Hi,
I need to disable the 12VDC defrost heater of the RV refrigerator while running ONLY on battery power (using inverter), and monitoring the status of the thermostat (contacts open or closed). The heater uses a minimum of 10Amps and can run for an hour or more. Unfortunately, the wire between the thermostat and heater can not be accessed, which would have made this an easy project. While the power to the circuit is switched off using a SPDT switch, I need to monitor if the thermostat is activated or deactivated (open/closed), displaying closed status with a LED. The only way I can think of, and I am sure will not work, is to wire the LED to the other terminal of the SPDT switch which will supply 12VDC to the LED, while not supplying power to the heater. The way I show it in the picture, I believe the load will wipe out the LED/R1. I am trying to keep the circuit as simple as possible, without using an Arduino or a lot of other IC parts.

Another thought was to put the SPDT switch on the GRD side of the heater and monitor the heater lead for 12VDC and some how activate the LED, without the heater. The LED can be on with the thermostat activated or deactivated.

Thanks in advance for any assistance

Don

 

Yes, that would work (assuming the centre connection shown on the switch is the pole).

 

Yes, that would work (assuming the centre connection shown on the switch is the pole).

I neglected to show a value for R1, which I normally use a 220 ohm resistor. I also came across a 12VDC LED (see attached) and was wondering if I would still need to add a resistor to this LED. I could not locate any information regarding this in the online documentation. Not much information... I know.

Your thoughts,
Don

 

No resistors needed for those leds, they will draw 15mA @12V.

 

No resistors needed for those leds, they will draw 15mA @12V.

Thanks Everyone!!!

Don

 

I neglected to show a value for R1, which I normally use a 220 ohm resistor.

If you use a separate resistor and LED then 220Ω is too low for 12V - LED current 50mA. You need 470Ω (20mA) to 1k (10mA).