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Author: Subject: Coils: What happens if they're connected the wrong way round?
Browser

posted on 30/4/09 at 08:29 AM Reply With Quote
Coils: What happens if they're connected the wrong way round?

Probably a daft question. A mate at work's mate has a twin cylinder motorbike, one coil per cylinder. Up until recently it was running fine, he had some need to disconnect either one or two coils, didn't find oout which, now it will only run on one cylinder.
From the days when my cars had the older-type cylindrical coils I can remember there being a + & - on the LT terminals, but why is this important? Surely they just connect to either end of a coil inside the casing, so polarity (apart from ensuring your tacho works properly if it's coil-driven) can't really be much of an issue can it?






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tegwin

posted on 30/4/09 at 08:36 AM Reply With Quote
If you wire the coil backwards the magnetic flux will flow in the wrong direction.... which would not give you the charge you need on the main winding..... Might make your engine run backwards and the world implode.... not a good idea!





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Guinness

posted on 30/4/09 at 08:45 AM Reply With Quote
I don't know the science behind it, I leave that to my esteemed colleauge Tegwin.

But when I first had my ZZR running it sounded odd. Deneo had me swap the +ve and -ve leads on the coils and it sounded better.

Mike






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02GF74

posted on 30/4/09 at 09:03 AM Reply With Quote
coil is a transformer with primary and secondary windings.

you now ask if there are 2 windings, then why aren't there 4 terminals?

answer is that the primary and seconday have comon connection at the - terminal,. which is grounded by the points.

when points are open, the common point is disconnected from 0 V so the coils are in series thus increasing the voltage at the output.





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nitram38

posted on 30/4/09 at 10:05 AM Reply With Quote
If it is a pure coil with no electronics or diodes etc, then it shouldn't matter which way around it is connected. The only exception is if one of the terminals is connected to earth via the casing, because if it is connected the wrong way around it will blow a fuse.
If the coil already is fubar, then trying it won't do anything other than blow the fuse






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daviep

posted on 30/4/09 at 10:21 AM Reply With Quote
quote:
Originally posted by 02GF74
coil is a transformer with primary and secondary windings.

you now ask if there are 2 windings, then why aren't there 4 terminals?

answer is that the primary and seconday have comon connection at the - terminal,. which is grounded by the points.

when points are open, the common point is disconnected from 0 V so the coils are in series thus increasing the voltage at the output.


WOW that just about sounds technical enough to be true

But its not

When the points are closed a current flows through the primary winding setting up a magnetic field. When the points open the the current flow stops and the magnetic field collapses.

As the magnetic field collapses inwards it travels across the primary windings and induces a voltage of around 300V into the primary winding. Due to the secondary windings proximity to the primary the voltage is also induced into the secondary.

Because the secondary has more turns on the winding than the primary but the same voltage is induced in to each turn the voltage produced by the secondary is much higher.

The two windings do not need to be connected together at all as demonstrated by a wasted spark system where both ends of the secondary winding are conected to a spark plug.

To answer the OP's question: If you connect the +VE and -VE round the wrong way at the coil you get reverse polarity at the spark plug. The spark jumps from the earth electrode to the center. This causes the earth electrode to be eroded away quicker than the center electrode would erode if operating with normal polarity.

A wasted spark system always has one plug running reverse polarity.

Sorry it's so long I'm not very good at explaining things.

Regards
Davie

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daviep

posted on 30/4/09 at 10:40 AM Reply With Quote
Read this from NGK

Regards
Davie

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MikeRJ

posted on 30/4/09 at 11:21 AM Reply With Quote
quote:
Originally posted by nitram38
If it is a pure coil with no electronics or diodes etc, then it shouldn't matter which way around it is connected.


Traditionally you get a better spark with a negative polarity (i.e. negative HT voltage w.r.t. ground), since it's easier for a spark to initiate from the hotter centre electrode. This means a lower voltage is required to initiate the spark.

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aerosam

posted on 30/4/09 at 11:52 AM Reply With Quote
BOOM!






maybe.





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