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AC/DC adaptor outputs questions

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

Reply to
Dan Beck
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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):

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Reply to
Bob Monsen

Hi Bob,

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

Reply to
Dan Beck

allow

and

outputs

correct,

prematurely,

lot

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!

Reply to
Lord Garth

correct,

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

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Reply to
Jonathan Westhues

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