Confirming PSU spec for steppers.

[m.marino]

Okay,

I have been reading and talking to folks (Thanks Jazz) on the power supply issue. This is what I understand and what I want to make sure of.

1. Mains power (fused at plug) To
2. Fused Switch (main Switch as will wire in a secondary for the motors) This is feed to a + rail - rail and GND
3. Positive rail Feeds:
   
   1. A Circuit Breaker going to the Switch for the Soft start for the transformer (will be asking on how to build one of those)
   2. The PMDX-126 BOB (Which has built in Circuit Breaker with auto reset)
   3. The on board relay (on the PMDX-126) for the spindle (30A relay) Currently this feeds a Kress 1050 FME. Does this need a Circuit Breaker as well?
   
   
4. Negative Rail Feeds same as listed above.
5. GND includes all of above as well as grounding the shielding on the stepper cables, the computer frames (control box and computer), Machine frame, and the unshielded side of the PMDX board.

Okay that is so far, now onto the power supply that is going to be going in shortly. The way I am looking at setting it up is as follows:

1. From Circuit breaker in number 3.1 to Switch for motor power (both +/- plus GND if that seems best)
2. From there Negative and GND go to the Soft start for the transformer (need help on designing one of these so that I can build it in)
3. Positive goes to a Relay (12V) attached to the PMDX in the set up in NO position so that the motors cannot be powered unless the board has power.
4. From Soft start to 750VA 50+50 Standard Range Toroidal Transformers: CM0750250: 750VA 230v to 2x50v This is to power four 4.2A peak current Nema23 steppers and by what I have read, should meet even heavy running requirements.
   
   1. I am going with the 7.5A 70V in Parallel as that gives my 15A output in theory minus any loss and should more then cover the 12.3A needs to drive the four stepper motors (I recall from Physics that current is on demand and Voltage you get what is there, a 3A item only draws 3A but will take all the Voltage that comes with those 3A).
   
   
5. This is where I am a bit confused. should I put another fuse here between the Transformer and the Rectifier or should I run directly to them?
6. The Rectifier is a 35A 200V Metal casing rectifier and will be mount to a ali' plate to help with heat transfer and I have thermal paste (does the bolt/post need to be isolated?).
7. Next is The Capacitors and I am looking at 5 4700 uF units (23.5 uF to meet a need for 21.4uF)
8. Okay I am looking at this and trying to figure out how to wire in the the resistor to drain off power when the system shuts off. The idea I have is to put a relay in place that is in the NC position with the resistor (50W as they are not expensive and give some added safety margin) set to drain off the power when the switch closes. Now I could power this relay from the PMDX as with the other relay in place the motors should not normally be able to be powered if the board power is off. Other then that I am at a dead end on this one. Also the resistor should go to ground when it is activated correct? Also could use a double check on the Ohms I need for that Wattage.
9. After the Capacitors the power is then run to a common rail from which the fuses (5A) for each Driver is in line with the + and the _ runs back to a common.

If that all makes sense and anyone wishes to help with the Soft start modules and other questions I have posted here in, please do. Also hopefully this will help some other folks with design and structure building. I plan on putting this all on a board and Then mounting on standoffs in the control box. Yes it is bit of over kill but then again I make a part of my living from this machine and it needs to be safe and run well.

For those who want to get a bigger picture of the electronics of this System I am using a AMD based PC running XP Pro SP3, using Mach3, That goes to a Smooth Steeper Ethernet card and then to the PMDX-126. Which then passes the data onto AM882's Digital drivers. This drives 2 motors on X, and one each on Y and Z axis. Spindle is currently a Kress 1050 FME. I have Jazz, James, and a few others to thank for aid in the development of this machine and in the new thread it passed the test you can see a picture of the detail it can do. The reason for the new power supply is that I owe the one I am using back to the person who has so kindly let me use it this long.

Michael

edited to correct a typo