Strobe Light teardown, experimentation and subsequent failure - Page 1
Forum section: electronics / general

author: sonnytiger
author_rank: Frequent Contributor
timestamp: December 28, 2013, 06:18:56 pm
content: Just me taking a look at an old ass strobe light form the 70s (In what other era could you get away with calling a strobe light a disco strobe?)I also think its from the 70s due to the style of the PCB inside resembling that of the fluke meter calibrator I took apart a while ago (which I know is from the 70s).I did have a clip showing the inside of the control box but I have lost it and don't want to take I apart again. I do remember it being very simple, consisting of one larger transistor and another smaller one and a pot and some resistors and a couple of capacitors. I guessed it was a multivibrator circuit, anybody think that is likely?http://youtu.be/j8JsMJlnvQ8Thanks for watching if you do!

author: urbis
author_rank: Unknown
timestamp: December 29, 2013, 10:16:18 am
content: Great video

author: CJWarlock
author_rank: Contributor
timestamp: December 30, 2013, 12:00:11 am
content: DIY Strobes Kits (and ready-to-use mounted kits) based on a very similar scheme are still on the market. So, this has to be some good scheme.Anyway, just a small thought about capacitor's voltage mentioned in the video. The use of 450V rated capacitor for 160V could be due to so called voltage derating - lowering the voltage for capacitors that heat up or work in a device that heats up singificantly on the inside (near such capacitor). However I know of such voltage derating only in case of tantalum and partly-tantalum capacitors. So it's only my suspicion. The second option could be they just had 450V capacitors available at the moment or they were the only capacitors that had screw terminals.Anyway, it's true that electrolytic capacitors could get really hot (and usualy do) in such strobes and generally it's not a good idea to use electrolitic caps in strobes but it's cheaper, so people use them.I've constructed some strobes based on such scheme, some even with the big old russian electrolytic capacitors from the 80's, I've experienced the components getting very hot (current limiting resistor self-desoldering, capacitors so hot they had to be cooled with a 100x100mm 12V fan), and the amazingly looking effect of xenon tube lighting constantly.Technical suggestion: try to use more a camera-stand, could really help to see what's what in the picture.

author: sonnytiger
author_rank: Frequent Contributor
timestamp: December 30, 2013, 04:01:15 am
content: Thanks for the reply, what other capacitor type could get up to the required capacitance? I would love to get a mount of some kind will have to try and cobble something together or find a cheap one on ebay.

author: SeanB
author_rank: Super Contributor
timestamp: December 30, 2013, 05:38:35 am
content: The way those strobe units work is by half wave rectifying the mains and using that to charge the capacitor. Resistor is there to limit charge current to a level that is not enough to destroy the tube by it getting continuous current ( as you did cook the tube by running around 1kW of power to it for a second or two two will likely need a new one anyway. The ring on the glass at the one electrode says it is well cooked) and to limit the current through the tube if the trigger occurs at a mains peak.The tube is triggered and gives a single flash, which discharges the capacitor. The capacitor will be charged on the next mains cycle, and if the trigger pulses are too fast ( getting above 60Hz) then the tube will trigger, but there will be not enough charge in the capacitor to make the flash, so it will appear to skip cycles. You cannot really get this to go above about 20 flashes per second reliably with this simple circuit. As well the trigger circuit uses a capacitor to make the pulse, this also needs to charge and is charged by the main capacitors before the Thyristor in the trigger discharges it.The 2 capacitors in series is there to increase the life of the capacitor, as there is a larger surface to cool the heat generated. Those capacitors are fine though, replacing them will not do anything. Bigger values will overload the tube and shorten the life of the tube. Smaller values will have a dimmer flash, the compromise is between tube life and brightness, most of the time the tube might be rated for 1 million flashes at low power or 1000 flashes at max power.

author: sonnytiger
author_rank: Frequent Contributor
timestamp: January 02, 2014, 05:27:59 pm
content: I figured some of this out but you filled in a lot of blanks for me thanks! One thing on the caps though, I measure 300 volts across two of them meaning they are in series, so this would increase the voltage to a level appropriate for the tube, right? Or are they in series for both reasons?