233 replies to this topic

[Andrew]

Hey guys. What do you think about using thyristors instead of relays for firing units?

I tried one [rating: 600V 16A] and am impressed by its size/power ratio...

This is my scappy test unit.

Are thyristors widely used in commercial firing units?! I mean, they add to your firing boxes security.
No problem when your box gets a hard kick which might set of an relay...

I made something similar for my AS level Electronics project many years ago. Albeit more sophisticated; it was remote controlled and coded to eliminate someone's garage door setting it off. It was tremendous fun getting shocked all the time, blowing up resistors getting funny colour plasmas in discharge bulbs and welding capacitors to doors etc.

On an engineering note, capacitors and the charging units from disposable flash cameras do not last long when subjected to such abuse. They do not present one with a long term durable solution to e-match ignition

[MFX]

Out of interest does anyone on the forum have or even still use a "Theatre of Fire" firing system. If anyone has one that's broken or you still use one but would like it maintained let me know as I have considerable experience of repairing them as well as bulilding additional field boxes and even new compatible desks.

[marble]

On an engineering note, capacitors and the charging units from disposable flash cameras do not last long when subjected to such abuse.

It depends on the brand, ive got a rubycon one here that has been used for a year and is still in great shape (same uf rating and low esr)

[Andrew]

It depends on the brand, ive got a rubycon one here that has been used for a year and is still in great shape (same uf rating and low esr)

Nice expensive ones last a lot longer. The cheap ones from the flash units are only designed to last for 100 flashes, which translates to about 5 HP short blows before the dielectric disfigures, the foil burns up and the contacts melt. I'll try and post some photo of the inside of the capacitors when I did the same in my A-Level project. It does not matter how good the capacitor is, if you rag it to f*ck, you'll still over heat the contacts and the foil will burn up. Electrolytic capacitors are not designed to take that sort of punishment. If you want a long lasting system ultra low ESR Tantalum capacitors (a £1000 job to replace cheap electrolytic caps!) are the way to do it, or limit the power dissipation in the capacitors by not shorting them, always make sure there is at least a line resistance in the 10s of ohms. After all they are designed to dissipate and HV low-current across a device that has a cold start impedance of several kilo-ohms. Even then there is a choke to limit the current when the gas in the flash bulb turns to plasma.

Also, the charging circuit is not designed to be shorted, this part also dies pretty quick. You need to either isolate the capacitor from the charging circuit prior to applying the potential to the fuse circuit, or turn the power off to the system a few seconds prior the blowing the fuse. You might thing that a DPDT relay would be ideal, but even the capacitance in a 50m line is sometimes enough to cause a sufficiently high current to weld the contacts shut; another problem I had which I over came by turning carnivore on the relay and adding hugh contacts that could cope with the surge current. Solid state switching is the only way to really tackle this one, or better still, use a lower voltage, then relays and solid state systems are good.

[cooperman435]

Just about to go to bed after a few hours now getting my firing box ready to use. Really pleased with it so far and tested a few emaches through it with fantasticly instant results.

Heres the box with a length of wire and a distrubution block attatched. Ive shorted out the cue 1 to show the continuity system working.

if you want a better look at the other pictures and discriptions of it all go here : Firing Box Page

[portfire]

Hi all.finally took some pictures of my 5 channel firing box (havn't used it yet).The channels are selected by a 2 pole 12 way way rotary switch with each selected channel been indicated with LEDs round the switch and above the terminals.There is also a 555 flasher/bleeper circuit,warning when the fire button is armed.It still needs some work BTW,at the moment it cant handle more than 9v (the flasher circuit) but there's two relays in side,so with abit more work it will run off 9v and be able to handle a higher voltage.






As you can see it's abit crowded so i might have to move it to a bigger box when i update it,but i may never use it as i'm not that good with electronics and the main reason i made this was just to challenge myself.I'm working on a more robust 1 channel box with no fancy bits which i'll be using.

regards
dean

Edited by portfire, 25 May 2007 - 05:37 PM.

