R23, R24, R25 - 1.8K resistor

Hi Guys,

For the resistors R23, R24, R25 on RAMPS v1.4, there is a note mentioning that the PCB is labelled 1K, but 1.8K can be used to accommodate higher voltages. What would the effect of using 1.5K resistors be? Do these resistors relate to the heating?

Thanks,
Chris.

Those are the current limiting resistors for the LEDs, which are run from the 12V supply voltage. If you choose to run with a higher voltage than that - the board can take up to 35V with a little modification -you need to choose a replacement that will keep the LEDs from burning out. Get it too low and the LEDS fry, get it too high and the LEDs are dim or don't light at all. This is non-critical, even if you destroy the LED it won't affect anything else, you just won't get a visual indication that the output is on.

1.5K resistor would be fine at 12 v - just a bit less current and a slightly dimmer light.

1K at 12 v, minus the approx 2v LED forward voltage means 10 mA though the LED. 1.5K would give 6.7 mA

Your average small LEDS can handle 20 to 30 mA max, so .the resistance value is chosen large enough as Andrew points out to avoid exceeding that, while small enough to give usable brightness. 6-10 mA will give usable light.

You're hardly ever going to be looking at these LEDS, so a bit dimmer isn't going to hurt.

Awesome. Thanks.

The show can go on!

Cheers,
Chris.