Using 12VDC and a car coil to create an ignitor

[dbrune]

I am trying to put together a really simple ignition system for our indirect heaters that are in areas where no electricity is availible. The goal here is to use about a 7Ah 12DVC battery, a coil off a car, a push button and an ignitor rod. The problem I am running into is how to get the 12VDC to oscillate for the coil like an old points distributor does for a car. Anyhow I think that is the problem. I would really like to find a "black box" that does this i.e. wire the 12VDC to it with the push button interrupting the negative leg and from the "black box" continue the 12VDC to the coil. Then again I could be approaching this completely wrong. Any suggestions?

Darren

 

[zimbali]

Hi there,
you don't have to make an AC voltage. What you need to do is simply disconnect the current to the primary of that coil you've got. What happens is an impulse voltage (due to a rapid change in current, i.e. v=L di/dt) induced into the primary and luckilly it osscillates itself for some miliseconds, that will be transmitted to the secondary as an impulse with a peak of N times more (N=N2/N1 and depends on your coil specification). Distributor in a car just DISTRIBUTES this secondary voltage to different plugs on different cylinders. So if you have a single-cylinder car you don't need any distributor and you can still have your ignition system for that imaginary car.
If you'd like to find out more about signal shapes of secondary and primary sides you can search "ignition signal shape" in "google IMAGES".


If you share what you know, you'll never forget it.

Cheers
Zimbali

 

[DougMSOE]

Been there,done that. What zimbali said except that the voltage generated in the secondary is strictly from the sudden collapse of the magnetic field first set up in the coil. The other point is that with spark coils the secondary voltage is much higher than Vprimary= N2/N1.
Typically, from a 12 volt battery yous should get between 30KVDC to 90KVDC.
I still use one of these setups for my experiments. The only difference is that the primary is driven from a bistable, monostable or astable firing circuit as the experiment requires. Have fun!

 

[dbrune]

I guess I need this dumbed up a bit as I have no idea what you two are trying to say.

The "circuit" will be dead until an operator comes up to the heater to lite the pilot and hopefully will do so by simply pushing a momentary push button. The coil should generate a secondary voltage as long as the operator pushes the momentary push button. Sometimes you need just a second of spark and other times a few seconds to light the pilot. Once the pilot is lite then a manual valve is opened to light the main burner. Really simple little 1.0MM BTU indirect heater.

Now that I have written this I believe what I need to know is how a coil actually works. I have always just taken them for granted, I know it is sad but true. I will do a search like Zimbali suggested and see if I can learn something today.

Thanks for the information and help.

Darren

 

[busbar]

Would a piezoelectric striker like a “Lightning Bug” do?

Hypothetically, a mechanical oscillator/chopper/buzzer from a small DC relay with a series NC contact would be guaranteed not Factory Mutual or American Gas Association approved.

 

[dbrune]

i have done some research on the web and now i understand what you guys are talking about and think i have a way figured out. i talked to the electrician here and we have devised a way to bench the system. thanks for all the information. could be a lot of fun but what the heck its Friday, no?

darren

 

[skills]

OK, it seems we have a disconnect going on here. I think you are looking at piezo igniters and thinking that a mechanical pushbutton and a coil will work without excitation. A current flowing through closed switch will run in primary and when interrupted create a collapsing field to produce high secondary voltage. You will NOT be able to take a button and coil and build igniter without SOME source on current i.e. battery, supply, what have you.

The little heater 'igniters' you're thinking of are piezo-electric and produce a high voltage when mechanically compressed.

 

[dbrune]

Skills,

You seem to be on the same page with me. I understand a battery will be needed. The system will work off of a 12VDC 7Ah battery. I just mocked the system up and got it to spark for everytime I depressed the push button. So for multiple sparks I had to manually cycle the pushbutton. What I need is something that will continue to spark while the push button is held in.

Here is what I thought might work but did not. The push button is placed between the NEG lead on the coil and the NEG of the battery. I thought that if I put a relay between the push button and the NEG of the battery I could get the relay to chatter and cause the multiple spark effect.

Here is how I wired it and the result. The NEG of the battery was wired to one side of the coil on the relay while the other side of the coil was wired to one leg of the N.C. contact of the same relay. Then the other side of the N.C. contact of the relay was wired to one leg of the N.O. contact of the push button. The other side of the N.O. contact of the push button stayed connected to the NEG lead on the coil. This completed the loop on the NEG side of the battery. The POS side of the battery was wired straight to the POS terminal of the coil. What happened is I got a hum from the relay and no spark what so ever.

I was thinking that if a V-8 car engine revs to 7000rpm that would be 933.3333 sparks per second. I would think that the relay would not chatter that fast but then again I think I am trying to use the relay for something it was never intended to do. Any ideas on how to achieve the multiple spark with common parts from an automotive parts store?

