CNC for SPG 2217

Hi Neil,

Well you have a slight conflict going off here with these motors when it comes to voltage. Nema 34's require much more voltage than 23's to get decent performance from them. Nema 23's will give great performance with 65Vdc but 34's will only be average on same voltage. For best performance from 34's then you really need drives that can run at least 100+ vdc which is far too high for 23's.

Now it's here where you have to decide if you want to have a balanced machine or one that will have slight compromise.?

The compromise is using one PSU that provides for Both motors in which case you'd size it for the drives running Nema 23's. This will mean the 34's are running below there full potential.

Balanced machine would use PSU sized for the 23's and one for the 34's.
In practise this isn't has bad as it sounds because the best drives suited to 34's will actually use AC Mains voltage so you won't need a PSU for these at all.! . . . The down side is they cost quite a bit more money than lower voltage drives using DC so any saving from not needing an extra PSU is lost. In which case the Mains drives are still best as they are easier to install and give better performance.

Now if you go with the Compromise route then you will need drives capable of 80Vdc Max voltage and I suggest using lead shine EM806 Digital drives for all motors. Running 68Vdc toroidal PSU. Like these below.
http://www.zappautomation.co.uk/elec...ion/em806.html
http://www.zappautomation.co.uk/elec...er-supply.html

If going balnced route then Still go with EM806 Drives and 68Vdc PSU for the nema 23's. But for the 34's go with mains voltage drives like Kinco 2M2280N http://www.zappautomation.co.uk/elec...n/2m2280n.html

These drives & PSU will give you a nice balanced machine that gives you best performance from all motors. It does come at a cost thou.!

Regards the Motors and current then the 75% you have read about could be related to PSU requirements or the Idle current when motors are at stand still.?

In practise and setting up the drives you set them to the motors rated peak current IE: 23's = 4a & 34's = 6a. The drives then handle current requirements of the motors and limit to 6a Max.
The idle current is related to when motors are at stand still which is when they actually pull the most current. So the drives have an option to reduce current when motors are at idle for more than 1-2 seconds. This reduction can be 75% or as is often the case adjustable between 40 -100% on the drive.

The other 75% you may have seen could be related to Total current requirements for all motors.? Depending on the type of PSU being used will determine your total current requirements.!
Often people think they must size PSU with same current as total number of motors used IE: in your case 2 x 4a & 1x 6a = 14A . Which if using Regulated linear supply you would actually need more than 14a to avoid current clamping and PSU shutting down. Often you'll see Unregulated supplies being recommended to avoid this but still they must have current similar to motor totals due to how they work.

Now If you use toridial type PSU then you can get away with much lower current requirement due to them having capacitors which act as reserve and buffer type system and the fact the PWM of the drives only draw current in the ON cycle leaving spare capacity in the Caps.
With this type then you would size PSU current requirement using between 60-75% of total motor current requirements. Hence the 75% figure you may have seen.?

Hope this helps and just ask if I've just blown your brains.! . . Lol