Ignition voltage

[os_tempore]

Well, after my first post I'm getting into this more and I'm going ti build my own base/firing system. Because of that, I've got all the options.

The base system is 12vdc. But knowing electronics and not rocketry, does the voltage matter at the ignition point?

Case in point, 12vdc will heat a wire to combustion. 210vdc will do it significantly quicker and therefor become hotter much faster.

So, would it behoove me to solder in a 210vdc step up converter with 1/2 motors up to L1 and L2 motors (if I go all out)?


The circuit will look like this: switch controlled 12vdc supplied to converter. Converter output fed into 2200uf flash capacitor. Capacitor to SSR which is controlled via giant momentary push button. The SSR will dump the V into the ignitor very quickly and should nearly explode the wire (ie extremely quick white hot).

 

[rcktnut]

12vdc will do the job. All you need to do is ignite the pyrogen on the igniter. For APCP propellant, too fast (explode the wire) may not be good. I use a 12v 7ah SLA battery, works just fine.

 

[os_tempore]

12vdc will do the job. All you need to do is ignite the pyrogen on the igniter. For APCP propellant too fast (explode the wire) may not be good. I use a 12v 7ah battery, works just fine.

I'm also attempting to hedge against failures in cluster motor ignitions.

I could also dip them to make them more sparky. I also thought that putting at least a flash capacitor with decent gauge wire would shunt the current with less loss.

 

[Zeus-cat]

The limiting factor for many systems is the amperage you can run through the system. Igniters have very low resistance; something like 2 or 3 ohms. So very high voltage means very high amps and that could fry your wires.

I clean the clips for my club's launch system after every group launch. We lose 3 or 4 sets of leads a year and I suspect it may be due to firing 3 to 4 motor clusters off one set of leads. Three or four igniters on one set of leads drops the effective resistance below one ohm which drives the current way up. We've had leads simply quit working reliably for no apparent reason. I cut off the alligator clips to put new ones on and saw that that the wires were blackened. They literally burned inside the insulation. Increasing the voltage as you suggested would be very hard on your ignition system and igniters.

 

[tfish]

I built my wireless system 12 years ago(?)
https://www.rocketryforum.com/threads/wireless-launch-control-system-v2.48227/

I use a 12v 7amp gel cell. My test light is a 12v Halogen headlight bulb.

MY cheap ebay wireless thing ...triggers 30 amp automotive relays.

Works great.. on Q's to A8-3's


Tony

 

[os_tempore]

The limiting factor for many systems is the amperage you can run through the system. Igniters have very low resistance; something like 2 or 3 ohms. So very high voltage means very high amps and that could fry your wires.

I clean the clips for my club's launch system after every group launch. We lose 3 or 4 sets of leads a year and I suspect it may be due to firing 3 to 4 motor clusters off one set of leads. Three or four igniters on one set of leads drops the effective resistance below one ohm which drives the current way up. We've had leads simply quit working reliably for no apparent reason. I cut off the alligator clips to put new ones on and saw that that the wires were blackened. They literally burned inside the insulation. Increasing the voltage as you suggested would be very hard on your ignition system and igniters.

I'm wondering if the black wiring (burnt) is due to the wires gauge being too small for the voltage/amp requirements and it overheated internally from that. Have you tried heavier gauge wire? Kinda like a 50w bulb won't heat up a 16ga house wire, but a 1000w bulb will.

The dc/dc converter puts out 210vdc, but at only 50ma. The flash capacitor should only dump the 210vdc at 50ma into the ignitor. I plan on using 12ga with paddle connectors for the ignitor leads.

 

[Art Upton]

Stick with 12 volts is my advise.

 

[lr64]

Rather than going to such high voltage, suggest putting the 12V battery close to the pad, and activating with a relay or tfish's eBay thing. I haven't done the relay thing, but if the wires are long I suggest a relay (or solid state equivalent) that isn't too sensitive, plus shielded or twisted wires. And consulting with someone who's actually controlled things using long wires, for the parts I forgot. Alternatively, one could set up a supercap near the pad, with a circuit that only discharges it through the bridge wire when it gets close to 12 volts. You'd have to wait a second or two for the cap to charge after you hit the button. Of course, you're an electronics guy and can probably think of better ways. I don't think it's a good idea to have long wires outdoors at 210 volts, and it solves a nonexistent problem.

