Check my math!!! (Please)

[Hack]

I am looking for a new power supply for powering 3 of these motors. I will be wiring them bipolar parallel. They are rated at 6.3 Amps per phase and 1.4 VDC. Will be using Gecko 202's with a rating of 24 - 80 Volts

I am under the impression that you want about 20- 25 times the motors rated voltage for your power supply so in this case around 28 - 35 VDC.

I am also under the impression that you want approximately 2/3 the combined amperage rating. So in this case 6.3 * 3 * 2/3 or about 12.6 Amps.

If I am thinking correctly, I need a 30 VDC power supply rated at 12.6 amps. Does anyone make such a creature? Does the fact that these motors will be run in bipolar mode make any difference in the amperage rating? How critical is the amperage rating.

The closest power supply that I have found is this. Any input on this power supply? Any help would be appreciated.

Thank you

Dan

[joecnc2006]

is it me or am i doing the math wrong those are 27.5 x 16oz = 440oz/in motors? seems kinda expensive at 139 each. But i could be wrong.

[Joe Petro]

Two words: Ebay, Ebay.
Do a search for "stepper" and "toroid" or "power supply".
Heck, for the amount you are willing to spend on those motors, do a search for "servo".



Joe Petro

[unterhaus]

Switchers are ok, but you probably need to put a capacitor across the output. I think I would go down to my basement and put together an unregulated power supply with one of the transformers I have down there. If you were shortchanged on basement electronic supplies, you probably can find a suitable 24V transformer, which will yield around 34V, no load. I think your amperage calculations are ok, but it seems like the conventional wisdom is to skip the parallel configuration and just use two of the windings. Anyone comment about that?


that's a reasonable price for those motors if you are going to pay retail. I would never do such a thing with my own money, my no-brainer limit for brushless servos is $50 and with cables, I'll go to $100. At work, if I needed steppers that size I wouldn't hesitate for a minute at the $139 price.

[smarbaga]

yes i agree with jo, the e_bay thing is the place to go, unless you are building this for resale and the buyer requires new, still ebay may have some.
that power supply is a switcher, they can be finicky with inductive loads.
again as jo said the a linear supply would be ideal say a transfo that puts out
20 - 24 vac at 10 amps will probably do the job well with a 35 amp bridge and somewhere around a 20,000 uF capacitor.
complete it might cost you $40 us and a bit of work.

[Surgical]

I am headed the geckodrive way too and am probably going to use these motors.
http://www.kelinginc.net/SMotorstock.html
(Nema23 425oz-in)
Joe pointed me to those motors.....
At $49 each.......

[ger21]

Originally Posted by Surgical I am headed the geckodrive way too and am probably going to use these motors. http://www.kelinginc.net/SMotorstock.html (Nema23 425oz-in) Joe pointed me to those motors..... At $49 each.......

Be sure to look at the torque curves when comparing motors. The motors Hack has should have much more torque at higher speeds, because the inductance is 1/4 of the Nema 23's you linked to. Oriental also makes a 400oz-in Nema 23 motor, but the torque drops off more than 4 times faster than Hack's motors.

2 years ago, all these low cost chinese steppers were not even available. I paid about $65 each for used Pac Sci 250oz steppers, and that was a very good deal at the time.

Dan, as was mentioned, you're best bet is to probably build your own linear supply. There is a .pdf at www.campbelldesign.com and there is also info in the Gecko stepper motor white paper available in the file area of the Geckodrive yahoo group. There's also quite a bit of info here as well, if you search for it.

[ViperTX]

Also....you generally have 2 phases energized at one time.......

[tekno]

www.campbelldesign.com seems to not be working anymore. do you have the full link to the PDF?

Originally Posted by ger21 Be sure to look at the torque curves when comparing motors. The motors Hack has should have much more torque at higher speeds, because the inductance is 1/4 of the Nema 23's you linked to. Oriental also makes a 400oz-in Nema 23 motor, but the torque drops off more than 4 times faster than Hack's motors. 2 years ago, all these low cost chinese steppers were not even available. I paid about $65 each for used Pac Sci 250oz steppers, and that was a very good deal at the time. Dan, as was mentioned, you're best bet is to probably build your own linear supply. There is a .pdf at www.campbelldesign.com and there is also info in the Gecko stepper motor white paper available in the file area of the Geckodrive yahoo group. There's also quite a bit of info here as well, if you search for it.

[ger21]

Originally Posted by ViperTX Also....you generally have 2 phases energized at one time.......

The formula's Dan used are from Gecko's white paper, and should be correct. According to that white paper, you should rarely even need the full 12.6amps. But if it were me, I'd shoot for 15amps to have a little headroom just in case.

Voltage can be a trial and error thing to determine. Ideally you'd want to use the lowest voltage to give you the performance you need. Any higher voltage results in excess motor heating. You might even try picking up a cheap 24V ~10amp supply to test your steppers with. You should be able to get one on Ebay for around $20. This may give you some direction into how much voltage you really need.

[ViperTX]

So, does Dan's white paper state that only one phase is energized at any particular time.....I seriously doubt it....

[ger21]

Originally Posted by ViperTX So, does Dan's white paper state that only one phase is energized at any particular time.....I seriously doubt it....

Are you trying to say he needs more current than Gecko says he needs?