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