Introduction: NiCrome "hotwire" Ignition for Propane Flame Effects
I'm going to give a run-down of the nicrome ignition system (aka Juniper) that we used on 2PiR this year.
2PiR uses high velocity, high speed, computer sequenced effects. Because of these traits, it is poorly suited for more conventional pilot flames, such as the low pressure stainless steel wool style or the bernzomatic torch type. If you are making a flame effect for anything that is not high-repetition, high velocity, and terrible on pilots, please consider a different style of pilot than hotwires.
Reasons for using NiCrome:
-Can be extremely reliable
- Won't blow out: good for use in areas you can't access easily
- Can ignite extremely short bursts somewhat more reliably than "orange flame" pilots (this is a debatable point, keep in mind that we started using NiCr wires as a last resort)
- It can look really cool if done well
Reasons to not use NiCrome:
-You need between 9 and 12 amps to get it to autoignition temperature (for propane), at 120 volts, that is a whole bunch of watts. This style is not recommended for generator use.
- You will need to either get a power supply that is 12v x (effects * 15) amps if you are running the ignitors in parallel. If you run them in Series, you can run a bunch (we got 16) on one circuit, but you have the Christmas Lights problem if anything goes wrong.
- They need to be protected very well from shorting to the chassis or shocking bystanders (more on this later)
- It's way overkill for most effects
- The wires look like the inside of a toaster, and that's uncool.
Step 1: Me Talking You Out of Using NiCrome
So if you are reading this, you have probably built a flame effect or two. If you really haven't gotten deep into ignition woes, just quit reading here and don't worry about stuff like this. Normal, dumb, steel wool and 1/2 psi propane will work amazingly well for making a yellow flame that will light just about anything.
If you are doing something for an art car or whatever, just know that from here until the finished project was (for us) around 80 man hours, 4 priority shipments from McMaster, and a whole lot of wasted money. Your mileage may vary, but using a system like this will be amazingly expensive and time consuming compared to more conventional pilots.
Step 2: Jank
Nicrome: McMaster parts:
1/8 lb. Spool 8880K75 $8.10
1/4 lb. Spool 8880K16 15.77
1 lb. Spool 8880K46 47.94
We got a pound, it's a whole lot. We've used around 50 feet of the spool we got, and have hardly made a dent in it. I'd suggest gettin' the q.p.
You'll also need some way of connecting this to power. At this point, you'll probably just want to do the easy thing, screw-lock it onto the business ends of some 110, and I don't blame you, but first, coil it. Coiling seriously increases the efficiency of the hotwire by an amazing amount, because the heat bounces around the inside of the coil and also compresses the air in there, giving you more heat for less.
To coil well, get a wood screw or a coarse thread machine screw, and wrap your wire tightly around it, then unscrew the screw out of the middle.
Once you've got a length appropriate for your application (around 9.0-15.0 Ohms for 110v, depending on how serious your effect is), you'll need to place this NEAR the stream of propane. Don't put it right in the middle, or it will get "blown out" by the cold propane, and never achieve autoignition temperatures while mixed with oxygen.
That's our test rig in action, and also why it's called "Juniper". We made NIMBY smell like a gin factory.
Step 3: Stand + Infrastructure
So now you've lit propane with a glowing wire. That's not useful at all unless you've got some sort of stand, and you can do it in a nice manner.
Your stand needs to
-Shield the nicrome from wind. Nicrome is EXTREMELY wind sensitive
-Be okey with being bathed in flames. your metal will get very hot, since it is inside fire.
-Be able to transmit power to the nicrome and not disintegrate at hot temperatures.
-Be adjustable: The point where your column of propane is ignitable is dependent on pressure, altitude, and the will of god, so you need to be able to adjust each ignitor both into and out of the column, but also towards and away from the nozzle.
You will need at some point heat resistant wires. Copper conductor wires are completely unsuitable for this application, and they will vaporize, leaving a cool greenish residue on the nicrome coil. This is less than optimal.
I'm going to explain things with the pictures and captions here.
McMaster part numbers:
Ceramic tube "thermeez"
88175K31 $14 for 25 feet
heat insulated wire: 800 degree rated, 14 gauge.
And probably the most dangerous thing I've used in a while, is KOPR-Shield, a copper suspension that reduces the resistance of plugs by a phenomenal amount. Our system used drop cords to connect the different ignitors together, and we were getting an extra 7Ohms from the plugs! (Cheap home depot shit), so with this Kopr Shield we reduced that to .5 Ohms!!! The downside is that any stray bits of this conduct better than wire, and it's only slightly safer than throwing all your electrical cables in a puddle of water.
Step 4: Shielding
If you put these right in the stream of propane, the fuel cools down the coil, and there is no fire, only suck. The second snag is the mount points for the nicrome. Most ways of joining two wires (like screw terminals) have a bottleneck, where things will get really hot and disintegrate. Well, not in all electronics, but they will here. Also, you don't want to shock people.
We positioned the ignitors at the edge of the flame (as seen in the pics from Fire Arts Festival), but also obscured them behind a perfsteel cage. To make this, we made a + sign of perfsteel, then hammered it together. It not only breaks the speed of the fuel, but also hides the fact that our ignitors are glorified toaster bits.
To get around the melty bit, we had one of our very skilled people, Ian Baker, tig weld the nicrome wire to some nuts, and then we bolted the 14 gauge thermal wire to those. After we did that, we had no failures that weren't a result of our own sillyness.
The safety measure that you really want to get in here is keeping these live wires from shorting to ground and either electrocuting people or causing mayhem. We got around this by grounding all the chassis to the ground wire of our 3 prong power, and putting the thing on a GFCI circuit. Then, because I'm paranoid, I taped a screwdriver to a 2x4 and grounded the thing, the GFCI blew, which was a good test, because about 6 days later, I accidentally stuck a screwdriver across those, and didn't feel a shock at all. GFCI's are great stuff.
I so seriously need to sand down and paint all of those, but even Bar-B-Que black will get cooked off... I guess this is a work-in-progress then.
Step 5: BURNINATE!!!