If a power strip has multiple USB ports, why can’t they all charge at max power at the same time?
In: Engineering
Because if one input powers 6, then the 6 inputs are 1/6 the power of the regular input. Each USB can hold 1/6 of the original power.
Same reason that you can’t just plug in full-wattage heaters into every socket in your house.
Sure, the socket may be rated for that, but the thing supplying it likely isn’t rated to run EVERY SINGLE socket at max 100% of the time.
So though you might get, say, 2A from a single port, you can’t get 2A from EVERY port at the same time if the whole strip has a limit of 5A for all ports, and it has, say, five ports.
The adaptor that does let you do that will be bigger, more expensive and use more power generally (i.e. be less efficient when you have less plugged into it).
Most regular devices can’t function on a lower power draw and a higher one will short them out, and because of this each regular outlet in the wall and on a power strip need to conform to strict standards. Each device also has their own converter to handle changing from alternating to direct current with limiters setting the voltage and amperage to exactly what the device needs. But these aren’t smart converters or anything so they need that rigid consistency I mentioned. It’s also why each outlet on a strip is in parallel so that another device doesn’t cause added resistance and drop power draw down the line.
USB charging devices, on the other hand, can handle varied power draw up to a certain amount that is typically far above the standard regular or fast charging USB port standard. You still need to convert from AC to DC current. The power strip has a built in converter, but making small, efficient converters is expensive. To save money, USB power strips have a singe converter that converts to a set voltage/amperage (the normal or fast charging standard) and runs along the entire set of USB charging ports. Since USB charging can handle such varied power within allowances, there’s no risk to the devices. And since they’re all sharing the same line of electricity, each device has to share if there’s more than one plugged in.
So back to your question, why can’t they just put a bunch of converters in, one for each USB port, and have each converter in full parallel? Well… They can. They just don’t, because they’re cheap.
TL;DR because the manufacturers are cheap.
The reason for this is simply cost/size. They use a transformer to reduce the voltage to 5v from 120v/240v. It’s much cheaper (and smaller) to use a single transformer at a specific wattage say 10w across all the usb ports (so 2a for a single port and then split as more devices are plugged in) than to give each usb port their own transformer.
What you’re asking for is absolutely possible, but the most expensive part of the power strip are those transformers so you’d expect the price to increase at the same multiple of how many usb ports there are. Also the size will significantly increase as well.
Apologies, but this sounds like a question specific to your power strip that you are asking for a ubiquitous answer for.
A power strip with USB ports can be designed so each port could output whatever power the designer desired and USB supports.
Your specific power strip probably has something like a 5V 10W supply shared amongst all USB ports. Regardless of how many USB plugs are available or how many things you have plugged in, if it can only supply 10W, you’ll only ever get 10W out. Maybe that is a 2A draw for one phone or a .5A draw for 4 phones.
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