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Studio Ring Flash Xenon Tubes

Thread starter #1
Hi, I am an IT engineer and electronics is not really my strong point.
I am making a studio ring flash for the wife's studio as new ones just cost way way to much.

I have ripped apart 6 Olympus T20 flash units and salvaged the triggers, Photo-Flash capacitors and Xenon tubes from them.

I want all six to fire with the one trigger and one charging circuit.

I have drawn up the below circuit made from various information I have found on this site but like I said before my electronics understanding is limited so was hoping someone that does know something could look over the circuit and tell me if there is anything odvious wrong with it before I build it.

Here are the specs of the parts I have

-> Capacitors I have for C1,C2,C3,C4,C5,C6 are all the same and have wrote on them Photo-Flash 330v 450uF Auto-Cap FLX

-> The 6 triggers have the following specs
Trigger Coil (Trigger Transformer) for Xenon Tubes Secondary Voltage (Max unloaded) 11 kV
Primary VOltage (Max unloaded) 300 V
Trigger Energy (Max) 10 mWs
Trigger Power (Max) 0.5 W
Transformer Ratio 1:36
Primary Inductance 20 uH
Trigger Capacitor 0.047 - 0.22 uF

-> For R1 the power resistor I have purchased 1 x 47R 100W Aluminium clad wirewound resistor, Resistance tolerance 5%

-> The flash tubes are all 28ws CB254200Xe Lamps

-> Rectifier Diodes are all 1N4004 1AMP 400V (not to sure about these, are the amps enough?)

-> SCR 400V 0.4A Igt 30mA http://www.datasheetcatalog.org/datasheet/MitsubishiElectricCorporation/mXvrrvu.pdf

-> MOC3020M Integrated Circuit x 1 K3020 http://pdf1.alldatasheet.com/datasheet-pdf/view/176764/FAIRCHILD/MOC3020M/+0WW775UwYhRDpKxHeyUKwvDC/+/datasheet.pdf

Can someone please look at this circuit for me and the components I have and tell me if it will work.

Thank you very much in advance.



Thank you

Jamie
 
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schmitt trigger

Well-Known Member
#2
This looks like a circuit which would indeed work.

-However, I would increase the trigger cap substantially.... at least 0.6 uf.
-Also you DO require a current limiting resistor in series with the SCR's gate. Its value would be ≈ 300v/ Igt. Otherwise both your SCR and coupler will be history.
-You might need a small series resistor to each trigger transformer, to equalize the trig cap's current. I would measure the trig's transformer primary resistance and would take 1/10 that value.

Lastly, you need some sort of indicator (neon lamp or so) to indicate that the main caps have fully charged. This indicator would also act as a "bleeder" to discharge these caps. I'm pretty sure you know this, the charge stored in these caps is lethal.
 
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Mr RB

Well-Known Member
#3
And maybe think about that 2.5kW 7amp initial charge condition... Like change the 47 ohm resistor to a sane value. ;)

And 1N4004 diodes are a very poor choice due to their low voltage rating.
 

schmitt trigger

Well-Known Member
#4
And maybe think about that 2.5kW 7amp initial charge condition... Like change the 47 ohm resistor to a sane value. ;)

.
You are absolutely correct about this one.... To limit the surge current to a safe value (say 1 amp) the resistor should be at least ~ 300 ohm.
 
Thread starter #5
Hi, thank you schmitt trigger for your time commenting, I really do feel in over my head with this but I said to her indoors I would do so,, well you know how it is..

I still have a million questions.

I would love a LED to tell me when each cap is charged but I have no idea how to do that or where to put in the circuit, I have a bucket load of 5v LEDs so making use of some would be great.

You said "Also you DO require a current limiting resistor in series with the SCR's gate"
What value would you recommend for this?.

I have Circuit maker but dont have a spice for a xenon and cant find one anywhere so cant virtually test this circuit so its going to be a live test so I dont want to cook it..

