Welcome to the SeeMeCNC Community

so reading thru some other forums there seems to be some consensus on adding a resistor to the 5 volt rail of an atx power supply to help it provide better power. I have a Corsair 750 watt atx on my max. but the bed heating times have not reduced themselves much. I have the rev 7 onyx bed and 12 gauge wire from the power supply and to the onyx. I currently do not have a resistor on the 5 volt rail, I did however leave a set of wire 5+ and gnd hanging just in case. I do use a terry towel on the bed to help with heat times.

your thoughts would be appreciated.

Tom C

This might be a stupid question, but I've never heard of anyone using 5V to power the heatbed before... you're not doing that are you? Everyone uses 12V or 24V (Check what your heatbed is rated for).

That is not what he means.

The power supply outputs 5V as well. When something is connected to it, somehow the PSU runs better.


I am not a great fan of "Wasting" the power with a resistor.

Find a bunch of 5V led strips and add those.

(I do not have a corsair power supply)

I do have a corsair power supply. Most modern power supplies do not need a dummy load, when they are functioning properly. My suggestion is to use the 5V rail to power a USB port, and then charge things off it (not wasting the power, and also nice if you want an R pi for octo-print) You can then, if you find you lack random USB gadgets to plug into it, either buy a USB fridge (cold caffeine is critical), or wire up a dummy plug with a resistor wired between the power and ground rails, if you don't have anything more useful for it.

I personally use the 5V rail to drive a PT100 amplifier as well. You could also look into 5V fans to better cool the rambo. If you do use a resistor, make sure it is either rated for the power dissipation, or is cooled. Those buggers can get hot if misused (one of the guys who teaches electronics in the industrial tech department at my college likes blowing components up, and resistors catch fire nicely)

I have found that a load resistor does help the psu put out a bit more voltage and not drop so far when under load.

ok guys thanks I have a 5 watt 12 ohm resistor I can use, that should not draw too much current. I was just gonna zip tie it directly to the fan on top of the power supply. +1 on the 5 volts for something usb. I am planning o octoprint in the future. already have the pi B and the screen ordered.

Tom C