DIY igniters

[Reed Goodwin]

In my search for reliable ways of igniting AP, I have often been left wanting more from the Copperheads supplied with AT reloads. In the past I have tried making my own igniters and pyrogen, but with varied success. I recently decided to abandon the pyrogen from scratch idea and focus on making the wired bits cheaply so I could just get some Magnelite and dip some igniters. Today I started doing some testing, using the solderless igniter technique that was on the InfoCentral site before they moved (it's still accessible through website archives). I have been experimenting with different bridge lengths and number of wraps around the wire to try to find some good, reliable areas. I did some looking on here and read that I should be aiming in the 1-2Ω range and that I want the bridge to glow as brightly and as long as possible before melting, so that's what I've been aiming for. The sweet spot for me seems to be about 1.2-1.4Ω

Materials-wise, I've been using the twisted pairs of wire from Cat5 cable as the igniter and then some 32awg nichrome wire I got from McMaster-Carr a while back. In trying to be reasonably scientific about this, I've been measuring the resistance of each test igniter and length of the bridge. I've also been recording the tests using my digital camera running at 60fps. Since I don't have my launch system with me right now, I've resorted to just holding the igniter leads to the 12V lawn mower battery I have.

So far I've only conducted 10 tests, though more are slated for tomorrow. I've had a couple that just sparked and didn't really heat up, and a couple with crummy video, but I've taken the good videos and compiled them along with some data about each test here: https://www.youtube.com/watch?v=5NzfuxaAEl0

I'll update this as I go along. I recall there was a good DIY igniter thread on TRF v1.0, so I figure starting another one isn't a bad idea. Any feedback is welcomed. I'm no electrical engineer, only aerospace, but I've got some semblance of an idea of what I'm doing, I think.
Reed

 

[Reed Goodwin]

After doing some more tests this morning, I remembered that the leads I had been using weren't actually Cat5 cable but rather were from this 2-conductor phone line I had. They are the same gauge, but the insulation is different, the Cat5 stuff being harder and not as easy to melt.

My roommate also pointed out that the inconsistent results I was getting in my tests yesterday were likely because the insulation was melting off the wire, shorting the igniter out. The tests I've done with the Cat5 cable don't exhibit that behavior. Also, the phone wires gave off a white smoke that would sometimes burn off in a flash of flame. The Cat5 wire, on the other hand, produces a nasty dark brown smoke.

Reed

 

[skycopp]

Keep us posted. I for one am very interested in your results. Can't watch your video while at work but I will when I get home.

 

[ttabbal]

You're being way more scientific than I was. I bought a pyrogen kit, shooter's wire, and nichrome from N3 and just made a bunch up. I used a too long bridgewire because it was easier to work with, ended up about 8 ohm. They work great with the club launch gear (relay based 12V car battery system).

I'm planning to build some for 18mm and 24mm loads. The ones I have are a little too large for the nozzles on those small reloadables. I'm going to use some wire-wrap wire and the nichrome with a thinned out pyrogen to keep it from building up too much on the leads. I'll try to remember to post some pics of them for the others on the board.

 

[Reed Goodwin]

Yeah, I'm sure that most of these igniters would light the pyrogen without hesitation, I guess I'm just looking at the difference certain setups have on the performance of the bridge before I start using pyrogen without need to. Because of this testing, I know I'm going to need more Cat5 cable since that phone line stuff isn't really up to par.

I think I'll do about 2 more tests, maybe more later, to increase my sample size with the Cat5 leads, but it seems I'm narrowing down. When I'm done testing, I'll post a spreadsheet of the data.
Reed

 

[Reed Goodwin]

Alright, I've completed a total of 20 tests. The igniters using Cat5 cable were MUCH more consistent than the ones using the phone wire. I will be shooting for a gap of about 11/16", wrapping about 8-9 times. This usually gave me about 1.2-1.3Ω. One note about my testing is that I used the same leads repeatedly, cutting off the burnt bits and then re-wrapping the tip. I measured the leads, and found that the difference between the starting length of the leads and ending length would have only varied the resistance by ~0.1Ω (the lowest my multimeter would resolve), indicating that they would not have a terribly significant effect on my measurements.

https://www.youtube.com/watch?v=hm1EKQrJTl4&feature=player_embedded

That is a compilation of most of the tests (test #s 3, 4, 5, 6, 7, 10, 11, 12, 13, 14, 16, 17, 18, 19, 20 in that order). The wire type and resistance of the igniter is indicated on each video. More information can be found in the attached spreadsheet of the data. Also included in the spreadsheet is a quick test I performed to measure the resistance of the nichrome per unit length.
Enjoy!
Reed

View attachment 03_Igniter_tests.xls

 

[Reed Goodwin]

Quick question about pyrogen dips like Magnelite and Quikdip: do they come as powders that you then add the acetone to, or are they pre-mixed?
Reed

 

[quickburst]

Quick question about pyrogen dips like Magnelite and Quikdip: do they come as powders that you then add the acetone to, or are they pre-mixed?
Reed

Nice work Reed. The coils work as I expected. I had never seen video of the heating process.

