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Choosing a Power Supply

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sparky961:
I have a long term project on the go that involves servo drivers, and as I get farther along on the project and add more devices that need power I'm thinking I'll need to get a pretty big power supply at some point soon.  Can anyone offer advice on what to get (and what not to)?

The drivers can accept unregulated 20 to 60 VDC.  48 VDC seems to be a common voltage and I think that would work well.  The four drivers are rated for 12A peak, 6A continuous... so if I'm somewhere just above 24A I should never have a problem with current requirements under normal conditions.  The problem I see is that things get expensive with those sorts of ratings.

I've been leaning toward something like this (Ebay link): 350W 48V DC 7.3A

... but I'd need to put 3 of them in parallel if I were to meet the calculated demand.... which seems possible, but doesn't seem to be the best solution.

Am I thinking about this the wrong way?  Do I really need to have that much current available to the system?

awemawson:
Buy a suitable transformer  bridge rectifier and capacitor. Far the cheapest way to go at that power and unregulated. Output voltage will be 1.414 times transformer voltage. So take the voltage you want, divide by 1.414 and that's the transformer secondary voltage you need. Then just choose one who's power rating is right

sparky961:

--- Quote from: awemawson on August 30, 2013, 02:51:45 AM ---Buy a suitable transformer  bridge rectifier and capacitor. Far the cheapest way to go at that power and unregulated. Output voltage will be 1.414 times transformer voltage. So take the voltage you want, divide by 1.414 and that's the transformer secondary voltage you need. Then just choose one who's power rating is right

--- End quote ---

You've confirmed what I figured may be the case.   I already have a suitable bridge rectifier and caps, but I was having a harder time finding a big enough transformer than I was a pre-fab switching power supply.  Freight will be a killer on the size of transformer I'd need.  Alas, I'll poke a bit deeper here and there.  Maybe I can find one at a local surplus outlet, though most places I used to frequent have turned into Chinese crap resellers.

John Rudd:
sparky,

Cant you get hold of a defunct microwave oven and rewind the transformer?

Might be a bit onerous but its for nothing but the cost of the copper wire.........

kwackers:
Have you measured the current pulled at 48v?

As an example if you have a 2.5A stepper motor running at 48v the average current is a lot less due to the driver 'chopping' the supply. As the voltage drops the 'on' ratio increases and the average current goes up.

You'll probably find something similar with your servo drivers. Just make sure you've got enough capacitance to supply the current for the initial start!

You can also get 15A 48v supplies from fleabay.

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