[Mariss Freimanis]

I should mention I also looked at the NEMA-34 motor. It is a dog at 7.7mH. What makes a dog or a non-contender is motor inductance apart from everything else. Let's churn the numbers: Vmax = 32 SQRT mH. That makes the maximum supply voltage 89VDC and it's beyond any of our drives. That makes the corner frequency at 789 RPM and peak power output of 253 Watts. Way beyond what a G250 can do and just barely beyond the reach what a G203V can do. You want big power from a big motor? Use a G203V. Big motors need big drives.

Little drives work best with little motors. Little drives also cost less than big drives. Little motors still put out really decent power with little drives.

Have a sense of proportion: Nearly everyone emphasizes holding torque when they mention a motor. It is nearly the most useless specification available. It is silly and naive. A rusted bolt has 10s of thousands in-oz of 'holding torque'. What makes it different? The difference is there is zero speed associated with it. If you get anything, get this: only POWER GETS THINGS DONE!!. Power is torque times speed. Torque is meaningless without an associated RPM. Holding torque is just that; torque at zero RPM. No power at all at zero RPM.

Drives move motors and motors develop power. Power is always a product (torque * RPM) of torque and speed. Power is work and it's expressed in Watts. You have a milling machine? Power is how many chips of hot metal it carves away. You have a plasma cutter? Power is how quickly it can accelerate from one point to the next.

The G250s are very small drives. They optimally power motors to the tune of 100W or so. The best Olympic trained athlete can crank out about 100W of power long term. The 26-mile Marathon kind of endurance. I have seen more than a few machinists working on manual Bridgeport sized machines. None of them looked like they were Olympic quality athletes. 100W of power into a benchtop sized machine should be more than plenty for everyone.

You need more than that? Don't be cheap. Buy a bigger drive.

Mariss

[tauntdesigns]

Thanks again,

I had wondered about the nema34's and had hoped you would explain about the inductance.... I had passed on using them, but didn't know why.... Glad I did.

I'm on the bottom side of the electronic learning curve but, I'm taking notes and someday it'll sink in.

I have 2 of the nema23 (276's) on my bench lathe and plan on using g251's on it. My bench mill uses 3 g203v's and work beautifully.

Thanks again,
Jack

[Teyber]

The $60 48V/7.3A Keling PS can power up to 11A of motors and should be a good candidate:

http://kelinginc.net/SwitchingPowerSupply.html

CR.

hey!

for, say, 4 axis 11a most likely won't be enough for most drives though will it?

how many amps could this handle, although over twice the price?: KL-600-48 48V/12.5A $149.95
115V /230V

i too am wondering if the 540 will be weeks, 1-3 months, or a year to come out.

Regards

[Crevice Reamer]

hey!

for, say, 4 axis 11a most likely won't be enough for most drives though will it?

how many amps could this handle, although over twice the price?: KL-600-48 48V/12.5A $149.95
115V /230V
Regards

Originally Posted by dansutula
So... any suggestions for the best (lowest cost / highest performance) power supply for a G540 and the Nema 23 motors?
Regards,
Dan

The $60 48V/7.3A Keling PS can power up to 11A of motors and should be a good candidate:

http://kelinginc.net/SwitchingPowerSupply.html

CR.

The original question that prompted that answer was loooking for the most PS bang for the buck. The K350-48 will adequately power four 2.8A motors, or any combination up to 11A.

To power four 3.5 A motors, you would need a 48 V 10A power supply. The KL600 is overkill and over price--But if you want to spend THAT much, also look at the $170 KL5020. That supplies 50V and 20 Amps.

CR.

[LeeWay]

I am not certain that you have to have the max amps either. How often would all 4 axes be driving full tilt? The most I have at any one time running is 2. X and Y. If it's going home, then the Z moves first alone to safe Z, then off goes X and Y.
A more complicated machine might need more amps when doing 3D work, but for a standard 3 axes machine, I think if you cover 2 motors at full amps with the PS, you have it licked.
Might need a little higher if you are driving 2 motors on one axis.

[Crevice Reamer]

I am not certain that you have to have the max amps either. How often would all 4 axes be driving full tilt?

