Fun with cheap Chinese tantalum capacitors

[AKNscale]

Hey guys, thank you for posting all this useful info! I just ordered 5 batches of these and will, thanks to this, test them as suggested!

Jbub: what did you solder the caps to in order to make the ladder?

[Jbub]

I had some HO scale tie strips. Don't solder them to close as I did. If they blow they will take out others close by. I would do 2" spacing as @Steveruger45 suggested. I'll be honest though, I'm not sure if I'm going to use these. I may have found a better option on digikey. There are some polymer tantalum 20v 100uF that are 2mm thick. I'm thinking 4 of these stacked 2x2 are the same dimension with only 40 fewer uF in capacitance. It's a little more expensive at 1.50 a cap but piece of mind can be an expensive thing.

[AKNscale]

That makes sense

[Steveruger45]

Hi guys,
Yep, I agree,  those poly-tantalum caps do look a good idea. At least they are made by a recognized brand, namely, Panasonic and the size also gives a little more flexibility on where to put them in the model. This can be a big plus in itself.
To put things in perspective a bit, I can report that I have got to an acceptable comfort zone with my cheapo caps with the earlier posted burn-in tests. 
I have 10 locos with these cheapo caps in and not one failure after installed to date.
They also look identical to the AVX branded ones too, as previously posted.
However, I will not be buying any more either.

[Steveruger45]

Just ordered 20 of those 2mm thick 100 uF x 20v poly tant caps off digikey.
I should get them middle of next week and once received I will put them through the same burn-in tests and advise on the results.

[peteski]

While I have not really looked very deeply into features of those caps, I believe that one of the benefits is that they do not fail in the same destructive fashion (blow up)  like the standard solid tantalum caps.

[MK]

Just ordered 20 of those 2mm thick 100 uF x 20v poly tant caps off digikey.
I should get them middle of next week and once received I will put them through the same burn-in tests and advise on the results.

I doubt Digikey would stock second rate components.

[Jbub]

I believe they are moisture sensitive level 3 so keep them sealed in the bag they come in and only take out what you're going to install when you actually are going to do the soldering

[AKNscale]

I followed along with the bandwagon after really thinking about the risk I'd want to take with the caps, and decided that I don't think I'm prepared to take that chance like y'all. I decided to order some of the caps Jbub had found and my order came in today.

Here are the resistors, thank you for the recommendation peteski:


And here are the caps:

They came nicely packaged on this reel, in a resealable bag.
The main reason I brought this up is because I wanted to show the difference in size between the 16V caps I and others I've seen use, and these ones found by Jbub. Here's the height comparison:

[Jbub]

Just remember to keep them in that sealed bag until you use them. They are sensitive to moisture and if they sit our for more than 168 hours they have to be "baked" to dry them out for soldering. The reasoning is when they have too much moisture in them they will break or pop open when the heat is applied for soldering

[jdcolombo]

Hmmm.

Going to have to try these polymer caps.  Actually, there is a package of 220uf, 16v, that is 7mm long by 6mm wide by 2mm high.  You could stack two of those and have 440uf in about the same space as two regular tantalum caps stacked side-by-side.  The 220uf version is pretty pricey - $5.10 each in quantities of 10.  So two of those would be about $3 more expensive than 4 of the 100uf.

Here's the Digikey page for that one:

https://www.digikey.com/product-detail/en/avx-corporation/TCN4227M016R0070/478-9522-1-ND/5001734

John C.

[AKNscale]

@Jbub : Will do, thank you again for the excellent advice. I honestly had no idea what it meant other than don't get them wet, lol.

@jdcolombo : While a little pricey, those could be a good option, especially if you have little height and a lot of length. These might be perfect for the new ESU LOKSound swap in boards. However, the reason for me looking into other options was because I was wanting a cap with more voltage leeway. Though I've never had any issues with the 16V 220uF caps from SBS(I think they're AVX) that I've been using, my ESU system runs at 15V(though the track power probably runs in the low 14's) and having the extra leeway of 20V makes me feel a little better.

[peteski]

@Jbub : Will do, thank you again for the excellent advice. I honestly had no idea what it meant other than don't get them wet, lol.

A lot of various (epoxy-encapsulated) SMD components like tantalum caps are moisture sensitive.  Most LEDs are too.  They are stored and shipped in a moisture-controller environment. This is because the encapsulating resin can absorb moisture. Then, when they go through the soldering process (that heats them for the duration), the rapidly escaping steam from the absorbed moisture can crack the component's epoxy case, reducing it's reliability or even damaging the component. This precaution is mainly for the industrial soldering process. It is not as problematic for hand-soldering, but if possible then yes, keep the components in a low humidity environment until the time they are soldered.

Having said that, I have been hand-soldering SMD components for couple of decades (storing them exposed to fairly humid environment in my basement workshop) and I have yet to see a failure of an LED or a capacitor.  But it never hurts ot be extra cautious.

[Steveruger45]

Great experienced advice Pete. Thanks

[Maletrain]

Reading this makes me wonder about the "end-of-life" failures of the caps that survive the "burn-in" test.

In the way of background, many manufafctured items have what is called a "bath tub curve" shape to their failure rates over time.  That is, the failure rate starts pretty high, but goes down quickly with time-of-use, reaching a low, but  non-zero rate after what is usually selected as the "burn-in" time for a particular type of item.  That low rate may stay almost flat or may gradually increase over time until it starts increasing again at a substantial rate.  The plotted curve looks like a bath tub, hense the name.  The point at which the curve starts to increase at a substantial rate is usually picked as the end of service life, when the part should be replaced pre-emptively to avoid failures in-service.

So far, this discussion has only addressed the burn-in aspect.  What is the failure rate of those caps that have survived the burn-in?  What is the expected service life for 95% of the (successfully burned-in) caps?  Given the failure modes of these caps and the likely effect on a valuable model, it seems like it would be worth knowing these in-service risks before using cheap caps.