Strobe Light Circuit

[jkb56]

Hey all,

Hope someone can provide some suggestions with an application I have.

I'm needing to put 4 12 volt D.C. alarm type strobe lights up, but I need them to flash all at the same time. I can pick up simple alarm strobe lights from one of my suppliers, but from past experiences the capacitor charge / discharge to fire the strobes will not be the same, and will vary with each unit.

I seriously doubt if it would be as simple as taking one unit, taking it apart, finding the value of the capacitor, multiple that times 4, and substitute a larger capacitor in the circuit to fire all 4 strobes from the same output.

Don't have a real concern with the flash rate, one flash every two seconds would be ideal, but as long as all 4 flash together. Will be putting the main circuitry in a splice box, then just running a pair of wires out to each strobe light. I figure the longest wire run would be 'maybe' 8 feet, the shortest wire run probably 3 feet. And can be flexible with the wire gauge, so I don't believe the resistance of the wire will come into play.

If anyone thinks that taking one strobe light circuit and substitute a larger capacitor into that circuit would work, I'd certainly would go that route, but I have to wonder if I would overload the circuit by trying to charge a larger capacitor in that circuit.

Don't want to even consider off the shelf automotive type strobe packages, as they are expensive, and typically have a strobe bulb designed to be installed into headlights or taillights after drilling a 1 inch hole for mounting. Those bulbs are too large for my application anyway, and even though they offer multiple flash patterns, I doubt if I could get all 4 to fire at once, about every two seconds. These were more designed for police and security vehicles, and to flash at different rates.

Hope someone has some suggestions of diagrams out there...

Thanks,

 

[dougy83]

To keep them synchronised, you would have to run another wire to all strobes to carry a trigger signal. I'm not sure how exactly your strobes are triggered, but it's likely that there's a neon that triggers an SCR - the neon will have to be removed from 3 of the 4 strobes, and a 1k resistor connected from the neon to the SCR gate of all 4 strobes.

If you can post a picture of the strobe innards I may be able to point out which components are which, and what to change.

 

[bigkim100]

Google is your bestest friend
I simply googled "flash slave trigger" and these popped up, along with several hundred others.

**broken link removed**

Flash Slave Trigger

 

[bigkim100]

Sorry, keep forgetting...cant cut and paste shortcuts here...I think its because its considered the work of the devil

 

[jkb56]

'Alarm type' strobe units

To keep them synchronised, you would have to run another wire to all strobes to carry a trigger signal. I'm not sure how exactly your strobes are triggered, but it's likely that there's a neon that triggers an SCR - the neon will have to be removed from 3 of the 4 strobes, and a 1k resistor connected from the neon to the SCR gate of all 4 strobes.

If you can post a picture of the strobe innards I may be able to point out which components are which, and what to change.

I haven't purchased one of these strobes yet, let alone 4 of them. Was hoping to find out if it would work before investing in 4 of them. Have seen several of these type on the outside of stores next to security cameras, but all operate independently on 12 volts D.C. And because each run independently, they flash at different rates. If watched long enough, there will be a point where they will all flash at once, but then go out of sync again.

No doubt variances in the capacitor / resistor that charges then fires these. I had planned on removing the 4 neon bulbs, housing them in an amber housing, then running wiring back to a control circuit that would control and fire them all at once.

Again, these are alarm type strobes typically found on siren boxes to indicate a visual as well as an audio indication that an alarm has been triggered, not a photo type strobe light.

These have been around for years, and are a simple circuit design. I kind-of doubt if there are any SCR gates in the circuit. The 12 volts D.C. just charges the capacitor, and at some point it discharges firing the strobe. The flash is consistent, so there must be some component in there that discharges the capacitor at a regular rate.

I may have to break down and purchase them without knowing if this will work and experiment with them. I'm figuring that a certain value capacitor fires one strobe and that if I want to fire 4 of them, I will for sure need a larger capacitor in the circuit. Just wondering what else I might have to substitute into the circuit to make it work?

 

[mneary]

You should not attempt to use a common flash capacitor for the strobes. The voltage and currentss are high, and the lamps don't share well.

The cheapest way to manufacture a reliable strobe trigger uses an SCR, so it is extremely likely that you'll find an SCR in your strobes. All you need to do is wire a MOC3020 or other suitable random-phase opto TRIAC instead of each SCR.