Zapping something quickly isn't always the best way to proceed. A while back, I was trying ignitors made from surface mount resistors, because space is very limited in a Jetex motor. With a 3S lipo capable of dozens of amps, they'd fail instantly, before heating anything else up enough to catch fire. With a little 9V alkaline battery, with its own internal resistance, they worked. I guess, though, that with cluster motors, you don't want the ignition to be too slow, either.

 

[os_tempore]

Rather than going to such high voltage, suggest putting the 12V battery close to the pad, and activating with a relay or tfish's eBay thing. I haven't done the relay thing, but if the wires are long I suggest a relay (or solid state equivalent) that isn't too sensitive, plus shielded or twisted wires. And consulting with someone who's actually controlled things using long wires, for the parts I forgot. Alternatively, one could set up a supercap near the pad, with a circuit that only discharges it through the bridge wire when it gets close to 12 volts. You'd have to wait a second or two for the cap to charge after you hit the button. Of course, you're an electronics guy and can probably think of better ways. I don't think it's a good idea to have long wires outdoors at 210 volts, and it solves a nonexistent problem.

Zapping something quickly isn't always the best way to proceed. A while back, I was trying ignitors made from surface mount resistors, because space is very limited in a Jetex motor. With a 3S lipo capable of dozens of amps, they'd fail instantly, before heating anything else up enough to catch fire. With a little 9V alkaline battery, with its own internal resistance, they worked. I guess, though, that with cluster motors, you don't want the ignition to be too slow, either.

You're right, I didn't actually point that part out. The launch base is going to have it's own 12vdc power within it. On dc long runs of wire kill delivered amps, unless you get to crazy gauge (which is why our grid is ac). The battery to the step up converter to the flash cap and relay is only about 12 inches of 12ga wire.

Though, you and the others may be right in that just a cap is good enough for starting. It'll remove the bottle neck and allows the cap to take the pounding instead of the battery (lifepo4, so not too capable in the high discharge amp catagory). Interesting experiment with the resistors. Did you use "quick dip" , or were you relying on the resistor itself for enough heat production? I wonder if you were on the right track and if you were to slam some amps into something like a very thin/short bit Kanthal wire for the heating element, if that'd get that you're looking for.


My hardwired line is just for control of the relay, lights, flashers etc. I'll do a build post on it - probably. I may power the relays from the control box with its own battery to keep the systems from crossing. The launch pad battery would be the juice into the fixtures alone and nothing controlling it. For the wireless relays, I agree that'd be neat. My concern is any RF interference that could prematurely launch the rocket. The ones I found use 433mhz, which is very close to some common bands used in amateur radio and some aircraft. I'd hate to have someone put their radio a bit and launch my rocket, or cause a failure to launch from background rf. I didn't see that they were coded of fhss like the newer R/C controllers are.

 

[lr64]

Unless you're not going to dip the igniters in anything, you're thinking way too much power. Check nakka-rocketry.net Richard Nakka has made an igniter from a grain of wheat bulb that can work with a refrigerated, mostly discharged 9V alkaline battery. I favor more power than that, but not as much as you are contemplating.

Another thing I've made ignitors from is carbon fiber, either tow or, more easily, a splinter of unidirectional composite*. I just wrap wire around either end of a quarter inch of it and pinch with pliers. Carbon fiber can take a pretty powerful zap. Enough to make a small mushroom cloud if you accidentally short some high voltage lines with a few ounces of it. And the most amazing 60 cycle hum. (No, it wasn't me.) You should check the resistance when using carbon fiber as a bridge wire, because yours might not be the same as what I have. I don't think I've bought anything from these guys, but they offer a lifetime supply for $10:
https://sollercompositesllc.com/product/t700-12k-carbon-fiber-1in-long-chopped-tow/
Again, I don't know what my carbon fiber is, so you may have to adjust the length.

* I suspect you can turn tow into composite with a little epoxy or even thin cyanoacrylate. The composite is easier to wrap wires around, because it's rigid.

 

[lr64]

Some older RC equipment on 72 mHz had PCM. You could make it lock up, or go to fail safe, by turning on another radio on the same frequency. However, you couldn't make the servos move, except to the fail safe position. There were several different implementations, so it would be worth checking compatibility.

 

[lr64]

BTW, for real excitement, zap a small diode with house current. But put it inside something or wear safety glasses! It might have been overkill, because the guy who did it was igniting flash powder, which is notoriously easy to set off.

