I am trying to devise a simple circuit to monitor when a 24v nav lamp
has blown. Found this http://www.gammatron.com.au/datashee...0Datasheet.pdf
but at AU$54 it is pretty pricey. Should not be to difficult to make
up, but I need to know he values of the components. I already have
the switch, LED and a resistor to monitor when lamp is on.
TVMIA.

CS wrote in
:

I am trying to devise a simple circuit to monitor when a 24v nav lamp
has blown. Found this
http://www.gammatron.com.au/datashee...0Datasheet.pdf but at
AU$54 it is pretty pricey. Should not be to difficult to make up, but
I need to know he values of the components. I already have the
switch, LED and a resistor to monitor when lamp is on. TVMIA.


Instead of putting the LED/resistor ACROSS the bulb, let's install a
little shunt in SERIES with the hot lead to the bulb that will rob 3
volts from the bulb's voltage when it's operating. We'll then use the
LED and a smaller current limit resistor in series with the LED to
protect the LED from overcurrent if the bulb shorts. INstead of the LED
operating on voltage provided by the switch, the LED will now light ONLY
if there is CURRENT going through a GOOD bulb, remaining dark if the
bulb blows....which it will do LOTS less operating from 21V, not 24V, at
only a tiny difference in brightness. If you're worried about the
voltage, notice how the CHARGING voltage is 28V when the engine is
running, which is what's blowing the bulbs in the first place.

switched shunt
+24VDC----|-/\/\/\/\/\--|-----to light
| |
|-LED--22ohms-|
A K

A=anode
K=cathode

Measure the current the bulb draws by leaving the switch OFF and putting
an ammeter (VOM on 10A scale) across the open switch terminals which
will make the bulb current go through the ammeter. Use the formula:

Ohms = 3V divided by AMPS to figure out the value of the shunt.

Use the formula AMPS X 3 VOLTS = WATTS to find out how many watts the
resistor gets then use a resistor spec that's about double what you
calculate.

The only way for the LED to light, now is when the lamp draws current
through the shunt, not just because there's voltage to ground. The
brightness of the LED is adjusted by varying the value of the 22 ohm
series resistor. You could easily make that a 100 ohm variable resistor
so you can set it like you like to see it. Use any 100 ohm thumbwheel
pot and set the pot to maximum resistance. Then, the first time you
light off the light with this circuit, just reduce the resistance to
increase the brightness but don't go to zero because 3V will destroy the
LED with overcurrent. If the LED gets warm, it's too much.

This circuit works on 12V too, but the bulbs never blow operating on 12V
(14.2V charging minus 3V shunt = 11.2V on 12V bulb.) We haven't
replaced a light bulb in years....

Sorry there's no fancy computer circuitry, LCD screen, big keyboard....
(c;]

Shhh....don't tell anyone, but his same circuit monitors the tower
lights blinking on the 2000' tower at the TV station to make sure it's
lit up so it doesn't attract airplanes.

By the way, the current through the LED is only about 20-80 milliamps
and you cna use the tiniest wire you got to remotely mount the LED far
away from the shunt, which needs to be right were the light's wiring is
now. Our LED panel is over the hatch to the forward compartment and
head so you can easily notice it every time you have to pee, which is
quite often, considering our beer consumption...(c;]

CS wrote:
I am trying to devise a simple circuit to monitor when a 24v nav lamp
has blown. Found this http://www.gammatron.com.au/datashee...0Datasheet.pdf
but at AU$54 it is pretty pricey. Should not be to difficult to make
up, but I need to know he values of the components. I already have
the switch, LED and a resistor to monitor when lamp is on.
TVMIA.
Put the monitor led in series with the lamp, with two or tree
normal diodes accross the led to limit the voltage/current.
20 ohm resistor in series with the led is a good idea.
The shunt diodes must be able to carry the lamp current.
The read leds need the least voltage.

Larry wrote in news:Xns9B5E990567CE2noonehomecom@
74.209.131.13:


switched shunt
+24VDC----|-/\/\/\/\/\--|-----to light
| |
|-LED--22ohms-|
A K

A=anode
K=cathode

M

The LED in series with 22 ohms across the shunt looked queer when I
downloaded it.

On Nov 22, 9:04*pm, Sjouke Burry
wrote:
CS wrote:
I am trying to devise a simple circuit to monitor when a 24v nav lamp
has blown. *Found thishttp://www.gammatron.com.au/datasheets/GM050%20Datasheet.pdf
but at AU$54 it is pretty pricey. *Should not be to difficult to make
up, but I need to know he values of the components. * I already have
the switch, LED and a resistor to monitor when lamp is on.
TVMIA.

