# Igniting model rocket engines **URL:** \ **Category:** Factual Questions\ **Created:** [December 27, 2014, 10:43pm UTC](https://boards.straightdope.com/t/igniting-model-rocket-engines/708306 "2014-12-27T22:43:13Z")\ **Posts on this page:** 11\ **Page:** 2
**Author:** ![Amateur\_Barbarian](https://avatars.discourse-cdn.com/v4/letter/a/59ef9b/32.png) [@Amateur\_Barbarian](https://boards.straightdope.com/u/Amateur_Barbarian)\ **Post date:** [December 29, 2014, 2:41am UTC](https://boards.straightdope.com/t/igniting-model-rocket-engines/708306/21 "2014-12-29T02:41:04Z")
9v are pretty marginal in terms of the amount of current they can deliver, so I can see a very slightly degraded one not having enough juice. Most of the controllers I’ve used, bought and built, had multiple cells. The voltage is a little lower but the current is much higher, and it’s amps that fire the igniter more than volts. Build your own controller and use at least four AA cells, if not D cells or a lantern battery. You’ll never have a failed ignite again. ---
**Author:** ![jz78817](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/jz78817/32/1028_2.png) [@jz78817](https://boards.straightdope.com/u/jz78817)\ **Post date:** [December 29, 2014, 2:50am UTC](https://boards.straightdope.com/t/igniting-model-rocket-engines/708306/22 "2014-12-29T02:50:14Z")
> [@joemama24\_98](#): > > Do different brand batteries in the same format deliver different amperage? yes, and it all depends on the cell chemistry. the physical form factor has been pretty much set into AAA, AA, C, D, and 9 Volt. back in the day, the cell chemistry was carbon-zinc or “dry cell,” which is what a cell is if labeled “heavy duty” or “extra heavy duty.” These cells were 1.5 volts. Then, alkaline cell chemistry came along which was still 1.5 volts nominally, but had lower internal resistance and greater energy capacity. When nickel-based rechargables hit the market, they had a slightly lower nominal voltage of 1.2 volts, but had such a low internal resistance they could deliver much more current to the load. ---
**Author:** ![Johnny\_L.A](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/johnny_l.a/32/1084_2.png) [@Johnny\_L.A](https://boards.straightdope.com/u/Johnny_L.A)\ **Post date:** [December 29, 2014, 2:55am UTC](https://boards.straightdope.com/t/igniting-model-rocket-engines/708306/23 "2014-12-29T02:55:02Z")
> [@Amateur\_Barbarian](#): > > Build your own controller and use at least four AA cells, if not D cells or a lantern battery. You’ll never have a failed ignite again. Or buy an [Estes Electron Beam launch controller](http://www.amazon.com/Estes-302220-Electron-Launch-Controller/dp/B0006NAQ50). ([This is what mine looked like](http://modelrocketbuilding.blogspot.com/2014/02/estes-solar-launch-controller-fs-10_20.html).) ---
**Author:** ![Amateur\_Barbarian](https://avatars.discourse-cdn.com/v4/letter/a/59ef9b/32.png) [@Amateur\_Barbarian](https://boards.straightdope.com/u/Amateur_Barbarian)\ **Post date:** [December 29, 2014, 4:02am UTC](https://boards.straightdope.com/t/igniting-model-rocket-engines/708306/24 "2014-12-29T04:02:41Z")
A “controller” is just a battery with leads out to the launch pad. A launch button is fancy. A safety key or arming switch is a good idea. But the whole thing is just a battery on one end and an igniter on the other, and I launched many a shot with just a battery and the leads. I also built one or two really fancy ones with safety keys, continuity testers, battery gauges and built in chargers for a nicad block. It’s a fun thing to build, and easy, and easy to make the Estes stuff look crummy. 🙂 ---
**Author:** ![bump](https://avatars.discourse-cdn.com/v4/letter/b/7c8e57/32.png) [@bump](https://boards.straightdope.com/u/bump)\ **Post date:** [December 29, 2014, 4:59am UTC](https://boards.straightdope.com/t/igniting-model-rocket-engines/708306/25 "2014-12-29T04:59:32Z")
> [@Joey\_P](#): > > I did these in middle school as well (and then on my own around the same time). This would have been in the early 90’s. I remember them going off nearly every single time. Duds were pretty rare. I launched a shitload of model rockets as a pre-teen and teenager (1984-1990 or so), and I honestly don’t recall ever having a dud igniter. Some electrical problems with my screwy Centauri launch pad/igniter setup, but nothing that wasn’t easily fixed. ---
**Author:** ![Carl\_Pham](https://avatars.discourse-cdn.com/v4/letter/c/e9a140/32.png) [@Carl\_Pham](https://boards.straightdope.com/u/Carl_Pham)\ **Post date:** [December 29, 2014, 6:57am UTC](https://boards.straightdope.com/t/igniting-model-rocket-engines/708306/26 "2014-12-29T06:57:49Z")
I never had a problem. But then I used a 12V car battery. _Lots_ of current. ---
