20 Nov
2022
20 Nov
'22
1:41 p.m.
Another possible option would be to use the two power supplies separately
(one for the Pi, one for everything else) and tie the grounds together
(with a wire connecting all the GND pins). This has the added benefit of
helping you isolate which part of your system isn't getting enough power!
On Sun, Nov 20, 2022 at 12:56 PM Jake via sudo-discuss <
sudo-discuss(a)sudoroom.org> wrote:
I'm saying a 4A supply is not going to change
anything, i'm sure your
power supply is not the limit. For one thing, a regulated supply like that
doesn't lower its voltage if you overdraw its current limit - it overheats
or fails.
If your issue is resistance over the wires you're using, which I think is
likely, it wouldn't matter if your power supply were 1000 amps, because the
resistance would lower the voltage according to ohm's law.
If you want to meet up and look at everything together, I can show you how
to see exactly what's going on (with a voltmeter) and we can find an
appropriate power supply and wire it up so it works!
-jake
On Sat, 19 Nov 2022, Andrew R Gross wrote:
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That explanation is excellent, thank you!
I do believe I'll need your help acquiring a 4A power supply, though,
since
the current prototype is experiencing power loss
on a 3A wall wort. Part
of
this (much of it) might just be resistance along
its wire. It's got like
a
6 foot UBS cable.
Can you recommend a part? I genuinely wouldn't start contemplating
Frankenplug up there if I wasn't reaching the bottom of the idea barrel.
*Andrew R Gross, (he/him)*
412.657.5332 - shrad.org <http://www.shrad.org>
On Sat, Nov 19, 2022 at 12:22 AM Jake <jake(a)spaz.org> wrote:
> the Pi does not need 3 amps. That would be 15 watts. Since the Pi has
> USB sockets, its theoretical demand could include those sockets, but
the Pi
> itself probably tops out at less than 1.5
amps:
>
> "...the RPi 4B power dissipation tops out at approximately 6.4 Watts..."
> which is 1.28 amps.
>
>
https://raspberrypi.stackexchange.com/questions/114239/pi-4-maximum-power-c…
>
> to answer your other question about power supplies, first I can say that
> there are definitely 4-amp 5V supplies and I can probably find one, but
it
> won't be necessary, I think 2 or 3 will
be enough for what you're doing.
>
> As for why you can't put regulated power supplies in parallel, think of
it
> this way: a regulated power supply (like all
the ones you looked at)
has a
> chip which is adjusting the power production
in order to achieve the
> correct voltage at the output terminals, which is in this case 5.0
volts.
>
> If you connect two power supplies together, their output terminals see
the
> voltage that they're both connected to,
so if one does the job of
making 5
> volts, the other says "well I guess
that's taken care of, so i don't
have
> to do anything" or worse, they're
exactly equal, and they both
> simultaneously try to do the job of making 5v, but end up tripping over
> each other and bumping into each other, causing chaos. In most
situations
> it will probably work OK, but only because
switching power supplies can
> usually do more power than they're rated for so you're getting lucky.
>
> When people do "power injection" with long addressible LED tapes, the
> resistance of the LED tape's power wires ends up helping them by
creating
> electrical distance between the power
supplies.
>
> -jake
>
> On Fri, 18 Nov 2022, Andrew R Gross via sudo-discuss wrote:
>
>> I need to power a device with an LCD screen running on a Raspberry Pi.
>>
>> Both need 5 V. The Pi needs about 3 Amps. The screen needs between 0.5
> and
>> 1 A, depending on brightness. So I figure I can power both off of a
> shared
>> 5 V power supply as long as it provides at least 4 A. But I can't find
a
> 5V
>> 4A power supply. So I'm wondering... could I just wire two 5V 2.5A
power
>> supplies in parallel? Would this work? I
feels wrong but I can't think
of
why.
[image: image.png]
*Andrew R Gross, (he/him)*
412.657.5332 - shrad.org <http://www.shrad.org>