Help adding usb charging station to monitor

[nednerb]

My Dell Monitor has a built in 12vdc 1A out to power a set of dell speakers. I want to know if its possible for me to tap into that power to run a 5vdc 1A 4 port usb hub. This hub would not be connected to a computer, it would only be used for charging.

I have a car usb charger that I could rewire to take the 12vdc 1A and drop it to 5vdc 1A, which is what the hub requires.

What I don't know is how that 1A is distributed when the speakers are being used and there are 4 devices trying to charge themselves from the hub at the same time.

My goal was to eliminate another wall wort from taking up precious power strip real estate, please let me know if this solution is practical.

Thanks!
Brenden

 

[(*steve*)]

I have a car usb charger that I could rewire to take the 12vdc 1A and drop it to 5vdc 1A, which is what the hub requires.

If it's a switchmode device it will require substantially less than 1A at 12V to produce 1A at 5V (closer to 500mA)

What I don't know is how that 1A is distributed when the speakers are being used and there are 4 devices trying to charge themselves from the hub at the same time.

If the draw from the 12V supply exceeds 1A, bad things may happen. Nothing will "distribute" it (by which I assume you mean limit and share).

My goal was to eliminate another wall wort from taking up precious power strip real estate, please let me know if this solution is practical.

It may be. You just have to measure the load imposed by each of these devices and ensure the sum does not exceed what you can drive from the monitor.

 

[CocaCola]

Are you suggesting keeping the speakers hooked up as well? If so forget about it, I doubt the output has much headroom, it's likely optimized for the speaker requirements with no room to run other devices...

If you are not using the speakers, with a switching 5V regulator you might be able to milk 2A @ 5V out of that tap, but the USB car charger you have likely only puts out 500-1000mA... Whatever you get out will be split 4 ways and that likely isn't enough to make most devices happy.... Most new cell phones want about 1000mA+ to fast charge, so basically one device at a time unless they are low drain devices... You might also have undesirable interference in the monitor tapping off that port, only testing will answer that question though...

 

[nednerb]

Hmm...I doubt the car charger is a switchmode device, but I am not sure. I am not married to this converter if that would help, I am sure there is another 12v to 5v converter that I could get, but if the original 12v source only has 1000ma, getting a 5v converter with a higher amperage shouldn't help any right?

CocaCola - the idea was to keep the speakers hooked into this power supply as well, it makes sense that it would be tailored to only power the speakers and not have enough room for anything extra. I don't think I have the equipment to be able to measure what the speakers draw when in use to see if there is any extra room.

Steve - As to 'distribute', you are correct, my question was how the 1A output would get shared among the speakers that are on and the 5v converter that is charging 2 cell phones and an ipod video all at the same time. I am starting to think the answer is poorly.

Concerning what you said about the powered USB hub, the power supply that came with it is only rated to 5v, 1000ma for all 4 ports. If what you say is true perhaps this hub isn't going to cut it, though quick charging isn't really important to me. Unfortunately, when shopping for powered usb hubs I have found that the current output of the power supply is never listed.

-Brenden

 

[CocaCola]

Unfortunately, when shopping for powered usb hubs I have found that the current output of the power supply is never listed.

If the hub is truly USB compliment it should put out about 500-900mA at each port, so the power supply should be at least 2000mA for a 4 port hub... BUT, do note that MANY hubs are not USB compliant and don't supply the full current specified by the USB standard... Heck a lot of USB ports on computers don't even comply with the full USB specifications...

Also note that the USB standard for USB chargers is now up to 5A, well above the 500-900mA a communications USB port puts out...

Battery Charging Specification 1.2: Released in December 2010.
Several changes and increasing limits including allowing 1.5A on charging ports for unconfigured devices, allowing High Speed communication while having a current up to 1.5A and allowing a maximum current of 5A.

This is why most new phones have smart two way communication with when charging, they will default to a slower charge rate depending upon the port they are plugged into... Or they will exploit the higher current if it's there and charge faster...

 

[(*steve*)]

Here is an example of a switchmode 12V to 5V power supply.

This will help because to provide 1000mA at 5V, this requires around 500mA @12V (or even slightly less).

A normal linear regulator would require a little over 1000mA from the 12V source to provide 5V at 1000mA.(and it gets a lot hotter)

 

[nednerb]

Thank you both for all of this excellent info.

Several thoughts now come to mind:

1)Can the usb hub I bought be powered with a power supply with more amperage? Perhaps if I crack it open something could be altered to allow for this increased amperage?

As I am sure you can tell from our conversation we are on the edge of my knowledge, but I am willing to learn and figure it out.

2)This is the hub that I bought. How can you tell that this is switchmode or linear?

3)I am thinking of abandoning this hub for this hub, this way I combine the two parts of this plan into one unit. So this hub takes the 12v and puts out 5v 2.1A. It's not 5A but it's better.

I am also thinking of abandoning the speakers for the time being, so we can take those out of the equation. Now I have 12v 1000ma converting down to 5v 2.1A, can I do that?

 

[nednerb]

I wanted to follow up since this may be useful to other people out there who want to take advantage of dell's 12v out on this and other monitors that they make. It works great. I wired a 5.5mm jack to a 5A car power supply that I got here. After plugging that into the 12v supply, it powers the raspberry pi, a pair of usb powered speakers and one port left over to use as a charging station for my phone/ipod.