G250/251 - signal gnd needing resistor-why?

[Chris D]

Hi all,

Perhaps someone can elighten me. I remember reading somewhere that the drives would need a resistor (1k I think) to signal ground. Without it, my steppers sound awful and I seem to get a lot of "noise" at the controller. With the resistors, the steppers are nice and quiet and it appears as though so far I am not having electrical noise problems on the controller side.

I am just wondering what is actually happening with the resistors on the signal ground?

Thanks

Chris

[ger21]

http://www.cnczone.com/forums/showpo...65&postcount=1

[Mariss Freimanis]

OK, post #2 is somewhat misleading.:-) It addresses (my portion) the reason for the 100 Ohm resistors but the post is embedded in a reply from someone who had those very same resistors blow.

Not mentioned is my reply why they blew. The person lost the ground connection to the G251s and all motor supply currents passed thru these resistors. The blew of course (many Amps squared times 100 Ohms is a LOT of heat). The problem resolution was to restore the broken ground wire connection to the drives.

Mariss

[Chris D]

Mariss,

I have not looked at the most recent manuals for the G250/251 as I printed mine out when I bought the drives when they first came out. If you have not added this to the manual, I would highly recommend it.

Without knowing that these resistors are needed, the performance of the drives were very poor, but still functional. If someone doesn't visit this forum to find out the requirement, they are going to have a very poor performing product. Perhaps you already added the resistors on the circuit board in more recent designs?

Chris

[skullworks]

I was the one with the "magic smoke event" and Mariss posted response was spot on as usual.

I had a common binding post for motor power and motor power gnd and had run equal length 18ga wires to each G251. It seems that the sum of all the 18ga wires was too much to get good clamping. I re-did all the power lines in 20ga. and replaced the resistors I had added to the BOB and all worked fine there after.

The 1/4W 100 Ohm resisters do not affect actual drive function - they serve to filter out cross talk on the common signal ground when the drives are idle to keep them silent.

edit: BTW the drives I had were from the first run, I do not know if these resistors are needed on later runs.

I drive them straight off the parallel port using EMC2 and the results have been far beyond my expectations.

[Mariss Freimanis]

The current G251 version (REV9) has a 33 Ohm resistor built in.

Mariss