Price of the Freerunner spare parts
joerg.twinklephone at gmx.de
Fri Mar 28 01:18:49 CET 2008
Engineering says: you can't have both, 1A charging _and_ protection for every
case of missmanagement (DAU, stupid user).
USB is specified for 500mA MAX. Period! (and devices have even to announce
when they want more than 100mA). Anyway a stupid charger consisting of a
transformer, a diode bridge, and at best some 5V-regulator, usually doesn't
know of *any* announcement via USB-protocol regarding 100->500mA (it probably
has only 2 of the 4 wires it needs for *real* USB).
So the situation is (or to be clear: SHOULD BE. This has to be checked
carefully for Freerunner, cause there are indications it's not at least like
connect any charger:
- - NEO will take no more than 100mA (actually 200-300mA, BUG! (AFAIK))
have intelligent host (PC) OR
set charge mode to 500mA by GUI applet:
- - NEO will take no more than 500mA (yet to be tested?)
connect original OM-charger (with 47K resistor) OR
set charge mode to 1000mA by GUI applet (not yet implemented?):
- - NEO will take no more than 1A (PMU 50633 limit) (this seems to work, more
Alas there is *absolutely* *NO* way for NEO though to tell when your braindead
850mA charger will start to slowly melt down overnight when you set 1A charge
mode via applet. It's very unlikely there will ever be any trouble other than
very rare occasional broken chargers, but we just can't guarantee it's safe,
for nobody knows all the chargers in this world.
However it's not our fault when sth really bad is happening, for every
charger/host is supposed to be short-circuit safe (mustn't burn, otherwise
probably mustn't be sold), and it's the USER who has to think *before*
enabling 1A mode. Hey guys, when connecting your 110V device to a 230V outlet
in Europe, whom do you blame for the smoke?!
For the Y-cables to connect to 2 USB-hostports: these are absolute fake, they
don't balance the current in any manner, so if one port is blowfused (cause
it once was strong) or it is weak, or dead, or disabled, the whole surge goes
to the other stronger port (Blam!). And these Y-cables not even do correct
negotiation for at least 500mA per port!!! So with these Y-cables, all you
can safely expect are no more 100mA! Everything beyond breaks specs again.
I (for own use) will check the writing on my charger, then guess whether it's
reasonably safe to enable 500mA or 1A, and maybe come back after 10 min to
check whether it's still charging and charger does not start to smell.
For PC USB-hosts I have no problem to force 500mA (though this should be
nonsense because will happen automatically), and i will *never* try 1A, not
even with Y-adapter.
bottom line: USB is specified for 500mA at MAX, and even this needs
intelligent host (alias charger). Everything beyond has to have some
intelligence with it, either the one of the user not messing with chargemode,
or the one of OM-designers creating and checking for a proprietary way to
signal >500mA charger capabilities (=48k).
(PS: For the record: If i got this right, the 48k even means "I'm a charger
and I can do *2*(!)A", just GTA02 can't take more than 1A. This might change
your friendly engineer jOERG
Am Do 27. März 2008 schrieb steve:
> Thanks Kevin,
> I recall asking engineering what would happen if somebody disabled this
> check ( hey its open source) and the general impression was that if the
> charger was not capable of fast charging then you would not have nice
> outcomes. I think the worse case might be if you tried to draw more than
> 500ma from a PC USB. Somebody not in marketing should answer that question.
> -----Original Message-----
> From: kev.forever at gmail.com [mailto:kev.forever at gmail.com] On Behalf Of
> Kevin Dean
> Sent: Thursday, March 27, 2008 12:22 PM
> To: List for Openmoko community discussion
> Cc: steve
> Subject: Re: Price of the Freerunner spare parts
> On Thu, Mar 27, 2008 at 2:58 PM, joerg <joerg.twinklephone at gmx.de> wrote:
> > Correct, it checks for 48k-OHM resistor on ID-pin of mini-USB, then
> enables 1A
> > instead of 100/500mA USB-standard.
> > You also may enable 1A-mode (and 500mA mode) via some small GUI-app IIRC.
> This is possible via userspace with Bobby's application.
> However, the flaw to this is that it will force fast charge even if
> the charger isn't capable and hints that this could be... bad. :)
> For the record, it APPEARS that with the Python application, the iGo
> works just fine as a charger.
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