power supply needed.... please help

[goneflyin]

I'm in need of some serious help. Here's where I'm at.

I'm converting my little mill to cnc so I decided to go with the linistepper boards and 425 oz/in motors. I bought 4 of the linistepper boards as well as the beak out board which simplifies the connection of the four controllers to the printer port.

My problem is in finding a suitable power supply for this setup. I don't want to have an individual power supply for each of the driver boards, it just seems a bit ridiculous, but I can't find anything which seems suitable. I looked at my older hobby cnc controller and pictures of their new ones and it looks like it has a 24v transformer, going through a bridge rectifier, then into a large capacitor, and then into the driver board. A setup like this make much more sense to me, problem is that I'm not very knowledgeable about electronics and I could really really use some help in figuring out how I'm going to power these boards.

The motors I bought are NEMA 23 BIPOLAR STEPPER MOTOR 425 oz-in, 1/4” Diameter shaft with a flat

KL23H286-20-8B (Dual Shaft) Specification Price: $49 Rated Current: 2.8A, Rated Voltage: 4.17V (in Bipolar Parallel) Torque-Speed Curve

If you can help me please please do.

Chris

[irving2008]

Originally Posted by goneflyin I'm in need of some serious help. Here's where I'm at. I'm converting my little mill to cnc so I decided to go with the linistepper boards and 425 oz/in motors. I bought 4 of the linistepper boards as well as the beak out board which simplifies the connection of the four controllers to the printer port. My problem is in finding a suitable power supply for this setup. I don't want to have an individual power supply for each of the driver boards, it just seems a bit ridiculous, but I can't find anything which seems suitable. I looked at my older hobby cnc controller and pictures of their new ones and it looks like it has a 24v transformer, going through a bridge rectifier, then into a large capacitor, and then into the driver board. A setup like this make much more sense to me, problem is that I'm not very knowledgeable about electronics and I could really really use some help in figuring out how I'm going to power these boards. The motors I bought are NEMA 23 BIPOLAR STEPPER MOTOR 425 oz-in, 1/4” Diameter shaft with a flat KL23H286-20-8B (Dual Shaft) Specification Price: $49 Rated Current: 2.8A, Rated Voltage: 4.17V (in Bipolar Parallel) Torque-Speed Curve If you can help me please please do. Chris

Chris,

Building a power supply is not hard, but to be honest you might be better off buying a ready made one.

You do realise that those motors run in Unipolar mode (since the Linistepper is a Unipolar driver only) are rated at 2A per phase whereas the standard Linistepper 'out of the box' is a 1A per phase setup so you'll be getting half the torque out of the motors that they are capable of.

Anyway, since these are unipolar the maximum current will be 2A per motor (or 4A if you mod the Linistepper board). For 4 motors you can assume 4 x 2A x 80% = 6.4A, so you are looking for a 150W power supply - there are lots on eBay for around $30 -$50 (example) so there is little point in building your own, you couldnt acquire the parts for that.

[photomankc]

I think those motors are going to be disappointing with that driver. The unipolar torque on them would be something like 305 oz/in at 2A. If you are running it at half that then you are looking at maybe 150 oz/in? The mH rating for unipolar is 6.8. 32*SQR(6.8) is 83. That's the max voltage they could be run at. Something in the 12 or 24V range is not going to be able to get the coil energized fast enough to move at high speed.

With the right driver those motors would be fine but I think the linistepper is not a match for them.

[irving2008]

Originally Posted by photomankc I think those motors are going to be disappointing with that driver. The unipolar torque on them would be something like 305 oz/in at 2A. If you are running it at half that then you are looking at maybe 150 oz/in? The mH rating for unipolar is 6.8. 32*SQR(6.8) is 83. That's the max voltage they could be run at. Something in the 12 or 24V range is not going to be able to get the coil energized fast enough to move at high speed. With the right driver those motors would be fine but I think the linistepper is not a match for them.

Photomankc, 100% agree with you and I'd meant to add that to my post but forgot! However its not true to say thats the 'max' voltage. its the optimal voltage to push the required current through the coil. You could run them at 150v off a line-powered driver.. but it would be a waste of money and driver.

Bottom line, a Gecko driver at 50v/3A and wired Bipolar would be a better match than the Linistepper, but then again the Linistepper is cheap... even tho the Linistepper documentation does say its best for 1A or so motors and 12-24 volts....

[Kelinginc]

Originally Posted by goneflyin I'm in need of some serious help. Here's where I'm at. I'm converting my little mill to cnc so I decided to go with the linistepper boards and 425 oz/in motors. I bought 4 of the linistepper boards as well as the beak out board which simplifies the connection of the four controllers to the printer port. My problem is in finding a suitable power supply for this setup. I don't want to have an individual power supply for each of the driver boards, it just seems a bit ridiculous, but I can't find anything which seems suitable. I looked at my older hobby cnc controller and pictures of their new ones and it looks like it has a 24v transformer, going through a bridge rectifier, then into a large capacitor, and then into the driver board. A setup like this make much more sense to me, problem is that I'm not very knowledgeable about electronics and I could really really use some help in figuring out how I'm going to power these boards. The motors I bought are NEMA 23 BIPOLAR STEPPER MOTOR 425 oz-in, 1/4” Diameter shaft with a flat KL23H286-20-8B (Dual Shaft) Specification Price: $49 Rated Current: 2.8A, Rated Voltage: 4.17V (in Bipolar Parallel) Torque-Speed Curve If you can help me please please do. Chris

Check here for the power supply

http://www.kelinginc.net/SwitchingPowerSupply.html

[goneflyin]

Yes I spoke with James about the motor values and he suggested replacing a couple of the resistors to get the board to safely drive the 2A motors.

If you can suggest a power supply I would definately consider buying one rather than building one.

Chris

[H500]

Those motors need 2.8 amp. If you use the linistepper, your power supply will need to be about 600W at 24v. You will need BIG heat sinks.

Your old hobbycnc drive will work much better if you can use it with a 40v supply. The linistepper is a very poor choice for those motors.

[irving2008]

Originally Posted by H500 Those motors need 2.8 amp. If you use the linistepper, your power supply will need to be about 600W at 24v. You will need BIG heat sinks. Your old hobbycnc drive will work much better if you can use it with a 40v supply. The linistepper is a very poor choice for those motors.

Only in bipolar parallel, in unipolar they are 2A per phase, and so at that current per phase he will require 24 x 4 x 4 X.8 = 310W. I don't quite see how you got to 600W.

on a 24v supply Each TIP122 transistor will dissipate approx 25W average and there are 2 of the 4 dissipating at any time so the total dissipation for 1 driver is about 50W. Assuming all transistors are bolted to the same heatsink it will need a heatsink of around 2degC/W without fan cooling, or probably get away with 6degC/W with fan cooling. Thats a finned heatsink around 6" x 4" x 1.5" fins vertical - per driver...

I agree, the linistepper is cheap, but a poor choice for these motors and by the time you've added decent heatsinks etc its not cheap any more...

[H500]

I used 24 x2.8 x2 x4. =537. RMS current was assumed.