View Full Version : PS help

11-16-2003, 11:38 PM
Hey, I am in need of a little help moderately soon. I need to make a 48-54v PS, or buy one if its cheap. It's to run my steppers and gecko drives. I got the G201s if any of you are interested in knowing;)

I am having problems finding my transformer and knowing what size capacitors I need, I knwo I need like 80v capacitors, but thats about all I know.

For the bridge rectifiers, I know pretty much what I need to know, although I am not sure if they will need heatsinking or not. I can figure that out from just messing with it though.


11-20-2003, 09:36 PM
Hi Jon,
Mariss has some PS Info (http://www.geckodrive.com/ycom/documents/C163R16_power_supplies.pdf) on his site.

If your using premade bridge rectifiers, the case on the larger sizes is aluminum and they do need to be heatsinked. I prefer to oversize my rectifiers, usually using 25A minimum. Its cheap insurance.

Also bear in mind that the Gecko's are PWM (chopper) and the steppers will draw much less than their rated current from the power supply when you drive them with 10-25X their rated voltage. IOW if your total rated current is 12Amps for the motors, the average draw will be less than 4Amps, I've read that actual current draw will be 20% or less but I have not tested this. But I'd still size my PS for no less than 1/2 the total rated current. I don't like to work them to their max.

More capacitence is better on this type of simple unregulated PS. If you size your cap using Marriss' formula, going bigger is better, and he recommends it. He should know, he is Gecko Drive.

I can't help much with finding transformers, I'm scrounging mine from old PSs that aren't worth repairing where I work. To figure your transformer AC output, multiply your desired DC Volts by .707 , IOW for a 50V PS you'd need a 35VAC out transformer. To work it the other way multiply the AC output of a transformer x 1.414 , 35VAC X 1.414 = 49.5 VDC after its rectified and filtered with a cap.

G201's are nice drives, I have a set for my CNC Router project. I plan on starting assembly soon and having it done this winter. A friend is using G210's on his CNC plasma cutter and loves how smooth they are. Hes running his 150oz/in motors at 20X their rated volts and wants to up it to 25X to see what difference it makes.

Also Mariss offers a G901 pulse multiplier board for upgrading G201s to G210. I have the original G201's and the IC is soldered to the PC Board, but I can still cut it out, desolder the pins and install a socket to take the G901. I only paid $75 ea for my G201s about a year ago, so I figure the modding is worth the savings. Last I heard there were no more original ones left and I'd gotten some of the last few. All the later G201s have the socket so the upgrade is easy, if you ever need to.


11-20-2003, 09:41 PM
All electronics: http://www.allelectronics.com/cgi-bin/category.cgi?category=790500&type=store

Has a 50v at 2 A,
they also have a 24V at 5A You could use two in series in phase.
You didn't say how much pwer you needed.

11-21-2003, 08:39 AM
woops I forgot the amps, the total of the motors is like 13 amps. and I will be running them at 2 amps a peice(selecting on the geckos)

I do know a good chunk, and I noticed that your calculations are backwards. a 50v power supply would have a peak voltage of 70 some volts or around there.

I recently built a 12v power supply, and without a load it puts out 17v but with it puts out only 12.

pminmo: I saw those, I was hoping for a single transformer, but I am debating on the 50v ones and these 24v transformers I saw at a different site(cant remember off the top of my head)

The main thing Im looking for is finding a transformer, and figuring out how much capacitance I need, Ill check those PDF files and see if I can find what I need.

-edit- I see that 10,000uF will do according to his pdf files.


11-21-2003, 06:52 PM
The standard way to rate a PS is its no load Volts output and its max load Amps, not its loaded Volts and Amps, and here in lies the confusion. Check out Mariss' PS Info (http://www.geckodrive.com/ycom/documents/C163R16_power_supplies.pdf) and you'll see that he rates PS's the same way.

My calculations are accurate, and yes you will get some sag under load, especially if your filter cap is undersize. If your sagging 17v to 12v under load (30% sag, or 5V ripple) your cap is definately undersized, use that PS on a 12V radio and your going to have one heck of a hum problem. As I said "More capacitence is better on this type of simple unregulated PS...".

One advantage of steppers in is that they don't need as tightly regulated of a PS as a radio does for proper operation.

One more thing about Electrolytic Caps, buy new ones rather than using old ones, they dry out with age and heat, loosing some to almost all of their capacatence. If you used old Caps on your 17V PS, that probably added to the sag/ripple, by being under their rated value.

For transformers, if your looking at center tapped ones, you can use 2 and hook to the outer wires on one and one outer and the CT on the other. IOW 2 24VAC CT xfmrs, can be set up to put out 36VAC X 1.414 = 51VDC at the rated current of the xfmrs. Just be sure to connect the secondaries and read the VAC on the wires your going to use to make sure that their in phase, boosting rather than bucking, before you connect them up.

How are you figuring 13A current draw out of 3-4 (?) steppers with 2A each draw? Geckos power the windings (as explained on the Yahoo group CAD_CAM_EDM_DRO, by Mariss) by putting full current (2A) on one winding, then stepped percentages reducing the current on one and increasing the current on the other (microstepping) to maintain 2A on both, until it gets to the last microstep where the full 2A is on the other winding, creating one full step and 2A continous draw per motor. 3 Steppers with Gecko Drives, set to 2A per drive, would draw 6A. Or are you driving 6 steppers with 6 Gecko Drives?


11-21-2003, 09:05 PM
UMRK had a good idea by using 24vac and 12vac. Just make sure they are in phase. http://www.allelectronics.com/cgi-bin/category.cgi?category=110&type=store for a suitable rectifier.

11-22-2003, 08:13 PM
I found this ebay item, i have not bought any but they look ok. For $50 it may be worth a try.. i'm definately looking at buying some.

They can also be hooked in parallel so if you buy two you'll end up with 48V 20A


Traco Power TSL480-155PX Industrial Power Supply
Input: 93-264VAC Auto-ranging, 50/60Hz
Output: 48-55VDC Adjustable, 480 Watts, 10A

Screw-Terminal Input and Output
Universal Input Voltage
Output Voltage Adjustable
Short-to-Ground for Negative Voltage!
Metal Case (Aluminum), 9x5x5in
Easy Snap-On Mounting on DIN-Rails

-155 Model Is Custom -148 Model with Wider Operating Temperature Range
Low Harmonic Emissions on Input ('P' in the model#)
Extremely Low Output Ripple and Noise ('X' in the model#)
High Efficiency
Overload Protection
Parallel Operation Possible
CE Compliance to European EMC and Low Voltage Directive
Compliance to EN 61000-3-2 (PFC)
Conducted Emissions to EN 55011, Class B, and FCC Part 15 Level B
Noise Immunity to EN 50082-2
Safety Approvals to IEC 60950, EN 60950 (SELV) UL/cUL 1950, and UL 508

These power supplies are brand new, still in box. They were used both as bench power supplies on our manufacturing/test line, and as in-unit 48v power for a product that we manufactured for the telecom industry. Unfortunately, we are closing the business and are forced to sell our entire inventory of these $300+ units for pennies on the dollar.