Darren

 

[IRstuff]

If you're just mocking it up, why not just use a regular distributor base with points and spin it with a DC motor?

TTFN

 

[dbrune]

the reason is this is going into the field on a natural gas heater. the enclosure will be air purged so it walks the Class I Div II rating. know that a dist and a DC motor will do the trick but it is not feasible in the field.

darren

 

[IRstuff]

Ok, how about:

http://www.cabelas.com/information/...-Continuous-Ignition-Multi-Spark-Ignitor.html

TTFN

 

[skills]

Ok, get a 7805 5 volt reg. A LM555 and wire it for 500hz 50% duty cycle and use a TIP42 or large power transister. When you press button you are starting the 555 on it's 500 hertz train and the 555 is wired to TIP42's base. I have done this to simulate a car engine before and it works fine. I also have built these igniter devices and a 555 @ 500 hertz or 200 hertz through a power transister works swell.

 

[melone]

I didn't quite follow the circuit diagram that you were explaining, but is this the hi-level description:

Use the pushbutton to activate a normally open relay. The N.O. relay connects the output of the distributer to your sparking mechanism.

Is this correct?

 

[dbrune]

melone,

there is no distributor involved. that is what i am trying to eliminate. for simplicity sake this is a one cylinder engine that needs a continuous spark as long as the push button is pushed.

skills,

thank you. i will try this tomorrow.

darren

 

[brlewis]

It occured to me that if all you want is a device to ignite your furnace you could save alot of headache trying to cludge something together from parts by buying a furnace ignition module. Most RV stores sell replacement parts for trailer and motorhome furnaces that have 12VDC ignition systems. There are dozens of places that sell these parts.

 

[peebee]

Re: "the enclosure will be air purged so it walks the Class I Div II rating" -- natural gas heaters are generally not considered hazardous, are you absolutely sure you need the Class I Div 2 rating?

Re: "know that a dist and a DC motor will do the trick but it is not feasible in the field." There's no reason you couldn't stick the motor & distributer in a purged enclosure.

There's lots of igniters available for natural gas burners. Why are you trying to build one, especially if this really is an XP installation?

 

[elfgriper]

Dbrune,
The 555 idea is a good one. Lookup se555 data sheet for instruction on how to use one. It only takes a couple of caps and resistors to build the circuit. A se555 will handle up to 18 volts so a 12 battery will be fine. You'll have to add a output transistor circuit to get enough power though, try using a couple tip121 darlington transistor (high gain 4amps capable)mounted on an heat sink to get started. To keep the output transistor from being damaged during the off time add a rvs diode across the coil Band on the + side.
You may also get away with using a turn signal blinking device from a car to get an oscillator to drive the output transistors. Keep in mind that you'll need some extra current to make the blinker work as it takes current to heat the bi metalic strip inside the blinker device to oscillate.
-elf

 

[skills]

Yes, a flasher might work; but, it takes a good bit 2.2 amps of current to flasher it at ~ 1hz.

 

[dbrune]

Thanks for all the replies and ideas.

peebee,
The motor and dist in the panel are out of the question. This is something that a company like Shell or PMEX would be looking to purchase. The Class I Div II rating is at these company's request so that is the rating I have to deliver.

brlewis,
These companies have specific ways they want the heater to be lite. This is usually with an ignitor rod and it is at the tip of the pilot assembly. This then lights the burner which can be anywhere from 150M Btu to 12MM Btu.

Again thanks for the ideas and I will let you know how it works out.

Darren

 

[AniCabling]

During my high school days, we made a project similar to your concern. The project was building a simple direct current buzzer where there the coil and contact points and armature were in series to the battery and switch. The coil was made up of magnet wires. I wounded two sets of coils, one was the primary made of bigger wire and the secondary was made of fine wires. This resembled the ignition coil of a car.
This is how it works. When the switch is closed, the current flows through the contact point, to armature and the primary coil creating a closed circuit creating an electomagnet. The magnetized core then pulls the armature, thus breaking the circuit. When the armature returns and connect to the contact point, the circuit is closed again, the coil is magnetized, thus having a continuos on and off cycle. This creates a pulsating DC in the coil. The pulsating DC creates magnetic flux and transforms the battery voltage to a high secondary voltage depending on the ratio of the turns between the secondary and the primary. The higher the ratio, the greater the induced voltage in the secondary. However a capacitor is needed between the the contact point and the armature so as to prevent the contact point from damage or pitting due to induced current.

I just dont know if a 12 volt dc door bell placed in series with ignition coil and battery will work. If it works, this will serve as your on and off machine to create pulsating DC to the ignition coil.