55 replies to this topic

[CCH Concepts]

dont worry no insult taken. i love to debat. there not enough people that understand the difference between debat and argument. i alsay have people telling me im auguing with them, when im simply trying to have a conversation.

so many times i have realsised mid conversation that a pre concepection i had (say for instance something i had been told by someone i respected and had till then questioned) was wrong, and wouldnt have had i not debated it.

back to the point. on a one off scale stick with a relay as it will be alot simpliar to build/design, but be sure the parellel the contacts with a capcitor otherwise the contacts will spare with high current and you wont bet a very long lift time out of this expensive relay.

if you intend on producing a fair few of these, getting a well balanced FET output on a single SMT chip would be considerably cheaper. but digger you did make a v good point if the igniter current required is low, i had read it required 500 - 1000 mA. if its alot less than this then an effienct control circuit is the way to go.

this relay isnt to bad, on time takes 10ms max, but mean time is 3ms. will switch on ttl levels.

relay

but check out this IC, its cheaper and will trigger two channels at 1 amp and will connect direct tot he micro-controler. a few of these would be alot neater on board and more cost effective.

H-bridge

out of interest what did you think to my other suggstions?

[CCH Concepts]

even better, cheaper and 4 channel output.

H bridge 2

[Arthur Brown]

Best estimate of firing time and current that I have is 500mA for 20milliseconds. For commercial igniters DIY igs will differ.
However no cct I have ever seen in practice has an instant current rise or a constant discharge current. Also people are inclined to use series and parallel wired igniters on one cue giving the risk of larger currents flowing on the output cct or the additional resistance of series igs needing higher voltages to fire.

Looking at a length of parallel igs wired, if you account for all the lead resistances it becomes easy to see how the igs will fire in sequence and in order NOT instantly

[digger]

dont worry no insult taken. i love to debat. there not enough people that understand the difference between debat and argument. i alsay have people telling me im auguing with them, when im simply trying to have a conversation.

so many times i have realsised mid conversation that a pre concepection i had (say for instance something i had been told by someone i respected and had till then questioned) was wrong, and wouldnt have had i not debated it.

back to the point. on a one off scale stick with a relay as it will be alot simpliar to build/design, but be sure the parellel the contacts with a capcitor otherwise the contacts will spare with high current and you wont bet a very long lift time out of this expensive relay.

if you intend on producing a fair few of these, getting a well balanced FET output on a single SMT chip would be considerably cheaper. but digger you did make a v good point if the igniter current required is low, i had read it required 500 - 1000 mA. if its alot less than this then an effienct control circuit is the way to go.

this relay isnt to bad, on time takes 10ms max, but mean time is 3ms. will switch on ttl levels.

relay

but check out this IC, its cheaper and will trigger two channels at 1 amp and will connect direct tot he micro-controler. a few of these would be alot neater on board and more cost effective.

H-bridge

out of interest what did you think to my other suggstions?

Interesting.

I could not see info on the relay. However I personally would never use a relay for safety reasons as dropping the device could cause contact chatter, and the contacts can fuse. I am not saying solid state components will not fail in a dangerous state, but careful selection should help prevent this.

I still think there is no need to complicate the design with anything more than a FET for the output. Here is one that a forum member uses on his output stage Clicky Clicky. These can be had for as low as 47p each and they have some useful features, 7 amp drive, current limiting, thermal overload, fast switching etc etc etc.

Even if it was 7A or 8A required to fire the ematch the energy required is still very small as the blow time is very short (a few milli seconds) so the number of Joules used is small.

There are some pretty good electronics guys who frequent this joint, some even design circuits for some pretty big contracts. So I am sure they can offer better advice than me.

The other suggestions I have not thought about, I only have a limited amount of time and I spend far too much on here.

Edited by digger, 01 October 2009 - 10:12 PM.

[CCH Concepts]

Best estimate of firing time and current that I have is 500mA for milliseconds. For commercial igniters DIY igs will differ.
However no cct I have ever seen in practice has an instant current rise or a constant discharge current. Also people are inclined to use series and parallel wired igniters on one cue giving the risk of larger currents flowing on the output cct or the additional resistance of series igs needing higher voltages to fire.

