Max safe amps for car charger in us?

[worwig]

This is an informative thread. Thanks to all.
So my understanding is that as long as a charger (AC, car charger, or whatever) has the same voltage as the original charger, you can plug it into a phone, a tablet, etc. (with the right plug, USB, or one of those barrel connectors). If the amperage of the charger is higher than required, it will do no harm to the charger or the battery/device: it will charge at a suitable rate determined by the battery and regulator. If the amperage of the charger is less than required, it will not charge at a maximum rate, but a lower rate, or not at all if there is not enough juice, so to speak; and again, there is no harm to the charger or the battery/device.

.....snip stuff about a tablet charger....

Yes, generally, the voltage is what is critical.
But a smartphone is a little different then a tablet or laptop power supply.
The short story.
The voltage MUST be very close. That is, for a 5 volt smartphone, use a 5 volt adapter/USB port. 12 volt tablet, use a 12 volt charger. Anything other voltage risks damage. As for current, you normally want the rated current, OR MORE, normally. Thus, you want a 1 amp charger for an S3 which pulls 0.8 or so maximum amps. You would want (for example) a 2 amp OR MORE charger for a 2 amp laptop.

The long story:
But it is complicated. For example, smartphones batteries are over 4 volts when nearly charged. They are charging from 5 volts. Due to diode and such inefficiencies, the current will be a little less when running at less than 5 volts and a little more at more than 5 volts. So, if your 5 volt adapter is only good for 0.75 amps, and the phone tries to pull 0.8, the voltage will typically just drop a bit below 5 volts, and the smartphone pull will drop a bit to say 0.75 amps, and all is well with the world. As the battery gets charged, the voltage will rise, and everybody is happy. Additionally, smartphones are designed to be powered from a mystery USB port. So their design is able to handle a USB port with much less than 1 amp available, and not damage anything.

BUT, for example my tablet runs at 12 volts. It has two batteries, or a bit over 8 volts. The drop from 12 volts to 8 volts is enough that the inefficiencies don't play into it like on the phone. And it is designed to always to operated from the manufacturers charger, only. My tablet needs just over 2 amps. If I run it at 12 volts, but with only 2 amps available, the tablet will pull the voltage down. This lower voltage, means that the tablet has to work harder to keep going, so it pulls even more amperage and going well over 2 amps, causing the voltage to drop even more. The current then goes even higher, and the voltage even lower. And so on, until the 12 volt supply burns up, or the table simply runs off of the battery and won't charge. Tablets and laptop expect a proper charger voltage and the proper minimum amount of current. Anything else is an experiment.

This may or may not be clear if you haven't worked with electronics a lot. Basically, make sure a tablet/laptop not only has the proper voltage, but make sure it has at least the correct amount of current. Anything less, may be an issue beyond just not charging right. But a USB device like a smartphone will be OK with less then the rated current.

 

[xRocksaltx]

The answer to your question is yes. If the maximum draw of your device is 1 Amp and you connect it to a 1.8 Amp charger it will draw 1 Amp.

It will charge at the maximum safe rate determined by the regulator in the phone. The current is referred to as current DRAW. That is, the unit being powered will draw current from the charger at the rate it consumes it. Until you hit the max of the supply, when it will not go up any further.

Think of this like a household light bulb. The voltage is 110v. Let me make the math easier to do and lets pretend its 100v. Your house has a master fuse of 100 Amps. The max power you can draw before the fuse blows is 100x100=10000 watts. Your 100 watt light bulb does not blow because 100 amps is available, it draws what it needs. 1 Amp. 100v x 1A = 100 watts. Remove the bulb and replace it with a 50 watt bulb. The current draw drops to .5 Amp because thats what it needs. 100v x .5 Amps = 50 watts. But if the electric company is having a bad day and only 45 watts is available to your house, the 50 watt bulb will dim because its draw exceeds the max available. Your light bulb is not harmed by the fact 100 Amps is available to it.

The battery in your phone is not like a light bulb. Its a smart device. It is capable of controlling its rate of charge and, as the battery fills, it reduces the charge until it is full and stops charging altogether. An automobile battery charger does the same thing, hard charge at first, taper off as it fills, trickle when its full. So, if your charger is capable of 1.8, but your phone is limited to 1.0 there is excess capacity available at the charger. Get a Y connector and plug in another phone. If your charger is capable of 50 A. get 50 Y connectors and plug in 50 phones. There is no harm in having more capacity than any single device requires.

