Igniter Bridge Wire Testing Results

[GregGleason]

In my continuing pursuit to add to my understanding of igniter systems (see this TRF thread) I needed to do an experiment.

First some back-story, I had been taught that the bridge wire was sized according to the size of the motor. The theory goes like this: Smaller bridge wires (i.e., thinner wires) go with smaller motors and larger bridge wires go with larger motors. After thinking this through, I now believe that this is not the case. The bridge wire should be sized to the amount of current (amps), at least that is now the theory in which I will operate.

My earlier bridge wires were made from 36 gauge nichrome, which I believed were too thin to last and effectively heat the pyrogen to its autoignition temperature. With my new theory, I believed that the "sweet spot" to a 12 volt / high amp system (that you would find from a car battery) would be either a 32 gauge or 30 gauge wire.

So in this experiment, I made 4 igniter wires. I made 2 igniters with 32 gauge nichrome wire and 2 with 30 gauge wire. The bridge wires were made as a 4-7-4, where the shooter wire contacts were wrapped 4 times and soldered, and the heating element section was wrapped seven times. The entire 4-7-4 section was about 0.50" or 0.63" in length. The shooter wire contacts were treated with Ruby flux and then soldered with silver-based solder. I didn’t test the resistance, but in hindsight that would have been a good idea. The battery used was a booster batter to jump car batteries and the igniter switch system was an AeroTech Interlock Launch Controller that was modified with alligator clips and wires spliced in.

The result was that the 32 gauge didn’t work so well. It took a while to heat and glow. Whereas the 30 gauge had a strong red-hot glow for over a second. I may post video later.

I understand that this is just a small data point, but when I plan to make igniters in the future for club launches, I will use 30 gauge nichrome wire.

Greg

 

[GregGleason]

Here is the video of the test with 30 gauge nichrome bridge wire:

https://www.flickr.com/photos/9960539@N07/8735191232/in/photostream

Greg

 

[GregGleason]

Another observation from the test is how different 32 gauge vs 30 gauge nichrome wire is from each other. I was hoping that the 32 gauge would be the winner of the competition, mostly because it is thinner than the 30 gauge, which means that it is easier to wrap around the copper shooter wire. The 30 gauge wire needs a bit more coaxing to go around the copper leads, but it is doable.

The nichrome was purchased from Jacobs:

https://jacobs-online.biz/nichrome_wire.htm

The specs for the nichrome 60 – Chromel C:

30 gauge - 6.75 ohms/ft - 0.0100" (0.2540mm)
32 gauge - 10.60 ohms/ft - 0.0080" (0.2032mm)

Greg

 

[TheTellurian]

The 32 ga. has a higher resistance than the 30 ga. What you want to do is trim the 32 length back till you get the glow disired and use that to wrap. Or you might try 3-7-4 or 3-7-3 etc. I used a 40 ga. for some igniters, which had a low resistance but would glow nicely on a 12V battery. It did require about 4 inchs of length but being so thin could be wrapped without shorting in about 1/2 inch.


Richard

 

[GregGleason]

The 32 ga. has a higher resistance than the 30 ga. What you want to do is trim the 32 length back till you get the glow disired and use that to wrap. Or you might try 3-7-4 or 3-7-3 etc. I used a 40 ga. for some igniters, which had a low resistance but would glow nicely on a 12V battery. It did require about 4 inchs of length but being so thin could be wrapped without shorting in about 1/2 inch.


Richard

I can see where that would work, but I wanted to move on to the next stage as quickly as possible with my current (no pun intended!) work practices. I don't have a lot of disposable "rocket time", so once I hit a solution that is acceptable I log it and go on to the next thing.

Greg

 

[blackjack2564]

Stick with 32 gauge. Day in and day out is more compatible with a variety of club systems.

I think you are getting a lag with the AT system you are using.
See what happens hooking up direct to a battery. Just hold the igniter leads to terminals...much better testing accuracy.

Matters not how many wraps at solder joints, but the sweet spot is 6-10 for heating element depending on size of igniter desired. [for small or large motors]

Good luck, you are on the right track. The real trick is the "secret sauce" pyrogen.

 

[GregGleason]

Stick with 32 gauge. Day in and day out is more compatible with a variety of club systems.

