Originally posted by thuffner3
Imformation overload, Homebrew CNC
(Post #1 )
I downloaded the resistor calculator. If my controller has "FETS"
my motors require 5.00 ohm /7.2 watt resistors.
If my controller has resistors. my motors require 4.25 ohm/6.12 watt resistors.
FETS and RESISTORS are alien to me. as are the watts for the motor power resistors.
Can I find the required power riesistors given the info above?
And do I have a decent setup for a homebrew system?
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I think you mean FETs and Transistors, not resistors. Both of them are semiconductors designed to control the flow of electrical current. FETs do that using a low voltage, and Transistors (or TRNs, is the same) use a low current. The way both of them are used in Stepper control is like a valve, full ON or full OFF creating square waves of electrical current that when enter the stepper 'makes' the steps.
The resistors needed are a way to limit the current that you push to the motor (remember, the 'valves' are full ON or OFF). Think of them as a 'pipe' that limits the flow but is not capable of cut it.
Because the different technologies that FETs and TRNs uses, the resistor is different in both cases. A resistor has two main parameters, resistance (the diameter of the pipe) and wattage (the pressure the pipe is able to resist). Resistance is a parameter that must be as close as possible to the desired, and wattage is a parameter that must be equal or higher than desired. With your calculations, you need:
In case of FETs: resistors as close as possible to 5 ohms, and 'at least' 7'2 watts, so you can use 5 ohms 10 Watts, or 5 ohms 25 Watts, for example.
In case of TRN's: 4'25 ohms and at least 6'12 watts, so you can use 4'25 ohms and 10 or 15 or 25 watts.
In order to locate the power resistors, you can go to radioshack or similar where you buy electronic components. Or ask to a TV repairer or similar person where to go in your neighborhood. Be sure to buy the closest value of resistance and a value of wattage equal or higher.
To know if you are using FETs or TRNs, from the link you have posted I've read the manual of the controller and there is no info about it, so the best way is to see the reference number in them (look at the front of the dispositives that are 4 in a row, these are the FETs or TRNs). Put that reference number in google, and the answers will say 'FET bla bla bla' or 'Transistor bla bla bla'. That's the easy way.
Hope it helps..
/U