Once the magic smoke comes out, things don't work any more.

John Kasunich
jmkasunich@fastmail.fm
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Sat, 06 Jan 2007

Finalized design of power input section

I've spent far too much time thinking through a wide range of issues related to handling the main power for the spindle and axis motors. Some of the issues I've been struggling with are:

1. Inrush Limiting: The 48V 10A power supply that I'm going to use for the steppers draws over 80 amps peak inrush current as its charging its output capacitor. The DC bus capacitors of the future spindle VFD will draw even more.
2. ESTOP: I want the power to the steppers and spindle to remain off until I bring the machine out of estop, and turn off if I go into estop.
3. EMI/RFI: I've used small VFDs before to run three phase motors on machine tools. They produce an lot of electrical noise. Without filtering, they completely destroy AM radio reception throughout my house (and I suspect in the neighbors houses too). I had to add EMI/RFI filters to those drives, and I will need to filter the input of this system as well.
4. Main Disconnect: I want to be able to flip a single switch to completely power down the machine.
5. Voltage Doubling: Initially the machine will run on 120V AC power. Eventually I want to run a 240V circuit to feed it, so I can get a little more spindle power without worrying about overloading the circuit. But that will come later. The spindle VFD needs a rectified 240V line (about 340V DC) to run the motor to full speed. Until I have a 240V feed, I need a voltage doubler circuit to run on 120V input.

And of course I want to build everything (or as much as I can) with parts that I already have in my well stocked junk boxes. I've spend the last couple of days digging through boxes, collecting parts, staring at them and thinking, digging some more, staring some more, brainstorming with the guys on IRC, etc. I've finally come up with a design I like. I have the parts pretty much laid out, and a suitable piece of aluminum to mount everything on. I've started mounting things, but there isn't much to see yet.

(posted: 06 Jan 2007 23:50) (permalink)