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SoliForum - 3D Printing Community → XYZ Printing DaVinci → 12 volts but not heating
The resister that acts like a fuse released its magic smoke and so I replaced it with the resister of smallest value I had. That was a 100ohm resister. I soldered it to the mother board and hooked everything up. The extruder was not heating though. I checked it with my meter and found that it was live with 12v. Does anyone know why it is not heating? maybe the amperage is too low?
With a 100 ohm resistor and a 12 volt supply, the current to the heater (extruder or heated bed) is limited by ohms law to 120 mA. This is insufficient to power the heater so it will no work. Additionally the power in the resistor will be as high as 1.44 watts while the resistor is rated for much less. As far reading the 12V, please advise where you checked it. It could be related to the larger resistor value or another issue.
You really need a fuse (for example http://www.mouser.com/Circuit-Protectio … ricing|0). If you use a resistor, it should be the same value that was removed. If the value is too high it could over heat and damage the board. If the value is too low, it could not open when required and cause the trace to open instead.
With a 100 ohm resistor and a 12 volt supply, the current to the heater (extruder or heated bed) is limited by ohms law to 120 mA. This is insufficient to power the heater so it will no work. Additionally the power in the resistor will be as high as 1.44 watts while the resistor is rated for much less. As far reading the 12V, please advise where you checked it. It could be related to the larger resistor value or another issue.
You really need a fuse (for example http://www.mouser.com/Circuit-Protectio … ricing|0). If you use a resistor, it should be the same value that was removed. If the value is too high it could over heat and damage the board. If the value is too low, it could not open when required and cause the trace to open instead.
They do not use fuses in the Dav Vinci printers. Instead they use Zero ohm resistors that will act like a fuse since any short would exceed their wattage rating and cause them to open. Most PCB's in fact these days use Zero Ohm resistors instead of fuses. You usually only find fuses now on the mains input.
The use of a low ohm resistor is is a bad choice for the use of a fuse since the power and time required to clear it will not be consistent. A zero ohm is additionally is a worse choice as they are usually rated in a maximum resistance only with a high tolerance or none specified at all (for example http://www.vishay.com/docs/31017/rcwp99.pdf). Additionally the resistance between manufacturers could vary such that a single manufacturer would need to be specified on the BOM to get a consistent result. As I said before you could end up with a burned PCB near the resistor or have the trace open before the resistor.
I won't argue that this is becoming more common in PCB design. It is more common because a zero ohm resistor is 1 cent and a fuse is at least 50 cents. The choice to use them is cost a cost reduction, not good design practice.
nevertheless, with skilled enough soldering, an fuse could be added without any adverse effect, could it not?
Too low of a fuse rating and you will get nuisance trips (the fuse will open when there is no fault condition), too large and the trace will open instead of the fuse. As long as the average (or "must trip" if available) trip current for the fuse ( http://www.littelfuse.com/~/media/elect … et.pdf.pdf as an example) is lower than the trace fusing current ( http://www.ultracad.com/articles/fusingr.pdf one reference, you can find many) you are fine. With that said, if you size your fuse at 125-200% of the load current you will avoid nuisance trip and burning the trace instead of the fuse. I believe the extruder is around 45 watts so 3.75 amps nominal. Based on this you would want a 5-7.5 amp fuse. You easily could solder on a through hole fuse ( http://www.littelfuse.com/~/media/elect … et.pdf.pdf for example) instead of a surface mount fuse.
That was a lot of research and linking on someone else's behalf!
Evidence of a great community!
Sure enough a shorted the heater wires cleaning the head this morning. Saw a little spark and decoupled.
This thread gave me the steps needed.
http://www.soliforum.com/topic/12398/fu … -extruder/
SoliForum - 3D Printing Community → XYZ Printing DaVinci → 12 volts but not heating
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