Need some help getting my I3 powered up

Hi guys,

I have just finished assembling my Prusa i3 (type= Prusa research? Anyway, the one with the orange 3D printed parts). Upon preheating for the first time, I noticed that the extruder got VERY hot, exceeding the max temperature. After a while, I discovered that the person working on it before had misconnected the two PSU cables with the extruder and bed heater connections.This caused the extruder heater to keep on heating up past the max limit. Weird thing is that the PSU did power the arduino and the LCD.

After that I switched the extruder and bed heater cables to their right connector, just like the PSU cables to their correct connector. My problem is: The PSU is now unable to power the Arduino and the LCD. Literally nothing happens when I turn on the PSU. But when I connect the PSU to the wrong connectors again (the ones of the extruder and bed heater), the arduino DOES get power. And also when I connect the extruder and bed heater to the PSU connectors, the extruder starts to heat up rapidly again. Just like in the innitial situation.

Does anyone know what's up? Did I mess up the PSU ports and are they now unable to power the arduino? Can I swap the ports in the firmware so that the PSU ports will power the heaters and the extruder and bed heater ports power the Arduino? I would really appreciate all the help I can get.


-Garvin



Ps. I attached an image to explain my problem a little better. The red text is the wrong, innitial, situation where the cables where misconnected. The black text is the situation in where the cables are correctly connected but where the Arduino is not getting power

The correct pin out is in the schematic below:



Check if the fuses are still ok, that there's power on all the PSU wires. If you use a single PSU you can connect the +12V to connector B+ and A+ and ground to B- and A-. I'm not sure why you would swap the PSU input wires, unless you've got a 12V and 24V PSU.
Check if there's a short in the extruder heater. If it's shorted the arduino doesn't get any power, but the hot end should heat up. The heater cartridge, 12V at 40W should be around 3-4 Ohms. Current is 40/12 = 3.3333 A, resistance = U/I = 12/3.3333 = 3.6 Ohms.

Edited 1 time(s). Last edit at 10/07/2015 12:29PM by imqqmi.

You're great help, thanks! I'll try to figure out how I'm gonna test wat you said, as I'm a noob with electronics.

I'd get a digital voltmeter (DVM) like this one (although there are cheaper options than this one).

Use the resistance setting at the lowest Ohm range (indicated by the greek omega symbol). Usually this is the 200 Ohm range, sometimes also combined with a buzzer to test connections or shorts. 0 Ohm means short circuit. Not all DVMs are accurate and meter a couple of ohms while it's shorted. You can take out the fuse, put the DVM clamps on both ends and see what it measures. If it's very close to 0 ohm, it's good.
Testing the heater cartridge, measure it while it's disconnected from the board, put the clamps on the wires and see what it meters. Around 3-4Ohms should be good. Below 3 ohms you can consider it's shorted out and needs to be replaced, above 4 ohms is also not good, replace it with a new one.

To check the voltage, put the meter in V mode, some DVMs allow you to set the range, usually for metering 12V you need to set it to 20V. Put the clamps on the PSU and see what it meters, if within 11.5-12.5V is ok, too low is probably not good, you'll need to check if you can adjust the PSU. Some have a potmeter to adjust the voltage, it usually is indicated with Vadj. Remove the PSU from the board before adjusting the Vadj and only connect the DVM.
Don't put the DVM in amperage mode (A) when connected to the PSU with a wire on each clamp as it will basically short the PSU and the fuse in the DVM will burn out. You should meter voltage in parallel to the device and amperage in series. Youtube has a huge amount of electronics basics.

If you need more help, let me know!

Alright, so replacing the fuses fixed my problem. Thank you very much for the help!

Edited 2 time(s). Last edit at 10/08/2015 08:02AM by Garvinroelans.

Well done! Glad to help