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Registered Member #3989
Joined: Thu Jul 07 2011, 05:10PM
Location: In a van down by the river.
Posts: 52
Can't I just input a tone from a frequency generator on my laptop and drive a big car amplifier to drive a flyback or ignition coil instead of a speaker? So long as the primary wasn't too close to 1 ohm dc resistance right?
Registered Member #543
Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
Download wrote ...
Theoreticaly yes, but your car amp can't amplify the 300kHz+ signal
I can't begin to imagine where this 300 kHz figure comes from, but it would be unsuitable for driving a 'traditional' petrol engine ignition coil, with or without an amplifier.
The primary t = L/R of ignition coils is optimized for use with pulses in the range of hundreds of Hz, while the secondaries are designed to be most efficient at the highest pulse frequency when the inductor has the least time (dwell time) to store energy in its magnetic field. Using a negative resistance oscillator, I determined the secondary self-resonant frequency of three different European ignition coils to wander (low Q!) around 1 kHz.*
Take a few ignition coils and measure the resistance and inductance of the windings yourself.
As for LOPTS or 'flybacks,' those made for use in TVs are optimized for use at 15.625 - 15.750 kHz depending on video standard. They will work at higher frequencies but core losses will grow and over-heating will occur.
And neither ignition coils, nor TV LOPTs, are designed to be energised by sine waves.
So 'theoretically' - as you put it - no - though an audio sine wave input will undoubtedly produce some voltage across the secondary.
* I should have been content just to measure L for the secondary, without all the palaver of determining fo, but my modest Peak Atlas LCR meter won't measure the inductance of high resistance windings.
Registered Member #1526
Joined: Mon Jun 09 2008, 12:56AM
Location: UK
Posts: 216
As an aside, I remember reading a car mag years ago in which they demonstrated a huge amplifier by feeding it 50Hz and driving power tools off it. Pretty darn cool.
Anyways it can generate sine wave, square wave, triangular waveform, saw tooth waveform and impulse sound waves of any audible frequency up to 20k hertz.
Is a square wave better than a sine wave because a square wave shuts off and on faster or more abruptly?
I have a bug zapper and some car ignition coils to play with, the bug zapper makes a 1 centimeter arc at 60hz is shunted and does not get hot even when shorted. I was going to try them with an old car amp and the tone generator this evening.
Anyways it can generate sine wave, square wave, triangular waveform, saw tooth waveform and impulse sound waves of any audible frequency up to 20k hertz.
Is a square wave better than a sine wave because a square wave shuts off and on faster or more abruptly?
Yes. Both ignition coils and TV LOPTs are designed for pulse operation. You are looking for the biggest difference in voltage for a given difference of time (known as the instantaneous rate of voltage change, which is given by the dv/dt calculus in volts per second.) A pure - that is to say, imaginary - square wave would go up in zero seconds, and go down in zero seconds - signs and wonders! - but in real life time is taken to store energy in the magnetic field - so no vertical climb whatever you try to do. And it also takes time for the magnetic field to collapse on the down side of the pulse. This is how we can calculate the optimum drive pulse repetition rate and duty cycle by measuring the resistance and inductance of an ignition coil primary. It's all about time constants.
Registered Member #561
Joined: Sat Mar 03 2007, 02:46AM
Location: Adelaide Australia
Posts: 230
Proud Mary wrote ...
Download wrote ...
Theoreticaly yes, but your car amp can't amplify the 300kHz+ signal
I can't begin to imagine where this 300 kHz figure comes from, but it would be unsuitable for driving a 'traditional' petrol engine ignition coil, with or without an amplifier.
The primary t = L/R of ignition coils is optimized for use with pulses in the range of hundreds of Hz, while the secondaries are designed to be most efficient at the highest pulse frequency when the inductor has the least time (dwell time) to store energy in its magnetic field. Using a negative resistance oscillator, I determined the secondary self-resonant frequency of three different European ignition coils to wander (low Q!) around 1 kHz.*
Take a few ignition coils and measure the resistance and inductance of the windings yourself.
