Mini Rambo 1.3a board input power  

RE:

It took me a bit to find the schematic, but it appears that while the voltage signal for the fans appears to be named "12V4", the actual voltage is dependent on the voltage that you supply the board with. The only thing between the start of the "12V4" signal and the "Primary" power input connector is an inductor filter (designed as a pi filter, but the capacitors appear to not be installed according to the schematic), a couple fuses, and TVS diode for ESD and reverse voltage protection. So, if you are powering the Mini Rambo with a single 24V power supply, there will be 24V on the "12V4" signal (and all the "12V..." signals).

[RANT] It would have been nice if the UltiMachine engineers actually put a text block in the power supply section of the schematic stating the designed voltage range for the power input... Based on the TVS diodes, 30V appears to be the max designed voltage at the "Primary" input voltage connector. [/RANT]

The bed heater output (voltage signal "12V3") appears to be separate and isolated from the rest of the board power. The reverse voltage diode for "12V3" appears to have a reverse voltage breakdown of 50V, so keep your bed voltage below that.

The hotend heater output (voltage signal "12V2") is the same as "12V4", so should be the same as what is connected to the "Primary" power input connector. In your case, it should be 24V.

Note, technically you asked for power output, and I only gave voltage output so far. To calculate power (watts since we are in DC land, AC would be volt-amps), simply multiply the voltage at the output you are interested in by the minimum fuse rating. (When designing the board one should take into account the amperage rating of everything, but when taking an existing and proven design the fuses should be lower amperage rating than anything else on the circuit so we can take a shortcut and only pay attention to the fuse ratings.)

The lowest value fuse for the fans is the one between "12V2" and "12v4" which is 0.75A, so the maximum power to the fans is 18W at your 24V input voltage. I think the fans are the only thing on the "12V4" signal, so that 18W capacity is shared between the two fan outputs.

The lowest value fuse (only fuse) for the extruder ("12V2") is 5A, so that power would be 120W at your 24V input voltage. But, this is only partially true. Because the "12V2" voltage is the source for everything except the motors and the bed heater, you need to subtract the power being used by the CPU (Atmega 2560), the USB driver (Atmega 32u2), thermistors, motor driver logic, and how much power the fans are actually using (I doubt you are pulling a full 18W from the fans at all times) from that 120W.

The lowest value fuse (only fuse) for the bed heater ("12V3") is 15A, so max power would be 360W at your 24V input voltage.

I may have forgotten a couple things, I'm only an Electronics Technician by training (Associates degree in Electronic Engineering Technology), not a full EE (no BS, MS, or PhD).

RE: Mini Rambo 1.3a board input power

What a nice concise reply.  Thank you. 

I have had the Mini Rambo 1.3a lying around since I got an Einsy Rambo board to upgrade my Prusa.  I am planning on using the Mini Rambo in a printer build, but wasn't sure about the output voltages when using a 24v power supply.  I had seen the schematics before and I was confused about the 12v... signals for those outputs.

Basically I am building a MK2.5S clone but using 24v components for the bed heater and hotend heater.  The upgrade for an MK2.5S has a 5v hotend fan that uses the power from an endstop connection and the the signal from its fan connection.  I have the y cable for that purpose.

I want to also use a 5v part cooling fan (like an Mk3S has) by using another y cable to the endstop connection to power it and to its signal pin on the original fan connector.  

Would that be feasible?