Tantalum or Non-polarized Capacitors ?.

[ronniedee]

Can you substitute a polarized tantalum cap for a Non-polarized Cap?  My friend is building a box and could not find a particular value but found it at radio shack as a tantalum.

Also if a tantalum cab be used as a substitute, how do you determine where the + side should ne inserted in the circuit?

[Saint Louis Toneworks]

i cant them to work.I posted a topic last night and people say you can..but unless I put a electrolytic the circuit fails.  I am new but I have found if you change a value or anything other than what the diagram calls for it wont
function.

i advise to hook it on breadboard solderless and test it first see if it works

[armdnrdy]

Can you substitute a polarized tantalum cap for a Non-polarized Cap?  My friend is building a box and could not find a particular value but found it at radio shack as a tantalum.

Also if a tantalum cab be used as a substitute, how do you determine where the + side should ne inserted in the circuit?

If you post a schematic...it will be much easier to give you direction.

[R.G.]

Can you substitute a polarized tantalum cap for a Non-polarized Cap?  My friend is building a box and could not find a particular value but found it at radio shack as a tantalum.

Can you? Yes, if you take into account the "special cases" that electrolytics need.

Should you? Maybe, maybe not. You first have to know what those "special cases" are.

And as a more global statement, you (or your friend) are simply going to have to get used to ordering parts from a mail order supplier.

All electrolytic caps must have a polarizing DC voltage to enjoy a long life. This goes for aluminum and tantalum, and the newer and weirder niobium caps that are beginning to become available. The DC provides the electronic forces that keep the insulating oxide layer insulating, especially for aluminum. Electrolytic caps work very well where there is a DC + AC signal to be dealt with. They work poorly for small AC signals with no DC across the cap, and they die quickly if there is any reverse DC or a larger AC signal that reverses the voltage across them for any significant voltage x time. The different metals vary in how much reverse voltage they can take before decomposing quickly. For aluminum, it's a fraction of a volt. For tantalum, I don't remember the exact number, but it's slightly larger, maybe a volt or two. I don't know for niobium.

In any case, don't ever reverse the voltage, even instantaneously with signal if you want the cap to live a long, useful life.

Another of the special cases is capacitance tolerance and value drift. Aluminum is horrible. Tolerances are wide to start with and drift is big. Tantalum is better for both tolerance and drift, but in all cases, good design practice is to never use an electrolytic in a position where the capacitance value is important for signal filtering.  They drift too badly. Of course, one other part of practical design work is that you do whatever you have to to get it to work, then do the perfect thing when you get the perfect part mail-ordered from Timbuktu.

Also if a tantalum cab be used as a substitute, how do you determine where the + side should ne inserted in the circuit?

Two ways. You either (1) know circuits well enough to estimate the DC + AC voltage by looking at the schematic and scribbling a few calculations, or (2) you measure it with a meter when you build the circuit.

i cant them to work.I posted a topic last night and people say you can..but unless I put a electrolytic the circuit fails.  I am new but I have found if you change a value or anything other than what the diagram calls for it wont function.

You're at the beginning of a long, interesting road. As a beginner, you don't know all the special cases and details of parts that get non-specified parts to work. I was there myself when I started. Eventually you have learned enough of the special needs of parts that it becomes second nature to put in alternate parts.

As Kenny Rogers sang, you gotta know when to hold 'em, know when to fold 'em. Takes time.

[blackieNYC]

Back when I was a youngin' we used to recap Recording gear a lot, even preemptively (saves you more than you'll spend)  and we'd buy the Panasonic electrolytic series that had the lowest "tan delta", a parameter whose definition may exceed our purposes here, as well as my complete understanding.  A little more complicated than equivalent series resistance, here it is anyway http://www.radio-electronics.com/info/formulae/capacitance/esr-df-loss-tangent-q-tutorial-basics.php.  And there there is this http://www.nichicon.co.jp/english/products/pdf/aluminum.pdf
But i still have a question there doesn't seem to be a simple answer to - how can one estimate the reverse voltage maximum? Not in the sense of putting the thing in backwards, but subjecting the cap to AC signal in series?  If there is a 4vp-p AC signal passing thru the cap, what is the FWR voltage rating one should select at a minimum? The easy answer is "the biggest cap you can fit in the enclosure".   Or "buy 35v caps only". With non polarized caps at the output of that high gain op amp circuit, you won't need much more than your 9v supply. Maybe.

[merlinb]

But i still have a question there doesn't seem to be a simple answer to - how can one estimate the reverse voltage maximum?

A couple of hundred millivolts for electrolytics. Once you get above a volt or so, they start leaking.