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So I have a simple circuit with a 24VDC input, a 2200ohm resistor, an LED, a solid state relay, and a float switch controlling when the LED (and SSR) are turned on.

I'm curious if running the resistor and LED directly inline like this on the 24V is going to harm the resistor over a long time. The SSR and float switch are behaving as expected and being able to run the LED, which is just simply a visible marker that the SSR is connected, in series like this instead of parallel works a lot better with my current setup.

schematic

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Even if you put the resistor straight across the 24 VDC source the power through it would still be below the resistor rating.

\$P = I^2 * R \$

\$P = 0.26 W \$

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  • \$\begingroup\$ And in a circuit such as this there isn't anything else to worry about with the resistor? \$\endgroup\$ – clifgray Jun 12 '17 at 20:57
  • \$\begingroup\$ Heat can destroy resistors. If the resistor is able to dissipate the heat there is no problem. Sudden short surge currents can also destroy resistors but I can't see that happening in this case. I would be more worried about the float switch glitching so whatever is connected to the SSR gets upset... \$\endgroup\$ – Dejvid_no1 Jun 12 '17 at 21:07
  • \$\begingroup\$ You say you'd be worried about the float switch just because it is a potential source of errors or because something inherent in my setup makes you suspicious. Right now it is just turning a pump on and off and works fine so I'm not adding too many complicating factors. \$\endgroup\$ – clifgray Jun 13 '17 at 19:15
  • \$\begingroup\$ Your setup is probably fine. In my "mini FMEA" I see the switch as a potential source of error, but I'm not saying it won't work for a long time. I have no idea of what type of switch you use. But if it is exposed to a harsh environment it could corrode leading to contact issues. \$\endgroup\$ – Dejvid_no1 Jun 13 '17 at 20:09

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