help - incandescent pilot light - AC, DC, or does it matter?

W

wahzoo

Guest
I have a mechanical latching relay that provides 24VAC for pilot
indication when it is turned to the "on" state. What is the best type
of lamp to get for the pilot? The wires carrying the pilot 24VAC will
be 18AWG and run for not more than 80 feet.

For this app, the smaller and simpler, the better. I'd like to mount
the pilot thru a switch plate about 1/8" thick. (This is for a house
low-voltage lighting system by the way.)

I've looked into using LED's but don't have space for the extra
electronics involved.

I've looked into neon, but don't think any work with less than 65VAC.

I see small T-1 incandescents in the 2003 Mouser catalog and see a
voltage rating of 28.0, but they don't say whether that is AC or DC.
(?)

Also, 24VAC has a widely used in US HVAC systems. Where does 28V?C
come from? Is it a different standard or are they just covering
24-28VAC?

Any advice appreciated.

--wahzoo
 
An led needs only a resistor in series with it, and if you look around you
can find 24 volt leds packaged with the resistor, with the intent of being
used as a panel mount pilot lamp. Leds last longer than an incandescant
light bulb but the bulb types can generally be brighter. The voltage rating
is AC or DC, either one works, but an led will only light for 1/2 cycle of
the AC. Neon on the other hand will need higher voltage.You will lose some
of the voltage due to the 80 feet of wire. How much depends on the current
that the pilot draws.
bg
wahzoo wrote in message <22e07013.0312261158.b12b12a@posting.google.com>...
I have a mechanical latching relay that provides 24VAC for pilot
indication when it is turned to the "on" state. What is the best type
of lamp to get for the pilot? The wires carrying the pilot 24VAC will
be 18AWG and run for not more than 80 feet.

For this app, the smaller and simpler, the better. I'd like to mount
the pilot thru a switch plate about 1/8" thick. (This is for a house
low-voltage lighting system by the way.)

I've looked into using LED's but don't have space for the extra
electronics involved.

I've looked into neon, but don't think any work with less than 65VAC.

I see small T-1 incandescents in the 2003 Mouser catalog and see a
voltage rating of 28.0, but they don't say whether that is AC or DC.
(?)

Also, 24VAC has a widely used in US HVAC systems. Where does 28V?C
come from? Is it a different standard or are they just covering
24-28VAC?

Any advice appreciated.

--wahzoo
Click to expand...
 
"wahzoo" <cantreallysay@hotmail.com> wrote in message
news:22e07013.0312261158.b12b12a@posting.google.com...
I have a mechanical latching relay that provides 24VAC for pilot
indication when it is turned to the "on" state. What is the best type
of lamp to get for the pilot? The wires carrying the pilot 24VAC will
be 18AWG and run for not more than 80 feet.

For this app, the smaller and simpler, the better. I'd like to mount
the pilot thru a switch plate about 1/8" thick. (This is for a house
low-voltage lighting system by the way.)

I've looked into using LED's but don't have space for the extra
electronics involved.

I've looked into neon, but don't think any work with less than 65VAC.

I see small T-1 incandescents in the 2003 Mouser catalog and see a
voltage rating of 28.0, but they don't say whether that is AC or DC.
(?)

Also, 24VAC has a widely used in US HVAC systems. Where does 28V?C
come from? Is it a different standard or are they just covering
24-28VAC?

Any advice appreciated.

--wahzoo
Click to expand...
Some of the telephone systems I've interacted with use a nominal voltage of
28v, but in this instance I suspect it's situation of applying a slightly
higher voltage rated lamp for longevity.

If the lamp will be in the "on state" at a high duty cycle, or the
indication is a critical element of an important system, you might consider
one of the pilot light indicators with integral LEDs. These assemblies are
available with all necessary elements contained within the shell of the
device, and the burn time is very long.

If you have difficulty finding a suitable unit they are available at any of
the electrical wholesale houses.
Louis

Since this
 
On Fri, 26 Dec 2003 13:39:33 -0700, "bg" <bg@nospam.com> wrote:

An led needs only a resistor in series with it, and if you look around you
can find 24 volt leds packaged with the resistor, with the intent of being
used as a panel mount pilot lamp. Leds last longer than an incandescant
light bulb but the bulb types can generally be brighter. The voltage rating
is AC or DC, either one works, but an led will only light for 1/2 cycle of
the AC. Neon on the other hand will need higher voltage.You will lose some
of the voltage due to the 80 feet of wire. How much depends on the current
that the pilot draws.
Click to expand...
---
Since an LED is a diode, on the AC half-cycle when it's not conducting
only leaksge current will flow through it and the series resistor,
allowing the voltage across the LED to rise high enough to puncture its
junction and destroy the LED. In order to keep this from happening a
diode can be placed in parallel opposition across the LED. Another
diode can be placed in series with the combination, facing in the same
direction as the LED, in order to keep from having to increase the
wattage rating of the series resistor.

--
John Fields
 
wahzoo wrote:
I have a mechanical latching relay that provides 24VAC for pilot
indication when it is turned to the "on" state. What is the best type
of lamp to get for the pilot? The wires carrying the pilot 24VAC will
be 18AWG and run for not more than 80 feet.

For this app, the smaller and simpler, the better. I'd like to mount
the pilot thru a switch plate about 1/8" thick. (This is for a house
low-voltage lighting system by the way.)

I've looked into using LED's but don't have space for the extra
electronics involved.

I've looked into neon, but don't think any work with less than 65VAC.

I see small T-1 incandescents in the 2003 Mouser catalog and see a
voltage rating of 28.0, but they don't say whether that is AC or DC.
(?)

Also, 24VAC has a widely used in US HVAC systems. Where does 28V?C
come from? Is it a different standard or are they just covering
24-28VAC?

Any advice appreciated.

--wahzoo
Click to expand...
The bulbs will work fine on AC or DC. A bulb rated at 28 volts will
have a life about 10 times longer than one rated for 24 volts when
powered from 24 volts. By the way, if you want to use an LED, get one
that is two color (one color for each polarity, with two leads) and
all you need is a 2000 ohm 1/2 watt series resistor to run it off 24
volts AC.

E.G. T1 red green
http://rocky.digikey.com/WebLib/Lite-on/Web%20Data/LTL-14CHJ.pdf
T1-3/4 red green
http://rocky.digikey.com/WebLib/Lite-on/Web%20Data/LTL-293SJW.pdf

--
John Popelish
 
On 26 Dec 2003 11:58:16 -0800, cantreallysay@hotmail.com (wahzoo) wrote:

I have a mechanical latching relay that provides 24VAC for pilot
indication when it is turned to the "on" state. What is the best type
of lamp to get for the pilot? The wires carrying the pilot 24VAC will
be 18AWG and run for not more than 80 feet.

For this app, the smaller and simpler, the better. I'd like to mount
the pilot thru a switch plate about 1/8" thick. (This is for a house
low-voltage lighting system by the way.)

I've looked into using LED's but don't have space for the extra
electronics involved.

I've looked into neon, but don't think any work with less than 65VAC.

I see small T-1 incandescents in the 2003 Mouser catalog and see a
voltage rating of 28.0, but they don't say whether that is AC or DC.
(?)
Click to expand...
---
It's either 28VDC or 28VRMS
---

Also, 24VAC has a widely used in US HVAC systems. Where does 28V?C
come from? Is it a different standard or are they just covering
24-28VAC?
Click to expand...
---
The 28V comes from aircraft electrical systems, which the small
incandescents were designed to be used in.

--
John Fields
 
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