Lost in the world of power supplies

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aarvidsson
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Lost in the world of power supplies

Post by aarvidsson » Tue Feb 18, 2014 12:20 pm

Hi all,

I'm looking at getting a 300W Chinese spindle for my ShapeOko 2. Trouble is, I can't seem to get the hang of how the darn thing works when it comes to speed control. Is the following a good idea

http://www.ebay.com/itm/DC-12V-48V-300W ... 3f2acfccd9

or is there something to look out for in the speed adjustable power supply? Is there any difference between the one I linked above and a http://www.ebay.com/itm/PWM-Speed-Contr ... 33890de3a2 (apart from the fact that this one won't accept 220V input power)?

The main reason I'm asking is that I can't seem to get the hang of PWM. What is it, does it have any bearing on my application as long as i do NOT want to control spindle speed with software (a trimpot or similar is fine by me) or am I so lost I can't be steered back to any hope of ever getting it? :)
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cvoinescu
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Re: Lost in the world of power supplies

Post by cvoinescu » Tue Feb 18, 2014 1:04 pm

The second link is a speed control unit that's often bundled with that type of spindle. I would not plug that into 120 Vac, though -- I would always use it with a DC power supply (say, 48 V). I care for my life.

The adjustable power supply is neat, and may be cheaper (and certainly more efficient) than a power supply plus a separate speed control unit. I don't see where it says what the adjustment range is. The external potentiometer is connected where the voltage adjustment trimpot usually is on those supplies, but that has a very small range (a few volts). I wonder whether they made the range wide enough (you want 12 V to 48 V for that type of spindle), or they've just soldered wires instead of the trimpot (no data in the listing).

A distinct advantage of the separate speed control unit is that it can be used with external PWM control, so you could use G-code to control the spindle speed via GRBL. You can't do that with the adjustable power supply.
Proud owner of ShapeOko #709, eShapeOko #0, and of store.amberspyglass.co.uk

aarvidsson
Posts: 150
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Location: Frosty Sweden

Re: Lost in the world of power supplies

Post by aarvidsson » Tue Feb 18, 2014 1:13 pm

Catalin,

Ok, I somehow got in my head that the motor was somehow speed controlled via a fixed voltage, and not that the input voltage by default regulated the speed of the spindle (which seems to be the case with the adjustable power supply). I enjoy being wrong, that means I'm learning something new :)

Unless I'm reading it wrong it says "Speed ​​:3000-12000r / min. (12V-3000 transfer, 24V-6000 transfer, 36V-9000 transfer, 48V-12000 rpm)" or am I looking at the wrong thing?

The ability to use G-code to control spindle speed is an interesting one, but not something I feel I need to start with (especially as I'm looking for a "quiet" spindle solution and it is my first).
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cvoinescu
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Re: Lost in the world of power supplies

Post by cvoinescu » Tue Feb 18, 2014 2:29 pm

That spindle is reasonably quiet, especially at lower speeds. However, once the endmill touches the stock, expect the usual racket -- it'll drown the sound of the spindle.
Proud owner of ShapeOko #709, eShapeOko #0, and of store.amberspyglass.co.uk

Nigel K Tolley
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Re: Lost in the world of power supplies

Post by Nigel K Tolley » Tue Feb 18, 2014 3:17 pm

If you want an easy way to think of how PWM works, it is just like if you had a flywheel on a switch. Leave it on and it gets faster, cut the power it shows down. Turn it on and off fast, & it is going to spin at a speed below maximum. Have a controller turn it on and off a thousand times a second and it is a speed controller.

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aarvidsson
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Re: Lost in the world of power supplies

Post by aarvidsson » Tue Feb 18, 2014 5:14 pm

Nigel, that's easy enough for even me to get. Much obliged :)

Said spindle has been purchased, now all I have to do i a) move from my house to the new apartment and b) actually assemble my ShapeOko. Well, I've got something to do for quite some time, it seems!
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Oud
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Re: Lost in the world of power supplies

Post by Oud » Mon Mar 24, 2014 5:27 am

http://www.youtube.com/watch?v=mVx02s1f ... e&index=34

Here's a good video that explains the basics of PWM. Its targeted more at using PWM in an AVR microcontroller but still covers a lot of the basics and explains things quite well. Hopefully that helps =]
Stock Shapeoko2, First pre-order batch.

wz9v
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Re: Lost in the world of power supplies

Post by wz9v » Mon Mar 24, 2014 6:36 pm

Look at the maximum voltage your motor needs (my 400W was up to 53v) and get a supply as close to that rating. The power rating in watts should be equal to higher than the motors power rating. To control the speed it would be better to have a speed controller between the motor and the Power Supply. The ones usually used with these motors have an internal clock controlled via potentimeter and an external input (PWM).
Shapeoko 2 - Mechanical kit 4731
Z-Axis Acme Screw Upgrade / Makita RT0701C / Re-enforced Y and X-Axis / External Belts on Y / Extrusion work top

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