Machsupport Forum
Mach Discussion => General Mach Discussion => Topic started by: Beezer on October 24, 2006, 11:52:30 PM
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I picked up a pair of Nema 34, 637 oz./in. steppers off ebay which I will either use to upgrade the Nema 23's I currently have on my router now or use for a new project in the future but I am wondering what size power supply I should get? The motors phase current is 6.3A.
I am thinking I will use a 48VDC switching power supply but not sure what amperage it should be. I have seen some good deals on 48V/5A supplies but not sure if one of them would be adequate to run two motors. Perhaps one for each motor?
Any ideas fellas?
Carl :D
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Build your own, Bob Campbell has a good article on how to do this and work out what you need.
You will find it here http://www.campbelldesigns.com/files/power-supply-part-1.pdf
Hood
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Thanks Hood. That is a very good article. Building your own power supply seems like it could be more expensive then buying a ready made one though, since you have to buy all the seperate components. The Toroidal transformer I would imagine is not under $30.00? The 48V/5A switching power supplies I was looking at were $30.00. I guess it all depends on what size power supply would be best for my motors and whether one was available ready made or I need to build one to get the exact specs I need to get the most out of the motors.
The one problem I have at the moment is that I am not sure what is the voltage of the stepper motors. I don't have them in my hand yet since they haven't come in and the the data sheet on them doesn't list a specific voltage. It just shows a chart that shows the Torque and the speed at given voltages (24vdc, 45vdc & 75vdc).
Here is the datasheet. It is model M-3431-6.3 http://www.motionsolutions.com/images/size%2034%20motor%20&%20encoder.pdf
:)
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Watch what you are doing with switching power supplies, some drives dont like them.
The voltage of your steppers is really not important as you will be wanting to supply a lot more volts than what they are rated at, I think the usual figure is min 5x max 20x, most steppers I have seen are 5V.
You are best to run steppers on as high a voltage as your drives will allow.
Hood
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You can run them at any voltage between 24 and 75.
You will need 6.3A per phase per motor so 6.3A * number of phases * number of motors = size of power supply. (roughly)
Graham.
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I plan on using Gecko 201 or 202 drives. Depending on which ones I find at a good price. ;)
Also my motors are 4 wire so does that mean they have 2 or 4 phases?
Carl
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If your using Geckos, the required current per motor would be 6.3 x 2/3, or 4.2 amps per motor. See the Gecko docs.
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Now what do you do when the motors you use don't all have the same specs? Do you use the same formula when trying to figure out
the power supply required? For example I have two of the motors that I listed below but I am looking for one more Nema 34 motor that has about the same holding torque but it is doubtful I will find one with the exact same specs unless I try and purchase a new motor direct from the manufacture at a much higher cost.
So if I use the formula mentioned further below, 6.3A * number of phases * number of motors = size of power supply, for the first two motors do I just take the same formula and use that for the third motor and add the two totals together?
Thanks,
Carl
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Heres what Gecko have to say about it.
"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."
Hood
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Ahhhh. Ok... Now do you take that Amperage value and multiply it by the number of phases?
For example. If my motor is rated at 6.3A per phase and I take 2/3 of that value, gives me 4.2A per phase in Biploar parallel but the motor has two phases so do I multiply 4.2 by 2 giving me 8.4A for that one motor? Is this correct or do I just take the 4.2A as my value for the one motor?
Sorry for so many questions but with my first machine I just used a 24VDC power supply which is under rated voltage wise for the steppers I was using. This time around I want a power supply that will get me the max performance out of my motors but going with more power doesn't leave me much room for error. :)
I just picked up the third and final motor off ebay so now I can go ahead finalizing power supply requirements. It's a PacSci Powerpac Nema 34 , 3.3A Bipolar series, 65V, 97W. It's an 8 wire motor so I need to decide if I am going to connnect them in Bipolar series or parallel. Can't remember which one is better. It's been awhile since I did this with my other machine so I have forgotten alot that I learned. :D
Thanks for all your help everyone. I would really be up a creek without a paddle if it wasn't for people like you guys. :)
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According to what Gecko say and also what I recollect that Bob Campbell says it is just current per phase and not multiplied by amounts of phases.
So for your 6.3A/phase it will be the 4.2A for parallel. There is certainly no harm in going bigger if you can pick up a transformer or PSU at the right price which is bigger than you actually require.
Hood
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There is certainly no harm in going bigger if you can pick up a transformer or PSU at the right price which is bigger than you actually require.
Oh. I thought the purpose of these calculations was to figure out the correct power supply required so you didn't go oversized. If I can use a power supply that has abit more amps yet still being at the proper voltage rating makes things abit easier. I was looking at a few toroidal transformers to use in building of a power supply but their amperage output was abit higher then I figured I could use, but if I can safely go abit larger then it gives me a few more options to choose from. I guess you adjust the max amperage that the motors get through the Gecko drives?
Cool. Thanks,
Carl :)
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You probably know this but just thought I would mention anyway that the voltage of an AC transformer will need to be less than the DC output you want. When you rectify and smooth (with the capacitor) the AC you will get 1.4 times on the DC, eg 50V ac will give you 70Vdc.
Hood
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But I am assuming I should not go over the max DC voltage rating of the lowest rated motor which is 65V taking in consideration back EMF? The other motor can handle 75V. If I select a Toroidal transformer of 45VAC which would give me 63VDC I should be ok or should I go with 40VAC giving me 56VDC to be safe?
Carl
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Carl,
the voltage limit is determined by the max voltage of the GECKO drivers not the motors.
the power supply AMPERAGE can be as high as you want as long as it is high enough to supply the max current of all the motors together.
remember you can not have too many AMPS AVAILABLE but your VOLTAGE must NOT be higher than the GECKO drivers can handle.
Chuck
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Yes but the Gecko's max voltage is 90VDC and the one PacSci motor I got has max 65V on the label. Wouldn't I have to be cautious not to go over that voltage or is that just a guidline the motor's manufacturer uses? My other two motors can handle 75VDC according to the data sheet. It gets abit confusing when different motor manufacturers use different ways to list their motor specs I find. :)
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The max of the Geckos is 80V and its best to really stay around 75V especially if your mains power can wander a bit.
Where in the specs of the motors does it say a Max voltage, I have never seen that on the specs of the motors I have had but then again I have only had a few different kinds.
Hood
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Ahhhh. Ok... Now do you take that Amperage value and multiply it by the number of phases?
For example. If my motor is rated at 6.3A per phase and I take 2/3 of that value, gives me 4.2A per phase in Biploar parallel but the motor has two phases so do I multiply 4.2 by 2 giving me 8.4A for that one motor? Is this correct or do I just take the 4.2A as my value for the one motor?
Only one phase of each motor is energized at any time, so no, you dont need 8.4 per motor, just the 4.2A. At least that is how I have allways understood it.