Did you want me to argue with all that guff or agree with it? Because he's got some bits right and some bits that sound confused.

However nothing you pasted there changes the calcs I posted before. I've seen the specs of your motors, and of your 5410 drivers. Your proposed 36v unreg 150W PSU is plenty and it's a good match for your motors and drivers.

RB, I just wanted to show how they figure it on forums that all they deal with is steppers. I mean NO disrespect to you just trying to understand this stuff better. As my screen name says I'm on the short bus learning this stuff!

There are some problems with the numbers being used in this thread.

Motor; 7.9Amps/phase Resistance- .41Ω/phase
The motor is also marked 65V(this is the max. voltage)
7.9Amps
337Watts

Max amps for driver 5Amps 36Volts


Now using your formula: Amps squared*Ohms = Watts
5*5*.41= 10.25W * 2phases = 20.5W

Out of all the Watts formula why use that one? Wouldn't P = V*A be the one to use? 36V*5A =180W * 2phases = 360W

This is more in line with what is used with all the other information I have ever seen for stepper drives. I know I don't have even a minuscule amount of the electronics knowledge that you do. So please help me to understand and get my thinking right!

While I'm at it, why don't the answers to the Watt formula come out the same? How do you know which one to use? The only one i use is P=IE so I never realized that you don't get the same result!

 

Well, look at it another way; in terms of average voltage across the windings.
E=IR, so since I=5 and R=.41, E=2.05v.
To get 2.05v out of a 36v supply, you'd need to PWM it with a 5.69% duty cycle. 2.05/36*100=5.69444...

 

RB, I just wanted to show how they figure it on forums that all they deal with is steppers.
...

No I don't know that particular forum. But if they are anything like the CNCZONE forum then they are probably a big gung-ho with max values for things.

The thing I think you are missing is the fact that the chopper stepper driver works as a SMPS. This means it does both voltage and current conversion.

So it can produce 4.9A 1.3v out (6.3W) running at 70% efficiency it will require 9W input. That will be 36v at 0.25A input.

Your 5410 driver has a microstepping mode of 3.5A/phase. Microstepping 2 sinewaves (90' out of phase) requires 1.4 times the current, so total motor current when stopped (or moving at slowish homemade router speeds) is 3.5A * 1.4 = 4.9A.

Yes stepper motors need significantly more power when running at high speeds, particularly when accelerating large loads to a high speed. But based on your very sketchy information of 4'x8' CNC machine we can make some assumptions.

It is highly unlikely for all 3 axes to all be accelerating at high speeds all the time! The normal case on a router table is for the vert axis to be still (using 6.3w) and one axis to also be still (6.3W), with only one axis moving at high speed (maybe 50W worst case). If both X and Y are moving at full speed that sounds like 100W but it is not, in that case to maintain the correct tool speed at a 45' angle means both the X and Y axes both have to slow down to 70.7% of their full speed, and hence use less power.

If you are *really* intent on squeezing the very last bit of power possible from your 7A motors you need different drivers as your 5410 drivers will only run at 3.5A. On the other hand if you want pretty good working performance using the stuff you already have (which seems obvious from your posts) then the 3.5A drivers will work fine and so will the 150W PSU.

 

Well I have to say I am enjoying watching you guys duke it out as to which power supply I should put on my router. I started putting the table together last weekend, and will have some pictures up this weekend hopefully. I have to thank you guys because I wouldn't have made it this far without you.

It looks like the last piece of the puzzle when it comes to the electronics is the power supply. I'll let you guys sort that one out. What all of you are saying makes sense to me, but I don't know enough to decide which way it right. I'll have to cross that bridge when I get there haha.

 

RB, like I said not trying to disrespect you, just trying to learn I thank you for your explanations

The guys that post the answers on both of those forums for power supplies and drivers are supposedly knowledgeable. One of them is the designer of 'GECKO' drives.

I can't seem to find a reference any where to a step driver being a SMPS. But it makes sense to me after you explain it. The motor coils act like the inductor in a SMPS?

The literature on stepper power supply is woefully bad. All of the companies selling both power supplies and drivers suggest using really big wattages on there products. Even the driver in this thread says 10 Amps for each driver!

The big routers and even some of the smaller ones don't couple the stepper motor direct to the lead screws that move the axis. They use a reduction of 3 or 4 to 1 so the motors turn faster.

This thread has really blown my mind! I have to rethink all I thought I knew about steppers. Could you point me in the direction of your source of knowledge on stepper drives and motors? So I can try to reprogram my thinking. Google searching it just shows the same old "We need more power, Scotty" version. Thank you, Cary

 

Yes the key is word "chopper" in the description of the stepper drive. Like SgtWookie said it uses a low duty cycle to chop the power to the stepper motor, combined with the high inductance of the motor you get voltage and current conversion.

Google for "Jones on steppers" it's a dry read but very good info on stepper and drivers.
Then mostly it's from real world experience using linear and chopper stepper drivers.

I know of Maris (the GECKO guy) from the CNC forum and he really knows his stuff. But theres a difference between some very industrial thinking and/or pro-end apps moving some big heavy steel and machines operated for continual production etc to the OP's need to connect his existing motors and drivers to a PSU and get it happening.

And sorry Shortbus and jchal3 I got you confused at some point there thinking you were both the original poster.