Re: 12v->5v noise

Pierre Martel

A pi4 need 3 amp just to run normally. not talking about any device powered by the USB or other power connector on the pi. 

A LM7805 will supply 1 amp max continuously and this is with a pretty large amount of dissipated power. If you go from 12v to 5v. just make the calcul of the power that it will need to dissipate. At 1 amp. 12-5= 7 volt times 1 amp = 7 watt that need to be dissipated.  I would go with a better designed buck converter circuit that will dissipate less power. and i would filter it a lot more by putting it in a grounded metal box with ferrite on the input and output wire and with small capacitor like 1uf or 0.1uf at the input and output also. 

Le jeu. 24 sept. 2020 à 09:13, Randon Loeb <randonloeb18@...> a écrit :
I had hoped that device would service all my usb needs, but I believe a pi needs 2-3 amps?

On Thu, Sep 24, 2020 at 1:42 AM Tom Flynn via <> wrote:
I think a 7805 puts out 1.5 amps his device puts out 15.  Does he need 15 amps?

On Sep 23, 2020, at 10:45 PM, Siegfried Jackstien <siegfried.jackstien@...> wrote:

If you have enough power... Use an7805
That sure is quiet even if it wastes some power in heat...
Sure its possible to make a switcher quiet... Meanwell psu are really good... But for shortwave i would additionally add some filters and ferrites.. If a switcher used... 
Or use 7805... Grin
Greetz dg9bfc sigi

Am 24.09.2020 05:16 schrieb Randon Loeb <randonloeb18@...>:
Was all excited to try my remote shack (rpi3 controlling ft-891 over wifi) but unlike my in-house testing with pi powered off a wall wart, when I power it off battery through a 12v->5v converter I get noise that (at least on 20m) raises an s1 floor to s9. Basically the rig is in my car powered off a lifepo (not the car battery), I mention because space is tight.

I believe it is mostly coming from the converter, this one:

It seems to send noise through cables connected to it (well technically the usb power hub I made), but also through the pi and into the radio via the usb cat cable. But any cable plugged into seems to sort of act like an antenna.

If I power the pi off of a 5v cellphone battery pack, noise drops down (seems like maybe a little, but at least S6 floor drop). As I say, I tested this pi in close proximity to the radio before off a wallwart, so I don't think pi itself is creating the noise.
Only thing I want to mention is that I created my own little USB power hub to connect to the converter using some jacks I have, and I assumed it is correct or at least harmless to ground the usb jack cases, was that wrong?

For now I am assuming the converter is noisy.

Anybody have experience with that one? Is there a better go-to? Besides ferrites (will try in the morning) any other way to quiet this one down? I have a few buck converters lying around and will see if I can come up with something, but open to any suggestions.
Randy KN4YRM

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