I think you are getting a lag with the AT system you are using.
See what happens hooking up direct to a battery. Just hold the igniter leads to terminals...much better testing accuracy.

Matters not how many wraps at solder joints, but the sweet spot is 6-10 for heating element depending on size of igniter desired. [for small or large motors]

Good luck, you are on the right track. The real trick is the "secret sauce" pyrogen.

Thanks for that input CJ. It's good to know that I am getting closer to my goal.

I hadn't considered that my launch system may not have been a good analog for a club system. So I may do another test with the igniter leads to the booster leads.

You are so right about the "secret sauce". Good recipes are so hard to find!

Greg

 

[blackjack2564]

T

You are so right about the "secret sauce". Good recipes are so hard to find!

Greg

Yes they are!

 

[patelldp]

I'm just curious what you all use as a binder. Nitrocellulose from acetone dissolved ping pong balls?

 

[blackjack2564]

I'm just curious what you all use as a binder. Nitrocellulose from acetone dissolved ping pong balls?

Epoxy.

 

[GregGleason]

Pm me if you need one

PM sent, sir.

Greg

 

[ksaves2]

Ditto on the 32ga. I sometimes get a batch that just go pop and a chunk of pyrogen flies off and the thing doesn't burn. Oh cripes, a no good batch for the burnpile.? Well, I thought about it and decided to take a hemostat or a needle nose pliers and put some cracks along the length of
the suspect igniters. Just grip it and gently crack the pyrogen along its length in 3 or 4 spots depending on the length of the pyro head. You don't want to mangle it, just crack it. I've done that and never had a failure now.
What I think happens is perhaps there might be some gas build up just over the nichrome in the pyrogen and the "cracking" allows this to escape and gives the wire more time to impart heat before breaking. It's the only way I can explain why a single batch was useless poppers and when cracked, they started working like igniters.

Keep this in mind if you end up with a batch of "poppers". This technique might save them.
As far as recipes, I've seen some daring folk crush sparklers in PP ball lacquer (they do work). Raw thermite powder in lacquer with thick gauge nichrome to impart enough heat to get it going. You might as well play the Jeopardy song while waiting for that to go and clone thermalite base dip with an MTV (magnesium, teflon, viton) coating over half the length of the thermalite layer.
For "instant on", the guru's (of which I'm not) use thermite powder some of which I think has been doctored to start at a lower temperature and
could be very dangerous. I've been told one way is to put the powder into a soda straw wrapper by pouring it through the plastic straw and removing it. The powder is then in the thin paper wrapper. Put one of yer fast igniters in it to start the powder and that's it. I tried it once and it
really didn't start any faster than the plain igniter. Been told that thermite needs to be "fresh". With thermite, DO NOT use superfine reagents.
They are out there on epay. I experimented 6 years ago and I was glad I was 20 feet away from a first test with a 1.6ml canister using a launch switch. The test blew like a couple of silver salutes (M80's). If conditions are right, don't let anyone tell you otherwise, thermite can explode. One really would need to talk the ear off a drag race guru or a person who can get a cluster of different sized motors to light off at the same time. I'd use whatever mesh they recommend. Thermite ignition is an art form if you ask me.

 

[cwbullet]

The trick is the mixture and type of epoxy. I get the best results with West.

 

[cavecentral]

Just grip it and gently crack the pyrogen along its length in 3 or 4 spots depending on the length of the pyro head.

Funny - on my dipped igniters a crack means failure. I use 36AWG Nich. this must be the difference. I found the pyrogen acts as a heat sink and the crack is a break where the Nich just fries without lighting anything. No continuity, done. If 32AWG stay together long enough this could save some old dried out ignitors.

 

[Manticore]

Thanks for that input CJ. It's good to know that I am getting closer to my goal.

I hadn't considered that my launch system may not have been a good analog for a club system. So I may do another test with the igniter leads to the booster leads.

You are so right about the "secret sauce". Good recipes are so hard to find!

