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DC Charger Voltage Drop?

Hey all! Long-time lurker, first-time poster. I don't have any instructables up on the site, but I have used many and I do have a biting question....currently, I am trying to create a USB car charger for my MP3 player out of an old CD Car Power Adapter.

The MP3 player is a Creative Zen V, so it, of course, usually just charges on my computers with a USB to Mini-USB cable. In the next few months, I am picking up a new stereo for my car with an Aux. input and as I like recycling anything I can, I figured I could just make a charger myself so I could keep my player charged when I'm driving. The old CD Car Power Adapter in question has an output of 6V DC at 500ma. From my research, USB operates on 5V DC at a maximum current of 500ma, so the adapter I have seems almost perfect...?

My question is this, how would I lower the voltage of the adapter from 6V to 5V? My second question is, I've read conflicting information on a number of sites....so, IS my information that USB 2,0 operates at a maximum of 500ma correct? If any of you folks would happen to know, and be so kind as to answer, I would be very grateful!

I don't want to end up accidentally frying my player!


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dagleykd (author) 7 years ago
Hmmm...ok, I do have a few other DC Car Power Adaptors laying around, one has an output of 4.5v at 600mA.....I know USB supposedly operates between 4.75 and 5.25, is there a way I could easily up the voltage on that one? And if there was a way, would the extra 100mA hurt my MP3 player?
.  With 4.5V you may not get a full charge (or it may not work at all), but it shouldn't hurt anything. Volume may be reduced. Try it and see.
.  As long as the supply is rated for 500mA or more, you will be OK. The supply only puts out what the load calls for. The rating is the maximum the supply will put out.
dagleykd (author)  NachoMahma7 years ago
Ok, thanks for the help, I may just test-wire up the 4.5v adapter and see if it will charge....if not, I was thinking I may look through some old electronics and see if I can find a 5v regulator, I have heard they can be found in some old computer power supplies, and I have some of those laying around. Not sure where else I could look.

Buying a regulator from Radio Shack is $5.00 up here, which would cost half of just buying a USB car adapter from the shop. I know 10$ isn't a lot, but I don't like just getting rid of stuff if it's relatively easy to make use of, and tinkering with things is a hobby of mine, so... :)
NachoMahma7 years ago
.  The player will only pull as many mA as it needs, so a 500mA supply is great for your application.
.  Whether or not that extra volt will damage the player depends on how the player is designed. To be safe, I'd use a 5v regulator (eg, 7805) between the adapter and the player.
USB is designed for 500mA max per port (5 x 100mA loads).
dagleykd (author)  NachoMahma7 years ago
Awesome! Thanks Nacho! I was pretty sure the player would only pull the mA it needed, and I had actually looked at the wiki for USB and read that, but I found the wording a bit confusing, so I figured I would get a second opinion as a lot of the other sites I looked at about USB current and voltage were contradicting each other.
.  Oops. A 7805 may not work. The 3 that I looked at require an input of 7V or greater. You may be able to find some other 5V regulator (or a different 7805) that will work with a Vin of 6V.
.  Or just run the car's 12V into the 7805 and forget about the 6v circuit you have.