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#1




Help for a null electric guy
I got the stepper and now I need to power them. How do I do that?
First. I got the steppers from MotionKing the current and resistence is 5 A and 0.65 ohm. I suppose now the voltage needed is 5 x 0.65 = 3.25 volts for 4 stepper would be 4 x 3.25 = 13 volts Now according to "Calculate voltage and VA..." thread, I will need a power supply that drives min 13 x 3 = 39 v to a max of 13 x 20 = 260 v With that the power supply would be (VA) 39 V x (4 x 5 A ))= 780 VA min to a max 260 x (4 x 5) = 5200 VA Does is how I understand it, and I know I'm wrong. Please correct me. Appreciated for life 
#2




Richy, you are making a lot of mistakes with that calculation. What is the "inductance" of the motor?
Also realise that the power supply is not directly connected to the stepper motor. You need another component in between....the drive(r) http://www.mechmate.com/forums/showthread.php?t=278 
#3




Richy, as Gerald pointed out, the math is not correct.
5A x 4 motors = 20A power supply. The voltage will depend on the inductance of the motors. I'm guessing that a 35VDC power supply would work if the motors are wired halfcoil or parallel, (using the Oriental Motor chart and motors with similar ratings.) The formula is 1000 x SQRT(inductance) = MAXIMUM voltage. A motor with 1.5Mh of inductance would be 1000 x SQRT( 0.0015) = 38.7V. You will need a Gecko G203v (or other stepper driver) per motor to actually drive the motor and you will need a PMDX122 breakout board (or similar) to interface the stepper drivers to your computer. It's not hard to do. Review the sections on this forum about the electrical system. Gerald has posted some excellent photos that show the components, how they are all connected and the general layout. 
#4




Quote:
Inductance is 2,4 mH I already knew the power goes with driver. I've got a Gecko G203Vfor it and the PMDX122 controller. Now according to Richards, 1000xSQRT(2,4/1000)=48,9 v If max current of the motor is 5 A, the the power would be 5x4(motors)=20 A Since Power = VA then the power I need is 48,9 x 20 = 979 W is that correct? Thanks again for couching me 
#5




Richy, If I were building a power supply for those motors, I would try to find either a 25VAC toroidal transformer or a 30VAC toroidal transformer. The 25VAC unit would produce about 35VDC after rectification and filtering and the 30VAC unit would produce about 42VDC (depending on your actual input voltage. The math shows that you would need a 750VA 25VAC unit or a 1,000VA 30VAC unit. What the math doesn't show is how much current the steppers are really going to pull in your shop. You may be able to use a transformer with a VA rating 25% less than what I've suggested.
Also, remember, that Mariss's formula computes the MAXIMUM voltage. The actual motor will determine how much voltage it can handle, but I like to use about 70% of the computed voltage to keep heat down without sacrificing too much speed. 
#6




Thanks a lot Richards. Really.

#7




I like the heading of this thread. It sounds just like me
There are a number of builders working on their power supplies at the moment. I went through every bit of calculations on the forum before I want to place my order. This is how I work it out: Motors: Motion king 34hs9801 Wiring config: Unipolar Rated voltage 4.1mH: 32 x the sqroot of 4.1 = 65 volts VA size: motor max amp rating = 4amp x 4 motors = 16 amps only need to supply 67%x16 = 10,72 amps VA value = Amps x Volts = 10,72 X 65 = 696,8 watt So I can use a 800watt at 70vdc or 600w at 56V?? Breakout board will be pmdx122 = 9V AC Drivers = Gecko G203V Also need = 25 amp rectifier and capacitor of 7000 Mf or bigger. I know that Gerald and Mike must be getting tired of all the checking, but I am asking nicely. (We really need a icon of a sweating man on his knees) Kobus, I need your input as well because my set up will be the same as yours. Much appriciated 
#8




Hi Johan,
I used the stuff from Greg....CNCDIRECT in Edenvale The 300VA transformer 42v AC and the 8A rectifier board. The bridge rectifier is one of those 25A square jobs that is bolted to the case. So far nothing got hot or smoked. I also used his BOB...it comes with it's own small transformer. Last edited by Kobus_Joubert; Mon 14 July 2008 at 08:14.. Reason: added last line 
#9




Johan,
You've basically figured everything out. The toroidal transformer you need should be 40VAC to 45VAC, which would give you 1.4 X 40 = 56VDC or 1.4 X 45 = 63VDC after rectification. That also means that a 500VA transformer would probably be adequate if you use the 66% rating. (4 motors X 4A = 16A. 16A X 0.66 = 10.66A. 10.66A X 40VAC = 426VA or 10.66A X 45VAC = 480VA) The capacitor should be about 20,000uF for best results. The formula is Capacitor = (80,000 X Current) / Voltage The larger the capacitor (within reason), the less ripple. The less the ripple, the smoother the motion of the stepper motor. Be sure to use a capacitor that has a voltage rating about 1.5X the voltage of the power supply. Also, be aware that capacitors dry out over a period of time. As they dry out, they get hotter. As they get hotter they dry out faster. At some point they can short out. (You don't want to be around an exploding capacitor.) Everything else that you've listed looks correct to me; however, I have never used that brand of stepper, so I have no idea whether the computed voltage is the best voltage. If the motors are excessively hot, drop the voltage about 25%. If the motors are at room temperature, consider raising the voltage a little. 
#10




Thanks for all the advice. My wiring will be supervised by a friend that is a qualified electrical technician. The smoke colour should hopely be transparent at start up.

#11




Quote:
Rated voltage 2,4 mH: 32 x sqrt 2,4 = 49,6 V VA size: motor max amps rating = 5 A x 4 motors = 20 A only need to supply 67% x 20 = 13,4 A (why 67% ?) VA value = Amps x Volts = 13,4 X 49,6 = 664,6 W Then you said: So I can use a 800watt at 70vdc or 600w at 56V[B]?? Would you say a little more about this conclusion? Thanks 
#12




Hi Richy,
I ordered my power supply from www.cncdirect.co.za after I did this calculation above and after Mike adjusted my answer in post#9. The supplier send me a 300VA transformer and a 12A PSU board with his mach3 pc board as advertised. Everything is still working perfectly on my test bench. 
#13




Got the same from Greg at CNC Direct. No problem at all so far on the WORKING BBB..

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