Jands HP12 Technical Manual - 1.4
Equipment Description
1-3
Revision 2 - 26 April, 2000
HP SERIES DIMMER
TECHNICAL MANUAL
1.3.1
Overloads and Inrush
Cold lamp filaments consume considerably more power than warm filaments. This means
that the first time the lamp is turned on to full, the surge current can be several times
greater than the rated current for the lamp.
This cold surge current may be enough to trip the output circuit breakers. If this
“nuisance-tripping” of the circuit breakers is a problem, the filament Preheat facility may
be utilised. See section 4.1.4.5 for instructions on enabling the Preheat facility.
Lamp filament resistance is roughly proportional to temperature. A filament preheated to
900
°
K (630
°
C) has a resistance about three times higher than a filament at room
temperature (300
°
K, 30
°
C).
Preheat turns on the selected channels a very small amount (around 1% at 240 volts and
4% at 110 volts) which heats the lamp filaments and increases their electrical resistance.
When the lamp is then turned on full, the surge current is much less and the circuit
breaker will not trip.
Other advantages of using Preheat are an increase in lamp life (due to the reduction of
thermal shock to the filaments), and a reduction of lamp heat up time (the lamps will
flash slightly quicker).
1.3.2
Short Circuits
The SCRs and triacs are protected by the circuit breakers during shorts produced by
damaged wiring or blown lamp filament fragments across the filament supports.
The stress on SCRs and triacs during short circuits depends on:
•
The operating temperature of the devices prior to application of the short
•
The impedances of the mains supply, dimmer chokes and output cables
•
The let-through energy of the circuit breaker when breaking the fault
•
The moment during the mains waveform when the short is applied
The triacs in the HP12-TR will survive output short circuits under most conditions. The
more rugged SCR pairs in the HP12-SC, aided by higher choke impedance, will survive
output shorts under extreme conditions (high operating temperatures, high supply fault
current availability, zero cable length from dimmer to short).
1.4
Outdoor Systems
It is recommended that at outdoor shows where the power is locally generated the
following steps be taken to ensure a trouble-free show:
1.
Run the console from an extension cord that is plugged into the same power
source as the dimmers. If this is not possible a DMX isolating unit should be
inserted between the lighting console and the dimmers.
2.
Disable the neutral detect system. Generators often have poor regulation on
their output power and it is very likely that under certain circumstances this can
cause the neutral detect feature to trip.