Once the magic smoke comes out, things don't work any more.
John Kasunich
jmkasunich@fastmail.fm
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Wed, 14 Feb 2007
Slow but steady progress on electronics box
Over the last few weeks I've made some progress on several of the subassemblies that go in the electronics box.
The 48V 10A power supply for the steppers originally didn't have any terminal blocks of any kind. Input power was to be soldered directly to the transformer termainals, and output power taken from the cap screws. I re-arranged the bridge rectifier and cap a little to make room for a short terminal strip. I also added a totally unneccessary heatsink for the diode bridge - its an old Pentium I sink that was laying around taking up space.
Although the enclosure seems big, it will fill up fast. So I wanted to avoid taking up a lot of panel space with the Gecko drives. Fortunately I found a nice heatsink that was part of a "bookshelf" drive (tall, narrow, and deep form factor). I drilled and tapped it for four Gecko drives, even though I only have three at the moment. I might want to add a rotary table in the future, and I don't want to have to remove the existing Geckos (or risk getting metal chips in them). Mounting the drives reminded me once again how much I hate heat sink grease - the stuff manages to get everywhere.
Other assemblies that go into the box include the cooling air blower and the input power assembly, as well as the PC. With the exception of the PC, I have everything mounted now.
In the top left are two contactors that will be used to connect either the lathe spindle motor or the mill spindle motor to the spindle VFD. They're not mounted yet, and won't be for a while. Just below them is the 48V power supply, and below that against the left wall is the heatsink with the Gecko G202 stepper drives. On the bottom you can see the plate that holds the cooling air blower. When the door is closed, the opening in the front will be blocked. Some of the air will go to the left, then up between the left sidewall of the cabinet and the fins of the Gecko heatsink. The rest will go to the right, and cool the PC (which will be in the big empty space).
At the top right is the input power assembly, with disconnect switch, fuses, and estop relays. The green item in the top center is the base of the future spindle VFD. Because I'm using permanent magnet AC servo-motors, an ordinary VFD won't work. I could hunt for a large servodrive on ebay, but I earn my living designing motor drives, and I plan to build the spindle drive using bits and pieces from my junk box, along with the Mesa 5i20 board FPGA, and software in the PC. The green "base" assembly is part of a scrapped standard VFD, and includes the fan, heatsink, and not much else. The PC board attached to it is soldered to the top of a 75A 1200V IGBT six-pack module. I still have to come up with gate drive and current sensing, as well as a DC bus capacitor. The entire VFD project is something for the future - initially I will use the two contactors to switch single phase 120VAC to the existing (crappy) single phase spindle motors.
(posted: 14 Feb 2007 01:59) (permalink)