Homebuilt power supplies for GeckoDrives
 

This is an example of a typical power supply with a 75V 300VA output to drive 4x Gecko 200 series drivers.




Major components:

- Toroid transformer 300 VA (VoltAmpere) producing 50 Volt AC (Alternating Current) when plugged into your mains. About 125mm (5") outside diameter. Price about $70.

- Rectifier to convert the 50Volt AC to DC (Direct Current). The DC voltage is 1.414 times higher, giving just over 70V. (The Gecko's limit is 80V). The rectifier need only be sized for around 6 Amp, but such small rectifiers need soldered wires. Here a 25 Amp rectifier is being used because it has a metal case and pluggable connectors. About $3

- Capacitor must handle the 70 to 80 Volt and the Gecko people say that it should be about 7000MicroFarad or bigger. I used a 100V, 10000MF electrolytic capacitor at $18

- Fuseholder. Fuses only make the early gecko's more "repairable" if something goes wrong. If your shipping charges to California and back exceed the cost of the gecko, you need not bother with fuses. The later G203V has its own fuse.

Overall size of power supply: 150x150x125mm [6x6x5"]

The three major components are the transformer, rectifier and capactitor. They are discussed individually in sub-threads at the top of this page.

CAUTION: THESE ARE DANGEROUS VOLTAGES AND CURRENTS. CAPACITORS CAN HOLD CHARGES WHEN APPARENTLY SWITCHED OFF, THEY CAN EXPLODE IF INCORRECTLY USED. FOOLING WITH THIS STUFF BY YOURSELF IS PROBABLY ILLEGAL.

SERIOUSLY CONSIDER BUYING A READY-MADE SUPPLY

A bracket from the local hardware store......


.....becomes the frame of the power supply. Cut, bend, trim some corners, drill some holes.....

150 x 80 x 100 translates approx to 6 x 3 x 4 inches. About 2.5mm thick

Having tried a few setups in my little case I have discovered that I think it is a little small, so I have begun making another setup, and building it all into a stand alone cabinet where both computer drive system, and computer screen will be built into, so far this is my electrical back plate...

It is lasercut, and the Riser plate for the Drives is also lasercut...

I have also included a little picture of my Homemade Power supply... Delivering 1.15Kw at 77Volt's DC unloaded, and stays stabil at 70Vdc loaded.... Nice, has a little bigger footprint due to the size of the toroidal.. 8 inches...

Beautiful!!!! She's a work of art.

:eek:...and Doug knows power supplies

I'm also very happy with the build up of it... Now onto tthe wiring of the things... Enough to do....

You may want to reconsider the location of the bridge rectifier.There was a post recently on CNCzone that showed a pretty ugly failure when the bridge overheated and shorted due to a loose screw holding the bridge to a painted metal surface. You have no heatsink at all for your bridge. If it's very lightly loaded you may get by with it, but maybe not. See http://www.cnczone.com/forums/showthread.php?t=50845

Mike, I think the CNC zone guys are over-reacting to the "heatsink" not being good enough for a faulty rectifier. The metal case rectifiers are typically good for 25 Amps without any heatsink. On our first MM I also had the rectifier mounted to wood for quite a long time - it stayed cool to the touch. Personally, I don't like wood in the control box because things can go wrong and I don't want surplus fuel for the ensuing fire. In this particular application, there is no "heatsink" concern - it will run cool if nothing is faulty.

a little progress
 

I recieved most of my parts for my kitchen table project, the boss said that it's not going to happen on our kitchen table though:):) I am using a pretty big box so I should be able to fit everything and still have alot of room to spare. I have had my computer on order from Dell for 3 weeks now. I think the hold up must be the parallel port, not sure what else would delay the delivery. I have everything else for the test run and I am anxious to try to make the motors turn:D:D

Looking at the pictures on the first post, does the -ve pole of the capacitor must be grounded?

By definition, the negative side of a stepper power supply IS ground. Mariss, at Geckodrive, recommends that ALL grounds be connected. It took me a while to accept that theory because I came from the "old school" that favored floating (not connecting) logic ground and chassis ground, and floating the grounds of independent power supplies. However, after changing to Mariss's method, things work just as well, if not better. In other words I haven't had any problems since I started to use his method.

So Mike, are you saying you tied ALL grounds/commons together...

1. The power supply negative.
2. The Gecko heat sink.
3. The Control Box metal case(including the front panel)
4. The AC ground lead ( USA 3rd pin in an AC plug/socket) tied to earth ground via the electric feed.
5. The PMDX-122 GRD pin?
6. The Gecko COM pin to the PMDX-122?

I thought I read about ground loop problems elsewhere on the Forum even to the point of one builder isolating the Printer Port Connector.

Regards,
John

John, 1, 2, 3, and 4 are tied together. Points 5 & 6 are tied to the ground of the PC.

On my PCs, the power supply is connected to earth ground (large round pin in the power cord) and to the power supply's case. In my shop, I have run a grounding strap from the PC's power supply case to the common ground point on the CNC machine. All axes of the machine have a grounding strap that goes from that common ground to the individual axis. All ground points in the control box are also tied to that common ground. ONE END of the shields in all shielded cables connects to that common ground. The OTHER END of the shield is NOT connected.

As nearly as possible, I have a Star-type connection (in contrast to a daisy-chained connection). With a single ground "stud" and by grounding only one end of the shields in the shielded cables, the chance of creating a ground loop is virtually non-existent.

My PC is on a different circuit than my Shopbot (in fact, it is fed from a different power panel), but by connecting the PCs power supply ground (via the power supply's case) to the Shopbot's ground with the grounding strap, I can be certain that a 5V signal produced by the PC's power supply is seen as a 5V signal by the controller box.

As I said earlier, I had a difficult time accepting the fact that the grounds should be tied together. But, now that I've actually done it and spent a good deal of time thinking about it, it makes sense. If two devices each have their own power supply then the grounds must be connected between those two devices or the signal will not be referenced to a common voltage. Without a common reference point, 5V produced by one device could be seen as 2V or 10V by the other device.

One way that that type of problem has been handled in the past has been to connect every signal via an opto-isolator. With an opto-isolator, the ground and signal on one device cause an LED to illuminate inside the opto-isolator when a signal is active. The other device has its input circuit connected to its own ground and to the collector on the opto-isolator. When the LED goes active, the photo-receptor inside the opto-isolator sees that LED's signal and produces a valid signal to the second device. Since the connection is just a light beam, there is no possibility of having mismatched voltages. I still use opto-isolators when I interface two devices that use different voltages, such as connecting a 24V proximity switch to a 5V computer card. I also like to use opto-isolation when a signal has lots of electrical interference from other devices. The response time of the opto-isolators filters out much of the electrical noise.

Hi, when we say that ALL grounds are to be connected, does that include my 24VDC din rail power supply I'm using to power the e-stop circuit. Thanks

Andrew,

Normally ALL grounds are connected together. Ground is the reference point from which all voltages are measured. In other words, if the grounds are all connected, the 24VDC DIN rail power supply would be 24VDC if measured from any point in the circuit. If that ground were not connected to a common ground, the 24VDC could be any voltage when measured using the ground of a different power supply as ground reference.

Bonding DC common to ground is fairly common in industrial wiring. The only time it is not is if you need an isolated circuit.

power supplies
 

Thanks for the advice Mike and Pete, I wasn't sure if the negatives of two dc power supplies could be connected.

If you wish to bond all the -ve of power supply, u do it by connecting it to the chassis ground, not just jointing the two power supply -ve or 0V terminals together with a single wire.