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I recently bought a Nexus 4. I had a couple of spare chargers laying around. I used a charger that apparently had an issue exactly like: https://www.youtube.com/watch?v=mrpBTG0a6K8. If I used my own charger the phone was completely fine. The touch screen didn't glitch out. I tested the "bad" charger with a multimeter and the voltage was a constant 5 volts. Since my multimeter doesnt have the ability to measure amps, I am assuming the glitchiness was coming from an unstable current source. (?). The "bad" charger is 5v at 1 amp. The nexus 4 can go up to 1.2 amps.

Since most forums dealing with this problem are in android forums and the people aren't as technical as I like (the most technical it ever got was "the charger is faulty"), I am wondering if anybody knows the true cause of the problem. I confirmed it is not hardware because when I plugged in my old phone and the issue is the same. It also seems like this problem is quite massive (look at the amount of results on google)

I would also like to know if there is any damage done to my phone. (The "bad"charger was 5v 1 amp and the nexus 4 can handle 5v 1.2 amp.)

user1950278
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  • My guess would be some sort of high frequency ripple caused by poor voltage regulation disrupting the touchscreen. If you could look at output on an oscilloscope, that would give you some more information. - Whoops, missed the bit about you under-powering it. Disregard me. – dext0rb Aug 01 '13 at 05:56
  • @dextorb I just used another charger with the same specs as the 'bad" charger...which is also under-powering it...and there is no glitch...so it would seem like a high frequency ripple is it. Could you please elaborate about that and if there is any damage associated with it? – user1950278 Aug 01 '13 at 06:15
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    I like the answer "the charger is faulty", sounds about right. :-) – Anindo Ghosh Aug 01 '13 at 06:59
  • The reason you might be seeing 5v on your multimeter, is that it is averaging out what it sees. If there is a lot of fluctuation in the power (ripple, either high frequency or high peak to peak difference), your multimeter is too slow (and dumb) to figure it out. Like a fly moving too fast for you to see. So 5v isn't always 5v. – Passerby Aug 01 '13 at 07:47
  • Related question: http://android.stackexchange.com/q/43630/15323 – JYelton Aug 01 '13 at 08:06
  • @Passerby So would this fluctuation be causing the problem? Also, what are the effects of this besides the immediate interference? – user1950278 Aug 01 '13 at 16:05
  • High ripple can eventually kill capacitors, if the dell capacitor plague is any evidence. It probably isn't very good for the battery either. – Passerby Aug 01 '13 at 18:56

1 Answers1

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Note:

This answer was written assuming the device (phone) required 1.2A and that the charger was insufficient. As @Passerby rightfully points out, phones typically can charge on much less current. That said, while the typical 5V USB (500mA) might be adequate for charging, it is not necessarily sufficient for operating it with screen, backlight, etc. plus charging. I was not able to find detailed specifications for the phone.

Ripple may be the issue, but if you are still having touchscreen problems with a clean power supply, connect the phone to a solid bench supply and measure what it uses when you've got the screen on, and the battery needs charging. At least then you then will know whether a 1A supply is okay.

Original Answer:

I don't think you understand current/amperage as it pertains to devices and power supplies.

Your phone is rated for 5V 1.2A, meaning it requires 5V 1.2A, not that it can handle it.

The "bad" power supply is underrated for the device: it can only supply 1A but the device needs 1.2A. You're not supplying enough current, and because the load is demanding more current than the power supply can deliver, unusual behavior ensues.

It's very possible you've damaged the phone. Stop using the underrated supply and get one that is 5V and at least 1.2A. Once you power it with the proper supply, then you can determine if the phone is permanently damaged.

Edit:

You mentioned in comments that another supply with the same rating (5V 1A) appears to work.

Not all chargers are built the same. Some are capable of supplying more current than they are rated for, but only for a limited amount of time (overcurrent capacity). Depending on the quality of the supply, it may have overcurrent protection, thermal protection, etc. While it's true that noise/ripple may also be a factor, I would be far more suspicious of too little power. If you continue to use the underrated supply that appears to work, you might be okay, but you also might find the supply getting hot and eventually dying altogether.

It's possible the manufacturer of your second supply, Apple, has actually under-rated the supply to err on the side of caution. If you built a bridge to handle no more than exactly 100 tons, would you post a sign saying "Capacity: 100 tons?" No. Well-built power supplies will generally do the same.

