Linear vs. Switch Mode power supplies for steppers

[doogle]

Hi!

First post here! Has been useful just lurking so far though. Looks like an excellent community and I can see myself spending a lot more time on this site

I recently purchased a 3-axis router (no motors, spindle or electronics) and I'm trying to work out what I should get for the power supply. I need 48V at a little over 10A. So I have the choice of going the linear route, using a toroidal transformer, bridge rectifier and caps (although this looks nice, can anyone comment?)
Or I can get a switch mode supply (which might work out cheaper seeing as a guy at work might have a suitable one for me for free). I haven't found much about using SMPSs for stepper motors and stepper motor drives (I'm planning on using gecko G201s) but I did see one thing (can't remember where) about possible issues with them because of the nature of motors and back EMF (IIRC).

I was wondering if anyone could tell me the pros and cons of both types of power supplies when used for steppers and stepper drives, or indeed if SMPSs are just not suitable and I should go with a linear supply?

Thanks!

[TOTALLYRC]

Originally Posted by doogle Hi! First post here! Has been useful just lurking so far though. Looks like an excellent community and I can see myself spending a lot more time on this site I recently purchased a 3-axis router (no motors, spindle or electronics) and I'm trying to work out what I should get for the power supply. I need 48V at a little over 10A. So I have the choice of going the linear route, using a toroidal transformer, bridge rectifier and caps (although this looks nice, can anyone comment?) Or I can get a switch mode supply (which might work out cheaper seeing as a guy at work might have a suitable one for me for free). I haven't found much about using SMPSs for stepper motors and stepper motor drives (I'm planning on using gecko G201s) but I did see one thing (can't remember where) about possible issues with them because of the nature of motors and back EMF (IIRC). I was wondering if anyone could tell me the pros and cons of both types of power supplies when used for steppers and stepper drives, or indeed if SMPSs are just not suitable and I should go with a linear supply? Thanks!

If the regulated power supply has enough amps to do the job, then go for it.

Many of the suppliers out there sell a regulated supply to go with there steppers drives.

The pmdx module looks good but i have no experience with their products.

I only use unregulated supplies but that is because that is what came with my machines.

[irving2008]

The main issue with SMPS is how well they regulate under spiky loads. A linear supply will have a big (10000uF+) output capacitor that provides a reservoir to meet the peak demand so a linear supply can be derated for peak v normal operation.

Most SMPS cannot handle a large external reservoir capacitor because of the inrush charging current at startup can prevent the SMPS inverter starting (the supply sees it as a short circuit on power on) so becasue an SMPS actively current limits it therefore must be higher rated to handle peak current demand. One that soft current limits is obviously better than one that limits by shutting down.

A linear supply can (empirically) be continuously rated at N * motor phase current * .67 where N= # of axes where the peak current is N * 2 * motor phase current. An SMPS should be rated nearer the latter figure although statistically not all axes are stepping simultaneously so some derating up to 70% could be allowed.

In a nutshell, 3 x 4A steppers need a 8 - 10A linear supply but more likely a 16A SMPS to be safe (i.e. not lose steps under extreme conditions).

In your situation, if you can get an SMPS for free go with it... you can always get a bigger supply later and flog the original on eBay