capacitor question...

[Nickk2057]

hello... i was wondering what type of capacitor this is... trying to find out the type it is so i can make the french inverter circuit... any ideas.. so i can go to the parts store to get it

[IanB]

The circuit symbol just indicates an unpolarized capacitor.

To know what kind of capacitor is best in that circuit needs information about the circuit as a whole, a recommendation from the circuit designer, or details in the parts list or circuit description.

If in doubt, just use any small unpolarized capacitor of that value and with a suitable voltage rating.

[amspire]

It is not polarized, so it is almost certainly a low esr ceramic 2.2 microfarad capacitor.

If you have any dead PC motherboards lying around, it will be full of 1uF surface mount caps and probably 10uF ceramic caps (the big ones), so you can pinch it them from there. Perhaps some 2.2uF as well, but there capacitors are not particularly accurate, you can replace a 2.2uf ceramic with two 1uF caps in parallel.

How can you tell the value? If you do not have a capacitance meter, get a 9V battery and a 1Meg resistor. Put a multimeter across the capacitor. Connect the capacitor and resistor together. The other end of the capacitor goes to the battery negative. The other end of the resistor goes to battery positive.

If the voltage across the capacitor rises from 0V to 6V in just over 1 second, it is 1uF. A bit over 2 seconds it is 2uF. A bit over 10 seconds it is 10uF. These capacitors can easily be out by over 20%  - it doesn't matter when used for decoupling or filtering DC.

Edit: I am assuming this is a low voltage capacitor. I do not know what the "french inverter circuit" is. If it has mains across it, DONT use a ceramic capacitor.

[c4757p]

the french inverter circuit

Sounds frightening. Not entirely because it's French. Careful with that capacitor.

Can you post the rest of the schematic?

[Nickk2057]

sure thing.. but its a snipit of a video cause i have not found an accrate diagram o the net about it... hope t is th oes to se about... and please.. its for 110v and not 220v...

as you see there are two NPN transistors and two NPN mosfets there

[Nickk2057]

and here s the video of where i was trying to get to if it helps much...

[c4757p]

Oh, those are just timing capacitors in a multivibrator. Any old ceramic will do. Just make it's rated for 12V - some of those little SMD ceramics have pretty low voltage ratings, especially in large values like 2.2uF.

[c4757p]

Make sure you test that circuit before it blows something up. It is completely unregulated, so the output voltage could vary significantly between the person who drew that schematic and your build of the circuit using the parts you had.

One more warning with that circuit - if the oscillator shuts off, it will stick with one MOSFET turned on, sticking a high DC current straight up the poor transformer. Don't play with the circuit while it's running or you can kiss the transformer goodbye.

[Nickk2057]

haha... don't worry.. i make sure with my analog tester and stuff.. on the inputs and such.. tho i better be sure to put a good fuse on there too as an addition on there

[Nickk2057]

tho trying to find a good multi meter is kinda a hassel... with me on a stricked income its a real problem

[c4757p]

Eh, even a shitty one will do a good job for now. I survived with an old turd from Radio Shack for quite a while before I started investing a bit more in my workbench.

One warning, though - if you have a cheap multimeter, it will be assuming that the voltage output of this circuit is a sine wave (it's not), and that will affect the reading. Don't trust it too closely.

[Nickk2057]

oh i will keep watch with my analog oscilloscope i hooked up to the analog input on my computers sound card... with a resistor on the low voltage side of course

[Nickk2057]

plus it will be watched with the input amp meter (which i got from a small car charger) and a volt meter

[c4757p]

All of those will be off due to the non-sinusoidal waveform.

[Nickk2057]

and by the way... how will i know that those caps are that size that i am looking for?

[c4757p]

If you don't have a capacitance meter, read amspire's comment, he gave a pretty good suggestion.

[Nickk2057]

i guess i will put a couple pots in that to control the phase i guess

[Nickk2057]

hopefully i get a square wave pattern... if i can that is.. but i know most motors dont like those... unless its a ac+dc motor