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Power Strip USB Charger Combo Answered

I'm currently building a bedside table, which will include a charging station for 2 laptops, 2 DS lites, 2 Iphones/pods, a palm phone, and rechargeable batteries.

This means that there will be a need for at least 5 usb ports, and 4 mains outlets.

I was wondering what peoples ideas were for generating these sources of power.  I know I could use a power strip and a usb hub with a wall adapter, but I was wondering what other more sleek ideas people had.  I have everything necessary to build my own systems, including a 5v power source; but I posted in the hope someone might have some really sleek and elegant solution for me.

Winning prize goes to the person with the sub $10 solution!


How much current is the 5V power source able to provide? If it offers at least 1A then it can easily handle 5 USB devices.

$10 isn't going to be enough to get the wire, USB headers, power strip and any other odds an ends you need to make it a nice looking setup. So you will need to start salvaging parts from anywhere you can. Any time i see an old computer out for trash pickup in my neighborhood i go and grab it. I always take out the USB headers as well as the motherboard standoffs and screws. If a HDD is still present i take that and the PSU. Anything i think i could use in a later project. I keep a couple of large bins at home for storing this stuff. You may want to start doing the same.

Alright! I dug through my closet this morning, and found a 4 port usb hub, plenty of usb cables, and a 5.2 volt wart.

I could just run a usb extension to my computer, I assume that load wouldn't be too much for my 5V rail. Input?

My preference would be to have it run separately, but when I plugged my 4 port usb hub into the wall, it did not charge my phone. Is there a simple conversion that I can use to enable charging without a computer present? I'm willing to totally break the hub, I don't need it for anything else anyways.

I'll go cruse thrift stores today too.


What kind of phone is it. Some smart phones require a signal or small voltage to be present on the data lines so it knows its connected to a good source before it will enable charging. Powered hubs don't get all there power form the wall anyway. Its just supplemental power to assist the power already coming from the PC. You start loading up all the all the PC's USB ports then add a hub and the voltage drop on the PC is enough to prevent things that need a full 5V from working/charging. If the wal-wart you have is a not the one for the hub then check it with a DMM to make sure its outputting 5.2V. Often times the voltage mentioned on the wal-wart is higher then stated on the brick but comes down to that voltage with a full load on it. But if it is able to output about 1A or more then it could easily be plugged into the hub to charge USB items.

Here is a little schematic showing how to get the right voltages onto the data pins to enable a smartphone to charge. Pay attention to the resistors set up as voltage dividers. You want to have 2V on the D+ and just under 3V on the D- to get it all to work.

5V Charger.JPG

So I don't need to pay attention to the left side of the schematic?

How many mA is it safe to pull using that setup, or does it not matter since it's data anyways?

Is there a good source of 5v that I can find easily? Just use the 5v from a PSU?

I hate how complicated this is, it seems like USB would be so simple.

Current is like water in a well. Water just sits there waiting for something to draw it out of the well. The USB devices will only draw the amount of current they need. The reason you need a power source that can offer 1A or more is so it can support up to 4 or 5 devices. Each device will draw about 200mA. If your 5V power source isn't able to offer enough amps the devices won't power on/charge or they will blow out the power source.

This only gets complicated on the few smart phones that actually look for a signal on the data lines before allowing the battery to charge. About the only thing simple about USB is that all devices are plug and play. But when you are doing more then just plugging in a thumb drive to a PC and get into power management things git more interesting. Things are almost never as simple as they seam in electronics. 

The schematic i posted is one i made for an instructable i did converting a set of PC speakers into a dock for my iPod Touch. The speakers used a 5V wal-wart. Problem was when i checked it on my DMM it only put out a few mV. Yet somehow it was able to support the speakers, but wouldn't be enough to also power and charge my iTouch. So i used another 9V wal-Wart i had laying around. So the speakers use 9V while the iTouch only needed 5V. So i pulled out a 7805 voltage regulator i had and connected it up an iPod docking cable. I plugged in my iTouch and nothing happened. After a bit of research i learned about the need for power on the data lines. Broke out my trust voltage divider calc and worked out the resistors i could use that i already had on hand.  You can check out the instructable to learn more. 

So for a power source you have allot of options. Find a wal-wart that meets the 5V @ 1A spec or get a larger one. Maybe one that offers 9V or more at about 800mA. Then using a 7805 voltage regulator you will get the 5V @ about 1A you need. A PC PSU is an option if your willing to go that route. 

I'm familiar with electric theory, my question about draw was in regards to the data lines. I was curious as to how many devices could be run off of the data voltages provided buy that 4 resistor setup. Or if it doesn't really matter because the data draw would be negligible.

Ideas as to what the average draw of a usb device charging would be? I would guess 500mA.

I'm surprised there isn't really a market for products like this. (Chargepod doesn't count with it's ridiculous price and proprietary adapters.)

I'll go through my parts bin tomorrow, I think I have some 12V-5V as well as a few variable regulators, if that'll help. since I have 12v adapters all over.

The power draw on the data lines is negligible. So a single set of voltage dividers can support 4 or 5 devices.

In fact there are a great many products on the market. You can find AC to USB wall adapters all over the place. Most of them provide 1 or 2 USB ports. You can also buy replacement wall outlets for your house that still give you the 2 AC outlets but also have 2 or 4 USB ports on them.