Hello,

I am building a coil that is built like an ignition coil; that is, it has an inner coil that is the secondary, the primary is on the outside. I need to make sure what the polarity is. Normally I could just measure the voltage and my meter would tell me if its neg. or pos. BUT, the voltage is too high( 3KV ) so my meter won't read it.

Any help is much appreciated.

Thanks,
William

 

Well I'm a little confused. Coils or rather the transformer you have described is an AC device, it will not pass DC so has no real polarity.
You will only be able to use a DVM in it's AC voltage function and of course that carries no polarity information.

Possibly you are asking what the phase relationship between the primary and secondary and it is of course either 0 degrees or 180 degrees. To determine polarity you can inject a small AC voltage into the the primary and use a 2 channel AC coupled scope to see the phase relationship. One can switch between the phase relationship easily by choosing which end of the winding goes to your circuit common on either the primary or secondary windings.

If you indeed are planning to use this transformer to generate a DC voltage via a rectifier then the output polarity of the rectifier will only depend on what direction you wire the rectification diodes in not the phase relations ship of the transformer.

This help?

 

Helps a little bit.

It seems I too am confused. I mean, how then does an ignition coil produce high voltage from a DC source?

Thx

 

The primary ignition breaker switch (or solid state equivelent) creates a pulsating current into the secondary winding and it's that AC voltage spike that gets 'transformed' up by the winding ratio of the coil. It's not a DC voltage being produced and would not measure as a steady DC voltage value.

 

An ignition coil (transformer) does not have DC on it. The points open and close to make AC in sync with the motor rotation.

 

hi bill,

Any coil carrying a current will produce a back EMF if the current is suddenly switched OFF.
The voltage/energy if the back EMF is determined by 'Lenz's' law.

-emf= di/dt, all that means its the emf generated is a function of the current at the time of switch OFF
and how fast the current is switched OFF.
The higher the current and the faster the switch OFF the greater the back EMF.

As you are winding your own transformer would you post some information.
There are a number of other factors you must consider in a transformer design, especially the core.

We maybe able to suggest some ideas.

EDIT: Ron, Don't agree with your explanation,have a look at this:
http://www.howstuffworks.com/ignition-system.htm

__________________
Eric " Good enough is Perfect "
I will NOT answer PM's requesting technical help, please use the Forum
PIC tutorials: Nigel's www.winpicprog.co.uk/ Bill's: www.blueroomelectronics.com/

 

Does a spark plug care if the high voltage is positive or negative?

__________________
Uncle $crooge

 

Only, if its jumping to an opposite polarity, or a lower potential of the same polarity.

__________________
Eric " Good enough is Perfect "
I will NOT answer PM's requesting technical help, please use the Forum
PIC tutorials: Nigel's www.winpicprog.co.uk/ Bill's: www.blueroomelectronics.com/

 

Probably not, but do we know what the application actually is? He said There are plenty of applications where the polarity does matter.

__________________
Ron

 

Hi ericgibbs,

Quoting from your link: “The primary coil's current can be suddenly disrupted by the breaker points, or by a solid-state device in an electronic ignition.” Items F, G and H in the pictue.

In my tractor the hot side of the coil goes to +12 volts. The cold side goes to a “contact” to ground. The contact opens and closes with the revolution of the distributor. I see two switches that are linked with the motor rotation. The rotor that chooses which plug gets the spark and the (in your case ignition module) in my case the contact that drives the primary.

I am willing to go and put an o-scope on the primary of the coil and see.
rons

 

The polarity of high voltage affects how ions are made.
One polarity makes corrosive ozone and the other polarity makes ions that are pleasant.

__________________
Uncle $crooge

 

hi agu,
In the UK you can buy domestic ion generators, claims are, they make you feel better ???. Bit like that old 'sea ozone ' myth.
Have you seen such a device in Canada?

My old TV is good source of ions, 'good or bad' I'm not sure, certainly dosn't make me better or that could just be the lousy programs.

Regards

__________________
Eric " Good enough is Perfect "
I will NOT answer PM's requesting technical help, please use the Forum
PIC tutorials: Nigel's www.winpicprog.co.uk/ Bill's: www.blueroomelectronics.com/

 

Lots of traffic here, I really appreciate the input.

>Does a spark plug care if the high voltage is positive or negative?

Actually, it has to be a positive spark.

>As you are winding your own transformer would you post some information.
>There are a number of other factors you must consider in a transformer design, >especially the core.

The scenario is: 12v pulsed DC in, 3KV out.
What I have so far is: 4 turns of fat insulated primary and 1000 turns of 23ga magnet wire secondary. The 3KV will be DC via full-wave bridge rectifier.

Any suggestions?

P.S. how do you do those boxes around the previous text?

 

We've lost sight of the original problem.
An output attenuator would work, but since most 1/4 watt resistors are rated at 250V, it would require at least 14 resistors in series. That's doable.
Another way would be to reduce the supply voltage on the primary side to a volt or so (assuming the original supply is 12 volts).
There is probably some other, more clever way to do it.

__________________
Ron

 

Reply with the "quote" button to capture someones text. I have to ask out of curiosity: what turbo charged car are you putting this into?