Author Topic: Electronic Ignition Design  (Read 60680 times)

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Offline Goeytex

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Re: Electronic Ignition Design
« Reply #15 on: December 16, 2010, 01:39:44 pm »
So here's the plan.

Using a switch mode controller IC and small transformer , a capacitor is charged to 300v. This takes
approximately  3.5 milliseconds.  When the magnet passes the hall sensor a signal is sent to the microprocessor.
The microprocessor then sends a  timed pulse to a transistor ( actually a MOSFET or IGBT) which then discharges
the capacitor into a CDI coil.  This produces a 30KV spark.   

If the engine is starting, the microprocessor delays sending the pulse to the transistor for about 15 crankshaft degrees.   When the microprocessor sees the engine running for 5 seconds, the delay is removed and the normal timing kicks in.  This could also be done by detecting RPMs over 1000 or so.  After the plug fires the capacitor is recharged  and the cycle repeats for each engine revolution.

One charge and discharge cycle take place in about 4ms, so that equates to a theoretical maximum RPM of  15,000. 

There will be a test mode that can be entered when the engine is not running.  The flywheel will be marked for 0 - 40 BTDC. with a pointer installed.  When in test mode, the flywheel is manually turned. The LED will light when the Hall sensor detects the magnet.  Turn the flywheel slowly until the LED just lights. This is the firing point.  The pointer will show where the timing is set by where it points to on the flywheel. when the LED lights up.   Adjust timing by either moving the sensor bracket or using the flywheel center hub adjustment. 

I think this should work somewhat better than using a Chrysler electronic ignition module and a 6/12 volt coil.  The spark should be a lot stronger and not break down under high compression / high rpms.

Cost ?   Who knows, but the parts come in at about $35 plus the coil.  I see some marine outboard CDI coils for about $30 or so.     


Bill
Bill Roth
12405 Blossomwood Dr
Austin, TX.
Email: bill.roth@comtrotech.com

Offline Rocket Ron

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Re: Electronic Ignition Design
« Reply #16 on: December 16, 2010, 03:04:19 pm »
 Just like aftermarket Ing. on Harley's that use kick start ?
Ronnie McClain
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Offline Goeytex

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Re: Electronic Ignition Design
« Reply #17 on: December 16, 2010, 03:45:30 pm »
Ron, 

I don't know a thing about Harley Ignitions, so I couldn't say
one way or the other.
Bill Roth
12405 Blossomwood Dr
Austin, TX.
Email: bill.roth@comtrotech.com

Offline Goeytex

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Re: Electronic Ignition Design
« Reply #18 on: December 17, 2010, 08:16:31 am »
I was just researching prices on MSD ignition stuff.  Wow the prices are insane !   

Part # 4154 Hall Sensor.  Price 142.00

$142.00 for a hall sensor ?   Nuts !    Put a $2 sensor on a 50c board.  Put some epoxy on it, attach some wires,  and charge $142.00 !    These guys are crazy !

MSD Briggs Ignition Kit   PN 41510   Price  $322.00  ( includes Coil & Switch)
MSD Sensor                 PN 4154     Price $142.00
-------------------------------------------
                                 Total                 $464.00   


-------------------------------------------------
MSD Programmable Ignition  Box  4217      $288.00
Coil  8232                                            $ 60.00
Trigger                                                $142.00
Coil Wire                                              $ 18.00
-----------------------------------------------------
                                                          $508 .00

The above connects to a PC where it can be programmed for timing curve
and rev limit. 

The Prices above are from Summit Racing  and are only for singles or possibly an opposed
twin ( if you get the $100 dual coil)
Bill Roth
12405 Blossomwood Dr
Austin, TX.
Email: bill.roth@comtrotech.com

Offline THawley08

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Re: Electronic Ignition Design
« Reply #19 on: December 17, 2010, 10:41:42 am »
Gotta remember you are also paying for the MSD name.
Tommy Hawley
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Offline ANIMAL96

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Re: Electronic Ignition Design
« Reply #20 on: December 17, 2010, 05:26:03 pm »
PM SENT
ALLEN J HARRELL

Offline Goeytex

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Re: Electronic Ignition Design
« Reply #21 on: December 17, 2010, 08:02:52 pm »
There have already been several inquiries about purchasing an ignition system.

