Newbie question,

I converted a CNC bridgeport to Mach and installed dudong servo drives, the mill has been up and running for 6 or 7 months with no issues, until yesterday, when the Z axis over shot the upper limit switch and it seems to have cooked a servo drive.

I tried a search for servo drive and fuses and have found very little information.

Anyone have a suggestion as to how large a fuse to use, the servos are 120volt DC brush type 25 amp max draw.
The drives are good for 160 volts and 35 amps.

Do you fuse for the max motor or the drive and do you use fast acting or slow blow fuses.

Thank you for any help with this
Ted

I don't think you can fuse servos as such if you open the connection you may blow the servo anyway.

Most servo drives have auto load limiting built in to protect them.

Mach3 seems to have problems with limits sometimes I have a Boss BP as well. I ended up using the first limit (Zup) as a limit and the second limit switch as a safety that is NOT controlled from MACH3 . IF it overruns the first limit then it trips the drive offline with the hitting of the second switch.

IF it overuns the upper limit at speed it will severly JAM the quill into the housing AND can cuase damage to the quill assy.  Then you have to take the covers off the drive and manually unscrew the quill IF it is not stuck to tightly.

Been there done that a few times BEFORE going to the safety switch. Overrun limits YES, Stuck or damaged quill NO (;-).

Just a thought, (;-) TP

Thank you for the reply,

Any chance you have a wiring sketch of how you are using the second limit switch.
Are you interupting the power to the drive or the servo...?

That sounds to me to be a very good safety idea, this is the second time the mill has not stopped on the limit switch and I'd really like to stop it from doing it again.

Thank you,
Ted

I just put the upper switch inline of the Drive enable line from Mach3 to the Z servo drive. So if the switch opens it shuts down the drive before damage can occur. I also have a manual bypass button install to be able to back the Z axis off the switch.

IF it fails the drive stops. You then push the bypass button and jog back off the switch.

(;-) TP

Thank you, very cool idea and it will save me some grief down the road.

Thanks again,
Ted