SpudFiles

As I have mentioned in previous posts, I am planning a handheld burst disk Hybrid, which I will build in roughly 4 weeks. I have already finished designing the
Construction Material (Sch 10 Threaded T304 Stainless Steel),
Fuel (MAPP gas),
Layout (Over/Under, 3" Chamber with detachable barrels 1.5" and 2.5"),
Ignition Source/Type (Voltage Multiplier/Booster for source, Spark strip for sparks),
and Chamber Fan (51 CFM!!)

My wiring plan for the ignition is to make a Guano Grip out of PVC and parts from a stick lighter (The plastic trigger and spring specifically), which when pressed will press onto a momentary switch, which is wired from a 9V battery and from there running to the boost converter (see above). The boost converter will be connected to two wires, a positive and negative, (Here is where my problem is) which will connect to the spark strip inside the chamber and produce sparks when the Guano grip's trigger is pulled.

My wiring plan for the Chamber fan is very similar, just another battery with the fan's rated voltage wired up to a lever switch which is (Here is where my problem is as well) running power to the chamber fan inside the chamber.

The problem with this plan is that I have to wire through the steel chamber wall. My question is, what is the best way to do this?
One method I thought might work would be to simply drill a hole in the wall, feed the INSULATED chamber fan AND ignition wires through, and fill with Epoxy or JB Weld. But the cannon will likely be going to 10x mix and higher, and I really don't feel like dealing with an epoxy bullet pressed against my cheek.
The other method I was considering would be to drill two holes, one for the + wire and one for the -. Then push partially insulated (insulation cut away just where the wire would be inside of the chamber wall) wire through, and drop some copper solder through into the holes. As copper has a very high conductivity relative to steel (see this table list) I was wondering if it would ignore the surrounding steel and continue through the wire?

If anyone has other methods for getting current through the steel wall unobstructed and pressure resistant, please let me know! Thank you!

A couple thoughts, I had attempted to use a voltage multiplier circuit for my hybrid and was not sucesfull although for your much smaller one may work entirely fine, something to consider. As for a Hogh voltage feedthrough people have used automotive sparkplugs and various epoxied arrangements. For mine I drilled out a compression fitting to clamp a copper rod inside a drilled through plastic rod. This has given me no issues at a 10x mix and probably 50-100kv.

wdr0 wrote:A couple thoughts, I had attempted to use a voltage multiplier circuit for my hybrid and was not sucesfull although for your much smaller one may work entirely fine, something to consider. As for a Hogh voltage feedthrough people have used automotive sparkplugs and various epoxied arrangements. For mine I drilled out a compression fitting to clamp a copper rod inside a drilled through plastic rod. This has given me no issues at a 10x mix and probably 50-100kv.

I may just go back to the normal taser ignition because you aren't the only one who has said that these boosters have a very limited lifespan.

The compression fitting method sounds promising, I will look into it further. Could I just put some electrical heat shrink tubing over the copper to act as my insulation? I think that would work even better.

Preliminary knowledge: what is your electronics experience?

You should be able to use the chamber itself as ground, and then feed in + voltage through insulated connectors.Depending on your ignition voltage source, you can use the chamber as ground as well, but this depends on how the circuit is built. Since it's potted there's really no telling. I would just feed both ignition terminals through the chamber insulated.

As for the feedthrough, you can use plastic threaded rod through tapped holes with a smaller hole drilled through the center and tapped for a bolt. Wires leak at hybrid pressures, and the combustion byproducts will most likely lead to corrosion of the copper core of your wires (to a certain point).

Make sure to shield any fancy electronics from your ignition module! You can use a grounded piece of blank copper plated PCB to do simple shielding.

mark.f wrote:Preliminary knowledge: what is your electronics experience?

You should be able to use the chamber itself as ground, and then feed in + voltage through insulated connectors.Depending on your ignition voltage source, you can use the chamber as ground as well, but this depends on how the circuit is built. Since it's potted there's really no telling. I would just feed both ignition terminals through the chamber insulated.

As for the feedthrough, you can use plastic threaded rod through tapped holes with a smaller hole drilled through the center and tapped for a bolt. Wires leak at hybrid pressures, and the combustion byproducts will most likely lead to corrosion of the copper core of your wires (to a certain point).

Make sure to shield any fancy electronics from your ignition module! You can use a grounded piece of blank copper plated PCB to do simple shielding.

