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Offline Hood

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Re: Power Supply Unit
« Reply #20 on: January 10, 2011, 09:36:47 AM »
Yes you will get help here I am sure, I am no electrical whiz but its straight forward enough, must be I managed ::) But there are lots of guys here that are experts so you will be sure to get answers.

Hood

Offline Hood

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Re: Power Supply Unit
« Reply #21 on: January 10, 2011, 09:39:03 AM »
Oh and by the way, when you are not sure its always best to ask, especially where electricity is concerned.
Hood

Offline kolias

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Re: Power Supply Unit
« Reply #22 on: January 10, 2011, 11:52:34 AM »
Oh and by the way, when you are not sure its always best to ask, especially where electricity is concerned.
Hood

That is 100% correct and I always do, thanks
Nicolas

Offline kolias

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Re: Power Supply Unit
« Reply #23 on: January 10, 2011, 02:54:59 PM »
To size the components of the power supply unit I follow the steps from the .pdf document Hood provided earlier. http://campbelldesigns.net/files/power-supply-part-1.pdf

I also attach a snapshot of my motors spec in case I misinterpreted something. Please note that the drivers for my motors are Unipolar and we cant change this for now. So I have 4 motors and each is 2.76VDC, 3.0A and I came up with the following:

Desired power supply voltage: 2.76 * 20 = 55.2VDC

Desired transformer voltage: 55.2 / 1.4 = 39.42VAC (This I don't understand; assuming this 39.42VAC is the household voltage where the transformer will be plugged, all households are either 120VAC or 220VAC)

Then I calculate the desired transformer current:
3.0A * 4 motors = 12.0A * 0.67 = 8.04A
39.42 * 8.04 = 316.93VA (if this is correct what will be the next transformer std size?)

Next comes the size of the filter capacitor: (I don't know where this item is located in the schematics provided by “cambelldesigns”)
C = (80000 * 8.04) / 69 = 9321.73uf (here I’m in the dark because I don't understand which current and voltage the “cambelldesigns document uses).

So the above is the 1st step in the selection of the components. If someone can check the above and answer my questions will be appreciated/
Nicolas

Offline Hood

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Re: Power Supply Unit
« Reply #24 on: January 10, 2011, 04:18:47 PM »
Before going any further what is the max voltage your drives can handle as that will determine the calculations.
Hood

Offline kolias

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Re: Power Supply Unit
« Reply #25 on: January 10, 2011, 06:00:36 PM »
In the exact words the manufacturer (Keling) said: "You can use the power supply from 24-72VDC"
Nicolas

Offline Hood

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Re: Power Supply Unit
« Reply #26 on: January 10, 2011, 06:32:09 PM »
Ok well I would go as high as I could on the voltage, most recommendations are for up to 25 x  motors rated so  about 70V Dc would be ideal. AC would then be 70/1.4= 50v which will be a standard toroidal I would imagine, 110v primary 50v secondary.


Next VA would be 50 x 8.04 = 402VA so probably 500VA would be a standard size, doesnt matter if you go more than the calculated value for this but dont go lower, although 400VA would be close enough I would think if thats what you found..

So toroidal transformer with 110v primary  50v secondary and 400VA or more


Capacitance needed would be  (80000 * 8.04) / 70 = 9188uF So you are looking for a capacitor of that capacitance and a voltage of at least  your DC voltage. If you cant get capacitors of that capacitance value you can link 2 or more  in parallel (positive to positive and negative to negative) to get to the value required.


Hood

Offline Hood

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Re: Power Supply Unit
« Reply #27 on: January 10, 2011, 06:43:28 PM »
Oh and also should have mentioned you can go higher on the capacitance if required.
Hood

Offline kolias

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Re: Power Supply Unit
« Reply #28 on: January 10, 2011, 08:09:49 PM »

Capacitance needed would be  (80000 * 8.04) / 70 = 9188uF So you are looking for a capacitor of that capacitance and a voltage of at least  your DC voltage. If you cant get capacitors of that capacitance value you can link 2 or more  in parallel (positive to positive and negative to negative) to get to the value required.

Hood

So capacitance 9188uf and voltage 50VDC?
I dont know what is available but can I go higher on the 50VDC?

Is filter capacitor and capacitor the same item?

And how about the bridge rectifier? What specs I need to buy this one?

Thank you Hood
Nicolas

Offline RICH

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Re: Power Supply Unit
« Reply #29 on: January 10, 2011, 09:04:19 PM »
The capacitor is a capacitor but the word "filter" comes into the description  because it takes out some of the ripple that stills exists after the rectifier has changed the AC to DC.
Said a different way, you have a flowing river of AC which is turned into a lake of DC, the bigger the lake the less ripple in the waves you will see in the lake at the discharge.
If you want to have a bigger lake, no problem. You will find that the standard formula provides for say 10 percent ripple and you can have less if you increase the size of the capacitor which is good.

The capacitor ( about the size of a beer can ) in mine is way over size as compared to the calculated value. So when your dumpster diving though the bins just look at the cap and it should give the Uf and also say it's good for like 1000Volts ( the volt rating should be better than say 20 - 50 % over the power output voltage ). A lot of the bigger ones will say 1000 volts. Buy 2 or three if they are real cheap....think i bought five of them  for $2 each.

RICH