Spark made with electronics

[Hero999]

Suppose the capacitor is fully charged, then the mains polarity is reversed, the capacitor's voltage is now placed in series with the mains, so the voltage across the diode is double the peak mains voltage.

 

[SimonTHK]

and just to be 100% sure, I should put 230v to the side with low number of windings right? (normal 12v output side) and get around 4450v

 

[cowana]

That's right.

Make sure the resistance/inductance of the low side isn't too low, or the mains voltage may overheat it.

Andrew

 

[Hero999]

and just to be 100% sure, I should put 230v to the side with low number of windings right? (normal 12v output side) and get around 4450v

Yes, that's the idea.

Don't operate this without a spark gap though as it might damage the insulation on the transformer. There shouldn't be a problem with a 100nF capacitor bur I've tried this circuit with a larger capacitor before and it totally ruined the transformer's insulation when it was open circuit. I'd recommend using a 3mm spark gap, then increase it, if you have any problems.

Make sure the resistance/inductance of the low side isn't too low, or the mains voltage may overheat it.

The capacitor delivers a brief pulse and the 100k resistor limits the current to a very low level, so there's no chance of the transformer overheating.

The only risk factor is destruction of the secondary insulation which increases when operating it off load with a larger capacitor, as mentioned above.

 

[tcmtech]

For long term use the ignition coil system is best being it is actually designed to create high voltage sparks on purpose.

 

[SimonTHK]

For long term use the ignition coil system is best being it is actually designed to create high voltage sparks on purpose.

I might look abit more into that then, since it is going to be used for many many thousand times.

I thought about using just a normal spark plug from a car, to be sure I use some good materials.

Thanks to everyone who write in this thread, interesting reading and I learn alot by it compared to school and thevenin xD

 

[SimonTHK]

Suppose the capacitor is fully charged, then the mains polarity is reversed, the capacitor's voltage is now placed in series with the mains, so the voltage across the diode is double the peak mains voltage.

Thanks man, this is great stuff to know

 

[Reloadron]

I might look abit more into that then, since it is going to be used for many many thousand times.

I thought about using just a normal spark plug from a car, to be sure I use some good materials.

Personally I would run with either automotive ignition or furnace ignition coil. Both, as you mentioned are designed for exactly what you want as to a spark. One big merit is if you can get an oil burner ignition coil it will run directly off mains power so you need only switch that on/off.

I would use a spark plug because the materials are designed for a constant high voltage arc.

For the timing you are looking at likely on for a few seconds (maybe 3 to 5) and off for 300 seconds (5 min). Gas would be controlled by a solenoid valve and you could likely hit ignition and gas at the same time. All in all this should make for a pretty cool (or hot) prop display.

There is just something about a fire breathing dragon...

Ron

 

[Mikebits]

What about one of those Piezoelectric starter thingamjigs like in a BBQ grill starter?

 

[Reloadron]

What about one of those Piezoelectric starter thingamjigs like in a BBQ grill starter?

I thought about that. Years ago I helped a friend make a small gas fired furnace for melting down aluminum. The gas tended to want to blow out unless we used a constant ignition spark. We finally got smart and included a pilot to keep the air fuel mixture ignited less a constant spark but with the blower running less a pilot system we needed the constant ignition. That sort of precluded using a grill starter.

I don't know what the original poster has in mind for the fuel mixing. WE used parts and junk we had lying around. The blower was an old DC brush type military blower. We ran it off a full wave bridge and variac. That thing got with it.

Ron

 

[Hero999]

What about one of those Piezoelectric starter thingamjigs like in a BBQ grill starter?

He wants to use a timer to control the ignition so a manually operated piezo ignition is not an option.

 

[ericgibbs]

He wants to use a timer to control the ignition so a manually operated piezo ignition is not an option.

hi hero,
My concern is the timing of the spark and the main gas valve.
There seems to be no safety feature included in the designs.

I could just imagine the main gas valve being opened and the ignition being a little late [or not at all] , he would get an explosion rather than a flame, or a gas cloud.

I would recommend a prelit pilot light, that could still be done using the igniter spark to light the pilot. Only if the pilot is lit will the main gas valve be allowed to open.

IMHO the OP will have to take care not to gas or blow up his audience.

 

[Hero999]

I agree.

If he has a pilot light, there needs to be some mechanism to ensure that if it blows out the gas is cut off.

This is why in the the law UK doesn't allow people who don't know what they're dong to work with gas.

I don't see the need for a pilot light, a more intelligent control system is needed.

There needs to be a temperature sensor so the controller knows that the gas is lighted. The controller should send a certain number pulses to the ignition until the gas lights, if there's no ignition after a certain number of pulses, turn the gas off and don't turn it back on again. If the flame lights but is extinguished, an attempt at relighting it could be made or the gas could just be shut off.

It's probably also a good idea to make it so that a single point failure can't cause an explosion, for example if the microcontroller fails there's no chance the gas could be turned on without the igniting it.

 

[Reloadron]

Generally in a gas fired system the flame detection is done using either a "Flame Rod" where the conductive properties of a flame are amplified or using a UV detector sensitive to the UV spectrum of the flame. Generally thermal sensors are not used because if the main flame has a blowout a thermal sensor will not offer a quick enough response to shut off the main gas supply.

Gas On, closely followed by Ignition, closely followed by a proof of flame. Failing proof of flame the main gas valve is shut off. That being a simple version.

The original poster seems to want a dragon to breath fire and I have no clue what the inside of this dragon's mouth or nose looks like as to ventilation. I would think a closed combustion chamber is one thing and an open air (ventilated) flame is another animal. The original post mention a flame every 5 min (300 seconds) but I didn't see any mention of flame duration so again I am clueless on that note.

