Studio Ring Flash Xenon Tubes

[Jamie Pocock]

I was thinking of building something similar using a pile of old flashes to make a small ringflash for macro work. You might want to add the ability to shut off half the flash to provide some shadowing if your wife plans to use it at all for macro work. Are you using a bundt pan for the reflector? I havent gotten around to collecting all the parts yet, so I will watch your posts with interest. also remember you can connect smaller higher ohm resistors in parallel to make a higher wattage bridge. Caleb

bundt pan is indeed what I have use with a bicycle handle grip on a peace of copper water pipe to hold the flash, the rest of the unit including the camrea mount and a fibra glass back case is yet to be made.

 

[Jamie Pocock]

This is the flash head I have made. Just got to get my head around the circuit.

**broken link removed**

 

[Jamie Pocock]

How fast does it need to charge? I would consider using a higher value resistor, like in the 1k 20 watt region. You could use 4x 1k 5W resistors.

Fast charge circuit is what I am after, the quicker the caps can charge the better.
In a studio shoot 8 - 10 seconds is unacceptable to a photographer. The flash would get put down and never used. One second or faster is the target.

 

[Jamie Pocock]

I have found the full circuit diagram for the flashs I am ripping apart
T-20_tech.pdf
It is 1.73MB but shows all the components. I would like to use as many as posible as the original flash can charge in 1 second.

Thanks Jamie

 

[Jamie Pocock]

You might want to add the ability to shut off half the flash to provide some shadowing if your wife plans to use it at all for macro work.

I was thinking after reading your above comment I could make a perspex diffuser that can rotate in the head with 50% dark 50% semi transparent (Zebra defusser) thats my trademark now don't steal it LOL.

 

[CalebG]

I was thinking a switch to cut off 3 capacitors from the charging circuit, It would enable faster charging for the remaining 3 tubes. If you want to get really creative you could a 3 way slide switch 1 would turn on all tubes, 2 would turn on 3 tubes evenly spaced around the ring, and 3 would turn on only 3 tubes on one side. I suppose you could also get a larger capacitor that would provide enough uf to run all the tubes at once, It would greatly simplify the amount of parts you need to cram into the case although I think you will still need the trigger coils for each tube. what are you planning on using for the back cover maybe a tupperware bowl?

 

[Jamie Pocock]

what are you planning on using for the back cover maybe a tupperware bowl?

I will be using fine modelling wire to build up a mesh frame that the flash head can be removed from if I ever need to work on it.

The frame will then be fiberglassed, once dry I will sand it down smooth and tidy up the edges etc, then I will be painting it in a black matt latex to give it a soft but quality finsh and feel.

The handle is going to be changed so it has a standard tripod screw thread on it and a hole tapped into the ringlight so I can use a tripod if needed on the same fixing point, cuts down on weight.

I cant start on the above until I know how much room to leave for my finshed circuit which I am still reserching and scratching my head about.

Jamie

 

[Jamie Pocock]

I was thinking a switch to cut off 3 capacitors from the charging circuit

Good idea, when the circuit is working this mod should be somthing I could manage.

Jamie

 

[Jamie Pocock]

If you must use the 450µF caps, then the voltage should be only 250VDC.

I am in the UK and our mains is rated at 240AC

So should be easy to step that down.

Question about bridges

If I replaced the bridge in my original circuit with a single diode and a resistor would that effect cap charge times being half wave and not full?.

 

[user_88]

There are several cap charging and firing circuits to look at on this site:

Linear Technology - LT3750 - Capacitor Charger Controller

The advantage would be battery power, portability, and getting away from mains voltages.

It may be that you could get one charging circuit to supply charging current to several capacitors.

 

[Jamie Pocock]

There are several cap charging and firing circuits to look at on this site:

Linear Technology - LT3750 - Capacitor Charger Controller

The advantage would be battery power, portability, and getting away from mains voltages.

It may be that you could get one charging circuit to supply charging current to several capacitors.

Yes this looks perfect, I am going to order one and play with it..

 

[Jamie Pocock]

More Help Please

Hi, I have taken on board much of what was said and made a test circuit in Multisim10
I can not get the SCR or Optocoupler to work, is this a problem with Multisim, or is it somthing I have done.