Greg

Hi Greg:

I have combed the internet and have found an excellent pyrogen......burns hot and slow with lots of sparks and fairly resistant to cracks due to its rubbery binder. I have tried this composition very succesfully using the famous "Bob Dahlquist Carbon Film Resistor" 10-Ohm - 1/4 Watt resistor or the smaller 1/8 Watt variety (Bob Dahlquist - Tripoli has an excellent paper on-line; recommended reading). I have tested about 15 compositions, some my own, and this one appears to be a winner.
This pyrogen appears to fire EVEN when you coat the igniter multiple times. Most pyrogens will pop without burning when multiple coats are applied; not the case here. A nice pyrogen "match-head" is good for those hard to ignite propellants, unless you use a booster of course. I also lightly sand my propellant grains and core prior to loading/launch. This "activates" the propellant's surfaces for complete and rapid ignition (as the motor designer intended in the first place). Should you decide to boost-up your igniters with a propellant slivers or shavings or the famous drinking straw with a pyrogen or pyrolant, Richard Nakka's website is full of information.
I will post a video soon so you may decide for yourself..... As to how to give you the magic formula.......I don't think I'm allowed by the forum....correct?
Best regards,

Paul

 

[bobkrech]

Hi Greg:

I have combed the internet and have found an excellent pyrogen......burns hot and slow with lots of sparks and fairly resistant to cracks due to its rubbery binder. I have tried this composition very succesfully using the famous "Bob Dahlquist Carbon Film Resistor" 10-Ohm - 1/4 Watt resistor or the smaller 1/8 Watt variety (Bob Dahlquist - Tripoli has an excellent paper on-line; recommended reading). I have tested about 15 compositions, some my own, and this one appears to be a winner.
This pyrogen appears to fire EVEN when you coat the igniter multiple times. Most pyrogens will pop without burning when multiple coats are applied; not the case here. A nice pyrogen "match-head" is good for those hard to ignite propellants, unless you use a booster of course. I also lightly sand my propellant grains and core prior to loading/launch. This "activates" the propellant's surfaces for complete and rapid ignition (as the motor designer intended in the first place). Should you decide to boost-up your igniters with a propellant slivers or shavings or the famous drinking straw with a pyrogen or pyrolant, Richard Nakka's website is full of information.
I will post a video soon so you may decide for yourself..... As to how to give you the magic formula.......I don't think I'm allowed by the forum....correct?
Best regards,

Paul

Paul

You can post a link to outside references.

Bob Darhlquist was a great guy and rocket man who died too young. You can download his igniter paper here. https://aeroconsystems.com/cart/images/custom/DahlquistIgniter1.pdf

He also used a high voltage capacitive discharge ignition (HVCDI) system which is that the mining industry, fireworks displays, and professional rockets use. More reliability, energy and safer than the DC systems we use in the rocketry hobby.

Bob

 

[CarVac]

Paul

You can post a link to outside references.

Bob Darhlquist was a great guy and rocket man who died too young. You can download his igniter paper here. https://aeroconsystems.com/cart/images/custom/DahlquistIgniter1.pdf

He also used a high voltage capacitive discharge ignition (HVCDI) system which is that the mining industry, fireworks displays, and professional rockets use. More reliability, energy and safer than the DC systems we use in the rocketry hobby.

Bob

What a cool system!

 

[troj]

I will post a video soon so you may decide for yourself..... As to how to give you the magic formula.......I don't think I'm allowed by the forum....correct?

You're welcome to post the formula in the Research forum.

-Kevin

 

[Adrian A]

Paul
He also used a high voltage capacitive discharge ignition (HVCDI) system which is that the mining industry, fireworks displays, and professional rockets use. More reliability, energy and safer than the DC systems we use in the rocketry hobby.

Bob

Some professional rockets and spacecraft use capacitive discharge, but others use direct battery current. The latter technique wins the design trade in most spacecraft applications due to lower mass and lower volume needed per channel.

 

[bobkrech]

Some professional rockets and spacecraft use capacitive discharge, but others use direct battery current. The latter technique wins the design trade in most spacecraft applications due to lower mass and lower volume needed per channel.

CD systems are not necessarily heavier than a DC system as the wire gauge is usually smaller, think shooters wire verses extension cords, for long cable runs where IR losses can be high unless you use large gauge wire. The choice usually boils down to the timing requirements and the safety margins required.

There are 3 different pyrotechnic ignition systems in common use today: lower voltage DC; several hundred volt CD; and several kilovolt CD. The higher the voltage the the faster the initiation and the greater the all-fire/no fire safety margin.

