I've got a Kelling KL-G540-48 on order for my older Taig CNC mill. It's got the old dovetail ways on the Z axis rather than the new box ways, and the controller it started life with was the older quadrature drive controller rather than the newer step/dir controllers that are shipping now. The mill still has the original 200 oz-in steppers it came with, and this is what I'll be using with the G540.

I'm reading through the Gecko drive threads here, and I've got the Gecko and the Kelling docs sitting in front of me. But one bit of information I'm having a hard time tracking down is the specs for the motors on the mill. I've searched the Microproto site, Nick Carter's site, and here, and I can't find that information. Coil resistance is no problem, that's an ohmmeter. But the current limit is another question, and that's one I need to have before building the DB9 connectors for my motors.

If anyone can shed any light on this, I'd appreciate it.

Thanks,

Tom

I also posted this on CNCZone, and got a fair bit of feedback, all of which is good food for thought. I posted the original question when I was well away from home and wasn't able to just go LOOK at the thing and find out the answer. So this morning I did. Turns out the motors still have their manufacturer's stickers on them, and years of coolant and abuse haven't reduced them to unreadable messes. So here's the scoop on the motors: (My apologies for people who read CNCZone, too... Much of this is copied from my reply there)

All four axes have Shinano Kenshi SST57D5101 motors on them. I'm pretty sure this was typical of the Y2K era Taig CNC mills. Shinano Kenshi apparently no longer makes this motor, but as things turn out they have pretty good documentation on it. (Which was amazingly easy to find once I had the part number... Sorry, still slapping my forehead for getting jazzed about my new controller while I was away from the shop and couldn't answer my own questions.)

Here are the specs on the motor:

Shinano Kenshi SST57D5101
1.8 deg/step
9.2-12.9 V/Phase
0.7-1.0 A/Phase
9.2 Ohms/Phase
20 mH/Phase
14.3 kg/cm Holding Torque
430 g/cm Rotor Inertia
NEMA 23 Frame

Just to double check my math, here's what I get for my calculated values:

Wired as half-winding:

Max running voltage:
32 * sqrt(20mH) = 143.1V (The 48V supply in the Keling unit is well under this, so I should be safe)

Current set resistor (using 1.0A and selecting next lowest resistor):
47 * 1.0 / (7 - 1.0) = 7.83 kOhm
I've got a drawer of 7.5kOhm resistors.

Wired as full-winding:

Max running voltage:
32 * sqrt(40mH) = 202.4V (Still safe)

Current set resistor (getting fuzzy here... 0.5A?):
47 * 0.5 / (7 - 0.5) = 3.61 kOhm
I've got a drawer of 3.32kOhm resistors.

As far as I can tell I should be well within spec for the G540 and the 48V supply that comes in the Keling controller. But by all means let me know if any of my assumptions or calculations are wrong.

Thanks again for all the feedback, and my apologies for asking questions before laying eyes on my mill and reading off part numbers. Feeling kinda foolish, but I'm glad for the help.

Tom

P.S. Many many years ago, a friend and I were dragging our sorry butts out of the final for a class we took on modeling stellar atmospheres. He turned to me and said, "I just wanted to look through a @#$% telescope!" After reading through the G540 docs, the stepper motor whitepaper from Gecko, the motor specs from Shinano Kenshi, and stumbling through the calculations, I have to agree. "I just wanted to cut metal!"

Just to keep things in sync I copied my last response from the Zone below. Short story is if you can rewire the motor in parallel then they will work OK.

Quote:

If the above specs are correct, rewiring the motors to Bipolar Parallel would make a 1 A 127 Volt motor into a 2A 61V motor. This is well within the specs of the G540 and it should run fairly well with 48-50V.

Well, that is kind of what I said. In series configuration that are definitely not a good match. IF they can be rewired in parallel configuration they would perhaps be OK. Judging by the new information the OP provided his motors wired in parallel would still have a per phase inductance of 10mH. While they will work OK they are above Geckos suggestion of about 3mH for max power output from the drivers. If I had these motors on hand I would use them though.

Quote:

You are comparing apples to oranges. The G540 cannot draw more than 3.5A per motor. The POWER SUPPLY however must supply enough amps for total motor consumption. A single 3.5A motor connected to a 12A PSU will only draw 3.5A of the PSU capacity. FOUR 3.5A motors connected to the same PSU will need to draw a minimum of 8.4A. At no time will the above G540 be asked to draw more than 3.5A per motor. This is far below the 7A rating of the internal fuse, so that does not apply to the PSU size calculation.

