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Can someone help me with this circuit? Answered

I'm working on a fireworks ignitor based off of Bill Gurstelle's design in his book Absinthe and Flamethrowers, and I'm having some trouble. Instead of two switches, mine has three switches.  Like Bill's design, it runs off of eight AA batteries. One end of the battery pack goes to a toggle switch and a keylock switch, and the other goes to a pushbutton. They both end at a bolt. I have two long wires with alligator clips on both ends. Each clip clips to the bolt, then to a piece of nichrome wire which is wrapped around a fuse. In theory, when all of the switches are flipped, the nichrome wire lights the fuse. But this isn't happening. I've tested all of the switches, and they all work. The bolts and the nuts holding them in place both conduct electricity, but no power is arriving at the bolts. All of the components were purchased from Electronic Goldmine, except for the battery pack, which I bought at Radioshack. The ignitor is housed in a wooden (and therefore nonconductive) box. What's wrong?  (Attached is an awful drawing/collage I did of the circuit. If you need a picture of the machine itself, I can take a picture.)





Best Answer 8 years ago

Set your meter to measure low range volts (12).

Turn all switches ON.

Have a helper press the push button switch.

Touch the meter probes to the bolts.

Do you see approx 12 v. there?

    IF yes then everything is fine.

    If no, then have the helper let go of the pushbutton.

    If yes now then you have a normally closed pushbutton and it needs to be a normally open.

     If no then put the probes at the battery output.

Power there?

     If no then the battery pack is your problem.

     If yes then move one probe to the other side of the pushbutton and leave the other probe to the opp. side of the battery.  Have you helper press the button.

Power there?  if no then it's either the push button or the wire leading to the push button.

     If yes then move the probe from the push button to the bolt, press the button and test.

     If no then the problem is either the bolt, the wire leading to the bolt or the solder connection.

If yes then move the probe from the opp. side of the battery to the toggle switch and test.

If no then it's either the toggle switch, wire leading to the switch or the solder connection.

If yes then move to the key switch and test.  Is the keyswitch on?

If no then it's the keyswitch, wire or solder connection.

IF yes then move to the bolt and test.

IF no then it's either the wire leading to the bolt or the solder connection.

If yes then you didn't test right in the beginning since you changed nothing.  Maybe you had one of the switches turned off.

You have to test each piece in line by actually testing for voltage not resistance.  Unless you're careful testing resistance only checks the switch not the connecting line.

Find where your voltage stops and that's where your problem is.

I suspect your toggle switch might be the problem. If it has multiple pins on it, you must be connected to the correct 2. If it only has 2 pins on it, then that is not the problem. I have also seen battery packs like you show in the diagram that have slight RUST or corrosion on 2 or 3 terminals (where the battery touches) or at the end of the SPRING. (the one that touches battery negative). Use a piece of sandpaper to knock off the rust if you see any. All of the other "commenters" also gave good ideas. get yourself a CHEAPY digital ohm meter. Harbor freight tools has one they sell for about 3 bucks and they work GREAT.


8 years ago

Test everything.

Buy a cheapo VOM (volt-ohm meter), and check the voltage at the bolts. If V = 0, then track down the problem. Remove the batteries, switch the meter to ohms, and check the continuity of each section.

Then check the continuity of the long wires.

If it's not the wiring, then the problem lies with the ignitor...

. Yep. It's almost impossible to troubleshoot circuits without a VOM (or DMM).
.  Do a quick continuity check. If continuity is OK and it still doesn't work it's probably a bad switch (or ignitor) - do voltage checks, starting at the battery.
.  My first guess is that you have one or more of the batteries installed backwards.

All good suggestions, but I more or less have tose things covered. I checked every part with multimeter to see if power is running through it (I'm not so great with multimeters, so I set it to a mode that raises the needle when the two probes touch, and attached them to each side of the components to see if the needle raises), and all the components seem to work. I just installed fresh batteries yesterday, and made sure to put them all in correctly, but I'll check again. Gmoon: what do you mean when you say "If it's not the wiring, then the problem lies with the ignitor"? Do you mean the problem lies within the original schematic? Because there is no one component that is "the ignitor". Thanks for all the help, Noahh

yes there is. the nichrome wire is your ignitor. Period. I say this having used them for ten years in support of NASA's microgravity combustion sciences. I have a bit of experience under my belt using nichrome and 

All the other stuff is your ignitor supply circuit. 

What I was saying is that there is no electrical component (Like a Glo-Plug) that lights off the pyrotechnics.

Yes there is. That's the piece of nichrome wire. Not trying to be argumentative, just saying what IS.

The nichrome wire IS your igniter.

A glow-plug is just another type of igniter. 

You have several points that can be your problem:

1) your supply
2) your defeat switch (the key lock switch)
3) your permissive (the toggle switch)
4) your ignition switch (the push button)
5) your wiring (all the various connections you show using the bolts and aligator clips and ?wire?)
6) the igniter itself (the nichrome wire)
7) the fireworks fuse

My primary area of concern, presuming all other elements are intact and correctly wired, would be the intrinsic impedance of the circuit (both resistance and parasitic capacitance and inductance) which can lead to too little current (via to high an intrinsic resistance) or to little on time to deliver the required current thru the igniter (via the dynamic resistance, ie, impedance or sum of time variant resistance via parasitic inductance and/or capacitance plus that of the static impedance, ie summed resistance from battery to load and back).

As others have indicated, a volt-ohm-ammeter would go a long way to assisting you in troubleshooting the circuit. They can be purchased for as little as $10 at radio shack and other similar stores.


8 years ago

I think your key-lock switch might be the problem. The operating voltage for that particular switch is not listed on Electronic Goldmine, but the description of a similar key-lock switch says it operates at 120 volts ac. http://www.goldmine-elec-products.com/prodinfo.asp?number=G8081 I'd re-test the key-lock switch, and then try the circuit without it.

The switch may be bad but that switch rating is for max. voltage. The switch will work for any voltage lower than that.

Then check that electricity is getting through the chain by testing it as it leaves the battery pack then as it gets through switch number one and, if successful, check it gets to switch number two and so on until you find the place that it isn't getting through.

Make sure your nichrome wire isn't too long, or it will present too much resistance and will not draw enough current to achieve ignition temperature.. I'd keep the nichrome to ~3" max. Also, remember that you may have to hold the push button down for a tiny bit longer than you might think to achieve temp. It does take a few tens of msec before the wire comes up to temp and could take longer depending on your circuit's intrinsic impedance.


8 years ago

check all your connections oveer again. Check EVERYTHING. Also check if the batteries are still good.