Need help modifying camera flash to work continuously  - Page 1
Forum section: electronics / beginners

author: SH@RK
author_rank: Contributor
timestamp: April 25, 2013, 02:53:47 pm
content: HiI am interested in making camera's flash circuit work for all the time I need itSo here is the picture of the circuit , it is from disposable camerasince the main working formula in this thing is that the big capacitor will dumb the energy stored into the tube and the tube will shine til the capacitor's voltage is not enough .There is also the small capacitor which will ionize the gas in the tube (we will discuss it later)So let us start by finding how much energy we need to turn the tube onLike designing the circuit from the last stage and step by step going backword to the batteryFor a working cycleThe capacitor will charge til almost +300V and after triggering the remaining voltage is about 50VThe capacitor is 330V and 160uFThe formula to calculate the energy used isEn = 0.5 * C * (Vi2- Vf2)= 7 joules = 1.94E-6 KWh = 7 WsIf I am supplying the tube with +300VDC I thing I will need 24mAsI do not know what to do nextSo :1:- Is everything I did is correct until now ?2:- What do you thinks I should do next ?3:- Can you help me to make a block diagram to show the process so I can predict what I will need to make the circuit ?4:- Do you think it is possible to make the flash work continuously without flickering ?Thanks

author: AlfBaz
author_rank: Super Contributor
timestamp: April 25, 2013, 02:58:51 pm
content: I think you may need to consider the lamps duty cycle befor anything else

author: eKretz
author_rank: Frequent Contributor
timestamp: April 25, 2013, 03:01:01 pm
content: Yup, the heat will eat it alive if you make it stay on indeterminately. It might live a little longer if you just lengthen the pulse a wee bit, though. Something in the double-digit percent range at max probably.

author: SH@RK
author_rank: Contributor
timestamp: April 25, 2013, 03:18:52 pm
content: Quote from: AlfBaz on April 25, 2013, 02:58:51 pmCan you explane the duty cycle thing because I do not understand it .ThanksQuote from: eKretz on April 25, 2013, 03:01:01 pmI will worry about the heat in the endI think there are tubes that can last longer like in those expensive new cameras the flash lasts for 1 or 2 secondsSo we can change it later if it can not surviveI do not have to stick to those parts , I will use any extra parts to make it work as I wantThanks

author: G7PSK
author_rank: Super Contributor
timestamp: April 25, 2013, 03:34:06 pm
content: The working life of most flash tubes is seconds only. The fact that they appear to last so long is due to the very short time of the discharge.What you need is more likely to be a CFL from a laptop or a pump tube from a laser.

author: AlfBaz
author_rank: Super Contributor
timestamp: April 25, 2013, 03:42:32 pm
content: Quote from: SH@RK on April 25, 2013, 03:18:52 pmhttp://en.wikipedia.org/wiki/Duty_cycle

author: iamnothim
author_rank: Regular Contributor
timestamp: April 25, 2013, 03:59:51 pm
content: I have one of the best on camera flash units Nikon makes for my D3s DSLR. The SB-900.If I hold my finger on the D3s shutter release for a burst of exposures (12 frames per second) the flashwill only fire about 3-4 times. That's because of the cycle time of the battery / flash is much less than that of the camera.The battery can't provide enough energy for the flash to reload and fire.In a studio this isn't a problem because a huge external power supply is used for the flash.

author: SH@RK
author_rank: Contributor
timestamp: April 25, 2013, 04:15:12 pm
content: Quote from: G7PSK on April 25, 2013, 03:34:06 pmLet us worry about the tube laterI can get like 10 tubes and make them work one after the other so the tube will not dieThe CFL is not an option because the Flash tube Is much much much stronger and smallerThanksQuote from: AlfBaz on April 25, 2013, 03:42:32 pmThe tube is from cheep camera so I can not get datasheet to find itAs for the battery I want to get 100% even if I have to use tow or three batteriesThanksQuote from: iamnothim on April 25, 2013, 03:59:51 pmThat is my question , How much should the battery give so the flash will not reload but will work directlySo the battery is the limited source so let us find how much the battery should give and then find a solution for the limitation of the batteryThanks

author: XynxNet
author_rank: Regular Contributor
timestamp: April 25, 2013, 05:05:40 pm
content: Quote from: SH@RK on April 25, 2013, 02:53:47 pmKeep in mind that this energy is dumped into the flash tube during microsecounds.For big flashes, flash currents can be in the 10-100A range.Additionally you cant start the flash tube with 300V. Thats why there is this small capacitor. When flashing it dumps its energy into the inductor which discharges some kV into the tube to ionize the xenon gas, allowing the big cap to discharge trough the flash tube.Didn't read you knew this, sorry.

