# Phone charging problem with vehicle power adapter [closed]

Let's compare 2 situations:

1. My smartphone is totally discharged. I plug a standard phone charger (standard 5V adapter, with micro-USB, wall adapter), then the battery increases of, say, 1% percent every 10 minutes. You can use the phone at the same time in normal conditions (messaging, but no video), it's still charging. Normal behaviour.

2. The same smartphone is totally discharged. I plug it on my car's "lighter adapter" with the following devices:

CAR 12V LIGHTER PLUG --> LIGHTER ADAPTER TO USB --> USB-TO-MICRO-USB CABLE --> SMARTPHONE


Then I notice, that even if I use the phone in same conditions as before (i.e. no GPS or other high-current-consumption tasks), while someone is driving (i.e. motor of the car on!), the battery doesn't charge. At best it keeps the same percentage: if battery was 5%, it will stay around 5% for hours, but no increasing charge.

Why?

Is the problem:

• the car lighter power 12V adapter that has a current-limitation system (how does this work?)
• the lighter-plug-to-USB car adapter (see picture before)? Do such devices include a current-limitation system?
• something else?

Is there a solution: how to get a properly charging phone in car?

## closed as off-topic by Olin Lathrop, Enric Blanco, laptop2d, Dmitry Grigoryev, PeterJJul 13 '17 at 13:32

This question appears to be off-topic. The users who voted to close gave this specific reason:

• "Questions on the use of electronic devices are off-topic as this site is intended specifically for questions on electronics design." – Olin Lathrop, Enric Blanco, laptop2d, Dmitry Grigoryev, PeterJ
If this question can be reworded to fit the rules in the help center, please edit the question.

• As I'm not native english, the words (cigarette)lighter-plug etc. may be incorrect or non-idiomatic. Native english speakers, feel free to edit! – Basj Jul 7 '17 at 0:33
• This question isn't really on topic here, since it is about using off the shelf devices rather than designing them. Chances are you need a "better" car adapter, either in the power it delivers or in signalling the capability to deliver such power in a way more compatible with your phone. There exist pluggable inline current meters, but it's not 100% certain they will not interfere with that very capability signalling. – Chris Stratton Jul 7 '17 at 0:42
• The pictured charger is likely a super old type with a linear regulator limited to 500 mA or a first generation switching regulator and limited to 750 mA. They probably don't have the signaling resistors for any recent phones to know what current they can draw. So the phones self limit to standard usb current of 500mA or less. And they are also likely set to 5.0 V, instead of a better 5.2 or 5.3 volts, which allow for voltage droop as current draw increases. All this makes your phone discharge faster than it can charge. There are multiple questions here on usb charging design. – Passerby Jul 7 '17 at 4:49
• @Passerby Sad because the informations you gave were useful to understand how it works (about regulators, about the 5.2 / 5.3 V part, etc.). Now this question/answer will be buried, though it provided electronic informations that could be useful... – Basj Jul 7 '17 at 12:00
• @Passerby: Reopened. – Dave Tweed Jul 7 '17 at 12:41

## 1 Answer

The pictured charger is likely a super old type with a linear regulator limited to 500 mA (lm7805) or a first generation switching regulator and limited to 750 mA (Mc34063). I'm assuming this based off the case it has, which is typical for those types of chargers. Newer chargers have higher capacity regulators/circuits, and are capable of delivering multiple amps.

They probably don't have the signaling resistors for any recent phones to know what current they can draw, as older cell phones did not require them and only charged at slow currents. So newer phones self limit to standard usb current of 500mA or less, as if they were connected to a regular computer usb port. Look at the usb battery charging specification or the data available on iPhone charging signalling.

And they are also likely set to 5.0 V, instead of a better 5.2 or 5.3 volts, which allow for voltage droop as current draw increases. A 5V supply with a cheap usb cable with small cable gauge/size, i.e. higher resistance will see a higher voltage drop at higher currents, bringing the voltage at the device down to outside of USB specs. For example, my Galaxy S7 will charge at a higher rate from a 5.3V 1A supply compared to a 5V 1A supply, with the same wire. The phone detects the voltage in determining how much it can draw.

All this makes your phone discharge faster than it can charge, unlike a properly designed or up to date charger. Newer standards like Quick Charge are even more complicated, requiring variable voltages, higher current, and complicated signaling or negotiation.

• The OP should also know that chargers do have different "charger signatures", so the unidentified "my smartphone" may not understand the (unspecified) charger signature provided by the car adapter. See a collection of "signature" topics at this page, electronics.stackexchange.com/… @Basj – Ale..chenski Jul 8 '17 at 6:15