Another thread has discussed controlling a cheap DC-DC converters such as this one: http://www.ebay.co.uk/itm/NEW-LM2596-DC-DC-adjustable-power-step-down-module-/130704327784?pt=LH_DefaultDomain_0&hash=item1e6e95c468
As I've been thinking about how to power several 5V Nano/CAN nodes plus LCD etc., I too have looked at these. It appears, however, that their ratings are suspect. I'd surely like to be proven wrong.
The components, particularly the input and output capacitors, used just don't seem to match the claimed specs, at least not for any length of time, and possibly not safely. The LM2596 chip can handle the voltages and current, but not with those capacitors.
This ad specs <=24V inputs and outputs. The input capacitor is, however, 220 mfd, 35V and the output capacitor is 220mfd, 15V. To start with, that 15V output capacitor is going to have a short life if the output is set at 24V. At most, the output should not exceed 10V. The input side is questionable as well. The LM2596 data sheet says that the input capacitor must be rated at least 1.5 times input voltage (though it admits that this is somewhat conservative). A nominal 24V lead-acid battery, for example, will sometimes be nearer, or even over, 30V, especially when hooked to a charger and a 35V-rated capacitor will likely not survive for long; a ca. 50V capacitor is needed. The LM2596 spec sheet also says that the input capacitor should be able to handle transient currents of 1/2 the current draw of the converter, and they give a graph to find the approximate current capacity of typical low ESR electrolytics. From those curves, a high-quality 220mfd, 30V capacitor can handle about 700mA. Checking capacitor data sheets, I have found a few (expensive) that have higher current capacity, and many that have much lower current capacity. Which did the manufacturer of this board choose? One should probably not draw more than 1.4A from this board, despite the 2A (or more with heat sinking) claim.
What happens when an electrolytic capacitor fails. Some times not too much other than causing failures downstream; the electrolyte dries out and it stops working. Other times, however, it overheats, a little hole is burnt in the top of the can, or the circuit board underneath catches fire. Not so frightening when it is the power pack for a laptop. This happened to one of mine two weeks ago, and not in a tolerant environment - we were in hospital. Luckily the unit failed quickly enough that there was just a charred board rather than a conflagration. More frightening if buried inside something like a wheelchair.
So, a more realistic rating for this board, and it may be a convenient choice if one stays within this range, is INPUT: up to 20V, OUTPUT: up to 10V at <1.4A. As one says here in Italy "mi raccomando".