How can I ignite these three rocket igniters?

[Max CR]

First off, let me say that what I am working on has taken me a few days to get to work and I just can't figure it out. It is really frustrating so any help is really appreciated.

I have three igniters. They are connected to a circuit. Once a switch is turned to "on" the three igniters are supposed to ignite.

This is the diagram

I am using two nine volt batteries each charged at 9.50 volts. Now, if I remove the igniters from the diagram and test the voltage of each side of the wire, the voltage reads about 9.50 volts at all locations. Now, when I attach the igniters to these wires, and to a test ignition, only one of the igniters ignite. the batteries are connected in parallel, and the igniters are connected in parallel also.

 

[negitron]

I thought your batteries were to be in series, for a nominal 18 V.

 

[Max CR]

They were in series but then I removed them in parallel. This is because when I tested the circuit with the batteries in parallel only one igniter ignited.

Also, as takled about in my previous post, the voltages near the igniters were rapidly jumping from one voltage to another. I found out this is because of the clips I was using. Apparantly, they can't be used in this sort of project.

 

[negitron]

Try using something other than 9 V batteries. Those small rectangular batteries have a very high internal resistance and cannot supply a large current--typically less than an amp, because they are comprised of 6 smaller 1.5 V cells (usually AAAA-size) in series. I would suggest a small 12 V lead-acid gel cell, such as used for alarm systems, UPS units and emergency lighting since these have a much smaller internal resistance and can supply several tens of amps easily.

 

[Max CR]

Ok now where can I buy this item? It needs to be inside of my rocket which means that it neeeds to be light.

 

[Max CR]

Ok. Now I need to buy this item from radio shack because that is the only hardware store in my area. The problem is that I cannot find this item that they sell.

 

[negitron]

I thought the battery was 200 feet away?

 

[Max CR]

No. That is a different circuit. i already figured out how to launch the rocket frmo 200 feet away using one car battery. Once the rocket is in the sky, another circuit will be turned to on which will ignite a different part of the rocket in the sky.

That is what I am trying to figure out. I am trying to figure out how to launch these three igniters.
Thanks

 

[negitron]

Ahh. In that case, use lithium cells. They are very light and can source a lot of current.

 

[Max CR]

Ok. I looked into these batteries. It appears that their voltages are about 3 volts. I have found that the igniters need atleast 9 volts to ignite. I have found this through trial and error. Do you think we will definately be able to know what batteries my circuit needs if we had detailed information about the voltage and amperage required to ignite the igniters?

It seems like getting those batteries will just lead to more trial and error.

 

[flatmaster]

Also, I would suggest putting the ignighters in series. This would ensure that they all light and at the same time.

Also, Unless I'm mistaken, I believe you can buy model rocket motors with an ejection charge that also lights the next stage.

 

[Max CR]

I understand that the ejection charge can do that but the ejection charge in this design is beign used for other applications. Therefore, I need to use a battery to ignite tthe followign stage.

Why exactly does putting the batteries in series ensure that they all light at the same time?

 

[flatmaster]

Not only the batteries, but put the ingighters in series. Actually, I'm rethinking that now.

 

[negitron]

Not only the batteries, but put the ingighters in series.

No, don't do that. What will happen inevitably is that one will fire and fuse open first, leaving the rest on an open circuit and unable to fire. Like those annoying Christmas tree lights. One goes out and the entire string is dead.

 

[flatmaster]

No, don't do that. What will happen inevitably is that one will fire and fuse open first, leaving the rest on an open circuit and unable to fire. Like those annoying Christmas tree lights. One goes out and the entire string is dead.

That's right. I see it now. Once again comes the glorious lesson of being wrong.

You do want the batteries in series though. Double the voltage, double the curent.

v=ir

i = v/r

 

[negitron]

That's right. I see it now. You do want the batteries in series though. Double the voltage, double the curent.