At this point I am only developing a system for testing and evaluation and I don't know
if anything will be offered for sale or not. 

If I am successful with this and can keep it simple and not too expensive I may consider
making some for sale on a limited basis. 

If it works out really really good,  I may clam up and get all secretive,
evasive, and twitchy and only use them on my own mowmachines ..   :P
Bill Roth
12405 Blossomwood Dr
Austin, TX.
Email: bill.roth@comtrotech.com

Offline Rooster

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Re: Electronic Ignition Design
« Reply #22 on: December 17, 2010, 08:31:47 pm »
Lol....I think we are starting to bring the racer out in him
Bert stole my cookies!!
 I think he used them to bribe Ed into something naughty?

http://www.cutlooseracing.com

Offline George Herrin

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Re: Electronic Ignition Design
« Reply #23 on: December 17, 2010, 11:37:15 pm »
There have already been several inquiries about purchasing an ignition system.

At this point I am only developing a system for testing and evaluation and I don't know
if anything will be offered for sale or not. 

If I am successful with this and can keep it simple and not too expensive I may consider
making some for sale on a limited basis. 

If it works out really really good,  I may clam up and get all secretive,
evasive, and twitchy and only use them on my own mowmachines ..   :P

Yup the racer is shining thru
George Herrin #6
Indian Power.. You gotta Go big to beat em or Go HOME
8 time ARMA National Champion
4 time USLMRA National Champion
Retired from BP
www.herrinmowersports.yolasite.com
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My other racer is a 1/5th scale Dirt Late Model!!!!

Offline Goeytex

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Re: Electronic Ignition Design
« Reply #24 on: December 18, 2010, 09:32:58 am »
Spent the last day day or so  looking at aftermarket ignition stuff and reading a lot of tech articles.

It seems that CDI ignition is only really needed in the most extreme conditions, such as super high compression or when running nitrous.  MSD has done a great job of marketing and convincing folks into believing that CDI is best way to go.  It's kinda like the Angus Beef Association that has convinced the public that a hamburger made from meat from a black cow tastes better than one from a brown or white cow. Propaganda and marketing.

In any case there are some relatively inexpensive aftermarket ignition modules that can work fine on a mower engine up to 10,000 RPM.  

One key to using these modules is to match the coil to the module. For example,  you don't want to use a coil for a CDI ignition with a GM HEI module. The Module will operate in current limit mode and get too hot.

Coils are rated in primary resistance, secondary resistance, primary inductance and, secondary inductance. The turns ratio generally determines the voltage step up. But consider the primary resistance.  This is what determines the saturation current. Saturation current is the current drawn after the coil has been "charged up" ( coils don't really charge but it's the best way I know to explain it). This current can be calculated by Ohms law where Current = Voltage / Resistance. For example: a 1 ohm coil and a 12 volt system.  12v / 1 ohm = 12 amps. If the ignition module limits current  at 5.8 amps then it will get very hot, especially with a high dwell angle. But if the coil primary is 2.4 ohms then the saturation current become 12v /2.4 ohms or 5.45 amps. Now we're close to matched.

Some of the after market HEI modules can go up to 8 amps before current limiting kicks in.  So with onE of these, an ideal coil will have a primary resistance of about 1.5 ohms. 12V / 1.5 ohms  = 8mps . This makes sure the coil is fully "charged" so that when the current is quickly removed (HEI unit triggered) it can provide the energy needed to step the voltage up to 30 - 40KV . (None of this really applies to CDI as it works differently)  

HEI modules can be triggered with a magnetic reluctance sensor, or a Hall Sensor. A Hall sensor is typically more accurate.  

Dwell is defined as the number of CAMSHAFT degrees that current is applied to the coil's primary. In the older points systems it was the when the points were closed.  On an 8 cylinder it was about 22 degrees and on a 4 about 45 degrees. Too much dwell and the coil gets hot. On an electronic system like HEI, dwell is managed in the triggering system. But since we may be using a rigged up triggering system on the crank instead of the cam some kind of interface between the trigger and the ignition module is needed for ideal performance.  (A cam trigger would be nice as it would allow elimination of the waste spark and help keep the coil and ignition module cooler.)

This is where I will be focusing my efforts rather than redesigning the wheel. A control box between the Trigger device and the Ignition module can retard/ advance timing, provide a tach output, do rev limiting , etc.  

