Resistor Igniters

[Updup]

Was trying to decide if I should put this in the electronics section, or this one, I chose this one, but if anyone thinks it should be moved, I will do just that.

 

I was wondering what you guys think about using resistors as igniters? Here is a page I found, written by somone who seems like he knows his stuff, both pyrotechnic and eletronics, and he makes it seem like they work really well, with the right values (Note: there are 4 pages, so more info than just the first page).

 

A quick search on Youtube found several results, including this video where a 10 ohm resistor lights a fuse with ease

 

 

I read this post about the subject and it proved interesting aswell

 

Not only would these be good because no pyrogen is reqired (One could still be used though) They are cheap, 1000 for 8 bucks!

 

I just think its an interesting concept, but would love to hear what youguys think.

Edited November 14, 2010 by Updup

[Arthur]

Resistors as igniters is a well tried concept. The usual two problems are the slow response and the fact that resistors change to low flammability construction, oh and they usually need a lot of power to fire them which makes long wires a problem.

 

ODA sells the resistor chips that commercial igniters use, but these need dipping in pyrogen.

[Richtee]

I wanna know what's white all over the end of that visco, or did they just scrape off the coating?

 

And as mentioned, most resistors now are "flameproof". You'd want to be sure you did not get these.

[dagabu]

Danny Cregan has done pretty exhaustive testing with carbon film resistors and has settled on the 1/8th watt, 2.4 Ohm resistors at Mouser LINK

 

They can be fired from a 12V system or a CD blaster box.

 

BTW- ODA does not offer or sell "resistor" chips, they sell nichrome bridge wire chips. I have both their blaster box and their chips, you can light a match down 300 meters of bell wire.

[Arthur]

My bridgewire chips from ODA came through customs as resistor chips, which is accurate and uninteresting enough!

[Updup]

Danny Cregan has done pretty exhaustive testing with carbon film resistors and has settled on the 1/8th watt, 2.4 Ohm resistors at Mouser LINK

 

They can be fired from a 12V system or a CD blaster box.

 

BTW- ODA does not offer or sell "resistor" chips, they sell nichrome bridge wire chips. I have both their blaster box and their chips, you can light a match down 300 meters of bell wire.

 

Heh, whats a CD blaster box? Also, what kind of 12v system? Like what batterys are used, as there are car batterys or 8 AA batterys, 8 AAA batterys...

[Mumbles]

CD, at least what I am familiar with, is capacitive discharge. They're usually wired systems, but pretty powerful little things. If I'm not mistaken they work something like a taser or stun gun.

[dagabu]

Both the Angry Spark lll and the ODA Blaster Box are capacitive discharge boxes that are about the size as two packs of smokes and cost about under a hundred bucks. Extremely transportable and can light an e-match down 1000' of wire.

 

Small 12V, 2 amp lead acid batteries can be found for around $10.00 each and can light an ematch down 500' of wire but also can melt the wire if a dead short is made by the e-match fusing.

[cds333]

Seems like it would work great; the only thing is you would need more watts of battery power vs. a nichrome based system... I would imagine the guy in the vid used a car battery since he said 12V... Resistors are designated by their max wattage as well as their resistance in ohms, and greatly exceeding their wattage rating will result in catostrophic failure much like sticking both ends of a piece of 28g solid strand wire into a light socket, but that can't be achieved by simply shorting it with a 9V battery. But by all means if you have the watts to spare this seems like a great alternative to costly ematches.

[Richtee]

CD, at least what I am familiar with, is capacitive discharge. They're usually wired systems, but pretty powerful little things. If I'm not mistaken they work something like a taser or stun gun.

Well... not really. The Taser thing is a high voltage/low current deal. Cap discharge is the opposite. A high current pulse. Needs 'restoring" for subsequent firings, but recharge time can be on the order of many milliseconds.

[dagabu]

Seems like it would work great; the only thing is you would need more watts of battery power vs. a nichrome based system... I would imagine the guy in the vid used a car battery since he said 12V... Resistors are designated by their max wattage as well as their resistance in ohms, and greatly exceeding their wattage rating will result in catostrophic failure much like sticking both ends of a piece of 28g solid strand wire into a light socket, but that can't be achieved by simply shorting it with a 9V battery. But by all means if you have the watts to spare this seems like a great alternative to costly ematches.

 

The blaster box is capable of igniting several of the 2.4 Ohm resistors I mentioned at once.

[Arthur]

My findings in the UK are that professional igs for stage pyro are silly money (£1.50 each) but very consistent. Chinese and eastern European igs are cheaper they are probably £1 each in small quantities but by the case igs come down to 20 - 50pence according to the wire length.

 

The problem with most DIY igniters is the power needed for them to work and the speed (or lack of ) with which they fire. Which limits the safety distance the cable affords.

 

One UK supplier now offers Chinese igniters without the pyrogen tip (which you DIY) these can be posted lawfully.

[dagabu]

We get them from ODA here in the states, they are made in China as well and it would be my guess that they are made by the same place. I like the 54 gauge wires.

[billofca]

I've evaluated quite a few CD blasting machines while I worked for Dyno Nobel at their detonator plant. Dyno is the worlds largest explosives manufacturer for mining and quarrying high explosives.

