Pyro Firing Current

[timtheenchanteruk]

I have a self built (fully inspected/tested/approved) firing unit, which works fine

 

however, it does not seem able to fire more than 2 pyros simultaneously so I am wanting to upgrade the battery it it so it can.

 

I need to know what the firing current of a pyro is so I can work out what battery is needed

I think it has a 2.5Ahr in it at the mo off the top of my head

 

Thanx

[DC FX]

I have a self built (fully inspected/tested/approved) firing unit, which works fine

 

however, it does not seem able to fire more than 2 pyros simultaneously so I am wanting to upgrade the battery it it so it can.

 

I need to know what the firing currant of a pyro is so I can work out what battery is needed

I think it has a 2.5Ahr in it at the mo off the top of my head

 

Thanx

 

 

This is one of those really hard questions to answer for so many reasons:

 

1. Although the Amperage needed to fire most common Pyro it can also depend on the length ogf your normal run of leads due to line drop

 

2. How many effects you are setting off at one time

 

3. How your box is wired

 

All I will say is that most home made firing boxes (in the film industry anyway) run off 12V 50Amp Car batteries, we do however have long runs of Twinflex and are sometimes letting off alot of Pyro in one shot

 

Let us know the details of the maximum loading you be putting on the box etc and I could possibly help

[Lincoln]

... generally 1/2amp for igniters

 

Couple of documents to help you from the training courses...

 

The issue is probably more to do with you trying to fire devices in parallel rather than in series.

 

Series/Parallel Wiring Guide

Series/Parallel Wiring Data Table

 

 

Our most to date has been 180 waterfalls off a 12 volt battery - but that was assisted with a capacitance discharge unit !

 

 

Lincoln

 

Association of Stage Pyrotechnicians www.stage-pyro.org.uk

[Simon Lewis]

Just out of interest....

 

Is it not possible to reduce volt drop by using a more appropriate cable?

 

Does not series connection add an increased risk of multiple units not firing should there be a cable break?

 

Simon

[Brian]

There is a very good reason to use cheap 'bell wire' cable costing 5p a metre. It's called time. At the end of the job you just chop it and bin it. It turns a 3 hour get-out into a 1 hour get-out.

 

As to the second part, yes there is an increased risk but it is much easier to test.

 

Consider 20 devices in parallel which would give around 0.08 Ohms total excluding the interconnect. Now if one of those goes open you have around 0.084 Ohms total - a difference which you cannot measure. In series it goes from 32 Ohms when good to infinite when open - much easier to fault find.

[Simon Lewis]

Brian,

 

Makes perfect sense... I've obviously spent too much time only thinking about loudspeaker connections!

 

However, my colleague who teaches electronics and maths to music and media students has made a note of this example to illustrate series / parallel connections, and calculation of power and Ohm's law... Lucky students ;-)

 

Simon

[timtheenchanteruk]

Hi, Its a 4 channel box, so I would like to be able to fire all 4 channels simultaneously,

 

I prefer to do it that way, then if using say 4 jets across the front of a stage and someone is too close to one, I can disable one (or two to even up) and not lose the effect completely (producers/directors don't like it when they are told it didn't go off cos I didn't set it off)

 

the run is approx 50-80 feet depending on where the pyro is, using a line level type of multicore to a breakout box, then single lines of whatever (a mic type cable or bell wire etc depending on what and where it is)

[Jivemaster]

That would work best if each channel had a firing circuit rather than sharing one circuit. You may have found a limitation of single psu systems.

[soundo26]

... generally 1/2amp for igniters

 

Couple of documents to help you from the training courses...

 

The issue is probably more to do with you trying to fire devices in parallel rather than in series.

 

Series/Parallel Wiring Guide

Series/Parallel Wiring Data Table

 

 

Our most to date has been 180 waterfalls off a 12 volt battery - but that was assisted with a capacitance discharge unit !

