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Electronic Theatre Controls Inc

Inrush Current and ETC LED Fixtures

Inrush current refers to the maximum amount of current drawn immediately upon power up of an electrical device. This can vary depending upon the type of load on the circuit. In an incandescent scenario, inrush is high until the filament warms up and resistance increases.

In the case of a switching power supply like those used in many electronics including ETC LED fixtures the inrush current is much higher than the nominal operating voltage.  In some cases the current can be as much as 75 times higher for a short period of time, usually worst at the first half- cycle.

This can create an issue with circuit breaker protection for a line of fixtures all coming from the same non-dim source.  The amount of fixtures that you can use at nominal voltage that will cause your circuit protection to engage is much higher than the amount of fixtures you can use upon inrush.  To compound this, most circuit breakers have different inrush trip curves.   To find the trip curve of a particular breaker, it is best to find the datasheet of the breaker in question.  This makes it impossible for ETC to calculate across the board how many fixtures can be on a circuit as it can vary widely and is reliant upon the breaker installed in the system. 

To avoid inrush problems, a good solution is to develop a startup sequence.  This means that not every fixture would be started at the same time.  This is common practice among high end audio gear for the same reason.  This allows a device to power up past the inrush point before another fixture hits its’ inrush point.

Below is a graphic with a scope shot of a fixture upon startup.  The green line is the current the fixture is drawing.  This is a good visual illustration of what is happening when a fixture is powered on and then how it normalizes.

Inrush Current.jpg

ColorSource PAR Inrush

120V- 35A (First half-cycle)
240V- 49A (First half-cycle)

  • 9 Fixtures/ R20

Nominal Power Consumption at Full Intensity 

Voltage (V) Current (A) Watts (W)
120 0.75 90 
240 0.4  89 

D22 Inrush      

120V- 17A (First half-cycle)
240V- 25A (First half-cycle)

  • 20 Fixtures/ R20

Nominal Power Consumption at Full Intensity 

Voltage (V) Current (A) Watts (W)
120  0.47 56.5
240  0.25  60 

D40/ D40XT Inrush

120V- 15A (First half-cycle)
240V- 40A (First half-cycle)

  • 10 Fixtures/ R20

Nominal Power Consumption at Full Intensity 

Voltage (V) Current (A) Watts (W)
120  110

240

0.5

120

D40XTI Inrush

120V- 15A (First half-cycle)
240V- 40A (First half-cycle)

  • 10 Fixtures/ R20

Nominal Power Consumption at Full Intensity 

Voltage (V) Current (A) Watts (W)
120  110
240 0.5 120

D60 Inrush

120V- 15A (First half-cycle)
240V- 40A (First half-cycle)

  • 10 Fixtures/ R20

Nominal Power Consumption at Full Intensity 

Voltage (V) Current (A) Watts (W)
120/240 13.5/0.68 161
240  0.68  163.2

D60 XTI Inrush

120V- 46A (First half-cycle)
240V- 77A (First half-cycle)

  • 10 Fixtures/ R20

Nominal Power Consumption at Full Intensity 

Voltage (V) Current (A) Watts (W)
120 1.03 123.6
240  0.54  129.6 

Source Four LED Inrush

120V- 11A (First half-cycle)
240V- 15A (First half-cycle)

  • 9 Fixtures/ R20

Nominal Power Consumption at Full Intensity

Model Voltage (V) Current (A) Watts (W)
Lustr+ 120 1.11 129.9
Daylight 120 1.39 163.63
Tungsten 120 1.35 157.4
Studio HD 120 1.07 127.1
Lustr+  240  0.56  135.36 
Daylight  240  0.72  172.32 
Tungsten  240  0.70  166.8 
Studio HD  240  0.56  135.36 

Source Four LED Series 2 Inrush

120V- 50A (First half-cycle)
240V- 107A (First half-cycle)

  • 9 Fixtures/ R20

Nominal Power Consumption at Full Intensity 

Voltage (V) Current (A) Watts (W)
120 1.45 174
240  0.81  195.12 

Source Four Mini LED Inrush

120V- 3A (First half-cycle)
240V- 4A (First half-cycle)

Nominal Power Consumption at Full Intensity

Voltage (V) Current (A) Watts (W)
120/240 ? 14
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