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voltage coming out of a coil ? 

 

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 Post subject: voltage coming out of a coil ?
Posted: Sat Feb 26, 2005 9:57 am 
Getting Side Ways
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can someone please tell me what voltage i should be getting out of a coil in a 6cyl el falcon ? testing it shows it jumping from 8-12volts, i would expect alot more.

 

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Posted: Sat Feb 26, 2005 10:21 am 
Oompa Loompa
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Where are you trying to measure this?

If you are trying to measure it out of the secondary then I think this might be useful:
---------
What happens in a vehicle ignition coil is that 12 volts from the battery is applied to one end of the primary coil of the ignition coil, causing a current to flow through it when its other end is earthed (this earthing is controlled by the ECU, or in older systems, a set of points, but more about that later). This current builds up a magnetic field around the coil windings and the coil ‘core’ (the primary only has a few hundred windings). The secondary coil, which has thousands of windings is also wrapped around the coil core, so it is also sitting in the same magnetic field. The thing to remember here is that, by applying 12 volts to the coil primary, energy is consumed to produce the magnetic field – the coil is storing energy. This energy takes time to build up, so the current needs to flow through the primary coil for a little while before it has built up to a maximum (called saturation).

At the appropriate time for a spark (decided by the ECU, or in earlier ignition systems by the distributor and mechanical and vacuum advance systems), the power to the coil primary is switched off. When the power to the coil is switched off, current stops flowing in the primary coil, and the magnetic field collapses, releasing all of the energy stored in the field. This is where something weird happens – the energy came in to the coil from a 12 volt source, through a coil with a few hundred turns. It has to get out of the coil by the ‘coil secondary’, which has many thousands of turns. The voltage on the way out is multiplied by the ratio of the primary to secondary turns, so a measly 12 volts in ends up being 15,000 or so volts out – easily enough to create a spark in the right conditions. In old ‘distributor’ systems, this huge voltage is directed out of the coil lead, onto the rotor in the distributor, through the rotor button, and on to the appropriate spark plug lead for the right cylinder to fire.
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 Post subject: Wow
Posted: Sat Feb 26, 2005 11:26 am 
Getting Side Ways
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Wow, you are the God of coils... I will call you Yoda !
So, from the coil output i should be reading much greater then 12 volts. Going on what you are saying the secondary windings have failed. would this be correct.

Thanks Yoda !

 

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Posted: Sat Feb 26, 2005 8:39 pm 
Oompa Loompa
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The EL should have a coil pack (that is, a nice big coil with 6 leads coming out of it). The best way to test it is not to measure voltage out of the secondary but to measure the resistance of the primary circuit (where it gets power from the car), and between the primary and secondary windings. You would then need to compare these within specifications.
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Posted: Sun Feb 27, 2005 1:55 am 
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EF has the coil pack, the EL has the good old distributor...

 

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Posted: Sun Feb 27, 2005 8:48 am 
Oompa Loompa
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South wrote:
EF has the coil pack, the EL has the good old distributor...


Ahhh, I didnt know that. That means that it is even easier to test then :)

Like I said before, to test a coil, check resistance not output voltage :)
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Posted: Sun Feb 27, 2005 10:48 pm 
Getting Side Ways
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one thing to remember is that with the new ECU controlled ignition systems without primative points to burn and pit, they are able to run much higher primary coil currents which can produce up to 70kV on the secondary side once energised, so dont try to measure the output voltage. To test a coil all you need do is get a good multi metre and measure the resistance of the primary coil windings and the secondary coil windings. Refer to your manual for resistance details. Remember that the primaries are the 2 plugs on the coil and the secondaries go from the spark plug looking out put to ground or the coil body. Also check that there is no leak off from the primaries to ground through the coil body.

 

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Posted: Mon Feb 28, 2005 7:33 am 
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i used to run a mallory coil on a 5lt holden ute years ago, it had a 50,000 volt output via a stock points distributor, only ever got 1 boot off of it, that was enough for me :lol:
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Posted: Mon Feb 28, 2005 12:31 pm 
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dddp! wrote:
i used to run a mallory coil on a 5lt holden ute years ago, it had a 50,000 volt output via a stock points distributor, only ever got 1 boot off of it, that was enough for me :lol:


LOL At least you knew it worked.

 

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Posted: Tue Mar 01, 2005 2:01 am 
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how often did you do your points and was it a dual point dizzy? If it wasnt I bet that the size of the coil woulda been huge as to get the coil ratio from primary to secondary windings right up

 

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Posted: Tue Mar 01, 2005 11:48 am 
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points were checked every 5000ks with the normal service, single point dizzy, never got around to a dual point, yes it was a big bugger, it bolted to the firewall, had a look on the net and this is about the closest looking one to the one i had that i could find
http://www.centuryperformance.com/detai ... =MAL-29440 one i had was orange, but it's probably the same one anyway
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Posted: Wed Mar 02, 2005 12:21 am 
Getting Side Ways
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That is one huge a** coil but kinda what I expected as Ive seen them before cause my mate had a super coil for his rambler hornet

 

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