Series or Parallel Caps?

Beginning Member Join date : 2012-06-06

I think you have answered my questions! The ones (caps) that I was most concerned about were the 3 "special" caps that are .1uf @ 1600 V. I am rebuilding an Oscilloscope, so I do not have one to use on the caps to determine which is the foil side and which is not. With that being said, in cruising the "Nat" there was a Utube video on how to do what I am asking for. They used guitar amp in place of the o'Scope. I could not tell the difference with a amp on the 3 1600 v caps and I was baffled. Then the last part of your reply cam into focus and it made since as they look like two caps joined together under the same plastic covering. I will proceed from here. Thanks.

I did make "heads or tails" of the bunch. I had my head where the sun does not shine!

Site Administrator Join date : 2010-11-22

smyers10 wrote:: Another question, I have three Radial caps (C-22, C23, and C24 these the caps are 0.1 uf at 1600 Volt) that are referred (in the old directions) as "place the banded ends to the .." My replacement caps are not banded and I do not know what the band in the old directions was referring to.

Was this the "Foil end". Yes that means the foil end goes to a return path to ground ( or lower potential side ) to reduce noise.

If this is the case, how do I check to see which end is the "foil"end.

Most manufactures don't designate a lot of the time and some times when they do, they mark them incorrectly.
There is a video on YouTube addressing this.

I did a search on the web but what i thought was there is gone. However I did find something that may help you test for which end is the foil end of an unmarked or miss marked cap.

What if the capacitor doesn't have a banded end?

This marking of the outside foil was very common in the "good ol' days" of electronics, but, sadly, most capacitor manufacturers nowadays do not bother to mark the outside foil, so we're left to fend for ourselves. If the capacitor has no banded end, the outside foil connection could be on either end, so there is no easy visual method to determine the best orientation of the capacitor. However, if you have access to an oscilloscope, you can do a simple test to determine which is the outside foil terminal. Set the scope up to the most sensitive vertical scale (20mV or less, preferably) and connect the scope probe across the capacitor (ground to one side of the cap, probe tip to the other). Grab the capacitor tightly with your fingers, and note the amplitude of the induced 60Hz AC signal (or 50Hz if you are on the other side of the pond). While still holding the capacitor tightly, reverse the scope leads and you should see a dramatic difference in the amplitude of the induced AC signal. The orientation with the lowest induced signal is the one you want, and the ground lead of the scope is connected to the outside foil in that position. Mark it, and connect that side of the cap to the lowest impedance point in the circuit, typically the driving source plate when used as a coupling cap, or the grounded end if used in a shunt position. If you cannot see a large enough induced AC signal by holding the capacitor between your fingers, place the capacitor on top of an AC line cord (that is plugged into the mains wall socket, of course!) instead of holding it between your fingers and you will see a larger signal on the scope. If you are new at this, start with a 0.022uF cap or thereabouts, as it is easiest to see the difference between the two orientations. The induced signal is smaller at 60Hz with larger value capacitors, and is more difficult to see on the scope.

In the case of some types of capacitors, such as ceramic disks, multi-layer ceramics, or silver micas, there is no "outside foil", because the capacitor is made of a single-layer, or stacked layers of dielectric material and conductor. The orientation of these capacitors makes no difference. Also, some higher-voltage film caps (typically the 1000VDC/450VAC and higher values, such as the Orange Drop 716P high-voltage units) use a "series-wound" technique that has two separate sections, side by side, with a common "floating" connection layer, usually at the bottom of the layer stack. These caps will have no inherent shielding either.

_________________
I'm a Science Thinker, Radio Tinkerer, and all around good guy. Just ask Me!

Site Administrator Join date : 2010-11-22

smyers10 wrote:

I have ordered new caps for my Oscilloscope.
I know that the supplier can not give me the exact ones,

I can not make heads or tails of the ones he sent.

Did you get a shipping document with them?
If so then type to me the Parts description provided for both.
Do the Parts Have printing on them?
If so, forward those also.
That way I can decipher them by comparison.
-------------------------
Unlike resistors, when you connect two in series, you halve the micro farads (correct) and when you add two in parallel you add the uf. Is this correct? Yes

Find the overall capacitance and the individual rms voltage drops across the following sets of two capacitors in series

Find the overall capacitance and the individual rms voltage drops across the following sets of two capacitors in series when connected to a 12V AC supply.

a) two capacitors each with a capacitance of 47nF
b) one capacitor of 470nF connected in series to a capacitor of 1μF

a) Total Equal Capacitance,
Find the overall capacitance and the individual rms voltage drops across the following sets of two capacitors in series

CT =

((   C1       X   C2 )      / ( C1 + C2 ))   =
         22uf X 47uf /   22uf + 47uf
                 1,034uf    /           69uf       = 14.98uf Total Capacitance
Or try this:
                  1
_________________
(1/22uf ) + (1/47uf)
( 0.0455 )   + ( 0.0213 )

                  1
           _________         =                14.98 uf Capacitance Total
                 0.667

-------------------------
What happens to the stated voltage on the cap? I mean, if you add a 22 uf (200v) and a 47uf (450 v) (in series) You have to a

you get a 69uf cap, but at what voltage rating? The lesser of the two, or the greater of the two?

The voltage is distributed unequally across the series capacitors. without going into the Math, it's just suffice to say that the Highest voltage will be across the smallest capacitor.

So if the voltage supply is more than the least voltage you will destroy the circuit in question.

Hope this clarifies your questions. study

_________________
I'm a Science Thinker, Radio Tinkerer, and all around good guy. Just ask Me!

Beginning Member Join date : 2012-06-06

Another question, I have three Radial caps (C-22, C23, and C24 these the caps are 0.1 uf at 1600 Volt) that are referred (in the old directions) as "place the banded ends to the .." My replacement caps are not banded and I do not know what the band in the old directions was referring to. Was this the "Foil end". If this is the case, how do I check to see which end is the "foil"end.

Beginning Member Join date : 2012-06-06

I have ordered new caps for my Oscilloscope. I know that the supplier can not give me the exact ones, I can not make heads or tails of the ones he sent. Unlike resistors, when you connect two in series, you halve the micro farads and when you add two in parallel you add the uf. Is this correct? What happens to the stated voltage on the cap? I mean, if you add a 22 uf (200v) and a 47uf (450 v) (in series) you get a 69uf cap, but at what voltage rating? The lesser of the two, or the greater of the two?

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