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Power Supply & Spindle Questions

Discussion in 'CNC Mills/Routers' started by eleethesontai, Jul 22, 2017.

  1. eleethesontai

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    Hello,

    almost ready to pull the trigger on my cnc only a couple of things I can't figure out or decide.

    1) I am going to use the Panucatt Gradus M1 controller with the Bigfoot drivers with 4 nema 23 269oz steppers (Hybrid - Nema 23 Bipolar 1.8deg 1.9Nm (269oz.in) 2.8A 3.2V 57x57x76mm 4 Wires). I am not sure what power supply I need? Do I match the amps on the steppers or the drivers. The website says that Bigfoot takes 3a @ 48v? (I would like to find a power supply that I can order with the steppers from steppers online, since I'm already ordering the steppers there)

    2) I need to get a quiet cut spindle because I live an an apartment. I was looking at the quiet cut spindle that smw3d offers. What I am curious about is I see a lot of spindles that look similar but don't say quiet cut, are all spindles quieter than routers and if so what are some affordable options other than smw3d that I may have missed (aside from sites like ebay or amazon, I prefer to buy direct on big purchases. I have bad luck with ebay/ and china purchases)?

    Also smw3d website recommends the 400w @ 48v power supply, they want 40 at steppers I can buy them a little cheaper but they don't have a 48v 400w only a 48v 500w will that work?
     
  2. Joe Santarsiero

    Joe Santarsiero OB addict
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    Hi elee, I'll try to make this simple.
    For stepper driver power supplies you want to make sure the voltage is in range of the drivers. The current capacity of the PS should be greater than or at least equal to 2/3 the sum of the motor current ratings.
    For the DC spindle PS just make sure you match the voltage. If the supply has a higher watt rating it is okay.
    Same goes for the stepper driver PS current rating. If it's higher, then this just means it can supply more current if demanded.
    Joe
     
  3. eleethesontai

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    Joe,

    thank you! so I do match the Motors not the drivers? as you said (2.8*4)*(2/3)=7.466 amps. According to an article I found (Power Supplies) I need 7.84a @ 74v = 582w

    The gradus driver says the big foot is 3a @ 48v so if I understand correctly a 48v @ (3*4*.66)=8 8.33 (which is a more common and affordable power supply) should work. But does that mean the driver will not give the motors the full 74v?

    also in calculating the amps I keep seeing 2/3 (as you said) and .7 as this article said what is difference in the 2 formulas?
     
  4. Joe Santarsiero

    Joe Santarsiero OB addict
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    I'm sorry. Current is limited/controlled by the driver. This is usually controlled through a dipswitch or trimpot. Since at 3A those drivers are so close to the 2.8A and You'll be setting them by hand, I would actually use (3A*4)*.66=7.92A. If you have a driver with a dipswitch setting of either say 2.6A or 3.2A I'd choose 2.8A motor rating and set the drive to 2.6A.
    I think you may be looking at it a bit harder than necessary(but don't take that as me trying to persuade you not to.) All in all its so close to 8A and 8 is higher let's just call it that.
    Regarding all of those calculations; there are some parts that are mere results to what is important to get going.
    For instance, when looking for a stepper driver PS you should only concern yourself with what is relevant to the drivers...its current capacity and voltage. Since P(watts)=I*V, the power rating in watts is the result. If you have drivers that require 48v and are limited to a specific current, then your power source should supply electricity at that voltage and be able to keep up with the current demanded. If we look at the common regulated power supplies we use in diy cnc we can see that they're mostly quite sufficient in the Current ability department. So a shortcut was made for sizing them that states you should just check that current spec to make sure it is above a certain value to be sufficient. That value is .66(or .7 rounded up) of total motor current rating or drive current setting. More here: Power Supply Basics - Step Motor Basics - Support | GeckoDrive

    When it comes to DC spindles they're usually rated in watts at a specific voltage(Watts computes to hp faster which is a spec used to determine machining requirements). DC Spindle PS wattage should be at or higher than the spindle. To make sure a PS will provide enough current for a DC spindle check the current spec. Just work the equation I=P/V So a 600 watt/ 48V spindle will require a 12.5A supply. Or if you have a 48V 14.5A supply then it is roughly a 700watt supply which will work for our spindle example.
     