Almost. You do double the open-circuit voltage, but remember that you're also putting the batteries' internal resistances in series so your actual load voltage and current will be somewhat less than doubled because your load resistance in series with the battery internal resistance act as a voltage divider.

 

[Max CR]

Ok. Now you are saying that I should put these two 9 volt batteries in series? Also, after looking through my notes, I found that if I have two batteries charged at 10 volts in parallel in the circuit, then all igniters ignite simultaneously.

Now, if I were to use these lithium cells, it appears that the voltage will be three volts which my understanding shows is just too low. The only problem is I cannot charge my batteries up to 10 volts and have them stay at that voltage.

Any ideas?

 

[minorwork]

No, don't do that. What will happen inevitably is that one will fire and fuse open first, leaving the rest on an open circuit and unable to fire. Like those annoying Christmas tree lights. One goes out and the entire string is dead.

Bad advice. More likely is a parallel wiring results in a fuse close of one of the igniters pulling all the amps leaving not enough for the rest of the igniters. There is a reason the law required series wiring of the blasting caps in the mine. Setting off twenty shots at a time in the mine required the caps to be wired in series. One check for continuity ensures that all caps are made up. The blaster charged a large capacitor to ensure a large amperage flowed thru the series circuit igniting all the shots. Wiring in parallel would require the testing of each circuit for continuity. Series wiring ensures that all are in the circuit. If one is not made up, then none will go off. Parallel wiring may result in only one shot going off because the rest are not making a circuit. Not good when men will have to load out the shot material with maybe several live sticks of Tovex in the gob.

Wire the blasting caps or igniters in series and use a car battery for your three rocket igniters. Test for continuity with a high impedance quality meter such as a Fluke 77 or find a galvanometer. Illegal to use the Fluke in the mine. Only the galvanometer.

The following link mentions the advantages of series wiring and the disadvantages of parallel wiring of your igniters. The problems generally manifest on larger numbers of igniters but it helps to understand what is going on and get it right the first time.
http://www.pyromate.com/Basics-of-Electrical-Firing.htm

 

[Max CR]

Bad advice. There is a reason the law required series wiring of the blasting caps in the mine. Setting off twenty shots at a time in the mine required the caps to be wired in series. One check for continuity ensures that all caps are made up. The blaster charged a large capacitor to ensure a large amperage flowed thru the series circuit igniting all the shots. Wiring in parallel would require the testing of each circuit for continuity. Series wiring ensures that all are in the circuit. If one is not made up, then none will go off. Parallel wiring may result in only one shot going off because the rest are not making a circuit. Not good when men will have to load out the shot material with maybe several live sticks of Tovex in the gob.

Wire the blasting caps or igniters in series and use a car battery for your three rocket igniters. Test for continuity with a high impedance quality meter such as a Fluke 77 or find a galvanometer. Illegal to use the Fluke in the mine. Only the galvanometer.

The following link mentions the advantages of series wiring and the disadvantages of parallel wiring of your igniters. The problems generally manifest on larger numbers of igniters but it helps to understand what is going on and get it right the first time.
http://www.pyromate.com/Basics-of-Electrical-Firing.htm

Ok. Now there is a problem I can see with this. Say that I use the igniters in series. If the circuit is turned to on, I can see the first igniter in the series to ignite first. Then, I can see this igniter becoming burnt out which will then ruin the continuity of the circuit. Thsi will then cause the other two igniters to not igntie. If this hapens, then I am in trouble. These three igniters need to ignite simultaneously. That is why I chose to use a parallel circuit.

let me know what you think.

 

[minorwork]

Ok. Now there is a problem I can see with this. Say that I use the igniters in series. If the circuit is turned to on, I can see the first igniter in the series to ignite first. Then, I can see this igniter becoming burnt out which will then ruin the continuity of the circuit. Thsi will then cause the other two igniters to not igntie. If this hapens, then I am in trouble. These three igniters need to ignite simultaneously. That is why I chose to use a parallel circuit.

let me know what you think.

