USB Hub Limits Cell Phone Charge Power

Thread Starter

SidewinderAIM9M

Joined Mar 22, 2020
7
Can someone please explain to me why my phone slow charges when plugged into a USB hub that is supplied with 2.2amps when the power connections in the hub are not impeded in any way except maybe by a small amount of additional resistance from the trace on the board? Why when I connect my multi-meter to the hub output do I get 2.2 amps but my phone won't pull the maximum current it needs? Is there some way to fool the phone into using the full current its charge circuitry allows? This is driving me crazy.
 

dl324

Joined Mar 30, 2015
10,734
Welcome to AAC!
Is there some way to fool the phone into using the full current its charge circuitry allows? This is driving me crazy.
I suspect current is being limited by the hub. For USB2, maximum output from a port should be 500mA. For USB3, the maximum is 900mA.
 

Thread Starter

SidewinderAIM9M

Joined Mar 22, 2020
7
Welcome to AAC!
I suspect current is being limited by the hub. For USB2, maximum output from a port should be 500mA. For USB3, the maximum is 900mA.
Thanks for the reply, however current isn't being limited by the hub. I am drawing 2.2 amps out of it at 4.96 volts when my multi-meter is attached to the usb output, yet my phone says slow charging and charges maybe 5% in a day. If I plug the phone directly into the wallwart supplying the 2.2 amps to the hub, I get normal charging.
 

djsfantasi

Joined Apr 11, 2010
6,421
@dl324 has got the point. It’s unlikely that you can ever supply 2.2A to your phone. The USB Spec requires negotiation between the host and client. Your multimeter isn’t negotiating. However, I thought that USB said if negotiation fails, current is limited to 500mA.

Perhaps that’s a pre-USB3.0 spec. Someone help me here?

UPDATE; dl324’s post reminded me of what I was trying to remember. My post was effectively correct. His post explained it better.
 
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dl324

Joined Mar 30, 2015
10,734
Thanks for the reply, however current isn't being limited by the hub. I am drawing 2.2 amps out of it at 4.96 volts when my multi-meter is attached to the usb output, yet my phone says slow charging and charges maybe 5% in a day.
Your phone is USB compliant. Your meter isn't. A USB compliant device won't take more current than a host allows it to.
 

Thread Starter

SidewinderAIM9M

Joined Mar 22, 2020
7
@dl324 has got the point. It’s unlikely that you can ever supply 2.2A to your phone. The USB Spec requires negotiation between the host and client. Your multimeter isn’t negotiating. However, I thought that USB said if negotiation fails, current is limited to 500mA.

Perhaps that’s a pre-USB3.0 spec. Someone help me here?

UPDATE; dl324’s post reminded me of what I was trying to remember. My post was effectively correct. His post explained it better.
I am not trying to supply 2.2A to the phone just enough current to slowly charge it. I tried removing all the chips and just directly wired the USB ports to in the input and it still doesn't work. 500ma will charge the phone, hell even 250ma would charge it but I left two phones and nothing else on the hub all night and they lost charge. It just doesn't make any sense unless the phone is expecting a digital signal in order to draw power, but I even directly soldered the input digitals to one of the USB outputs and still nothing. I tried removing the digital, shorting the digital pins, etc. No dice. Could it be that the phone has a threshold voltage that needs to be greater than 4.96v, and that the 5.05 or so volts directly from the charger is why it works? Maybe I will just hook up 5.25v from a PSU and see if that does anything. At this point I don't care about data transfer I just don't want to have a power strip full of wall bricks for USB charging when 2.2 amps to six or seven devices should be enough to get them close to full charge overnight.
 
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djsfantasi

Joined Apr 11, 2010
6,421
I am not trying to supply 2.2A to the phone just enough current to slowly charge it. I tried removing all the chips and just directly wired the USB ports to in the input and it still doesn't work. 500ma will charge the phone, hell even 250ma would charge it but I left two phones and nothing else on the hub all night and they lost charge. It just doesn't make any sense unless the phone is expecting a digital signal in order to draw power, but I even directly soldered the input digitals to one of the USB outputs and still nothing. I tried removing the digital, shorting the digital pins, etc. No dice. Could it be that the phone has a threshold voltage that needs to be greater than 4.96v, and that the 5.05 or so volts directly from the charger is why it works? Maybe I will just hook up 5.25v from a PSU and see if that does anything. At this point I don't care about data transfer I just don't want to have a power strip full of wall bricks for USB charging when 2.2 amps to six or seven devices should be enough to get them close to full charge overnight.
Instead of trying things blindly and possibly damaging your phone, USB Hub or USB host, please read the USB spec.

You’ll thank yourself later.
 

Thread Starter

SidewinderAIM9M

Joined Mar 22, 2020
7
Instead of trying things blindly and possibly damaging your phone, USB Hub or USB host, please read the USB spec.