**broken link removed**

and here is the zipped Multisim file of the above circuit .

**broken link removed**

ignore the lamps, just put them in place to make a load, cant find Xenon tubes for Multisim.

Any help is very much appreciated.

Thanks in advance

Jamie

 

[Jamie Pocock]

More

Also if anyone can see any stupid mistakes in the circuit please do say, like I said before my electronics skills are limited at best, this has already taken me over a month to get this far.

I am aware the trigger transformers for the Xenons are not in the diagram, it looked very cluttered so I removed them to free up room and simplify

Thanks

 

[schmitt trigger]

The mistake I spot is that U1's collector is not tied to anything. You need a small auxillary DC source here. (5v)
Additionally you tied the base to the SCR's gate. It should be the emitter to the gate, and add a small series resistor, whose value depends on the maximum gate trigger current.

Lastly, you can't (at least in the real world) tie a 6v battery directly to a LED, you also need a current limiting resistor.

 

[Jamie Pocock]

Thank you very much, again you have been very helpfull, got to go out now but I will be sure to make the corrections later.

Thanks again

 

[Jamie Pocock]

OK, Made the changes and got the trigger part working, Thanks schmitt trigger

I have added a battery source (4 x AA) to power the trigger circuit, I then tought about it and decided to make it power the flash as well, making it portable.

Is there any reason I should not do this? for example will the batterys get drained fast.

The power section is to be internal now, with a standard ICE conector to couple the flash to the mains. Little worried about the weight of the head but keeps everything together neat and tidy.

Also I have spent about 4 hours trying to add a neon lamp to the capacitors, to come on when fully charged, the problem I keep getting is the lamps come on, then start to drain the capacitors, if you don't fire the flash quick enough there would not be enough energy stored to power the Xenon's.

Also earthing, I don't understand basic principles of safe and effective earthing, is what I have done safe earthing?

Again if anyone can point out any odvious flaws I would be very gratefull, I am starting to put this together today.

**broken link removed**

And here is the link to the saved Multisim 10 project


https://www.micracom.co.uk/flash/JamsStrobeMKIII-battery trigger.zip

 

[Jamie Pocock]

OK, Built it and it works but with a major issue.

Any help to explain why this is happening would be very welcome.

Caps all charge, trigger fires the six Xenons, but they do not go out instantly, they stay on for a few seconds, but not all of them.

Is there a way to completly discharge the caps after a fire?
Would adding neons to the caps do the trick?

Please help..
Jamie

 

[mneary]

The charge on the capacitors is being replenished before the tubes have taken it below the point where the flash tube will extinguish. I'm guessing that R3 isn't really 47k or this wouldn't happen.

What is the purpose of R1?

 

[Jamie Pocock]

Correct

I am impressed, you are absolutely correct, a typo on my part, it is in fact a 100W clad 48 Ohm not Kilo, from what you have said I have ordered a 220Ohm to put in series with the 100W 47 Ohm bringing the resistance to 267 Ohm, I want the circuit to fast charge so dont want to much resistance there.
If the tubes still stay ignited I will gradually add additional 100 Ohm resistors until I get the tubes to go out.
Once I find the magic number I will order a single resistor.

I know this is bad way of doing things money wise but with my little electronics know how its a workable way for me.
.
Thanks again for the help

Jamie

 

[Jamie Pocock]

A thought

If I were to keep adding 50watt light bulbs in series with the resistor, am I not effectivly adding cheap resistors.

If yes, how can I work out the resitance of the bulbs once I find my target so I can order the resistor?

Also I have various inductors here, the circle type with copper wire around found in computer PSU's, is the job of these to slow the change of flow of current?, could I add one to solve the problem?

If yes would it be before or after the resistor.

Although not shown in my schmatic I already added a coil on the mains input before the bridge with two small capacitors running to earth and another cap crossing the + to - with a resistor in parallel with the cap, again taken from a PSU design I was looking at, I assume it reduces nasty spikes from the mains entering the bridge .
Since I had all the parts I thought it can't hurt adding it............
Jamie