Thanks RICH, good explanation

Dont go any higher than the 50vac secondary on the transformer as that will put you over the max for your drives. When you rectify and smooth  AC the DC value is approx 1.4 times greater hence 50vac becomes 70vdc.  You can go a bit less on the 50vac secondary but try and keep at the 50 or close.

As for the rectifier, you need it to be rated at least for the 70vdc and 8 amp that you calculated for.

Hood

In the exact words the manufacturer (Keling) said: "You can use the power supply from 24-72VDC"

This appears to be at odds to what you've said at the beginning of your post where you stated 42V max. Are you mixing up max recommended motor V with max driver V. (The motors are Keling - not the drivers).

Certainly if the drivers are these http://www.probotix.com/stepper_motor_drivers/ProboStep (which are the only unipolar drives I can see at Probotix) then the max V is 44V.

From your link the (unipolar) motor inductance is 2.2mh, therefore your "ideal" voltage for "max" speed & torque is 32 * sqrt 2.2 = 47.4636704 Vdc. BUT this is over the 44V limit of your drives. You said your supplier recommended limiting to 42V - a tad below the limit of 44V.

So 42Vdc gives a transformer secondary of 42/1.414 = 29.7029703VAC.

Generally (in the UK anyway) transformer secondarys come in 12, 15, 18, 22, 25, 30... VAC so your nearest fit is 25VAC which will give you 35.35Vdc. This as has been stated earlier is not the "ideal" for your motors but it's the best you can do with your drivers.

Unless of course I've cocked up somewhere  

Ian

Thank you Ian for your input and lets see if I can clarify the data.

Keling told me by email that for the 4 motors I have the voltage range on my power supply should be from 24-72VDC

Probotix states in their manual that the 4 drivers I have the power supply voltage should be limited to about 42VDC (your link for the drivers is correct)

I thought about it that the transformers secondary must be available in certain std. size and my next question here would have been what size my choice should be. So you have answered my question before I even asked. I will get one at 25VAC

There is something that confuses me and I would like it to be clarified. You said the transformers secondary comes in .......25VAC. I thought that these transformers have a primary side which is the AC volts and a secondary side which is the DC volts. So is the 25 volts AC or DC?

Thanks for your time
Nicolas
 

No a transformer just steps the AC voltage down  from the input to the output so you still need to rectify and smooth the Ac to make it DC.
Hood

The secondary would be AC and depends on the ratio of the primary to secondary windings. Some transformers have multiple taps on the secondary windings
 so you have a choice of voltages available. The AC is then is made into DC by the rectifier. That component is is usualy a group of diodes which clip off the tops and bottoms
the AC sine wave. The AC sine wave is sort of like a female who has a period which is  repeatable over time with a highs and lows.

RICH

The AC sine wave is sort of like a female who has a period which is  repeatable over time with a highs and lows.

RICH

Brave man

LOL..........thanks Rich, now I get it but I should have thought about before by myself. Guess too much to digest at once.

So now that Ian said to get a transformer with 25VAC secondary, what will be the VA of this transformer? 402VA?

Nope, 25v x 8.04A = 201VA although as said before, more will not harm.
Hood

Sounds good so far, I'm going to this store this morning to see what is available regarding toroidal transformers, capacitors and rectifiers.

Then I would like to know what gauge wiring I should use plus I want to put a fuse on both the incoming 110VAC and outgoing 25VDC. Before I proceed with the build I will post a wiring schematic including materials list and if all is ok then I will do my purchasing. Who knows, I might have a new power supply even before the one I ordered from China arrives LOL......

Nicolas