USB Charger: run cellphone off your laptop when an outlet is not available

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John Faughnan - 22 Jan 2004 21:08 GMT

The other day I paid about $20 for a widget that allegedly charges my
cellphone via my laptop USB port. This is part of a logical trend to
using the USB port on a laptop (or a powered USB hub) as a universal
slow speed charger for PDAs, iPods (mini only), digital cameras,
cellphones, etc [1]. The idea is that you carry a charger for the
laptop, or you carry a powered USB hub, and no other chargers.

In practice charging the cellphone via the USB widget is very slow.
I'm not sure overnight is long enough! HOWEVER, it does enable one to
extend cell phone talk life while traveling. I discovered this while
traveling with an almost discharged cellphone. I set my laptop power
profile [2] appropriately and plugged the USB adapter into my
cellphone. I continued to talk for another 1-2 hours. The cellphone
power level stayed flat or increased slightly, so the power input was
about equal to digital communications demand.

Caveat! Most cellphones were not designed to charge off a USB port.
I've no idea what using one of these devices does to the cellphone
LiOn battery. I suspect there's no overcharge protection, so if you
left your cellphone plugged in for a few days the battery would
probably be damaged. I also suspect, however, that it's probably
harmless to use to power a working cellphone as described here.

Belkin sells one of these. I've seen it sold online for about $15.00:

http://catalog.belkin.com/IWCatProductPage.process?Merchant_Id=1&Product_Id=132105

john
jfaughnan@spamcop.net

meta: jfaughnan, jgfaughnan, charger, adaptor, adapter, power adaptor,
power adapter, converter, convertor, USB, mini-B, USB sync,
synchronization, HotSync, laptop, portability, travel, cellular,
mobile phone, sprint, Samsung, portability, efficiency, convergence,
transformer, AC/DC, wall wart

[1]http://groups.google.com/groups?selm=5c0dbfb4.0312121044.6d00220%40posting.google.com
and
http://groups.google.com/groups?selm=5c0dbfb4.0401161137.3f143a2c%40posting.goog
le.com]

[2] In XP use a custom power profile for this -- never sleep but do
blank screen and spin down drive -- I called my power profile
"Cellphone Charger". Similar setup for OS X.

Reply to this Message

Ian Stirling - 22 Jan 2004 21:15 GMT

In comp.sys.laptops John Faughnan <jfaughnan@spamcop.net> wrote:

> The other day I paid about $20 for a widget that allegedly charges my
> cellphone via my laptop USB port. This is part of a logical trend to

http://www.ebuyer.com/ do one for around $1.5 (in the UK) for the nokia
3* series of phones.

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Steven M. Scharf - 24 Jan 2004 05:54 GMT

> Caveat! Most cellphones were not designed to charge off a USB port.
> I've no idea what using one of these devices does to the cellphone
[quoted text clipped - 4 lines]
>
> Belkin sells one of these. I've seen it sold online for about $15.00:

The charging circuitry and overcharge protection is inside the phone, it has
to be for a Li-Ion battery. It will not damage the phone to use a USB
charger. Most Li-Ion cell phone batteries are 3.6V. The cigarette lighter
adapter adapts from 13.6V down to around 5-6V. The USB port puts out 5V.
It's just perfect.

Reply to this Message

John Faughnan - 26 Jan 2004 05:27 GMT

That's very helpful Steven. I'm fascinated by how the USB connector
and power standard is becoming the de facto solution to the multiple
charger problem. It seems to be an unintended consequence of the
original design. I wonder if any of the USB designers thought of their
devices as a future "universal charger".

john

> The charging circuitry and overcharge protection is inside the phone, it has
> to be for a Li-Ion battery. It will not damage the phone to use a USB
> charger. Most Li-Ion cell phone batteries are 3.6V. The cigarette lighter
> adapter adapts from 13.6V down to around 5-6V. The USB port puts out 5V.
> It's just perfect.

Reply to this Message

David Gunter - 28 Jan 2004 01:15 GMT

In regards to the USB power decision, I think it due to the fact that
most devices need around 5V to operate: Webcams, drives, etc. Thus I
don't think that any of them thought of a charger purpose. Who knows!
But eventually, somebody thought of it.

-david

> That's very helpful Steven. I'm fascinated by how the USB connector
> and power standard is becoming the de facto solution to the multiple
[quoted text clipped - 3 lines]
>
> john

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Replace spam with david in the email address if you want to send email
to me personally.

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Barry Watzman - 28 Jan 2004 01:45 GMT

There is only 500ma (2.5 watts) available, and only at 5 volts. This is
enough for some devices, but many devices require more current and/or
voltage.

> In regards to the USB power decision, I think it due to the fact that
> most devices need around 5V to operate: Webcams, drives, etc. Thus I
[quoted text clipped - 10 lines]
>>
>> john

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Steve Norris - 30 Jan 2004 17:09 GMT

FYI - A company named Si5 (direct link below) has a set of speakers
that take 4 aaa bats. They sell an "USB adapter" cable for their
speakers that is simply a USB ->-> (standard) Power Plug. Should work
on most anything needing low wattage 4 -> 5 volt power (or charging).
Cost only about $9!! Their speakers are so-so but whatever you do,
don't buy them on their website ($9 or $79). They are vavailable @
Target for $20!!

http://mindfireis.com/cgi-bin/PnGC/PnGC_print.pl?mid=si_technologies&page=produc
t_category

> There is only 500ma (2.5 watts) available, and only at 5 volts. This is
> enough for some devices, but many devices require more current and/or
[quoted text clipped - 14 lines]
> >>
> >> john

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Joe - 24 Jan 2004 23:05 GMT

I do not think you need a Phd to know this.

>The other day I paid about $20 for a widget that allegedly charges my
>cellphone via my laptop USB port. This is part of a logical trend to
[quoted text clipped - 39 lines]
>blank screen and spin down drive -- I called my power profile
>"Cellphone Charger". Similar setup for OS X.

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