author: iamnothim
author_rank: Regular Contributor
timestamp: April 25, 2013, 05:05:55 pm
content: I can't help you with the battery calculations, however as G7PSK wrote the flash "bulb" is not designed to operate continuously. Especially a low grade bulb in your picture. So you have 2 problems.Thinking about the battery some more, you will never be able to have batteries keep up with a continuos flash discharge. The battery will be drained rapidly. I use 4 Sanyo Eneloop 2500mAh High Capacity AA batteries in my SB-900. They are drained after a night (sometimes during) of shooting high speed sequences of skateboarders. Even if I set the camera to continuos flash mode, I get 3 flash exposures before the flash shuts down. Then I wait for the flash to recharge for the next sequence I get 3 more exposures. More importantly, after 4 or 5 iterations the flash shuts down because it got too hot. I have to wait 5 minutes or so for it to cool down and work again. This is because of a heat protection monitor built into the flash that kicks in.That would be problem number 3EDIT. I just reread your first post. You want to "make the flash work continuously Without Flickering" What you want is a light, not a flash. I'd look at the high output LED's that are used in micro flashlights.

author: Corporate666
author_rank: Unknown
timestamp: April 25, 2013, 05:36:15 pm
content: Quote from: SH@RK on April 25, 2013, 04:15:12 pmWhat you want to do cannot be done. At least not in the way you want. What is the reason you want to try to operate a flash lamp continuously? Is it because of the brightness? Flash lamps have a low luminous efficacy.. an LED will produce more lumens per watt by far.To prevent the appearance of flicker, you would need to operate the flash lamp at about 60Hz but that would be way outside the duty cycle they can support. So you would need multiple flash lamps... maybe 10, maybe 100 - to be able to get 60 pulses per second... how many you would need depends on the duty cycle. Then, the flash lamps will have a very short life span if used in this way... maybe a couple of minutes, or maybe just some seconds. So if you want long life, you might need to have 10 times more flashlamps than mentioned before. And finally, the quality of light will be bad and will not be consistent because the flash lamps are degrading so fast being operated at the rate you want.Unless you are building something for a company to test the life cycle of flash lamps, I can't think of a reason why you would want to do this. If you just want a lot of light, you will get much much more light for your money and for your power by using an array of high efficiency LED's like the Cree XB-D or MK-R.

author: G7PSK
author_rank: Super Contributor
timestamp: April 26, 2013, 10:51:13 am
content: If you need a really powerful point source of light you need these (lamp carbons)and 90 volts at 200 or 300 amps

author: JuiceKing
author_rank: Regular Contributor
timestamp: April 26, 2013, 11:18:04 am
content: It sounds like you'd like to make a stroboscope. Even if you can recharge the capacitor faster, you need to give the xenon tube some time to deionize after it flashes.There are some good notes about stroboscope principles of operation here:http://www.ietlabs.com/pdf/Manuals/1531_im.pdf- Ken

author: BravoV
author_rank: Super Contributor
timestamp: April 26, 2013, 11:39:03 am
content: Let me summarize it, to OP, if your quest is to build a circuit that will turn a xenon flash tube that will behave like an ordinary fl lamp tube does, which has the light on continously, then stop.It won't work even you have the circuit and the capacitor that capable of supplying the required energy to make the tube "constantly" on.Hope this helps to save your time and energy.

author: David_AVD
author_rank: Super Contributor
timestamp: April 26, 2013, 11:41:02 am
content: I have a theatrical strobe that can run in bursts (a few seconds max). but even that calculates the energy going into the Xenon tube (over time) and prevents continuous operation.

author: AlfBaz
author_rank: Super Contributor
timestamp: April 26, 2013, 02:10:37 pm
content: Quote from: G7PSK on April 26, 2013, 10:51:13 amShould get one of these. When he's not using it as a light source he can do some boilermaking on the side

author: Razor512
author_rank: Regular Contributor
timestamp: April 27, 2013, 04:15:19 am
content: I tried it once and the bulb popped. took apart an old disposable camera, then basically attached the wires to a florescent lamp starter, then left the trigger place connected to the camera.I was planning on pressing the shutter release the second I turned the florescent lamp on but the bulb popped instantlyWith how bright the camera flash is it would have been awesome to run it non stop (even if it would only last a few seconds)

author: amyk
author_rank: Super Contributor
timestamp: April 27, 2013, 08:17:05 am
content: Believe it or not, someone has thought of and produced a writeup of this topic over a decade ago:http://donklipstein.com/contxe.html

author: Marco
author_rank: Super Contributor
timestamp: April 28, 2013, 02:02:56 pm
content: OP, we can't just forget about the bulb ... you just don't understand the magnitude of the problem. By stretching the duration of the flash to seconds you're increasing it hundred fold. It's not just a question of it dying after one use, it will die during the use.Also you're talking about 10s of kW of power ... if you really want to DIY a very high power continuous light source I think your best bet is modifying a welder into a carbon arc lamp.