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Thread: Need something to drain residual voltage from an old school chaser

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    Imagine's Avatar
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    Default Need something to drain residual voltage from an old school chaser

    Righty ho - this one follows on from a problem I had last night in the Good Gig Bad Gig section of these here fine boards.

    I was out with the Retro setup, and regular followers will know the problems I've had in converting to LED lamps. In a nutshell, I HAVE to have an incandescant lamp on each channel to draw off the residual current from the chaser unit, otherwise the LEDs don't go off. Simple enough, everything is LED with the exception of my Infinity Tunnel....it sort of works.

    Until that is, one of the incandescant bulbs goes pop as it appears to have done last night and you're in a venue with a bit of a sensitive consumer unit controlling the electricity. This in turn tripped the RCD on the stage and everything went very dark and quiet for about 10 mins until we could find the offending breaker/run an extension to the bar the other side of the hall....not ideal.

    I know I could use my own RCD on the lighting side of things which would stop the dramatic "everything off" situation I suffered last night, but this would still mean the lighting going off until reset.

    So, those of you with electronic type knowledge....is there some sort of circuit I can buy/build which I can stick into each channel to take the residual current but without the chance of going pop as old school lamps do, allowing me to convert ALL of the lamps to LED?

    Ideally, it needs to suck the equivelent of a 25w lamp from each channel (because that's what's happening at the moment), and be something I can easily buy or build (I'm not an expert in electronics of this sort). I know I can build a board which takes an incandescant lamp hidden from view which Peter mentioned in the past, but I now want to get away from lamps altogether on this rig.

    Hopefully that makes some sort of sense?

    Just a thought.... (and not being any sort of electronics expert I'm probably waaaay off the mark!)

    Would something like this wired into the start of each channel do what I need?
    Last edited by Excalibur; 20-05-2019 at 07:29 AM. Reason: Tidying.

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    Dinosaur Excalibur's Avatar
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    Quote Originally Posted by Imagine View Post

    Ideally, it needs to suck the equivelent of a 25w lamp from each channel (because that's what's happening at the moment), and be something I can easily buy or build (I'm not an expert in electronics of this sort). I know I can build a board which takes an incandescent lamp hidden from view which Peter mentioned in the past, but I now want to get away from lamps altogether on this rig.
    Aha, so that's why the power went off. Oh the joys of modern safety systems, which throw half a venue into darkness because a bulb blew somewhere. Been there........................

    I've looked at your resistor, and I'm even less of an expert than you, but I note it needs an external heatsink, so I don't see you building it into your enclosed screens, at least not without ventilation. Now since I like simple, I'd make a dummy/mirror "screen". It would simply be a very small box of lamps which you plug into the chain, and would give you the advantage of seeing what the screens are doing. I'd add the RCD protection for your lights as well, which might limit the power cut to your equipment only. ( Unless the venue's box trips at twenty milliamp less ).
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    Quote Originally Posted by Excalibur View Post
    Aha, so that's why the power went off. Oh the joys of modern safety systems, which throw half a venue into darkness because a bulb blew somewhere. Been there........................
    Could have been. I'd say it's probably the most likely cause but obviously can't be certain.

    Quote Originally Posted by Excalibur View Post
    I've looked at your resistor, and I'm even less of an expert than you, but I note it needs an external heatsink, so I don't see you building it into your enclosed screens, at least not without ventilation.
    And this is why I need help. I can't see it being a problem to build in (or even build a case to put them in before the first box) which I'm more than happy to ventilate if needs be. Question though....would the heat be any more than that of four 25w lamps?

    Quote Originally Posted by Excalibur View Post
    Now since I like simple, I'd make a dummy/mirror "screen". It would simply be a very small box of lamps which you plug into the chain, and would give you the advantage of seeing what the screens are doing. I'd add the RCD protection for your lights as well, which might limit the power cut to your equipment only. ( Unless the venue's box trips at twenty milliamp less ).
    Do keep up at the back!

