# Thread: Help with current set resistor math

1. ## Help with current set resistor math

Trying to finish wiring my router. Using gecko 202's with these motors. Wiring will be bipolar parallel. I need help in finding a current set resistor.

From what I read in the gecko manual the following formula applies:

R = 47 * I / (7 - I) so for the motors mentioned above I would have:

R = 47 * 6.3 / (7 - 6.3) or 423000. Now what does this number mean and where can I get a resistor this size?

Thank you

2. Might want to check your math.

If your numbers are as written, and a "K" suffix is NOT there, you should get 423, not 423000.

BTW, I don't have a Gecko manual and merely recalc'd your math. Thus, if the resistance was expressed in thousands of ohms (K ohms) you probably need to say so to avoid confusion to us non-manual challenged responders.

If K is not there, it is 423 ohms or something reasonably close. If "K" suffix was there and you left it out, it is 423K ohms.

You can use resistors in series or parallel to get the EXACT 423 or 423K ohm value you want. Any electronics handbook will explain how to do series or parallel resistor summing problems.

3. I have a geko controller. How I understand it, is the resistors on the geko set the max currrent which the controller will supply to the stepper motor. The way to determine the current the motor will use is to consult the spec sheet. I had a look at the link you provided from what I can tell the max current that motor can draw is 6.3 amps. I can't tell how you are going to wire them so you will need to sort that out then depending on how you set the motors up you can determine which resistor to use on the geko.

4. WOW I need to learn to read. The max current the motors will draw is 6.3 amps this mean s according to your formula you need a 423 ohm resistor. If you use a 470 ohm resistor which is easy to find your current will be 6.363 amps. If you use a 430 ohm resistor your current will be 5.82 amps. Resistors are commonly +/- 5% of the listed value so more than likley you wont get the exact current you calculated for. In the final analysis I'm not sure how fussy stepper motors are but a little lower current will probably be a better thing. Stepper motors get hot and less current means a little less heat. I hope this helps good luck.

5. ## Confused

I am still confused. Do I need 423 Ohm resistors of 423 k Ohm resitors for the motors listed above?

Dan

6. 423K is the correct answer. Use the nearest standard 10% value, 470K.

Mariss

7. Based upon YOUR posted formula solved with YOUR numbers, 423 ohms.

Did you put in the values correctly???

As in: did you put in AMPS or should it have been MILLIAMPS??? Afterall, the difference is only a factor of 1000.

As in: did you put in resistance in OHMS or should it have been OHM Values in K ohms???

Again, the difference is only a factor of 1000.

Again, didn't go to Gecko to research the formula and input units required for same. But the math for the numbers and equation posted definitely works out to 423 ohms....

8. Originally Posted by NC Cams

As in: did you put in resistance in OHMS or should it have been OHM Values in K ohms???
Yes. And if you didn't know, Mariss IS Gecko.

9. Yes, I didn't know who really was "Gecko"

My prior post #7 was to post #5, not post #6

10. Im watching this thread with some interest.
Using the formula supplied and the spec sheet of the motor supplied by you the value of the resistor is in the hundreds, no K suffix. Eletronics can be a bit intimidating to be sure. But using the info supplied by you and looking at my own geko instructions go with the values of resistors in the hundreds ( no K suffix)
Your motor will draw 6.3 Amps max which is equivalent to 6300 milli amps. Make sure you have the numbers in the formula exactly as provided in the geko manual. Ignore the milli amps and use 6.3 Amps as your current figure. Induction motors (such as steppers ) are fairly forgiving so get the current as close to 6.3 amps as you can with available values of resistors. Unless you are super picky you should be ok.

tc spooner