Monday, 11 June 2007

Rewire

Well I got dissed at work today for my two line post over the weekend so I thought I had better post something more substantial even though I don't have much news. I spent most of the weekend rewiring HydraRaptor when I wasn't watching the Formula One Grand Prix.

I got a solid state relay from eBay for £16 to control the vacuum cleaner. I have had reliability problems with SSRs in the past so I went for something with plenty of headroom.



It's rated at 660V 25A with 250A 1200V surge capability. It's completely over the top and I know I could have got something a lot cheaper but it looks impressive.

The vacuum cleaner is rated at 1300W so it can theoretically draw 5.4A although it measures a bit less. This plus the rest of HydraRaptor exceeded the rating of my mains inlet which was 5A. If it was a plain socket I might have chanced it with a small overload but it was a cheap filtered inlet from an old PC PSU so I didn't want to risk it. I had to upgrade to a 10A inlet socket and upgrade the mains lead . I installed a 3 pin outlet socket on the back of the machine for the vacuum and I then had to fuse back down to 3A for the rest of the internal wiring.



I also installed the spindle motor speed controller and a 12V 3A power supply. While it may seem wasteful to have two separate power supplies it does have one big advantage. The main controller and the stepper motors are powered from a 24V 100W PSU. All the heads will be powered from the 12V supply and linked to the main controller with an I²C bus. Both PSUs have floating 0V rails so there will be no motor current flowing down the comms ground between the two controllers. This will allow me to use only single ended 3.3V signals rather than differential or RS232 signals which would normally be needed to combat ground bounce. Here is a block diagram. As you can see there are no signal grounds shared with power grounds and there are only four wires from the main machine to the heads. Once I am able to make PCBs I will shrink the motor controller using surface mount components and mount it on the Z axis together with a similarly shrunk extruder controller.



Here is the current state of the machine, getting ever more complicated :-



Just software now to complete the milling machine and then on to extruder.

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