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PostPosted: March 31, 2011, 11:05 am 
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Sorry guys if this is a pedestrian question but when electricals are involved I can use all the help I can grab.
I now have a new gas engine and I have set up a conventional resistor- and- coil high voltage ignition system. What I am not sure about is how to connect the resistor/coil to the battery properly. I have gone through various Haynes and Bentley diagrams and all I have got is more confusion. Maybe some of you could describe in details (including wire gauges, etc) how you have wired this particular area of your engine.

Thanks in advance .

Philippe :?:


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PostPosted: March 31, 2011, 11:30 am 
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With the ignition in the normal on position, the coil should be powered through the resistor. This reduces the voltage a bit which increases the life of the points.

When you turn your ignition to 'start' then you need the coil to be powered directly, giving it the full 12V. This allows for a stronger spark for starting. That or it compensates for the drop in general system voltage due to the starters drain. It's probably a bit of both.

Not knowing what parts you have, I can't say where you would connect them. Going on the assumption that you are not running any kind of ECU... Take a feed that is live when the ignition is on, probably from the fuse box, run this to the resistor (which should be mounted on the chassis somewhere to act as a heatsink) and then run that to the ignition coil.

For the starting circuit, there should probably be a takeoff on the starter solenoid to supply full voltage to the coil during cranking.

Do you also need help with the other side of the circuit(the distributor, points & condenser)?

This is just how I would attack the issue. Not knowing exactly what you have, it's hard to say much more. Hope it is of some help :)

Tom...
edit: Just found a nice diagram showing the above circuit on another forum... http://www.trifive.com/forums/showthread.php?t=21100


Last edited by Tom17 on March 31, 2011, 11:37 am, edited 1 time in total.

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PostPosted: March 31, 2011, 11:34 am 
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philippe2 wrote:
Sorry guys if this is a pedestrian question but when electricals are involved I can use all the help I can grab.
I now have a new gas engine and I have set up a conventional resistor- and- coil high voltage ignition system. What I am not sure about is how to connect the resistor/coil to the battery properly. I have gone through various Haynes and Bentley diagrams and all I have got is more confusion. Maybe some of you could describe in details (including wire gauges, etc) how you have wired this particular area of your engine.

Thanks in advance .

Philippe :?:



I've never heard the ignition termed in quite that way. Resistors used to used quite frequently on points type ignitions, often with a bypass relay of some sort. The theory being that with a cold engine the whole 12 volts would be applied to the coil providing maximum spark at startup. After that, the resistor would kick in reducing coil voltage to around 9 volts thus reducing the arc across the points and overall spark output. That would extend the life of the points. In this example the coil and resistor would be connected in series. If a bypass relay was used then that circuitry would usually be connected to the starter. Actuation of the starter would bypass the resistor.

If what you're refering to is a Capacitive Discharge Ignition (CDI), then that's a competely different animal. You're gonna need to describe your ignition better.


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PostPosted: March 31, 2011, 12:04 pm 
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Or you could just get an internally ballasted coil and skip the whole external resistor part. The ignition coils are different. Are you sure the one you have is for use with an external resistor?

Unless you plan on starting the car in sub-zero temperatures, you probably don't need the benefit of the external resistor circuit.

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PostPosted: March 31, 2011, 2:02 pm 
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Thanks for your feedback. Yes I should be more precise. My distributor is of the electronic type , not the point type and I will be using MicroSquirt to control advance. Before writing my question my understanding was that an ordinary coil would overheat at low rpm (with the exception of starting) and that a resistor was needed to be set up to prevent that.

Philippe


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PostPosted: March 31, 2011, 2:13 pm 
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My understanding that the point of the ballast resistor is to give a stronger spark while cranking. As such, a coil designed for a ballast system will be designed to run continuously at less than 12v. If you run said coil without a resistor, then you will likely overheat it, yes.

If you have a coil that is designed for use without a ballast system, it should be designed to run at 12v. It will not overheat if you continuously run it at 12v.

A coil designed for 12v may have a resistor inside also, but this is a current limiting measure and should not affect the rated voltage requirement of the unit itself.

Tom...


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PostPosted: March 31, 2011, 2:33 pm 
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Phillipe, and easy way to determine if your coil is OK to run without the external resistor is to measure the primary resistance. If it reads around 3.1 ohms, +-1-%, then it is self-blasted and needs no additional resistor. Coils that require an external resistor run around 1.5 ohms. There are coils with other resistance values out there. But this is a good start.

I believe the Microsquirt is similar to the Megasquirt in that you can set the maximum dwell time. This will help with the coil temp at low speeds. But make no mistake about it, coils normally run HOT. So hot that you cannot hold your hand on them. This is normal.

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PostPosted: April 1, 2011, 11:15 am 
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Do you also need help with the other side of the circuit(the distributor, points & condenser)?

This is just how I would attack the issue. Not knowing exactly what you have, it's hard to say much more. Hope it is of some help :)

Tom...


:?: Actually I may need more coaching on the other side of the coil.

