[MrWild]

My idea/goal is to be able to switch a main control and drive enclosure to three different machines with different power requirements. Yes I know, only one machine can be used at a time. Because of the different motors for each CNC device, I designed this to use a dial face on the Pot that goes from 0 to 3.5, with the rest of the range in Red. As has been stated, anything above 3.5k, acts as no resister so that bit of range got red. I checked the Pots and they are fairly precise and linear. Is this a bad idea? Could you explain why it's bad if it is?

I also figured out why I blew the mosfets on the one drive. I put a fuse in the power supply's drive(s) side, then checked the fuse with the power on. I'll direct wire from supply to the drives before powering up next time. John came by and put the wires back on at my direction. Monday we'll quality control and change the fuse for direct connection. (I'm a working quad now.)

I'm sure I know the answer to this, but I'll ask again to be sure. A old six wire 2.5v, 4.6A motor can be used to test the drives. The motor will only have a tape flag on the shaft. There will be reduced power due to the reduced amps which shouldn't matter. The motor will be wired half winding. The power supply is a switched 24v 10A switched supply adjusted to 27v. Is this okay?

Thanks, pictures soon.

[UUU]

Would a three-position rotary switch with fixed-value resistors be better? Easier to use, repeatable results every time.

[Mariss Freimanis]

MrWild,

Connect your potentiometer as a rheostat (pot wiper shorted to CW end of the pot), then wire a 12K resistor across the two-terminal rheostat. Now you have 0 to 3.5K variable resistor.

Doing this does make the setting somewhat non-linear; the scale (percentage of full turn) becomes:

00% of full scale is 0.00Amps
10% of full scale is 0.48Amps
20% of full scale is 0.92Amps
30% of full scale is 1.33Amps
40% of full scale is 1.71Amps
50% of full scale is 2.07Amps
60% of full scale is 2.40Amps
70% of full scale is 2.71Amps
80% of full scale is 3.00Amps
90% of full scale is 3.27Amps
100% of full scale is 3.50Amps

Mariss

[MrWild]

THANK YOU very much. This build has been a real teaching/learning experience. My two visiting home Nurses that come every three weeks, helped build the computer part of the mid tower control box. They had never even seen the inside of a computer so I slowly walked them through it during three visits. For the fourth visit, I showed them the comp working with Linux and Linux CNC. My Aide that comes 1-2 times a week, along with John and Bob all took a turn at placing wires and double checking each other's work. Peggy, my Aide learned to solder. (shhh, don't tell anyone, not in her job) She's a funny one, and does a little dance of triumph when she learns something new and was especially tickled when the X2 ran a program after she helped rewire part of a Hobby CNC drive set up (the new build will be replacing that.) I should have been a school teacher. It's very rewarding patiently walking someone through something like this and watching their amazement when it works.

MrWild,

Connect your potentiometer as a rheostat (pot wiper shorted to CW end of the pot), then wire a 12K resistor across the two-terminal rheostat. Now you have 0 to 3.5K variable resistor.

Doing this does make the setting somewhat non-linear; the scale (percentage of full turn) becomes:

00% of full scale is 0.00Amps
10% of full scale is 0.48Amps
20% of full scale is 0.92Amps
30% of full scale is 1.33Amps
40% of full scale is 1.71Amps
50% of full scale is 2.07Amps
60% of full scale is 2.40Amps
70% of full scale is 2.71Amps
80% of full scale is 3.00Amps
90% of full scale is 3.27Amps
100% of full scale is 3.50Amps

Mariss