Read the link. Much better and more authoritative than this old retired coal miner. Your picture of the chain of events in the series setup is eliminated by having enough amps available at your blaster. The one in the mine was pretty heavy and it took about 15 seconds for the capacitor to come up enough to light the ready light. For your rocket motors I think a 12 volt car battery will be enough. You're not trying to set off 20 shots at a time and some of those shots might have three or more sticks of Tovex. Just pretend that what you are doing can be so unforgiving that you can't take chances.

How would you test your parallel circuit? Series is simple. Check the two wires you hook to your blaster or battery and in a series an open on any igniter will be revealed. Not so on a parallel arrangement. http://www.pyromate.com/Basics-of-Electrical-Firing.htm" Also refresh the page as I have altered my previous post somewhat.

 

[Max CR]

I know how to test the parallel circuit and check for continuity. When I am using a circuit with the igniters in parallel, the igniters just do not ignite simultaneously. I guess that havign the igniters in serieis would seem like a better idea because then they will all ignite at the same time, guaranteed, correct?

Now, I have used an equation. I am usign three estes igniters each which have a resistance of 0.8 ohms

V=IR
V= 0.15 Amps x 2.7 ohms = 0.36 volts

Clearly, 0.36 volts will not be enough. What is the problem?

I also cannot use a car battery because thsi particyular circuit will be used in flight and a car battery will just be too heavy.

 

[minorwork]

I know how to test the parallel circuit and check for continuity. When I am using a circuit with the igniters in parallel, the igniters just do not ignite simultaneously. I guess that havign the igniters in serieis would seem like a better idea because then they will all ignite at the same time, guaranteed, correct?

Now, I have used an equation. I am usign three estes igniters each which have a resistance of 0.8 ohms

V=IR
V= 0.15 Amps x 2.7 ohms = 0.36 volts

Clearly, 0.36 volts will not be enough. What is the problem?

I also cannot use a car battery because thsi particyular circuit will be used in flight and a car battery will just be too heavy.

OK. I've been looking around and have found a couple of other links. http://books.google.com/books?id=sd...vntDw&sa=X&oi=book_result&ct=result&resnum=1"

http://oai.dtic.mil/oai/oai?verb=getRecord&metadataPrefix=html&identifier=AD0278832"

If you can't test, since I understand the beast is already in the air, then you need to put a little shotgun shell powder in with the igniter or something else easily ignited by a brief heating to combustion temperature. I'd often considered building a 2 liter water first stage with a trigger detection of some type (accelerometer?) of the decrease of acceleration when the water ran out and so fire off the chemical engines. Never did it though. Have to consider how tuff those Estes igniters are and how reliable. I've had problems in single igniter launches before and found the igniter open electrically.

To make a series set of igniters go off well you need enough voltage and enough amperage. 500 mfd 35 volt capacitors don't weigh much. Charge them to twenty four volts. Amperage is the same in all the igniters in series circuits. Parallel would be ok if you could guarantee each igniter had the same resistance and all were hooked up. The parallel arrangement uses more power which translates to unneeded weight in your case, I think. You could charge the capacitor(s) on the ground and they could be the ignition source. Don't know what you've got going though. At liftoff they could break an umbilical line and the craft could be running then on internal power provided by the capacitor.

 

[Max CR]

I am looking to make this as simple as possible. I have a switch which will be turned to on by a separate system. Now, this switch then needs to cause three rocket engines to ignite simultaneously. I also have 9 volt batteries to use as the capacitor.

Now, working with what I have, do you believe the batteries should be in serieis or parallel? Do you believe the igniters should be in seriies or parallel?

Thanks

 

[minorwork]

I know how to test the parallel circuit and check for continuity. When I am using a circuit with the igniters in parallel, the igniters just do not ignite simultaneously. I guess that havign the igniters in serieis would seem like a better idea because then they will all ignite at the same time, guaranteed, correct?

