Film-Tech Forum ARCHIVE: Kelmar Deluxe Dimmer Problem

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Posted by Tom Wienholt (Member # 1510) on 10-17-2012, 08:46 PM:

My Kelmar dimmer had recently had some issues. When the circuit breaker for the house lights is powered on, the led's on the dimmer light up normally and the house lights come on in the HIGH position. However, when the automation pulses the dimmer for MID or LOW, or if the buttons on the dimmer are manually pushed, the LED changes into the desired lighting level, but the lights do not dim! The low level knob on the dimmer is in the lowest setting. The bypass circuit is not wired. After powering off and back on, the problem is still there. Any ideas?

Posted by Tony Bandiera Jr (Member # 2365) on 10-17-2012, 08:51 PM:

Yep the Triac for the output is shorted. Check all your attached lighting for shorts and if they are ok replace the triac and you'll be happily dimming again.

Posted by Tom Wienholt (Member # 1510) on 10-17-2012, 09:12 PM:

You mean check the actual light fixtures for shorts? There are 8 recessed lights in the auditorium. How exactly can I check this?

Posted by Richard May (Member # 2627) on 10-18-2012, 06:49 AM:

It usually happens when they are changing bulbs with the lights on. The bulb breaks in the socket and shorts. Takes the triac out all the time. See if any bulbs are broken or blown. Then ask if they broke any while changing them.

Posted by Stephen Frazza (Member # 2320) on 10-18-2012, 08:36 AM:

I agree. 99% of the time, any problems I have with Kelmar dimmers it has been the triac.

Posted by Richard Hamilton (Member # 321) on 10-18-2012, 09:17 AM:

Why is this in the "Digital" forum? Are Triacs and lightbulbs digital now? Maybe there should be a "Tech-Forum" for issues that affect both film and digital?

Posted by Tony Bandiera Jr (Member # 2365) on 10-18-2012, 03:30 PM:

It's here to make you ask why Richard. [Razz]

Yep, good point on the changing bulbs issue....that is a #1 cause of triac failures any any dimmer. Also, in rare cases, when an incandescent bulb blows it can create a momentary short that can take a heavily-loaded or marginal triac out.

Tom, only real way to test for shorts in any given fixture is to disconnect each one and use a meter on the ohms setting, checking for shorts hot to neutral, hot to ground and neutral to ground. It is a job for an electrician in most cases.

Posted by Tom Wienholt (Member # 1510) on 10-18-2012, 05:28 PM:

Thanks for the suggestions. Here is what is weird...this has happened once per week for the past month. The problem lasts for one day forcing us to turn the lights off and on with the breaker during shows. Then the next day it works normally. This is the case again today. Dimmer has worked perfect all day. Not sure how this is possible.

Posted by Tony Bandiera Jr (Member # 2365) on 10-19-2012, 12:46 PM:

Ok, other things to check: Swap a control board from another auditorium and see if the problem moves with the board. If so, bad control board. If not, bad triac is still #1 suspect.

Best advice for now though is get an electrician in to check for proper voltage coming in to the dimmer, and any loose connections in the breaker panel feeding the dimmer as well as the feeder to that panel.

Also try disconnecting the automation wires next time it acts up. If it works normally with the automation disconnected, then your automation has a short or bad relay.

Posted by Jim Cassedy (Member # 4115) on 10-20-2012, 02:41 PM:

Several years ago I had a problem at a very old theater where
the original motor driven autotransformer type dimmer had been
replaced with a solid state one which blew triacs every few months.

In this theater, rather than wire a new control circuit from the
auditorium to control the full-power 'cleaning lights', they
had decided to keep the original set-up, which used a double pole
switch key switch in the back of the auditorium that switched
the houselights from the the dimmer output to an entirely
different 120V circuit.

Most of the time, this switching took place after hours when the
janitors came in, but there were occasions when it got switched
at full load and that would somtimes blow the triac.

We eventually 'solved' the problem by inserting a huge filter
choke , which we made from one of the big transformers out of an
old arc rectifier, into the dimmer output circuit.

This worked to 'absorb' the spikes when the house light circuit
was switched to or from the dimmer under load conditions.

We did this almost two years ago, and as far as I know, they've
never had a triac blow since. (Or I've had heard about it!)

Obviously, if anyone else tries this, you've got to make sure
the windings of whatever you're using to make the 'choke' coil
can handle the full amperage load of you lighting circuits or
it will overheat or burn up.

Posted by Tom Wienholt (Member # 1510) on 10-23-2012, 12:04 PM:

Ok, so I still have not determined the problem. But, I have more interesting info. The dimmer only acts up on Sundays. A church uses the auditorium on Sunday mornings so the dimmer is turned on at 7am and by the time we show movies around 1pm the dimmer does not dim! The dimmer then does not function properly until Monday after it has been turned off overnight. Then it works fine until the next Sunday. Here is what is interesting. Last night I left the dimmer on in that auditorium overnight because we were getting our floors waxed. When I came in today, the dimmer would not dim! So, apparently, when the dimmer is left powered up for several hours without the lights being dimmed, it seems to not work. I don't get it...

Posted by Tony Bandiera Jr (Member # 2365) on 10-23-2012, 06:33 PM:

Ok, so something is overheating and not allowing the dimming action. Still leads me to the triac as #1 suspect, BUT I would try moving the control board to another auditorium, leave it on all night in that other auditorium and if it doesn't dim, the control board is bad. If it DOES dim...triac in the first (problem) house is bad.

Posted by Tom Wienholt (Member # 1510) on 10-23-2012, 06:37 PM:

Ok I'll give it a try. Thanks!

Posted by Louis Bornwasser (Member # 3063) on 10-23-2012, 06:55 PM:

These are electronic dimmers. SOMETIMES wiring can be an issue. The voltage wire is probably correct. The neutral must be isolated and exactly parallel the hot wire. 20 ft from panel to dimmer and 50 feet to load; the neutral should be the same.

I have seen shared neutrals and neutrals that were teed off that worked strangeley. louis

Posted by Tom Wienholt (Member # 1510) on 10-26-2012, 03:23 PM:

First I would like to thank everyone for the help. I replaced the triac and the dimmer now works great. To make sure, I left the house lights on overnight and when I came in today it worked. I'll keep the triac in mind for future issues. Thanks again!