Now all this applies to current capacity, but not voltage. Plug your phone directly into 100v and watch your teeny lil regulator cook itself to death in but a tiny little instant. All USB chargers are always 5 volts.

A moment, if I may on the cables to connect to the charger. Every piece of wire has resistance. The resistance of the wire consumes power by turning it into heat. The resistance of a given piece of wire is a matter of its diameter and length. For our purposes the length is short enough that the amount of heat generated is negligible. What do you get in a "charging cable" ? Maybe a lil larger diameter wires on the charging lines. I bet not. I bet its a marketing scam. I have never felt a USB cable get warm while in use charging. I got one of these lil cables on a retractor that winds it up when not in use. The wire bundle is really thin. I have never felt it get warm even when used to charge my tablets. I have never noted a slower charge when using it over one of my larger cables.

I do note that my little Sedio charging stand charges my phone slower that directly connecting the phone to the cable. Why? It has some electronics in it that deals with and lights some led's. That consumes power leaving less available for the phone. If I connect it to a 2A charger instead of the one that came with my phone I bet the charging rate goes back up to the full rate. Will I harm anything by doing so? Nope, not a chance.

Sent from my cm_tenderloin using Android Central Forums

You can supply more power(current) than your battery can handle. Most batteries can handle a charge rate of 1C. In the case of the Samsung S3 the battery it is 2100mA. It can be safely charged at 2.1A. Rest assured your phone has a circuit built in to properly charge a lithium ion battery and can regulate the source current to properly charge its battery. The battery has no regulator in it and it not smart in any way.

http://www.google.com/url?sa=t&rct=...eTRslEVQBOrxHLQ&bvm=bv.50723672,d.b2I&cad=rja

The fact that your phone can charge at a higher rate that what comes from a USB port shows that it is capable of a larger amount of charge current than .5A.

I do not believe the cord has anything to do with charge rate, but I could be wrong. It may be the phones charging system can detect it is being provided more current than what is being delivered by the USB port and changes it status to AC instead of USB. I use my cable in car and computer and it recognizes it both ways.

 

[PaceyPimp]

Not sure what it is but i had the Note 2 and i clocked a full charger using an external charger in 4 hrs and in the phone even longer. Then i moved to the LG Optimus G Pro that has the Snapdragon 600 and i can tell it chargers faster. When i had a .5amp charger for my car the Note would not charge just stay the same % then i got a dual 2.1amp and it would charge but a bit slow so i changed the cable to the original cable and no change. When i changed to the LG Optimus G Pro it charged a but faster in the car and at home then the Note II. Now then i have the Xperia Z Ultra with the Snapdragon 800 i feel the difference its huge. It really seams to use the the faster 2.1amp charge and i can latterly watch it go up all while on bluetooth wifi and GPS navigation. So Props to the Snapdragon 800 and i am using and original Note II USB cable. I wonder if i use a charge only cable if it will help as its already charges so fast. Not sure the cable has to due i think its more the device. Please people explain my results. Thanks you.

 

[wigsplittta]

I have a 2amp Samsung charger and it charges my phone super fast (I know u guys hate it but it also will fully charge my backup iPhone 4 not 4s in about 30min) and I have noticed that when I use my 2amp taplet charger my phone will actually last all day. The real ? I (&everyone else has) have for starting this thread witch I have read to its entirety (Every darn word of it) will these tablet chargers hurt our phones and if so would the damage to my battery be noticeable within a year

 

[Super Dave426]

I had purchased some 6 foot cables from Amazon in the past and needed replacements so I remembered that I like Monoprice for cabling needs. I picked up a bunch of their Premium Cables, under $3 each, and these cables charge my S3 a lot faster than the ones from Amazon, so without any scientific explanation I know that some cables will charge faster than others. I really like the ones from Monoprice, they have a little spring in the connection that locks the Micro USB in the phone. Plus Monoprice has lifetime warranty on their cables, just order a few because you pay for shipping, not a lot. but it isn't worth it for 1 item.

 

[unholygod91]

This is a very old post, but it confused me. The the math changes, Watts=volts * amps, but the 12v, 50a, 100w. Only, my wall adapters are all 5v but different amp outputs