From: James Cameron <quozl@laptop.org>
To: Microcontroller discussion list - Public. <piclist@mit.edu>
Sender: "piclist-bounces@mit.edu" <piclist-bounces@mit.edu>
Date: Sun, 16 Feb 2020 19:05:05 -0800
Subject: Re: [EE] large USB power banks
Thread-Topic: [EE] large USB power banks
Thread-Index: AdXlQMw7vmgiWR8bRpyZ9AXRrCttnA==
Message-ID: <20200217030505.GG16626@laptop.org>
References:
 <MWHPR01MB284515D5A184FF178C566F1FE0150@MWHPR01MB2845.prod.exchangelabs.com>
	<15c8c6b973b5343c2becb83c6d63a638@mtlp000086>
	<CACZQxzOWKK+kJVug5PiGy=1vxgy4yjp6dOHbKQj=F6t1rLO0sg@mail.gmail.com>
	<20200216234805.GC16626@laptop.org>
	<c9cf8123-040a-f583-97e0-5a4e6f61f2ae@triad.rr.com>
In-Reply-To: <c9cf8123-040a-f583-97e0-5a4e6f61f2ae@triad.rr.com>
Reply-To: Microcontroller discussion list - Public. <piclist@mit.edu>
Accept-Language: en-US
X-MS-Exchange-Organization-SenderIdResult: Pass
X-MS-Exchange-Organization-PRD: mit.edu
X-MS-TNEF-Correlator:
received-spf: Pass (protection.outlook.com: domain of laptop.org designates
	209.85.214.177 as permitted sender) receiver=protection.outlook.com;
	client-ip=209.85.214.177; helo=mail-pl1-f177.google.com;
dkim-signature: v=1; a=rsa-sha256; c=relaxed/relaxed;
	d=laptop-org.20150623.gappssmtp.com; s=20150623;
	h=date:from:to:subject:message-id:references:mime-version
	:content-disposition:in-reply-to:user-agent;
	bh=+xxukkEkRaXqVYcgBjftpBppK2huQd0PWS4qIQ2KiUk=;
	b=Gl/TlUS8KBilitXVQwD8+R7yiv33WYNkhJ0Du/6zE9H1k+mU9WA1DkVDPSXBkA8RuB
	L9ARmeIeQdF9UvVS47zo9wweYQKB/Hi/xW2kuLMRXS4vArNaTWCfxEis1q3LU2TD8B3P
	oxj3uYBhxIk5eFLZahpimtni4n3mqze5MyYRkOnWFJPVEik4pLVuQrCIYMpn7hI/i1FF
	ZvVE5cEayrccjitKgWH9jkFbvJgMChSbIN6lCHhZAyXTcLyZrLOLscBC83VtPKCCShlR
	DiHxs9CqzLvl95loqw5N2Yc7UinROZeNPmkkQbbFIsDrdiyE8DrLf8rmm1ymuRRIg5hJ	XbVQ==
authentication-results: spf=pass (sender IP is 209.85.214.177)
	smtp.mailfrom=laptop.org; mit.edu; dkim=pass (signature was verified)
	header.d=laptop-org.20150623.gappssmtp.com; mit.edu; dmarc=bestguesspass
	action=none header.from=laptop.org;compauth=pass reason=109
user-agent: Mutt/1.9.4 (2018-02-28)
errors-to: piclist-bounces@mit.edu
list-id: "Microcontroller discussion list - Public." <piclist.mit.edu>
list-post: <mailto:piclist@mit.edu>
x-beenthere: piclist@mit.edu
x-mailman-version: 2.1.6
x-received: by 2002:a17:90a:ec02:: with SMTP id
	l2mr18051202pjy.12.1581908713503; 	Sun, 16 Feb 2020 19:05:13 -0800 (PST)
x-topics: [EE]
Content-Type: text/plain; charset="us-ascii"
Content-Transfer-Encoding: quoted-printable
MIME-Version: 1.0

You probably mean to attach multiple USB tails.

Here's what I've seen.

Should a device, plug, or cable develop a short, then the fault
current of the power supply will be delivered.

Subsequently, the power supply may limit at maximum current, but as
this is usually larger than the maximum current, and way above the
current limit of the typical device, plug or cable; you get smoke and
fire.

So you should add per-cable fusing.

On Sun, Feb 16, 2020 at 09:31:40PM -0500, John Ferrell wrote:
> I have a repurposed PC power supply on my bench That I have been tempted=
=20
> to use power/charge multiple devices. What risks might I be taking?
>=20
>=20
> On 2/16/2020 6:48 PM, James Cameron wrote:
> > I've also used single cell USB power banks in some quick hacks.
> >
> > Where I've wanted less than 5V, I've taken power directly from the
> > cell terminals on the PCB.
> >
> > This defeats the discharge protection, so you have to add your own, or
> > procedures.
> >
> > It can also confuse any coulomb counter in the pack.
>=20
> --=20
> John Ferrell de W8CCW
> "We must never become too busy sawing to take time to sharpen the saw."
> Source: Ergonomic Trends
>=20
> --=20
> http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive
> View/change your membership options at
> http://mailman.mit.edu/mailman/listinfo/piclist

--=20
James Cameron
http://quozl.netrek.org/
--=20
http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist
.