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

 

[dspDad]

Your relay idea will work. Use a double pole double throw relay. Set one pole to make the relay chatter as you did previously, and use the other pole to send an interrupted current through the coil. (use the normally closed contact for both relay and coil)

A solid state system would be preferable in a production environment, but getting reasonable transient protection on a 555/transistor solution requires allowing the input of the coil to swing about 300 volts in most cases.
Relays will arc a bit, but tolerate high voltage transients quite nicely in the short term.

If arcing is excessive, an ignition timing capacitor across either the coil or the points will reduce arcing, and are available at auto-parts places.

I'd like to watch a 12M Btu burner burn.
Sounds like thermal adrenaline.

 

[RAMConsult]

There may be more than an adreline rush if all this arcing and sparking takes place near an open source of natural gas or in an enclosed space that is not purged properly. Any time I've encountered a pilot ignition system for a burner this size it has been part of a UL or FM approved burner management system. Why re-invent the wheel?

 

[dbrune]

This arcing and sparking will take place next to an open source of natural gas...the pilot assembly and burner nozzle on one end. This is in a flame arrestor assembly so there is no classification. On the other end the coil is in a purged NEMA 4 box and in a Class I Div II area and that meets those requirements.

The reason for reinventing the wheel is that my client requires a Chevette not a Corvette. I can build a Class I Div II ignition system for $200 whereas I can buy a system for $400 from a vender. I can build a Class I Div I igintion system (read NEMA 7 enclosure) for $800 or buy one for $1600+ from a vender. We are building 4 to 5 of these heaters a week so it adds up.

Darren

 

[BrianR]

Don't forget that a 0.2uF to 0.5uF 600V capacitor is needed across the points (or switch contacts) to establish the resonant frequency of the coil primary. To charge toe coil field the voltage must be applied for 20mS or longer before the contacts open to generate the spark.

 

[OperaHouse]

This seems like a simple enough project. A 555 timer driving a transistor. If you have a continuing use for these I know a small electronics manufacturer that would be happy to make the populated circuit boad in very small quantities. You can then package it in your case. I know they have made battey operated propane grill lighters. A board like this wouldn't cost that much. Let me know if you are interested.

 

[etarhan]

Dbrune, have you ever seen a very old type doorbell? that is exactly what you need. It had a coil which magnetically pulled a hammer which hit the bell and almost at the same time, the movement of the hammer caused the electrical continuity between the supply and the coil to be cut off, so that as long as the button is pressed, the cycle repeated itself. The mechanics is very simple. In one of the former replies to your message, someone mentioned a relay. You can use it if you can bend the contacts properly.

Good Luck,
Engin

 

[dougjl]

Model T's worked with a spark box that simply sparked the spark plug when battery power is applied. I am not sure how you can set up this system for a burner if not approved by FM and UL. We can't even change anything on our burner management systems ourselves. We have to go to the vendor to get any change made and they have to get thier design approved by the powers that be before they will issue the change..

good luck,
Doug

 

[60hzhmmm]

dbrune, dspdad is entirely correct. Your original relay idea will work just fine. It just must be a double pole double throw relay.

THE BUZZER
12V+ to push button
other side push button to relay NC1
other side of relay NC1 to relay coil
other side of relay coil to 12V RTN

THE IGNITOR
12V+ to coil+
coil- to relay NO2
other side of NO2 to 12V RTN

KEY element!! Exactly as BrianR said you
MUST put a "coil condensor" (the standard coil
capacitor) that would normally be used on that
coil. With out the "condensor" you'll get diddly squat.

The condensor goes from NO2 to the other NO2 just like
the condensor across a distributors points.

This WILL light up your life!

Have fun.. Stand back.