# Low voltage igniter?

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#### iamthemik

##### Member
does anyone know where i can buy igniters that would ignite the second stage of my rocket. the electrical system is a simple mercury switch and a capacitor i ripped out of a camera flash. the capacitor is charged using the camera's flash charger (the kind that makes that buzzing sound as it charges).

ive tried making my own igniters using a strand of steel wool and black powder. they worked great but very unreliable. flashbulbs are also out of the question because theyre virtually impossible to find (i found some once but they were horribly expensive).

#### powderburner

##### Well-Known Member
A cheapo 50-bulb string of lights ($1.50 to$2?) will give you plenty of material to develop and test some new igniters. Funny how one of those little bulbs flashes right off when you run a full dose of 110 through it. You would need to do some testing to see what happens with a 12V auto battery (and a BUNCH of amps)
Some of the stores around me are already putting Christmas stuff on the shelves---maybe you could find some lights in your town?

#### GL-P

##### Well-Known Member
I wish I thought of that! MMM.... no more copperheads!!!

#### Loki

##### Well-Known Member
Originally posted by iamthemik
does anyone know where i can buy igniters that would ignite the second stage of my rocket. the electrical system is a simple mercury switch and a capacitor [...] any ideas/links are greatly appreciated
Don't do that.

Mercury switches for staging aren't safe. It can certainly work, but there's too much chance of accidental ignition. Most clubs have rules against this method.

#### Missileman

##### Well-Known Member
I agree with the post above about not using the mercury switch.
There are much safer and inexpensive methods.
As for low current ematches.
Performance hobbies has both Davyfire and Oxral but I am not sure how well they will work for ignition without dipping them.

#### UhClem

##### Well-Known Member
An odd question. The subject says low voltage but the body of the message indicates that a very high voltage source is being used.

If you really are using a flash capacitor, then almost any igniter you use will fire. Surface mount resistors have been used with these voltages with great success.

The energy stored is easy to compute: E = 1/2 * C * V^2

Assuming a typical 300uF capacitor charged to 300 volts you get 13.5 Joules of energy stored. An electric match requires less than 0.01 Joules to work reliably.

I wouldn't use a Copperhead because you are more likely to arc over between the copper layers than to ignite the pyrogen.

Be sure to provide for a way to discharge the capacitor just in case you need to disarm this beast after charging. This will eliminate the hazards of accidental ignition and high voltage.

#### iamthemik

##### Member
i just tested it out with an estes ingiter. the capacitor didnt have enough power to heat the wire. how would i be able to measure the joules stored in the capacitor.

i built this rocket two years ago and kinda gave up on it. if i remember properly, i put a 100 ohm resistor in the circuit so id have current flowing thru the igniter longer.

EDIT: i just tested the igniter again. this time without the 100 ohm resistor. The rush of current was so great that the igniter exploded. i'm going out now to buy more resistors and hopefully a smaller resistance will work!

#### thomasrau

##### Well-Known Member
For second stage I have always used Daveyfire 28F's dipped in pyrogen. Lately I've been using ignitor "chips" from firefox. The chips are soldered onto wire leads then dipped appropriately. In tests I've had them fire with a AA battery.

Use a timer or g-switch, do not use a mercury switch.

#### iamthemik

##### Member
i replaced the resistor with a 5 ohm one and the little estes igniters work very well with it. il also reconsider the mercury switch but if that doesnt work out then im thinking il put a safety switch that arms the ignition once the rocket is launched. thanks for the help.

#### BlueNinja

##### Well-Known Member
G switches are 8.00 from Perfectflite.

#### DynaSoar

##### Well-Known Member
Originally posted by iamthemik
does anyone know where i can buy igniters that would ignite the second stage of my rocket. the electrical system is a simple mercury switch and a capacitor i ripped out of a camera flash. the capacitor is charged using the camera's flash charger (the kind that makes that buzzing sound as it charges).

ive tried making my own igniters using a strand of steel wool and black powder. they worked great but very unreliable. flashbulbs are also out of the question because theyre virtually impossible to find (i found some once but they were horribly expensive).

I assume the mercury switch will be mounted vertically so that decelleration after booster burnout will force the mercury up to the contacts. Anything else would send it off at an angle after arcing over.

You're running the risk of the vibration of launch and flight setting off the second stage early. Despite what the sims will say about the G forces involved, unless this is a massive bird, the aerodynamics force of turbulence will still shake the rocket adequately to throw the mercury all over.

Best case, you'll get lousy performance. Worst case, your booster will fly free, unstable, while still under thrust. You won't have much control over how much of which case occurs. This is why merucy switches have fallen from favor among the experienced.

You can buy a brand new single event timer from Xavien for $40, and a G force trigger for$34, both of which make the mercury switch AND camera piece unnecessary.