Pretty close to absolute zero experience, this is all just what I have pieced together from common sense. I have a bit more experience with soldering, though.

Your solution with the chamber acting as the ground makes perfect sense, but what stops it from traveling back into you? The ignition will be a 20,000,000 volt taser, I changed my mind about the boost converter because of the extremely limited lifespan. Is 20 million volts enough for the ignition? :bom: And what do you mean by "potted" when you were referring to how the circuit is built?

If I understand correctly, you are saying to drill and tap into the chamber and then screw in a plastic rod, which has a bolt screwed into the rod, right? What are the plastic rods called/is there a specific material I should look for?

My understanding of potted

https://en.wikipedia.org/wiki/Potting_(electronics)

WizardNoodle wrote:

mark.f wrote:Preliminary knowledge: what is your electronics experience?

You should be able to use the chamber itself as ground, and then feed in + voltage through insulated connectors.Depending on your ignition voltage source, you can use the chamber as ground as well, but this depends on how the circuit is built. Since it's potted there's really no telling. I would just feed both ignition terminals through the chamber insulated.

As for the feedthrough, you can use plastic threaded rod through tapped holes with a smaller hole drilled through the center and tapped for a bolt. Wires leak at hybrid pressures, and the combustion byproducts will most likely lead to corrosion of the copper core of your wires (to a certain point).

Make sure to shield any fancy electronics from your ignition module! You can use a grounded piece of blank copper plated PCB to do simple shielding.

Pretty close to absolute zero experience, this is all just what I have pieced together from common sense. I have a bit more experience with soldering, though.

Your solution with the chamber acting as the ground makes perfect sense, but what stops it from traveling back into you? The ignition will be a 20,000,000 volt taser, I changed my mind about the boost converter because of the extremely limited lifespan. Is 20 million volts enough for the ignition? :bom: And what do you mean by "potted" when you were referring to how the circuit is built?

If I understand correctly, you are saying to drill and tap into the chamber and then screw in a plastic rod, which has a bolt screwed into the rod, right? What are the plastic rods called/is there a specific material I should look for?

You can find nylon threaded rod and bolts. Get a big enough size to drill through the center accurately, but not bigger than, let's say, 1/4".

As far as the chamber as the ground goes, using it for ground for your DC circuits is completely safe. You could also mount the ignition module inside the chamber and run power to it through the chamber and use the chamber as ground as well.

And no stungun will output 20 million volts.

mark.f wrote:

WizardNoodle wrote:

mark.f wrote:Preliminary knowledge: what is your electronics experience?

You should be able to use the chamber itself as ground, and then feed in + voltage through insulated connectors.Depending on your ignition voltage source, you can use the chamber as ground as well, but this depends on how the circuit is built. Since it's potted there's really no telling. I would just feed both ignition terminals through the chamber insulated.

As for the feedthrough, you can use plastic threaded rod through tapped holes with a smaller hole drilled through the center and tapped for a bolt. Wires leak at hybrid pressures, and the combustion byproducts will most likely lead to corrosion of the copper core of your wires (to a certain point).

Make sure to shield any fancy electronics from your ignition module! You can use a grounded piece of blank copper plated PCB to do simple shielding.

Pretty close to absolute zero experience, this is all just what I have pieced together from common sense. I have a bit more experience with soldering, though.

Your solution with the chamber acting as the ground makes perfect sense, but what stops it from traveling back into you? The ignition will be a 20,000,000 volt taser, I changed my mind about the boost converter because of the extremely limited lifespan. Is 20 million volts enough for the ignition? :bom: And what do you mean by "potted" when you were referring to how the circuit is built?

If I understand correctly, you are saying to drill and tap into the chamber and then screw in a plastic rod, which has a bolt screwed into the rod, right? What are the plastic rods called/is there a specific material I should look for?

You can find nylon threaded rod and bolts. Get a big enough size to drill through the center accurately, but not bigger than, let's say, 1/4".

As far as the chamber as the ground goes, using it for ground for your DC circuits is completely safe. You could also mount the ignition module inside the chamber and run power to it through the chamber and use the chamber as ground as well.

And no stungun will output 20 million volts.

Hey, I'm just repeating what this says.
I have no idea what the difference between DC and AC are, is a taser DC?

First off I encourage you to look at this working pressure guide:
http://www.wheatland.com/images/standar ... 081114.pdf

If you use HDGT http://www.thehalls-in-bfe.com/HGDT/ you'll see that the pressure of a 10x hybrid will actually exceed the working pressure of sch 40 threaded pipe.

