cell phone charger voltage issues, slow charging vs fast charging

Thread Starter

sdowney717

Joined Jul 18, 2012
648
I modified some older wallwarts which have a 5vdc output and even 2 amps to work as usb phone chargers. They do charge the phones, but the phone will say slow charging. So I installed an app that shows the charge current, and it comes up 470ma or sometimes less.

I have another real good fast charger of 5vdc and 2 amp output that came with a hotspot. The app reports a charge current of 1200ma.

WHY is it complaining about slow charge if the cruddy charger says it puts out 5vdc and 2 amp power? Does the phone test the charger output and does not someway like it, so throttles the charging?
 

ArakelTheDragon

Joined Nov 18, 2016
1,264
I do not agree.

When it says 2A, that means the maximum is 2A, but it can be less. Even the power bank that I built charges slowly when the phone is on. There are specifics to charging a capacitive load (battery). If the charger is designed for a resistive load you may have problems. What was the charger for originally?

Can you turn off the phone and check the result? Can you add a 0.1R resistor in series and check the result? Can you give the model of the battery ?

It is not recommended to use more than 1200mA for a phone.
 

dendad

Joined Feb 20, 2016
3,084
And some phones need the apropriate voltages on the USB data pins to tell it what the charger can supply.
Search for "USB charger resistors" or something like that for more info.
 

Thread Starter

sdowney717

Joined Jul 18, 2012
648
Charger originally came from a Pricom 3100, a print server that creates an ethernet port on a centronics printer.
Charger says 5vdc and 2 amp output. I removed the original wire and connected a usb wire soldered direct to the charger board. I just used the 2 wires out of the 4 wires that are in a usb cable. I think they were red and black wires.

Phone is a Samsung Galaxy S4 and the standard OEM battery that comes with that phone.
 

ArakelTheDragon

Joined Nov 18, 2016
1,264
The RED and black wires are the power supply. The white and green ones are the data cables. If you want to, start connecting the white and green ones to the red and black one in order to achieve on the data cables:
10
01
11.

Then see will there be a difference.
 

ebp

Joined Feb 8, 2018
2,332
"Does the phone test the charger output and does not someway like it, so throttles the charging?"

Very definitely. USB 2.0 specified the current from a single host or hub port to be 500 mA maximum - and even that is only supposed to be available for a "high power device." A well-designed charger in a phone will not draw more than 500 mA unless it is "notified" that it can by resistors connected to the data lines, as dendad noted. Some will also throttle the input current to prevent the input voltage from falling below the specified minimum. Your Samsung phone no doubt has a decently designed charger that won't attempt to draw more current than it should, regardless of how much is available. My Samsung table will take half an amp from a standard USB port and twice that from a charger that is rated to deliver 1 amp. None of this has anything whatever to do with the nature of the load.

Do not mess with connecting data lines directly to the power lines.

This is worth a look:
https://www.maximintegrated.com/en/app-notes/index.mvp/id/4803
 
Last edited:

ArakelTheDragon

Joined Nov 18, 2016
1,264
Connecting the data lines to the power supply will give the needed combination of 1s and 0s if there is such a combination needed.

When a phone is connected to a USB port 2.0 ot can draw a maximum of 1A by standard, not 0.5A. How much it draws, depends on the protocol initiated in the OS. It can be even 100mA.
 

ebp

Joined Feb 8, 2018
2,332
"Connecting the data lines to the power supply will give the needed combination of 1s and 0s if there is such a combination needed."
No. Resistors are used and the sensing is analog, not digital. Read the USB specifications documents.

"When a phone is connected to a USB port 2.0 ot can draw a maximum of 1A by standard, not 0.5A."

No. Read the USB specifications documents.

Read the USB specifications documents.
 

BobTPH

Joined Jun 5, 2013
2,057
You need a resistor divider, setting a specific voltage on each of the data lines in order to signal to the phone that it can supply more current. If you do not have these it will default to 500mA.

Bob
 

BobTPH

Joined Jun 5, 2013
2,057
"When a phone is connected to a USB port 2.0 ot can draw a maximum of 1A by standard, not 0.5A."
No. Read the USB specifications documents.
That is not correct, it can only draw 500mA unless it uses USB protocol to negotiate more.

Bob
 
this http://www.ti.com/lit/ds/symlink/tps2514.pdf may explain some of the wierdness.

http://www.ti.com/lit/ds/symlink/tps2514.pdf#page=5 suggests it can go up to 1.5 Amps.

It just gets totally wierd. I have some Motorola phones and the cable matters. That's where the D+D- stuff is done, otherwise you get low charging times.

In so many cases. chargers won't even work with my Motorola phone(s). Forget port rated at 2.1 A. Nothing ever happens. In some chargers the ports aren;t labeled.

So, I have a Garmen GPS and it will charge on the port rated 0.5A and 2.1A. The Motorola phone will charge on the 0.5 A ports. The ports are not labeled.

I bought a 12 V charger at Staples. No charge on either the 0.5A or 2.1 A port.

I had an original Razer cell phone and the service manual indicated that 100, 500 and 1000 mA was available for charging. I thing with the wrong cable, you get 100 mA. So, you basically need a data cable to get the higher charge rate.
 

ebp

Joined Feb 8, 2018
2,332
It is all a bit messy and there is a lack of conformance to the USB standards.

Ignoring "standby", the only negotiation by data exchange during device enumeration in USB 2.0 is "low power" versus "high power." A port is supposed to default to low power - 100 mA. If negotiated, a port may then supply and the device draw up to 500 mA. There is no provision for negotiation of any higher current. Higher current for charging is covered in the USB Battery Charging Specification, Rev 1.2. The higher currents are not negotiated by means of data exchange but by resistors connected between the data lines and the power lines. This requires connecting cables with data lines but it frees simple dedicated chargers from doing digital data communications with the chargee.

I have seen lots of USB hubs and USB expansion boards for PCs where not only was there no means of controlling current after doing the low-high power negotiation, there wasn't even any sort of decent current limiting to the ports. I've seen expansion boards that had provision for PTC type over-current limiters, which don't really meet USB specs but at least do something useful, but had zero ohm jumpers in place of the PTCs. Current would be limited only when something burned up - the cable or traces on the expansion board or the motherboard. I have never seen a hub or expansion board with a proper power management IC. Part of the intent of doing proper power management is to prevent overcurrent in a connected device from messing up the operation of another device.

Many cables use only 28 AWG conductors for both data and power. This is fine for data (impedance of the pair is very important for reliable data), but not satisfactory for power if the current requirement is high or the cable is long. With some chargers, the voltage drop in such a cable can result in the charger either running at reduced current simply because the required power is not available at its input, or actively backing off the current drawn on the assumption that it is asking for too much (similar to a PV MPPT tracker, the charger sets a minimum input voltage that would correspond to the minimum in the USB specs). Lots of early chargers were simple linear regulators - the current into the battery was equal to the current from the USB port. A bit of voltage drop in the cable might make no difference at all to charging rate. Later chargers, before the USB charging spec was introduced, used high-efficiency switchers to squeeze the maximum current into the battery from the 5 V 500 mA input - e.g. a battery at 3.5 V could be charged at nearly 700 mA from the same 2.5 W input power. This is still used, but now at substantially higher power.
 
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