As for LOPTS or 'flybacks,' those made for use in TVs are optimized for use at 15.625 - 15.750 kHz depending on video standard. They will work at higher frequencies but core losses will grow and over-heating will occur.
And neither ignition coils, nor TV LOPTs, are designed to be energised by sine waves.
So 'theoretically' - as you put it - no - though an audio sine wave input will undoubtedly produce some voltage across the secondary.
* I should have been content just to measure L for the secondary, without all the palaver of determining fo, but my modest Peak Atlas LCR meter won't measure the inductance of high resistance windings.
My understanding is that flybacks are in the 300kHz range. I didn't notice the ignition coil part though
Registered Member #1225
Joined: Sat Jan 12 2008, 01:24AM
Location: Beaumont, Texas, USA
Posts: 2253
Download wrote ...
Proud Mary wrote ...
Download wrote ...
Theoreticaly yes, but your car amp can't amplify the 300kHz+ signal
I can't begin to imagine where this 300 kHz figure comes from, but it would be unsuitable for driving a 'traditional' petrol engine ignition coil, with or without an amplifier.
The primary t = L/R of ignition coils is optimized for use with pulses in the range of hundreds of Hz, while the secondaries are designed to be most efficient at the highest pulse frequency when the inductor has the least time (dwell time) to store energy in its magnetic field. Using a negative resistance oscillator, I determined the secondary self-resonant frequency of three different European ignition coils to wander (low Q!) around 1 kHz.*
Take a few ignition coils and measure the resistance and inductance of the windings yourself.
As for LOPTS or 'flybacks,' those made for use in TVs are optimized for use at 15.625 - 15.750 kHz depending on video standard. They will work at higher frequencies but core losses will grow and over-heating will occur.
And neither ignition coils, nor TV LOPTs, are designed to be energised by sine waves.
So 'theoretically' - as you put it - no - though an audio sine wave input will undoubtedly produce some voltage across the secondary.
* I should have been content just to measure L for the secondary, without all the palaver of determining fo, but my modest Peak Atlas LCR meter won't measure the inductance of high resistance windings.
My understanding is that flybacks are in the 300kHz range. I didn't notice the ignition coil part though
Im not sure what kind of TVs you have been around, but i know mine squeals in the audible range, probably about 15KHz. CRT computer monitors' flybacks operate at higher frequency, but im sure it is still lower than 300KHz. I don't think the horizontal output transistor in them would like switching 300KHz.
Registered Member #543
Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
Download wrote ...
My understanding is that flybacks are in the 300kHz range.
The TV PAL line output frequency was handed down to Man on tablets of stone, and then mass-produced under Divine Licence in vinyl wood grain finish except for the hand-crafted limited edition signed by Jesus personally in his carpenter's workshop.
In the UK and many other countries using the PAL 625 line system with 50 Hz mains, this frequency is 15.625 kHz because 625 lines x 50 Hz / 2 = 15625. In the NSTC TV system used in the USA, the line frequency is 15.734 kHz.
Computer monitor CRT horizontal output frequencies can be much higher than this to accomodate a greater number of lines - e.g. 1024 lines @ 60 Hz would require 64.512 kHz once the vertical blanking interval has been taken into account
The AC flybacks prized by 4HV members are either of the 15.*** kHz kind, or if they are ancient relics of the British 405 line system (finally closed down in 1985) 10.125 kHz (50Hz × 405 ÷ 2) which made a loud high pitched whine due to magnetostriction in the LOPT core, and upset dogs far and wide.
Registered Member #72
Joined: Thu Feb 09 2006, 08:29AM
Location: UK St. Albans
Posts: 1659
I did precisely this a few years ago, with an audio amplifier into an ignition coil.
Using a sine-wave generator to drive the amp, I found a resonance of about 6x magnification at 8kHz due to the coil's self capacitance. So run as a flyback (which is how a standard breaker type car ignition system uses the coil) it wouldn't be much good north of 1kHz, which is consistent with the max rpm you'd expect from an engine.
The financial danger of driving a kV-generating piece of kit from an expensive fragile amplifier should be self-evident, be careful where the output goes.
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can I use a car amp to drive a coil?
