Help With Power Supply

[FLUTE HEAD]

DRIVER Here is a link to the 3 drivers i put together. I needed somone to check myself
for the right power supply. My 3 motors are rate each @ 2A 3.4ohms, I guess this equalls 6.8volts. The drivers limit is 5-30vdc (etched on circuit board). Being that this is not a chopper drive, I'm told I will need current limiting resistors in series. The motors will be connected for bipolar. I don't mind making my own supply but would prefer to buy for the right price. Any links to cheap power supplies? What type of supply, unregulated? I'm just getting feet wet in electronics.Is there a power supply that may do the same as the current limiting resistors? thanks, matt

[sendkeys]

[pminmo]

I've done some business with this outfit and been happy:

http://www.mpja.com/listitems.asp?dept=3&main=1

I have one of these I think I got for $20 on sale:
http://www.mpja.com/productview.asp?product=7722+PS

Also this place:
http://www.allelectronics.com/index.html

Phil

[arvidb]

If you manage to find a power supply of 6.8 VDC you won't need any limiting resistors. You will get the full holding torque but the motors will not be able to turn very fast (or rather, they will be very weak at higher speeds).

On the other hand, if you want to go faster you will need a higher voltage power supply and limiting resistors. For a 24 VDC supply, your resistors need to be (24 V-6.8 V)/2 A = 8R6 (8.6 ohms). Their minimum power handling capability needs to be (24 V-6.8 V)*2 A = 34.4 W.

So yes, you can use a low voltage power supply and not need the resistors, but you will lose lots of power at higher rotational speed. An unregulated power supply is fine, but you could use a regulated one as well, if you can find a bargain for it.

And hey! You should not get your feet wet anywhere NEAR electronics!

Arvid

[FLUTE HEAD]

ARVID, I noticed you did not double your final watts amount of 34.4 watts. I hear it s a good idea to do so. Is this necessary?

[arvidb]

Strictly speaking no, it is not necessary if you are very careful about how you mount the resistors. You have to be sure they don't raise the ambient (or heatsink/case) temperature above the maximum for the amount of power they are to dissipate. You can find this info in the resistor data sheet.

But even if it is not necessary it might be a good idea to have some margins, to make the mounting less critical. If I found a good deal on some 50 W resistors, I'd go for it. Just make sure you don't spend more on resistors, heat sinks, mouting hardware and a big power supply than a chopper drive and a smaller PS would cost you.

Arvid

[FLUTE HEAD]

WELL NOW IM LEANING TOWARDS LINEAR CURRENT LIMITTING WITH A PAIR OF POWER TRANSISTORS. I got this info from doug jones on his site "jones on stepping motors". I don't fully understand where exactly and how many transistors i will need for each motor/driver. He does offer an example calculation but I'm new to electronics and do not 100% understand. Any info on this? Supposed to cost less than some power resistors.

[tachus42]

Transistor current limiting might not be a straight forward add on to the boards you have, as they wern't designed with that in mind. You will also need a big heatsink to cool the transistors as you can't allow them to get as hot as a resistor can. I'd stick with resistors initially, also "jones on stepping motors" gives a good over view but there are a few errors in there, so be careful!