My distributor is a stock pointless Bosch (VW) designed to work with the 1998 VW 2.0 L Jetta ECU. I am not using the VW ECU but I am keeping the distributor. I will map the advance setting and maybe the knock control from a new module called MicroSquirt which I have not explored yet. The VW distributor's only external visible wiring is a set of three thin wires : red-black, green-white, brown-black. At this point I have no clue as to how to connect my coil negative terminal to this distributor and neither Haynes nor Bentley have helped.

Thanks.

Philippe :cheers:


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PostPosted: April 2, 2011, 8:15 pm 
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98. ... Motronic system (coil on plug)? VAG lists everything in "tracks", if you can get the # off of the original ECU I could find something I'm sure. If not perhaps the # off of the ignition pickup for cross referencing.

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PostPosted: April 2, 2011, 10:31 pm 
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oldejack wrote:
98. ... Motronic system (coil on plug)? VAG lists everything in "tracks", if you can get the # off of the original ECU I could find something I'm sure. If not perhaps the # off of the ignition pickup for cross referencing.



Thanks oldjack,

I think the 2.0 L VW (ABA) had a waste-spark type of ignition system: two coils firing simultaneously in two cylinders sparks, one of them indeed being wasted. I may go this route; but I still have a good deal of reading to do.

Philippe


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PostPosted: April 2, 2011, 10:47 pm 
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here's a start, might be enough. .. http://www.vems.hu/wiki/index.php?page=MembersPage%2FGrmRacer
I don't know the operating voltage though, maybe 5 volts maybe not.

Quote:
The Hall GND lead is connected near Pin26 on the EC36 connector.
The Hall signal lead is to be connected to Pin 27.
The Hall supply is connected to pin 28.


edit>> it is a 5 volt system.

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PostPosted: April 2, 2011, 11:02 pm 
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oh yeah, brown is ground, red is power, black stripe means main power branch, white strip means switched (ignition) power branch, green is signal. As I recall the stock ecu is a falling edge trigger.

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PostPosted: April 3, 2011, 10:08 am 
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oldejack wrote:
oh yeah, brown is ground, red is power, black stripe means main power branch, white strip means switched (ignition) power branch, green is signal. As I recall the stock ecu is a falling edge trigger.



:lol: Thanks again oldejack, there is a wealth of info in your reply and I will follow the leads.
Take care.

Philippe


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PostPosted: April 3, 2011, 1:23 pm 
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Gentlemen,
I hope this isn't out of place. On the old ballast resistor/coil ignition systems, the coil was rated at 9 volts. The ballast resistor or resistor wire on GMs was rated at 1/4 ohm. During crank the coil was fed 12 volts (or whatever was left during cranking) thus "overvolting" the coil with a subsequent increase in the spark.

Whatever you are going to run, a 9 volt coil will eventually overheat if fed a consistent 12 volt supply. On the other hand, a 12 volt (rated) coil will only operate properly during crank if a resistor is used. The remainder of the time it will be running on about 9 volts through a resistor - minimized red spark.

With the ignition modules and coils that we have now, it isn't necessary to use a crank bypass system. In the old days of mechanical ignition points, we were limited mechanically to a certain level of dwell, based on the shape of the distributor cam and the ignition point configuration. Some early high performance systems used a dual point setup to extend dwell time. During dwell (points closed) a magnetic field is being developed by the primary coil windings.

When the points are pushed open, the magnetic field begins to collapse. The primary tries to jump the point gap, however the condenser (capacitor) directs this arc through its body, absorbing it and redirecting it to ground. The magnetic field then collapses into the coil secondary windings where it exits as literally billions of tiny sparks appearing as just one.

On a typical (point/condenser) 4 cylinder engine, the average dwell time would be about 52 degrees. The longer the dwell, the greater the magnetic field. Considering there are 720 degrees between cylinder firings, 52 isn't much.

That's where ignition modules vastly improved the quality of spark. It's quite possible to build a module that will vary the dwell time based on rpm alone. That's the basic principle of electronic ignition. Dwell can begin any time the designer wants to close a transistor based on piston position and rpm and turn dwell off with the same inputs. Add an ECU into the mix and dwell/ignition timing can be set anywhere on the map at any time allowing much longer dwell periods.

Very few younger techs properly understand dwell as it is no longer taught much in Trade Schools. Also the oscilloscope has largely disappeared from the automotive repair scene. In my younger days I spent at least a half my day using a scope as I was a Tuneup Specialist.

In the past, I've modified old (carbureted) Toyota mechanical ignition systems a number of times using an updated Toyota EI distributor with a Ford Duraspark II Module and a Ford ignition coil. It's a terrific combination, easy to do and the parts come cheap from your friendly local recycler. That combination will provide at least 50Kv as Vs the 15-20 Kv available from mechanical ignition systems.

We once used a standard GM 4-pin Module and coil on a Chev racing engine that turned over 7000 rpm. That was better than any aftermarket system available. Never missed a beat and as locost as you can get.

If you have an old EI type distributor with mechanical or vacuum advance, there is almost certainly a way to trigger an ignition module, you just need a wiring diagram and a little know how.

Sorry to be so long winded, there's more to know on this if there is any interest.

Geoff


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