Does this make sense (electrical wiring/circuitry)

it seems "hacking" is where all the modding and all the electrical work goes on so here's my question

while trying to figure out how to wire up a few devices in my car that are normally powered via usb i came upon the fact that it's not as simple as "stick [x] resistor(s) on 12v line, congratulations you now have 5v power supply to work with" and that the simplest and most cost effective solution is to use some cheap car cell phone chargers, because these will probably provide .5-2a each one will only power 1 device with ample headroom

so my plan is to get a handfull of cheap car chargers, harvest their circuit boards, solder the usb power wires from the various devices/charging cables onto the output (one on each board), then wire all the inputs together in parallel, and then wire that in parallel into the cigarette lighter circuit

so, any flaws in my logic?

I did something kinda like what your talking in my car without any of the soldering like this..(I did this years ago 2008)

bought 4 of these

bought this because it had switches 

mounted it with velcro

Here is a better one

but now they have this

just realized it was sold out but you get the idea..

erm maybe....ive never actually tried it myself but im guessing the circuit and fuse that supplies the cigarette lighter in the car has a current and volt limit, if your trying to draw more than that its going to break or just not work.

or just get these kinda things :P

OK so the you got a 12V source with a (usually) 15A fuse (so just check the Amp rating on all the devices added up is below 15A....expect it will be much lower)  then you could grab a adaptor like this

A bit Vero (stripboard) how ever many voltage regulators you need (one for each usb device) id go with LM7805, 2x 47uf electrolytic caps for each voltage regulator and you got a whole heap of 5v connections ready to go for a couple of $


Any questions, just give me a shout! 

sweet, good info thanks guys.,

Also found this today..

This link also has a link to other hidden MP3/USB Aux hack..

i ordered some strip boards, a handfull of 7805's, and a bunch of 47uf caps, it seems like basically the same idea, but it should at least look a bit nicer

i just wish i could've bought the parts from a store like radio shack so i could have parts now, but for the same price as 2 caps at radioshack i got 25 off ebay

i'll be sure to update when i have it set up and tell how it went, maybe post pictures of the setup

Did you also order some heatsinks?
LM7805 can supply up to 1A, but with 5V out and 12V in you're dropping 7V. LM7805's are "linear regulators" (not switching, those are much more efficient) and they dissipate all excess power into heat.

So if you're charging a phone at 1A, P=U*I = 1*7=7W. The limit for a LM7805 without heatsink is like 1-2W, and then it gets really hot (far too hot to touch).

I would get some of these:


You can trim the output voltage with the small blue potentiometer. They can deliver like 2A each, and are switching supplies so don't get too hot to touch.

They also have a nice wide operating range, so they don't care if your car's battery is being charged (at which it may get up to 13-13.5V).

The LM2596 Step Down Modules are cool. But, using them will give the build a MUCH larger footprint. 

Also think OP will get more out of a build using a LM7805 in this classic barebones PSU design, as the fundamentals of Vin->  noise filter cap->  Regulator-> noise filter cap-> Vout are right there opposed to just slapping in a switching regulator module and not get how it works?  

IMHO that's worth the price of a slightly warmer ABS box.