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AC/DC adaptor outputs questions

D

Dan Beck

Jan 1, 1970
0
Hello all,

I am mostly a lurker here, but here are some simple questions--please allow
me to give some background...

The AC/DC adaptor for my portable MP3 player died; I measured outputs with
my DMM to confirm. The outputs on the device are supposed to be 5.0 VDC and
1.5 amps. I went to Radio Shack to see if I could find an exact
replacement; no luck, but the guy there set me up with a device that outputs
4.5 VDC and 700 milliamps. This Radio Shack device simply is one of those
wall devices you would use to power your desktop speakers. I jury-rigged
the connector, and this new AC/DC adaptor seems to work fine with my MP3
player.

The new wall device is much larger in physical size, than the now dead
device that came with my MP3 player, but yet this new device only outputs
less than half the stated current, at a LOWER voltage. Can this be correct,
or are the ratings on the dead device too high? If all the stated ratings
are accurate, is it correct to assume with the new, replacement device
recharge times will be longer? Will I wear out the new device prematurely,
because of excessive load?

I recognize these questions are probably merely academic, because not a lot
of money and time has been invested in this little project; I am just
curious.

Thank you in advance for reading.

Regards,
Dan
 
L

Lord Garth

Jan 1, 1970
0
Dan Beck said:
Hello all,

I am mostly a lurker here, but here are some simple questions--please allow
me to give some background...

The AC/DC adaptor for my portable MP3 player died; I measured outputs with
my DMM to confirm. The outputs on the device are supposed to be 5.0 VDC and
1.5 amps. I went to Radio Shack to see if I could find an exact
replacement; no luck, but the guy there set me up with a device that outputs
4.5 VDC and 700 milliamps. This Radio Shack device simply is one of those
wall devices you would use to power your desktop speakers. I jury-rigged
the connector, and this new AC/DC adaptor seems to work fine with my MP3
player.

The new wall device is much larger in physical size, than the now dead
device that came with my MP3 player, but yet this new device only outputs
less than half the stated current, at a LOWER voltage. Can this be correct,
or are the ratings on the dead device too high? If all the stated ratings
are accurate, is it correct to assume with the new, replacement device
recharge times will be longer? Will I wear out the new device prematurely,
because of excessive load?

I recognize these questions are probably merely academic, because not a lot
of money and time has been invested in this little project; I am just
curious.

Thank you in advance for reading.

Regards,
Dan

The most important factor is the output voltage. Whether it is AC or DC and
if DC,
the plug polarity. Add to this that if DC, whether your power supply is
regulated.
The output current should be equal or greater than the expected demand.

Your output voltage is lower because you don't have sufficient current.
This
MP3 player seems to be a power hungry beast!
 
B

Bob Monsen

Jan 1, 1970
0
Dan Beck wrote:
The new wall device is much larger in physical size, than the now dead
device that came with my MP3 player, but yet this new device only outputs
less than half the stated current, at a LOWER voltage. Can this be correct,
or are the ratings on the dead device too high? If all the stated ratings
are accurate, is it correct to assume with the new, replacement device
recharge times will be longer? Will I wear out the new device prematurely,
because of excessive load?

One possible problem would be that you aren't recharging your batteries
all the way. This will lead to additional charge cycles, which may lead
to premature battery death.

As far as the new device is concerned, you should definitely get one
that has the same rating as the old one. When they say 700mA, they are
really saying that if you draw much more than that, the voltage will
droop, and it may overheat. There are usually fuses or breakers buried
in them that will prevent fires, but the droop in voltage may affect
your charging even more, causing even more cycles on the batteries.

I'd get another one. You should have looked harder. You can get them
here, online (For the USA):

http://www.excesssolutions.com/cgi-bin/category/11320
 
D

Dan Beck

Jan 1, 1970
0
Hi Bob,

Bob Monsen wrote in message
One possible problem would be that you aren't recharging your batteries
all the way. This will lead to additional charge cycles, which may lead to
premature battery death.

As far as the new device is concerned, you should definitely get one that
has the same rating as the old one. When they say 700mA, they are really
saying that if you draw much more than that, the voltage will droop, and
it may overheat. There are usually fuses or breakers buried in them that
will prevent fires, but the droop in voltage may affect your charging even
more, causing even more cycles on the batteries.

I'd get another one. You should have looked harder. You can get them here,
online (For the USA):

http://www.excesssolutions.com/cgi-bin/category/11320

thank you for the sage advice and URL. A new device will be purchased;
probably a new battery for the MP3 player as well. It sounds like I may
have prematurely used up charge cycles :-(

Regards,
Dan
 
J

Jonathan Westhues

Jan 1, 1970
0
Dan Beck said:
The new wall device is much larger in physical size, than the now dead
device that came with my MP3 player, but yet this new device only outputs
less than half the stated current, at a LOWER voltage. Can this be correct,
or are the ratings on the dead device too high?

Traditional wall-warts are usually just line frequency (50/60 Hz)
transformers. Modern wall-warts are often tiny switchmode power supplies.
This allows them to use lighter magnetics (because they operate at higher
frequencies), and it also improves the output regulation. The Radio Shack
unit is unlikely to be of the latter type.

Jonathan
http://cq.cx/
 
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