Rockbox mail archive
Subject: Re: Hello. Help!
From: Fred Maxwell (rockbox_at_anti-spam.org)
It is almost always a bad idea to substitute a higher current capacity
unregulated AC adapter (wall wart) for the one supplied with a piece of
equipment. That is because the voltage output is related to the load on
an unregulated adapter. If you have a low-load on a high-current
adapter, the voltage coming out of the adapter will be higher than the
rated voltage. So while the 12v/1800mah adapter will produce 12v with
an 1,800mah current draw, it's probably producing far more than that
with the smaller draw of a Rockbox.
At one time, I did a bit of study on this and posted a lengthy piece,
complete with links to the website of a firm which manufactures wall
warts. Here's that web site:
And here is the relevent section:
"Most wall-mount power supplies have no active regulation. They are
designed so that the voltage will be X when the current is Y, just like
the label says. Many engineers are confused by this, thinking that a 12
volt, 1 amp power supply can be substituted for a 12 volt 500 mA power
supply. This might be true, but the voltage at 500 mA will be higher
than the voltage at 1 amp. How much this varies depends on the load line
of the transformer. A load-line is a graph of voltage versus current.
PowerStream can supply load lines for our products, not every
manufacturer does. Cheaper transformers have fewer windings, and wilder
voltage swings with load."
Without matching the load lines of the stock supply and the aftermarket
supply, one cannot know if they have a satisfactory substitution. I
know that many people get lucky and nothing burns up, but often, it's
over-taxing the regulation in the unit into which it is plugged.
Manuel Dejonghe wrote:
> Hi Kyle,
> the adaptor is likely to be a problem to the batteries than to the
> device itself.
> (see http://rockbox.haxx.se/twiki/bin/view/Main/BatteryFAQ#Q10_Can_I_use_a_different_charge).
> If due to the power fluctuations, it may be the adaptor delivers more
> than 12V which may heat up the regulator. This regulator saves the
> batteries from getting charged with too much power, but heats up, and
> the heat may damage other things.
> If the problem was solved before with new batteries, then I would say
> you unit is in a good shape.
> You should try to conditioner your new set of batteries (3 cycles of
> complete charge and discharge with your favorite charger (your new
> adapter) and your favorite discharger (rockbox running all night
> Furthermore, you have to know rockbox only predicts how long the
> batteries will last. First of all, this is based on the
> capacity-setting (see menu->general->system->battery iIrc) and the way
> rockbox developer think you are using it. If you keep the backlight on
> or the disk spinning more than usual (games, constant browsing), it
> will drain the batteries more than expected.
> Last but not least, iIrc, the charging only starts a few seconds (40)
> or a minute after having plugged in the adaptor if it's been charging
> or switched on (very) lately.
> I hope that helps you a small bit,
> On Mon, 30 Aug 2004 03:44:10 -0700 (PDT), Kyle McGee
> <mcgee_kyle_at_yahoo.com> wrote:
>>I have a Archos recorder 20 and now I have some big
>>I live in India and have for the last 3 years. I have
>>used the recorder here and in Nepal, but the batteries
>>have consistently given me problems.
>>First, they last only a few hours. Even with the
>>software indicating that there are 10 hours left, the
>>recorder will surely last only a few hours.
>>Second, the batteries have died now twice. The message
>>on the screen indicates 'not charging' when I plug it
>>in and the adaptor seems to be fine. The unit with
>>other adaptors also indicates the same message. This
>>happened in Kathmandu (Nepal)first and I replaced the
>>batteries with the same brand only a higher MA (1800).
>>They have now died in India. I can not replace the
>>batteries here, but I will have to wait until I reach
>>a big city like Calcutta or maybe Bangkok.
>>The original adaptor that I got was for US voltage, so
>>I bought a local adaptor in India that is 12 Volts and
>>Could the adaptor be the source of the problems? The
>>power often fluctuates here. Could this be ruining the
Page was last modified "Jan 10 2012" The Rockbox Crew