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Electronic Theatre Controls Inc

SCR Misfiring and LEDs

What is SCR Misfiring

An SCR is like a small switch that some dimmers use to pass or block current, allowing power through a circuit or cutting it off. By alternating between passing and blocking current like this, a controllable amount of power may be output to a circuit - this is called line voltage dimming, and it's how many lights including things like screw-in bulbs actually dim.

SCR misfiring is a somewhat common byproduct of dimming LEDs. LEDs don't always provide the electrical resistance necessary for the SCR to switch correctly, meaning that the lights might not turn on, might not dim at all, or might flash erratically - fast like a strobe light or rarely are both possible.

Will SCR Misfiring Affect My LEDs

SCR misfiring is always a possibility when dimming LEDs if your system uses certain dimmers. D20-style modules, the Smartpack dimmer, and the Colorsource dimmer all use SCR technology to do line voltage dimming. SCR misfiring tends to get worse and more likely with more LEDs on a circuit, but it's never a guarantee and every LED out there will work a little differently.

How To Resolve SCR Misfiring

There are several options to fix or prevent SCR misfiring.

  1. Use an ELV-type dimmer instead. ELV10 and LED10 modules, the Foundry and Echo 600W dimmers, and the ERP 300W dimmer all use different technology to limit the amount of power on the circuit for line voltage dimming. SCR misfiring cannot occur on ELV dimmers.
  2. Unison DRd, Smartpack, Sensor+, and Sensor 3 all have programmable rack settings to adjust which can stop SCR misfiring if it's occurring. This works for most, but not all cases - this is not a guarantee. Unison DR and Sensor Classic have no such feature, so this solution is not an option without upgrading dimming racks.
  3. Put a resistive ghost load on the circuit. This can sometimes fix SCR misfiring, though how much resistive load is needed will depend on the circuit. It will always use energy while the circuit is on, which eats into the energy savings from switching to LED in the first place.

Please see this article for additional technical information on the causes of SCR misfiring, and instructions on how to adjust settings in step 2 above.

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