 

[Rocketjunkie]

**All igniters - starters - ematches are current activated devices.** It doesn't matter what the voltage is as long as it's enough to force enough current.
For example you might need 40 amps for a cluster of 7 Aerotech first fires (5A each) but 10 amps is plenty for CTI (ematch 1A each) starters. If wired in parallel, 12V is plenty.

 

[lr64]

You can't get the right current without the right voltage. V=IR. Of course, with something like a 9V battery, the internal resistance is part of the circuit.

I used the phrase "house current" colloquially. 115V and 60 Hz. Probably overkill for that poor little diode!

 

[Art Upton]

You're right, I didn't actually point that part out. The launch base is going to have it's own 12vdc power within it. On dc long runs of wire kill delivered amps, unless you get to crazy gauge (which is why our grid is ac). The battery to the step up converter to the flash cap and relay is only about 12 inches of 12ga wire.

Though, you and the others may be right in that just a cap is good enough for starting. It'll remove the bottle neck and allows the cap to take the pounding instead of the battery (lifepo4, so not too capable in the high discharge amp catagory). Interesting experiment with the resistors. Did you use "quick dip" , or were you relying on the resistor itself for enough heat production? I wonder if you were on the right track and if you were to slam some amps into something like a very thin/short bit Kanthal wire for the heating element, if that'd get that you're looking for.


My hardwired line is just for control of the relay, lights, flashers etc. I'll do a build post on it - probably. I may power the relays from the control box with its own battery to keep the systems from crossing. The launch pad battery would be the juice into the fixtures alone and nothing controlling it. For the wireless relays, I agree that'd be neat. My concern is any RF interference that could prematurely launch the rocket. The ones I found use 433mhz, which is very close to some common bands used in amateur radio and some aircraft. I'd hate to have someone put their radio a bit and launch my rocket, or cause a failure to launch from background rf. I didn't see that they were coded of fhss like the newer R/C controllers are.

Using the "super shared freq of 433" you need to use digital codes to prevent false launches or garage door openings.

The Fire transmitter needs to send a unique digital code and the pad receiver needs to decode and verify it's code before the Launch relay is energized.

You should be able to find a chip that does all that for you and set by dip switches [80s tech] or other means to set the code with today's tech.

 

[Tractionengines]

Lighting black powder up easy, and only takes a little bit of direct contact, or heat wave, from something briefly.

BUT for lighting composite motors... Ignition takes getting the propellant up to burning temp, and keeping heat going long enough that the case is pressurized. (This pressure is a combination from the igniter burn, pyrogen burning, black powder pellet, and propellant burn, etc.) During the pressurization time, the burn rate of the propellant increases. If you apply too much heat too quickly, and the pressure spikes, and then drops because you don't have enough burning propellant, you can snuff out the burn and have a "chuff". As motors and core diameters increase the need to bring up the amount of burning propellant AND case pressure in a balance takes longer.

Your "Flash Capacitor" vaporizing a wire, will likely not get enough volume of propellant burning to sustain the pressure. If it keeps burning, the propellant will re-pressurize the core, and you'll have a chuff followed by a slow ignition. (Or) the propellant burn will stop during the pressure drop, and you'll have a chuff followed by a failed ignition.

 

[Tractionengines]

To further the explanation this is why VERY FAST propellant motors like Warp-9 don't have ejection charges, even though the delay grain burns during the thrust phase, the sudden drop of case pressure at the end of the propellant burn, will actually snuff out the delay grain sometimes. So motor ejection was not reliable, and these motors require electronic deployment.

 

[os_tempore]

Unless you're not going to dip the igniters in anything, you're thinking way too much power. Check nakka-rocketry.net Richard Nakka has made an igniter from a grain of wheat bulb that can work with a refrigerated, mostly discharged 9V alkaline battery. I favor more power than that, but not as much as you are contemplating.

Another thing I've made ignitors from is carbon fiber, either tow or, more easily, a splinter of unidirectional composite*. I just wrap wire around either end of a quarter inch of it and pinch with pliers. Carbon fiber can take a pretty powerful zap. Enough to make a small mushroom cloud if you accidentally short some high voltage lines with a few ounces of it. And the most amazing 60 cycle hum. (No, it wasn't me.) You should check the resistance when using carbon fiber as a bridge wire, because yours might not be the same as what I have. I don't think I've bought anything from these guys, but they offer a lifetime supply for $10:
https://sollercompositesllc.com/product/t700-12k-carbon-fiber-1in-long-chopped-tow/
Again, I don't know what my carbon fiber is, so you may have to adjust the length.

