Problem- 20A Switching Power Supply

[droddis]

I've now completed the build of my hobby cnc board, and tried to use the motors using an old AT Power supply i found lying around. I did not modify the power supply in any way I just connected the Board to the power supplies -5V and +12V to give me around 17V.

The motor on the X-axis was hissing, but the other 2 weren't.

There was also no movement, when i tried to jog using mach 3.

The Motors are rated at 2.8Amps, 1.8 step.

Is this because the power supply doesn't have enough amps???
or something else???? I know i need a minimum of 16.8Amps, but i have no way of measuring the ampage as my multimeter will only do a max of 10A DC.

I was looking at this to replace the AT Power Supply

http://cgi.ebay.co.uk/250W-12V-20A-S...ayphotohosting

and was wondering if it would be suitable, its from china and i dont really want to wait for the shipping, ( IF there is another way) as i'm getting impatient and what to see these motors move.

Does anyone have any ideas.

Thanks
David

[blackbeard52]

you could build one... www.buildyourcnc.com or http://www.procooling.com/index.php?...s&disp=52&pg=2

Bob

[droddis]

Would the one on ebay be suitable or not????

I looked at building my own PSU but could find anywhere in the uk to buy the components from at a reasonable price, and unfortunately i only have one spare computer supply, so....

Thanks David

[blackbeard52]

David I dont know why those wont work. I am kinda shocked at the price so a little leary as to quality. However, They should be ample voltage and certainly enough amperage. Make sure if they are not adjustable that you use a limiting resister so that you dont fry the motors and driver.

[HobbyCNC]

Originally Posted by droddis I've now completed the build of my hobby cnc board, and tried to use the motors using an old AT Power supply i found lying around. I did not modify the power supply in any way I just connected the Board to the power supplies -5V and +12V to give me around 17V. The motor on the X-axis was hissing, but the other 2 weren't. There was also no movement, when i tried to jog using mach 3. The Motors are rated at 2.8Amps, 1.8 step. Is this because the power supply doesn't have enough amps??? or something else???? I know i need a minimum of 16.8Amps, but i have no way of measuring the ampage as my multimeter will only do a max of 10A DC. I was looking at this to replace the AT Power Supply http://cgi.ebay.co.uk/250W-12V-20A-S...ayphotohosting and was wondering if it would be suitable, its from china and i dont really want to wait for the shipping, ( IF there is another way) as i'm getting impatient and what to see these motors move. Does anyone have any ideas. Thanks David

WHY would you need a power supply for a driver board kit you claimed to PayPal you never received? Or is this the replacement we sent that you also claimed you never received?

[blackbeard52]

OOOOOpppssss

[KYYADA]

Hello: Right up front I am not positive on this so you may check it out yourself. -5V was used on AT power supplies for logic circuts on ISA slots. It is produced by a small IC chip which I doubt could produce enough power for your motors. It has tagged along on ATX power supplies but is not used anymore.

Good Luck!

[blackbeard52]

Yeah I think you may be right. However the 12v side is probably all he will use and if he doubles the supplies as mentioned in the previous post its much more speed.

bob

[droddis]

I used the -5v and the +12v to give me an output of 17V because when the i measured the voltage on 12V to ground it gave me a reading of 11V, as the board needs 12 to 42VDC, i used the -5V to lift it up a little, the ratings according to the PSU are as follows.

Input - 230V~4A

Output - 300W
+3.3V 20A Orange
+5V 30A Red
+12V 10A Yellow
+5VSB 2A Purple
-5V 0.5A White
-12V 0.8A Blue
PS-ON Green

I assumed that if you scale the voltage then it would be the same for ampage and that i would get 10.5A, but i think i was incorrect, i knew this wouldn't power all 3 of my 2.8A motors, but i thought it would do one.

I was playing around today and noticed i order the printer parallel lead and not a straight through one, so if my power calcs are correct then this could of been the reason for no movement. If it is, then my straight through one is on its way

David

[blackbeard52]

I used the -5v and the +12v to give me an output of 17V

I just reread this.... You should have hooked the +5 and +12 together...The plus 12 VDC will have an output current rating of anywhere from 7 to 14 amps DC. The 5 VDC output rating will range between 20 and 40 amps depending on the output wattage rating of the supply .... if you hook up these two you can get +17 volts and about 40+ watts. Now a bit of caution. You will probably need to insert a limiting resister for the amp rating of the motors to keep from burning them up zapping them with 40 amps of current.

the -5 and -12 are not used in this senerio...I have attached a PDF to explain how to hack a single ATX power supply

[KYYADA]

If you hook the positive side to +12V and the ground side to +5V you will get 7V. It is a common computer hack people use to slow down fans and keep them quiet. If you do this keep in mind if the little fan ever shorts out you will cause a short circut in the system and could damage fragile components. The power supply hack above looks good. Did you try just +12V to see what happens? It may work till you find a surplus supply.

Good Luck!