Need Help!- Cheap power supply?

[Robotics Guy]

I'm building a small CNC machine as a hobby project and just realized I hadn't considered how electricity was going to get from my wall outlet to the motors. In other words, I need a power supply The motors I'm using are 2-phase 2A and I guess I need to run them at about 30V. So, that's 4A per motor, times three motors, means I need about a 30V 12A power supply. I've been looking at them today and many cost hundreds of dollars. Is there a cheap source to buy these from, or a guide on how to build it myself?

Motors: http://www.mpja.com/prodinfo.asp?number=17748+MS

[jschmitt]

You only need a max of 2 amps per motor. The rule of thumb for minimum power supply is 2/3 x amps x number of motors. So it looks like a 4 amp would work. Find out what drivers you are going to use and match the voltage to the driver.

[der_fisherman]

Are you able to solder well? Can you get hold of electronic components easily? If yes to both, I can strongly recommend a power supply I built last year with a PCB from Elektor magazine.

It cost me around $50 to build (could be built even cheaper if you have a suitable enclosure and or transformer etc..), works perfectly, can be programmed (with some resistors) to supply from 10 to 40 volts at 10 amps. Extremely stable output.

Its a switched mode supply (using some clever chips for all the complicated stuff!) with a few external components) so you only need to pay for the amount of electricity you use, not like normal linear mode power supplies which take power all the time no matter what you are doing (or not!).

Its actually about 85% efficient.....which is extremely good.

It was originally designed for a HiFi system, so the voltage is very, very clean (actually cleaner than you should ever need for CNC!).

It is actually technically speaking a slight overkill, but in the best possible manner. Over current and over temperature protected, what more could you want?

Check out the attached .pdf for full details.....

If you need further help then just ask.....it is for me really lucky that I stumbled onto it, its a really good tip.....

regards.

[Robotics Guy]

Thank you both for helping.

jschmitt -

This video:

YouTube - Stepper Motors - Application and Use Part 3

YouTube - Stepper Motors - Application and Use Part 3

Says "Therefore, if you have a 2 A/PH motor, the motor will require 4 Amps total. If you are driving two motors of this type, 8 amps of current are required." The motors I'm using are two phase, two amps per phase, right? Maybe the video's wrong. I certainly don't know, I'm very new to this stuff..

der_fisherman -

Yes, I can solder. The guy in the video I linked to also said that switching power supplies often times don't work well, or at all, with CNC machines because the starting load is very high. If the supply you built works well for you, maybe that guy's just off his rocker Thanks very much for the excellent article, I'm reading it now and it would be great if it works for me!

[Al_The_Man]

A switching supply is not really necessary for a P.S. for servo or steppers, the linear type is far simpler and generally more rugged.
But both will work.
Al.

[dertsap]

http://cgi.ebay.com/36V-DC-9-7A-350W...3%3A1|294%3A50

i've bought a few supplies from these guys , they are good supplies and well priced

[der_fisherman]

I am using 3 x 2 amp motors with no problems at all.

Your colleague seems to forget a lot about power supplies if unregulated, unless they are simply HUGE and able to supply MANY times the required current, suffer from modulation as and when each motor takes current.

This can affect other motors starting torque if two or more motors are switched on at around the same time (which happens often on a well designed stepper motor setup.....

If an unregulated power supply is HUGE, then a lot of power is wasted just sitting there doing nothing even.

A well designed SM power supply suffers only from voltage drops if you exceed the maximum current. Increasing the size of the output caps can also bridge such possibilities in a very civilized manner, if needed......it also regulates the voltage perfectly otherwise

Remember this power supply I attached the Elektor article of, was designed for a very HiFi sound system, a sound system which actually "misshandles" a power supply far more than any CNC can......and dropping voltage or modulation on a HiFi powers supply will simply ruin the music completely and it will not be HiFi anymore.......

So your colleague appears not to understand power supplies at all......sorry to have to say that....anyone with a modicomb of electronic knowledge will bear me out......

