dimmer problems

[ibwats]

hi all

 

I'm currently at a school and we've been having some problems with some channels on our dimmers.

 

the equiptment we've got are 2 jands hubs, and for a controller a tempus M24

 

the problem that we have is that some of our channels will suddenly turn on to full and then won't turn off. this somtimes happens during shows, and a light will suddenly come on and not turn off. to fix this in the past we have been just switching off the power to that channel on the dimmer becasue we don't a light playing up during a show, after the show or in the interval, we plug it back in, turn all the lights down, but the one that was playing up is still on. because of this we are slowly running out of channels to use. meaning piggybacking, and sparks, which arn't fun.

 

if anyone knows of a way in which we might be able fix this problem I would love to know, any ideas are welcome.

 

thanks

Ian.

[Richard Bunting]

Correct me if I'm wrong, but wasn't the output of a M24, D54, not DMX? and isn't the input of the Hub, DMX?

[Don Allen]

Just concentrating on troubleshooting your dimmer output problem, normally when a dimmer channel becomes hard on and cannot switch off after a power reset on the dimmer and desk, it has probably got a shorted triac as it is a Jands Hub. (other dimmers may have back to back SCR's).

 

One of the most likely causes for shorted triacs are a lamp as in bubble or globe etc going short circuit in it's final moments of life and drawing excessive current. The Jands Hub has 40 amp triacs which are 4 times the rated current of the dimmer channel but a shorted lamp can draw much more than this.

 

Another like cause is having too great a load on the dimmer circuit, 2400w max for the hub. Not as likely to cause a triac to go short circuit as the breaker should trip under a fault condition.

 

In situations where dimmer channels are in short supply and one fails, some people tend to lead in the socket of the faulty dimmer channel and add it to another dimmer channel which then may fail due to an overload and so the merry-goround continues.

 

Always know what load you are putting onto a dimmer channel and try to have a few spare channels available for a show in case you need a replacement.

[ibwats]

hi all again

thanks heaps for that, it kinda makes a bit of sense, some of it went right over my head, but the bit about lamps about to short out and drawing out more power kinda fits. it seems to be that the lamps that stuff up are the old ones, I always thought that it was a problem with the dimmer, becasue the lamps just take the power, but I'll have a look at the lamp now too.

 

about the desk, it's a M24 but somhow it seems to have both D54 and 512 going into the back, we've got 2 sorts of dimmers, the hubs(DMX512), and some old things that are covered in dust(D54), we're not as worried about them.

 

so provied that it's the lamps that are stuffing up the channel, how would we fix it??, is it somthing we could do ourselves, or do we need to get somone in??

 

thanks again everyone

[JimWebber]

hi all....

 

....the problem that we have is that some of our channels will suddenly turn on to full and then won't turn off. this somtimes happens during shows, and a light will suddenly come on and not turn off....

 

 

Ian, I'm not sure if I read your original post correctly, are you saying that a channel is constantly on, or is it a case of a channel randomly "deciding" to flash to full, and then clearing?

 

If the light is constantly on, then I would agree with a probable SCR/Triac failure.

 

If it is an intermittent problem, it would also be worth investigating the controller, perhaps trying a different one if you can. If you are DMX, then pretty much any controller will do.

 

Again, if it is a random thing, is your DMX line correctly terminated?

 

Just a few random thoughts...

 

Jim

[ibwats]

um..

what I mean is that the light will be working perfectly normally, then suddenly it will turn on to 100% and stay on, and the only way that we can turn it off is by either pulling out the plug, or switching the power switch for it's channel on the dimmer.

 

sorry if it wasn't clear the first time.

 

ian.