# How can I ignite these three rocket igniters?

#### Max CR

Now the thing is I want to make this as CHEAP as possible. Can you help me find on radio shack's website thsi capicotor and battery you are talking about? It is very difficuilt to keep looking back and checking to ese what works and what doesnt.

#### minorwork

Those will do, though you can most likely get away with using the smaller CR2016 or the even-smaller CR1216 size; since they'll be charging the cap, instead of firing the igniters directly, they don't need to source a lot of current although it may take a minute or two for them to fully charge the cap. As for a capacitor, you want a high-density type with capacitance in the Farad range and a minimum working voltage of around 15 V. It won't be very cheap (and definitely not available from RadioShack), however if you can recover it intact, it can be re-used indefinitely.
The 2032 delivers more milliamps and so maybe downsize the capacitor?

#### Max CR

Ok so I will use those batteries. Now what capacitor should I ues? What i dont understandi s why I am going to use a 3 volt battery if each igniter requires 9 volts to ignite. Even in series, that will only be 9 volts total for three igniters.

#### minorwork

Ok so I will use those batteries. Now what capacitor should I ues? What i dont understandi s why I am going to use a 3 volt battery if each igniter requires 9 volts to ignite. Even in series, that will only be 9 volts total for three igniters.
You're scaring me again. Each igniter in parallel will see 9 volts. Should be enough voltage if you can deliver enough amps quick enough to maintain that voltage for long enough to fire the igniter. Ergo the capacitor.

#### Max CR

Aright. Now why wouldn't I just use a regular 9 volt battery as the power source? Or two 9 volt batteries?

#### negitron

The 2032 delivers more milliamps and so maybe downsize the capacitor?
No, but 2032s will charge the cap faster than the 1216s. This may or may not be important to the OP. If he needs to fire very shortly after connecting, then the higher amperage batteries are more suitable, at the cost of increased liftoff mass.

#### negitron

Aright. Now why wouldn't I just use a regular 9 volt battery as the power source? Or two 9 volt batteries?
Weight. Four CR2032s or 1216s weigh MUCH less than even one 9V battery, even the lightweight lithium ones. If weight isn't a concern after all, then a 9V lithium battery will do fine.

I also feel compelled to point out that "cheap" and "reliable," while not necessarily mutually exclusive, are not often considered together in a single design for a reason.

#### Max CR

Ok. I will just stick with the 9 volt battery sicne I am not interested in spending any more money. Now, as for the capicotor, you said that i need to have a capacitor rated at 11 amps, I believe.

This one appears to be able to get the job done. What do you think? http://www.radioshack.com/product/index.jsp?productId=2102508

Any ideas?

#### minorwork

Ok. I will just stick with the 9 volt battery sicne I am not interested in spending any more money. Now, as for the capicotor, you said that i need to have a capacitor rated at 11 amps, I believe.

This one appears to be able to get the job done. What do you think? http://www.radioshack.com/product/index.jsp?productId=2102508
Negitron suggested a Farad which is a lot of capacitance. Reasonable sized ones are limited to low voltages such as 5 volts or so. Your voltage rating in capacitors is determined by what is in the space between the plates. Too high and there is an arc between the plates and you've a short or if there is enough power you blow up the capacitor. You can tell these because they are swelled up and maybe cracked. I've heard the little ones blow in my computer. Sounded like a black cat firecracker. In the late 90s there was millions of faulty electrolytics let loose and installed. What a nightmare. Hospitals were corrected first but nobody cared about the coal mine or personal computer power supplies. A true pain in the neck for me. And job security.

Here be some http://www.hifisoundconnection.com/Shop/Control/fp/tcat/28042/SFV/30046". You won't like the price or size.

You're on the right track testing a single 9 volt battery. You might consider more than 1 of those capacitors across the positive/negative leads. In parallel mind you. Test. Test. You'll get it.

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There just has to be a cheaper alternative to all of this. How about adding three 9 volt batteries in parallel in the circuit? That is where my line of thinking is right now. I don't want to spend anything over $20. As I said before, I was able to successfully do this once before using two batteries in parallel charged at 10 volts with the igniters in parellell also. The only problem with doing this again is that the batteries will not stay at 10 volts because they are not desigend to do so. How can I work out this situation from here? I have tried putting the batteries in series but that did not work. It seems the batteries have to be in parallel so their amperage will add up but yet the voltage also needs to be 10 volts or above #### minorwork I'm going to have to pick up one of those disposable cameras and see what it will do. Lots of stuff on YouTube on this. This http://www.youtube.com/watch?v=8XXfEoDIF0Q". Three cameras for$9 from wal mart. Good price. Three hundred volts available from a single AA cell.

