Film-Tech Forum ARCHIVE: Dimmer chaining

This is topic Dimmer chaining in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.

To visit this topic, use this URL:
https://ft-forum.com/ft/cgi-bin/ubb/ultimatebb.cgi?ubb=get_topic;f=1;t=009410

Posted by Dominic Espinosa (Member # 2122) on 07-15-2008, 07:19 PM:

Here's a new one for me.
I have a theater with a pair of Xetrol dimmers AND a Kelmar dimmer.
The Kelmar appears to be the "master" with half the house lights attached to one of the xetrol's and the other half by the other one.

For some reason now, one of them is not dimming when the show starts, it has to be manually dimmed by hitting the button on the front panel of the dimmer.

Any ideas?

Posted by Gordon McLeod (Member # 33) on 07-15-2008, 09:06 PM:

The Kelmar control works on pulling the control lines to ground some of the older Xetrols went high
Most likely they have added a seperate relay to buffer the two

Posted by John Walsh (Member # 168) on 07-15-2008, 09:38 PM:

Xetrols just had a 12vac power supply which operated the 'up' relay, or the 'down' relay. The 'common' connection was not grounded.

I think Gordon is right; there is nothing wrong with either dimmer, just the relay (or whatever) that operates them both at the same time. If so, that's harder to help figure out because it just depends on how your installer wired it.

If you still need help with this, it might help to tell us which dimmer is not working, and go from there. I assume it works OK when the lights are raised?

Posted by Noel Mackisoc (Member # 4852) on 07-21-2008, 04:12 PM:

You might first check the operation of each individual dimmer by jumpering the appropriate control terminal (up/dn) to its common. This would tell you if the control problem is with a specific dimmer or an external source, such as an isolating relay as John suggests.

Yes, the control lines for Kelmar and Xetrol dimmers are incompatible and must be isolated from each other.