Power supply with multiple voltages

Thread Starter

ClaudioMartins

Joined Sep 23, 2018
4
Hi

The Project:
I am building a system that works with CNC machine centres.
I am adding a 4th and 5th indexing axis to my machines and have succeeded in having the machine control send commands to my board, the motors indexing rotary tables and then the board triggering an input in the machine to let it know it has reached its position.
I have not setup homing and limit switches as of yet but will use the industry standard of 24v switches.

My Issue:
The project requires 48v dc, 24v dc and 5v dc power.

The 48v dc must supply 6-8 amps to 2 motors (288w-384w).
It's not an exact number since the motors are rated for 8 amps each (stepper motors) but will not need full amperage as only 1 will run at a time and never under large loads.

Then I will need 24v dc running to limit switches that in turn run to a reed relay or HF relay (3ms switch time, 140mA draw) to trigger microcontroller pin.
24v is needed since other technicians will be working on systems, need the same standard and reliability as most industrial CNC systems.

Lastly the 5v needed for the circuit board and peripherals (LCD, switches etc. Estimate 2A to have wiggle room for upgrades).

Total current draw with overhead room = 10-11 amps

My Solutions:
I have a few options of doing this..
Option 1 = Multiple transformers where I then rectify and filter voltage, however transformers will make system large, heavy and expensive, especially with higher current draw at 48v.

Option 2 = Switchmode power supply feeding 48v dc @ 10.5 amps (can get them at good price), use linear regulators with monsterous heat sinks to bring down to 24v dc and 5v dc. Currently this is where my experience ends. Linear regulators is what I have used in low voltage regulation in the past. I am aware this particular option will be highly inefficient and believe the regulators will not survive long with so much heat, if they survive at all. Unless I use regulators stepping down slowly ie...37v...24v...12v...5v. Still highly inefficient.

Option 3 = Switchmode power supply feeding 48v dc @ 10.5 amps (can get them at good price), use buck converters to bring down to 24v dc and 5v dc (using LM2576HVT-ADJ/LF03).

Looking for assistance:
- If anyone has any better ideas about this project or comments that might assist me.
- Which option would be best or if there are better options?
- Someone to guide me and teach me, or send me to a resource on how to do the heat calculations for the LM2576HVT-ADJ/LF03 chip. My brain turns to Jelly with all those formula options.

Thank you in advance
Clauds
 

MaxHeadRoom

Joined Jul 18, 2013
28,576
Personally, particularly on CNC applications I try and stay away from SMPS, especially on stepper/servo supplies.
What I would often do is purchase a Toroidal transformer for the higher voltage/current rating and then wind on one or a couple of overwinds.
This is usually very easy to do, you can easily add a 5v regulator, the stepper supply does not need regulation and often the 24vdc does not.
Usually this entails 1.5 to 2 turns/volt for overwind.
Max.
 

MaxHeadRoom

Joined Jul 18, 2013
28,576
It's not an exact number since the motors are rated for 8 amps each (stepper motors) but will not need full amperage as only 1 will run at a time and never under large loads.
Incidentally the current operating demand for steppers is constant from zero to max rpm regardless of load.
Unlike servo's where current varies over its operating rpm and load range.
Max.
 

Thread Starter

ClaudioMartins

Joined Sep 23, 2018
4
Thank you both...

Personally, particularly on CNC applications I try and stay away from SMPS, especially on stepper/servo supplies.
What I would often do is purchase a Toroidal transformer for the higher voltage/current rating and then wind on one or a couple of overwinds.
This is usually very easy to do, you can easily add a 5v regulator, the stepper supply does not need regulation and often the 24vdc does not.
Usually this entails 1.5 to 2 turns/volt for overwind.
Max.
This has certainly intrigued me, I've never thought of that... simple, effective, easy.
If I may ask, why not an SMPS? (unless you are concerned about the return voltage from machine sudden stops?)
I can still get the SMPS cheaper than the toroidal transformer unfortunately... But if there are things I am ignorant about, I would love some guidance and would certainly pay the extra money :)
 

MaxHeadRoom

Joined Jul 18, 2013
28,576
I have found (as others have) when using SMPS for steppers/servo's they can often have a short life, due to the nature of the load. Which makes it a little false economy as they are often hard/impossible to fix.
There is no real need for regulation for drive supplies.
If these are for other than personal use, the reliability factor may come in to it also.
I also believe that Mariss, the owner of Gecko stepper drives comes down on the issue the same way.
If reliability is an issue I would rather pay the little extra, as I have have experienced more failures with SMPS than linear variety.
Antek is a good source of Toroidal power transformers.
Max.
 

Thread Starter

ClaudioMartins

Joined Sep 23, 2018
4
Incidentally the current operating demand for steppers is constant from zero to max rpm regardless of load.
Unlike servo's where current varies over its operating rpm and load range.
Max.
Sorry, I wasn't clear... I would adjust the drivers max amperage given since the steppers would not need full current...
Fully aware that steppers are nothing like AC or DC motors. But thank you for taking the time to point it out :)
 
Top