Current resistors 201's

[m8kingit]

I revamped my cnc master's controller, now I'm wondering if i should use the same size limit resistors that they used. When i asked them, what the amperage was on these motors, they told me they were only 5 amp, however i measured the resistance on the resistors that they used and got 236k ohms, which tells me that either the motors are 6 amp or they just screwed up. Can it hurt me to use the same size resistors as they did? I know they're probabling lying, because they also said the drives were not geckos and that they designed them themselves. They are definitely gecko 201's, i opened the case.

My questions are , should i go ahead and use the same size resistors, would I really notice if i used ones for a 5 amp motor instead? Is there a wattage that I should be using with the currentresistors that i choose?

40 volts dc 5-6 amp motrs
thanks in Advance
Mark

[Richards]

The formula is 47 X Amps / (7 - Amps) = Resistor (K), so for the 5A rating, 47 X 5A / (7 - 5A) = 117K. If you use the 6A rating instead, 47 X 6A / (7 - 6A) = 282K.

A 1/4 watt resistor is fine. I use either 1/4W or 1/2W, depending on what I can find in my old-parts box.

If the motor runs too hot, replace the current-limit resistor with one having a lower value.

[m8kingit]

Thanks,but i've already read the formula over and over again. My actual question was that of whether i should go ahead with what was previously used 236k ohm resistors, meaning that these are possibly 6 amp motors and not 5 amp, but then again, would i really notice that much difference?
How does one tell if a motor is running too hot, Gecko states that 185 degrees f is normal?

[CoAMarcus]

Mark,

You will get 83% of the torque at 5A that you would get at 6A. Torque is directly proportional to current. If these are 6A motors and you run them at 5A no harm will be done; if these are 5A motors and run them at 6A you will have overheated and possibly damaged motors. Unless you have a datasheet on the motors I would recommend just running them at the 5A that they were run at successfully before.

Marcus

[m8kingit]

Originally Posted by CoAMarcus Mark, You will get 83% of the torque at 5A that you would get at 6A. Torque is directly proportional to current. If these are 6A motors and you run them at 5A no harm will be done; if these are 5A motors and run them at 6A you will have overheated and possibly damaged motors. Unless you have a datasheet on the motors I would recommend just running them at the 5A that they were run at successfully before. Marcus

Something comes to mind here. i have the formula from someones page from here that i copied and pasted years ago. i was just looking at it and realized that the people at cnc masters must have used this version of the formula to calculate their limit resistance. The fromula was the daem as the one at gecko
s site with the exception of the second part 47 x amps + resostance in k ohms
I measured the resistors on their board and they are exactly 235k ohms. Now if these are 5 amp motors this answer should be divided by 2 giving 117 k ohms.

I found this other page in my pc , I'm not sure who was the editor, but maybe this is a formula used for someone else's drives and cnc masters carried it over. i know their controllers left alot to desire, mine died just running the axis thru their motions, slowly.I'm not going to be stubborrn, I'll go with the 117k ohms when I can find somewhere that sells them. If anyone would like to see the page with the other formula , leaving off the (7-amps) i have it here somewhere.
Thanks for everyone's help
mark