Tablet/phone charging

[Kittyhawk]

This one baffles me!
At home I charge my phone or tablet by connecting the devices to an adapter which in turn is inserted into a wall outlet. 240vac into the adapter and 5vdc 2 amps to the device.
In the motorhome where we are now we have a different adapter which has 12vdc in and the same 5vdc 2 amps out. We use the same charging cable in both applications but the charging in the truck takes hugely longer than it does at home. Why would that be, and is there any way to fix it?

 

[MorrisWoodman12]

It could be that your motor home 5V/2A adaptor specification isn't correct or it's not well regulated so that it's output drops as the load current increases. Also does the 12V at the adaptor remain at 12V when you plug the adaptor with phone in?

 

[John Brown]

It could be that the one in your motorhome doesn't do the right thing with the d+ and d- connections. Google USB charging.

 

[minilathe22]

For fast charging, the charger and the device talk to each other and agree the best voltage/current etc parameters. Your mains charger is probably doing this, and the device negotiates a fast charge setup.

The 12v adapter you have, perhaps is just providing 5v and doesnt do any communication, therefore the device defaults to a slower (but safe) charging current.

I believe some USB specifications can even go as high as 20V now. but only if the device asks for it, to preserve backwards compatibility with older devices.

 

[John Brown]

For fast charging, the charger and the device talk to each other and agree the best voltage/current etc parameters. Your mains charger is probably doing this, and the device negotiates a fast charge setup.

The 12v adapter you have, perhaps is just providing 5v and doesnt do any communication, therefore the device defaults to a slower (but safe) charging current.

I believe some USB specifications can even go as high as 20V now. but only if the device asks for it, to preserve backwards compatibility with older devices.

While not disagreeing with anything you say, in a lot of cases the "communication" is something as simple as connecting the d+ and d- lines together at the charger end, or setting them to specific voltage levels with a simple resistor divider network, i.e. a resistor to 0v and another to 5v.

 

[minilathe22]

thats interesting, I assumed some form of digital communication was taking place...

I guess easiest solution is to buy a 12v charger that supports the same type of fast charging as the devices. I think Quick Charge and Power Delivery are the common ones.

 

[John Brown]

https://en.m.wikipedia.org/wiki/USB_hardware#USB_battery_charging

 

[TheUnicorn]

i know you are using the same cable, but it is also possible that that is a factor, twist one way it is fine, twist the other and the connection is weak or broken. I use a 'usb doctor', which tells me the voltage and amps going through at any given moment, others are available that will tell you a total charge that has gone through, it fixes nothing but does give you more information

https://www.amazon.co.uk/4-Digital-...=se&keywords=usb+doctor&qid=1723286281&sr=8-6

 

[Kittyhawk]

The 12vdc polarity into the charger is the right way round and my multimeter says 5.12vdc on the output side.
I should have added to the original post that this slow charging of phones from a 12vdc output is a well known phenomenon amongst motorhomers. It's not a big inconvenience - just that I don't understand what's going on and would like to fix it if I could. I installed the USB outlets and if price is anything to go by, they are the best there is.

 

[John Brown]

As was mentioned in another thread, the thing you plug into the wall socket, or the outlet in your motorhome are not really chargers. The charger is in your phone or tablet. Various methods, including shorting the d+ and d- lines together, indicate to the charging circuitry in the phone what the capabilities of the power supply(the thing plugged into the wall are.
My phone came with its own fast "charger", and to be honest, I've never bothered to see what voltage or current it works at(I'll check tomorrow if I remember), but I would expect an "outlet" in a motorhome to be fairly conservative by comparison to modern dedicated "chargers". As was also mentioned elsewhere, the same is true of EV "chargers", they're really only power supplies, the charging intelligence is in the vehicle. However, I believe that the specification for how the power supply signals its available power is more rigorously defined, as EVs have to he able to use public "chargers".
If you really want to get to the bottom of it, then I suggest you buy a cheap USB monitor, such as the one linked by The Unicorn in this thread. I have one which will tell me the voltages present on the d+ and d- lines as well as the voltage and current.

 

[Kittyhawk]

If you really want to get to the bottom of it, then I suggest you buy a cheap USB monitor, such as the one linked by The Unicorn in this thread. I have one which will tell me the voltages present on the d+ and d- lines as well as the voltage and current.

I'll see if I can find one of these things..

 

[John Brown]

Just checked out my "fast charger" that came with my Xiaomi phone. Defaults to 5V(as you'd expect), but then, presumably after some negotiation, increases to 9V.
Probably proprietary, I guess.

