Studio strobe power hack.

Hello again everyone. Today I shall share a usefull hack for cheap photographers like me. Story time; I bought a couple of monoblocks on eBay a couple of years ago, and after lots of thinking I settled with the Godox Mini Pioneer 300DI. Why? Because two of them cost me 270€. With shipping. So, what is the catch? They are pretty close to 300W/s. They do work. But the power control is miserable. 1/3 to full power... not what is advertised!

Last year I added a switch and some diodes but that didn't work too well, especially when I accidentaly flipped the switch with one bank of capacitors fully charged and the other bank pretty empty... result? A very strong weld inside the switch. Lets begin!

Here is the circuit diagram, pretty simple. Two 3A diodes are responsible for the capacitor charging and blocking revers current flow. A larger 60A diode with a surge rating of 950A is used for blocking the charge from one bank to the other and allows the bank to discharge into the flash tube. The strobe has a 10A/300A diode in series with the flash tube but I think that it might be pushing it so I used what I had on hand.

Please be carefull as there are high voltages and juicy capacitors inside. If you don't know the dangers then I suggest you don't do this.br />

Please ignore the yellow wiring and the power resistor. That is my old hack.

This is the flash end of the strobe, to take it apart we need to desolder the four wires and disconect the trigger coil.

The boar can then slide out the back, here are the conectors for tha back panel and their names.

The front end desoldered.

The hollow case.

The top control board. From left to right and top to bottom;
Sync terminal. "Isolated" with an optocoupler but the negative part of the IRLED is conected to mains with a resistor. So much for bein isolated... I do not recomend using these strobes with a PC cable.
Discharge diode. Used to double the tube voltage when firing. Page 5 of this document.
BTA16 Triac. Used for the modeling lamp tracking.
PIC12C508A. Sole purpose is for pre-flash control.
12v Zener diode to power stuff.
Buzzer and buzzer switch terminal, I cut the link to remove the anoying beep.
TL7805 voltage regulator.
BTA20 Triac. Provably to control the charging circuit.

Capacitor bank and provably a voltage doubling circuit. 7 800uF caps rated at 360V.
A total of 5600uF charged to 330V gives 304Joules.

Underside of control board. A small SH69P86 micro controller is provably responsible for all of the functions. Wich aren't many.

Underside of the capacitor bank. Again, please ignore my awefull hack.

As you can see, the track width is very small on this trace. Especially when it's the discharge path for the flash... Scrape away and apply some solder to help things a bit!

Onto the hack! First I removed my hideos hack and bridged it. Then I cut the track as to separet the bank into two banks of 2 and 5 caps (do as you wish here). And finally at the rightmost part I cut the trace from the charge circuit.

Here I placed the charging diode for the small bank.
Important note! You must place a resistor to the same place as the diode because the diode blocks the reverse voltage and the charge control will not know if it is charged or not! Mine simply didn't charge above 150v, some might continue.

I used a 4.7k resistor as it only draws 300uA. Values up to 100k work but the charge voltage goes up to 350V wich for cheap 360V caps is provably not the best idea. But hey if you want more power now you know!

Edit; Here is a picture from my other strobe of the resistor in place.

Here I have placed the switch, the second 3A diode, the powerful 950A surge diode and I have conected the main board again.

Important detail! The ground wire is conected to one of the scews, don't forget it.

Reconecting the flash head.

Back into the housing. This is where I soldered the 4.7k resistor, on top of the diode. I had to be carefull not to melt the wires. Yeah, I'm lazy.

New switch, uppside down but that can be fixed.

It lives!!

Now for some numbers with my trusty L-358!
The difference between low power and high power with the small capacitor bank is 2.2 f stops.
The difference between low power and high power with all the capacitors is 2.4 f stops.
The difference between 7 and 2 capacitors on low power is 1.5 f stops.
The difference between 7 and 2 capacitors on high power is 1.5 f stops.
The difference between low power with 2 caps and hig power with 7 caps is 3.7 f stops.

When I get hold of some more 3A diodes I will modify my other light!

Happy hacking!


Oh, and if you got this far, check out my photos as many studio shots are taken with these.
http://www.flickr.com/photos/oid-w/