# mp3 player and car chargers

I have an mp3 player that I have currently misplaced the AC adapter for. I have an old car adapter for a cell phone that I no longer have that should work to charge it, although I need to get the proper sized plug to fit my mp3 player. The conundrum comes in that the mp3 player asks for 5V input. The charger says it has a 4.5V output. What would happen if I used this to charge my player?

a) I’ll fry my player
b) nothing - as in literally nothing. it won’t charge
c) it’ll charge just fine
d) it’ll charge at a slower rate
e) it’ll charge at a slower rate but eventually wreck the battery of the player
f) something else will happen

I wouldn’t recommend it. I’ve seen far too many devices fried this way, usually because either polarity was wrong or the charging circuit in the charger went haywire. See, the charger for your cell phone says it outputs 4.5V, depending on the tolerance of the original cell phone this could be a rough estimate, especially if the charger is manufactured cheaply. Since your automotive voltage varies they could be using some sort of a regulator that delivers a fraction of the input voltage, which at 12V (or is it 14.4V, I can never remember) it would output around 4.5V.

Let’s not do that. There’s no guarantee that the voltage will be the nominal 4.5 V when the charger is connected to something it’s not designed for. Instead, go someplace like Radio Shack and pick up a universal car lighter adaptor with a selectable output voltage. Be sure that 5 V is one of the options. The other important factor is current; you want to be sure the current the adaptor can supply is at least as much as the MP3 player will draw when charging or in use. 1000 mA (1 A) should be plenty for this application. You’ll also want to match up the polarity properly. This is critical–incorrect polarity can destroy the device you are trying to power. Look for a diagram near the power connector, or check the owner’s manual for your player. The diagram will look like one of these two:

• -----(o----- -

or

• -----o)----- -

The first means the adaptor tip (or center conductor) is negative, while the second means it is positive. Remember, getting the polarity wrong can destroy your device and/or ruin the batteries, so be sure you have it right before plugging it in.

So probably e) then. Thanks. I’ve got all the specs on what it needs so it shouldn’t be hard to find one that’ll do the job. I was just hoping to be able to use what I had. Looks like I can’t though.