Thanks Jamie
 
#8
I would move the fuse to the hot side of the mains so it offers protection if the diodes fail.

Is this all in one enclosure? The energy storage should be located as close as possible to the lamps, to avoid radiated interference to nearby electronics. Independent trigger caps and SCRs might be necessary to get reliable triggering, especially if there is any distance involved.
 
#9
The voltage alone doesn't determine the power in the lamp; the capacitor does. 450µF at 350V is 55 watt-seconds.

A sane value for the resistor would be the highest value that provides an acceptable recharge time. 300 ohms delivers a peak current of under 1A. The caps should recharge to 90% in 2RC, which is (2*300Ω*3600µF), or 2.1 seconds. This will become 1 second (2*300Ω*1760µF) if you bring your capacitors down to 220µF each (which is what your lamps are rated for).
 
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schmitt trigger

Well-Known Member
#10
I would love a LED to tell me when each cap is charged but I have no idea how to do that or where to put in the circuit, I have a bucket load of 5v LEDs so making use of some would be great.

You said "Also you DO require a current limiting resistor in series with the SCR's gate"
What value would you recommend for this?.
You really need a neon lamp. These lamps fire up at ≈ 80 to 90 volts, so you'll have a bleeder resistor from the positive side of each cap consisting of two resistors (connected in series as a voltage divider) such that at the junction of both, about 90volts will be developed when the capacitors reach 300 volts. As it fires, the lamp will clamp the voltage down. The resistor values should be calculated such that the lamp's current is between 0.5 and 1 mA.

For the SCR gate resistor, you really need to know what the required gate current to trigger the SCR. I did a quick google search for the part# provided, but all I found were some e-bay pages without any technical data. Please find the datasheet and post the web link to it, and we'll go from there.

Also, if the SCR is a sensitive gate device, usually a 1k resistor from gate to cathode may be also needed, to prevent nuisance triggering.
 
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Thread starter #11
Thanks mneary
"Is this all in one enclosure?"

Yes all caps will be within a max of two inchs of the flash tube.

The triggers are right behind the tubes about 10mm.

The mains will be in another box with a lead that plugs into the ringlight.

This is what I have made to hold the flash tubes
Caps will be around the handle part

 
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Thread starter #12
I am more confused now than when I started....

Could someone be kind enough to alter my original drawing and post it back so I can build your version, I can see I will end up killing myself or my wife if I don't get this right.

It would be very much appreciated

Thank you Jamie
 
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Thread starter #13
I will send to the person who rewrites my original £30 GBP as a thank you through PayPal, thats about $50 USD at this time..

I would like to use my Xenons 28ws, my 330v 450uF photo-flash caps and the Trigger Transformers (spec at top of page) as I already have them, also I already have 12 neons six are rated 240v and the other six rated at 60-80v so if I could use them as charge indicators that would be even better.
I am in the UK so have a 240v mains supply

Thanks Jamie
 
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Thread starter #14
#18
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
 
#19
If you must use the 450µF caps, then the voltage should be only 250VDC. The easiest way is probably a transformer. Actually, a transformer isn't a bad idea, because it would help protect you from accidentally touching one terminal.

The transformer would have an output of about 175VAC, rated at 1A intermittent (probably a 100VA transformer would do it.) Values less than or greater than 175VAC would change the output as the square of the voltage difference.
 

Mr RB

Well-Known Member
#20
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.

This will enable a much smaller physical size resistor to be used and increases reliabilty of the whole system because current through all the diodes is greatly reduced. Cap charging current is also reduced, considering how violently they are discharged it can't hurt to charge them a bit more gently.

But charge time will be increased to 8-10 seconds or so. Maybe that is too long for your needs?

Re the diodes I think they are going to get some nasty spikes when the flash coils go off, and your 1N4004 are only 400v rated! You might need to go for some TV high voltage diodes in the kV rating range. But be careful these are lowish current items so again it will benefit from a higher value resistor and longer charge times.
 

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