what's the voltage of capacitor (Nigel's Tut)

[wejos]

hi guys,

this project's from Nigel's page.. little help please.

**broken link removed**

just want to ask what voltage are the capacitors? i'm assuming that it's electrolytic since they have polarity symbols.

i'm still on the 16f84 chip. and i'm going to use it for this getting-to-know-the-PIC and trying-to-learn project. should i make slight changes because of using 16f84 (obsolete) PIC, Nigel wrote there it's for the 16f28.

thanks a lot guys.

 

[wejos]

i'm sorry of this one also. the voltage of the capacitors?

**broken link removed**

 

[Nigel Goodwin]

As long as the voltage is higher than that across the capacitor, it doesn't matter what it is - as they are all small values, 25V upwards is likely, with 63V or 100V been common as well. Any of those is perfectly fine.

 

[be80be]

The rule is 2 times the volts so if you have 9 volts you want 18 volts but most capacitor have a higher rating any way. Most are all ways higher then 16 volts. If you used a wall wart that is 12 volts going in your 7805 your first capacitor would need to be higher then 24 volts.

 

[wejos]

please correct me if i read it wrong. since there's a 5v regulator the voltage of the capacitor should be higher than 5v? so i should multiply that by 2 then i will get ---25v is safe

 

[be80be]

Your regulator has more volt coming in say 12 you want a capacitor larger then that say 24 volts power out of it is 5 volts so 2 time that will be good 10 volts now most capacitor
that you buy are all ways bigger the 16volts so like Nigel said any would work.
What I'm saying is all ways use a capacitor that 2 times the volts in or bigger and you'll be ok

 

[Nigel Goodwin]

please correct me if i read it wrong. since there's a 5v regulator the voltage of the capacitor should be higher than 5v? so i should multiply that by 2 then i will get ---25v is safe

I've already said - anything higher is fine - I've never heard of any supposed 'two times rule' anyway. Certainly it's not used commercially.

 

[wejos]

thanks guys i get it now. your assistance is graciously appreciated, both of you. more power.

 

[wejos]

just being extremely cautious Nigel sorry. don't want to blow up stuff as i am too afraid to get electrocuted and stuff like that lols

 

[be80be]

Certainly it's not used commercially.

Your So right it's for hobby electronics if it was for a sony you put the lowest value you can use and hope you get by.
But if you all ways size them 2 times bigger you'll all ways be good

 

[wejos]

*listening*

 

[russ_hensel]

The rule is 2 times the volts so if you have 9 volts you want 18 volts but most capacitor have a higher rating any way. Most are all ways higher then 16 volts. If you used a wall wart that is 12 volts going in your 7805 your first capacitor would need to be higher then 24 volts.

I believe in an electrolytic the insulator is formed by the voltage applied. I have heard that if the voltage is way under the rated voltage that the indsulator may not form correctly. Thus it may be good to have a good safety margin, but too much may introduce problems of its own.

 

[be80be]

I was just tiring to help this person out here Not start a war most capacitor are over rated
that's why they blow out when you get them to close to volts going thew them so you will all ways be in good shape if you size them bigger by 2 times. Now the insulator in the capacitor is what is rated witch means that your not going to blow a hole in a 25 volt capacitor with 5 volts but it can happen with 25 volts.

 

[Mike - K8LH]

Please note that if you use a MAX202 or MAX232A or equivalent that you can use 0.1 uf (100nf) disc ceramic capacitors instead of an electrolytic. They're usually physically much smaller (installed inside of the machined pin socket in the picture below)...

 

[Nigel Goodwin]

I tend not to over rate capacitors too much.

Higher voltage capacitors are larger and also have a higher ESR and ESL.

Quite the opposite - higher voltage capacitors are normally lower ESR - which is why it's advantageous to replace faulty ones with higher voltages, if space allows.

Where this falls down though (drastically), is 'very' high voltage ones, commonly used as start-up capacitors in SMPSU's. These are usually between 1uF and 10uF rated at 450V or so - these, even when brand new, have particularly high ESR - but this is no problem for their useage.

But to go back to the original question, the capacitors used in my tutorial - they are all low values, so are physically small, and certainly the 1uF's I used were going to be rated at 100V, lower ones aren't any smaller, or any cheaper - so that's the only 1uF I stock.

Once you get to larger values, I keep multiple voltages - so for 470uF I keep 16V, 25V, and 63V - not so much for the voltages as the size, if I could get 63V working in the same size as 16V, I'd just stock 63V ones, but you can't

I don't generally stock anything below 16V, as it's too restricting.