EDIT: my appoligies for posting this in here. This one prolly must go to "General Electronics Discussion" board. My bad. *end EDIT
My power supply unit from a printer has 25V and 5V.
I am using the 25V and the OS discrete one axis driver.
My stepper has the folowing specs: 5.2V/Phase 1.4A/Phase. Supposedly the coil resistance should be 5.2/1.4=3.71, I have measured a1 to a2 and have a reading of 8 Ohms, but maybe it does not matter.
Then calculating the power resistor value
(25-5.2)/1.4= 14.14 Ohm
Calculating wattage
1.4*1.4*14.14=27.71 Watts
So I need a 14.14 Ohm resistor with wattage of 27.71 min. Looks like pretty high wattage requirements.
Now comes the part which I fail to grasp yet.
Some power resistors available from Newark
# 01F9907 50W
# 02F2439 10W
# 01F9753 20W
all 7 Ohm resistors. I cannot find 14 Ohm resistor.
If I put a pair of 7 Ohm resistors in series then I get 14 Ohm resistor but what will be their wattage?
If I use 7 Ohm 10W in series with 7Ohm 20W wil I get a 14 Ohm 30W resistor? I am talking loko here?
Wattage is amout of heat dissipated in the resistor, right? It does not add up if I serie the resistors, of gets lower if I parallel the resistors.
I need 27Watts minimmum. If I use a 30W resistor and my motor ratings are 1.4A/Phase
1.4*1.4*X=30W
1.96*X=30W
X=15.03 Ohm
My motor will draw its current rating 1.4A per phase. If I use a 15 Ohm resistor 30W then the voltage in the stepper will be
(25-X)/1.4=15 Ohm
25-X=15*1.4
25-X=21
25-21=X
X=4 Volt.
And my stepper will be operating under its specfications.
How can I use my stepper at full specs, current limiting resistors are puzzling me.
Using this calculator "2 Resistors in Parallel - Calculate One Resistor from Other and Total" from http://www.electronics2000.co.uk/ I input Total R= 14.14 Ohm and R1=30 Ohm so it computes R2=26.74 Ohm
But resistors come in different increments so it is difficult to me compute the resistors values to use my stepper at its full ratings.
Help anybody.
Konstantin.