USB power

What is the max current the USB bus can handle?
Is it just 500mA (as by USB 2.0 spec) Or is it possible to draw more if the PSU can handle it.

Lets say I use a 2A PSU Can the USB port then draw 1A without overloading the internal supply chain?

I want to connect a USB device that is known to consume about 750mA. And if the USB can supply then there is no need to add an extra PSU. So that would save 1 PSU, 1 mains socket and less cable mess. Thus less chance of failures. (if the USB port is capable of doing this)

A schematic of how the microUSB power input is wired to the USB2 and the rest of the board would also be enough.

The microUSB connections often get loose over time. It would be nice if there was an option to have 2 pinholes to solder a barrel connector on. This would be a more reliable power connection in the long term for devices that move from location a lot.

Maybe the information in this topic can answer your question for a little bit?: 404 Page not found - GL.iNet

Thanks, i have seen that topic but that is more about the Power supply, i like to know about the max power that the USB can handle…
I mean, if the USB is switched by GPIO6. Then there must be a tiny transistor, and i wonder if that can handle more then the 500mA that USB2.0 spec usually rates as max current per USB port.

So in case a PC has 4 USB ports then there is a 2A PSU (4x 500mA) or a little larger for headroom.
If you then only use one USB then that port often can deliver the full 2A. So then a device that uses 750mA can be attached without the need of a powered hub or a PSU for the device itself.

This is not meant to be (Since USB2.0 spec says max 500mA) But if you know what lies behind the USB port then you can make an educated guess if it is safe to cheat a bit.

So if I connect that 750mA consuming device might that overload some transistor or internal DC/DC converter?

My USB PSU can deliver more then 2A so thats not an issue, but can the AR150 itself handle the throughput?

I remember the USB of AR150 can deliver up to 1.7A. But I need to check.

Thanks, that should be more then enough.

This might be worth listed in the spec. sheet

something like:

USB 2.0 max …mA (When using a 2A PSU)

What would happen if you try to draw more than the maximum current?

Many things can happen, depending on how it is designed.

  1. if the client device is underpowered then it becomes unstable. Crashes, dataloss? (depending on what kind of device it is)
  2. the router itself can come in a situation where the client draws so much power that the router itself is not receiving enough power. So the router may become unstable.
  3. both 1 and 2 together

And in case it is on the edge, then it may work fine one day and become unstable on a sunny day.

With USB sticks, WiFi/BT dongles, that use less then 500mA this will not be an issue. And it would be best to use a powered USB hub when drawing more then 500mA.

But in my case i try to keep it as minimal as possible.
Powersupply -> router -> USB device (no hub, no extra wires)

If you load the PSU to its maximum all the time then that might soon fail. So always make sure there is headroom.

And last but not least use a decent quality PSU. (and thats a bit tricky if you don’t have the tools to measure this) Some PSU’s have very noisy DC converters, DC-DC converters operate in the RF range, and if that noise leaks trough into the router then that can cause interferece with the wifi radio. Leading to distorted transmission, and bad reception.

:slight_smile: more answers then what you asked for. I hope it gives a bit insight in the power drainage. A decent powerplant can avoid many headaches.

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If you try to draw more than the maximum current,the USB power will be shut down.

I have just tested both my iPhone and a Seagate 2TB HD on the GLI AR150.

The iPhone will run when the device is connected to the 1A iPhone USB charger. The HD will not.

The HD will run when connected to a surge strip that has USB on it. I do not know the USB power rating on the strip.

I’ve been testing different LTE dongles with the AR150. The results are mixed.

SIM7500E mPCI module + USB adapter

AT+CSQ is around 25

LTE: I can get a stable 10Mbps/10Mbps connection with a peak power consumption of around 3.5W.
WCDMA: The ppp connection is established but dies very soon.
EGSM900: The module registers to the network but the module resets immediately when trying to start the ppp connection.

Huawei E3372h (HiLink) LTE dongle.
LTE2100: Stable connection (need to check the power consumption)
LTE800: As soon as I change the 4G band to LTE800 the module starts to reset randomly.
2G: Immediate reset.

I’m powering the AR150 with a beefy bench power supply through the 5V pins. The E3372h (all bands) work when connected directly to the computer USB but fails if I have anything in between (eg. a USB charge doctor). I’m yet to test the SIM7500E connected directly to my computer.

2G seems to be most demanding. I read somewhere that there might be transient spikes of up to 1.8A.

I love the GPIO6 and the possibility to reset (or switch off USB to converse power) USB but there is something about the design (maybe it’s the transistor controlling the USB power) which makes it unsuitable for these high powered devices.

2G draw too much current and it doesn’t work very good.

The power issues seem have gone away. I replaced the small patch antenna I was using with a uFL → SMA(F) adapter and I’ve been experimenting with external antennae. I have a pretty bulky GSM antenna which for some reason is a lousy GSM antenna but works great as a LTE850 antenna. The other external antenna (patch antenna with a 3m cable) also works reasonably well. I can get a stable 2G connection with both antennae even though the bulky GSM antenna reports a CSQ lower than the original small patch antenna I used. The idle power consumption has also gone down. With 2G the idle consumption is around 0.7W (AR150 + SIM7500E) and jumps to 1.5-2W during transmit. In LTE mode the power consumption has also gone down (1.8W during download and around 2.5W during upload).