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# Thread: Newbie PSU calculations

1. Hi I am building a small gantry hobby router using 2 Y, 1 X and 1 Z closed loopback steppers,

Closed Loop Stepper Driver 0-7.0A 24-50VDC for Nema 23 Stepper Motor

Motor Specification
Part Number: 23HE30-5004D-E1000
Number of phase: 2
Holding Torque: 2.0 Nm(283.28oz.in)
Rated Current/phase: 5.0 A
Phase Resistance: 0.42 ohmsħ 10%

my calculations for the required power supply(s) is

4 motors x 5 amps each x 50 volts x 120% = 1200 watts

since not all the steppers will be running at full power at the same time I can reduce the requirement by 25% = 900 watts required

Are my calculations valid?

What is better, two switching power supplies, 450 watts or one 1000 watt?

https://www.ebay.co.uk/itm/402646721...r=672923118722

Any suggestions gratefully accepted

Thanks

2. Originally Posted by Soyb
Hi I am building a small gantry hobby router using 2 Y, 1 X and 1 Z closed loopback steppers,
Closed Loop Stepper Driver 0-7.0A 24-50VDC for Nema 23 Stepper Motor
Motor Specification
Part Number: 23HE30-5004D-E1000
Number of phase: 2
Holding Torque: 2.0 Nm(283.28oz.in)
Rated Current/phase: 5.0 A
Phase Resistance: 0.42 ohmsħ 10%
my calculations for the required power supply(s) is
4 motors x 5 amps each x 50 volts x 120% = 1200 watts
since not all the steppers will be running at full power at the same time I can reduce the requirement by 25% = 900 watts required
Are my calculations valid?
What is better, two switching power supplies, 450 watts or one 1000 watt?
https://www.ebay.co.uk/itm/402646721...r=672923118722
Any suggestions gratefully accepted
Thanks
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).

3. ### The Following User Says Thank You to dazp1976 For This Useful Post:

4. Originally Posted by dazp1976
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.

5. As a power electronics engineer developing switched mode power supplies and VFDs for some years, I have loads of PSUs in the garage to choose from but I've still used mains transformers and large electrolytics for my machines for the reasons JazzCNC gives.

Having said that, I've also got voltage clamps on my power supplies to limit any voltage surges during rapid deceleration of the machine. I notice that the LiChuan A4 servo drives I got recently for my current lathe conversion (thanks for the recommendation, JazzCNC) have built-in braking resistors that should take care of this to some extent in a similar way.

For my large machine, I bought a 3000VA site transformer from Screwfix (the steel housing version, not the yellow encapsulated type) and removed some secondary turns to reduce the output to 100Vac. This gives about 140Vdc on the cap and cost me less than £100.

I once made the mistake of combining a Leadshine switched mode PSU with a large electroloytic capacitor on one of my machines and found that it often wouldn't start up at the first attempt. This was because it saw the cap as a short circuit during startup and had a latching current limit. They don't all behave like that but a mains transformer is a bullet proof solution in comparison. And as JazzCNC says, during an overvoltage surge, a regulated PSU can latch off when you least want it to.

6. Originally Posted by JAZZCNC
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!.
Last edited by dazp1976; 22-05-2021 at 10:39 AM.

7. Toroidal and E core transformers don't behave much differently in this application, so I wouldn't get hung up on what transformer you go for. If you are into audio amps, the toroidals generate less of a stray magnetic field which can mean less risk of hum.

BTW, if you are bothered by the Bees Nest (TM) fans in the LiChuan servos, you can replace them with pukka Papst / NMB / Sanyo etc fans from CPC. I did this on mine and it has made the noise almost bearable.

8. Originally Posted by Muzzer
BTW, if you are bothered by the Bees Nest (TM) fans in the LiChuan servos, you can replace them with pukka Papst / NMB / Sanyo etc fans from CPC. I did this on mine and it has made the noise almost bearable.
Cheers for that. The fan in the servo drive is pretty damn loud.
I was originally just going to mount it open on the wall next to the machine until I heard the noise.
I've bought a bigger control box so I can get everything else + the servo drive inside it together and see if that helps.
If it still bugs me, then I'll give the fan swap a go

I'm still early days bench testing atm with my old parallel bob & Mach3 to get a feel for it (and confidence with servo's).
I'm playing will all setups, PWM, step/dir, axis, relay & opto modules etc.
I have loads of time on my hands to fiddle, and learning a fair bit :)

I'll start on benching the UC300eth next week with Mach and UCCNC.
I want to get a good feel for UC and get the controller working perfectly with both softwares first.
Then I'll fit up the new box and put them to machine.

Got myself a stepperonline driver for my Z last week too. DM860T (takes up to 80Vac or 110Vdc).
Putting 80Vdc to it which should give my Z (nema34 1080oz) a kick up the a**e

9. Originally Posted by dazp1976
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.

Originally Posted by dazp1976
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)

Originally Posted by dazp1976
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.

Originally Posted by dazp1976
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.!

10. I'm pretty sure if somebody can manage to wire up a functional CNC machine, then they can manage to wire up the required bits to create an unregulated power supply.

11. Originally Posted by m_c
I'm pretty sure if somebody can manage to wire up a functional CNC machine, then they can manage to wire up the required bits to create an unregulated power supply.
That's true, but the mistakes can be more energetic than in other parts of the machine. The first component to install should be the mains fuse, suitably rated for the job with an allowance for inrush. In the UK this can be in the plug-top but in other parts of the world a separate device is needed. This helps prevent backlash... from the rest of the family when the house goes black, taking Netflix with it.

Kit

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