If what he said was true, why would we have regulated power supplies in the first place, why go to all the trouble of designing SW power supplies???? He has not thought out his statemets at all well to my mind.....

Have a great day anyway!!

[BobWarfield]

Have bought both power supplies and toroidal transformers from these guys:

http://www.antekinc.com/

Good stuff,

BW

[Al_The_Man]

Originally Posted by der_fisherman So your colleague appears not to understand power supplies at all......sorry to have to say that....anyone with a modicomb of electronic knowledge will bear me out...... If what he said was true, why would we have regulated power supplies in the first place, why go to all the trouble of designing SW power supplies???? He has not thought out his statemets at all well to my mind.....

At no time did I infer there was no place for regulated supplies, I have been building and using Linear servo supplies for over 40yrs, and compared to the amount of failures of switching supplies that I have seen, I much prefer the ruggedness and simplicity of repair, should something happen to a linear supply. This was my personal opinion.
This type is still prevalently in use today for this purpose, I have yet to see a detrimental effect on the installations I have been involved in.
As I stated, both will work, it is your choice which you prefer.
(An Audio amplifier situation can hardly be compared to a servo/stepper drive supply)
Al.

[der_fisherman]

If you had ever seen an oscilloscope showing music being played and the peaks and troughs, from almost 0Hz upto 50 khz on a well designed (expensive) amp.

Then this being faithfully reproduced by a large power hungry stereo (Quad?) output stages and loudspeakers, you would not have made that statement at all!!!

The loudspeakers are also a very reactive inductive load on the power supply and push it through some very strong contortions....stepper motors are in comparison nice and "stable" loads, ramping up and down and changing direction etc......

Believe me, the difficult load to handle is that of a large audio amp......if your supply can handle music, steppers are a doddle.....

[BobWarfield]

Fisherman, you have what Al is trying to say all backwards.

As you say, steppers are a doodle compared to audio amps, so why bother providing them with audio amp quality power? It doesn't help and it increases the complexity of what you're up to. It simply isn't necessary and the steppers don't care about the extra trouble you have taken. You can build a simpler cheaper supply and they will be just as happy.

That said, if it amuses you, go for it.

Cheers,

BW

[der_fisherman]

The reason it amuses me (a good way to put it by the way, thanks!) to put in a high quality power supply is that I have already helped several people who started losing steps on their machine, but could not find the reasons.

These problems ONLY appeared under "certain" circumstances. There were not always many steps lost, very variable, always just enough to ruin the work.

It appeared to be a frequency or a mixture of frequencies from all the stepper motors, but our test equipment is not refined enough to say that as a fact.....

In each case we found that putting in a better supply (one of my spares) fixed the problems completely and allowed higher speeds to be achieved with seeming no loss of steps.....at least when the same job was run.....

To reiterate, I cannot say exactly what the problems were, but our educated guess was some inter reaction between the 3 axis and the currents being drawn by the motors and the frequency at which some of the motors were being driven.

I have to admit that all of the problems were where the available supply was being used at around 80 to 100% of its designed capacity......so a cheap analog supply that supplies say 200% of the maximum needed current will probably not show any problems.....but that is guesswork on my part....but that makes for a heavy transformer, not cheap either unless you have one lying around.....a bigger case and a larger fan to keep things cool.....

The major problem being with cheap supplies is that there is a lot of wasted power, even if the motors aren't actually running, heat is being generated, power is still being wasted.....

Some simple supplies are not even 20% efficient.....

Also if you are machining for several hours or more, you are simply wasting both money and contributing to the greenhouse effect.......

A reasonable PWM supply will use only 15% of less power when idling....and will only supply enough power as needed at any single point in time.....

Some of the components needed for a cheap supply can also be used in a slightly more expensive/better supply and the difference in cost is therefore very minor!!!

I like reliability and also being sure of not providing an extra source of possible problems, me being basically a lazy person.....!! I hate chasing difficult problems......none of these types of problem have affected me up to now thank God!!

But as you said/implied, each to his own.....everyone must decide for himself what he wants to do......its a free country!

Have a great day.