Warning lamp circuit

Thread Starter

gsd01

Joined Jan 26, 2021
1
Hi
I need help from someone in this forum with what I am sure is a very simple problem. I have a boat which has a separate oil tank with sensor which is on when the the tank is full and off when the tank is almost empty. I would like to install a warning lamp which lights when the tank is almost empty. Obviously a simple circuit would not work as the lamp would light when the tank is full and go out when the tank is empty. From my research I believe I need to include a relay to reverse the signal. Can anyone indicate what relay would be required and provide a simple circuit diagram?
This is a 12V DC circuit.
 
Last edited:

crutschow

Joined Mar 14, 2008
27,198
You could use a resistor and an LED indicator (below):
The LED lights when the switch is open (assuming the oil sensor is a switch).

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AnalogKid

Joined Aug 1, 2013
9,249
Can anyone indicate what relay would be required and provide a simple circuit diagram?
If you have specs on the sensor / switch / whatever, such as its contact ratings (voltage, type (AC, DC), current), please post them.

Also, specs on whatever the light or indicator is.

The basic plan is get a SPDT (single-pole, double-throw) relay with contacts that can handle the load. The "double-throw" part is what makes this work for you. The contacts must be rated for more than your device. Fir example, if it is a 12 W bulb, that's 1 amp of operating current; you want a relay rated for at least 2 A.

Something to conside ris that the relay will be activated most of the time. The coil current won't be large, but it will be a constant drain on the battery unless the overall circuit has an off switch, or is connected to something else that does.

ak
 
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