First Proper CNC Router

**diycnc** · 31-10-2019

Dont have a PSU to hand, so looking to put together a simple 70vac transformer, but im struggling to find a suitable toroidal transformer.
Only 230v to 70v transformers I have found so far are max 500va, which im not sure is sufficient for 3-4 motors. The current design is 3, but want to leave room for a 4th if i choose to upgrade later
https://www.rapidonline.com/vigortro...-x-35v-88-0007

**Clive S** · 31-10-2019

Originally Posted by diycnc

Dont have a PSU to hand, so looking to put together a simple 70vac transformer, but im struggling to find a suitable toroidal transformer.
Only 230v to 70v transformers I have found so far are max 500va, which im not sure is sufficient for 3-4 motors. The current design is 3, but want to leave room for a 4th if i choose to upgrade later
https://www.rapidonline.com/vigortro...-x-35v-88-0007

This company will make any voltage you want for you. https://airlinktransformers.com/cate...standard-range

I use a 500V a toroidal with 4 nema 23 on 2 different machines with out problems. The next size up generally is 625Va

**aprex** · 01-11-2019

Mine went from TME. Quick sending and good prices.

https://www.tme.eu/fr/katalog/transf...100028/?page=1

Best regards

**diycnc** · 01-11-2019

I think i need to check my PSU calcs. Can someone point me towards some example PSU design calcs?
Also, any idea if there is any benefit of AC vs DC?

**JAZZCNC** · 02-11-2019

Originally Posted by diycnc

I think i need to check my PSU calcs. Can someone point me towards some example PSU design calcs?
Also, any idea if there is any benefit of AC vs DC?

There is absolutely no difference. I've built loads machines using both and see no performance or reliability differences between AC or DC.
The AC is simpler for obvious reasons so my suggestion is go with AC.

Also, 525Va transformer will do what you need. 625Va will give you a bit more overhead, which you won't need, but does increase inrush and that could give you issues with MCB trips. However easily solved with D rated MCB.

**diycnc** · 02-11-2019

Thanks JAZZCNC. Will go with AC.

Only 70v toroidal transformer I can find is 500va, which I think should be plenty.
https://www.rapidonline.com/vigortro...-x-35v-88-0007

What size MCB would you recommend?

**Clive S** · 02-11-2019

Originally Posted by diycnc

Thanks JAZZCNC. Will go with AC.

Only 70v toroidal transformer I can find is 500va, which I think should be plenty.
https://www.rapidonline.com/vigortro...-x-35v-88-0007

What size MCB would you recommend?

I pointed you to one in post #47

**routercnc** · 02-11-2019

I went with a 10A Type D MCB in the end after trying a 6A Type D MCB that kept tripping on start up.

Note that my transformer was 750VA, 2x24v in series, (I'm running 5 steppers, with 2 steppers on X and Z) so you could try the 6A one first as they are not too expensive.

**Kitwn** · 02-11-2019

This is quite a good introduction...
http://www.skillbank.co.uk/psu/

The stepper driver must be rectifying the AC into DC anyway, though with little or no smoothing. My guess is that making drivers that can be fed with AC is done merely to reduce the cost of the power supply. Whether a smoothed DC supply noticeably reduces motor vibration compared to AC will need some research.

kit

**diycnc** · 05-11-2019

Thanks for the MCB advice. Will try 6A type D to start with.
After a little more reading, going to go for a 500va 230v primary, 2x 30v secondary. This should give me nominal 60vac when wired in series, and max voltage of 69vac when considering the mains can vary +10%, and transformer output by +6%.
A 2 x35 would give max of 81vac which is above the driver max of 80vac.

What's the recommended connectors for the high voltage wires from the PSU to the drivers?