Hey all, I'm kinda new here and I'm also a noob when it comes to circuits. For our end of the term project, we're suppose to generate a spark from a 1.5 volt battery. The thing here is that we're supposed to use capacitors, inductors and resistors. The one who could generate the biggest spark would get an extra incentive for the final grade. So any of you can suggest how I can go through with the project? Thanks so much.

 

I'll assume you can switch the battery on and off?

Study up on Tesla coils and try to interpret the concept down to a simple single pulse for excitation.

 

Does inductor include transformers, like automotive ignition coil ? No diodes?

 

I would suspect that understanding Tesla coil operation would be too big of a step for a circuit noob.

jore1000, do you have the parts in front of you? Have you tried connecting one of the battery poles to one side of the inductor, then briefly brushing the other inductor wire across the other battery terminal?

If your fingers are also touching both inductor leads then you may get a little jolt, which should be a clue that if you allow current to flow through an inductor, then break that current flow, a large voltage will appear across the two inductor leads. Does that help?

 

Thanks for some of the suggestions guys.

But we're supposed to construct a simple circuit using just capacitors, inductors and resistors. It doesn't matter whether you just use capacitors or any combination of which as long as when you short the circuit, it would generate a spark. The longer the spark or the bigger, the higher my grade is.

I have an idea though, so if I like put several capacitors in parallel with the battery, then I try to short it, it would generate a spark right? So if that's the case, what can I do with an inductor to further increase the spark?

 

Use a resistor in series with the inductor as to limit the current to an acceptable level. Connect the circuit to the battery for a few seconds and then open the circuit. At the point where you open the circuit you will see a spark.

 

jorel000, do a Google search on Induction ignition coils. Here's the Wiki on them; http://en.wikipedia.org/wiki/Induction_coil

In the very early days of internal combustion engines this was one way they made the spark.

 

Thanks everyone and mik3. I'll post a video on youtube when I finish my project.

 

Use a resistor in series with the inductor as to limit the current to an acceptable level. Connect the circuit to the battery for a few seconds and then open the circuit. At the point where you open the circuit you will see a spark.

When you say limit the current, you mean limit the voltage? Coz current won't be divided when in series with the resistor?

 

Greetings jorel000,

A few things to keep in mind as you work on this project.

- VERY IMPORTANT: Current in an inductor CANNOT change instantaneously. This fact will play a role in the success of your spark generator.

- Within reason, the more current you can establish in your inductor, the greater will be the spark you generate. Mik3 already eluded to the need for a resistor to set the current limit to a reasonable value.

- The lower the DC resistance your inductor has the larger the current you can induce in the inductor.

- You need to gain a clear understanding of what causes the spark to occur when you break the circuit containing the 1.5 volt battery, the low valued high wattage resistor and the inductor.

- Make sure that you use the freshest 1.5 volt battery you can find. The first spark generated by a fresh battery is bound to be the strongest one possible.

Are you winding your own inductor or are you requried to choose from a supply of inductors that are being made available to you?

I will await your reply before getting deeper into the discussion.

hgmjr

 

We're supposed to get or buy our own parts. Currently, I've tried experimenting with mik3's idea but to no avail. I suppose the spark didn't occur or was too small to see.

 

we're suppose to generate a spark from a 1.5 volt battery, capacitors, inductors and resistors.

If you were allowed active components (such as a transistor) this could be very easy, as it stands I'd hand wind a step-up transformer with enough turns on the primary to max out what the battery can safely supply (and an alkaline D cell can put out a lot) then, using a far thinner wire gauge, wind as many turns as you can afford for the secondary. A long, fairly thick steel rod would make a nice coil form for this.

As to wire and their ratings:

http://www.interfacebus.com/Copper_Wire_AWG_SIze.html

I'd ignore the column labeled "Current Carrying" as it's giving values much lower than the wire is capable of and you're only going to be using this on an intermittent basis anyway.

You simply need a switch to connect and disconnect the battery from the primary winding. Turn it on for about a half second then when you switch it back off one heck of a spark is going to come out of the secondary.

How easy could it be to build?

Buy magnet wire already in rolls.

