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I am trying to use a 24V 10A SMPS to supply power to multiple loads. The SMPS has 2 sets of V+ and V- outputs.

I wanted to power a 24V 5A motor connected to the SMPS, as well and use the 2nd output from the SMPS with a buck converter and power a 12V 8A load also.

I thought that in theory this works because the math all adds up, what I can't understand (I'm very new to electronics) is: Will the buck just use around the 24V 5A and turn it to 12V 5A or will it try to convert all the 24V 10A leaving the 1st load underpowered?

Chigs964
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  • Is it just one smps that is internally connected to both load connectors, or is it actually two buck converters? – Marcus Müller Apr 22 '17 at 13:39
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    Please read this https://electronics.stackexchange.com/questions/34745/choosing-power-supply-how-to-get-the-voltage-and-current-ratings/34746#34746 – Christian Apr 22 '17 at 14:10
  • @Marcus Müller it is one SMPS connected to 2 loads one directly to the SMPS and the other via a buck converter. – Chigs964 Apr 23 '17 at 03:21

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SMPSs are, in principle, constant power devices. So, for your setup you would have 240 watts available, and a load of (24 x 5) + (12 x 8) or 216 watts. Like you say, the math works out.

What this ignores is efficiency. SMPs are not perfectly efficient, and for a homebrew unit I'd be surprised if you get 90% efficiency. This boosts your load requirement to exactly 240 watts. Any further decrease in efficiency will increase your load requirements further.

Also note that, at these current levels, circuit layout will be critical, as will choice of components (getting your inductors right, for instance, may give you more heartache than you realize).

As a beginner you are definitely jumping into the deep end of the pool, so don't expect things to work the first (or even the third or fourth) time.

WhatRoughBeast
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  • Would then setup work if I went with a 24V 15A or 20A SMPS? I'm just worried that the buck converter will try to suck all the available current and in turn fry itself or leave my motor under powered. – Chigs964 Apr 23 '17 at 03:23