Harold's Junk Yard is only 5 miles away so I am gonna get a GM HEI module, some Bosche modules and whatever else I may need to do a bit of testing and see what I can come up with.


Bill
Bill Roth
12405 Blossomwood Dr
Austin, TX.
Email: bill.roth@comtrotech.com

Offline THawley08

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Re: Electronic Ignition Design
« Reply #25 on: December 18, 2010, 09:49:27 am »
Even if you didnt design one. A kit with instructions would be GREAT.
Tommy Hawley
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Offline Goeytex

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Re: Electronic Ignition Design
« Reply #26 on: December 18, 2010, 10:10:08 am »
A kit might be the way to go here. 

However, even kits need to be "designed" andin this case made "Redneck Proof".   :D 

In any case,  I plan to share my results except for the "secrets" that I have received
via PMs.   
Bill Roth
12405 Blossomwood Dr
Austin, TX.
Email: bill.roth@comtrotech.com

Offline Goeytex

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Re: Electronic Ignition Design
« Reply #27 on: December 20, 2010, 08:01:26 am »
Several Ignition modules seem to work OK. Chrysler, GM HEI ( 4 pin) , and
Ford Duraspark I & II.

All will get hot and probably fail  if not matched to the right coil and if the dwell issue
is not addressed.  Some may need a ballast resistor depending upon the coil used.

The automotive RPM limit of these units does not apply with a single or twin cylinder since the coil only
has to fire a fraction of the number of times per engine revolution.  So disregard the stuff from the automotive
guys about it only works up to 6000 RPM. That only applies to v8's.   

Coil saturation time is what determines RPM capability.  This is determined by primary coil resistance/inductance
and the applied current. The current is supplied by the ignition module and is fixed.  To get to 10,000 RPMs
this means the coil saturation time needs to be under 4ms per engine revolution when using a crank trigger.
This is not a problem with either of the units above and the proper coil.

With a cam trigger ( Not easy on a Briggs) the waste spark could be eliminated, reducing stress on the coil and the
control unit.  This would require putting a magnet on the outside of the cam gear and then drilling & tapping a small
hole in the block to screw in a sensor to detect the magnet when it passes.  While this is a bit of trouble,  it would
make for a very nice & reliable system. ( serious racers only ).

Bill   
Bill Roth
12405 Blossomwood Dr
Austin, TX.
Email: bill.roth@comtrotech.com

Offline FlatheadPuller

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Re: Electronic Ignition Design
« Reply #28 on: December 20, 2010, 10:01:26 am »
Bill for what its worth up until now I have always used a chrysler ign module and a magnetic proximity switch. Install a cap screw in the flywheel at where you wish and your done. The prox switch I use is a lot less money then a hall efects sensor. You could also use a pickup from dyna. They require no ign module. Just wire it to the coil. All done. They work off a magnet ring on crankshaft.
Dennis Bazzett
Grandville Michigan

Offline Goeytex

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Re: Electronic Ignition Design
« Reply #29 on: December 20, 2010, 03:25:54 pm »
The old Chrysler module is really nothing more than a switch.  It works well for
what it is.  But remember that it is 1970's technology.  This was before much more
efficient IGBT's and MOSFETS were commonly available.  

One of these IGBT's designed specifically for modern Ignitions can be purchased for about
$3.  Mount it on a $3 heatsink and you basically have an "improved" Chrysler module.

Hall sensors can be expensive,  but I make my own for about $10.

What proximity switch are you using ?  Can you provide a source and a part number?


With the old Chrysler unit, unless something is done to limit the amount of time it charges the
coil (dwell)  it will get unnecessarily hot and so will the coil.  

Some have indicated failures with Ford DuraSpark II and GM HEI Modules as well,  also due to
the dwell issue with a crank trigger  and/or using the wrong coil or no ballast resistor on a 6V coil.  

If all anyone wants is a good spark then stick with the stock Briggs ignition.

However, if you want the ability to retard timing at starting to save your starter, do multiple sparks at low RPM,
be able to open the plug gap to .050 for a better burn, etc ...then an aftermarket electronic system is needed.
And it doesn't have to cost $500.

Bill
Bill Roth
12405 Blossomwood Dr
Austin, TX.
Email: bill.roth@comtrotech.com

 

anything