diy power supply

[eloid]

question for nice diy power suppy, using 3-5 axis system with 500-800 oz
stepper and with gecko drivers what kind of current should I design it for,
also I herd guys allowing / provide more voltage to make them run better
was think about puting a adjustable regulator for just that purpose with
a maxt currtent clamp circuit? would like to know what other have made or done?

[yukonho]

It depends on your stepper voltage and max current ratings.
I believe the magic number is 20 X the steppers voltage rating, and you would need a power supply that could safely cover the max current rating of all your motors added together (although it is highly unlikely that this will ever occur, it does provide a safety margin.
Double check on that voltage info I gave you, just to be sure. Higher voltage is the best way to improve speed and torque from steppers.
No need for a variable set-up, just size it right for your steppers and make sure you have drives that can handle the voltage and current requirements.
Colin

[vger]

Originally Posted by yukonho It depends on your stepper voltage and max current ratings. I believe the magic number is 20 X the steppers voltage rating, and you would need a power supply that could safely cover the max current rating of all your motors added together (although it is highly unlikely that this will ever occur, it does provide a safety margin.

Yikes!! 20 X voltage ?? For a 12 volt stepper that draws 2 amps per winding in full step mode 1 winding at a time is on. Thats 24 watts (which turns into heat) all the time the stepper is on. So if you do 20 X voltage you are saying 240 volts?? The current would go up just the same 20 X as well... so 40 amps YIKES!!! That's 4800 watts !!!! (which turns into heat) You would have a very good hand warmer for a very short while before the motor windings melt (and the drive smokes). If you had 3 of them going and they survived somehow, you could heat a whole house.

For unipolar stepper motors, one winding (minimum) on at all times power is applied to the drives and if you are in half step mode, 2 windings are on at the same time. With bipolar fractional step drives it becomes more complicated, but the equivilant of at least 1 winding is on at all times. I might be tempted to try 2 X voltage (current will double too) with lots of cooling on the motor due to the 4 X wattage (heat).

Build your supply to be capable of delivering a current of at least 150% of the actual current DRAW of all the motors at once. Keep in mind that if you increase the voltage, the current will increase right along with it. Different steppers will handle over powering with differing degrees of success. You can put cooling on them to help to some extent, but there is a limit. Another thing to consider is the health of the magnet in the rotor.... Heat is a magnet's second worst enemy. Heat it up and it will loose its strength. So don't run them too hot.

My first intro to stepper and servo drives was in the military in 1972 after having 6 semesters of electronics before that (yes I learned vacuum tubes ) I've seen a LOT since then.

Steve

[ger21]

This will tell you what you need. Basically, 2/3 of the motors rated current and up to 20x the rated voltage.

http://www.geckodrive.com/photos/Step_motor_basics.pdf

[max_imum2000]

vger
your not completly correct
the new drives today will simply allow you to put higher voltage (20x) and limit the current to safe one (2 or 3 amp)
so your motor wont melt or anything.

[vger]

Originally Posted by max_imum2000 vger your not completly correct the new drives today will simply allow you to put higher voltage (20x) and limit the current to safe one (2 or 3 amp) so your motor wont melt or anything.

Ok, so... the drive limits the current. Then you are not actually supplying 20X the voltage to the motor.
When I retrofitted a pair of 2 KW servo drives last year with newer drives, the size reduction was amazing. Old massivly parallel bipolar transistor VS PWM FETs.

I missed the "gecko" in eloids post

Steve

[eloid]

Originally Posted by vger Ok, so... the drive limits the current. Then you are not actually supplying 20X the voltage to the motor. When I retrofitted a pair of 2 KW servo drives last year with newer drives, the size reduction was amazing. Old massivly parallel bipolar transistor VS PWM FETs. I missed the "gecko" in eloids post Steve

as per geckco application note

The power supply voltage should be
between 3 to 25 times the motor’s rated voltage. If it is less than 3 times, the drive may not
operate smoothly and motor heating is excessive if it is more than 25 times the motor’s voltage.

[SORCHEROR]

on the gecko drives infomation sheet it tells you all of that,the magic number is 4 to 20 times the voltage,obiviously smaller motors dont need as high voltage to operate with good performance,but the larger ones benefit with better top speed performance,and most drives cant go above 24 or 30,but if your lucky to have geckos,or the new keling drivers,they limit the current for max amps for each motor so not to burn them up,they still run hotter but in a safe zone,i run my 497 oz/in motors with rated volts of 3.3 at 48 volts,they get warm,but work flawless with geckos
steve

[eloid]

but what i want to know what are most people do when they mix motors
ie smaller motor for z larger for x,y ... so do u use muilt tap trans former
with different voltages. What if u want fine tune your power supply to a higher or lower voltage? or at a later time decide u need more voltage?
any good links or posts with schematics or pictures

[max_imum2000]

ok , a lot of people may think that the z-axis will require less power motors, and this is not true, actually z-axis needs as strong motor as the rest, again according to my experiance, and i think many will agree on that.

if you want to mix motors you might as well mix power supplies, and get each motor his own power supply , that way u can control each one as much as you want.

always aim for higher specs driver and motor than what u think you need.
i always leave more space than what i need to there is a place for imporvment.

here is the best link you can find information about cnc.
www.cnczone.com

hope i helped