Build a 555 circuit that operates at the rate you want them to flash, and hook the optos to its output. Be sure each opto's LED has its own current limiting resistor.

Replacing the SCR with the opto TRIAC is the only internal surgery you need to do to the strobe.

 

[dougy83]

doubt variances in the capacitor / resistor that charges then fires these. I had planned on removing the 4 neon bulbs, housing them in an amber housing, then running wiring back to a control circuit that would control and fire them all at once.

The neon bulb I was referring to gives a weak orange light and is often used in flash circuits to trigger an SCR which in turn utilises a transformer to provide the kilovolt trigger to the xenon flash tube. It is possible that the SCR is not used, and just a neon or diac is used as the trigger source.

I may have to break down and purchase them without knowing if this will work and experiment with them. I'm figuring that a certain value capacitor fires one strobe and that if I want to fire 4 of them, I will for sure need a larger capacitor in the circuit. Just wondering what else I might have to substitute into the circuit to make it work?

I wouldn't recommend running 8 foot of wire to each bulb; the instantaneous current is quite large during a discharge, not to mention the RFI you'll create. It's better to have the 4 separate strobe circuits complete (with triggering circuit removed), and run a common low-level signaling wire to each circuit.

 

[Hero999]

I doubt it uses a neon bulb, it more than likely uses a DIAC.

The cheapest way to manufacture a reliable strobe trigger uses an SCR, so it is extremely likely that you'll find an SCR in your strobes. All you need to do is wire a MOC3020 or other suitable random-phase opto TRIAC instead of each SCR.

I wouldn't recommend that, the opto TRIAC most probably won't have the current handling capacity and will blow up.

I'd recommend using the opto TRIAC to trigger the SCR. Indeed you could theoretically also use a transistor opto isolator but you probably won't be able to get one with a high enough voltage rating.

 

[dougy83]

I doubt it uses a neon bulb, it more than likely uses a DIAC.

The one on my desk ("Pulse ST1200") uses a neon bulb. It triggers an MCR400-6, which I'm guessing is an SCR (from the way it's wired), through a resistor. Running a common wire to the neon bulb-resistor junction of each strobe should allow them to trigger synchronously. The voltage on the common wire shouldn't go above 20-40V, so it's quite safe. This also has the advantage of triggering the strobes before the voltage across the bulk storage capacitor exceeds its voltage rating, as may happen with an external trigger that is too slow.

I wouldn't recommend that, the opto TRIAC most probably won't have the current handling capacity and will blow up.

The MOCxxxx can handle 1A for 1ms repetitive, which should be plenty for dumping the charge of a 10n cap. I've triggered strobes using 200mA NPN transistors to fire the transformer. The thing you'll have to watch, though, is the holding current of the MOCxxx triac output; you don't want it staying on due to the recharge current to the trigger cap. I don't personally think isolation is required, although it might be considered a nice-to-have by many.

 

[Hero999]

The one on my desk ("Pulse ST1200") uses a neon bulb.

How old is it?

That sounds very 1970s.

I have a strobe module and it uses a DIAC.

The MOCxxxx can handle 1A for 1ms repetitive, which should be plenty for dumping the charge of a 10n cap. I've triggered strobes using 200mA NPN transistors to fire the transformer. The thing you'll have to watch, though, is the holding current of the MOCxxx triac output; you don't want it staying on due to the recharge current to the trigger cap. I don't personally think isolation is required, although it might be considered a nice-to-have by many.

Oh, you're talking about triggering the transformer, I thought you meant ripping out the old SCR and replacing it with the opto-TRIAC.

 

[dougy83]

How old is it?

No idea, it's still in its box (so it must be brand new)

It's from jaycar, and they're still being sold (doesn't mean that the design isn't from the 1970's, of course)
**broken link removed**

Oh, you're talking about triggering the transformer, I thought you meant ripping out the old SCR and replacing it with the opto-TRIAC.

The SCR triggers the transformer; I have never seen it used in another manner. The Xe tube is connected directly across the bulk capacitor. This is normal as the Xe tube gas will not break down/conduct without a high voltage (maybe >1kV).

 

[Hero999]

Yes you're right, the SCR triggers the transformer which causes the tube to ionise. The tube behaves like an SCR allowing a huge current to flow.

I don't know what I was thinking.