Right power supply for 640ozin steppers?

[wesc]

Hi Folks,

I'm in the process of converting my Shoptask Bridgemill to CNC. I'm considering using the following motors

http://cgi.ebay.com/3-640-oz-in-Bipo...QQcmdZViewItem

640OzIn Steppers, 2.3V, 5.5A

using Gecko 210 drives.

My question is, will the following power supply work for me.
http://www.allelectronics.com/cgi-bi..._STATION_.html
($95!)

Is 24V enough? 6+6+21 amps is enough, i think. Acording to the Gecko manuals, you can drive servos at up to 25x the rated voltage or 57V. I see that Dan Mauch specs 36V supplies for similar steppers...

Thanks,
Wes

[CJL5585]

Is 24V enough? 6+6+21 amps is enough, i think. Acording to the Gecko manuals, you can drive servos at up to 25x the rated voltage or 57V. I see that Dan Mauch specs 36V supplies for similar steppers...
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Wes,
The power supply would allow your system to operate, but you would be limited to lower feedrates than you could attain with a 36 Vdc or higher voltage.

I agree with Dan that your voltage should be AT LEAST 36 Volts.

I run my system on 48 Volts which causes the motors to heat excessively after 3-4 hours of continious operation, but not many hobby projects take that many hours, so in reality it is not a problem. I am recommending a voltage range of 36 to 48 Volts. That will give you more torque and higher feedrates.

Jerry

[wesc]

Thanks Jerry.

I see that the power supplies are isolated. So, I should be able to parallel the two 6 amp supplies and put them in series with the 24 amp supply. That gives me 48V at 12A max -- not quite the full rated amperage of the 3 steppers combined (16.5A). Do you think that 12A will be enough?

-Wes

[ger21]

Geckos only need 2/3 of the motors rated current, which is about 10A for all 3 motors, so 12amps should be fine.

[CJL5585]

Geckos only need 2/3 of the motors rated current, which is about 10A for all 3 motors, so 12amps should be fine.

Same here.

Jerry

[pminmo]

Hmm... thats 5.5A per phase, or 11A per motor for a 2 phase motor or 33A total for 3 motors at 2/3 would be 22A?

[Oldmanandhistoy]

Hmm... thats 5.5A per phase, or 11A per motor for a 2 phase motor or 33A total for 3 motors at 2/3 would be 22A?

I would like to know the answer to this also. One other thing, if I buy a stepper motor and it does not say how many phases it has, how would I know?

John

[ger21]

Hmm... thats 5.5A per phase, or 11A per motor for a 2 phase motor or 33A total for 3 motors at 2/3 would be 22A?

Here's a quote from the Gecko stepper white paper.

"The choice of a power supply is determined by voltage, current and power supply type, i.e. switcher versus linear regulated versus unregulated and purchased versus in-house designed. By far the most problematic factor is voltage, so we will leave it until last.

The easiest factor in choosing a power supply is its current rating. The current rating of the supply is based on your motor choice. The drive will always draw less than 2/3 of the motor’s rated current when it is parallel (or half-winding) connected and 1/3 of the motor’s rated current when it is series (or full-winding) connected. That is to say, a 6 Amp / phase motor will require a 4 Amp rated supply when parallel connected and a 2 Amp rated supply when series connected. If multiple motors and drives are used, add the current requirements of each to arrive at the total power supply current rating."

[pminmo]

I believe gecko is referring to an 8 wire motor, and how it is rated. The motor spec'd in the original post is a 4 wire motor, rated at 5.5A per phase. The highest current point is roughly 141% of the single phase rating, assuming sine/cosine waves at their highest sum. (45, 135, 225, and 315 degrees) So at those angles if the motor was stopped it would be pulling 7.8A assuming the drive is pushing the motor to the rating. Worst case would be all three motors stopped and the max current angle then would be 7.8A *3 or 23.65A. The least case would be 100% or 5.5A *3 = 16.5A

Admittedly it's late and my brain is half fried at the end of the day, but I think I'm thinking correct. But I could be wrong.

[wesc]

So, there's 2 motors on ebay right now that I'm looking at. Both look the same and have similar specs. One is a 4 wire stepper (these URLs are for completed auctions, but both sellers have relisted the same motors again -- both at the same price too)

http://cgi.ebay.com/ws/eBayISAPI.dll...Pr4_PcY_BIN_IT

the other is an 8 wire model

http://cgi.ebay.com/ws/eBayISAPI.dll...MEWA%3AIT&rd=1

http://www.kelinginc.net/KL34H280-45-8A.pdf

which is specced as a "4 phase" stepper, which i believe really means it's a 2 phase stepper.

It seems to me that the 8 wire model would be better (they are the same price) because it'll give me more options in terms of serial/parallel wiring configurations.

Opinions?

Thanks for all your help in untangling all the confusing and sometimes contradictory information out there on steppers.

[jeffs555]

Admittedly it's late and my brain is half fried at the end of the day, but I think I'm thinking correct. But I could be wrong.

What you are missing is the duty cycle, which would be rather low with a 2.4v motor and a 48v supply. The average current out of the supply with a chopper drive would be much lower than 23.65A even if all the motors were stopped at the max current angle. He would probably need a large capacitor to supply the instantaneous current, but the average current out of the supply would be fairly low.

[ger21]

I believe gecko is referring to an 8 wire motor, and how it is rated. The motor spec'd in the original post is a 4 wire motor, rated at 5.5A per phase. The highest current point is roughly 141% of the single phase rating, assuming sine/cosine waves at their highest sum. (45, 135, 225, and 315 degrees) So at those angles if the motor was stopped it would be pulling 7.8A assuming the drive is pushing the motor to the rating. Worst case would be all three motors stopped and the max current angle then would be 7.8A *3 or 23.65A. The least case would be 100% or 5.5A *3 = 16.5A

Admittedly it's late and my brain is half fried at the end of the day, but I think I'm thinking correct. But I could be wrong.

I don't know enough to explain why I think I'm correct, but I own a Xylotex drive, 3 axis at 2.5a per phase. By your thinking, that means I'd need a 15a power supply. But Jeff, the owner of Xylotex, says that it will never draw more than about 4.5a, and in fact sells complete ready to run kits with 4.5a supplys. This is basically the same formula that Gecko uses.