I am wondering what might cause a USB A port that claims it can deliver 2.1 amps, to only deliver 300mA ?

The power source is direct to a car battery with 14 Gauge wire. Is it just poor design or poor installation?

 

Into what load? What happens to the voltage when the current is 300 mA and how are you measuring the current?

Ron

 

I have a USB port tester device. It plugs into the USB port, then the load plugs into that. It displays the voltage and current.
I tried several testers for averaging, and tried the same USB cable with the same USB tester and device on other USB A ports emanating or connected to other power sources.

That verified that the USB A outlets were weak, and that is is not the cable, the tester or the power source. That left only the USB socket itself (dual outlet, both weak)

 

By definition the port defaults to 100 mA. You can negotiate, via USB protocol, with the port to provide up to 500 mA. Are you sure the negotiation is taking place? Is your test device interfering with the negotiation? Don't know where the expectation of 2.1 A through the tiny little wires of a USB cable is coming from.

 

I am wondering what might cause a USB A port that claims it can deliver 2.1 amps, to only deliver 300mA ?

Which USB spec? 2.x or 3.x? Don't think any port can deliver 2.1A, regardless of spec version unless it's USB C.

 

If you are talking about one of these type devices as a USB tester I will ask again what are you using for a load? Does this all go back to your previous thread with the generator and the USB device you showed in the drawing? Knowing exactly what that device is would help. Does your load negotiate with your USB device as was mentioned above?

If all you want is a regulated 5.0 Volts I would just get a 5.0 volt regulator and be done with it. I glued a common LM7812 to a 5.0 volt device and shoved it in a 1978 Pontiac to monitor battery voltage. Twenty years later when I scrapped the car the thing was still working. Today on Ebay I can buy any of a dozen 12 volt to 5.0 volt converters which will work fine in automotive or 12.0 volt battery supplies for a few dollars. If your device is similar to what I linked to what is the voltage when you see the 300 mA?

Ron

 

No, this in in my vehicle and unrelated to any generator thread.

Yes, I'm using that device for testing. The load doesn't seem to matter.
The devices I tried were my cell phone and a tablet. On either, 300mA was the maximum current.

I can, however, routinely get 1.5 - 2 Amps through USB charging cables that are explicitly High Speed Cables. Not regular data USB cables.

However, nothing yet explains why these specific USB A ports will only transfer at 300mA when they are rated for up to 2.1 Amps and the same device, USB cord and load CAN and DOES show 1.5 - 2Amps current draw when plugged into a different USB power source.

It is absolutely something with the ports. Nothing else. Yet the ports are direct wired to the vehicle battery using 14 gauge solid copper stranded Primary wire. The cigarette light connected to the same power does produce up to 15Amps

Here is the Panel in my vehicle

 

Which USB spec? 2.x or 3.x? Don't think any port can deliver 2.1A, regardless of spec version unless it's USB C.

Hmmm....ok....let me post up a picture of a USB A cord charging at or near 2 Amps.....
I do it ALL the time.

 

Yet the ports are direct wired to the vehicle battery

Must be indirect, or else you'd get 12V out instead of 5V.

 

Hmmm....ok....let me post up a picture of a USB A cord charging at or near 2 Amps.....
I do it ALL the time.

The title said you were talking about getting 300mA from a USB port instead of the desired/expected 2.1A. There was no mention of the cable being a limitation; though it would likely be since no USB A cable was intended to carry more than 900mA.

The USB2 spec allows a USB host to provide up to 5 loads, and each load is 100mA. The USB3 spec increased the maximum number of loads to 6, and each load is 150mA.

Unless they changed something, all USB clients must start out in a low power state (1 load) and negotiate with the host for more. If the client isn't capable of negotiating (being a USB decoration), it can only draw 1 load.

 

Just as a side note I don't see this as a USB host type device with any negotiating going on to any USB standard. What I see here is a step down device taking automotive 12 Volts down to 5 Volts for charging or running 5 Volt devices like phones, tablet PC and other like gizmos. Lumenosity is using one of these devices to monitor the voltage and current to his load. With that in mind and less any USB specifications the load current will be whatever it is, If the device is capable of providing two amps and my load only draws 300 mA all I will see is 300 mA and that is as good as it gets or as high as the current gets. Here is an example of one of these gizmos. a Google of automotive 12 volt to 5 volt USB charger will bring up a dozen hits of similar gizmos. I don't see where any actual USB standards figure into this or any negotiating with a host. There is no data, no host and no client as I see it.

The measured current to the load will be a function of the load until the load current exceeds what the device is capable of providing.

