Primary Objective: Design a power supply to support 3-4 servos/steppers for a CNC machine. Mains 110v or 220v AC single phase, 60 Hz. Need a robust circuit.

Secondary Objective: Option to swap out transformer and fast burn fuse to drive smaller servos/steppers. Misc. components on a CNC machine typically run on 24v DC.

Background: http://campbelldesigns.net/files/power-supply-part-1.pdf

First draft:

Isolation transformer: I question the need for one since the bridge rectifier will 1.4*115vac RMS = 161vDC which is close to 200vdc. However if safety is to be gained, then by all means. Please confirm this is the solution for reducing voltage say to 50 or 100 after the rectifier ie 3:1.

Fast burn fuse (6-15amp as needed for safety)

Fast burn socket

(2) Current Limiting Inrush (slow ramp up when turned on
http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=495-2112-ND

(1) 15 amp bridge rectifier for 15 amp power supply
http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=GBPC1510DI-ND

(4) 1500uf for 15amp power supply (4 smaller are cheaper and better than 1 big cap)
http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=495-4235-ND

(4) Sanyo AC servos, 400w, 3.0amp, AC200v, BL Super P5 P50B07040DXS00M,

Not using Sanyo Driver, for reference only, PYRA030E0
Spec sheet for servo/driver http://www.sanyodenki.biz/products/INSTRUCTIONMANUAL/ACservo/PY2/M0001584J(PY2)-E.pdf

Relay for slow discharge of caps
http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=255-2843-ND (24v power source)

24v Power supply
http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=285-1813-ND

(1) 625k ohm resistor (.25-.5 watt)
http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=PPCHF634KCT-ND

Thanks guys...

 

I don't get why so much voltage supply to a low voltagee load? Have you been there before? What drives the motor from the supply?

 

No I have not, however the servo amp/driver as identifified in the above *.pdf for this servo is capable of 200v at 30amp peak for a single servo. That said, I would very much like someone to approve, or provide an alternate solution so I can move forward on this project. Please help. Thanks!

 

A schematic of how you are connecting all the parts together would help get answers.

 

It's been 20 years since I used pspice and equivalent. My apologies if there is a fatal flaw in this design... please help. Thanks!

 

A - You have the fuse 'in parallel' with the transformer. This needs to be in series so that you the fuse will function.

B- You have the bleeder resistor 'in series' with the cap. To provide bleeding path for the cap in needs to go to ground from the line to the relay.

 

on a second look, perhaps the fuse is workable this way. I'm not used to the way it was drawn. The current limiting resistor however will ALWAYS be limiting current in this way of connecting it. It should be redone so the current limit resistor is only in circuit for a short period then is bypassed. Usually this is done with a relay.

 

Thanks Kermit2:

1) Can you provide an example of the current limit circuit so I can implement?
2) Your responce on the bleed resistor has me confused. When the switch is opened, the relay closes and the cap slowly drains. One side of the cap is already tied to ground...

However, I am still curious if the transformer adds any safety to the circuit?

 

Using a transformer provides isolation. The rules of this forum do not allow the discussion of transformer-less circuits, which are considered too unsafe.

I note that your 24V transformer is shown with no rectifier. The symbol you use is for a transformer which would have an AC output, and so would not work with a DC relay.

 

Thanks Adjuster! I have heard conflicting converstations regarding the isolation transformer. As for the 24vdc power supply, I did not know what the correct diagram was so attempted to add comments to communicate its purpose.

 

this will implement 'momentary switch' on and off. Just to be clear you only need one off switch but can place it at either location shown by an 'x'.


For the bleeder you do not need a relay, a simple 1Meg to ground from the positive cap connection is all you need. It will always leak current when the circuit is on,but will be a very small current and so it is nothing to concern yourself with. When turned off it will drain the cap in a few minutes.

 

Any more suggestions? Thanks!

 

I made a mistake in the previous drawing with the positioning of the 'off' switch. It had a parallel path around the switch through the resistor. This drawing updates it and the previous version should not be used if the off switch is needed.

Also, your fuse has the same problem as my off switch did. Where it is currently placed there is a parallel path around it, so it will not blow as you expect under overload conditions.

 

Is this correct?

 

I think it is correct so far. What next?