# Can you put a resistor either side of an electrolytic capacitor in series?

I'm just starting out learning electronics and wondered if anyone could tell me whether it matters what side of an electrolytic capacitor you put a resistor to restrict the current going in and out? (The resistor and capacitor are in series.)

All the examples I've seen have put the resistor on the positive terminal of the capacitor but I'm wondering whether that's just convention. The reason I think that is because in a simple closed circuit involving a battery and LED, the resistor can go either side of the LED (in series) to restrict the current (and voltage) and protect the LED. This is because the current is the same no matter where you are in a closed circuit. With this in mind, does the same apply to a capacitor and resistor in series, i.e. does it matter what side the resistor is?

In a simple series circuit the current is always the same anywhere in the circuit. However that does not mean it will work as expected if there are any connections to other circuit elements you may have wired to it. Better to post a complete schematic drawing including voltage and ground connections to make sure all is correct.

depends on what the capacitor is being used for.

on your windscreen wiper delay, the cap is charged slowly and once the stored voltage reaches the threshold, the wiper circuit is triggered, the wiper motor runs and the cap is drained.

think of the cap as being filled.

put the resistor on the top and it fills slowly.

put it on the bottom and it fills instantly and drains slowly.

So does this mean if I attach a resistor to the positive (+) terminal of an electrolytic capacitor, it will restrict the current going into the capacitor and if I attach a resistor to the negative (-) terminal it restricts the current going out when the capacitor is discharging. Is this right or have I got the wrong end of the stick? ;-)

It makes a difference in the application.
(Likewise for an inductor.)

Sorry for all the questions, complete newbie. So based on the diagrams you posted, I can see how in the "low pass filter" diagram the resistor restricts how fast the capacitor charges. In the "high pass filter" I can see the capacitor charges up really fast and when it discharges I assume the resistor restricts the outgoing flow.

[quote author=s1mbr0 ] So does this mean if I attach a resistor to the positive (+) terminal of an electrolytic capacitor, it will restrict the current going into the capacitor and if I attach a resistor to the negative (-) terminal it restricts the current going out when the capacitor is discharging. [/quote]

No. Charging and discharging is done on one pin. A capacitor will not charge on the positive pin and then discharge on it's negative pin. You have to make a connection from the positive pin towards the negative pin to have it discharge.

Rather then trying to understand and remember a lot of rules it's better to learn via a structured path where one starts out learning DC fundamentals and then move on to AC fundamentals then on to semiconductors, etc. What you gain using that method allows you to build upon your knowledge such that each more complex topic is easier to master. Capacitors are not even introduced till you have DC fundamentals down pat, covering ohms law, series and parallel circuits.

Now I get it, just played around with a great application called "iCircuit" that simulates circuits. (It's available on OS X, iOS, Android, Windows Phone and Windows 8 - http://icircuitapp.com)

I can see I was way off base with my understanding of how to use capacitors in circuits. Now all your replies make a lot more sense. I was halfway through reading a book called "Make Electronics" and couldn't quiet understand their explanations on how an electrolytic capacitor worked in a circuit (I can see it was me, not the book which is great), hence the post. Anyway thanks everyone for the help and advice :)