 

Most CD blasting boxes have a battery pack and a charging circuit much like the photo flash unit on a good camera. It makes a faint whining sound while the voltage is being generated to charge the capacitors. Once the capacitors are charged, a "Ready" light comes on. The charge button has to be held down by the operator for the whole time the until is charging until the "Ready" light comes on, and then a second button is pressed to fire the output wire into the blasting circuit. Typical charging voltages are 350 VDC. The capacitor is sized to deliver enough energy to set off up to100 bridge wire electric blasting caps wired in series depending on the target design for the unit. Typical electrical blasting cap bridge wires are designed for 1.8 ohms nominal.

 

If we use ohms law to calculate the firing current for 100 series wired blasting caps, we use the formula I=E/R where I is the current in amps, E is the charge voltage, and R is the total series resistance (180 ohms in this example + wire resistance).

 

So then I = 350 volts divided by 180 ohms = 1.94 amps. Blasting cap recommended firing current is 2 amps, but a cap will fire on as little as 300 milliamps (0.3 amps). We can figure the power dissipated in each bridge wire with P=I^2 R. We square the amps times the resistance and in this example, 6.8 watts is delivered (peak value) across each bridge wire for 100 blasting caps in series. As the number of caps in series is taken down to say only 50 wired in series, the amps taken in the circuit are doubled to 3.8 amps, and the power drop across each cap is doubled to 13.6 watts.

 

For a single resistor fired with this same CD blasting machine, 194 amps would be shot through the resistor or 68 Kilowatts peak instantaneous power. Remember, as the stored energy in a capacitor is delivered to a near short circuit, the voltage and current drop rapidly along an exponential discharge curve according to the time constant. TC = R X C, and there are 5 effective TCs in the discharge curve. The actual current and power delivered is an RMS value. The resistor will explode violently shattering into hundreds of pieces. I have done that experiment with carbon resistors and that is exactly what happens.

 

The point here is if you want to shoot a single carbon resistor rated at 1/8 watt, stick to the 12 volt battery. A small 9 volt battery can deliver 4 amps into a short circuit, and that too would heat a resistor. To calculate the actual current the circuit will draw, you have to know the wire ohms per foot multiplied by the length of wire and again multipled by times 2 (out to the resistor and back) and add it to the resistor value to get total resistance; then do the ohms law to get amps and then the power calculation. Twenty (20) watts delivered into a 1/8 resistor will heat it nicely and quickly. For a single 2 ohm 1/8 watt resistor, using a 12 volt battery will deliver 6 amps. The delivered wattage will be 72 watts.

 

If we take four 9 volt batteries and wire two groups of two in series, and the wire the two groups in parallel, we will have 18 Volts at 8 amps available. Using ohms law for the same 2 ohm resistor, (18/2)we will get 9 amps (but fresh batteries wired this way will deliver a max of 8 amps). The power equation is 8 amps squared times 2 ohms = 128 watts. That should speed up the heating of the resistor quite a bit.

 

Bill

Edited November 18, 2010 by billofca

[cds333]

Is that ODA box just a capacitor and a coil with a 1:100 turn ratio?

 

Does anyone have a schematic for something like that that could be made inexpensively?

 

Thanks

[mike_au]

Ritchee: In order to get increased current (compared to a plain old battery) you also need to step up the voltage. The resistance of the wire+ignitor is constant. At 12V your average SLA can already supply as much current as the ignitors are likely to draw. In order to get them to pull a higher current you need to supply a higher voltage.

 

The main difference between a taser type circuit and a CD box is the presence of the capacitor. A taser creates high voltage at low current which is then immediately discharged across the probes, a CD box creates high voltage at low current which it pumps into a capacitor over a few seconds so that it can then be discharged as a high voltage, high current pulse.

 

Is that ODA box just a capacitor and a coil with a 1:100 turn ratio?

 

Does anyone have a schematic for something like that that could be made inexpensively?

 

No.

 

By coil I assume you mean an automotive coil. Automotive coils are good for making a spark (or a taser) but not so good as a general step-up transformer (you could use one in a pinch, but back EMF is likely to cause trouble).

 

The CD box would have a normal transformer and a capacitor (or maybe a cockroft walten generator), but since it needs to run off a battery (which is DC) it would also have an wave generator to make some sort of AC.

 

I don't have a schematic, but it wouldn't be too hard to make one up. Probably start with a simple 555 multivibrator circuit, stick a heavy duty transistor or FET on the output, run that into your transformer, put the output of the transformer through a rectifier and into the cap. Probably not the most efficient design but it should work.

[Richtee]

Ritchee: In order to get increased current (compared to a plain old battery) you also need to step up the voltage. The resistance of the wire+ignitor is constant. At 12V your average SLA can already supply as much current as the ignitors are likely to draw. In order to get them to pull a higher current you need to supply a higher voltage.

 

Well, of course. You typically need them to supply a higher voltage because you don't have 00 AWG firing cables, making the IR loss down them too great at low voltages. Same reason power transmission lines are run in the kilo-mega voltage ranges.

