Re: New wiring diagram version

Jerry Gaffke

Good to have an alternate drawing of how to wire up a uBitx.
We often have questions here from puzzled kit builders.


The 2 reverse protection diodes should be after the fuses, not before, so the fuses
will blow if the diodes conduct.  Those diodes might conduct the full current of
a small supply, in which case it could work as is.  (Though they should be Schottky diodes.)
They could fail with a short at high currents, which is also ok.  Or they could blow
molten silicon across the room and be open when you plug in your 20 Amp power
supply backwards, in which case you will destroy many parts on your uBitx.

I would instead add a schottky diode (lower forward voltage drop than a 1n4007)
in series with the fuse for the main supply into the uBitx.  We can afford to lose 0.3 volts there.

No real need for reverse protection on PA-PWR, as the IRF510's have their own intrinsic
reverse diode.  You might burn a board trace or coil between the PA-PWR connector and IRF510,
this would be easy to fix.  But reversing the main 12V into the uBitx will blow 
a bunch of stuff (including everything on the Raduino), and be very difficult to repair.

The fuse for the main supply into the uBitx should be 1 Amp, perhaps even 1/2 Amp.
But definitely not 5 Amps.  2 Amps could be about right for the PA PWR, maybe 3
if feeding it 20V.

Opinions will vary, we've had long discussions here about reverse protection.
But I doubt many will say this drawing is correct.
I have not looked hard at it beyond the power supply connections.


On Wed, Sep 4, 2019 at 05:27 AM, Adrien F4IJA wrote:
Hi everyone !

OK, you'll now find the new version of the wiring diagram in the wiki :

You will now be able to download an HD PDF and also, in the CAD folder you will find the SVG source file :
Adrien F4IJA

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