your thoughts wanted for making usb car charger using an old usb computer port

its been 20 yrs since my electrical class so I'm a little rusty on it. What I'm wanting to to is make a usb charger for my car using a duel usb port from an old computer each usb port has a separate cable that used to plug into the mother board I'm wanting to use the old usb cables and run a series to parallel circuit 12v power supply cigarette light to a 5v voltage regulator my question is will i need a regulator for each usb port (see picture "B") or just one with 2 positive and 2 negative wires going to each usb wiring connector?(picture "A") please forgive my not to scale horrible drawings

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thegeeke6 years ago
Why? Why? Why? You can get them for a few bucks at any department store or electronics store! It's not worth screwing up your electrical system or burning something out on your device!
inotnrml (author)  thegeeke6 years ago
wheres the fun and creativity and the challenge in buying on when for literally about $2 usd or less you can design and make your own and have the satisfaction that comes along with creating it yourself yes I see cigarette to usb adapters on ebay from .66-$29.99 usd plus shipping from China what fun is that
Ahh... I understand. I see a lot of people try to go the diy approach for things like this because they think they can save money. A lot of the time this isn't true to begin with and even if it is, they don't think about the fact that if they do something wrong, they can screw up lots of things like in this instance the car or whatever you plug into it. Just make sure that you test the voltages before you attempt to use it. :)
iceng6 years ago
No Problem..
Drawings convey concepts
But your lack of resistors and fuses is criminal ( very very wrong )

Did you know your computer power supply has a strong 5VDC power output.

What kind of car uses a 5 Volt battery ? ?

I would combine the two USB grounds and the positives + through a 1N4001
diode each then to a single regulator with a 100 uF 15V EL capacitor
and a 50 uF 10V capacitor on the output side with a fuse inserted to protect
the battery and regulator and a suitable resistor in series.

Values can be determined when we know more about the car.

A
inotnrml (author)  iceng6 years ago
I would tap power off of my cigarette lighter which is fused at the fuse box. then add my circuit in series with the cigarette lighter circuit. So I did not think a fuse would be necessary since its already fuse protected by the cars fuse box accessories circuit The car I'm planning on is an 09 Toyota Highlander with 2 cigarette accessories factory installed and just tap off the closest one for power then install my circuit
I'm curious why use a diode on the ground and positives. The capacitor would help to ensure a steady voltage with no spikes then correct, and why the resistor after the regulator wouldn't the regulator keep the voltage at 5v with a resistor lowering it some more?
iceng inotnrml6 years ago
A circuit 4 you.   . . . .   A

USB join.JPG
Recently, like in the last year or so,  I have seen 12V-to-5V, switchmode, DC-to-DC converters, at a very low price.

The artifacts in the attached pictures were obtained from a DollarTree(r) junk store, located somewhere in the Former United States. 

Actually they have a store locator, here:
http://www.dollartree.com/custserv/locate_store.cmd

It's a real switchmode DC-to-DC converter at a price comparable to that of those linear 7805 voltage regulators.  That is, provided you can find this dollar-store power converter in your neck of the woods.

I mean that's part of the reason I took a picture of this thing, because the availability of this thing may vary, and I wanted to offer some proof that there really is/was a dollar-store usb car-charger type power converter.
https://www.instructables.com/file/FTM8LPCGTE4JY5Y/
https://www.instructables.com/file/FBANZG9GSUT3DDO/
dollarstore-12to5-dcdc-convertor.jpgdollarstore-12to5-dcdc-convertor-barcode.jpg
rickharris6 years ago
the power supply in a car has HUGE spikes on it due to the nature of the beast.

These tend to kill a lot of delicate electronics unless considerable care is taken to remove them.