I have here a 100' roll of #18 that has an inner core of exactly 1". Take that, then buy a full 1 lb roll of something like #30 that also has an inner core of 1" and place them over the rod. It would be preferrable to somehow magnetically link the top and botom of the rod to make a closed magnetic field.

 

We're only allowed to use resistors, capacitors and inductors. Nothing more than that, so I'm kinda out of ideas on how to use the capacitor to generate the spark. Although, I think I could generate the spark by putting an inductor in series with the voltage source, then opening the circuit. At that point, there should be a spark I think.

 

We're only allowed to use resistors, capacitors and inductors. Nothing more than that, so I'm kinda out of ideas on how to use the capacitor to generate the spark. Although, I think I could generate the spark by putting an inductor in series with the voltage source, then opening the circuit. At that point, there should be a spark I think.

Do they require that you use a capacitor? You could just put it across the battery and disconnect both when you unhook it to make the spark.

Incidentally a roll of wire would be considered to be an inductor.

I suppose you could find one of those old style RF inductors that were wound in sections then wind the primary around it. I assume they will let you use wire and solder?

 

you never did answer question on wheather a transformer for your purposes is considered an inductor. You will never get a long spark from a choke as your switch is also your spark gap.
The Electronic Goldmine has a special on hV transformer, still an auto spark coil would be a good start.

 

you never did answer question on wheather a transformer for your purposes is considered an inductor. You will never get a long spark from a choke as your switch is also your spark gap.
The Electronic Goldmine has a special on hV transformer, still an auto spark coil would be a good start.

Oh sorry, I forgot to answer. Uhm, I just asked my professor if we could use transformers and he said yes apparently. We're just suppose to generate a 2mm spark, the longer the better.

 

With only 1.5V driving potential an auto ignition coil is going to have trouble doing anything spectacular.

I still like my idea of using rolls of magnet wire and a rod of steel to make a step-up transformer but we're not sure if "coil forms" are allowed - then again theyre part of an inductor.

I'm also thinking a homebuilt SPDT relay could come in handy, it's just an inductor with some contacts but you could make AC (actually pulsed DC) at some sort of frequency from it.

A 1F (or higher) supercap could also be useful here, think of the current one of those might be able to toss into an almost short circuit.

One thing we want to consider - when giving grades a teacher is going to consider creativity and I'll bet there's already going to be a lot of car ignition coils present at the competition.

Just tossing a couple of things around as these are all on the same size reel, average turn = 4.5"

3200' of #36 http://cgi.ebay.com/Magnet-Wire-36-...423?pt=LH_DefaultDomain_0&hash=item2a095d75f7
3,200' ~= 8500 turns

50' of #18 http://cgi.ebay.com/Magnet-Wire-18-...766?pt=LH_DefaultDomain_0&hash=item2a09816a6e
50' ~= 133 turns

8,500/133 = 64:1 so that sucks, you'd need to make your own form or take most of the #18 off the reel.

 

This should be a simple project. Our ancestors were making one and two inch sparks like this 150 years ago, using tin foil and waxed paper stacks for capacitors.

The tricky part is to keep the windings of the secondary coil VERY well insulated from themselves and everything else.

Go to www.books.google.com and search for "spark coil". you will get hundreds of hits on books dated 1881 to 1921 mostly.

The real problem with this will be the amount of copper wire needed for the $econdary winding. $$$ Scrounging wire from transformer secondaries would help, because you need lots of it.

 

Regressing back to a choke coil, 10 H, 85Ω, old D cell, best I could get was 1200 V , @ about 1/5 mm spark; just can't open switch fast enough.

 

This should be a simple project. Our ancestors were making one and two inch sparks like this 150 years ago, using tin foil and waxed paper stacks for capacitors.

The tricky part is to keep the windings of the secondary coil VERY well insulated from themselves and everything else.

Go to www.books.google.com and search for "spark coil". you will get hundreds of hits on books dated 1881 to 1921 mostly.

The real problem with this will be the amount of copper wire needed for the $econdary winding. $$$ Scrounging wire from transformer secondaries would help, because you need lots of it.

That is, in effect, a model T ignition coil. They took that same design and put the contacts on the camshaft as "points". COndensors had progresed quite a bit since the old foil & paper versions too so those were place across the points.