I would think that safety features would be in place to prevent accidental flame as in if things don't work it would be unwise to shove ones head in dragon's mouth and have the thing go off. This could lead to death or at the least a real bad hair day.

For this application I don't know how many safety features are needed or how quickly they need to respond. I am also not sure as to the air fuel mixture that will be used. I would thing more gas and less air to produce an orange flame (since it is a dragon) unlike the nice blue flame we see on a gas range in a home. UV sensors don't fare well with an orange flame where an IR sensor may do better or a flame detection rod. Beats me.

I do know the explosive force of one cubic foot (1 cubic foot = 0.0283168466 cubic meters) in a simple enclosed box is ugly.

Ron

 

[Hero999]

Generally thermal sensors are not used because if the main flame has a blowout a thermal sensor will not offer a quick enough response to shut off the main gas supply.

I have a gas stove.

It has an electronic ignition but will work without power if an alternative form of ignition is used.

I'd interested to know what kind of protection it has, I think it's thermal.

The knob has to be pushed in for awhile after the flame has been ignited, otherwise it turns off. I think this is because pushing the knob in bypasses the thermal cut out. Once it's hot a temperature activated valve keeps the gas flowing. I've noticed that there's a little rod on each stove, perhaps this is the temperature sensor?

I haven't timed how long it takes to turn off the gas when the flame is extinguished but it's probably awhile, there again, it's an exposed flame not like in a boiler or oven, where the flame is in an enclosed space.

The oven won't work without electrical power so perhaps a more sensitive sensor is used?

 

[Reloadron]

So Hero gets me to thinking. Something I try not to do much of on weekends.

Our older gas stove (kitchen range) used glow ignition. Think small incandescent bulb less the glass bulb. It was ancient and lousy. The new range uses a spark ignition rather than the old conventional pilot light. Interesting as once I ignite a flame if I remove the flame the gas does in fact continue to flow. I did have a rough time extinguishing the flame.

What you mention as to pushing in and holding is how an axillary room heater works in our addition. Also the way it worked on the old furnace we had. Both use a pilot light and a thermocouple (or thermophile) and pressing and holding in allows gas to bypass a shutoff so the pilot can be ignited. Once the pilot is lit you continue to hold the thing in until the thermocouple takes over and opens the gas valve being bypassed. When the thermostat called for heat a main gas valve would open and would remain open till room temperature was reached then shut off. The blower would continue to run till the plenum cooled down.

The new furnace uses a flame rod for detection as well as electronic ignition. Much different concept and much safer. When the thermostat calls for heat the first stage blower turns on and runs. This runs for a few min and test for airflow making sure thew flu is not obstructed. Once airflow test is passed and they system is purged the main gas comes on and the ignition. Within a few seconds the system checks the flame rod for flame. That test failing initiates immediate shutdown. If everything meets proof test the system runs till setpoint is reached and then the gas shuts down but blower continues to run to purge the combustion chamber before it shuts down. Pretty reliable and safe till January in North East Ohio, USA when it will fail.

Ron

 

[Hero999]

I don't see how my gas stove can possibly use a thermocouple, as I said before, it can work without power and thermocouples only produce 10 or so mV which isn't enough to operate a valve with, maybe the oven but not the stove. My bet is on it being a bimetal, oil or gas operated valve.

 

[Reloadron]

I don't see how my gas stove can possibly use a thermocouple, as I said before, it can work without power and thermocouples only produce 10 or so mV which isn't enough to operate a valve with, maybe the oven but not the stove. My bet is on it being a bimetal, oil or gas operated valve.

I think some use (as we drift off topic) a capillary tube to physically open or close a valve but there are so many flavors out there. As to the thermocouple don't underestimate the little guys. Earlier I mentioned a thermopile which is a bunch (technical term bunch) of individual tiny thermocouples in series placed in a single tube. Figure at about 400 Deg. C a type J TC delivers about 22 mV so if we have 30 of them in series we get around 660 mV which isn't bad. Using a good enough coil that can hold in (open) a gas solenoid.

This is a good basic explanation using the TC for the pilot and then 24 VAC for the main valve control. They come in a variety of flavors as to how they work. Our gas fired hot water heater uses a thermopile and has no electric connected to it at all. Long as it makes hot water I am happy.

A Google of subjects like thermocouple furnace valves or thermocouple gas valves will bring up countless hits. I always wondered how a tiny thermocouple with no current to speak of could open or hold open a gas valve myself till some years ago when I got into them for a project.

Ron

 

[Hero999]

I think some use (as we drift off topic) a capillary tube to physically open or close a valve but there are so many flavors out there.

That's a possibility and is what I was getting at with the gas or oil valve. I know they ysed to fill the capillary with mercury but the EU banned it so now it'll probably be a gas or oil.

As to the thermocouple don't underestimate the little guys. Earlier I mentioned a thermopile which is a bunch (technical term bunch) of individual tiny thermocouples in series placed in a single tube. Figure at about 400 Deg. C a type J TC delivers about 22 mV so if we have 30 of them in series we get around 660 mV which isn't bad. Using a good enough coil that can hold in (open) a gas solenoid.

That makes sense too, it could also be a thermopile.

There's no way of knowing without removing the cover which is illegal in the UK unless you're corgi registered. The temperature sensors just look like metal rods which could be either thermopiles or the oil reservoir of a capillary tube.

 

[Reloadron]

Why do I feel this urge to head for the basement and start taking things apart?

Hero, you bring up another good point in that here in the US anyone can open and work on their stuff. That would maybe explain the high rate of gas explosions? Seriously, don't hold me to that but there are no laws. If I want to do electrical work on my home I go to the city and get a work permit listing "SELF" as the contractor. The city will inspect the work in progress and completed. However, those laws vary state to state and city to city.

Ron