**Author:** ![Machine\_Elf](https://avatars.discourse-cdn.com/v4/letter/m/82dd89/32.png) [@Machine\_Elf](https://boards.straightdope.com/u/Machine_Elf)\ **Post date:** [December 29, 2014, 8:08pm UTC](https://boards.straightdope.com/t/igniting-model-rocket-engines/708306/27 "2014-12-29T20:08:09Z")
> [@Amateur\_Barbarian](#): > > 9v are pretty marginal in terms of the amount of current they can deliver, so I can see a very slightly degraded one not having enough juice. This. A classic 9-volt battery is not big enough to supply the needed current. If you measure the voltage across the battery terminals when you press the launch button, I’ll wager it dips way below 9 volts. I remember having similar issues when I was a kid. You need a battery that can deliver plenty of current. That means one of those massive [“lantern batteries.”](https://www.google.com/search?tbm=isch&hl=en&source=hp&q=lantern+battery&gbv=2&oq=lantern+battery&gs_l=img.3..0l8j0i5l2.1078.2406.0.2578.15.10.0.0.0.0.250.1266.1j3j3.7.0.msedr...0...1ac.1.34.img..8.7.1266.72VaWkzQcdg) Car battery works fine too, but is inconvenient (unless you’re using the one installed in the car you drove to the launch site). I recall pulling the fuses from firecrackers and using them to light model rocket engines. ---
**Author:** ![jz78817](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/jz78817/32/1028_2.png) [@jz78817](https://boards.straightdope.com/u/jz78817)\ **Post date:** [December 29, 2014, 8:28pm UTC](https://boards.straightdope.com/t/igniting-model-rocket-engines/708306/28 "2014-12-29T20:28:14Z")
car batteries are also extraordinarily unforgiving if you accidentally short them. ---
**Author:** ![Amateur\_Barbarian](https://avatars.discourse-cdn.com/v4/letter/a/59ef9b/32.png) [@Amateur\_Barbarian](https://boards.straightdope.com/u/Amateur_Barbarian)\ **Post date:** [December 29, 2014, 8:49pm UTC](https://boards.straightdope.com/t/igniting-model-rocket-engines/708306/29 "2014-12-29T20:49:52Z")
> [@jz78817](#): > > car batteries are also extraordinarily unforgiving if you accidentally short them. While a car battery can be a convenient field power source for many things, you probably want the launch site a good distance away from a car, and a fuse right at the connection. Using anything like a medium to large LA battery for rocket launches is like using a sledge hammer to drive tacks, and sooner or later something _B_A_D_ is going to happen with a short, a spill or just dropping the heavy sucker on your foot. A lantern battery is plenty sledge-y enough for the purpose. 🙂 ---
**Author:** ![kenobi\_65](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/kenobi_65/32/13178_2.png) [@kenobi\_65](https://boards.straightdope.com/u/kenobi_65)\ **Post date:** [December 29, 2014, 8:58pm UTC](https://boards.straightdope.com/t/igniting-model-rocket-engines/708306/30 "2014-12-29T20:58:43Z")
I’ve been launching low-power model rockets, on and off, for 35 years. I very rarely have issues with engines not igniting the first time; when I do have issues, it’s nearly always operator error. Modern model rocket igniters are actually pretty good. The advice about fresh, alkaline batteries is good. Even if your batteries are strong enough to light the little light on the controller, they may still be too weak to deliver enough power to fire the igniter. Another bit of advice: make sure that the igniter is fully inserted all the way into the engine, so that the pyro bit is fully in contact with the engine grain. Assuming that you’re using Estes engines, they should come with little plastic plugs to hold the igniter in place, so be sure to use them. One other bit of advice: make sure that you aren’t creating a short in your line. Make sure that the ends of the igniter aren’t touching each other, and that your igniter and clips aren’t touching the metal blast deflector on your pad. Yes, I know a few folks who use fuse cord – it does work, but it has the disadvantage of being difficult to abort once you light it. (Also, I believe it may also be illegal to use for model rocketry in some jurisdictions.) ---
**Author:** ![kenobi\_65](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/kenobi_65/32/13178_2.png) [@kenobi\_65](https://boards.straightdope.com/u/kenobi_65)\ **Post date:** [December 29, 2014, 9:21pm UTC](https://boards.straightdope.com/t/igniting-model-rocket-engines/708306/31 "2014-12-29T21:21:14Z")
> [@kenobi\_65](#): > > One other bit of advice: make sure that you aren’t creating a short in your line. Make sure that the ends of the igniter aren’t touching each other, and that your igniter and clips aren’t touching the metal blast deflector on your pad. After I posted this, I saw that Tangent had made the same suggestion, but I wasn’t able to get it to edit to acknowledge this. Sorry about that! [Previous page](https://boards.straightdope.com/t/igniting-model-rocket-engines/708306.md?page=1)