[erickmoraes]

Hello, everyone,

I'm choosing the power supply for my system, and found this guide by Geckodrive:

Support

Concerning the power supply choice, it says:

"The choice of a power supply is determined by voltage, current, and power supply type (i.e. switching versus linear, regulated versus unregulated, etc.). By far the most problematic and complicated factor is voltage, which will be discussed last.

The easiest factor in choosing a power supply is its current rating, which is based on your motor ratings. A motor control will always draw less than 2/3 of the motor’s rated current when it is parallel (or half-winding) connected and 1/3 of the motor’s rated current when it is series (or full-winding) connected. That is to say, a 6 amp per phase motor will require a 4 amp power supply when wired in parallel and a 2 amp power supply when wired in series. If multiple motors and drives are used, add the current requirements of each to arrive at the total power supply current rating."

It left me with a doubt, though:

If my motors are 3A/phase, and I will connect it in parallel, is my power supply rated current supposed to be:

3 motors * 3 (A/phase) * 2 (phases) * (2/3) = 12 A

or

3 motors * 3 (A/phase) * (2/3) = 6 A

?

I know this is probably a silly question, but I am quite in this matter.

[lucas]

First answer is correct.
You will probably get away with 10A if don't fully load all the motors at the same time, this almost never happens.

[109jb]

No. That is not correct. If using three 3 amp per phase motors you need

3(motors) * 3(amp per phase) * 2/3 = 6 amp

Another way to look at it is to look at what the gecko information said for one motor:

"That is to say, a 6 amp per phase motor will require a 4 amp power supply when wired in parallel and a 2 amp power supply when wired in series"

So, a 3 amp per phase motor will require a 2 amp power supply in parallel and a 1 amp power supply in series. Assuming you are using parallel wiring, each motor needs 2 amps. You have 3 of them so 3*2=6

[lucas]

I should have asked for a link to the motor spec's as only the datasheet of the motor will tell, not all manufacturers use the same standard.
I assume that a 3A/phase means 3A per coil, thus 3A in series and 6A in parallel.
The Powermax II (wich I have in front of me) has the series current on the sticker and an EAD has both (series and parallel).

[erickmoraes]

Well, guys, I am still confused. Both answers seem "corrent".

When I think about it, 12A looks the logical answer. But according to Gecko's example, 6A is the demanded current.

[BAMCNC.COM]

Why wouldn't you just buy the better supply?

[lucas]

Well, guys, I am still confused. Both answers seem "corrent".

When I think about it, 12A looks the logical answer. But according to Gecko's example, 6A is the demanded current.

Both answers are correct, it depends on how one interpretes this: "If my motors are 3A/phase..."
If that motor needs 3A/phase wired parallel then the total current required is 6Amp.
But if the motor needs 6A/phase wired bipolar it's 12A.

We need more info on that motor, do you have a link to a datasheet?

[erickmoraes]

BAMCNC.COM,

I already have a 8A power supply; I'd like to know whether it suits my needs.

lucas,

You will find the datasheet on this page: Neoyama - Tecnologia para Automação de Máquinas e Equipamentos

[109jb]

From the datasheet, the motor is a 6 wire motor and has the following specs

bipolar series
current rating - 2.1 amps
inductance - 8.0 mH

unipolar
current rating - 3.0 amps.
inductance - 2.0 mH


If wired bipolar series then the power supply requirement would be

2.1 * 3 * 2/3 = 4.2 amps.
voltage would be sqrt(8) *32 = 90 volts

If wired in half-coil mode, the power supply requirement would be

3 * 3 * 2/3 = 6 amps.
voltage would be sqrt(2) *32 = 45 volts

[H500]

What voltage are you using?

Keep in mind that Geckodrive's recommendation is just a rule of the thumb. I think even your 8 amp supply is more than enough. It doesn't hurt to be conservative, but if you already own a 8 amp supply, I wouldn't bother spending money on a slightly bigger one.

Note that the maximum voltage across the motor coil and the current flow are not in phase. In other words, it does not take 3 amps at 48v to deliver 3 amps into the motor at the coil voltage of say 7 volts.

[ger21]

Well, guys, I am still confused. Both answers seem "corrent".

When I think about it, 12A looks the logical answer. But according to Gecko's example, 6A is the demanded current.

6 amps is the correct answer.

[109jb]

Lower voltage will result in a drop of torque at higher rpm and also a lower rpm where the knee of the torque and power curves begin to drop. It sounds as though you have already looked at the Gecko Stepper motor basics document. The effects of lower voltage are shown in the graphs on that document. Personally, I would consider the "rules of thumb" from a respected manufacturer of stepper drives to be more gospel than a rule of thumb.

[erickmoraes]

Ok, guys.

I think that now there are no more doubts.

My power supply is 45V, 8A, and I think I will go with it. Thanks a lot everyone.

[109jb]

Your existing power supply is just about perfect. If it were me, I would run the motors in half coil mode.