* I suspect you can turn tow into composite with a little epoxy or even thin cyanoacrylate. The composite is easier to wrap wires around, because it's rigid.

That's pretty neat. I'm thinking of dipping the ignitor is "quick dip" for yet a bigger spark. Though I wondering if the amount of Spartan is akin to picking the right primer size for ammunition. Too much primer can blow it out and not enough and it's unreliable/slow burn to the main case.

I like high tech stuff (ie making things more complicated than necessary!). For sollercomposites, I've bought maaaany lengths of CF from them - T700 and otherwise. The guy that runs that place is pretty nice, too. They're good to buy from and sell good stuff too.

 

[os_tempore]

Lighting black powder up easy, and only takes a little bit of direct contact, or heat wave, from something briefly.

BUT for lighting composite motors... Ignition takes getting the propellant up to burning temp, and keeping heat going long enough that the case is pressurized. (This pressure is a combination from the igniter burn, pyrogen burning, black powder pellet, and propellant burn, etc.) During the pressurization time, the burn rate of the propellant increases. If you apply too much heat too quickly, and the pressure spikes, and then drops because you don't have enough burning propellant, you can snuff out the burn and have a "chuff". As motors and core diameters increase the need to bring up the amount of burning propellant AND case pressure in a balance takes longer.

Your "Flash Capacitor" vaporizing a wire, will likely not get enough volume of propellant burning to sustain the pressure. If it keeps burning, the propellant will re-pressurize the core, and you'll have a chuff followed by a slow ignition. (Or) the propellant burn will stop during the pressure drop, and you'll have a chuff followed by a failed ignition

Lighting black powder up easy, and only takes a little bit of direct contact, or heat wave, from something briefly.

BUT for lighting composite motors... Ignition takes getting the propellant up to burning temp, and keeping heat going long enough that the case is pressurized. (This pressure is a combination from the igniter burn, pyrogen burning, black powder pellet, and propellant burn, etc.) During the pressurization time, the burn rate of the propellant increases. If you apply too much heat too quickly, and the pressure spikes, and then drops because you don't have enough burning propellant, you can snuff out the burn and have a "chuff". As motors and core diameters increase the need to bring up the amount of burning propellant AND case pressure in a balance takes longer.

Your "Flash Capacitor" vaporizing a wire, will likely not get enough volume of propellant burning to sustain the pressure. If it keeps burning, the propellant will re-pressurize the core, and you'll have a chuff followed by a slow ignition. (Or) the propellant burn will stop during the pressure drop, and you'll have a chuff followed by a failed ignition.

Great info. Would the rapid ignition of that sparky dip for ignitors benifit the ignition cycle, or am I chasing the wrong rabbit on this?

If so, which is what it's starting to sound like, I think I will just keep regular caps and the lifepo4 in the launch pad base.

 

[Tractionengines]

Great info. Would the rapid ignition of that sparky dip for ignitors benifit the ignition cycle, or am I chasing the wrong rabbit on this?

If so, which is what it's starting to sound like, I think I will just keep regular caps and the lifepo4 in the launch pad base.

I would say for sure "chasing the wrong rabbit". I've seen launchers that fire the bridge wire on starters so forcefully, that it "pops" before the pyrogen lights. The shock wave pushes the "extremely flammable" material away without lighting it.

Its a balancing act, you need to bring up the temperature, AND internal pressure together, with no "dips" where either fall back.

NOTE: You can also get TOO energetic trying to get going faster. If you put SO much pressure that the nozzle can't release it to normal levels, then you'll CATO the motor. (Either split the case, or blow out one if the ends.)

 

[os_tempore]

I would say for sure "chasing the wrong rabbit". I've seen launchers that fire the bridge wire on starters so forcefully, that it "pops" before the pyrogen lights. The shock wave pushes the "extremely flammable" material away without lighting it.

Its a balancing act, you need to bring up the temperature, AND internal pressure together, with no "dips" where either fall back.

NOTE: You can also get TOO energetic trying to get going faster. If you put SO much pressure that the nozzle can't release it to normal levels, then you'll CATO the motor. (Either split the case, or blow out one if the ends.)

That's a fair point! The converter is $53 from Mouser, so my wife will be happy that's not being spent!


Ill still keep the caps, launcher base battery, and the other things I've described. I'll do away with the converter and flash cap. Now onto the design of the base!!

 

[lr64]

Suggest you make something dirt simple at first, so you'll have it around if you get an unexpected day of good weather and you want to launch on short notice.

