Fireworks Launch Box blows LED indicator status lights

Thread Starter

amtrakusa

Joined May 28, 2019
18
First Post - Greetings All!
I've had my hands in electricity for over 50 years, yes, shocked a few times..
Anyway, I'm responsible for a fireworks show each year on the Fourth of July.

The launch system is all hard wired and this year I'm building a new launch box that will have indicator LED lights letting me know I have a solid circuit ready for firing by running a small voltage (3 volts DC) out to the firework element (not enough to spark). After sending higher voltage (120 volts AC) out to burn the element (igniting the firework) the LED will now be off since it was dependent on that circuit.

I have a row of Double Throw-Double Pole switches with a LED just above each switch. Each switch is a ON-ON configuration with one side being MOMENTARY. The 3 volts is wired to the ON side of the switch, when you pull back the spring loaded toggle switch the 120 volt side is activated (and disabling the 3 volts) and when you let go of the switch it springs back to the 3 volt side. Here is a worded schematic. Sorry, not any good with computer pics and loading and stuff)


3 Volts (+) -------------( ON ---- ON ) -----------------LED-------------------------------------------FIREWORK ELEMENT
^ ^
( double throw-double pole switch ) ^ ^
^ ^
120 Volts (+) ----------( ON ----- MOMENTARY) ------------------------------------^ ^
^
^
^
3 Volts (-), 120 Volts(-) --------------------------------------------------------------------------------------------------------------------------------------


Ok, so my issue is about 50% of the time my LED permanently blows and also about 50% of the time my DTDP switch shorts out internally.
I've used the same wiring configuration with 2 separate switches and the LED survives each time but I do not want to have to pull 2 switches for each firework. It may be that I just need a better insulated DPDT switch. These are rated 250 volts 2 amps, 120 volts 5 amps so I think I'm good there.
I'm stumped on why my configuration works about 50% of the time with the LED surviving. I know running AC and DC current through the same line could probably be a problem but if it were the problem I'd probably be getting 100% failure.

My thoughts as to the issue, the direct short at the firework yields such unstability and abruptness in the flow of electricity it literally jumps around inside the DTDP switch and finds the other low voltage side sending current (ac) out to the LED.

I'll figure something out. Just putting it here in hopes someone sees an easy fix with out changing the LED status light and the spring loaded toggle switch. Like I said it might just need a better insulated switch, but I really like these miniature ones. Thanks to all who are at least intrigued. ALL insights into this are encouraged and welcomed.
 

Thread Starter

amtrakusa

Joined May 28, 2019
18
Cleaned up diagram..

3 Volts (+) ---- ( ON ---- ON ---- )---------LED-----------------------FIREWORK ELEMENT
. ^ ^
. (double throw-double pole switch) ^ ^
. ^ ^
120 Volts (+) ---- ( ON ----- MOMENTARY ) ---------------------^ ^
. ^
. ^
^
3 Volts (-), 120 Volts(-) --------------------------------------------------------------- ------------------------------------
 

Thread Starter

amtrakusa

Joined May 28, 2019
18
Ok, so my attempt at sending a better schematic failed. The only thing I would add is that the 120 line from the switch attaches past the LED, not before.
 

wayneh

Joined Sep 9, 2010
16,399
It may be that I just need a better insulated DPDT switch.
It's not the insulation, it's the internal switch configuration. You need one that is built to ensure disconnecting one side before connecting the other. It sounds like the one you're using does not have that feature. Sometimes you get lucky, sometimes not.

Can you link to the switch you are using? That might help narrow the search to a suitable replacement. Maybe something like:
https://www.mouser.com/ProductDetail/TE-Connectivity-Alcoswitch/A205SYCQ04?qs=sGAEpiMZZMvudeGI7i40XGztgZYVs5IEi3nSy8a5Az8=
 

dendad

Joined Feb 20, 2016
3,591
Do you have a current limiting resistor for the LED?

here is how I'd connect it up.
Firewotks.jpg
A switch like Wayneh mentioned above, and an extra fire pushbutton for safety so you need to hold the ARM switch and push the FIRE button.
The FIRE button could be common to all switches or one for each.
Another mod could be have a double pole switch and use the other pole to run a flashing LED to indicate FIRE selected.

