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Coil,Pos or Neg?


Guest matt

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Hi,

 

I have a repro Auto-Lite coil as sold by several dealers for Jeeps and Dodge's,I want to use it on my Clarktor with has a positive ground electrical system,my question is are coils specific to Positive or negative ground systems?

 

Thanks,

 

Matt.

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Hi,

 

I have a repro Auto-Lite coil as sold by several dealers for Jeeps and Dodge's,I want to use it on my Clarktor with has a positive ground electrical system,my question is are coils specific to Positive or negative ground systems?

 

Thanks,

 

Matt.

 

 

AFAIK the coil has no specific polarity & it was much more sensible when the switched battery input was marked SW & the other end of the winding that went to the contact breaker marked CB. Unfortrunately in modern systems it seems to be a -ve earth system then SW is now marked + & CB is now marked -

 

I see no reason why the coil should not work in a +ve earth vehicle provided you translate it in your mind to SW & CB terminals. It would be important to be certain whether the coil is for a -ve earth vehicle or a +ve earth vehicle.

 

I suspect but not completely sure that +ve earth vehicles used SW & CB whereas -ve earth ones use + & -

 

It helps to remember the ignition coil is a transformer. The input (ie primary) winding is fed with switched battery supply (SW) & the other end goes to the CB terminal which is also connected to one end of the output (secondary) winding. The other end of the secondary is the HT output.

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I see no reason why the coil should not work in a +ve earth vehicle provided you translate it in your mind to SW & CB terminals. It would be important to be certain whether the coil is for a -ve earth vehicle or a +ve earth vehicle.

 

 

 

Clive,

 

I seem to remember that if the coil is connected the wrong way round, that the spark jumps form the body of the plug to the electrode and resulting in a weaker spark. I always view the coil connections as the feed to the contacts being marked to the relevant earth polarity of the vehicle.

 

Richard

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Clive,

 

I seem to remember that if the coil is connected the wrong way round, that the spark jumps form the body of the plug to the electrode and resulting in a weaker spark. I always view the coil connections as the feed to the contacts being marked to the relevant earth polarity of the vehicle.

 

Richard

 

 

Ah yes I was forgetting that the polarity of the spark would be reversed. The problem is that the centre electrode of the plug should be -ve so that the spark jumps to the earth, wrong way round & a higher voltage is needed to get an equivalent spark. Also as the spark jumps it erodes the electrode a little & the centre electrode is designed for this. So I was talking bollox, so proper polarity coil for the appropriate earth system of the vehicle.

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Clive,

 

I was surprised you missed that point, always think of you as the vehicle electrics guru ;-)

 

Richard

 

 

Yes well don't rub it in. I have things going on here, I'll pm you on. But I dived in without thinking, I was tempted to modify the original post & extricate myself. But a bit of public humiliation I suppose is always entertaining!

 

There is trick for testing the polarity of the spark to try to see in which direction the electrons are flowing. By holding the HT lead several mm from the plug terminal & interposing a pencil lead between the two a flare is produced. If the polarity of the HT is correct a flare is seen between the pencil & plug, reversed polarity & the flare is between the pencil & the cable.

 

I have just checked that I have got it the right was round. But this book says that -ve earth or +ve earth coils may be used for either polarity of vehicle. But to ensure the polarity of the spark is correct then use the -ve terminal should go to the contact breaker for -ve earth vehicles & the +ve terminal should go to the contact breaker for +ve earth vehicles. So I wasn't 100% bollox after all ;-)

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It will work providing you observe the basic primary / secondary roles of the windings. The risk is possible long term "spark errosion" damage because the spark may well jump to the wrong place. They make such neat little holes.

 

In industry as we know, spark errosion is a technique harnesssed for steel cutting. Long term you would be best to get it right.

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I have just checked that I have got it the right was round. But this book says that -ve earth or +ve earth coils may be used for either polarity of vehicle. But to ensure the polarity of the spark is correct then use the -ve terminal should go to the contact breaker for -ve earth vehicles & the +ve terminal should go to the contact breaker for +ve earth vehicles. So I wasn't 100% bollox after all ;-)

 

Absolutely right Clive, and why more modern items are simply marked + and -. Provided you know what a particular "SW" and "CB" marked coil was intended for, then using it on different polarity system simply means assuming the markings are reversed.

 

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