 

 

Lincoln

 

Association of Stage Pyrotechnicians www.stage-pyro.org.uk

 

I agree with Lincoln here, but one thing that crosses my mind is that for two devices in any formation you should have no problems at all.........EXCEPTING.......when you use different batches of LeMaitre consumables purchased relatively recently. This is because they changed their supplier of igniters a short while ago and the newer ones fire off significantly faster than the old ones, no problem if you have all the same type in a series line but if you have an older device mixed with a newer device, the new one can be fired and the circuit is broken before the response time for the older device is reached. Information can be found on the Le Maitre site and the ASP site. :)

[Lincoln]

... That is why it says "IMPORTANT ALL IGNITERS THE SAME TYPE" at the top of the Data Table document.

 

A quick help for those wanting to know which Le Maitre igniters are the new type...

 

The batch numbers start with the letter "M"

 

and...

 

Hi, Its a 4 channel box, so I would like to be able to fire all 4 channels simultaneously,

 

I prefer to do it that way, then if using say 4 jets across the front of a stage and someone is too close to one, I can disable one (or two to even up) and not lose the effect completely (producers/directors don't like it when they are told it didn't go off cos I didn't set it off)

 

the run is approx 50-80 feet depending on where the pyro is, using a line level type of multicore to a breakout box, then single lines of whatever (a mic type cable or bell wire etc depending on what and where it is)

OK... you can achieve the above using a series switchboard which preserves the integrity of the series circuit regardless of how many single channels are selected.

 

See here Series Switchboard - Example shows just one circuit selected and that if any other circuits are selected they are added in series to create one big happy series circuit.

 

I shall let others assist you with the reasons why running mic cable (XLR-3) for pyro is not such a good idea !

 

Lincoln

[mac.calder]

Or we could link to this thread where lincoln covers the topic of XLR3 quite well. Here

[Brian]

I have a self built (fully inspected/tested/approved) firing unit...

Out of curiosity, when you say 'approved', who approved it? It's just that I wasn't aware of anyone who would offer such a service.

[timtheenchanteruk]

I should have made myself a bit clearer, to avoid the confusion, I am not actually using and XLR mic cable, rather a twin and screen cable with 4pin XLR on the end

 

The box was inspected and approved by a pyro tech, and the local fire service

[Tomo]

however, it does not seem able to fire more than 2 pyros simultaneously so I am wanting to upgrade the battery it it so it can.

This is almost certainly a 'battery internal resistance' issue.

 

No power supply is perfect - they all have internal resistances that lose energy as heat.

Therefore, when you draw current from the supply to fire the pyro the actual voltage across the battery drops due to this resistance - it's essentially an extra series resistor.

 

If you put too much load on the supply, it gets hot and supplies almost no power into the load.

(Vastly simplified, but it's the essential point)

 

To solve this, go to series-wiring and use a higher voltage.

 

The top-end pyro controllers available from LeMaitre et al use charge pumps and storage capacitors to allow a fairly high voltage and extremely large firing current from a relatively high-resistance battery - this is a fairly complex system though, and I wouldn't expect a layman to understand this!

[Jivemaster]

Pyro controllers for theatre often operate around 30 - 40 volts thats plenty for a few series igniters and some cable resistance and still a low voltage device. 4 x PP3 in series will supply this and be quite adequate for stage use (and you can buy twin PP3 holders Maplin/RS etc.) If your electronics is OK you could make a small step up unit battery in - 36v out and charge a small capacitor and discharge it into the pyros. 36 Volts from PP3 or AA cells should last you for years of normal pyro firing, prob the cells will expire by shelf life first.

 

For outdoor fireworks and ordnance clearance the favoured tool is a "Shrike Exploder" ( search it !) which uses more like 600v DC as there may be several kilometers of wire and dozens of matchheads to fire. If you must play towards one of these rip the works out of a disposable flash camera! 350V dc from a AA cell and a capacitor ( 160uF) to discharge. Please remember that there is the volts hazard during construction and also during use. There is also the anti terrorism hazard - What possible use have you for it when you get asked awkward questions. A REAL shrike has a safety cct to prevent you firing it into a person, A mickey shrike may not have. they are about as powerful as a Cardiac Defibrulator.