I hope when you say 120V, you are using an isolated DC supply and not the mains!
 
Last edited:

Reloadron

Joined Jan 15, 2015
5,609
Rather than use an LED I would consider just going with a model rocket igniter circuit and use a few model rocket igniters for ignition. This link contains a drawing in the pdf format. Page 13 shows the schematic and explanations. The igniters are also available from Amazon at just over $1.00 USD each or just roll your own. The incandescent lamp used in the illustration could likely be converted to a LED design with some minor effort.

Ron
 

Ylli

Joined Nov 13, 2015
976
I assume you are using the proper fireworks rated ematches. What are the no-fire and all-fire current ratings on the ematches? You want to be absolutely certain that there is no way you might provide a current above the no-fire current except when you really want to. Is this a CD system? Do you have a voltage available greater than 3 volts - a higher voltage would provide better control of LED current. Other than those comments, the basic circuit in post #6 would IMHO be the way to go.
 

Thread Starter

amtrakusa

Joined May 28, 2019
18
Wow! Thanks everyone for the replies! So, everyone here has better basic knowledge of the internals and minutia of this. I'll comment on each post so everyone can understand what I understand.

At the outset I'd like to say that this mornings testings indicate insufficient switch capabilities. I ran the test again using 2 separate dpdt switches being sure to deactivate the 3 volt side before activating the 120 volt switch, then deactivating the 120 switch and finally the 3 volt switch was released. The 120 volt line fried and the MOMENTARY side became a ALWAYS ON side. I took the switch apart and there was a little black residue on the internal red plastic housing.

Wayneh, my DPDT switch looks identical to the one you indicated from Mouser. Of course, I'm talking about the size & color, not configuration. At this point I have to agree the internals are my issue. Not enough gap of OFF between 3v and the 120v size. But, since I used separate switches this morning and the 120v switch fried it's apparent the spark inside the housing of the switch is greater than the switch was designed for.

Ylli, and speaking of spark your information of proper ematches. It's my own design. For the element I'm using a single strand of wire from a 30 gauge stranded wire that comes with a silicone sheath. >> https://www.adafruit.com/product/2001 <<There are 11 strands to make up the 30 gauge so the each individual wire looks like a human hair. I'm not sure what metal the wire is but when it pops it puts off a light green blue hue. The only spec I could find they may help you or someone here is that it's resistance is rate at 331 ohm/KM. The reason I like this for the element is it's durability. It bends and twists but does not break, very unbrittle. I know somewhere in all of this the distance I'm dealing with will be needed to be accounted for. So with that another variable of this launch box needs to be addressed. I'm using 8 hots with 8 grounds to have 64 individual ignitions. I've got 2 8T2P rotary switches in the launch box. So essentially 100 feet of ground from launch box to the distribution box and 20 feet of ground from distribution box to each individual element. And of course the same for the hot. So 240 total feet per circuit. I now know that my testing of this switching circuit (had it worked on the table) would have failed under the distance I will be incorporating later. If you know of a better, lighter gauge wire that will reduce my internal switch spark please let me know.

I do not know what the no fire and all fire ratings are. I'm using the empirical method here (basically trial and error). Also I do not know what a CD system is. I can adjust my DC voltage as needed to supply for the LEDS and other lighting aspects on the launch box.

Dendrad, I had not put in a resistor yet since I'm dealing with such low voltage for the LED. After I figure out the switching voltage system I will be putting one in. The resistor at this point may save the LED during testing but I've got a strip of 100 of them and anyway the issue currently is the frying of the switch. Pretty sure the resistor would at the least take a hammering with 120v trying to get thru each time.

Also, I'm trying to avoid having to throw 2 switches for each launch. I'll already have to rotate the rotary switches after each 8 fires to move to the next set of hot's and ground's.

