Schematic diagram flash

[Jacques Augustowski]

Hi,

I want to build a high power flash for large format photography, I received as a gift 24 1100uF x 450v capacitors. I couldn't find any schematic to get a circuit idea. I've seached the internet but it was of no avail. Is there a place were I can buy a service manual?

Thanks,

Jacques

[James E Galvin]

Before you get very far with this, are you an electronics person? Do you know about electrical safety? Have you designed interlocks? Do you know how to calculate a bleeder resistor? This is a VERY DANGEROUS project. The caps can hold a lethal charge for days. Faults can put lethal voltages where you don't expect it. I have designed cap banks, have worked with high voltage for years. I bought a commercial unit. Where I work, working on such a unit requires a safety observer, trained in CPR, ready to call the paramedics, and who knows how to turn it off!

[Eric Woodbury]

Jacques,

Jim is right. Be careful and don't attempt unless this is really your calling. I've been designing electronics for 30 years and I bought White Lightning strobes. I don't think you can improve on the design, so what is the point.

If you do continue, be real careful of inductance. Your voltages can exceed what you might think if your conductors are too far apart or take a bend somewhere. This can lead to your unit working and then the transistors getting blown later.

I would look for schematics as application notes from vendors of the FETs or maybe from Linear Tech. You need to pick a tube, so you have something to design around. Tube vendors may have a design.

Good luck.

EW

[Jacques Augustowski]

Jim and Eric,
I know electronics, I have built high voltage linear amplifiers for ham operation with 4 kv power supplies. I have a 2500w-s strobe, but I want something more powerful for my 8x10. I don´t need bells and whistles in my flash project. I really don't want to spend too much time in reverse engineering, B&H sells replacement flash tubes so buying the tube is no problem. I found schematics on low power hand held strobes, the principle is the same. Trigger coil inductance, trigger voltage and some other parameters will help me. I have already measured my strobe but I want to be sure I will not ruin my new flash tubes.
Thanks,
Jacques

[bglick]

I am curious, when you say you want more flash power for you 8x10 camera....what exactly do you mean? Why is a 810 camera different then a MF camera? Same coverage, maybe a few higher f stops if your seeking DOF... is that it? You plan to shoot at f22 and need to overcome the smaller aperture?

Is the subject moving? If not multi-pops works great.

If you get the bulb working from B&H, what would the guide number be for your finished product?

[Jacques Augustowski]

Hi Bill,
I am shooting portraits, so poping isn"t possible. I'am using f64 as a diafragm setting, also I am using a ISO 64 film

[tim atherton]

You need a small thermo-nucelar weapon for that....

[bglick]

So what GN will your flash produce?

[Jacques Augustowski]

At least 160

[John_4185]

GN 160 isn't bright enough for F64 at any reasonable distance.

Typo?

[James E Galvin]

Your caps will give you 2700 watt seconds. Not much improvement. Even both together is only one stop. But, open and trace the dircuit of the strobe you have. This is still a much bigger energy store than the filter in linear amps!

[James E Galvin]

If you open the strobe you have, two points:
There might not be a bleeder, assume the caps are charged. If you switch it off, and immediately pop it, the cap charge will be small. but not zero. The current in a linear amp is an amp or so, in the flash several KAmps. Note how connections are done, and the way wires are routed. KAmps produce large magnetic fields, the wires get substantial forces. This is not the same as a normal power supply.

[Jacques Augustowski]

IThe GN is in meters

GN 160 isn't bright enough for F64 at any reasonable distance.
Typo?

[Jacques Augustowski]

Jim,
Thanks for important information, you are right about the energy of my capacitors isn't enough. Tim is right, I would need a small nuclear blast. I would have to get 50000 uF at 400v to give a little bit more than 5000 w-s. Even with an efficient reflector pointing straight without any diffusion it will impossible to get my f64 with a 64 ISO film.
How did the photographers do 40 years ago shooting 8x10 low speed color films? High power flood lights??

[Brian Sims]

Will your subjects be wearing welding goggles?

This thread gives me a head-ache. There must only be about 6 people in the world who are LF photographers AND understand what you're talking about. Oh yeah...there's the six of them. :=)

[John_4185]

How did the photographers do 40 years ago shooting 8x10 low speed color films?

They didn't shoot single-flash at F:64.

[Nick_3536]

Instead of one super flash couldn't you use multiple smaller flashes?

OTOH Forget the googles and go with a full face sheild.