Studio Lighting – DIY: Home-made Power Pack Flashes (Part I)

The following article was contributed by Avner Richard, not only a great photgrapher, but also an electronic wizard.

Studio strobes are quite expensive, especially when dealing with high power strobes, or multiple heads – the power pack solution.
In this article I’ll present my strobe power pack project, which is an easy DIY electric project.

Please, please (please!!!) read the Dealing With High Voltage warning.

The first thing you will need is a xenon tube. Several types and models of flash (xenon) tubes exist on the market. Mostly, for a high power studio flash project, like this one, you’d want to get a round flash tube which is thick in diameter, and has a high power rating of some hundreds of watts-second (W/S) which is the same as Joules. If you need Flashtubes, Xenon Flash Tubes or other parts contact Avner via www.photoar.com

Now, lets have a look at the circuit schematic, and understand how it works .(see schematics after the description)

1. At the left you will find the main input of 220VDC, which will arrive to a bridge rectifier. If you cant find a bridge rectifier, you can build one very easily, using 4 diodes, as the schematic explains.
2. From this rectifier we have two outgoing wires: the positive and negative. They provide ~300-350 VDC to our circuit.
3. Cut the negative wire, and insert a fuse to protect our project.
4. For the positive wire, use a resistor instead, the resistor will limit the current, so the capacitors charge will be regulated and not too violent.
5. After you have connected the fuse on the negative wire and the resistor on the positive wire, connect the main storage capacitor(s). Positive to positive and negative to negative. If you use several capacitors, they should all be connected in parallel.
6. From this point those two wires will feed the flash tube with power. Make sure you use well insulated wires, thick enough to carry decent power. This circuit will surge several hundreds Amps (depending on your setup), from the capacitor to the tube in the moment of firing.
7. Connect the two wires to the tube’s electrodes. Check if your tube has a polarity, and respect it.
8. Now, as you can see, on the schematic you have to get the triggering system together. Connect the small trigger capacitors with its resistor as shown, and the trig. transformer’s common wire (thick) to the NEGATIVE main wire.
9. From now on, you have two wires that will command the triggering (the one coming from the trigger capacitor (thick), and the one coming from the trig. transformer (thin)). These wires have a potential of around 350v, which will be harmful to your camera’s PC Sync port. So…. you have to insulate this high voltage.
10. Using an optocoupler and SCR, connected as shown above, you will have, again, two wires going to the camera’s PC Sync port, but now with a few volts potential only, which is safe for your camera.
11. Please note that a power source of ~6 VDC is needed to feed the optocoupler. Hacking a small cellphone transformer, is the best solution. It will integrate all power sources in your project box. If you dont have a cell phone charger at hand, feel free to use simple batteries to reach 6V. The consumption will be close to zero! The optocoupler will draw only some 20mA for about 1/200 a second every time the flash is fired.
12. Finally, the second (thick) wire of the trigger. The transformer will be connected directly to the flash tube TRIGGER terminal.
    Try to keep this wire the shortest possible, even locating the trig. transformer right near the tube. This wire will supply a several Kilo-Volts, keep it well insulated, and spaced from other components.

Here are some tips for your experiments when trying to assemble the circuit

• Your main concern is to keep the capacitor empty after an unsuccessful firing attempt – it is highly recommended that you make a discharge switch for your experimental capacitor. (Use a small capacitor!! about 10uF).
• Connect a HEAVY DUTY (or just mains line power) switch with a light bulb in series with the capacitor’s terminals. After an unsuccessful attempt to fire the flash, unplug the circuit from mains power, and press your discharge button to fully discharge the capacitor. Now you are safe to work on the circuit again.
• Remember – always monitor your capacitor using a voltmeter to check it’s status

As you can see the circuit is not complicated, but might include components which are not yet familiar to you. Here is a list of the components along with descriptions:

• D1-4 => Fast recovery / general use rectifier diodes. Rated at min. 400v 1A.
• Fuse => rated at 230v 1A. or depending on your resistors/lightbulbs setup – see below
• R1 => is the current limiting resistor. Its value will affect recycling time. Recommended is a value of 47 to 100 Ohm, but power must be high, this resistor will be heating alot, please consider cooling if needed. – see the great idea for this item.
• C-store => This is the main power storage capacitor, it must be rated at 400v at least (450v recommended), and and have a value of 1000uF for every 50W/s of the flash tube. (i.e. for providing 350W/s to the tube, you will need 7x50W/s, thus a capacitor of 7000uF, or 7 caps of 1000uF, etc…)
  Storage capacitors are probably the most expensive part in this project, but still nothing near the substantial costs of purchasing a commercial product. Have a look at your local or online electronics store to get an idea of the costs. If you plan on using several capacitors to reach the wanted amount of power (for example 7 capacitors of 1000uF), be sure to use the SAME rated capacitors, preferably the SAME models exactly. You may also want to check some ebay auctions for old stock capacitors.
• C-trig => is the capacitor which will feed the triggering system when you fire the flash. A ceramic capacitor rated at 0.1uF, 400v. Those values also depend of your trig. transformer. But the above values are common.
• Trig. Transformer => is a coil which will receive the ~200v from the trig. Transformer and will turn it to several KVolts (4,000-10,000v), in purpose of igniting the xenon gas inside the tube.
• Q1 => is a silicon SCR. Should be rated at least at 400v 6A.
• IC1 => is an optocoupler, common moc3020 will do the job, or any other optocoupler rated at 400v at least.

Great idea:
Since power resistors are quite expensive, especially when reaching 75-100W values, and they will also need decent active cooling to avoid overheating, You’d want to try somthing creatinve.
A definitely creative solution will be to use standard cheap lightbulbs!! Lightbulbs are resistors, which make light, and are EXTREMELY cheap. The only thing you have to worry about is the impedance. Grab some lightbulbs and an Ohm-meter, and measure the bulb’s impedance. It should read around 30-50 Ohm, which is ideal as rating.
If you experience long recycling times, you may ADD lightbulbs to your circuit, in PARALLEL to the first bulb. The more bulbs the more powerful the unit can be (if you build a 100W/s unit, a bulb or two will do the job). Now, here is a nice trick – consider the option of using halogen bulbs! rated at 500W, they have an impedance of 10-20 Ohms, which will shorten even more the recycling time. The best thing about these bulbs is the low cost. Moreover – light bulbs are DESIGNED to stand high temperatures without any cooling. In this project the lightbulbs won’t be on constantly. The bulb will illuminate just after firing the flash, during the recycle time, then will fade out until next flash is fired. – not exactly model light, but still nice.

That’s it ! your work is completed !

Now that your basic flash unit is working, you can go on and see some variation on the home made flash (it has cool flavors of the flash unit: ring light, beauty dish, soft box and more). Combined with the homemade backdrop and the DIY reflector stand you can come up with a very low budget studio.

Dealing with High Voltage Warning

This project is dealing with high voltage circuitry. Please be extremely careful and stick to the given schematics!
Charged capacitors can still have juice after hours, days, and even weeks; never touch capacitors terminals unless you are sure it is fully discharged.
Never work on a circuitry while it is connected to the mains power !!!
Never work on a circuitry while its capacitors are still charged. Be sure to discharge them fully.
Neither the writer nor the publisher of this article are responsible to any damage caused by attempts to reproduce this project. This project was made for 200V voltage, for other curents, adjustments have to be made.
You are the only responsible to your equipment and life. don’t drink and weld.