Stepper motors draw their max amps when holding in place or hardly turning. As they run faster, they draw LESS current not MORE.

CR.

[LeeWay]

Steppers are likely different animals than I am thinking of, but when a normal motor starts and gets up to running speed, that is when the max amps are pulled.

I know when a 203V Gecko drives a motor, it reduces this current when it's not receiving steps. This is the cause of these motors not heating up like they do on a 201.
This heat is the result of the constant amps on the motor to provide the holding torque.
I reckon that I am only getting partial performance on my router then. I have a 62 VDC lab supply with only 6 amps. I am driving 3 425 3 amp motors. I may have to put a bigger supply on that rascal.

I guess when a regular motor isn't moving, it's basically asleep and when a stepper isn't moving, it just quiet and well behaved.

[Crevice Reamer]

I reckon that I am only getting partial performance on my router then. I have a 62 VDC lab supply with only 6 amps. I am driving 3 425 3 amp motors. I may have to put a bigger supply on that rascal.

The formula for max amps needed is .67 times the total of motor amperage. You have a total motor amps of Nine. Nine times .67 equals 6.03 Amps. Your present PS is adequate for amperage. However, you MIGHT be able to use a higher voltage PS for an increase in max performance.

For example, if those are KELING 425s then they can be powered with up to 83 volts, driver willing. Higher voltage equals faster rapids.

CR.

[Mariss Freimanis]

I ran some dyno tests with the G250. Here are the results:

Motor: Single-stack NEMA-23. 116 in-oz holding torque, 3.5A per phase, 1.73 mH.
Power Supply Voltage: 50VDC

Power supply current at zero RPM: 0.37A (standby @ 70% of rated phase current)
Power supply current at 60 RPM: 0.55A
Torque at 60 RPM: 110 in-oz

Corner Speed: 1404 RPM (speed at torque begins to drop)

Power supply current at 3,000 RPM: 0.69A at no load
Power supply current at 3,000 RPM: 2.87A at max load
Power output at 3,000 RPM: 107 Watts mechanical
Torque at 3,000 RPM: 49 in-oz
Motor efficiency at 3,000 RPM: 76% at full power

This is 192 lbs of thrust at 300 IPM on a 10 TPI screw.

Mariss

[Crevice Reamer]

Thank you Mariss! This is very educational. So Amperage DOES increase with speed & load. It is TORQUE that diminishes with speed. I was wrong. I guess I was confusing TORQUE with AMPERAGE.

Fifty volts and 3.5 Amps can go a long way with a small motor.

But by MY calculation, That 1.73 mH. motor should only be run at 42V max voltage.

CR.

[Mariss Freimanis]

Your calculations are correct. 42VDC is the maximum supply voltage. The motor got very hot at 50VDC while I took the data.

107 Watts (90 Watts at 42VDC) is a lot of power from a NEMA-23 motor.

About supply current. 4 G250 dives turning 4 unloaded 3.5A motors at 3,000 RPM would draw 2.76 Amps from a 50VDC supply. If all 4 motors were loaded to just short of stalling, 11.48 Amps are required from the supply. If the mechanical design allows for 50% derating of the motors, 7.12 Amps are required. When all motors are stopped, only 1.48 Amps are drawn.

Even this is overkill. What are the odds all 4 motors will be running at their design limits simultaneously?

Mariss

[Mariss Freimanis]

CR.

I just realized your question is of a theoretical nature. Look at it this way:

At 3,000 RPM the unloaded motor requires 34.5 Watts of power (50V times 0.69A) to keep it turning. All of those 34.5 Watts go up as heat in the motor because unloaded, there is zero mechanical power output.

At near-stall load, the power supply current increased from 0.69A to 2.87A. The power delivered to the motor is 143.5 Watts (50V times 2.87A). It still takes 34.5W to turn the motor so the difference, 109W, gets converted to mechanical power.

The dyno reads 49 in-oz at 3,000 RPM which is 109W as well (W = in-oz times RPM divided by 1351). The dyno accuracy is +/- 2 in-oz so it is coincidence the results are exactly the same.