Put the monitor led in series with the lamp, with two or tree
normal diodes accross the led to limit the voltage/current.
20 ohm resistor in series with the led is a good idea.
The shunt diodes must be able to carry the lamp current.
The read leds need the least voltage.

Just put a cheap amp meter in series after the switch. When the switch
is closed and
you have current flow to the light the meter will show amps when bulb
opens or burns out the amp meter will show 0 amps.

CS wrote:
I am trying to devise a simple circuit to monitor when a 24v nav lamp
has blown. Found this http://www.gammatron.com.au/datashee...0Datasheet.pdf
but at AU$54 it is pretty pricey. Should not be to difficult to make
up, but I need to know he values of the components. I already have
the switch, LED and a resistor to monitor when lamp is on.
TVMIA.

Sorry to dissent with most of you, but the original circuit makes much
more sense than anything else you propose. Someone with little
experience and desire to do some trials may be able to replicate it at
home with probably far less than U$D 10. The switch is the most costly
item of the assembly and the power diode follows.
Regarding the specifications of the components, they are not critical.
1) the diode must be any silicon diode able to sustain the power given
by the several amps of the lamp times 0.6V voltage drop.
2) The transistor can be any low power low frequency (low cost) PNP and,
3) for the resistors I would just start trying something like: R1 50-100
Ohm and R2 10 kOhm.
Some easy computation of the resistors could be done in advance but... I
am rather lazy and prefer trials and errors!
Daniel

On 23 Nov, 12:23, Daniele Fua wrote:
CS wrote:
I am trying to devise a simple circuit to monitor when a 24v nav lamp
has blown. *Found thishttp://www.gammatron.com.au/datasheets/GM050%20Datasheet.pdf
but at AU$54 it is pretty pricey. *Should not be to difficult to make
up, but I need to know he values of the components. * I already have
the switch, LED and a resistor to monitor when lamp is on.
TVMIA.

Sorry to dissent with most of you, but the original circuit makes much
more sense than anything else you propose. Someone with little
experience and desire to do some trials may be able to replicate it at
home with probably far less than U$D 10. The switch is the most costly
item of the assembly and the power diode follows.
Regarding the specifications of the components, they are not critical.
1) the diode must be any silicon diode able to sustain the power given
by the several amps of the lamp times 0.6V voltage drop.
2) The transistor can be any low power low frequency (low cost) PNP and,
3) for the resistors I would just start trying something like: R1 50-100
Ohm and R2 10 kOhm.
Some easy computation of the resistors could be done in advance but... I
am rather lazy and prefer trials and errors!
Daniel

Thanks. I should add that the bulbs are 24v 25w so 1.04A.

CS wrote:
Thanks. I should add that the bulbs are 24v 25w so 1.04A.

That's even better: if you will use your device only for 24V, the diode
needs to dissipate just 0.6W. Find a diode good for at least 3 times
this number and you are on the safe side. Just notice that the heat
(not large but neither totally negligible) will have to be removed and
redirected where it does not make any harm.

Daniel

"Daniele Fua" wrote in message
...
CS wrote:
I am trying to devise a simple circuit to monitor when a 24v nav lamp
has blown. Found this
http://www.gammatron.com.au/datashee...0Datasheet.pdf
but at AU$54 it is pretty pricey. Should not be to difficult to make
up, but I need to know he values of the components. I already have
the switch, LED and a resistor to monitor when lamp is on.
TVMIA.

Sorry to dissent with most of you, but the original circuit makes much
more sense than anything else you propose.

Agreed. But it can be made even simpler: buy a cheap $2 current relay and
connect the coil in series with the lamp or even cheaper: buy a $0.10 read
contact and coil the wire to the lamp 20 times around the reed contact. The
contact closes when current flows through the wire. Drive a small lamp or
LED with it and you're done. And for the life of me, I cannot understand why
this is not a standard feature in ANY safety related application like nav
lights or even tail/break lights on cars...

Meindert

Meindert Sprang wrote:
Agreed. But it can be made even simpler: buy a cheap $2 current relay and
connect the coil in series with the lamp or even cheaper: buy a $0.10 read
contact and coil the wire to the lamp 20 times around the reed contact. The
contact closes when current flows through the wire. Drive a small lamp or
LED with it and you're done. And for the life of me, I cannot understand why
this is not a standard feature in ANY safety related application like nav
lights or even tail/break lights on cars...

Meindert


Great! The reed contact idea sounds perfect. The only problem might be
mechanical if the cable is thick but, in that case, I guess you only
need few coils. It is a matter of finding just the minimum number of
coils to reach the threshold B considering Ampere law.

I will try it.

Daniele