Thursday, October 3, 2019

Alternative to Fuses in Low Power Electronics

The controller box for the CNC mill keeps blowing fuses.  After replacing the Y axis fuse AGAIN, I suspected the stepper motor on the Y axis.  When I measure resistance across the eight terminals on the X, Y, and Z motors, I get suspicious that the motor most recently blowing fuses has some internal short.

 X and Z motors show 1.7-1.8 ohms across pins 1 and 2, and 3.5 ohms across pins 1 and 3.  Y motor shows .6 ohms across 1 and 2, and 2.1 across pins 1 and 3.  This discrepancy makes me suspect the motor, especially because hooking up the working X motor's cable to the Y motor causes no motion.

A circuit breaker instead of a fuse would seem a better choice; something that does require disassembly and the very tedious and fine dexterity to replace this tiny fuse.  Are there such devices that might be an aftermarket replacement?  It seems to be labeled 3A LE, two leads, which bend very readily when trying to put them into the socket.

At least I can use it as a manual mill while waiting for technical support.

Things That I Have Forgotten Since I Last Used a Sherline Mill Manually

How tedious it is to use a mill just tall enough that you cannot change Z from a seated position and standing makes X and Y hard to reach.

That face milling aluminum is very limited.  In CNC mode, I face mill .001" at a slice.  Edge milling works much better.

That the drill press mill that I squared and trued to use in place of the very precise and small Sherline mill gets pulled loose from its clamps with any significant vibration,  Not an issue at .001" slices.

That I really do need to drill holes through this conference table to bolt the mill down.

Rebooting PC fixed it.


  1. That is a VERY fast acting fuse. A circuit breaker will not blow nearly as fast. Like 100 times slower.

    Using a breaker may well cause damage to your drivers if there is a short. The fuse blows faster than the driver can be damaged by the overcurrent.

    I'd fix the motor. But that is just me.

  2. Circuits with motors require slow reacting fuses. The same ampere rating, but slower reacting. Motors are seen electrically as an initial short, the winding offer no initial resistance. Inductive impedance is a product of current flow. Lord knows I have forgotten how to read a fuse's ratings.