 

The CD box typically uses (As Bill alluded to) a voltage tripler circuit. The DC bat voltage is fed into a power oscillator, generating an ac wave. That is run thru the cap/diode type voltage tripler or step-up transformer or combination thereof, charging a high voltage cap. THEN the system is ready to fire. These will take time on the order of seconds to recycle.

Edited November 28, 2010 by Richtee

[dagabu]

Is that ODA box just a capacitor and a coil with a 1:100 turn ratio?

 

Does anyone have a schematic for something like that that could be made inexpensively?

 

Thanks

 

Even between two CD boxes available like the ODA Blaster Box and Nichropulse Angry Spark lll, there are huge differences in the build but both end up throwing 300-700 volts down the line to pop the e-matches. here are the pics of the insides.

[cds333]

Mike: Sorry, by coil I meant step-up transformer; (based on ODA's specs of 2 AA batteries and 300V firing output the coil ratios would be 1:100 assuming the AAs are in series)

 

Dag: Thanks for taking the time to upload the pics. The first one (The ODA I assume) appears to have no ICs at all, nor any DC to AC conversion components. Based upon the yellow board traces, it doesn't appear to have any back side mounted components either, so all I can see is:

 

4 resistors, one of which is of a higher rating than the other three (the blue one I would assume is to buffer or possibly bleed the output of the main CD capacitor)

2 capacitors, one of which is the main CD cap

1 diode

1 led

1 transformer

1 transistor

2 DPDT switches

2 banana/screw terminals

 

 

Correct me if I'm wrong, (I'm not an electrical engineer, yet) but the ODA appears to be a straight DC setup?

 

 

Thanks

[dagabu]

Mike: Sorry, by coil I meant step-up transformer; (based on ODA's specs of 2 AA batteries and 300V firing output the coil ratios would be 1:100 assuming the AAs are in series)

 

Dag: Thanks for taking the time to upload the pics. The first one (The ODA I assume) appears to have no ICs at all, nor any DC to AC conversion components. Based upon the yellow board traces, it doesn't appear to have any back side mounted components either, so all I can see is:

 

4 resistors, one of which is of a higher rating than the other three (the blue one I would assume is to buffer or possibly bleed the output of the main CD capacitor)

2 capacitors, one of which is the main CD cap

1 diode

1 led

1 transformer

1 transistor

2 DPDT switches

2 banana/screw terminals

 

 

Correct me if I'm wrong, (I'm not an electrical engineer, yet) but the ODA appears to be a straight DC setup?

 

 

Thanks

 

The traces in the ODA box are parallel for the batteries, yes, the blue resistor is for the bleed. Yes, straight DC.

[cds333]

Cool, thanks; so other than the fact that AC travels over distances better, is there any advantage to using ACCD vs DCCD for firing resistors?

[Richtee]

Mike: Sorry, by coil I meant step-up transformer; (based on ODA's specs of 2 AA batteries and 300V firing output the coil ratios would be 1:100 assuming the AAs are in series)

 

Dag: Thanks for taking the time to upload the pics. The first one (The ODA I assume) appears to have no ICs at all, nor any DC to AC conversion components. Based upon the yellow board traces, it doesn't appear to have any back side mounted components either, so all I can see is:

 

The traces in the ODA box are parallel for the batteries, yes, the blue resistor is for the bleed. Yes, straight DC.

Well, I am assuming that the transistor is an oscillator circuit, and the transformer next to it is a step up. The doide clips off the high voltage AC (likely square) waveform to a positive value only and this pulsing DC is what charges the cap. Sooo... straight DC is kinda a mis-nomer.

Edited November 28, 2010 by Richtee

[dagabu]

Cool, thanks; so other than the fact that AC travels over distances better, is there any advantage to using ACCD vs DCCD for firing resistors?

 

Naw, high tension power lines are DC, the power that is released from the cap to the wire is DC, the energy is "pumped" into the capacitor is what he meant.

[Arthur]

Do you have access to a used, disposable film camera? The flash unit in one of these is suitable for a DIY blaster if you work competently. Yes it's similar to the ODA unit one transistor and one special transformer makes an oscillator of adequate performance to push power into a capacitor.

 

Various seriously expensive professional CD exploders have better switching and better waterproofing and also continuity checking. The NATO/UK Shrike also checks that the firing cct is under 400 ohms as over that it may misfire or it may be a person working on the command wire.

 

I actually prefer around 50v for a firing system. If your leads are too long then you need thicker leads to get less resistance.

[dagabu]

Do you have access to a used, disposable film camera? The flash unit in one of these is suitable for a DIY blaster if you work competently. Yes it's similar to the ODA unit one transistor and one special transformer makes an oscillator of adequate performance to push power into a capacitor.

 

Various seriously expensive professional CD exploders have better switching and better waterproofing and also continuity checking. The NATO/UK Shrike also checks that the firing cct is under 400 ohms as over that it may misfire or it may be a person working on the command wire.

 

I actually prefer around 50v for a firing system. If your leads are too long then you need thicker leads to get less resistance.

 

This LINK pops up a lot in CD firing circles for flash camera mods.