Think of it this way, your supply that says 1A might be able to supply a bit more, but it's designed for what it is labeled for. Heatsinks, capacitors, bridge rectifiers, etc. were chosen to dissipate a given amount of heat for a given amount of output power.

Here's one more example: Say an LED's datasheet indicates that its forward current is 20mA. That's for a 100% duty cycle, meaning, if you power the LED up, you can give it 20mA continuously and it will operate at the specified conditions for approximately the expected lifetime. The datasheet will also usually provide some higher current ratings and a corresponding duty cycle, i.e: "80mA at 20%" This means you can drive the LED with four times the current, but only if its on-to-off ratio is 20% to 80%.

A power supply isn't like an LED, but the idea is that you can exceed specs on certain devices sometimes. A good power supply will often show derating curves, which are specifications as how the supply behaves in abnormal conditions. Typically this is when the supply is hotter than it is rated for, but it can also apply to things such as supply undervoltage and load overcurrent, etc.

Your Apple USB charger is basically a smaller, simpler version of the power supplies I am referring to. It's not going to have these features and lengthy datasheets showing you its characteristics.

I'd recommend getting a power supply that is rated for 5V 2A or something, then you know it's going to be more than adequate for the load. For about $13 you could pick up a Meanwell RS-15-5 which is 5V 3A, and it will be able to charge two such phones at the same time.

You could check out the ripple on your supplies with an oscilloscope, but whatever your findings, I would not keep using a supply that's not rated for the load.

$13 is a lot less money than buying a new phone, or cleaning up after a fire.

JYelton
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  • Actually i found the solution after searching this site: http://electronics.stackexchange.com/questions/72513/how-can-electromagnetic-interference-from-a-usb-charger-cause-a-capacitive-touch . My only additional question is whether damage can be incurred because of this – user1950278 Aug 01 '13 at 05:58
  • In addition, why would using an underrated supply result in unusual behavior? Wouldn't the battery just charge slower?...Which in the case of li-ion battery actually prolong the battery lifespan? – user1950278 Aug 01 '13 at 05:59
  • In the case of simple resistive loads, like a light bulb, supplying too little current will illuminate the bulb weakly. This, however, is not the case with complicated devices like your phone. It has many subcomponents which require certain minimums to operate correctly. Supplying too little can actually damage components due to wrong voltages as a result of insufficient power. Also, a Li-Ion battery requires a charging circuit, which monitors the battery and charges it very specifically. It has minimum requirements just like the phone. – JYelton Aug 01 '13 at 06:01
  • Interestingly enough...I used a charger (this case an apple to usb adapter) with the same rating as the "bad" charger...there isnt that glitch. – user1950278 Aug 01 '13 at 06:15
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    I'll add more info to my answer to address this. – JYelton Aug 01 '13 at 07:05
  • After a lot of googling, it turns out that it is "charger noise"...still no info about whether it damages the phone :/...seems like its benign though – user1950278 Aug 01 '13 at 07:19
  • You do realize that A, the phone is also designed to charge off a computer 500mA supply B, also able to charge from 500mA car chargers and C, samsung and google would not design the phone to pull the absolute maximum current that the charger they ship with is rated at. The 1.2A is the charger rating, they would be inviting lawsuits from the fcc for mislabing or consumers when there is a high failure rate (let alone rma costs). Just like Apple, Samsung (the manufacturer) has adopted tiered chargers, where the charger announces how much current it can source. – Passerby Aug 01 '13 at 07:41
  • @Passerby You make a good point. I was under the impression from the OP the phone was labeled for 1.2A and the charger only 1A. If that's true, then how are you to know the *minimum* current required for the device? – JYelton Aug 01 '13 at 07:54
  • @JYelton the minimum depends on which charging mode the phone goes into. For the iPhone there is unsupported/0 (dumb chargers with no signalling on the data pins), computer/100~500mA, standard AC charger/1A and High Capacity/2.1A. Then you have to take into account if the screen is on or off (The iPad won't charge from a computer 500mA usb port if the display is on, but will once the display is off (slowly). Same for any radios, or cpu usage. And if the battery is fully charged, it switches into a trickle charge mode where the current draw can be a few tens to hundreds milliamps. – Passerby Aug 01 '13 at 08:03
  • @JYelton the max available is dependent on the charger source, the minimum required is dependent on the phone status and can vary wildly. (And I quote the iPhone versions because the small variety of official and inter-compatible parts as well as widely documented, unlike tighter lipped google or samsung.) – Passerby Aug 01 '13 at 08:05