I have done some testing similar to yours using shooter wire. Shooter wire insulation is a bit thicker and allows the coil to burn a shade longer.

To answer your question, QuickDip is actually three powders. The first is the binder and must be dissolved in acetone overnight. The second powder is the Fuel, which is stirred into the now liquid binder. The third powder is the oxidizer, which is added to the fuel/binder mix. BINGO! QuickDip.

I can't speak for Magnelite, I don't really know anything about it. From what I have read it is a conductive pyrogen. Conductive pyrogens would not require a bridge wire.

 

[troj]

I've used the wrapping technique you reference, and it works quite well.

It'll also be available again shortly.

As for dips, the ones I'm familiar with come as a slurry with most of the goop in one jar, and the oxidizer in another. The goop jar gets thoroughly mixed, then the oxidizer added, and everything thoroughly mixed.

Wrapping leads isn't too bad; takes a little bit of practice, but once you get it down, you came make quite a few sets of leads while sitting and watching TV.

I use shooter's wire that I buy by the spool.

-Kevin

 

[rocket999]

Cool info on the igniter wires.

If you want I can PM you (and anyone else who wants me to) some easy and cheap pyrogen formulas that work REALLY well.

Let me know.

Sam

 

[Reed Goodwin]

Thanks for the offer, Sam, but I already bought some pyrogen mix.
Reed

 

[SpartaChris]

You can make a conductive dip to replace your bridgewire if you're not into trying to wrap nichrome. It's simple, quicker than wrapping wire and just as reliable, at least in my experience. Plus a little goes a long way!

PM me for anyone interested.

 

[SpartaChris]

I can't speak for Magnelite, I don't really know anything about it. From what I have read it is a conductive pyrogen. Conductive pyrogens would not require a bridge wire.

Wow, I didn't know that. The directions never said anything about it being conductive, so I always used wrapped nichrome leads, though now I use my own conductive dip. Think I am gonna give this a try. I'll post the results here.

 

[rocket999]

You can make a conductive dip to replace your bridgewire if you're not into trying to wrap nichrome. It's simple, quicker than wrapping wire and just as reliable, at least in my experience. Plus a little goes a long way!

PM me for anyone interested.

Is the stuff you use just graphite/NC lacquer?

That works, but I just like nichrome because they are tougher than conductive pyrogen.

Sam

P.S. If it isn't graphite/NC lacquer could you PM me the formula?

Thanks!

 

[SpartaChris]

Close- I also mix in some BP for a bit more reliability. I finish it off by dipping it in clear nail polish and letting it dry before I dip into the pyrogen. You don't have to, but I like the added sealer.

The igniters are super easy to make, much faster than stripping and wrapping nichrome. Plus the dip is tough as nails and has never once failed to light. Plus a little goes a very long way.

It's a great way to go if you're looking for a simple way of making several igniters at once. Once the conductive primer is made, you just strip and dip.

Wire wrapped nichrome igniters are great as well. Fairly simple, but they take quite a bit longer to make. The one benefit though is once they are done, you just dip them into the pyrogen, whereas these need some drying time before dipping into a pyrogen. About 30 minutes on the initial dip, and up to an hour after the clear nail polish dip.

 

[rocket999]

Close- I also mix in some BP for a bit more reliability. I finish it off by dipping it in clear nail polish and letting it dry before I dip into the pyrogen. You don't have to, but I like the added sealer.

The igniters are super easy to make, much faster than stripping and wrapping nichrome. Plus the dip is tough as nails and has never once failed to light. Plus a little goes a very long way.

It's a great way to go if you're looking for a simple way of making several igniters at once. Once the conductive primer is made, you just strip and dip.

Wire wrapped nichrome igniters are great as well. Fairly simple, but they take quite a bit longer to make. The one benefit though is once they are done, you just dip them into the pyrogen, whereas these need some drying time before dipping into a pyrogen. About 30 minutes on the initial dip, and up to an hour after the clear nail polish dip.

