Hi all
I've built the attached circuit... It's a timer - the 4020 counts the pulses from a 555 and shuts off a relay at the end of the time period.
I'm using a 12v relay with a 120ohm coil in place of the smaller one supplied with the kit.
It all works fine - however I measured the voltage across the coil just now, and it reads 9V, I'm running from a lab PSU at 12.1V. The relay seems to operate fine, although I haven't put a load on it yet.
I figure the reverse polarity diode and PNP transistor should drop the voltage by 1.4 between them, but I have a 3V drop.... The BC328 should handle the coil current no prob.
The only mod I have made to what you see is an indicator LED in parallel with the relay coil.
Should I be concerned? I think I'll get rid of the reverse pol diode, but that won't buy much....
This relay will be used to switch a hot water system, so I am after reliable service....
cheers
Lee
I've built the attached circuit... It's a timer - the 4020 counts the pulses from a 555 and shuts off a relay at the end of the time period.
I'm using a 12v relay with a 120ohm coil in place of the smaller one supplied with the kit.
It all works fine - however I measured the voltage across the coil just now, and it reads 9V, I'm running from a lab PSU at 12.1V. The relay seems to operate fine, although I haven't put a load on it yet.
I figure the reverse polarity diode and PNP transistor should drop the voltage by 1.4 between them, but I have a 3V drop.... The BC328 should handle the coil current no prob.
The only mod I have made to what you see is an indicator LED in parallel with the relay coil.
Should I be concerned? I think I'll get rid of the reverse pol diode, but that won't buy much....
This relay will be used to switch a hot water system, so I am after reliable service....
cheers
Lee
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