Geckos and switching power supplies

[llamatrails]

From thread on 5/5/2010:
http://www.cnczone.com/forums/showthread.php?t=104578

Almost all of our OEM clients (OK, customers) use switching power supplies. The parity or break even point between iron supplies (xformer, rectifier and bulk capacitor) and switchers was passed a few years ago. Almost everyone uses switchers now. There are a few things to take into account when using switchers with motor drives. Switchers work at high frequencies (40kHz or higher) and have tiny output filter capacitors. Motor drives need big capacitors because a lot of energy moves between the drive and power supply. You need to put 10,000uF on the switcher output VDC for step motor drives and at least 30,000uF if you are using servomotors. They form the very necessary "flywheels" on the source supply. Avoid sophisticated supplies with overvoltage crowbar protection. The power supply "sees" more voltage on the output than it should and it shuts down. The voltage came from a regenerating drive (decelerating) and it fools a sophisticated power supply into thinking something is wrong. If you use an overvoltage protected supply, decouple it with a rectifier diode going to your external 10,000uF or 30,000uF capacitor. This makes the even most persnickety switching power supply behave like a *****cat. Mariss

I haven't found this information in any of the Gecko FAQs or in any if the different wiring diagrams here on cnczone.

Can this info be added to the FAQ ?

The capacitor wiring is straight forward, but could someone describe further the rectifier diode ? What would be an example of a proper diode part number/rating ? Should it just be in line on the +VDC output before the capacitor ?

I've also come across mention of a drain resistor for the capacitor. How would it wire in, and what would be a likely ohm/wattage for it ?

[CoAMarcus]

We can add that to the FAQ.

A bridge rectifier that I recently used to build a 48VDC power supply is a GBPC3504 that I got from Digi-Key. Here is a link to the specific component:

http://search.digikey.com/scripts/Dk...504-E4/51GI-ND

You wire a bridge rectifier into the power supply like it is shown in this diagram:

http://geckodrive.com/upload/2793powersupply.gif

A drain resistor is not needed for the power supply as the motor controls act as a suitable drain.

Marcus

[llamatrails]

Thanks for the reply Marcus.

I'm still not sure about the diode. You referenced a bridge rectifier to change AC to DC, but my question and reference to the posting by Mariss is for the use of a switching power supply which is already outputting DC. What type of diode would we use, in line, I guess ?

As for the drain resistor, thanks again, that clears that up.

Rick

[bobsch]

Since the output of the PS is already DC use a straight rectifier such as this: http://search.digikey.com/scripts/Dk...name=D4020L-ND

Put the diode in-line with the positive side of the PS, before the 10,000 uf cap.

[llamatrails]

Thanks, Bob. Now I got it.

Rick