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G8MNY > TECH 12.02.18 10:59l 45 Lines 2088 Bytes #999 (0) @ WW
BID : 8961_GB7CIP
Read: GUEST
Subj: Reducing Lamp Surge
Path: IZ3LSV<I0OJJ<GB7CIP
Sent: 180212/0953Z @:GB7CIP.#32.GBR.EURO #:8961 [Caterham Surrey GBR] $:8961_GB
From: G8MNY@GB7CIP.#32.GBR.EURO
To : TECH@WW
By G8MNY (New Jan 09)
(8 Bit ASCII graphics use code page 437 or 850, Terminal Font)
On an Over Head Projector I have used this surge limiter to greatly reduce the
chance of 250W lamp failure at turn on. This circuit is suitable for most low
voltage lamp systems.
high current
relay contact VOLTS COLOUR
\ 24 ¿ _..--ÄÚ White
ÄÄÄÄÄÄÄÂÄÄÄß ÀÄÄÂÄÄÄÄÄÄÂÄÄÄÄÄÄÄ¿ 21 ´ Ý ³
³ ³ ³ ³ 20 ´ Þ Ã Yellow
Lamp ³___1R5__³ Rstart ³ 18 ´ .úÙRelay ³
Supply 50W _³_ ³ 15 ´ . Operates à Orange
\_/ LAMP 12 ´ . ³
e.g. ÚÄÄÄÄÄÄÄ´ ³ 9 ´ / ³
24V +³ ÚÄÄÄÄÁÄÄÄÄ¿ ³ 6 ´ .' Ã Red
@ 12A 100u === ³12V Relay³ ³ 3 ´.ú' ³
16V ³ ÀÄÄÄÄÂÄÄÄÄÙ ³ 0 ÅÄÄÄÂÄÄÄÂÄÄÄÂÄÄÄÂÄÄÁÄ>TIME
ÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÁÄÄÄÄÄÄÄÁÄÄÄÄÄÄÄÙ 0 1 2 SECONDS
The delay time is really nothing to do with Rstart & the 100uF, but the lamp
temperature, as that determines the lamp resistance & hence the voltage drop
across the surge limiting 50W R. This means the turn on delay is reduced if the
lamp is already hot.
The 1R5 is made from several wire wound resistors to give the short term power
dissipation to wire wound on an a large former. The value is chosen to let the
lamp get to a good orange to yellow colour temperature before the relay applies
full power. Care must be taken for the location of this resistor & near any
fanned air flow is useful.
The value of Rstart determines the lamp on operating voltage for the relay it
may need to be a power resistor if the relay is not sensitive.
The 100uF Cap stops the relay humming @ 50Hz by smoothing the applied voltage.
Why don't U send an interesting bul?
73 De John, G8MNY @ GB7CIP
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