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So this 12 VDC LED rated at 1.5 watts i.e. 125 mA, The LED is run by a computer circuit which sends 12 V power to LED for on and off, exactly like a car turn signal blinker.
Which value fast blow glass fuse should I put here?
I tried 100 mA 5x20 mm glass fuse and it works but the LED acts weird sometimes and just stops working until I power cycle everything, 100 mA fuse never blew since installation.
I think LED acting weird has to do something with fuse value.
A fuse melts first in the midpoint between the terminals. 125mA is probably not enough to "blow" the the fuse but may melt the very midpoint. Surface tension holds the metal droplet in place. At these temperatures the fuse resistance is high. This would cause some odd behaviour in the LEDs.
I had this happen once. The fuse would blow only when the apparatus was bumped. The fuse was in tact ecept for a small gap where the metal fell out. Usually when a fuse blows the metal is vapourized.
The fuse value needs to be greater than the operating current plus any power-on inrush current,say 250mA.
Milli-amp fuses do insert a resistance in series with the LEDs as indicated by vir in the comments. This may also affect the operation of the LEDs.
You will have to test.
