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I am new to electrical. I am powering my router from 24V battery. But power requirement of router is 12V/1A. So I am using LM2596 buck converter.

The specification for this buck converter is as follows:

Input voltage: 4-40V

Output voltage: 1.2-37V

buck converter

Scenario 1:

It worked fine for a day. Next day when I connect a battery output to buck converter input, input capacitor started to burst(No output is connected). What might be the cause for this behaviour?

Input capacitor burst on connecting input

Scenario 2:

I bought another and tested it. The input which I provided is 24V and the output obtained is 12V. I connected the output to router. When I powered the router button on, voltage regulator emiited smoke and fired up.

What might be the cause for this behaviour?

fired Voltage regulator

What should I need to do to overcome this?

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    \$\begingroup\$ Those modules from ebay et. al. are known for using counterfeit parts all around. \$\endgroup\$ – PlasmaHH Aug 20 '18 at 12:37
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    \$\begingroup\$ Also, you need to check with the datasheet of the converter (you probably never got one if you bought from ebay, aliexpress, amazon marketplace, bangbanggood …) that the current you want to draw actually is supported at the input and output voltages you have. Again, it's not normal to buy a component to which you don't get datasheets and where things explode. Buy somewhere else – there's plenty of reputable distributors (mouser.com, digikey.com, arrow.com, element14.com, …) that ship worldwide and aren't more expensive (considering you've just burned 2× the price of a module). \$\endgroup\$ – Marcus Müller Aug 20 '18 at 12:43
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    \$\begingroup\$ But for your first case: a no-load bursting of an electrolyte capacitor probably means that you either reversed the polarity of the battery, or the capacitor was a complete failure, was thrown out by the factory producing it, then someone bought their electronic waste and "recycled" it by soldering it onto regulator boards and selling those under constantly changing reseller names. \$\endgroup\$ – Marcus Müller Aug 20 '18 at 12:45
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    \$\begingroup\$ Basically all distributors ship to India. Check, for example, this offer of a 24V in, 12V/1A out power module. That's how a reputable listing looks like: extensive edge data listing, and a link to a data sheet, which defines under which conditions it performs how. \$\endgroup\$ – Marcus Müller Aug 20 '18 at 12:56
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    \$\begingroup\$ Despite counterfeit / cheap / etc: for me identical modules work just fine. I agree with Marcus that you probably used/connected the module in the wrong way because the damage you show is very unlikely to occur under normal circumstances. \$\endgroup\$ – Bimpelrekkie Aug 20 '18 at 12:56
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Issue 1: Could be the physical board itself. Depending on where it was purchased, it could be poorly-designed, poorly-manufactured, using counterfeit parts, etc. This board looks to me to be a low-cost Asia-sourced unit, built in large quantity and sold cheaply - the PCB looks thin, there's no manufacturer label or serial number, etc. It is my experience that many low-cost direct-sell vendors found on places like eBay, Wish, etc. have issues with product quality - the items don't fully meet spec or don't last a long time. Some will gladly sell you a replacement, some will send you a new one for free. Some won't return your messages. There are larger domestic suppliers (Digi-key, Mouser, Farnell, etc.) which demand better quality and may offer support if you end up with a lemon - at a higher purchase price, however.

Issue 2: Could be the application - was there input protection installed? You didn't mention having things like a fuse, input polarity protection or inrush protection. A fuse disconnects the source from the load if something bad happens. Input polarity protection prevents a reverse-connected battery from doing anything. Inrush limiting protects the input caps from seeing damage due to high di/dt from the battery (which can deliver a lot more current than the wall-wart adapter which would have been supplied with the router!). You also could consider a TVS across the input of the buck to protect the cap from induced voltage stress if the wires are long and there's a sudden current interruption.

Issue 3: Could be the design. Example - limited power handling of the LM2596S. Because the integrated power switch isn't mounted on anything meaningful (as far as power dissipation is concerned) it isn't going to survive at peak power for very long. It's a 3A rated part but the device needs to be mounted on some serious copper to be able to deliver that. Did the supplier offer you any test data or qualification results showing what the device is, and if it needs external cooling?

So, consider input protection and inrush limiting at the very least. Also consider investing in a scope (even an old, used one is useful) and start looking at the waveforms if you really want to know what's going on. Check device temperatures when the circuit is running steady-state - is anything getting hot prior to failure? Are there any high voltages you can't explain? Excessive ringing? Your intended application, sadly, is not "plug and play" - a buck regulator in this sort of package isn't like a wall-wart adapter that you can just plug in and use. It takes a certain amount of knowledge to diagnose and resolve why there may be issues.

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    \$\begingroup\$ well, good advice, but considering the money for a used scope, I'd say: overdimension a well-spec'ed power supply from a reputable distributor before investing in measurement equipment. If a car hobbyist came on, asking why the cheapest nuts and bolts he could buy are constantly breaking, you'd also wouldn't recommend investing in a x-ray machine to find material defects – you'd just tell them to buy nuts that come from someone who guarantees their properties under the stress you put them under. \$\endgroup\$ – Marcus Müller Aug 20 '18 at 12:59
  • \$\begingroup\$ Issue 1: Sure, I agree with your points, yet in my personal experience with exactly the same modules, they just work fine. The damage shown in the photos above indicates very dramatic failure, the sort you get when the input voltage is reversed. So I think blaming the modules is a bit harsh, this is very likely user error. Also modules from reputable sources do expect the user to handle them correctly. \$\endgroup\$ – Bimpelrekkie Aug 20 '18 at 13:05
  • \$\begingroup\$ My point was: if a user just plugs something in and it fails, you cannot unilaterally assume the fault was one way or the other. Some investigative work must go into determining where the fault occurred; in the absence of that work, I will keep all options open (even the least plausible ones). \$\endgroup\$ – Adam Lawrence Aug 20 '18 at 14:10
  • \$\begingroup\$ Just because product is sold on Ebay you should NOT categorize it automatically as using fake parts. In addition, the parts supply chain is a completely separate issue to that of product design. Fake parts in the supply chain have seriously affected Mouser and Digikey too. The design used in this module (I've used dozens of them) is essentially from the reference materials of the chip designers (LM2596). The biggest issue with product like this is that it has in all probability NEVER been tested. Test is costly, and that is where you take your biggest risk in buying them IMO. \$\endgroup\$ – Jack Creasey Aug 20 '18 at 15:13
  • \$\begingroup\$ Where in my "Issue 1" statement did I automatically categorize anything? Counterfeit parts is one of many issues with non-traditional sales channels, which is why I outlined several possible concerns including poor manufacturing and controls. \$\endgroup\$ – Adam Lawrence Aug 20 '18 at 15:19

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