Newbie PSU calculations

[JAZZCNC]

I would go no less than 48v.
48V 800w will do it easily.

Generic 4 axis kits normally come with 2x 36V 350w supplies so the supply I suggest above is plenty :)
(36v is usually dissapointing).

That would be a mistake for several reasons. First, 48V is too close to the drive's maximum voltage so any back EMF from the steppers when slowing down could damage the drives as it returns to drives and spikes above 50vdc.

Secondly, the regulated DC supply will cause problems for similar reasons, because steppers basically become dynamos when de-accelerating the voltage being feedback to the PSU will cause the supply to clamp and possibly shut down. This will be erratic and unpredictable and leads to all kinds of issues that not always obviously related to the PSU.

This is why Unregulated PSU is often used or better still toroidal transformer with smoothing capacitors for DC drives which will absorb any back EMF. Also, an unregulated toroidal setup allows lower power requirements, approx 60% of total stepper current, because of the way it works with the pulse modulation of the drives only needing power 50% of the time.

Using drives that accept AC input is becoming more popular because it removes the need for smoothing capacitors and rectifiers needed for converting to DC voltage, but still the use of an Unregulated PSU or toroidal transformer is required for the reasons stated above.

[dazp1976]

That would be a mistake for several reasons. First, 48V is too close to the drive's maximum voltage so any back EMF from the steppers when slowing down could damage the drives as it returns to drives and spikes above 50vdc.

Secondly, the regulated DC supply will cause problems for similar reasons, because steppers basically become dynamos when de-accelerating the voltage being feedback to the PSU will cause the supply to clamp and possibly shut down. This will be erratic and unpredictable and leads to all kinds of issues that not always obviously related to the PSU.

This is why Unregulated PSU is often used or better still toroidal transformer with smoothing capacitors for DC drives which will absorb any back EMF. Also, an unregulated toroidal setup allows lower power requirements, approx 60% of total stepper current, because of the way it works with the pulse modulation of the drives only needing power 50% of the time.

Using drives that accept AC input is becoming more popular because it removes the need for smoothing capacitors and rectifiers needed for converting to DC voltage, but still the use of an Unregulated PSU or toroidal transformer is required for the reasons stated above.

You'll have to build him a toroidal DC then if tha's the case.

1: Even if you could get one in the uk it will be at stupid cost!!!!!. Importing coats even more!
2: Op likely (like me) wouldn't have a clue or the confidence to have a go at building one.
3: Not going to buy different drivers (again).

I'd have gone either DM860 type drivers and 60Vdc switched. Or ones that can take up to 70Vac straight off a base toroidal, all day long.
He has what he has!!!!!
Just turn the regulated down to 45V if you're that concerned.


I use DM860 and 60V right now and it's never failed me.
I've also recently got my first Lichuan A4 servo set (for spindle use), and I'll be going that route later down the line.
Overspent for the next 6 months!.

[JAZZCNC]

You'll have to build him a toroidal DC then if tha's the case.

1: Even if you could get one in the uk it will be at stupid cost!!!!!. Importing coats even more!
2: Op likely (like me) wouldn't have a clue or the confidence to have a go at building one.
3: Not going to buy different drivers (again).

Well, I'm not sure why you think got to import toroidal transformers.? There are plenty of places to buy them in the UK.
Building a DC toroidal PSU isn't difficult or rocket science and there are many examples on this forum, I would also gladly help you or anyone else if asked.

I'd have gone either DM860 type drivers and 60Vdc switched. Or ones that can take up to 70Vac straight off a base toroidal, all day long.
He has what he has!!!!!

Why do you assume that.? he could just be asking because he's thinking to buy those drives.! (Which would be a mistake IMO, but that for the OP to decide)

Just turn the regulated down to 45V if you're that concerned.

That doesn't get away from the fact it's still a Regulated PSU.

I use DM860 and 60V right now and it's never failed me.

Just because it's working for you doesn't mean it's correct or advisable, fitting a regulated linear PSU is like playing Russian roulette and it will at some point give issues that may not always be obvious that they are coming from the PSU.

It doesn't cost much more to do it right the first time and it nearly always works out cheaper in the long run because as you stated above you don't need to "buy drives again" and the machine always works much more reliable, so why when going to so much trouble to build a machine would anyone spoil it for the little extra it takes to do it right is beyond my reasoning.!