Powering 2 5V devices from USB charger cube (newbee)

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JackPollack

Joined Feb 29, 2016
18
All of my AV switching and converters are housed in a very small space - I just added a HDMI switch to the mix and dont have room to add another USB cube to power the switch. Currently I using a 2 port USB cube that outputs 2A on each port. The current draw from the existing equipment is about 250ma on each port, and the new HDMI switch draws about 250ma as well. I thought I would be able to power the new device in parallel with one of the other devices but when I try this both device dont power up. I have tried several different brand USB cubes and also the USB port on my DVD player & TV. All dont work with parrallel power to the devices even though the current draw is far below the max output of the cubes.

I tried with a more wall-warty type "transformer"/brick (5V, 750ma) and it does work so I dont think it is a current issue. Unfortunately the wall wart doesnt fit in the space I have.

Why are USB charger cubes not working and wall wart working?

I thought that it might have been that the chargers were more of a regulated 5v and wall wart was putting out a higher voltage. I measured both with no load on them and they both read 5.06v

I tried some current limiting resistors on the power of one of the devices but didnt help.
Are there some caps, diods, resistors, etc. I can used to isolate the 2 devices and get them to power from the charger cubes?
 
Last edited:

sarahMCML

Joined May 11, 2019
228
All of my AV switching and converters are housed in a very small space - I just added a HDMI switch to the mix and dont have room to add another USB cube to power the switch. Currently I using a 2 port USB cube that outputs 2W on each port. The current draw from the existing equipment is about 250ma on each port, and the new HDMI switch draws about 250ma as well. I thought I would be able to power the new device in parallel with one of the other devices but when I try this both device dont power up. I have tried several different brand USB cubes and also the USB port on my DVD player & TV. All dont work with parrallel power to the devices even though the current draw is far below the max output of the cubes.

I tried with a more wall-warty type "transformer"/brick (5V, 750ma) and it does work so I dont think it is a current issue. Unfortunately the wall wart doesnt fit in the space I have.

Why are USB charger cubes not working and wall wart working?

I thought that it might have been that the chargers were more of a regulated 5v and wall wart was putting out a higher voltage. I measured both with no load on them and they both read 5.06v

I tried some current limiting resistors on the power of one of the devices but didnt help.
Are there some caps, diods, resistors, etc. I can used to isolate the 2 devices and get them to power from the charger cubes?
2W per port is only 400mA. If you're already drawing 200mA from one, and try to draw another 250mA from it, it's not surprising that it's shutting down! They may also be signalling different requirements to the other USB cubes at the same time, confusing them.
 

DickCappels

Joined Aug 21, 2008
9,632
Building on @sghioto 's concept in post #2 it might be that you need to sequence the two loads.

Power up with the load for one power cube connected and then after things have settled down add the load to the second load. That might tell us wether or not sequencing the loads will help.
 

bassbindevil

Joined Jan 23, 2014
687
The USB ports on a TV or DVD player may only be sized to run a thumbdrive or 2.5" hard drive. Is your 2-port USB cube from a reputable brand, or some no-name thing? What are you using as a splitter to connect multiple devices to one USB socket?
 

MisterBill2

Joined Jan 23, 2018
14,280
I have seen small 5 volt switcher supplies rated 5 volts and 2 amps, and a couple of them rated at much more current, 5 amps. For the one that did not work powering them all, did you measure the actual voltage under full load?
I would not ever suggest using a battery charger wall device to power any other mains powered connected device because not all battery charge devices are isolated from the mains. Charging a battery in a single device that is not an issue, powering a mains-connected device it might be a serious problem.
 
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