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I need to replace the following cap:

enter image description here

It was placed at the input of a device that runs off 24Vdc, like the following schematic.

schematic

simulate this circuit – Schematic created using CircuitLab

I'm repairing the unit after an explotion due to a maintenance where the board was fed 220Vac instead of 24Vdc... Bottom line, while repairing the unit i found this Cap (C1) shorted and i need to replace it, but i've never seen a tantalum cap with this markings.

Of course, it's a 47uF cap, but the rest of the data i ignore.

I assumed that K is for tolerance (10%), and 20 for 20V, but this makes no sense in a circuit that runs on 24Vdc, so i need to find out the voltage rating of this cap (sure, i could simply replace it with a 40V and be safe, but i want to leave things as original as possible, and also want to learn to read this codes, it will become usefull in the future...)

So, could you fill the next list and perhaps explain how this code is selected?

R+: ?

476: 47uF

20K: ?

633: ?

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  • \$\begingroup\$ I'd go with a higher voltage rating (at least 35V in my opinion). The question is, do they offer the same capacitance at a higher voltage in the same package? (I haven't looked) ... It is very likely the reason it went bad. \$\endgroup\$ – Tut Mar 23 '17 at 18:48
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Here is what I found after doing a quick search online:

enter image description here

Furthermore, you can look at the following link to find more information about their device marking and the R+ at the top of the Capacitor.

Kemet Capacitor Marking

Initially, what threw me off was the date code located at the bottom. I thought this would represent the ESR (Equivalent series resistance) of the capacitor.

In the end, it seems like the capacitor is rated for 20V which makes very little sense for the application you have at hand. Therefore, it would probably be a good idea to review the design and possibly thinking about adding some Galvanic isolation to prevent further damage to the system due to ESD.

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Looks like it is 20V, 47microFarad tantalum capacitor.

That link goes to a page that explains all the details of Kemet tantalum capacitor markings.

Here's the summary:

enter image description here

Why there's a 20V tantalum in a place it could be exposed to 24V is a question you'll have to ask whoever designed the board. Looks like a recipe for disaster if you ask me.

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  • \$\begingroup\$ A receipe for disaster indeed, especially as both AVX and Kemet recommend derating to 50% rated voltage under normal use conditions. \$\endgroup\$ – Peter Smith Mar 24 '17 at 16:37

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