/2 of the shortest spark period. Account for the input resistance but is usually high enough, 10 to 20 Kohm
 

bluejets

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The CDI for mopeds needs a bipolar trigger. The CDI give a spark when the trigger voltage goes positive but needs to see a negative voltage to arm before the next positive pulse for the next spark.
The typical Hall effect output is an open collector swinging from GND to VCC+ and repeating. Never goes negative.
A simple C-R network to differentiate the signal will remove the DC component and output bipolar pulses. That is what I have done and work fine.
Make the time constant 1/2 of the shortest spark period. Account for the input resistance but is usually high enough, 10 to 20 Kohm
Thanks for the input, however, as I said first up, there are many different variations on CDI unit types available.
The particular one I use is 4 pin DC unit and is working fine as is with the circuits supplied.
 

bluejets

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Some info on different type of CDI units in common use that I found on the internet back in the beginning.
 

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michelko

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Hi, this is an
realy
interessting write up. Thank you.

Michael
 

mnay

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thanks for sharing this information. Great alternative to the expensive units.
Mike
 

Foketry

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Thanks for the input, however, as I said first up, there are many different variations on CDI unit types available.
The particular one I use is 4 pin DC unit and is working fine as is with the circuits supplied.
Very very interesting your application of an industrial CDI for scooters
I liked this idea and bought a 6-wire CDI GY6 with advance adjustment because for a multi-cylinder engine, for example 4 or 8 cylinders there are 4-8 pulses per revolution instead of just 1 pulse and the advance becomes incorrect already at a few engine revs
https://www.amazon.it/dp/B07PHV6VQC/ref=cm_sw_r_oth_tai_bSPnDb7P0KX8M
I connected this unit with its trigger pickup and it works very well , with the adjustment trimmer I can bring the advance to zero
http://s.aliexpress.com/EZrIvmiE

I built your circuit to drive the CDI with Hall sensor, but it doesn't work with this CDI, maybe I was wrong or, as Tornitore writes, another type of circuit is needed ?

Can you give me some suggestions ?
thank you
 

editor123

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Not to blow my own horn but we published an excellent ignition system in Issue # 34 of Model Engine Builder. David Sage and John Gedde are the designers. It will handle a V-8 up to around 10,000 RPM. Within the Bay Area Engine Modeler's Club, there are probably 30 of those systems operating with no failures (except for the one builder who bound the Hall Effect Sensor and secondary ignition wires together). The circuit turns off after a short time of non operation so the battery doesn't discharge and the coil won't burn out. Most of us use the Ford Coil Over Plug coils because of their reliability and low price (about $5 each in lots of 8). This is not a CD ignition system, it has no spark advance, it is just a very well thought-out circuit. The entire circuit is shown mounted on a battery box for an engine box. The white connectors are temporary as I work out the details of a completely 3D printed distributor for 2-8 cylinder engines.
Under box ignition and battery.jpg
 

Foketry

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I carefully read the post published by Egge in this forum and I built the circuit following the project attached to the post.
In Italy it is not possible to buy the FORD coil, I had to use a coil for scooters but the absorption from the battery is very high, about 3 A. The battery must be large and I cannot hide it under the engine base.
Instead the CDI mentioned in this tread absorbs max 0.5 A and with a small Lipo battery it is possible do dozens of engine starts.
Now my problem is that I failed to make the circuit for Hall sensor

thanks for the info Editor
 

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bluejets

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Very very interesting your application of an industrial CDI for scooters
I liked this idea and bought a 6-wire CDI GY6 with advance adjustment because for a multi-cylinder engine, for example 4 or 8 cylinders there are 4-8 pulses per revolution instead of just 1 pulse and the advance becomes incorrect already at a few engine revs
https://www.amazon.it/dp/B07PHV6VQC/ref=cm_sw_r_oth_tai_bSPnDb7P0KX8M
I connected this unit with its trigger pickup and it works very well , with the adjustment trimmer I can bring the advance to zero
http://s.aliexpress.com/EZrIvmiE

I built your circuit to drive the CDI with Hall sensor, but it doesn't work with this CDI, maybe I was wrong or, as Tornitore writes, another type of circuit is needed ?

Can you give me some suggestions ?
thank you
Hi Foketry,
Didn't get in to the 6 pin versions but I did supply full details of many of the different system that were available including my 4 pin version.
So I have really no idea of what you might have done to try to get a 6 pin version operational.
I'll include the file on the different types here once again as trying to find these things sometimes can take a lot of trowling though posts.
 

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editor123

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I should also mention that the ignition circuit will also trigger from points or a reed switch. Both are nearly indestructible. The reed switch will function very nicely for single cylinder farm-style engines. Triggers with a magnet just like a Hall Effect Device.
 
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