Switching vs Linear Power Supply

[TheBulk]

Which should I get?

Is there really a difference in the end result?

[zeed]

The main reason I decided to go linear was I already had a transformer,plus it is dificult to find higher voltage switching supply(60-70V)

[DonFrambach]

Although I'm far from an expert, I think that, electronically, it would make no difference for a CNC machine. Switching power supplies are much smaller and lighter and, I think, cheaper.

There is, theoretically a little more noise in the DC output of a switching power supply so some radio operaters like linear supplies. High quality regulated switching power supplies put out little noise and seem to work fine.

I'm using a switching power supply for my system.

[Hyrum R]

I've used both, and I highly prefer a linear power supply. Reason? Because I burned up a couple cheap switching power supplies. When they were working, I couldn't tell any difference in how the machine ran vs. the linear power supply. Eventually, sawdust would get into the power supply, causing the fans to stop working, which caused it to melt down. I was very fortunate to find a very large used linear power supply on eBay for about $80. I've since put all my components up inside a cabinet, so dust isn't as much of an issue. The switching power supplies I had weighed maybe 4 lbs. total. I wouldn't be surprised if my linear power supply weighs upwards of 25 lbs. The 23,000 uF capacitor makes it look really impressive.

[zeed]

Do you have anything else in your linear supply besides bridge rectifier and capacitor?

[Al_The_Man]

Previous post.
http://www.cnczone.com/forums/genera...er_supply.html
Al.

[Hyrum R]

Do you have anything else in your linear supply besides bridge rectifier and capacitor?

It's just a transformer, capacitor, and a 20 amp fuse mounted to a nice metal chassis. This could possibly be the exact one I have, but I paid a lot less for it than that!
http://www.mpja.com/prodinfo.asp?number=6646+PS



Mine was rated at 10 amps on the eBay listing, but it has a 20 amp fuse in it. I don't think I'm near its limits with 3 little 269 oz-in motors.

[TheBulk]

Thanks for the responses guys

[vanjast]

Linear supplies are bulkier (the heavy transformer required) and are less efficient (generate more heat loss) than a switching supply.
Switching supplies would generally be much cheaper for the same power rating, as the components are a lot smaller.

If anything, a (over)loaded linear supply would be more problematic with motor positioning than a switching supply, as power ripples would be more pronounced in linear supplies. There also might be a frequency band where loaded switching supplies interfere with the motors, where your step frequency is close to the operating frequency of the supply.

Under normal load conditions, there would be no noticable difference

[RomanLini]

I'd like to add a couple of points;

1. Linear supplies are generally much more reliable. They have larger components and are more rugged where SMPS are made ina very competitive industry using the smallest cheapest parts they can get away with. But SMPS can be made more reliable with good fan extraction.

2. You are correct that a linear supply can produce more mains frequency ripple on the PSU voltage, but generally stepper drivers are extermely tolerant of mains frequency ripple and it has little to no effect on motor operation.

Given an unlimited budget and no weight/size constraints I would use a linear PSU with a nice big transformer and big caps etc.

Most people don't need anywhere near the amount of PSU amps that they think they do. I have a linear PSU on my machine with a 5 amp ammeter on it's front panel. My Machine has three 2.6A 400oz stepper motors, and at hold the PSU ammeter never shows over 2 amps. Even on some fast traverses and accelerations the PSU barely reaches 3 amps.