On your comment of an isolated DC circuit. I'm just using 2 AA batteries. They share ground with the 120 neutral line. The other point of contact would be the 120 volt (+) line momentarily connects with the DC ground as the element fires. After that, DC ground is released. Your thoughts on what is happening to the batteries when the 120 v hits the element is encouraged. I really don't know but so far the batteries have remained solid and consistent. Your comment as to hoping I'm not using the mains, it appears as I understand what I've done, I am. But that doesn't "seem" to have caused my issue.

As to your schematic drawings, thank you. The 555 processor I'm familiar with but have never worked with. Also, my understanding of knowing what I'm looking at in a schematic drawing is limited and for that I apologize. I would have to have my hand held to build something like either one of those (well maybe not the first one) and I know this forum is not for that.

As I close, again, thanks very much for everyone's insights. Joining a forum is like opening a box of chocolates. But I can say everyone here has been extremely gracious with your insights. At this point I'll be trying a heavy gauge three position switch with a ON - OFF- MOMENTARY ON configuration, hoping the (and with some luck Weynah mentioned) OFF position will separate the contacts between 3v and 120v enough to prevent my issue as well as being able to handle the internal spark that is created. If someone knows of something I can put on the 120 v (+) line coming into the launch box to reduce the voltage please let me know. Maybe some type of diode. As it stands the current is way overkill to ignite the powder in the ematch. I tried a 48 volt DC 2 amp source but it does not have enough punch to make it through the line at distance.

Again, many MANY thanks to all!
 

Wolframore

Joined Jan 21, 2019
1,748
30 ga wire is not the right wire to use there's too much resistance for what you're trying to do. You really need to check the resistance on your ematch to do some useful calculations.

AWG 30 - has 103Ω at 1000 feet... so it's about 10Ω per 100 feet. Your squibs are most likely .2-1 ohm... you are dropping more current/voltage through the wire than through the squib. It won't take much to burn them out like fuses.

The right way to do this is to have the current source at the launch area so that all your long runs do is to send the signal for fire. This can be achieved to through solid-state or relay switching. A secondary relay might activate some additional banks so you can keep 8-12 on at a time.

12V battery - think how much current can be sourced from a car battery - would be plenty if done properly. You need to know what the all fire current is... what your doing may be dangerous or at best unreliable if not designed correctly.

Are you using 120V AC from a wall plug?
 

Ylli

Joined Nov 13, 2015
976
A relay system (with the high current only at the 'pad') gets a little tough with 80 channels. You really need to look into using a commercial/reliable ematch or squib or this. What happens if you try to fire an channel and nothing happens? How long do you wait before approaching the firing area? I would hope at least 10 minutes - you don't want to be looking down on the firework when it unexpectedly launches because of a 'hang-fire'.

A CD ("Capacitive Discharge") system is one in which a capacitor is charge to a fairly high voltage and then 'dumped' across the load. A camera flash is an example of a CD system. You would use batteries and an inverter to charge the cap. Using the power line directly is a definite NO-NO and discussion of direct line connections is frowned on or even banned on this forum.

You really need to back up and start at the beginning and do it safely.
 

Ylli

Joined Nov 13, 2015
976
Here is an example of a well respected launch system for the rocketry hobby. (I am not associated with and am not recommending this company, but the rocket club I used to belong to does use the equipment).
http://wilsonfx.com/
 

Thread Starter

amtrakusa

Joined May 28, 2019
18
30 ga wire is not the right wire to use there's too much resistance for what you're trying to do. You really need to check the resistance on your ematch to do some useful calculations.

AWG 30 - has 103Ω at 1000 feet... so it's about 10Ω per 100 feet. Your squibs are most likely .2-1 ohm... you are dropping more current/voltage through the wire than through the squib. It won't take much to burn them out like fuses.

The right way to do this is to have the current source at the launch area so that all your long runs do is to send the signal for fire. This can be achieved to through solid-state or relay switching. A secondary relay might activate some additional banks so you can keep 8-12 on at a time.

