Can we use LED PAR56 bulbs with an older SCR dimming system?

[SCJones]

A church I'm relamping uses an older (ca1970) SCR dimming system for their Sanctuary. They have 24 300w PAR56 halogen spots on the ceiling in banks of 4. There is a replacement PAR56 bulb by Green Creative which claims it is dimmable, at 40w. The easiest thing would be to just replace the bulbs but we are unsure if the SCR dimmer would control them properly. Thoughts?
The hanging chandeliers were changed to LED bulbs a few years ago and they seem to work on the SCR dimming, but can be glitchy at lower light levels.
The church is on a budget so we are looking at lower-cost options.
Also this is general illumination of the Chancel, not looking for these "Broadway theater-style" lighting systems.
Thanks for any advice.

 

[tortuga]

They have 24 300w PAR56 halogen spots on the ceiling in banks of 4. There is a replacement PAR56 bulb by Green Creative which claims it is dimmable, at 40w.

Do you have a old dimmer for each bank? So 1200 Watts per dimmer? Older SCR dimmers are forward phase or leading edge.

we are unsure if the SCR dimmer would control them properly.

Presuming your going from a 1200W incandescent purely resistive load on each of 4 banks to a 160 Watt electronic or DC load, I would swap the dimmers out with lagging edge or 'reverse phase' ELV (Electronic Low Voltage) dimmer.
You'll need a ELV dimmer rated over 160 Watts for each bank, I'd use one of the dimmers Green Creative publishes as compatible:

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greencreative.com

 

[jaggedben]

A church I'm relamping uses an older (ca1970) SCR dimming system for their ... The easiest thing would be to just replace the bulbs but we are unsure if the SCR dimmer would control them properly. Thoughts?
...

Why not buy one or two first and find out?

I think if by 'properly' you mean safely and with functional dimming, then it might just work. The dimming quality may be different, but then it's up to you if it's acceptable. For example if you care about color temperature and not just luminosity then the LEDs may not be that great. But since you don't require broadway style lighting it would likely be just fine.

 

[SCJones]

Do you have a old dimmer for each bank? So 1200 Watts per dimmer? Older SCR dimmers are forward phase or leading edge.

Presuming your going from a 1200W incandescent purely resistive load on each of 4 banks to a 160 Watt electronic or DC load, I would swap the dimmers out with lagging edge or 'reverse phase' ELV (Electronic Low Voltage) dimmer.
You'll need a ELV dimmer rated over 160 Watts for each bank, I'd use one of the dimmers Green Creative publishes as compatible:

Loading…

greencreative.com

Thanks for that response. Each bank of 4 is on a separate dimming circuit at the user control panel. Problem is this is a massive system, the size of a Univac computer from the 1950s, fed with a 150 amp breaker. They are going to see if the mfr is still in business and can upgrade the panels for them.

 

[SCJones]

Why not buy one or two first and find out?

I think if by 'properly' you mean safely and with functional dimming, then it might just work. The dimming quality may be different, but then it's up to you if it's acceptable. For example if you care about color temperature and not just luminosity then the LEDs may not be that great. But since you don't require broadway style lighting it would likely be just fine.

Thanks. I gave them two of the Green Creative LED bulbs to try out. Issue is they need a 40ft manlift to reach the fixtures so to install and test is not an easy feat. But looks like the best course of action unless we can find the manufacturer or their successor to upgrade the system cost-effectively.

 

[winnie]

The compatibility of an LED bulb and a particular dimmer can be hit or miss. There is no solid answer without someone doing testing.

LEDs require some sort of driver that converts incoming AC to current controlled DC. This driver will tend to stabilize its output and resist any changes in LED brightness.

Dimmers vary the AC waveform in some fashion that changes the RMS voltage.

Dimmable LEDs act to somehow recognize the dimming waveform and adjust the controlled output. This means that the bulb might simply ignore one type of dimmer, but work perfectly with a different type of dimmer. It also means that the bulb might respond excessively to electrical noise.

I'd recommend simply trying one bulb with your current dimmers just to see what happens.

Jonathan

 

[qcroanoke]

Can you get a couple temporary light sockets and connect them to the load side of the dimmer to see how they act?

 

[tortuga]

Thanks for that response. Each bank of 4 is on a separate dimming circuit at the user control panel. Problem is this is a massive system, the size of a Univac computer from the 1950s, fed with a 150 amp breaker. They are going to see if the mfr is still in business and can upgrade the panels for them.

Or since you don't need a "Broadway theater-style" lighting system have your electrician bypass the user control panel and just install a 4 gang box with 4 300W LED dimmers in it.

 

[winnie]

Thanks for that response. Each bank of 4 is on a separate dimming circuit at the user control panel. Problem is this is a massive system, the size of a Univac computer from the 1950s, fed with a 150 amp breaker. They are going to see if the mfr is still in business and can upgrade the panels for them.

1) Are you sure this is an SCR dimming system, and not something like a variac autotransformer system?

2) Does this feed more than the 24 300W lamps? 150A seems a touch large for 7200W of loading.

-Jonathan

 

[SCJones]

1) Are you sure this is an SCR dimming system, and not something like a variac autotransformer system?

2) Does this feed more than the 24 300W lamps? 150A seems a touch large for 7200W of loading.

-Jonathan

I was told it was SCR so I don't for sure. Pretty sure if it was purely resistive dimming all the LEDs would be strobing. I had put some dimmable CFLs in back in 2004 and they worked on the dimmers.
They are getting the mfr info so I can look it up and hopefully contact them and see what can be done.
This is used for the entire Sanctuary - 10 7-lamp incandescent chandeliers, 8 halogen ceiling spots (guessing 150w), 3 50w pulpit floods, and the 24 300w PAR56 lamps.
The mantra of this church in the past has been "maximize wattage and minimize brightness". An overabundance of high wattage, focused/sharp beam lights. Even the fluorescents all had parabolic louvers so they put in way too many fixtures.

 

[GoldDigger]

Thanks. I gave them two of the Green Creative LED bulbs to try out. Issue is they need a 40ft manlift to reach the fixtures so to install and test is not an easy feat. But looks like the best course of action unless we can find the manufacturer or their successor to upgrade the system cost-effectively.

Be sure to remove all of the halogen bulb from that circuit before trying to test the LED bulbs. The dimmers themselves can behave very differently with a mixed load (generally pretty well) than they will with an exclusive LED driver load.
The "professional" dimmers are at least likely to be three terminal devices rather than relying on current through the load for power as typical box mounted switch replacement devices do. Which is a good thing. Such dimmers should operate properly (produce the desired waveform) regardless of load, leaving only the question of how the LED drivers react to that waveform.

 

[SCJones]

Be sure to remove all of the halogen bulb from that circuit before trying to test the LED bulbs. The dimmers themselves can behave very differently with a mixed load (generally pretty well) than they will with an exclusive LED driver load.
The "professional" dimmers are at least likely to be three terminal devices rather than relying on current through the load for power as typical box mounted switch replacement devices do. Which is a good thing. Such dimmers should operate properly (produce the desired waveform) regardless of load, leaving only the question of how the LED drivers react to that waveform.

Thanks for that. I've done that in a pinch with other installations, leaving an incandescent bulb in the circuit allowed the resistive dimmers to work well until the dimmers were changed. The plan is to replace a bank of 4 halogens with LED and see what happens with the dimming.

 

[Todd0x1]

are these some sort of entertainment lighting fixture like a par can? if so id just replace them with the modern equivalent led theatrical fixture.