a couple noobie questions

Hi,

I am assembling a Prusa i3 rework and have some noobie questions.

What wire thickness is recommended for the nema17 stepper motors?

What wire thickness is recommended for the heated bed 12Volt power wires
and the 12V hot end heater cartridge wires?

What resistance values should I be getting on my hot end and heated bed thermistors at
room temperature?

To wire the Z axis stepper motors, should I just solder the stepper wires in parallel and then
connect this to the Reprap electronics?

Thanks!!!!

cheers,
Jamie

Jamie,
I could give you a fish, but I think you need to learn to catch one yourself. Ohm's law E=IR is your friend with dc power. That's Voltage = Current x Resistance. Also P=IE. That's power in watts = Current x Voltage for dc power. Reprap power supplies usually are little on the small side, as well as the stepper motors, and drivers. So you don't want to throw away much power in wiring losses. Also all wiring losses become heat, which is bad for the device. So if you use Ohm's law to calculate voltage drop = current in circuit x resistance in ohms for the wire size you pick you'll know how much lower the voltage will be at the device you are powering. If you use Power = the current in the circuit x the voltage drop then you will know how much of precious power you are wasting. I think you'll discover that stepper wires don't need to be very large, while nozzle heater and heated platen wires are just the opposite.

Also a little hint about wiring. WOW! I have seen some real spaghetti here! So in that light a couple of good rules to follow: Do it real neat as you go tying, the wires down properly and cut off the ties as you add wires you forgot. Sounds wasteful but the idea "I'll neaten it all up after I have it working" is complete bull, that can't ever happen! Signal wires of any kind, for switches, sensors etc. should be kept as far from power wires as possible. If you are using shielded cable, which is a really good idea but much more expensive then you should twist the wires to sensors together tightly. Making the twist rate different for each set of twisted cables is also good. That acts as shielding, and is how Ethernet cables work. In any event when crossing signal over power try to do it at right angles. I always try to do panel layouts such that power goes on one side, and all signals go on another. That isn't always possible but still good to try for.

Edited 1 time(s). Last edit at 11/30/2014 02:25PM by garyhlucas.

Quote
jmorken
What wire thickness is recommended for the nema17 stepper motors?

22 ga is typically what steppers will come with. If you have a very long run stepping up to a larger gauge might get you a little but probably isn't necessary.

Quote

What wire thickness is recommended for the heated bed 12Volt power wires and the 12V hot end heater cartridge wires?

Voltage doesn't really matter. Current does. You can use a table like this to see what wire gauge for the current you'll be drawing. Use the chassis wiring column. Most beds will draw 15 amps or less so 18 ga is the minimum. If you want to play it safe, you can go up a gauge or two. For the hot end, less than 4 amps is drawn and 20 ga is usually fine.

Quote

What resistance values should I be getting on my hot end and heated bed thermistors at room temperature?

Depends on what thermistor you're using and what "room temperature" is. Usually a 100 kOhm (but sometimes 10kOhm or rarely something different) thermistor is used. That 100kOhm value means that at T₂₅ (25 degrees C/77 degrees F) the resistance should be 100kOhms. As the temperature goes up, resistance goes down with a NTC (negative temperature coefficient) thermistor so if you're room is warmer than 25 degrees C, then it will measure a little less than 100kOhms, if it's a little cooler than it will measure more.

Quote

To wire the Z axis stepper motors, should I just solder the stepper wires in parallel and then connect this to the Reprap electronics?

Depends if you want torque or velocity. Series wired will have more torque, but at the expense of velocity. The faster you go, the torque will drop off quicker. Parallel wired stepper will have less overall torque than series wired, but the torque will be maintained at a higher velocity. Many wire them in series as the z-axis doesn't usually have the need for high torque at faster speeds. If you're using RAMPS or another electronics that has an extra unused stepper driver, you can have the best of both worlds and use the extra driver for the 2nd motor.