I would not recommend taking your sch10 threaded chamber to 10x.

Remember it's threaded. So that means there is less cross sectional area of the pipe to withstand the stress. Also threads create a stress concentration which are further aggravated by impulse loads such as combustion. The above chart takes into account the threads, but not impulse loads.

I just don't want you blowing yourself up.

Secondly try looking into spark plugs. I am using one for a hybrid I am building right now. Check out these adapters http://www.ebay.com/itm/ANTIQUE-GAS-ENG ... Sw9GhYdVRe

They convert 14mm spark plug threads to 1/2" NPT.

WizardNoodle wrote:Hey, I'm just repeating what this says.

Stun gun manufacturers get a little ridiculous with their claims. For instance, the voltage claimed for that stungun could jump a ~20 foot spark gap.

As for the stungun, they output AC in the sense that it's pulses of current with lots of harmonics depending on the output load. Best to just insulate both terminals.

auxiliary wrote:First off I encourage you to look at this working pressure guide:
http://www.wheatland.com/images/standar ... 081114.pdf

If you use HDGT http://www.thehalls-in-bfe.com/HGDT/ you'll see that the pressure of a 10x hybrid will actually exceed the working pressure of sch 40 threaded pipe.

I would not recommend taking your sch10 threaded chamber to 10x.

Remember it's threaded. So that means there is less cross sectional area of the pipe to withstand the stress. Also threads create a stress concentration which are further aggravated by impulse loads such as combustion. The above chart takes into account the threads, but not impulse loads.

I just don't want you blowing yourself up.

Secondly try looking into spark plugs. I am using one for a hybrid I am building right now. Check out these adapters http://www.ebay.com/itm/ANTIQUE-GAS-ENG ... Sw9GhYdVRe

They convert 14mm spark plug threads to 1/2" NPT.

Thank you very much for your concern, I was looking at this table!
Also, the chart URL says "standard steel" but doesn't include "stainless", and nowhere on the page does it say "316", "stainless", or "seamless", but it does say "welded", which is the lesser pipe relative to seamless!
Are we talking about the same pipe? I wish to use 316L Sch ?10?40? Seamless Stainless Steel.

mark.f wrote:

WizardNoodle wrote:Hey, I'm just repeating what this says.

Stun gun manufacturers get a little ridiculous with their claims. For instance, the voltage claimed for that stungun could jump a ~20 foot spark gap.

As for the stungun, they output AC in the sense that it's pulses of current with lots of harmonics depending on the output load. Best to just insulate both terminals.

Yes, that is probably the best way to go. I will go search for a 50k volt taser

The reason why I provided that chart is because you can see how much of a drop in working pressure results from fastening pipes with threads. The chart you linked to on engineering toolbox is assuming the the pipe has no threads which greatly weaken the pipe. Yes seamless, stainless will be stronger than welded steel, but it will still be subject to stress concentration. I don't see sch10 stainless on that chart either. If you wish to calculate the theoretical burst pressure of any kind of pipe you can use Barlow's formula: http://www.engineersedge.com/calculator ... t_calc.htm

When in the land of hybrids it pays to do some safety calcs!

I believe a general rule of thumb is 50% reduction in working pressure for a threaded joint compared to the plain pipe.
And I don't believe sch 10 is even available threaded or used with threaded connections. It is too thin to maintain any levels of pressure capabilities when threaded.

auxiliary wrote:The reason why I provided that chart is because you can see how much of a drop in working pressure results from fastening pipes with threads. The chart you linked to on engineering toolbox is assuming the the pipe has no threads which greatly weaken the pipe. Yes seamless, stainless will be stronger than welded steel, but it will still be subject to stress concentration. I don't see sch10 stainless on that chart either. If you wish to calculate the theoretical burst pressure of any kind of pipe you can use Barlow's formula: http://www.engineersedge.com/calculator ... t_calc.htm

When in the land of hybrids it pays to do some safety calcs!

Does this table seem reliable? It is the same pipe that this is made from. If it is a reliably accurate table, I just need to find a supplier and buy those pipe nipples.

Oh yeah, I think you are on the right track there. Try checking out you locals dealers, you never know if you have something good in your backyard. I would throw a safety factor on top of those working pressures though because of the repeated shock loads. To do that, you gotta learn a bit more about fatigue: https://en.wikipedia.org/wiki/Fatigue_(material)