Author Topic: Transistor ignition  (Read 10498 times)

Offline GordonL

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Transistor ignition
« on: January 24, 2015, 05:45:35 PM »
I have been playing around with transistor ignition systems lately and have not been having too much luck. I have tried the simple with just a single transistor and the more complicated circuits with two transistors and resistors etc like the TIM-4. A couple of years ago I purchased the Jerry Howell kit. On the single transistor circuit I can get a weak spark sometimes. On the TIM-4 I get nothing. On the Howell I can make the LED light but no spark. I have traced the circuit several times and cannot find any wrong connections. I have tried several different coils from one I purchased from Howell to coils from automotive coil over plug etc. Nothing seems to work. I am using 4 AA batteries for power.

I realize that no one can analyze a problem without seeing the equipment but does anyone have suggestions on what I can/should be checking for? I am not an electronics expert but it seems like sooner or later something should work. Others talk about using these circuits and have spark jump 1/2".

Thanks: Gordon

Offline Roger B

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Re: Transistor ignition
« Reply #1 on: January 24, 2015, 05:50:20 PM »
Hello Gordon,

Can you give a few more details? Are you using contact points or a Hall Effect sensor? What sort of automotive coil did you try? Can you add some pictures/diagrams? A photo of a hand drawn sketch is fine.
Best regards

Roger

Offline gbritnell

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Re: Transistor ignition
« Reply #2 on: January 24, 2015, 06:44:43 PM »
Hi Gordon,
I have built the Howell ignition from the supplied kit and have 4 of them and they all work great. Like you said it's hard to diagnose on a forum but I would go back and check all your solder connections and locations. What are you using for a trigger, points or a Hall transistor? If you hook up a Hall wrong they will burn out in an instant.
gbritnell
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Offline Roger B

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Re: Transistor ignition
« Reply #3 on: January 24, 2015, 06:49:11 PM »
Are you using 'normal' or rechargeable AA batteries? AA batteries are certainly not sufficient for an automotive coil. I am using a 6V motorbike coil with a 6V 6AH sealed lead acid battery.
Best regards

Roger

Offline Don1966

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Re: Transistor ignition
« Reply #4 on: January 24, 2015, 07:16:36 PM »

The TIM 4 has a large diode with a band on it, make sure that this band is facing the correct direction by looking at the direction you were given to assemble it.
Gordon you need to place a voltmeter across the ignition coil with clips to measure the voltage across it. Use a jumper to trigger the circuit after removing any trigger devices you have connected and look at your voltage reading. The directions show how to trigger the module with points, place your jumper across these terminals. the meter will not be 6volts but at least 5 or more only when you trigger it. This will tell you if your ignition module is working.
If you have voltage all the time the large transistor could be shorted.

Regards Don

Offline PStechPaul

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Re: Transistor ignition
« Reply #5 on: January 25, 2015, 01:40:12 AM »
Here is a simulation of an electronic ignition that I am (still) planning to build, and the schematic for yours should be similar. This circuit uses stored energy in the inductance of the coil which is released when the points open, and the voltage is limited by the primary capacitor and a TVS limiter:



There are also capacitive discharge types that charge up a capacitor to several hundred volts (using a circuit similar to photoflash units), and then dump it into the coil primary. If you can provide a schematic or pictures of what you have it will help greatly.

Offline GordonL

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Re: Transistor ignition
« Reply #6 on: January 25, 2015, 09:56:56 PM »
Thank you for the replies. Now I really feel dumb. I did not realize that there are transistor ignition systems as well as CDI ignition systems. I have used the S/S system as well as the Hobby King system. I am trying to get a system which is compact and eliminates the points.It looks like the CDI system is actually the closest to what I am looking for. I guess that it is time to do some further investigation into the CDI. It looks like the coil is the main problem. This system is used on small engines so perhaps one of those coils would work.

The Hobby King works well but the spark plug cable is pretty clunky. Perhaps the outer shield could be removed and just grounded to the engine.

Gordon

Offline Don1966

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Re: Transistor ignition
« Reply #7 on: January 25, 2015, 10:13:05 PM »
Gordon glad you found you problem.

Paul I think you best check your circuit because the secondary of that ignition coil should be connected to ground. The transistor will burn up from the high voltage as will the zener diode and cap.

Regards Don

Offline PStechPaul

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Re: Transistor ignition
« Reply #8 on: January 26, 2015, 07:38:31 AM »
I found diagrams of the TIM4 through TIM7 ignition systems, and they use a different arrangement for the coil so it can be connected to ground rather than +12V. But other circuits are virtually the same as mine, and it should be no problem for the transistor and zener if properly rated, and if the capacitor is chosen correctly. The secondary of the coil should be connected to a spark plug or spark gap, which will also limit the primary voltage, but ultimately the circuit should be able to withstand an open secondary.

Some more information and schematics:

http://constructionmanuals.tpub.com/14050/css/14050_96.htm
http://www.wiringcircuit.com/auto/Transistor_Ignition_1185.html
http://www.jerry-howell.com/IgnitionModules.html (Jerry Howell's TIM-6x, but without schematics)
http://www.patents.com/us-5111798.html (patent)
http://www.auto-wiring-diagram.com/3511-typical-transistor-ignition-system-circuit-diagram-of-1965-ford-and-mercury.html
http://homemadecircuitsandschematics.blogspot.com/2013/01/make-this-enhanced-capacitive-discharge.html (capacitive discharge type)
http://newautoaa.blogspot.com/p/primary-circuit-of-ignition-system.html (detailed general ignition information)
http://chevythunder.com/ignition_systems_hei_operation.htm

Hmm... Most of those show one coil terminal grounded. The last link shows a separate secondary which is grounded.

