Current set resistor

[tooManyHobbies]

Originally Posted by kawazuki I believe I can get 3.48k ohm from RS here in the UK with 0.125w rating. I guess the resistance is ok - what about the rating? Will this be sufficient for a current set device? RS will happily sell in 10's and then only cost pennies / cents - as you say don't really need 999 spares !

http://search.digikey.com/scripts/Dk...me=3.48KXBK-ND

Min order quantity is 5 for a total price of 0.38 GPD.

A search for 3.5K finds some, but they are over 1 GPD in one's.

tauntdesigns: What makes you think that Mouser & Digikey have min order of 1000 pcs? Most, if not all, parts are available in low & high quantities.

Tom

[tauntdesigns]

I haven't looked in a while, but.............. When I was, the size I was looking for, I was having trouble finding in small qtys. Not all parts...... just the sizes I was looking for.

Cheers,
Jack

[m8kingit]

First of all I'm changing out my board on the cnc masters jr mill. After hearing about everyone's problem then experiencing a couple of my own.
The motors ahve no marking, so the best i can do is trust what Omar at cnc masters has told me, he said they are 5 amp. The best i can do is measure what resistors they used for the current set resistors.
So'm trying to calculate the current set resistor for my 201 geckos. I had someone else tell me that you just multiply the amperage by 47, but somehow that doesn't look right. According to the gecko site they say 47 x amperage divded by 7- amperage . I'm guessing that my motors are 5 amp on my cnc masters, but I measure 235 amp resistors on their board. I've decide to use mach3, so i'm trying to wire the g-11g and eliminate cnc masters mis engineered problems.

Any help is greatly appreciated!
Thanks
Mark

[johnt]

OK, I'm reading all this about the current set resistor, I'm still confused but I' probably not the only one.
My motors are 5.5 amps/phase
gecko says use 120 k resistor for a 5 amp motor and 270k for 6 amp motor.

LOTS of questions here:
1.Do i find one between those values or go with the 120k?
2.Does a lower value give more protection? I don't know if "protection" is even the right word, so I'll use "happy"... is the motor and/or drive "happier" with the lower value?
3.On that point, what IS the purpose of the current set resistor? FOr the health of the motor or drive?
4. Is a current set resistor different from other resistors? The kid at my local electronics store looked at me like I was from Mars when I asked him about it.
Thanks,
John

[chester1957]

Originally Posted by johnt OK, I'm reading all this about the current set resistor, I'm still confused but I' probably not the only one. My motors are 5.5 amps/phase gecko says use 120 k resistor for a 5 amp motor and 270k for 6 amp motor. LOTS of questions here: 1.Do i find one between those values or go with the 120k? 2.Does a lower value give more protection? I don't know if "protection" is even the right word, so I'll use "happy"... is the motor and/or drive "happier" with the lower value? 3.On that point, what IS the purpose of the current set resistor? FOr the health of the motor or drive? 4. Is a current set resistor different from other resistors? The kid at my local electronics store looked at me like I was from Mars when I asked him about it. Thanks, John

1. In a perfect world you would want 195k, so the closer you can get the more amps available to the motors.
2. The motor, the drives will only pass 7amps (the more amp run thru the drive the more critical heatsinking becomes) your motors won't like 7amps.
3. The current set resistor limits the number of amps that the drive will allow to reach the motors.
4. Gecko's use a resistor to limit the current to the motors, not all drives use this method, hence the term "current set resistor". It's just a plain old Radioshack resistor.

[johnt]

Chester, thank you, thank you, thank you!
A concise, plain english answer to all my questions.