12V battery - think how much current can be sourced from a car battery - would be plenty if done properly. You need to know what the all fire current is... what your doing may be dangerous or at best unreliable if not designed correctly.

Are you using 120V AC from a wall plug?
Hi Wolframore,
I'm only using 1 single strand of wire from the 30 gauge wire. The 30 gauge wire has 11 if these strands. I'm using the same basic setup as last year with the same gauge wires in place only adding the status/indicator Led's and moving from push button switches to dpdt switches.

The system has not been "calculated".
I know in a forum such as this that would be frowned upon but I use my gut on what would work and what not to use. I do extensive testing to ensure my system works and is safe. Is there a better, safer way? Undoubtedly. But all systems can be tweaked to be more safer, reliable.
The firing system worked perfect last year and I'm only modifying a small portion of it. (LED's and switch types) As mentioned I've been messing with electrical 50+ years and the empirical method has served me well thusfar.

I have considered just putting 64 relays in the distribution box and only using the launch box with 12 volt to activate the relays but that adds another level of complexity to my desire of having the status/indicator LED's on the launch box indicating ready at the ematch.

I'm thinking your term "squibs" refers to the switches. And yes, you are correct, they are underrated. That's why i will be upgrading them and trying to figure how to lower my AC voltage without having to introduce some type of transformer. I heard or read something like a type of diode can do what I want and this is my desire since space is limited in the launch box.

Yes, I'm using hoisehold
 

Thread Starter

amtrakusa

Joined May 28, 2019
18
Hi Ylli,
Thanks for the information. It makes sense to not hardwire from the household current but if I used the 64 relays in distribution box they would require a bank of car batteries, household current or some type of CD system I'd have to figure out. Next year I'll probably put that type of system together but I am limited on prep time this year. This show is not a professional show. All consumer grade fireworks are used and the show is in someone's front yard. I've probably banned myself from the forum at this point by using household current and if that happens, it's ok. As mentioned, the very best and safest designed system can be improved on. My current system worked flawlessly last year, not one miss fire or dud in over 700 fireworks. I manually build every ematch, my design, the entire system as well. And no, no one goes near the launch area for at least 30 minutes after the show ends.

Just have a couple of issues to hurdle this year and I'll be able to do it, help or not. I'm in the testing phase and thought someone might or could help.

Many thanks again for your thoughts, concerns and information.
 

djsfantasi

Joined Apr 11, 2010
6,714
How many fireworks are shot at exactly the same time? I don’t understand why you think 64 relays would require a bank of car batteries?

Your seat of the pants design effort is hurting you. Really, do some calculations. Then you’re not going to run into problems.

I’ve never designed a complete system, but have researched them. I was on the board of a vacation community and we had fireworks (consumer) twice a year.

First, why do you think you need 120VAC to fire the igniters? Really, anything over 12VDC is unsafe and causes issues.

I really don’t understand your comments that you are using one strand of 30ga. wire. Using it for what?

Your firing switch does not need to carry two different voltages. What it must do is supply two different currents at the same voltage.

The common of a SPDT (at a minimum) goes to your igniter. One leg of the switch goes to your supply voltage; the other leg goes to an LED and a current-limiting resistor.

Now for the calculations. First, the current-limiting resistor should limit current to a value small enough to light the LED and not ignite your fuse.

Second calculation. What is the resistance per foot of your wire running to the igniter. Multiply that by two times the distance in feet.

You must know how much current it takes to light your igniter. Do you? And you know the current required to light the LED and the LED voltage drop.

Now the third calculation. At your supply voltage and wire resistance, what current is available to the igniter? Is it enough? If not, you need wire with less resistance.

Fourth! Take into account the wire resistance to the igniter (remember, your wire runs up and back). Do you need to adjust your LED current-limiting resistor value?

Finally, I strongly recommend using a firing button in addition to the switch selecting a firework. With a firing button, you don’t need an on-off-on switch. As well as a key switch to disable the entire board.
 
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