filter for USB line.

[settra]

no.... i dont have one , and they are way too expnesive!! all can do is louben i use a speaker, and see JUST if there is an AC. thats why i sed 20hz to 20khz... (since its being played by a speaker)

 

[Nigel Goodwin]

no.... i dont have one , and they are way too expnesive!! all can do is louben i use a speaker, and see JUST if there is an AC. thats why i sed 20hz to 20khz... (since its being played by a speaker)

I hope you have a capacitor in series with the speaker?.

 

[settra]

as a metter of fact i dont i though about it (So the dc wouldent pass ) but i was bored. dont worry the speaker is a large one so it didint explode the point is this :

if the freuencies are low (around 1k -10khz) isint an inductor usless?? also, the capacitor should be near 1 farad, correct?

 

[KeepItSimpleStupid]

Take a look here for some car PC stuff including power supplies. https://www.mini-box.com/s.nl/sc.8/category.101/.f

 

[Nigel Goodwin]

as a metter of fact i dont i though about it (So the dc wouldent pass ) but i was bored. dont worry the speaker is a large one so it didint explode the point is this :

The point is without a capacitor in series with the speaker you're putting a huge load on the PSU, so it might very well buzz - you're not actually testing anything.

if the freuencies are low (around 1k -10khz) isint an inductor usless?? also, the capacitor should be near 1 farad, correct?

No, the capacitors are fairly low, around 0.1uF as far as I can remember?. Inductors are fairly low as well, along with the capacitor they make a low pass filter.

 

[settra]

the formula for a Low pass filter is Fcutoff = 1/2πRC . for a low pass this means that it filters enything above the fcutoff.. so, since the R is prety small (only the wires), then the C must be ass low as it can get. even if the R was 1ohm , if i used an uf capacitor (10^-6 farad) , that would be fcutoff = something near 100.000hz . this means that it would not filter anything at all. (not taking in acount that R is <<<1ohm ) am i being correct here??

p.s . i will try with the capacitor, but nothing will change, becouse, i can as well hear the exact same noise, from my car speakers when no music plays...

and Keepitsimplestupid, PLEASE. PLEASE. do not EVER suggest mini-box to anyone. it sells a bunch of crap, and as far as PSU's go, they suck ass.
(and yes this is sad, since i have a psu from minibox...)

 

[KeepItSimpleStupid]

I ordered their Open UPS platform, Not sure when I will get to the project though. It's just a piece of the puzzle. I want to back-up a network repeater, and I'm planning to upgrade too.

I'm sort of planning to use Chinese step-down converters with meters and their Open UPS platform. I might have 3 or 4 outputs available. Right now, I would need a 5 V 2A and a 6V output (4 x AA). If I upgrade, I might need a 19 V 1.7 V output, a 6V output and probably a 5V output. The router I want hasn't been released yet.

Right now, I am running a Chinese step down converter 24/7.

The UPS has to be unobtrusive because it has to stay somewhat hidden in a living room.

 

[settra]

so , something last, before i make my desicion on what path to follow. what would be a more acurate way to mesure the AC outpout of my alternator??? i just want to know, 1) if there is any AC. 2) what HZ it is.
is the way i use with the speaker acurate?? i tried adding a capacitor in serries with the speaker, and it had no noise (but then , it could be , because in such low frequencies, the capacitor might be open circuit)

(without osciloscope)

or should i start enother thread??

 

[Nigel Goodwin]

so , something last, before i make my desicion on what path to follow. what would be a more acurate way to mesure the AC outpout of my alternator??? i just want to know, 1) if there is any AC. 2) what HZ it is.
is the way i use with the speaker acurate?? i tried adding a capacitor in serries with the speaker, and it had no noise (but then , it could be , because in such low frequencies, the capacitor might be open circuit)

(without osciloscope)

You need a scope - but the capacitor/speaker would show any HUGE amounts of ripple, what value capacitor did you use?.

 

[settra]

0.1uF. but remember that i THINK that the frequencies we talkin about are around 1000hz...

 

[Nigel Goodwin]

0.1uF. but remember that i THINK that the frequencies we talkin about are around 1000hz...

Do the maths

Try a MUCH larger capacitor, 100uF or more.