A DC ignition system initiates in several milliseconds to several centiseconds, and the all-fire/no-fire current ratios are typically between 3 and 10.

A several hundred volt CD system similar to a photo flash device activates in the 10's of uS to below 1 ms range, and has higher safety margins, typically 10-100 or more. This system is use of series strings of igniters for multiple charges in mining, or cluster ignition, and prompt ignition of pyrotechnic devices where long wire runs are required and the IR drop of the wire is prohibitive for a CW igniter system.

A several kilovolt exploding bridgewire ignition system activates in nano-seconds, and had safety margins of greater than 1,000 to below 1,000,000. This type of circuit is typical for initiating high explosive devices such as explosive bolts and self-destruct charges which need very precise timing and rapid activation.

Bob

 

[GregGleason]

And finally a pyrogen test. The whole point of an effective bridge wire is to conduct enough heat at a fast enough rate to ignite the pyrogen. This is a 22 gauge shooter, with a 32 gauge nichrome bridge wire, with 4 wraps on the shooter leads, and 9 wraps for the heating element. The leads were soldered. So if I were NASA, I'd call it a S22-B32-4.9.4, 1 each. I didn't measure the resistance, but other similar configurations that I have made that are nearly identical measured in at about 1.4 to 1.8 ohms. Per CJ's instruction, instead of using my AeroTech InterLock igniter system, wire leads were connected directly to a 12v jumper battery (to more closely mimic club launching systems). Now this is just one test, but it looks very promising ...

https://www.flickr.com/photos/9960539@N07/8919958104/

I did do another test, with the AeroTech InterLock and the igniter lit. But it took about a second or so holding the button down.

Greg

 

[GregGleason]

I went to our club launch yesterday, which was going to be the final test of the igniter/pyrogen combination. At least, that was the hope.

This was the third igniter test of the day, after two others flights on AeroTech RMS E18-4W's. Both were successes. This is the video of the last attempt. This is my Wild Child Test Round on an AeroTech RMS E28-7T.

https://www.flickr.com/photos/9960539@N07/9001686473/

The launch looked like an "instant on", which completed the trifecta.

All it all, it was a good day.

Greg

 

[Handeman]

I went to our club launch yesterday, which was going to be the final test of the igniter/pyrogen combination. At least, that was the hope.

This was the third igniter test of the day, after two others flights on AeroTech RMS E18-4W's. Both were successes. This is the video of the last attempt. This is my Wild Child on an AeroTech RMS E28-7T.

The launch looked like an "instant on", which completed the trifecta.

All it all, it was a good day.

Greg

The Blue Thunder is almost always an "instant on". That's why they use slivers of it to add to igniters for larger motors. To get a good test, you need to light the old BlackJack, White Lightning, or Majave Green. These are much harder to light then the Blue Thunder.

It looks like your "lighters" are working quite well. Can you send me the formula?

Thanks....

 

[GregGleason]

The Blue Thunder is almost always an "instant on". That's why they use slivers of it to add to igniters for larger motors. To get a good test, you need to light the old BlackJack, White Lightning, or Majave Green. These are much harder to light then the Blue Thunder.

It looks like your "lighters" are working quite well. Can you send me the formula?

Thanks....

You are correct Handeman. The Blue Thunder is practically a "gimme" for ignition. So, for a test it didn't really provide much of a data point. Still, it was gratifying to see it go so quickly. The White Lightnings went quickly as well, but I'm not sure I have any videos of those launches to compare.

With regards to the pyrogen formula, the author has asked me not to divulge the contents, and I want to honor that request.

Greg

 

[Handeman]

You are correct Handeman. The Blue Thunder is practically a "gimme" for ignition. So, for a test it didn't really provide much of a data point. Still, it was gratifying to see it go so quickly. The White Lightnings went quickly as well, but I'm not sure I have any videos of those launches to compare.

With regards to the pyrogen formula, the author has asked me not to divulge the contents, and I want to honor that request.

Greg

Not a problem, I've got my own formula that is slow burning and very hot. It's worked on everything from F to M, even a EX K that had failed to light 4 times, so I was only interested in a comparison anyway.