The only thing I can guarantee is that when you make your first solo skydive that you will have this thought, "I hope all this stuff works." With the series, if there is no continuity you'll still have 3 good engines. With parallel, who knows.

Now, I have used an equation. I am using three estes igniters each which have a resistance of 0.8 ohms

V=IR
V= 0.15 Amps x 2.7 ohms = 0.36 volts

Clearly, 0.36 volts will not be enough. What is the problem?

You need a single pulse with enough voltage and amps to set off that blue stuff on the igniters which will set off the engines, hopefully simultaneously. That is why I would use, and have used in single stage launches, a little bit of shotgun shell powder in each nozzle. Not the fff or ffff rifle powder. They be ok for an ejection charge but burns too fast for the ignition aid purpose. Half of a pencil eraser or so is what I used. Still, if there be an open, you're screwed.

I also cannot use a car battery because thsi particyular circuit will be used in flight and a car battery will just be too heavy.

Get your calculator out and a formula and figure the numbers on a 35 volt 500 mfd DC aluminum electrolytic polarity sensitive capacitor charged to 24 volts. I'm just guessing it would work. Maybe two of them in parallel. Test this on the igniters alone in a little powder on the ground. You just need one good pulse. If you've any battery left after that you're carrying wasted weight. The capacitors are about a 25 cent piece around and about 2 inches long and light weight.

 

[minorwork]

I am looking to make this as simple as possible. I have a switch which will be turned to on by a separate system. Now, this switch then needs to cause three rocket engines to ignite simultaneously. I also have 9 volt batteries to use as the capacitor.

Now, working with what I have, do you believe the batteries should be in serieis or parallel? Do you believe the igniters should be in seriies or parallel?

Thanks

Is your switch electronic? A mercury inertia switch? 9 volt batteries is what you want to use instead of a capacitor. Right? negitron has already mentioned the internal impedance of the 9 volt batteries. They're made of a bunch of little bitty single cells. They work by a chemical reaction which is a negative. A capacitor works by the storage of an electric field with almost no internal impedance. This is why a capacitor storage for an electric car could be charged very quickly and discharged very quickly instead of the slower amp draw and supply of the chemical batteries.

Two 9 volt batteries in series is 18 volts. I don't know how many amps they will flow in a dead short. I think that the 24 volt charge on the capacitor will flow more amps quicker due to the little to no impedance.

But if you are going to use the heavy batteries. Go for the batteries in series as well as the igniters. Nothing so far has indicated you can't put that capacitor across the positive and negative of your power supply to give it a good shot of amperage when your switch closes. I think your problem stems from the lack of a good high amperage pulse. Those 9 volters just don't get it for that application. The capacitors across the positive and negative (watch the polarity of electrolytics) will improve the high amp pulse considerably.

 

[minorwork]

Radio Shack used to carry the capacitor. That's where we got them for a while at the mine. Used them to buffer the 24 volt power voltage levels in an RS-485 network system that monitored carbon monoxide levels on the belts. A micro computer and co sensor every thousand feet and we had about 6 or 7 miles of belt. The analog sensor like steady voltage and the digital drivers pulled a lot of current when driving the line with the data. To steady the voltage for the analog sensor and its analog to voltage converter in particular the capacitors across the 24 volt DC line worked beautifully. Had a capacitor at each microcomputer every thousand feet.

Hey I just found the capacitor. I was wrong on its capacity. These be the right ones. Apologies. http://www.radioshack.com/product/index.jsp?productId=2102508". It be smaller.

 

[Phrak]

You lack amps, not volts.

 

[minorwork]

You lack amps, not volts.

And a capacitor stores them.

 

[Max CR]

Ok. Now the only problem with me using the capicitor is that I am unfamiliar with how they work. How many capicitors should i put in the circuit in series? On the capicitor, how do I charge it and place positive and negative no both ends of it?