Looking at a length of parallel igs wired, if you account for all the lead resistances it becomes easy to see how the igs will fire in sequence and in order NOT instantly

this is were i though some output control would help. if the voltage any available current could be varied depending on set up would this not be a help.

plus one thought with making them fire instantly. has anyone seen a system that fires off of a charge capacitor similar to a camera flash, this could deliver the current a voltage in a instant rather than build up over time.

i have used this principal on relatively low voltage (1000-4000 volt) stun guns that have been used on friends and family when i was younger, due to low voltage and high current did result in some burns. my excuse was for this, was i was a geek with adhd, lol. not a good combo at times.

but this would in this application mean a very quick discharge of high current over a few ms, depending on time constant of the RC between load and capacitor.

[digger]

plus one thought with making them fire instantly. has anyone seen a system that fires off of a charge capacitor similar to a camera flash, this could deliver the current a voltage in a instant rather than build up over time.

i have used this principal on relatively low voltage (1000-4000 volt) stun guns that have been used on friends and family when i was younger, due to low voltage and high current did result in some burns. my excuse was for this, was i was a geek with adhd, lol. not a good combo at times.

but this would in this application mean a very quick discharge of high current over a few ms, depending on time constant of the RC between load and capacitor.

Proper blasting systems use this, I am not sure any firework system does though, for various reasons.

[CCH Concepts]

Interesting.

I could not see info on the relay. However I personally would never use a relay for safety reasons as dropping the device could cause contact chatter, and the contacts can fuse. I am not saying solid state components will not fail in a dangerous state, but careful selection should help prevent this.

I still think there is no need to complicate the design with anything more than a FET for the output. Here is one that a forum member uses on his output stage Clicky Clicky. These can be had for as low as 47p each and they have some useful features, 7 amp drive, current limiting, thermal overload, fast switching etc etc etc.

Even if it was 7A or 8A required to fire the ematch the energy required is still very small as the blow time is very short (a few milli seconds) so the number of Joules used is small.

There are some pretty good electronics guys who frequent this joint, some even design circuits for some pretty big contracts. So I am sure they can offer better advice than me.

The other suggestions I have not thought about, I only have a limited amount of time and I spend far too much on here.

not seen that IC before, pretty cool, but good to see if they do i SMT multi channel version.

the idea behind my business is to help people thats have ideas like this one but not the skill set to develop them. as I'm sure will be pointed out, there people out there that have alot more knowledge than me. but where the complexity is relatively low like in this instance and they more experienced will charge 1000's to help, i will charge 100's, well until i can compete with the big boys anyway lol.

[CCH Concepts]

Proper blasting systems use this, I am not sure any firework system does though, for various reasons.

i was thinking you could get the required energy instantly and power it from a 9 volt pp3 battery. what were the down falls?

[digger]

However no cct I have ever seen in practice has an instant current rise or a constant discharge current. Also people are inclined to use series and parallel wired igniters on one cue giving the risk of larger currents flowing on the output cct or the additional resistance of series igs needing higher voltages to fire.

Looking at a length of parallel igs wired, if you account for all the lead resistances it becomes easy to see how the igs will fire in sequence and in order NOT instantly

That may be true, but we are talking about micro seconds for current rise into a resistive load which is surely irrelevant to a fireworks display.

There would have to be a large difference lead resistance for sequential ignition of parallel igniter's.

So surely as long as the system can drive enough current for the design number of parallel ig's (given that the resistance of the leads to any single ig does not prevent it receiving the firing current) then they should fire more or less at the same time given variances in manufacturing of each individual ig. Surely Kirchhoff's circuit laws apply.

Correct me if I am wrong

[Arthur Brown]

12, 24, 36 and/or 48volt battery packs are used for fireworks, there are several reasons.
1/ it's usually enough
2/ it's usually safe
3/ it complies with the Extra low voltage regulations (50v max)

Capacitors charged to high voltages add the risk that they may be discharged into a wet person (fireworks in the UK means November and means cold and wet weather).

