Yet another power supply question

[TMaster]

Ok guys I've scanned the forums and googled forever but I just want to be clear on some things. I've been running my G540 with a 24V 6.5amp power supply for the last week and it seems fine. I have the 269oz, 2.8amp motors, with my taig cnc mill. I never run them over 50 ipm. And only 2 motors max move at the same time. The motors run super cool! So much better then the old driver I was using. Heck, I used to run my mill at 25 ipm!

I ran a few tests with the multimeter wired in, and I was only getting about 2.2 amps being drawn with 2 motors going 50-60ipm blended speed, no loads on the tables. So then I decided wow that is a really low amperage, so I held the X table with my hand and the amperage peaked at around 2.9 amps, I would say I had 10-15 lbs of pressure against it. I adjusted the voltage from 24v to 27v also. The amps varied slightly.

I am building another mill setup so I am going to need another power supply.

So my questions are:

Do I really need a 48V power supply with a similar setup? Would there be any benefit or advantage? I read that more voltage would make the motors hotter. I was thinking of just getting a 24V 8.3amp power switching power supply. I just see everyone and their moms saying go with a 48V :P

[debetto]

Originally Posted by TMaster Ok guys I've scanned the forums and googled forever but I just want to be clear on some things. I've been running my G540 with a 24V 6.5amp power supply for the last week and it seems fine. I have the 269oz, 2.8amp motors, with my taig cnc mill. I never run them over 50 ipm. And only 2 motors max move at the same time. The motors run super cool! So much better then the old driver I was using. Heck, I used to run my mill at 25 ipm! I ran a few tests with the multimeter wired in, and I was only getting about 2.2 amps being drawn with 2 motors going 50-60ipm blended speed, no loads on the tables. So then I decided wow that is a really low amperage, so I held the X table with my hand and the amperage peaked at around 2.9 amps, I would say I had 10-15 lbs of pressure against it. I adjusted the voltage from 24v to 27v also. The amps varied slightly. I am building another mill setup so I am going to need another power supply. So my questions are: Do I really need a 48V power supply with a similar setup? Would there be any benefit or advantage? I read that more voltage would make the motors hotter. I was thinking of just getting a 24V 8.3amp power switching power supply. I just see everyone and their moms saying go with a 48V :P

For stepper motors, torque drops off as speed increases. This drop off will be steeper with lower voltage. Higher volatge therefore allows for more usable torque at higher speeds for the same stepper motor. This means higher cutting speeds for a given load and faster rapids. The performance at the lower end of the speed range will be similar.

Also, take note that a stepper will draw as much current as it "needs" depending on the load, but not more than its rated current regardless of the volatge.

Hope this helps.

debetto

[TMaster]

Thanks, I have just decided to get a PS-240-48. 5 amp (240W) switching power supply. Its like having a 10 amp, 24V. So plenty of power for me.

[Crevice Reamer]

Hi TMaster.

You don't say what motors you are going to run with the new PSU. The formula for calculating PSU Amps needed is Total motor amps x .67.

So if you had three 3.5A motors, it would be: 3.5 +3.5 + 3.5= 10.5. 10.5 x .67= 7.03A needed from PSU.

You might find some useful info here:

http://crevicereamer.com/Page_2.html

CR.

[TMaster]

Thanks, I did state the motors and amps in the first post. 2.8 amp, 269oz motors.

By your calculation 2.8 +2.8 + 2.8 = 8.4 amp * .67 = (5.628 amps) This is a good place to start and be on the safe side; but this calculation really doesn't take into account all the factors involved. Your machine, motor speeds, the driver board, and the load on the motors, and power supply voltage. Considering I'm using a 24V, 6.5amp, 150W power supply right now, and I was pulling 2.2 to 2.9amps maxed out speeds for my setup, and some load. So we move up to the 48V, 5.0amp, 240W power supply. Thats doubling the voltage, hence half the amps that will be needed. When I get the new power supply I will see what the amp draw is.

[Crevice Reamer]

I should have said: You don't say what motors you are going to run with the new mill.

Higher Voltage may cause the motors to draw MORE Amps not less.

I would spend the extra $10 and get the 48V 7.3A PSU--For future expansion if nothing else. Any extra Amp capacity will just not be used.

CR.

[TMaster]

I should have mentioned it was the same setup as the one I have now, just I'm using the Gecko driver on one and the xylotex on the other. I will report back my findings

[TMaster]

Sorry for the delay on my testing, I have not tested the amps yet, but the 48V power supply is getting my steppers really hot. I even have the power supply adjusted down to 40V, and the Y axis motor is getting up to 65C in temps on the outside cover. The X and Z are 55c. I read that anything over 85c and you need to worry. Still I am not happy with the temperatures. I'm starting to wish I would have bought a 24V power supply that was just a higher amp capability. With the old 24 power supply I had the temps only seemed half as warm.

How are the temps on everyone elses 269oz steppers???

Anyone wanna buy a slighty used SP-240-48 PSU? lol

[RotarySMP]

The motors are designed for 85°C, and are reaching 65 and 55°C, what are you worried about?

Have you played with the acceleration and rapid settings? You should be able to run the machine machine roughly twice as fast.

If you double the voltage and then don't take the benefit by increasing the machine speed, why did you bother?

[TMaster]

I am running the speeds faster. I have my rapids at 35 ipm, and I've seen blended speeds up to 48 ipm.

I'm not real worried, but I like to keep things cool!

[Crevice Reamer]

What size current limit resistors are you using?

CR.

[TMaster]

They are 2.8K behind the stepper motors. The xylotex steppers are 2.8A phase.