Thanks

 

[Max CR]

Also, something that is really worrying me is a problem with putting the igniters in series. If I put the igniters in series, and the circuit is turned on, I am worried that the first igniter in the series will ignite and then burn out too quickly. If it burns out too quickly, it will prevent the other igniters from igniting. After the gun powder on the metal wires is done burning, it causes the clips to break. This may happen to the first one and prevent the other ones from igniting.

 

[minorwork]

Also, something that is really worrying me is a problem with putting the igniters in series. If I put the igniters in series, and the circuit is turned on, I am worried that the first igniter in the series will ignite and then burn out too quickly. If it burns out too quickly, it will prevent the other igniters from igniting. After the gun powder on the metal wires is done burning, it causes the clips to break. This may happen to the first one and prevent the other ones from igniting.

Test on the ground. The igniters may be too expensive to use for tests. Get some individual strands of wire from some scrap electrical cord. Get yourself three individual single wires. They'll be about the sized of a hair or smaller. Hell, use a strand from some steel wool though they are pretty brittle and break easily. We used to take such a little piece of wire in a slit on a paper match head and attach them to a piece of paper clip that had been pressed with some lineman pliers to leave a cross check pattern so the thin igniter wire itself would hold on, put some tape around the thing to hold it together and we had an igniter. Estes' were more reliable though. Wire three in a series circuit with bigger wire between them and test away.

Maybe a single 9 volt battery will do the job if you have a capacitor (that 4700 mfd one) attached across the leads. A capacitor reads as an open circuit after it is charged. Take two pieces of aluminum foil and put a sheet of wax paper between the aluminum sheets. You have made a capacitor. The electrical energy is stored in the electrical field between the two sheets. When you attach the + side of the battery to the positive side of the electrolytic capacitor and the negative side of the battery to the negative side of the capacitor, then the battery will charge the capacitor to the voltage of the battery. Now you have something like that balloon on a set of bagpipes where you store the air that you blow out so that you can breathe in between and still have air pressure to sound the reeds.

Another way to see a capacitor. You have a little air pump that plugs into the cigarette lighter of your car. This will be the equivalent of your 9 volt battery. This pump/battery can deliver a little bit of air/amps until it maxes out to its capacity of 150 psi/9 volts, but this takes a long time. What we need is a "lot of air all at once at the maximum pressure"/"a lot of amps all at once at the maximum voltage." So we make a storage device. For the air we use a tank. For the battery we use a capacitor. The 9 volt trickles into the capacitor enough amps that when released all at once will be more than enough to heat all the igniters in the circuit simultaneously to ignition temperature. Equal amps flow in each load in a series circuit. You put enough amps and voltage simultaneously at the igniters and all three will heat up as one. Test this with the cheap little wires suggested.

If 9 volts is enough voltage to set one off, then you need, for the series enough amps/current fast enough to keep the voltage levels up long enough to get all three to ignition temperatures. A 9 volt battery can only deliver so many amps to a load in a given amount of time because the generation of the amps is chemical and is a high resistance source itself since the current sees each of the little cells as a load too. This generates heat in the battery itself in a high load condition. Short out the leads of a 9 volt battery and you'll feel the battery get hot.

The capacitor stores amps if given time to charge to whatever voltage is powering it.

You may be able to get away with a 1.5 volt battery. Consider that the disposable cameras at the drug store use just such a power source to generate 300 volts to flash a strobe. Lookout with these. They can bite if they don't have a bleed-off resistor! Test, Test.

What happens if you have a 9 volt battery with a capacitor across the leads. The battery let's a smaller flow of electrons into the capacitor over a longer period of time so that when we need a lot of electrons to flow in a short period of time we now have, with the capacitor, a large easily moved supply of electron at 9 volts that can flow with little resistance to our igniter load. Test.

 

[negitron]

No. Capacitors DO NOT store amps. They store energy. Period. How many amps you can get out of a cap depends entirely on the voltage it is charged to (which will be your supply voltage) and the resistance of the load, assuming no reactive characteristics--for a very long wire there will be an inductive component which will further limit your maximum current but since this is going to be mounted directly on the rocket close to the igniters, it's not an issue here. If the igniters require a minimum of 9.6 volts to ignite properly, charging a cap with a 1.5 volt battery will NOT work. You still need to charge your cap with a minimum of 9.6 volts. And if you have them wired in series, you need 9.6 x N volts, where N is the number of igniters in the series.