I think I will have to build my circuit and see if if it blows up!  :zap:

Offline Allen Smithee

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Re: Transistor ignition
« Reply #9 on: January 26, 2015, 11:57:52 AM »
I would expect the actual coil to be an auto-transformer rather than an isolating transformer, so in reality the transistor is grounding a tapping in a single coil, "shorting" the primary to induce the flux change in the whole coil that generates the HT voltage. It's drawn as two coils by convention, but it's probably a single coil with a tapping.

AS
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Offline Admiral_dk

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Re: Transistor ignition
« Reply #10 on: January 26, 2015, 08:28:00 PM »
Sorry Don - but the ignition coil is wired correctly - you're right about the transistor and zener, they will not survive  :zap:

Paul change the transistor and zener into one of these special ignition IGBT's :   FGB3040CS,  IRG4PC30,  IRGS14C40 or NGB8202N.

There are more to choose from, but these special devices are extremely rugged and protected against too high voltage from an unloaded ignition coil and other mistakes. The transistor you picked will only withstand 160 volts and only 600mA. A normal ignition coil draws 3-6 A. and the voltage just after switching off reaches close to 300 volts if you have the right capacitor across the primary.


Offline Don1966

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Re: Transistor ignition
« Reply #11 on: January 26, 2015, 08:36:38 PM »
I am not going to argue with you, but this is the correct setup for an ignition system.
You will notic the HV winding grounded.

Don

Offline PStechPaul

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Re: Transistor ignition
« Reply #12 on: January 26, 2015, 10:28:58 PM »
The ignition coil I have (#1303 from NAPA) has only a (+) and (-) terminal and the HV terminal for the distributor wire. The case is painted and there is no connection to the internal coil(s), which are connected as an autotransformer. The primary is 5.37 mH with 1.38 ohms resistance, while the secondary is connected to the (+) terminal with 62.4 H and 9.9 kOhms resistance. The turns ratio is sqrt(62.4)/sqrt(0.00537) or about 340:1.

The components shown in the simulation are only the closest I could find in the standard libraries. I will use a 600V or higher power transistor and a high energy (500-1500W) TVS in place of the zener, and a 600V capacitor. The 1N5378B is rated 100V and 5W, so it might be able to withstand the excess energy stored in the coil if it is not dissipated in the spark. The energy stored is 0.5*I^2*L, and I depends on the dwell, applied voltage, and inductance. In the simulation, peak current is 2.4 amps, so energy is 28.8 mJ (W-sec). The duration of the spark is probably on the order of 100 uSec, so the peak power could be 28.8/100 = 288W. The primary of the coil and the capacitor form a series resonant circuit with a frequency of 5 kHz, so each half-wave would be 100 uSec.

It really doesn't matter much if one side of the primary is connected to ground or +12V. The voltage on the other end will still rise to several hundred volts due to inductive flyback effect. For grounded coils, a PNP transistor is needed and will be connected to +12V. But for my circuit, an NPN is connected to ground. There is a much wider assortment of high voltage NPN BJTs and MOSFETs, and even IGBTs, that can be used. And my circuit maintains most of the wiring of the convention points-activated ignition systems. I think I will need to add a capacitor across the 12V supply because the battery and external wiring probably do not have low impedance as is required to keep its voltage constant under high frequency pulse conditions.

As a finished project, I plan to add a PIC, which can be used to provide an adjustable dwell and spark advance/retard, as well as a tachometer based on the time between point openings. Hopefully I can build this and demonstrate it at Cabin Fever in April.

Offline Don1966

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Re: Transistor ignition
« Reply #13 on: January 27, 2015, 02:16:46 AM »
Paul it's your circuit do what you wish, but I am glad that your taking on, as per our discussion the timing advance. I look forward to see your progress and hope to see you at Cabin Fever this year.

Regards Don

Offline PStechPaul

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Re: Transistor ignition
« Reply #14 on: January 27, 2015, 04:54:00 AM »
The problem with timing advance is that the circuit can only act on the closing and opening of the points or the sensor. So it would need to be set up mechanically so that the points activate at the maximum advance, as it can only retard the spark. The simple circuit I show has no mechanism to change the timing. The more "advanced" unit might just maintain a certain current (and energy) in the coil, and then break the current to release the energy as high voltage upon a signal from the PIC. The degree of advance would actually be a delay determined by the RPM, so if the points actually open at 60 degrees BTDC, an actual advance of 15 degrees at 600 RPM would be a delay of

45 degrees * 100 mSec / 360 degrees = 12.5 mSec

To measure RPM, I could count the number of pulses in a one second period, but there are only 10 pulses per second at 600 RPM, so the resolution would be only 60 RPM. A better method may be to read the time between pulses, which can be done to a precision of 100 uSec for a count up to 65536, or 6.55 seconds, corresponding to 9.2 RPM. It would have a resolution of 1/65 or better than 2%  at 9200 RPM. I think the CCP capture mode would be perfect for reading RPM. It does involve floating point math, but that's not a problem when programming with C.