Continue to Site

# Electrolitic capacitors: max voltage question

Status
Not open for further replies.

#### sbayeta

##### New Member
Hi,
I'm using a 1000uF 16V capacitor in my power supply (12V AC rectified). The voltage on the capacitor terminals is 15.5V.

I'd like to know if the 16V parameter of my capacitor is a stress value, or if it's a nominal value meaning that my capacitor is safe with voltages less or equal than that.

Thanks

If I remember correctly that is the capacitors maximum safe voltage, if exceeded, the capacitor could pop, melt itself, unbond the solder, discharge too much/too little, spike, short, etc. I'd say stay just below the max voltage just to be safe.

personaly id use a 25 or 50 volt cap, since its quite possible to have a surge that would overflow the cap...

Even I use capacitors with atleast 15-25V higher ratings than required. Its is always better to use a higher voltage value capacitor than a lower one.

i have read someplace that the cap rating voltage should be with at least 20% greater than the voltage the cap is used in the circuit.

i read twice, but that seems a good bit too much. :S

Cap Voltage

I always try to stay at leist 10 to 15 volts above the circuit voltage level. It will also extend the capacitor's life and the circuit's reliability.

Electrolytic capacitors are 'formed' during manufacture by depositing an anodic film on the aluminium foil that makes up the anode, that will withstand the operating voltage plus (typically) 10%.

So you are quite safe to operate them at their specified working voltage.

Hi sbayeta,

just my 2 cents worth;

if a circuit runs 10-15 volts I use 25 volt caps

16-24 volts I use 35 volt caps

25-40 volts I use 50 volt caps

Using a higher voltage rating cap is *always* advisable IMHO.
It's cheap insurance :wink:

I have a question along the same lines what about the uF is that just a "safe" working value or would replacing a capacitor with a higher UF be a bad Idea? For exaple I have a 100uF 16V capacitor and was thinking of replacing it with a 150uF 20V.

not a good idea?

I did some further research on this and found that in doing repairs, it is not a good idea to change the uF of the capacitors used. So I could go with a 100uF 20V but shouldn't use a 150uF 20V. If anyone has more information on this feel free to say so, as I am just going off what I have read.

Think of it like a resistor. A resistor has a power rating (in wattage) and a resistance rating. You can replace a 300-ohm ¼ watt resistor with a 300-ohm 1-watt resistor. Only difference is that the 1-watt resistor can withstand a higher current/wattage (or heat) level. Having a higher wattage handling capability does not affect the circuit design, other than giving it the ability to handle more heat.

However, if you change the resistance value, then you change the current level across the resistor and across the circuit. That will definitely affect the circuit.

(In this example, uF rating is equivalent to resistance and wattage is equivalent to voltage – Just an analogy to try to put it in perspective :wink: )

Re: not a good idea?

tech_dragon said:
I did some further research on this and found that in doing repairs, it is not a good idea to change the uF of the capacitors used. So I could go with a 100uF 20V but shouldn't use a 150uF 20V. If anyone has more information on this feel free to say so, as I am just going off what I have read.
You may need to replace an electrolytic which is part of a CR time constant in some timing circuit. If so, don't change the value, or you will upset the timing.

Other than that, electrolytics are used as reservoir or smoothing and you can usually safely exceed the capacity specified. The only time I would add a word of caution is if the capacitor is very large, say, several thousand uF and is used as reservoir straight after a recifier and with no series resistor to limit surges. In that case the rectifier could possibly be damaged by the surge current.

As I said before, eleectroytics should be used within their rated (as marked) voltage. Straight after a rectifier the voltage can increase to 1.4 x the applied AC, so it is a point to watch.

iv always learnt to use atleast double the voltage iv seen these blow take an eye out easy .just thought id put my bit in .

I would absolutely no questions asked use a 25V rated cap. 15.5V and 16V capacitor is a recipe for POP!

speakerguy79 said:
I would absolutely no questions asked use a 25V rated cap. 15.5V and 16V capacitor is a recipe for POP!

Well answering a reply to a thread more than FOUR years old seems a bit pointless?.

Hey I wasn't the first. Didn't notice the date. How do people bring these to the front page?

They probably find them using a search engine.

Status
Not open for further replies.

Replies
12
Views
3K
Replies
19
Views
3K
Replies
12
Views
2K
Replies
15
Views
2K
Replies
22
Views
2K