[dr thrust]

hi last year i got cheesed off dragging a 12v car bat, nail board, thick cable around and it went flat half way in to my display .so now ive got an old slr camera flashgun by "national" its got a great big capacitor in it these things must last longer than 100 times? they look better built than the disposible ones and there cheap to buy off ebay, could you not have three or four in a box,case one for each ematch,and one ematch lights a piece of visco which lights two,three, four fireworks at the same time it worked for me last year i sent a rack of eight rockets off with one ematch useing the 12 v but now iam going to try the slr flashgun as a cheapo,smaller system, with bell wire they only need three volts but boy they whack out a spark, its a work in progress dont need anything fancy just something to light a firework

[BrightStar]

hi last year i got cheesed off dragging a 12v car bat, nail board, thick cable around and it went flat half way in to my display .so now ive got an old slr camera flashgun by "national" its got a great big capacitor in it these things must last longer than 100 times?

Hi Chris - I'm working on converting an SLR flash into a portable firing box at the moment.

A few quick tips - my flash gun was storing a deadly 30 joules or so at about 280 volts. You only need 8 joules for a good firing box (capable of firing 30 or more comercial matches in series) so I suggest replacing the main cap with a smaller one with the same or higher voltage rating. This has the advantage that it will also charge many times faster.

Also, I would add a 5 - 10 ohm power resistor in series with the output to protect the capacitor and switches. This is equivalent to several ematches in the series chain, but may well improve the lifetime of your gadget. You could also use an inductor in a pulse shaping network, but this could get complicated. I suggest experimenting a bit, as I'll be doing...

Edited by BrightStar, 01 June 2007 - 01:00 PM.

[MFX]

hi last year i got cheesed off dragging a 12v car bat, nail board, thick cable around and it went flat half way in to my display .

What sort of igniters are you using? Is the car battery in good condition? You shouldn't really need a huge battery and "thick" cable. We fire complete shows off 10Ah batteries and relatively thin cable.

[dr thrust]

hi chris m here (sunny bolton) i was using home made nichrome type ematchs, you know bit of wire then put a car bat to it . i think you are right the bat must of been on its way out (it was off my 70 mustang project and was getting knackered)so it got passed on to my pyro elec experiments! it started off ok then died half way into my bonfire display !!. i should of invested in one of them bat drop testers from machinemart.so far the slr gun capacitor is holding out its rated a 330v!and so far it has fused a small switch together that i was using to fire it ! theres loads of power there but i wont fire the nichrome?would it be better suited for one of them graphite jobs?. ive tried them all in the past christmas tree bulbs,ect didnt like them easy to break the filament!(hows my spelling holding up?).a lot of this "testing" was well back in the day and preinternet so didnt have anybody to quiz but this forums great!!!!!!. ps just found an old fire alarm system in a skip at work lucky me the skip rat!. its got a 12v yuasa lead acid bat well smaller than my old car bat and with a built in charger in the fire alarm houseing ,thats charging in my shed as we speak! so it may be back to old school yet,i like to keep it simple,blah blah

[Andy on Wight]

BTW, 50mA test current would be considered a tad high, the igniter specs I've seen say a max of 10mA test current to ensure non-ignition. I would guess from your description of the igniters that they're Chinese, possibly from Cosmos, though that's not certain.

Sorry for the late reply but I had an interesting discussion with the crew that have been using the system I designed and built for them last year. It has been well and truely used in all conditions (beach, grass and on a private jetty all in rain etc) and has given them no major problems. Only 1 display not done due to the fact a liner's wash managed to wash the whole display over with 5 minutes to go as it was set up on a beach.

I will be getting it back soon to give it a service and overhaul as some of the connectors are starting to show their usage in wet conditions. Will be having a real good talk to them whilst it is being serviced to see if I can improve it in any way and give some of my thoughts to them such as
1, changing the connectors to a multipin locking version rather than the D-Type currently being used
2, reduction of test current as suggested by pyrotrev.
3, visual ignitor box activation
4, audio warning of active firing as well as the orignal lashing LED on box.
5, getting the LEDs to switch off completely when iginitor fired.

I will take some photos and then I can develop it further (they are after more than the current number of cues as they will be doing a few larger displays). Was thinking computer firing but that may be beyond my capabilities besides it means more to go wrong.