 

[John Brown]

Just checked out my "fast charger" that came with my Xiaomi phone. Defaults to 5V(as you'd expect), but then, presumably after some negotiation, increases to 9V.
Probably proprietary, I guess.

No, I'm wrong, looks like it is part of a standard.

USB Power Delivery (USB PD) 1.0 supports 9V as one of its four voltage types, along with 5V, 15V, and 20V, at power levels up to 100W. Some USB cables can also support 9V, such as a 1 meter USB-C to USB-C cable that can support 9V/3A.

It's unlikely that your outlets in the motor home deliver anything over 5V at 2A, but I'm only guessing again..

 

[Tom K]

If you read through all the blurb on WIKI linked above it ultimately says your expensive adapter in the truck doesn't output enough power for fast charging. Was probably the bees knees when designed but has been overtaken by newer tech.

 

[Kittyhawk]

No, I'm wrong, looks like it is part of a standard.

USB Power Delivery (USB PD) 1.0 supports 9V as one of its four voltage types, along with 5V, 15V, and 20V, at power levels up to 100W. Some USB cables can also support 9V, such as a 1 meter USB-C to USB-C cable that can support 9V/3A.

It's unlikely that your outlets in the motor home deliver anything over 5V at 2A, but I'm only guessing again..

Further (and endless) reading online suggests that devices have some sort of on-board stuff that enables them to detect the original power source. If its 240vac then they suck up the 5v output at the max amps that the adapter delivers. If they detect that the original power source is 12vdc then they throttle back to 5vdc at 500m/amps. Apparently various electronic fixes can be tried but this is beyond my expertise so I suppose I'll just have go live with what I have.

 

[Kittyhawk]

If you read through all the blurb on WIKI linked above it ultimately says your expensive adapter in the truck doesn't output enough power for fast charging. Was probably the bees knees when designed but has been overtaken by newer tech.

The USB adapters in the truck are two months old, supposedly the best available and put out 5vdc, 2.5 amps.
My 240vac adapters at home put out 5vdc at 2 amps which lends weight to the opinion that devices are able to detect the original power voltage as per my post above.

 

[Tom K]

The USB adapters in the truck are two months old, supposedly the best available and put out 5vdc, 2.5 amps.
My 240vac adapters at home put out 5vdc at 2 amps which lends weight to the opinion that devices are able to detect the original power voltage as per my post above.

Yeah I have no doubt they are new and expensive unfortunately that doesn't mean they aren't crap. Are they a hard wired solution or just plugged into power output/cigar lighter? Do you have an inverter in the van?

 

[John Brown]

Further (and endless) reading online suggests that devices have some sort of on-board stuff that enables them to detect the original power source. If its 240vac then they suck up the 5v output at the max amps that the adapter delivers. If they detect that the original power source is 12vdc then they throttle back to 5vdc at 500m/amps. Apparently various electronic fixes can be tried but this is beyond my expertise so I suppose I'll just have go live with what I have.

Do you have a link? I'm curious about that idea.

 

[John Brown]

The USB adapters in the truck are two months old, supposedly the best available and put out 5vdc, 2.5 amps.
My 240vac adapters at home put out 5vdc at 2 amps which lends weight to the opinion that devices are able to detect the original power voltage as per my post above.

They don't "put out" 2.5 amps, they might be capable of supplying that current, but the charger circuitry in the phone/tablet determined how much current is drawn.

 

[Kittyhawk]

They don't "put out" 2.5 amps, they might be capable of supplying that current, but the charger circuitry in the phone/tablet determined how much current is drawn.

True. Further to what I read about devices 'reading' the power source and adjusting the accepted amperage accordingly, I probably didn't get it quite right.
This from some tech site online so could be a load of internet bollocks.
USB plugs have four terminals. The two either side are d+ and d- for charging and the two centre terminals are for data transfer. If devices detect live data terminals then charging is restricted to 500ma. For this reason, since 240v adapters are charge only the two centre terminals in it are bridged so not detected by the device and it accepts all the amps the adapter puts out. This is supposedly not the case with the small 12v adapters and the solution is to take it apart and put a dollop of solder across the two centre pin terminals. If this is the reason for slow charging then my solution would be buy a charge-only cable, if such a thing exists or to pull the two centre pins out of the USB cable plug. Cheaper to risk wreaking a USB cable than my expensive hard wired USB outlets.