Ron

 

I have 3A USB cables and standard USB cables.
My Adapter can supply up to 3A.

The cable definitely limits the current drawn from my phone.
My phone negotiates with the charger and then fixes the current drawing from adapter.
The high current cable helps to draw more current to charge the phone faster

 

Must be indirect, or else you'd get 12V out instead of 5V.

lol
Yeah, I think you're the only one who didn't figure out what I meant though.
I meant that the 14 gauge wire is going directly TO THE USB ASSEMBLY from the battery.
what it does once there is in question.

 

The title said you were talking about getting 300mA from a USB port instead of the desired/expected 2.1A. There was no mention of the cable being a limitation; though it would likely be since no USB A cable was intended to carry more than 900mA.

The USB2 spec allows a USB host to provide up to 5 loads, and each load is 100mA. The USB3 spec increased the maximum number of loads to 6, and each load is 150mA.

Unless they changed something, all USB clients must start out in a low power state (1 load) and negotiate with the host for more. If the client isn't capable of negotiating (being a USB decoration), it can only draw 1 load.

Ok. I specifically order "High Speed" USB A cables from places like MonoPrice and recently even from China.
On power sources capable, I often see current draw (over USB A) exceeding 2Amps. But 1.3Amps is more common.

When I'm charging a Bluetooth stereo speaker brick for exampe, it's common to see the current start out at over 2 Amps, then diminish during the charge until it reaches zero when fully charged

My thought is that......
The power SOURCE will provide whatever it's capable of.
The USB CABLE will conduct whatever it's capable of (high speed cables, more copper)
The DEVICE BEING CHARGED will draw at the rate the battery is capable of receiving, limited by circuitry designed to proted the device from too much current.

So I'm guessing there's something wrong with these USB ports because
The power source is the Car's battery (PLENTY current there)
The cable is a high speed USB cable (tested and proven to conduct up to 2.5Amps)
And the test device is capable of charging at at least up to 2.0 Amps

 

The cable definitely limits the current drawn from my phone.

Sounds reasonable. Rather than using client/host negotiation, don't phone etc chargers rely on sensing the voltage on the USB data lines to set the charging current? The charger cable, or USB port, includes pull up/down resistors to establish the data line voltage.

 

Sounds reasonable. Rather than using client/host negotiation, don't phone etc chargers rely on sensing the voltage on the USB data lines to set the charging current? The charger cable, or USB port, includes pull up/down resistors to establish the data line voltage.

Mine does. The phone controls the rate of charge even including battery internal temperature. It will draw a maximum current up to a limit and control the charge. It will distinguish the available current to start with a faster rate of charge when it can.

Ron

 

Here's the USB power outlet by itself on ebay.....
https://www.ebay.com/itm/12V-Car-Ci...058ee019:m:myiLG7pjr4-u-SBg7-shD_w:rk:21:pf:0

 

Sounds reasonable. Rather than using client/host negotiation, don't phone etc chargers rely on sensing the voltage on the USB data lines to set the charging current? The charger cable, or USB port, includes pull up/down resistors to establish the data line voltage.

Think of it like this.....

If you connect a given battery to a power source, it will still only charge at the maximum rate at which the battery is capable of drawing current....correct?

What happens if I try to charge a small 12.8v, 200mAh battery by connecting it to a fully charged, 650AH 12.6v car battery?
since the voltages are nearly equal, not much if anything since the car's voltage ( the "PUSH") is less than the smaller capacity but equal voltage battery.

so, anything I connect to this vehicle USB A outlet "should" charge at the maximum rate (up to 2.1Amps) that the cable and receiving device can accommodate.....no?

 

I don't know if this is the case with the OP, but perhaps. Most people unfamiliar with electronics have this notion that max current available is being pushed through a device... they don't understand the relationship of what the load represents as a simple or complex impedance.

 

Current levels beyond 500 mA are not negotiated digitally but by resistances.
https://www.maximintegrated.com/en/app-notes/index.mvp/id/4803

My guess is that the devices in question don't even do that. The reality in my experience is that a very large majority of standard USB 2 ports on anything are not compliant with the spec and will allow at least transient currents far above the 500 mA they should. I've seen USB add in boards that would allow sufficient current to simply burn some path open - tracks on the board, something on the mother board, cables, etc.

The only way you can get 4.2 A at 5 V from 12 V (nominal) in a tiny package is with a high-frequency high-efficiency switcher. When there are two outputs, each supposedly about half of the total current, then each requires its own switcher - there simply is no efficient way to "split" the current otherwise. Plenty of junk sold on ebay is ... JUNK!

Photos of the internal circuit would help, but it probably isn't possible to open the case non-destructively.