G201 resistor confussion why would a 5.5 amp vary so much over 6 amp

[journeyonline]

I have 3 g201 controls. I upgraded my motors and wanted to go with the square type vs the older round I had. All my axis have the newer square 640oz nema 34 stepper motors set to 6amp with 270k resistor. If I use the settings that my motors recommend 5.5 amp or 173k - I used 180k resistors the motors have no power, but with the 270k they have lots of power.

What is going on here?

[Mariss Freimanis]

Set your multimeter to Ohms and measure the resistors. I'm betting your 180K resistor may be an 18K resistor.

You can also set your meter to DC Volts and measure the voltage across the resistor while the drive is running. Then:

180K = Brown, Grey, Yellow, Gold and measures 13.5VDC across when in the drive
18K = Brown, Grey, Orange, Gold and measures 4.7VDC across when in the drive

Mariss

[journeyonline]

I messured the resistors and sure enough they tested at 180, and other ones at 270 so I double checked the Radio shack multipack they came from and found they don't include a 18k resistor in the pack. So I'm not really sure what is happening, but the 270k resistor works fine with the 640 oz motors.

All 4 resistors at 180k had this issue.

http://www.radioshack.com/product/in...ductId=2062303

[posix]

they don't include a 180k EITHER! it's a 180 you're putting on there, not 180k silly!

[posix]

take one 56k and one 120k and connect them in series to your g201. that's untill you've sorted out your radioshack purchase

[journeyonline]

I will give that a try,
Thank-you

[journeyonline]

Ok, that is it, the resistor is a 180 not a 180k. I have checked my meter and sure enough it has a small k on the 270k resistor but not the 180 resistor. Thanks for the help and education.

My next question is what will happen if I run the motors at 6 amps vs the 5.5 amps it is rated for? I have been running one of the motors this way for about about 6 monthes. This is a nema 34 640 oz motor.

[Mariss Freimanis]

journeyonline,

That is a mousetrap that has snagged many victims and you are this week's poster boy.:-) It's why I urge everyone to never take for granted a resistor is what the package says; always verify a resistor with an Ohmmeter. 5 seconds of quality multimeter time can save 5 days of hair-pulling. "Never trust anything" is a good mindset.

6A into a 5.5A motor shouldn't have much negative effect particularly if the motor has a square cross-section (it's not round). Compare the squares of the current: 6^2 is 36, 5.5^2 is 30.25. The ratio is 36 / 30.5 or 1:1.19 so your motor is running 19% hotter than it should which is not a big deal in the greater scheme of things. I wouldn't worry about it.

If it's a round motor, I'd back it off to the rated 5.5A. Round motors enter magnetic saturation much earlier than square motors when over-currented.

Mariss

[diycnc]

http://www.dannyg.com/examples/res2/resistor.htm

plenty of online calculators out there if you don't know the color codes.

[Mariss Freimanis]

diycnc,

Good advice except for the "Orange" band can look a lot like the "Red" band on many resistors (orangish-red looks a lot like reddish-orange). Color codes are good and should be memorized by anyone who expects to work with electronic components. Having said that, an Ohmmeter is the Gold Standard. If your meter says "10K" then by gosh it is a 10K resistor no matter what the bands say. On rare occasion I have seen miss-marked bands. More often I have seen the package text be at odds with the resistor color bands inside the package. Never trust, verify.

We even do this with surface-mount resistor reels. Spill a few chip resistors from the reel, measure a few. A few very rare times a reel has been miss-marked. The few seconds measuring has saved us 21 hours (15 seconds to remove and replace 5,000 wrong parts) removing and replacing a reel's worth of 5,000 wrong resistors or capacitors on each occasion. I just can't stress it enough; don't trust, verify.

Mariss

Mariss

[diycnc]

agreed i usually start with the bands then check with the meter.

[TOTALLYRC]

Originally Posted by diycnc agreed i usually start with the bands then check with the meter.

I normally start and finish with the meter since I don't know the color codes.
The other thing instead of trying to figure out what tolerance the bands signify, on the last project I did, I measured all of the resistors in my box of parts in advance. When I had to use multiples, I used the meter to verify the actual resistance.

Mike