Cool. I need to try that mix.

Do you have any kind of ratio for the BP/graphite?

Sam

 

[SpartaChris]

4:1 Graphite to BP.

I haven't tried any of the smokeless powders with this, as one batch is enough for hundreds of igniters and I don't make it to that many launches at the moment, but I'm confident it would work just as well.

 

[rocket999]

4:1 Graphite to BP.

I haven't tried any of the smokeless powders with this, as one batch is enough for hundreds of igniters and I don't make it to that many launches at the moment, but I'm confident it would work just as well.

Thanks!

 

[Handeman]

I picked up some 44 ga and 36 ga nichrome wire at LDRS and have started to experiments with ematchs and ignitors.

I had made some igniters with some 36 ga nichrome and homemade magnisium pyrogen and used them at LDRS for a J365SK, J350W, I400 Wicked White research motor and a H165R. Every one lit and came to pressure really quick. What I didn't do was document the number of wraps of wire I had used.

After watching the movies, I started experimenting and actually recording data on how they worked. I found that 10 wraps of 36ga nichrome gave 6 to 7 ohms resistance. When using a fully charged 12V battery, the wire glowed orange/yellow for 1.5 to 2 seconds before burning through or shorting through the insulation of the wire. The best number of wraps seemed to be 10 with a range of 8 to 12 working quite well.

Fewer wraps cause the wire to glow yellow/white and melt though in less then a second. About 0.25 seconds for 4 wraps. More wraps then 12 took up to a half second to begin glowing and after about 2 seconds would ignite the wire insulation. This seem to be too slow of heating time although I'm sure it would have ignited the pyrogen.

The number of wraps I used seemed to be very consistant with what Reed came up with considing the 34 vs. 36 gauge wires, although my resistance readings were more consistant with what ttabbal came up with.

I know my pyrogen works very well considering the success as LDRS. I'm hoping that getting the right number of wraps will make them that much more consistant.

BTW, does anyone have any advice on how to dip the igniters to prevent getting a lump on one end or the other. I had one igniter I tried in a H165 that wouldn't fit because one end of the dip was just a little too big to fit through the nozzle.

 

[Reed Goodwin]

Handeman,
After reading your post, I decided to do a couple more experiments with larger numbers of wraps since I hadn't really done any with the Cat5 cable. I made two igniters with 12-13 wraps, coming out at 1.8-1.9Ω of resistance and tested them. The one with 13 wraps heated the wire but it didn't glow before melting through the insulation and sparking. The one with 12 wraps also had a slow heat before glowing orange briefly before shorting out.

This seems to confirm my thoughts about 8-10 wraps being good with 32ga nichrome and 12" leads with a 12V lawn mower battery. And boy am I glad the testing came out like that since I already made about 40 igniters using about 9 wraps, haha!
Reed

 

[shreadvector]

Wow, I didn't know that. The directions never said anything about it being conductive, so I always used wrapped nichrome leads, though now I use my own conductive dip. Think I am gonna give this a try. I'll post the results here.

It is not conductive. It requires a bridge wire. Plenty of facts/instructions on their website.

https://www.rocketflite.com/

 

[rocket999]

BTW, does anyone have any advice on how to dip the igniters to prevent getting a lump on one end or the other. I had one igniter I tried in a H165 that wouldn't fit because one end of the dip was just a little too big to fit through the nozzle.

Try making the pyrogen a little thicker. This will stop it from running to the end of the wire.

Could you PM me your pyrogen formula?

Thanks!

Sam

 

[Handeman]

Handeman,
After reading your post, I decided to do a couple more experiments with larger numbers of wraps since I hadn't really done any with the Cat5 cable. I made two igniters with 12-13 wraps, coming out at 1.8-1.9Ω of resistance and tested them. The one with 13 wraps heated the wire but it didn't glow before melting through the insulation and sparking. The one with 12 wraps also had a slow heat before glowing orange briefly before shorting out.

This seems to confirm my thoughts about 8-10 wraps being good with 32ga nichrome and 12" leads with a 12V lawn mower battery. And boy am I glad the testing came out like that since I already made about 40 igniters using about 9 wraps, haha!
Reed

I agree about the 8 wraps. That seems the be the sweet spot for the 36 ga wire I got. What I don't understand is the low resistance. Your results seem to be consistant with what I got with the same number of wraps, but the resistance I got was in the 8 ohm range, about one ohm per wrap. When I use the 44 ga. wire and use about one wrap, 1/16" bridge, I still get about two ohms.