Also, contrary to the linked article, a a parallel connection does NOT require more energy to fire a given number of igniters; the amount of energy is EXACTLY the same in either case. Parallel requires more current, series requires more voltage.

 

[minorwork]

http://electronics.howstuffworks.co...ro.magnet.fsu.edu/electromag/java/capacitor/"

From the same site.

Like a Water Tower
One way to visualize the action of a capacitor is to imagine it as a water tower hooked to a pipe. A water tower "stores" water pressure -- when the water system pumps produce more water than a town needs, the excess is stored in the water tower. Then, at times of high demand, the excess water flows out of the tower to keep the pressure up. A capacitor stores electrons in the same way and can then release them later.

 

[minorwork]

No. Capacitors DO NOT store amps. They store energy. Period. How many amps you can get out of a cap depends entirely on the voltage it is charged to (which will be your supply voltage) and the resistance of the load, assuming no reactive characteristics--for a very long wire there will be an inductive component which will further limit your maximum current but since this is going to be mounted directly on the rocket close to the igniters, it's not an issue here. If the igniters require a minimum of 9.6 volts to ignite properly, charging a cap with a 1.5 volt battery will NOT work. You still need to charge your cap with a minimum of 9.6 volts. And if you have them wired in series, you need 9.6 x N volts, where N is the number of igniters in the series.

Also, contrary to the linked article, a a parallel connection does NOT require more energy to fire a given number of igniters; the amount of energy is EXACTLY the same in either case. Parallel requires more current, series requires more voltage.

You are exactly right about the capacitors storing energy. So do batteries. The capacitor has little internal impedance compared to the chemical battery. Also the capacitor is passive and the battery is an active energy source.

I had wondered myself at the link saying that about the series requiring less energy than the parallel.

Do you agree that the series circuit is inherently more reliable given an adequate power source? I think so given that an open in one igniter would not prevent the others from firing. An unacceptable situation I believe.

I had speculated that the flash unit in a disposable camera could provide enough voltage but I'm not clear if there would be enough current. What are your thoughts on that?

 

[negitron]

Do you agree that the series circuit is inherently more reliable given an adequate power source? I think so given that an open in one igniter would not prevent the others from firing. An unacceptable situation I believe.

IF the igniters fire before opening, then series would be better for those reasons. I'm not familiar enough with the ones the OP is trying to use to state that's definitely the case, however. Perhaps an experiment is in order.

The problem with series is that, as described above, you require 9.6 volts per igniter--really, you need a specific current to ignite them, but if you need 9.6 volts to provide that current for one igniter, then for 3, you'll need 28.8 volts. The problem here is that 30 volts worth of batteries is heavy; not something you want in a rocket where mass is absolutely critical. It wouldn't be a problem for a ground-based system, since you can hook up as many batteries as you need. But in a rocket, you need to minimize the mass of the infrastructure so you can maximize the payload.

Now, one thing you can do is something akin to what happens in a camera flash you mentioned earlier. The 1.5 volts DC from the battery is converted into a high-frequency AC, which is then kicked up to a higher voltage with inductors, converted back to DC and stored on a high-voltage capacitor. But, this is probably needlessly complex and beyond the OP's capabilities (no insult to him intended). I say if due care is used in making the connections and each igniter is tested individually prior to installation, parallel is the way to go. You can store your 9.6 volts from a set of lightweight Li cells (I suggest coin cells, since they're small footprint and this will essentially be a single-use application) on a high-density cap, as you suggest, and discharge it through the igniters; this should work fine, assuming that the quality-control in manufacturing the igniters is good enough to ensure they're all within a few percent of each other for resistance.