No, actually I am quite correct. Saying that a G540 can draw 8.4A through a 7A fuse is nonsense. The G540 has a 7A fast blow fuse, it will never, ever, ever draw more than 7A, the 7A internal fuse prevents that from happening. The problem with using rule-of-thumb formulas is that you have to understand the assumptions they make and what the numbers they give you actually mean.

The formulas that Gecko puts out (the ones everyone are so fond of using) give a good estimate of the voltage to use to drive a given motor and get the most power with least heating. It in now way implies that it is the max voltage that can be used. As long as you do not exceed the current or temp specs of the motor or driver then your OK, the extra voltage will produce more heat than power form the motor though.

In a similar manner the formlas that are floating around to size a power supplies current capaicty assume you are sizing a linear unregulated supply. When sizing an unregulated supply you have to oversize the current capacity to keep the supply voltage in the proper range (the more current you draw from an unregulated supply the more the voltage drops.)

If your using a good quality switch type power supply then there is absolutly no reason to use a 10A or 12A supply. It won't hurt anything but you spending more money for capacity that the G540 will never use.

_________________
Happy Machining!

Jeff Birt - Soigeneris.com
Proud Dealer of Taig, Precisebits, Gecko 540,
SmoothStepper and A2ZCNC products.

Man, that is GREAT news. It shouldn't be problem to wire them in parallel, so that's how I'll set it up when it arrives.

In terms of getting maximum performance out of my motors, it'd be nice, but it's not my ultimate goal. To be honest I think properly driven 200 oz-in motors are massive overkill for a machine this size. When I got the thing it had a 1/10 HP spindle motor on it. I'm glad to see Taig has moved on to bigger and better spindle motors. But it did make me laugh to know that the motors as specced should be able to pick me up off the floor if I grabbed onto the Z axis, but the spindle motor as delivered would stall on a 1/4" end mill taking a 1/8" deep cut.

I remedied the spindle motor some years ago with a treadmill motor. That's been working really really well. But it was some time after that conversion that the shortcomings of the motor driver electronics really started to bite hard. In short, there was no way the Z axis would be able to pick me up off the floor because I don't think the motors were being driven all that well. The spindle could handle a 1/4" end mill taking a 1/8" deep cut, but the steppers couldn't keep up with it and I lost steps in my parts. A lot of back-and-forth discussion on the taigtools Yahoo list and the assumption I was pushing things too hard led to lighter and lighter cuts, slower rapids, etc., but in the end it turns out I was losing steps even when the tool wasn't touching metal.

I'd love to have the ability to do 120IPM rapids, but honestly I'd be fine with 20IPM provided I never dropped a step. I'd love to be able to hog out metal with a 1/2" mill plunged 3/4" deep, but if I could do a 1/4" mill 1/4" deep and never lose a step, that's great with me. I'm a hobbyist, and only occasionally do something that would be considered a production part. Typically in those instances I've got time on my hands and can take things a little slow.

But I can't even count the number of parts I've ruined by losing steps when I'm hours into them. That is something I never EVER want to do again.

If the G540 can drive my motors, wired parallel, so that I never have to worry about lost steps ever again, I'm good with that. Getting better performance out of my mill would be icing on the cake, but it's icing I'm willing to do without provided I never miss another step.

Tom

My new controller showed up earlier in the week, but various things (like work) kept me from setting it up until yesterday. Among other things I found out that the 1+ year hiaitus from use in a dirty shop meant my mill computer was in pretty sorry shape. Next project: better fitting dust covers!

I had a new donor box waiting to be built out as a mill computer, so I started there and got things rolling last night. HOLY COW I'm in love with the G540. CRIPES that's smooth. I'm so used to hearing midband resonance as I ramp up the speed, but the thing just keeps singing a pretty tune.

I did the setup work in my study rather than out in the shop, so at this point the only physical axis I've run is my rotary stage, which I brought indoors for testing. But I tried it on all four outputs of the G540. I'm a very happy individual. Tonight I'm planning to re-terminate all the other motors on the mill and try a full four-axes-at-once test.

Being paranoid, I did what I could to try to make it lose steps. Without some outside assistance, the G540 really wouldn't. Even cutting air, my older controller was losing steps from time to time, but after hours of banging away at the G540, it always came back to the same spot every time. So this is already good news for me.

I also tried loading the motor at various speeds to see what it took to stall it. Theoretically I knew why having a high inductance would hurt, but it helped to have a very physical example sitting in front of me. Basically at low speeds the thing is a horse. At higher speeds the torque drops off really quickly, and is a little too easy to stall.

So for now I'm planning to keep things below 24ipm for rapids and 12ipm when cutting. But longer term I'm likely to replace my motors with something better suited to the G540 and the cutting forces the Taig can generate. But that'll have to wait for a while. Right now my available shop cash is somewhat below zero.

Tom