    GrayUK likes this.
  5. Joe Santarsiero

    Joe Santarsiero OB addict
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    Just to be clear your spindle should have its own dedicated supply.
     
  6. eleethesontai

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    again thank you for all of the information. So then if i understood all of that correctly then i am correct in getting a 48v 8.3a power supply? Also the spindle is 48v @ 400 watts per smw3d, yes i was aware that i need a seperate power supply for the spindle. My question about the power supply (sorry if i did a bad job explaining, not my strong suit lol, i talk to pcs betters than people) was if any of the "Spindles" are quiet cut. I only see two marketed as quiet cut (swm3d,inventables) but they look so similiar to the ones marketed as just spindle that i was wondering if there is a difference beyond the marketing name.
     
  7. GrayUK

    GrayUK Master
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    I can't say I have heard of a truly quiet Spindle in the .5kw to 3.kw variety, which is probably the power area you intend to shop. Perhaps there is? :rolleyes:
    Generally the Spindles in the 300watt power range are promoted as quiet, well compared to the power and performance of a much larger Spindle, yes they are somewhat quieter. I would say the sound ventures into the much higher, inaudible zone of hearing. Think dentist. :zipit:
    However, compared to Routers, spindles are quiet! :thumbsup:
    Check them out on YouTube.
    Gray
     
  8. Joe Santarsiero

    Joe Santarsiero OB addict
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    Yes. That size supply or one with more current capacity would work.
    I think it's marketing. In general, any spindle over .75kw is an AC spindle that requires a VFD. Under that are DC spindles and run off the supplys we are talking about. There are some smaller AC spindles that require a VFD, but they're pricey and aren't usually on hobbiest sites. The DC spindles are the ones usually marketed as quiet cut.
     
  9. Rob Taylor

    Rob Taylor Veteran
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    99% of the noise from any kind of spindle is going to come from one of two places:

    1) The airflow through the spindle, powered by the cooling fan. If the fan is well-designed, it'll be reasonably quiet, but air just makes noise no matter what. Higher airflow may be designed for at the expense of noise (as one would hope, realistically).

    Water-cooling would be the solution to this, but it requires more "cabling", a pump, reservoir and radiator. If the water circulation system fails, or the radiator is underpowered, you can destroy the spindle. On the other hand, you can run at very low speeds without worrying about motor cooling due to insufficient fan speed, though this isn't often something many people need to worry about.

    2) High-frequency vibration. A motor doesn't flawlessly revolve on a perfect one-dimensional line in space. Fluctuations in magnetic flux density, electrical current, spindle mass static and dynamic imbalances, etc etc all affect exactly how much the spindle is going to want to deviate from its center line. What allows it to do that is the bearings. Spindles typically have four bearings, in opposing pairs (like all bearings), that are usually sealed. The problem with this is that in order to accommodate for the heat of friction losses, the bearings have to have slop built into them so that there's space for the grease to flow and expand, the balls themselves to expand, and the raceways to shrink together as the whole thing moves under thermal expansion. The precision of how much slop is left after they come up to temperature dictates how much they're going to allow the spindle to vibrate. More expensive bearings (like ABEC 9s) will have smaller levels of slop built in so that they operate at much tighter tolerances. Cheaper bearings like ABEC 3s will have more room left- and the exact amount will vary more- in machining so that they don't have to worry about binding as much, or do as much QA testing to ensure the gaps are perfect.

    Solution? Well, woodworking router bearings are junk. "German/Japanese spindle bearings" are, well, I'd imagine variable at best. Personally I wouldn't necessarily trust them to be the grade they say they are, either- bearings are one of those things where the company that makes them has a reputation to maintain. Buying a spindle and replacing the bearings with a known high-quality brand of the highest grade you can afford that'll work at the operating speeds you're anticipating would be about the only solution there.

    Addendum:

    If you're building a machine with aluminum and steppers, this may be all for naught anyway. Steppers cog loudly and aluminum rings like a bell. For quiet motion control, you need iron (low vibration transmission), concrete fill (or sand, etc. to absorb remaining vibration) and servos (no cogging but $$$!). You could attempt to fill the alu extrusion with sand, that may go some way toward helping.
     

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