    I already HAVE 25w lamps in the chain in the Infinity Tunnel....it's them what caused the problem guv! Putting an RCD in place would admittedly keep the sound going, but would still lose the light (because at the end of the day, the screens are all powered from the same socket). I'm looking to do something a little more reliable and less prone to popping

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    Quote Originally Posted by Imagine View Post



    Do keep up at the back!

    I already HAVE 25w lamps in the chain in the Infinity Tunnel....it's them what caused the problem guv! Putting an RCD in place would admittedly keep the sound going, but would still lose the light
    Keep up? Keep up? I'm ahead of you, son. Not in the tunnel itself, but in a separate box. You shouldn't need to put them in series, as I had the same problem at 12 volts. I wired in some lamps in parallel by mistake, but they work just fine. Were I going to go down the route of resistors, I would make a dedicated box containing only them, possibly with a grille for letting the air to it. Keep your feet warm in those cold marquees, too.
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    Something like this: https://uk.rs-online.com/web/p/panel...stors/0159590/

    Just one per channel, per controller should be enough. Be sure to mount them on a heat conducting surface, preferably with thermally conductive grease. 4700 ohms @ 240VAC will see roughly 12.5W .. which is about half the rating of a 25W resistor - but those ratings assume they'll be adequately heatsinked.

    If in doubt, use a resistor with a higher wattage rating (not a higher resistance value).

    Or just one of these per channel

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    Quote Originally Posted by Nakatomi View Post
    Something like this: https://uk.rs-online.com/web/p/panel...stors/0159590/

    Just one per channel, per controller should be enough. Be sure to mount them on a heat conducting surface, preferably with thermally conductive grease. 4700 ohms @ 240VAC will see roughly 12.5W .. which is about half the rating of a 25W resistor - but those ratings assume they'll be adequately heatsinked.

    If in doubt, use a resistor with a higher wattage rating (not a higher resistance value).
    Perfick
    I'm assuming a big lump of copper plate will do the job of the heatsinking bit? Or is there a specific type of heatsink like the sort that sits on the back of a CPU?

    In all honesty, I'll probably make up some sort of box to put them in with a fan to help cool things.

    Quote Originally Posted by Nakatomi View Post
    Or just one of these per channel
    Nope! It used to run that hot before I went LED. Never again
    Last edited by Excalibur; 20-05-2019 at 08:36 PM. Reason: Fixed quote

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    Right!

    Looked at the datasheet for this series of resistors - the HS25 series would need a 1mm thick heatsink 535sq cm in size for the power rating of 25W.

    These fellers.. https://uk.rs-online.com/web/p/panel...stors/7205334/ - don't cost much more & are double the power rating & shouldn't need much if any heatsinking at all. FWIW I'd mount them on an earthed metal plate, spreading heat transfer compound liberally (but sparingly) before bolting them down.

    Then give them a nice long OBSERVED soak test before you take them out to a gig.

    Obligatory H&S notice here: be very very careful when you're dealing with mains voltages - yes Wayne I know you are & would never dream of making a shoddy installation, let alone grabbing the end of a potentially live wire.. BUT... If you're in any doubt whatsoever, do not even attempt this. Get a friendly elechicken to do it for you

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    WHOAH there! I've just clicked the link on the resistor you originally suggested, Wayne. 100m Ohms.. That's 0.1 Ohms. One hundred milliohms. Effectively a short circuit. The peak current through a 0.1 ohm resistor at 240V would be.. 2400 amps... for as long as it lasts before it vaporises. Or to put it another way.. 576kW! At the very least it'd go bang, take out a fuse in your chaser & very likely a triac too

    My suggested value of 4.7k Ohms : 4700 Ohms... 240/4700 = about 50mA. Which under normal conditions equates to approx 12.25W.

    The value of 4700Ohms (4.7k) should be low enough to stifle the current that leaks across the triacs (which is how yer LEDs light up a bit even when the channel isn't 'on') but if not, try two in parallel per channel - or a value inbetween like 3.6k (3600 ohms).

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    Cheers Justin

    Will give it a go with an old chaser and spare screen and see how things go (preferably not bang!)

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    Isn't there another option here somewhere that involves ditching the dumb triacs and converting the whole lot to low voltage LEDs?
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