New to Ignition Coils

[Suraj143]

Guys I'm new to ignition coils.

Today I bought a new ignition coil.Attached a picture.Its a dry type not oil type.

I just test it with a 12V / 1.2A SLA battery by just giving pulses by hand (connecting & disconnecting the negative probe).

The problem is the sparks are very small like 2mm length

 

[Boncuk]

Hi Suraj143,

a good horse never jumps higher than necessary.

Why should an ignition coil produce an arc of more than 2mm lenght if the gap of the spark plug is just 0.7 to 0.9mm?

Using an ignition coil off an electronic ignition circuit for cars (that one seems to be made for motorbikes) you might get an arc length of about 5mm (but a nasty shock when you touch wires).

The coil must have a primary resistance of </= 0.7 Ohm

Boncuk

 

[Suraj143]

Hi boncuk

I'm going to build an electronics fence driver using one of your circuits (attached picture).I change the circuit to 1Hz OFF time & 30mS ON time.

I have completed the circuit all hardware & PCB.

My only problem is to choose the correct ignition coil.

But you have posted that your design works with electronics coils only!!

I asked the shop keeper that I need an electronics ignition coil but they don't know what is "electronics ignition coil" They & gave me what I show in the picture.

I searched in web what other guys used, most of them were using oil type (barrel) ones.

Whats your idea?

 

[Mr RB]

That coil probably draws 6 amps or 7 amps at 12v.

Your 12v 1.2A LSA battery is very weak, that size used to be called a "camera battery" for camcorders. It's voltage is probably dropping to 7 or 8v when the coil is connected!

Try using a proper automotive type battery, or use a large capacitor 4700uF 16v across the battery and use very short ON duty cycle pulses with your circuit, to try and keep voltage high.

 

[shortbus=]

Ignition coils also give stronger sparks once they get in to a "resonance" area of operation. Think about the actual Rpm of a running engine verses a cranking RPM. The single pulse of a manual operation will not give the same out put as the multiple pulse when wired to your switching circuit.

The dry type coil is what you want. The one you bought is what is known as a "coil to plug" ignition coil.

 

[DerStrom8]

Boncuk, your average ignition coil produces 20-40 thousand volts, capable of jumping up to 35 or 40 mm. I would agree with Mr RB on this one. That battery is extremely small, and the voltage is probably dropping significantly when you're connecting it. Try getting a larger battery, like a car battery or a larger lead-acid one. It will also work better if you have an actual driver for it.

 

[BrownOut]

The coil is probably OK. As a primative test, I do the same thing as you, just shorting wires by hand and observing a small, weak spark. That generally indicates a good coil. Ignition coils depend on a very sharp turn off voltage to generate higher voltages. In addition to using a proper battery, using driver electronics that generate a proper excitation signal will produce the high voltage you want. Also, longer excitation "on" times produce a higher voltage, up to a point where the driver transistor switches modes on it's own.

 

[Boncuk]

Hi Suray143,

using the circuit for an electric fence you don't need a high pulse repetition rate.

For the ignition coil I recommend to search at a car wreckage place and remove it from a car. Most modern cars have electonic ignition systems nowadays and any one should suit your needs.

(Don't try the car brand "Lada" (Russia). It has most probably a point ignition system.) Better refer to high performance models like VW Golf, any BMW or high class Mercedes, even Maserati or Ferrari will do.

The values given in my schematic are for optimum performance.

Reduce the pulse repetition rate for the circuit safety. The transistor won't live for an extended time with such high currents and without heatsink.

R8 connected directly to the timer output takes care of sudden gate discharge, hence a very abrupt turn off of the MosFet.

Boncuk

 

[tytower]

So why wouldn't you use an oil based coil ?
Especially if you are controlling the pulse.
I dont see electronic as getting better much ,just getting cheaper

 

[tytower]

Ignition coils also give stronger sparks once they get in to a "resonance" area of operation. Think about the actual Rpm of a running engine verses a cranking RPM. The single pulse of a manual operation will not give the same out put as the multiple pulse when wired to your switching circuit.