Note how taking apart the cameras can get you shocked if you don't discharge the capacitor.

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#### minorwork

There just has to be a cheaper alternative to all of this. How about adding three 9 volt batteries in parallel in the circuit? That is where my line of thinking is right now. I don't want to spend anything over \$20. As I said before, I was able to successfully do this once before using two batteries in parallel charged at 10 volts with the igniters in parellell also. The only problem with doing this again is that the batteries will not stay at 10 volts because they are not desigend to do so.

How can I work out this situation from here? I have tried putting the batteries in series but that did not work. It seems the batteries have to be in parallel so their amperage will add up but yet the voltage also needs to be 10 volts or above
Cheaper, better, faster. Pick two.

#### negitron

It means you can do something better and cheaper, faster and cheaper or better and faster. But not all three.

It's an old engineering maxim.

#### minorwork

What does this mean? ...
This is the engineer's mantra. When management wants something done the engineer presents the three choices to management. Cheaper, faster, better. You can only get two. If the solution is cheap and fast it won't be better. If better and cheaper it will take longer to produce. If faster and better then it will certainly not be cheap.

These be the trade offs that concern any designed product. Where did the mantra come from? I don't know. I think the trade offs are some kind of state law.:

This applies in all areas. Your igniter problem in particular. If a capacitor were in existence that could be the same size as the battery and store the same amount of energy and could drain itself totally in in a second then it would be expensive. If you want the solution now it might be cheap and available from parts you already have but it will not be the best solution.

Clearer now? It is a humorous fact of life. Applies to wives too. Just don't tell mine.

#### Max CR

So I just did two tests. All three igniters were in parallel.

For my first test, the two batteries had a voltage of 9.65 volts. They were in series. There was ccontinuity.Only two of the three igniters ignited.

For my second test, the two batteries had a voltage of 9.65 volts. They were in parallel. There was continuity. Again, only two of the three igniters ignited. The same igniter did not ignite.

I am considering adding a third battery to the batteries in series. Thsi would bring the voltage up to about 27 volts. Do you think this would be good enough to ignite the three igniters simultaneously? What I dont udnerstand, is that each igniter seems to require 9.6 volts to igntie. However, they are getting more volts than that and there is still failure. Good it be the amperage that is the problem? Should I put the three batteries in parllel?

What other cost effective solutions could there be?

#### Phrak

What is the resistance of your igniters?

0.8 ohms each

#### Max CR

Now lets say that I put all of the igntiers in series. There is continuity throughout the series. Does that mean that all three igniters must ignite? Will the voltage and amperage be easily disributed? Is it possible for only one igniter to ignite and two not? I have spent nearly the whole day working on this with no success. This is extremely frustrating.

Any ideas?

#### Max CR

Ok. I am giong to try and put these igniters in series tomorrow. How does that sound? I mean, the regular controler to ignite an igniter uses four 1.5 volt batteries in series. That means that the igniter requires 6 volts to ignite. Say if I put the three igniters I have in series and I have two 9 volt batteries also in series, then this should cause the igniters to ignite, correct? Shouldn't just one 9 volt battery get the job done?

I can't get over how unsuccessful this is. I am trying to figure out WHAT will work?!?! Will thsi work?!

#### Phrak

0.8 ohms each
OK. Three in parallel will have a resistance of 0.27 ohms. And you never came back to say how your camera experiments went after everyone was so helpful, so why am helping now?

For greatest power transfer from batteries to igniters you want the batteries to have the same value of internal resistance. Get on your search engine and look up the impedence of 9 volt batteries.

Why are you using 9V batteries rather than 1.5V?

Commercial 9 volt alkaline batteries have a resistance of 2.8 ohms. For two in parallel 80% of the power goes to heating the batteries.

Panasonic quotes 0.13 ohms for their AA alkalines. Dollars to nickles.

What other sources of resistance do you have? What gauge and how long are the wires? is there a relay involved?

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Staff Emeritus
Any ideas?
You're scaring me. That was 4 minutes since your last message. If you're that impatient, I worry about you handling rocket engines. I also worry because minorwork gave you what looks to be a very valuable link, which you seem not to have taken the time to read.

Rockets can be dangerous. Placing the ignition source on the rocket and out of your direct control adds to the danger. Using an ignition source that was not designed by an expert adds to the danger. Focusing on cost and not safety adds to the danger.

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