You’ll thank yourself later.
Thanks. I don't know what the USB spec is but I will look for it. I would be really surprised if a half a volt ruined a phone though, and I don't really care enough not to try it. I will post how it goes when I get back around to it.
 

Papabravo

Joined Feb 24, 2006
13,718
Thanks. I don't know what the USB spec is but I will look for it. I would be really surprised if a half a volt ruined a phone though, and I don't really care enough not to try it. I will post how it goes when I get back around to it.
The USB specification is published by an industry group so that everybody can agree on what a proper implementation is. You can download it for free, but it is heavy reading. In essence it requires a device that wishes to consume power in excess of some pretty meager limits to ask for and be granted the ability to do that. So no negotiation -- no power. To further understand what is going on you could get a USB bus monitor to capture and unpack the USB bus transactions and then you would know for sure what the problem is. My guess is that it would be more time effort and expense than you are willing to expend.

https://www.usb.org/documents
 

dl324

Joined Mar 30, 2015
10,734
I don't know what the USB spec is but I will look for it.
The USB spec says a client needs to operate in a low power mode (1 load: 100mA for USB2 and 150mA for USB3). Things that are USB compliant will work well together. If a client asks for more than 1 load and the host refuses, the client is supposed to operate in low power mode.

A rub occurs when the client isn't compliant (a USB decoration in their terminology). If it just takes without asking, the host could deny it; but some hosts may allow it. This seems to be your case. Your meter takes more than 1 load without asking and the host allowed it instead of shutting down the port. Your phone is compliant and is playing nice.
 
USB is so hokey, I'm surprised it works at all. Ideally, phones should charge at the lowest level, but I've had chargers where they won't charge at all.

You have charging ports only or OTG (On the Go chargers) which is what the 5th pin is on the USB mini connectors. Then there are various, manufacturer, specific pull-ups on the data pins.

I did find one company that's making phone-specific cables which appear to work. I'll have to find that info.

Your probbaly better off with a non-hub charging station. e.g. A bunch of OTG ports.
 

Thread Starter

SidewinderAIM9M

Joined Mar 22, 2020
7
USB is so hokey, I'm surprised it works at all. Ideally, phones should charge at the lowest level, but I've had chargers where they won't charge at all.
This is my feeling exactly. It shouldn't be that complicated. LiPo cells charge to 4.2v, so if the phone has over 4.5v, it should be able to charge at full power. I more want to defeat the USB hub and protocol BS than wanting a super efficient charging system at this point. If I can't get it to work I will just use the OTG ports. I am curious about the cable. I just connected 5.25v directly from my power supply to the PCB and the phone no longer says slow charging, however I want to leave it for a while and see if it is actually drawing enough current to charge. The slow charge warning may or may not really mean anything.

The USB spec says a client needs to operate in a low power mode (1 load: 100mA for USB2 and 150mA for USB3). Things that are USB compliant will work well together. If a client asks for more than 1 load and the host refuses, the client is supposed to operate in low power mode.

A rub occurs when the client isn't compliant (a USB decoration in their terminology). If it just takes without asking, the host could deny it; but some hosts may allow it. This seems to be your case. Your meter takes more than 1 load without asking and the host allowed it instead of shutting down the port. Your phone is compliant and is playing nice.
This is great information, the phone being compliant seems to be the frustrating problem here. Of course I removed all SMD circuit components from the hub now. I don't think I will reinstall them since I probably won't be able to fool the phone if it is talking to the hub.
 

Thread Starter

SidewinderAIM9M

Joined Mar 22, 2020
7
You can install an app that will monitor power usage. It will tell you whether the battery is charging or discharging, and the magnitude of the current.
After reading this I remembered that I built my PSU with a current monitor. Looks like if the phone is plugged in below 4.9v or so, it draws 0.37A, if above 5.0v or so, it draws 0.46A, a 25% increase in power. Since the battery is 2500mah, it could easly charge over 1.25A without overheating, so 0.46A isn't great but it is better. What is interesting is that if the power output starts above 5, and then I slowly bring it down, charge current doesn't really change, it stays around 0.46A, the same is true if the phone is plugged in below 4.9v, as even turning the voltage up to 5.5 doesn't increase charge speed. So perhaps in the absence of communication with the charger, initial voltage is used in part to determine charge current. The amp apps I have downloaded don't seem to give a current reading unless the phone has been charging for a while, which seems to me to suggest that it is not a real time measurement. I tried another one just a minute ago but it isn't giving me a reading. I want to see what the current is if I skip the hub but I may have to wait until I get some kind of USB power meter or have the time to wire one through my multimeter. Thanks again.
 

Thread Starter

SidewinderAIM9M

Joined Mar 22, 2020
7
I got it! I shorted the two digital pins together used the PSU to supply an initial voltage of 5.25v, I am now drawing 1.05A. Wow what a pain in the ass. I have no idea why that worked.
 
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