Start by simulating a command wire with igs. 100m of wire at a (guess!) 10 ohms and 1 ohm for the ig. therefore 11 ohms total and only 9% of the supply voltage will hit the ig. will the voltage be enough to hold a high enough current for long enough to fire the igs.

[digger]

i was thinking you could get the required energy instantly and power it from a 9 volt pp3 battery. what were the down falls?

Recharge time between ques. Say you have 30 cues that you want to fire sequentially within a couple of seconds you are buggered. This is not important if you only have one cue like when blasting (OK maybe a few are used but they are independent channels with their own charging circuits).

So how much of your consultancy fee do we get for the info?

[CCH Concepts]

That may be true, but we are talking about micro seconds for current rise into a resistive load which is surely irrelevant to a fireworks display.

There would have to be a large difference lead resistance for sequential ignition of parallel igniter's.

So surely as long as the system can drive enough current for the design number of parallel ig's (given that the resistance of the leads to any single ig does not prevent it receiving the firing current) then they should fire more or less at the same time given variances in manufacturing of each individual ig. Surely Kirchhoff's circuit laws apply.

Correct me if I am wrong

yer totally, my thought behind this was the comment that people had found a delay occurring. this way you would get more than enough energy to trigger the ig's.

but where the problem comes in is is the device has a significant capacitive impedance on its output stage there could be a noticeable rise and fall time depending on the total Resistance of the load. at least in theory, i don't know in practice and this would depend on the output stage of the device firing the ig's.

this method may reduce this.

[digger]

12, 24, 36 and/or 48volt battery packs are used for fireworks, there are several reasons.
1/ it's usually enough
2/ it's usually safe
3/ it complies with the Extra low voltage regulations (50v max)

Capacitors charged to high voltages add the risk that they may be discharged into a wet person (fireworks in the UK means November and means cold and wet weather).

Very True

Start by simulating a command wire with igs. 100m of wire at a (guess!) 10 ohms and 1 ohm for the ig. therefore 11 ohms total and only 9% of the supply voltage will hit the ig. will the voltage be enough to hold a high enough current for long enough to fire the igs.

This is a pretty extreme example for fireworks as most shows I guess would use local control units to limit the cable resistance (and the amount of cable used). Is it voltage drop or current required to fire an ig (I assume both, power)? However only 6V is required for a guaranteed fire at 500ma (IIRC that is most ig's) in your example.

[CCH Concepts]

12, 24, 36 and/or 48volt battery packs are used for fireworks, there are several reasons.
1/ it's usually enough
2/ it's usually safe
3/ it complies with the Extra low voltage regulations (50v max)

Capacitors charged to high voltages add the risk that they may be discharged into a wet person (fireworks in the UK means November and means cold and wet weather).

Start by simulating a command wire with igs. 100m of wire at a (guess!) 10 ohms and 1 ohm for the ig. therefore 11 ohms total and only 9% of the supply voltage will hit the ig. will the voltage be enough to hold a high enough current for long enough to fire the igs.

this could all be designed into the device. if you taking about 9% if you put 134v down the line this would deliver 12 to the ig's, at that point it would be about the capacitors characteristics to deliver the current.

plus there is another way to go and make it modular. the electronics behind a DC-DC converter like this isn't complicated or expensive. you could have them at point of fire and have a low voltage line powering them.

[digger]

this could all be designed into the device. if you taking about 9% if you put 134v down the line this would deliver 12 to the ig's, at that point it would be about the capacitors characteristics to deliver the current.

plus there is another way to go and make it modular. the electronics behind a DC-DC converter like this isn't complicated or expensive. you could have them at point of fire and have a low voltage line powering them.

You don't need 12V to fire an ig. They will fire from a 1.2V NiCad easily (on a shortish lead). commercial igs are quoted as fire and no currents not voltages (the fire and no fire currents takes into consideration voltage). So as long as you can achieve the fire current you can forget about the voltage drop across the device.