 

[Tom Flint]

Above 16 volts, I've experienced the bridge wires on Estes igniters and other brands burning out so fast that they don't have time to light the pyrogen.

 

[os_tempore]

Thank you all for the advice and advisement. I'll stay with the 12vdc and setup enough capacitance to supply as much amps as I can get I'm going to stick with my high temp 12ga wiring throughout. For the connection to the ignitor itself, I'll figure out how to effectively move the amps without burning out my clips.

I'm sizing everything to the biggest motor I can see us using.

 

[lr64]

Just how many watts do you need? AWG 12 wire is supposed to have something like 1.6 ohms per 1,000 feet. So, if you were 500 feet away, running 1 amp through the bridge wire, you'd lose 1.6 volts. Which is not counting the local capacitor. And you'd be putting 10.4 watts into the bridge wire. I think it's more likely that you'll look at the price of that much wire and decide on some other option. But then, I'm cheap.
On the other hand, let's say you used 25 feet of wire from your capacitor. That would be 0.04 ohms. If you were going to be ridiculous and run 10 amps through the bridge wire, you'd lose a whole 0.4 volts. And the bridge wire would still be putting out 116 watts!
Have you read this page?:
https://www.nakka-rocketry.net/igniter.html#Xmas
It doesn't take all that much.

 

[tsmith1315]

I use regular outdoor extension cords and a 12V lead acid battery at launch control.

100’, and a 50’ in series if needed. They’re 10+ years old and live outside. The alligator clips are more of an issue, IME.

 

[Sooner Boomer]

Seems to me there are two ways to design/build a system to deliver high current; push all the current down the wires, or only send a command signal down the long stretch, and switch the current locally. The second method *does* require two batteries, but the "control" unit can be anything that will switch the relay, for example an Estes electron beam or e-launch.

 

[os_tempore]

Just how many watts do you need? AWG 12 wire is supposed to have something like 1.6 ohms per 1,000 feet. So, if you were 500 feet away, running 1 amp through the bridge wire, you'd lose 1.6 volts. Which is not counting the local capacitor. And you'd be putting 10.4 watts into the bridge wire. I think it's more likely that you'll look at the price of that much wire and decide on some other option. But then, I'm cheap.
On the other hand, let's say you used 25 feet of wire from your capacitor. That would be 0.04 ohms. If you were going to be ridiculous and run 10 amps through the bridge wire, you'd lose a whole 0.4 volts. And the bridge wire would still be putting out 116 watts!
Have you read this page?:
https://www.nakka-rocketry.net/igniter.html#Xmas
It doesn't take all that much.

There's been a lot of posts, I can understand how you didn't see what I said a few times prior - not sure why you're coming off as heated though. I'm not running anything through the long cord (between the control box and the launch base) except for a signal. The primary battery is in the launch base. The relays are all SSR's so low enough amp requirements to use 18ga for the 100ft run.

As far as what's needed for the ignitor in terms of amps, I'm simply attempting to mitigate any bottle necks in my circuit.

 

[os_tempore]

Seems to me there are two ways to design/build a system to deliver high current; push all the current down the wires, or only send a command signal down the long stretch, and switch the current locally. The second method *does* require two batteries, but the "control" unit can be anything that will switch the relay, for example an Estes electron beam or e-launch.

Yes, this is what I'm doing. I don't remember which post number it is though. The primary battery is in the launch base. The secondary battery is in the control box. Theres no crossover of power between the two battery systems. Likewise, there no power or return paths to the relays to eliminate any potential uninitiated firing. I'm wiring the box with a master switch that kills the entire circuit, then double safety on the firing line, ie a 2nd switch to connect the return leg and a big red button to energize the circuit. In that will be "show lights" to light the rocket up, a warning light on the pad to indicate power is on at the control box, and a green "go" strobe as an indicator the negative loop has been activated. I am debating on putting an indicator light for the actual ignitor being energized.

 

[Voyager1]

… The second method *does* require two batteries, …

A battery is not required at the wired launch controller if your pad relays are activated by a suitable line driver circuit. You can feed your pad battery voltage back down a third conductor to your launch switch box. Yes, you do have a voltage drop over the low current switch circuit, but that doesn’t matter. I’ve used this technique quite successfully over 30, 60 and 90m. It’s not ideal, but it works.

There are some documents and links that discuss igniter characteristics.

https://www.jacobsrocketry.com/aer/ignition_and_igniters.htm