Are you sure the battery in your meter isn't getting low? Something just doesn't seem right. Are you sure you're using nichrome wire and not a silver coated copper?

 

[Reed Goodwin]

My resistance readings are certainly correct (tested plain nichrome and it agreed with the igniters), and McMaster-Carr said it's nichrome, so I'm going with them on this one. I think the lower resistance can be explained by the different wire gauges. As the wire gets bigger, the resistance will drop, so the 32 should be lower than the 36, and the 36 should be lower than the 44. I'm topping off the battery right now and will run another test or two to be sure, but I think that the longer bridges just take a little too long to come up to fully glowing than the shorter ones. I'm no electrical expert, but that seems to make sense to me.
Reed

 

[Handeman]

My resistance readings are certainly correct (tested plain nichrome and it agreed with the igniters), and McMaster-Carr said it's nichrome, so I'm going with them on this one. I think the lower resistance can be explained by the different wire gauges. As the wire gets bigger, the resistance will drop, so the 32 should be lower than the 36, and the 36 should be lower than the 44. I'm topping off the battery right now and will run another test or two to be sure, but I think that the longer bridges just take a little too long to come up to fully glowing than the shorter ones. I'm no electrical expert, but that seems to make sense to me.
Reed

You are certainly correct about the larger size having less resistance. If you got it from McMasterCarr, they are very good and I'm sure you got what you ordered. I was just surprised there was that much difference between the 32 & 36 ga. I guess it doesn't matter as long as you can get the results you want.

Which reminds me, I have a bunch of H & I and J & K sized igniters hanging in the basement that I need to pack up. I love being able to make my own igniters for 5 to 10 cents instead of paying the $2 - $4 for them.

 

[shreadvector]

My resistance readings are certainly correct (tested plain nichrome and it agreed with the igniters), and McMaster-Carr said it's nichrome, so I'm going with them on this one. I think the lower resistance can be explained by the different wire gauges. As the wire gets bigger, the resistance will drop, so the 32 should be lower than the 36, and the 36 should be lower than the 44. I'm topping off the battery right now and will run another test or two to be sure, but I think that the longer bridges just take a little too long to come up to fully glowing than the shorter ones. I'm no electrical expert, but that seems to make sense to me.
Reed

Bigger wire gauge number indicates SMALLER diameter wire which produces MORE resistance.

https://www.wiretron.com/nicrdat.html

You probably have the Nichrome C (with iron) as opposed to the Nichrome A (which I have about 30 pounds of in 30, 31 and 32 ga).

 

[Reed Goodwin]

Ah, Fred I was looking for something like that page last night. Such handy info there...
Reed

 

[Reed Goodwin]

Well, I just finished using up all the cat5 cable I had. I am left with 97 wired igniters, ready for dipping and hardly a dent in the 2oz spool of nichrome. Methinks this spool will last a while. As should 97 igniters, especially at my rate of launching rockets lately (7+ months sans launch). Now to dip them this weekend. Any tips on how to hold them en masse after dipping so the pyrogen doesn't run to the tip?

Thanks,
Reed

 

[rocket999]

Well, I just finished using up all the cat5 cable I had. I am left with 97 wired igniters, ready for dipping and hardly a dent in the 2oz spool of nichrome. Methinks this spool will last a while. As should 97 igniters, especially at my rate of launching rockets lately (7+ months sans launch). Now to dip them this weekend. Any tips on how to hold them en masse after dipping so the pyrogen doesn't run to the tip?

Thanks,
Reed

That is a whole bunch of igniters!

That reminds me that I need to make more also... At least it's raining here and I can watch a movie while I do it!

Sam -going to put in "Mall Cop"-

 

[quickburst]

Well, I just finished using up all the cat5 cable I had. I am left with 97 wired igniters, ready for dipping and hardly a dent in the 2oz spool of nichrome. Methinks this spool will last a while. As should 97 igniters, especially at my rate of launching rockets lately (7+ months sans launch). Now to dip them this weekend. Any tips on how to hold them en masse after dipping so the pyrogen doesn't run to the tip?

Thanks,
Reed

Curl the plain end like a candy cane. Dip into your pyrogen and hang upside down, let dry overnight. No drips if you get the pyrogen the right viscosity (this takes a little practice, but you will be an expert after dipping the first few).

Coat them with fingernail polish if you want, this will protect them from bumps and scrapes.