The dry type coil is what you want. The one you bought is what is known as a "coil to plug" ignition coil.

Hmm thats the first I've heard of that --don't think so ,sounds convincing though
What other type than "coil to plug " are there?
Dry type? Whats that?

 

[Suraj143]

Guys I do not have a high amperage battery @ my home to test it manually.After reading your posts looks like the coil is enough to generate longer sparks.
Better I'd trigger the coil by the circuit & fine tune the pulse rate.I’m still neating up my circuit.I also bought a 12V/5A transformer.

@ Boncuk
I’m using below rate. note that I edited your circuit to my requirements & I also removed that D3 diode.I just set up my cct as a standard astable mode with a diode between pin 6 & 7 to make low duty cycles.

ON Time = 30mS, OFF Time = 1Sec
Is my rate ok?

 

[shortbus=]

Hmm thats the first I've heard of that --don't think so ,sounds convincing though
What other type than "coil to plug " are there?
Dry type? Whats that?

As to the 'resonance' as the circuit starts to work the cap charges to around 400V from BEMF instead of the 12v from a single pulse. Resonance may not be the correct electronic word, just what is used in auto text books, back in the day.

The old 'oil filled' coils were for points use. the new 'dry' coils are more like a transformer, with the core laminations and and windings exposed. Since the 'dry' type is used with electronic ignition they are much lower resistance thus less temperature rise. Many people don't know that a round 'oil filled' coil actually operated at ~6V after the starter motor stopped.

 

[4pyros]

Dangerous Testing;
http://members.shaw.ca/forcelabs/IgnitionCoil.htm

 

[4pyros]

Many people don't know that a round 'oil filled' coil actually operated at ~6V after the starter motor stopped.

Yes I rember the old load resisters well;

 

[DerStrom8]

ON Time = 30mS, OFF Time = 1Sec
Is my rate ok?

That seems a little extreme. Ignition coils generally work best at a duty cycle close to 50% (on time about equal to off time). You may need to experiment a bit to get the output you desire.

 

[shortbus=]

Yes I rember the old load resisters well;
View attachment 59959

And after they stopped using the ballast resistors, they (GM) went to using a stainless steel cored wire from the ignition switch to the coil.

 

[4pyros]

And after they stopped using the ballast resistors, they (GM) went to using a stainless steel cored wire from the ignition switch to the coil.

The old resister wire. Many shade tree mechanics replaced them with a regular wire and burned up coils left and right.

 

[Suraj143]

Guys good news I made the circuit & it worked very nicely.

I generated 1.5cm arcs with my 555 driver.I used a 12V/5A transformer.

Pulse rate is 30mS high time & 350mS off time.

Now I need to generate longer arcs because after installing to a fence will this reduce the strength?

 

[DerStrom8]

Guys good news I made the circuit & it worked very nicely.

I generated 1.5cm arcs with my 555 driver.I used a 12V/5A transformer.

Pulse rate is 30mS high time & 350mS off time.

Now I need to generate longer arcs because after installing to a fence will this reduce the strength?

With an electric fence, you really don't want to go much higher than that. Most fences use only about ten KV, which usually makes a spark between 5 and 10 millimeters long. You really don't want to go any higher than that, or you risk all sorts of problems. Having everything attached to the fence (provided it's set up correctly) shouldn't reduce the strength much at all. The resistance of the fence can't be more than a few ohms, so you will not really lose much energy at all. You should be fine with what you have.

Just out of curiosity, though, how big is the fence, and how is it set up?

Regards

 

[Diver300]

If you break the current with a switch, or just by disconnecting the wires, the coil energy is lost in the arc at the switch. You need a capacitor in parallel with the switch. That lets the current flow into the capacitor when the switch opens. The arc at the switch is therefore quenched much sooner and the voltage can rise higher.

I know it sounds counter-intuitive, but the right size of capacitor will increase the voltage. All ignition systems with points had a capacitor, called a condenser, in parallel with the points.