The increase in current (and Watts) from the supply matches the mechanical power drawn from the motor. That is why current increases with load.

Mariss

[Crevice Reamer]

Thanks Mariss! You sure have taught me a lot. There is a great amount of wisdom encapsulated into this thread--Thanks to your kindness and patience.

CR.

[[e-]OneEye]

From www.hobbycnc.com (no affiliation):

(NEMA 23)#23-305-DS8A 425oz-in bipolar rating, 305oz-unipolar rating,
4.2v, 3A, 200 S/R, 3.2mH, Size #23, Dual Shaft,
8 wire MOST power consumed, best with idle current reduction,
Faster speed over 2A version below. $49 each

At 3.2mH, SQRT(3.2)*32 gives 57.24V. Running them at 50V isn't a huge amount less than their max and might give close to max torque at higher speeds.

In shorthand contrast, the offerings from Keling have much higher inductance (on the order of 6.8mH) which puts the voltage needed for max torque much higher (SQRT6.8*32=83V+ as already said).

[jstransky]

How you are able to count the corner speed for different motors ?
How great difference make the drive ?

I'm running my unipolar (already mentioned mark) drive board just to 800 RPM - I get the information from seller that 1000 RPM is the max with no load on stepper.
Now I'm reading something differnet. Help me please !

Excuse my English.

Jan Stransky

[justfx]

Keep in mind, the specs listed are probably for running it as a unipolar. All of HobbyCNC's drivers are unipolar. While the inductance might be the same running it as a parallel bipolar, the amps will definitely be greater - based on other motor specs I would guess around 4.2A.

[Mariss Freimanis]

Jan,

Your English is far better than my Slovakian.:-) The drive makes all the difference. It is a rare NEMA-23 or NEMA-34 motor that won't spin up to 6,000 RPM unloaded with our drives (at least 3A/phase rated).

Mariss

[Santa Fe Al]

Hi Mariss,

I started a thread about motor size in New Machine Build- What size steppers ??????? in the stepper motor section.

You and your cheap Geckos are the main reasons for choosing the below motor for my setup. A few more weeks and I should be ready for you. Hint, Hint !!!

Am using 1/2 x 10 ACME screws for all axis.

NEMA 23 BIPOLAR STEPPER MOTOR 495 oz-in, 1/4” Diameter shaft with a flat

KL23H2100-30-4BM (Dual Shaft) Rated Current: 3.0A, Rated Voltage: 5.1V

I would probably have decided to use nema 34's at 600+ oz/in but, having followed this thread from its beginning, I can't even consider using any other drives unless I don't have a choice because of the 24 x 48 inch table with a Gantry.

The inputs I receive will be the deciding factor. Ger21 has already commented and things may be looking up.

Al

[Crevice Reamer]

Al: You must have missed a few pages. Just because your motor has a higher torque rating, does not mean that you can GET more power out of it.

Your 495 oz motor has 7 mH inductance. It needs an 85 volt power supply to achieve best performance. Running at 50 V will cost it about half of its power.

You could have saved $20 per motor and bought the 270 oz KL23H276-28-4B. IT only has 3.6 mH of inductance, so requires only 60V for best power.

IDEALLY, we will be able to find motors rated for 48V and 3.5 Amps. THESE will be better candidates for the cheap drives.

CR.

[LeeWay]

I do run the 495's at probably around 68 VDC. They could be better and this is why I will upgrade to some medium sized 34's.

The 425's seem to work just as well on 62 VDC as the 495's @ 68. Both are running ball screws. The mill is precision ground and the router is just rolled screws. These are all direct drive with the exception of the Z on the mill. My mill doesn't miss any steps @ 300 IPM. It does easily miss steps when it hits the hard stop though. Good for the machine not to cause any damage to itself. I may loose a little depth of cut because of this, but it makes up for that in speed.

Now the little Keling supply I have on my lathe is the 48 VDC 7.3 amp.
It is adjustable for output and can be set as low as about 39 and about as high as 55. You can set it to run at exactly 50 VDC if you want.
It seems this will be perfect for many of the smaller and medium sized Nema 23's.