[MFX]

1, changing the connectors to a multi pin locking version rather than the D-Type currently being used

Defiantly a good idea D connectors really aren't up to rugged outdoor use. If cost is an issue I've seen old fashioned centronics type connectors used on some systems and while I've not used them myself they look to be a better bet (They have "fingers" rather than pins so no pins to snap off just before the display see
http://en.wikipedia....ki/Micro_ribbon
and
Centronics.jpg

Of course "Industrial" or "Mil spec" connectors are better but cost a lot more and you often need an expensive crimp tool to wire them up.

2, reduction of test current as suggested by pyrotrev.

Typically I use 20mA MAX normally much less beware that if you go too low and make your continuity circuit too sensitive you may end up with false positives (High resistance joints showing as good ignitors). Another benefit of low test currents is better battery life.

4, audio warning of active firing as well as the original lashing LED on box.

With the option to turn the sound off for shows where you're sharing the firing position with sound, lighting etc. crew. Personally I can't really see much of a point to audio arm warnings an LED should be more than enough or maybe just an initial very short "BEEP" when the key is turned.

5, getting the LEDs to switch off completely when iginitor fired.

That could be a double edged sword and lead to confusion over whether something has fired when in fact it hasn't. Of course good practice is not to assume anything but you have little control over who may use the desk in the future. You could have two modes, when unarmed it does a straight continuity check, but when armed the led state is "frozen" and the LED's are turned of on each button push. At the end of the show you switch back to "safe" and are given a continuity display again (although as has already been pointed out igniters can short once fired so an after show continuity check mustn't be relied on to check for misfires).

[Andy on Wight]

1, changing the connectors to a multi pin locking version rather than the D-Type currently being used

Defiantly a good idea D connectors really aren't up to rugged outdoor use. If cost is an issue I've seen old fashioned centronics type connectors used on some systems and while I've not used them myself they look to be a better bet (They have "fingers" rather than pins so no pins to snap off just before the display see
http://en.wikipedia....ki/Micro_ribbon
and
Centronics.jpg

Of course "Industrial" or "Mil spec" connectors are better but cost a lot more and you often need an expensive crimp tool to wire them up.

Work in that type of field so have access to all required crimping tools

4, audio warning of active firing as well as the original lashing LED on box.

With the option to turn the sound off for shows where you're sharing the firing position with sound, lighting etc. crew. Personally I can't really see much of a point to audio arm warnings an LED should be more than enough or maybe just an initial very short "BEEP" when the key is turned.

More of an additional item to the circuit,not a continuos noise either but just a serious of bleeps just so everyone is aware its ready to go.


5, getting the LEDs to switch off completely when iginitor fired.

That could be a double edged sword and lead to confusion over whether something has fired when in fact it hasn't. Of course good practice is not to assume anything but you have little control over who may use the desk in the future. You could have two modes, when unarmed it does a straight continuity check, but when armed the led state is "frozen" and the LED's are turned of on each button push. At the end of the show you switch back to "safe" and are given a continuity display again (although as has already been pointed out igniters can short once fired so an after show continuity check mustn't be relied on to check for misfires).

My biggest issue really, as far as continuity goes when fired they are high resistance and the test circuit sees them as 'gone' but during the display they are still on even if a lot dimmer. Have done a number of tests with the ignitors to try an solve it but no success so far

Good points, MFX, developing a system is to keep it as simple as possiblewhich means there are fewer things to go wrng but have a coupo,e of 'luxury' items to make it stand out the bit better.

[MFX]

The only way I can think of to tell if an igniter has been fired or not from the desk is to measure the resistance of each hit pre-show and store that value, then after a hit is fired measure it again if is substantialy lower OR higher then it's likely that igniter has fired (of course for series/parallel strings you can only say that at least one igniter in that string has fired). The problem now is that your continuity test circuit becomes far more complex which reduces reliability/safety. On one of the desk's I built it was actually decided by the user that continuity check during a show is pretty pointless anyway as what are you going to do about it? run out into the field and repair the break? So when switched to arm the continuity LED's switch off so they don't distract/confuse him.

[Arthur Brown]

One pro firer I know, actually calculates the resistance of each cct then uses a meter to check each one before connecting them to the firing box.

Each cct is designed at so many ohms and if it isn't that when he starts he rechecks all connections. Especially useful with large series arrays!