The polarity marking of this (probably old but unused) tantalum capacitor seems to be missing:
Any idea what is the polarity of this capacitor? I am guessing the middle lead with the '-52' is the positive side.
Thanks.
Any idea what is the polarity of this capacitor? I am guessing the middle lead with the '-52' is the positive side.
Thanks.
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Are you sure it is a tantalum?
It looks more like a polystyrene type looking at the outer connection. Have you tried measuring leakage current with a limited current supply and seeing if it polarity concious.
It looks more like a polystyrene type looking at the outer connection. Have you tried measuring leakage current with a limited current supply and seeing if it polarity concious.
That was a quick! 🙂 You are probably right Mooly.
I think it was sold as being tantalum but now I am not so sure I got the right type of capacitor.
Thanks!
I think it was sold as being tantalum but now I am not so sure I got the right type of capacitor.
Thanks!
It is an unusual looking thing. The 2.2/35 kind of suggests 2.2uF which would have to be electrolytic or tant but the construction style looks all wrong for that. Or could it be 2.2nF.
It is worth putting in series with say a 1k and putting a 9 volt battery across them and seeing if the cap reaches 9v. Try it both ways around.
It is worth putting in series with say a 1k and putting a 9 volt battery across them and seeing if the cap reaches 9v. Try it both ways around.
Hi, if this is an old tantalum capacitor please note that these were/are notoriously unreliable. Never use these old types directly on power rails as they go out with a bang and a smell if they fail. Problem is that they like to fail and that they reward you with a plain short when they do 😀
These caused the bad reputation of tantalum capacitors even today whilst modern tantalums are perfectly fine to use. I repeat: modern tantalum and niobium caps are very very good also in audio. I don't know about the "coltan issue" today, this could be a principal reason not to use any part based on coltan.
These caused the bad reputation of tantalum capacitors even today whilst modern tantalums are perfectly fine to use. I repeat: modern tantalum and niobium caps are very very good also in audio. I don't know about the "coltan issue" today, this could be a principal reason not to use any part based on coltan.
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I will try that. If it is a tantalum capacitor I will not use it.
Thanks for the advice and warning!
Don't: it will ruin it if the polarity is wrong, even at low currents.
Normally, a chamfer indicates the (+) side.
If it tests OK in the right direction, feel free to use it: it will most probably work reliably for ever.
If you use it in bypass applications, be sure that the supply never becomes reversed (during power-up -down for example), and fuse the circuit properly
Is it better to avoid tantalum capacitors all together then?
Because for me it raises the question what the benefit of tantalum capacitors are compared to other types of capacitors... The small size?
Because for me it raises the question what the benefit of tantalum capacitors are compared to other types of capacitors... The small size?
In some applications where there will be low transient currents and a clearly defined maximum current, a solid tantalum capacitor can provide very low leakage and last essentially forever.
Tantalum caps slowly form to their working peak voltage by developing tiny shorts in their dielectric oxide layer from excess voltage. The heat from these shorts cause the tantalum metal to react with the manganese dioxide in the capacitor to form a new replacement tantalum pentoxide dielectric layer. This oxide failure "short circuit" current during the healing process is the leakage current, as thin oxide layers get breached and replaced with newly generated oxide. Eventually, with a bounded peak voltage, no more thin oxide regions will fail, so the leakage current falls to essentially zero.
This same self-healing mechanism can also cause destruction of the capacitor. If too much of the cap fails short at one time, the reaction between the tantalum metal and the manganese diode liberates too much heat, and the reaction runs away. Basically, the cap catches fire. If this reaction can happen with very limited current and only gradually, then it is safe and it will eventually stop. This is why tantalum is dangerous to use as a power supply bypass. The high maximum currents in a power supply circuit can cause a failed device to dissipate very large amounts of current, and the cap will usually catch fire, or sometimes, spray molten tantalum metal onto its surroundings through a hole in its case.
One solution to this is to heavily de-rate the voltage rating of a solid tantalum part. This high voltage rating and low operating voltage makes it less likely that anything but a very tiny portion of the oxide dielectric will fail at one time. Typically, specifying a part with a voltage rating that is at least twice the expected peak voltage across the capacitor will allow it to be safely used. So, if that 25V capacitor really is a tantalum, then it would be wise to use it with no more than 12V across it, and hopefully less. It's hard to get tantalum caps with ratings of more than 35V or 50V, so this too can limit their application.
Despite these problems, solid tantalum capacitors have somewhat attractive HF characteristics. Their ESR is not all that low, but the inductance and self resonance is fairly low, so they can provide well damped decoupling, which made them attractive to use with logic circuits through the 80s (again though, with the risk of a fire from under-voltage parts). Their mechanical construction is less inductive than larger wound aluminum electrolytics. So, they can be useful for some applications, but they have to be used carefully.
Tantalum caps slowly form to their working peak voltage by developing tiny shorts in their dielectric oxide layer from excess voltage. The heat from these shorts cause the tantalum metal to react with the manganese dioxide in the capacitor to form a new replacement tantalum pentoxide dielectric layer. This oxide failure "short circuit" current during the healing process is the leakage current, as thin oxide layers get breached and replaced with newly generated oxide. Eventually, with a bounded peak voltage, no more thin oxide regions will fail, so the leakage current falls to essentially zero.
This same self-healing mechanism can also cause destruction of the capacitor. If too much of the cap fails short at one time, the reaction between the tantalum metal and the manganese diode liberates too much heat, and the reaction runs away. Basically, the cap catches fire. If this reaction can happen with very limited current and only gradually, then it is safe and it will eventually stop. This is why tantalum is dangerous to use as a power supply bypass. The high maximum currents in a power supply circuit can cause a failed device to dissipate very large amounts of current, and the cap will usually catch fire, or sometimes, spray molten tantalum metal onto its surroundings through a hole in its case.
One solution to this is to heavily de-rate the voltage rating of a solid tantalum part. This high voltage rating and low operating voltage makes it less likely that anything but a very tiny portion of the oxide dielectric will fail at one time. Typically, specifying a part with a voltage rating that is at least twice the expected peak voltage across the capacitor will allow it to be safely used. So, if that 25V capacitor really is a tantalum, then it would be wise to use it with no more than 12V across it, and hopefully less. It's hard to get tantalum caps with ratings of more than 35V or 50V, so this too can limit their application.
Despite these problems, solid tantalum capacitors have somewhat attractive HF characteristics. Their ESR is not all that low, but the inductance and self resonance is fairly low, so they can provide well damped decoupling, which made them attractive to use with logic circuits through the 80s (again though, with the risk of a fire from under-voltage parts). Their mechanical construction is less inductive than larger wound aluminum electrolytics. So, they can be useful for some applications, but they have to be used carefully.
Your explaination about this self healing/destructing mechanism of tantalum capacitors is thorough, clear and interesting, thanks!
Modern tantalum caps can be ultra low ESR and very reliable as processes have changed and other production methods are used. Some types are even high temp or automotive rated. A cell phone is full of tantalum caps. Point being that they are expensive... I use these on a regular base and have not experienced any failure till now when used directly on power rails (this was once very different with the famous drop types). Still one should pay attention to surge/reverse currents and therefor read data sheets carefully. An attractive point is failure rate going down with age contrary to electrolytic caps.
https://catalogs.avx.com/TantalumNiobium.pdf
@widea: pay me the stamp and I send a few to try out.
https://catalogs.avx.com/TantalumNiobium.pdf
@widea: pay me the stamp and I send a few to try out.
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