View Full Version : wall wart question

08-07-2014, 02:31 PM
My buddy just bought a new tablet which comes with a charger that says it's rated for 2000mA. He asked me today if it would be safe for him to charge his phone with that charger. The charger that came with his phone is rated for 1000mA. I thought about it for awhile and realized I really didn't know.

So what's your take? Yes? No? Can't tell?


08-07-2014, 02:41 PM
As long as the voltages match, that is, the charger's rated output voltage and the voltage that his cellphone requires during charging are the same, it will be fine.

Of course the plugs need to be a mechanical match also.

The batteries will draw the required current during charging, there will be no harm from the fact that the new tablet charger is capable of delivering more current that required.

If it provides more voltage than the cell phone is designed for, THAT will be a problem.

Think of it like the battery in your car, if it's 12 volts and the factory battery was a 105 Amp Hour rated one, and you replace it with a higher quality 12 volt 120 Amp Hour battery, you just have more reserve capacity, but no harm will be done to the car's electrical system.

The old analogy for voltage and current being compared to water through a pipe is another way to think of it. Voltage is like the water pressure through the pipe, and current is like the gallons per minute flow volume through the pipe.

If the pipe is emptying into a tank like one on an older style toilet, once the bucket is full the float valve shuts it off. Once the battery is full , it stops accepting more current. But if the voltage is too high, just like having too much pressure in the pipe or the tank, bad things happen. The battery will heat up, swell, possible burst, etc.

With the cell phone, if the voltage is too high, the really bad thing that happens is all the magic smoke gets let out of it. And that's next to impossible to stuff back in there.

08-07-2014, 02:42 PM
There is not enough information to answer the question. 2000 Ma is a current rating. The voltage is the critical factor. Also the polarity of the adapter as well as the connector. If the voltage, polarity and connector are compatible, the current rating is not the critical factor. All devices with LiPo batteries contain charging circuits that control current to the battery during the charge cycle.

08-07-2014, 03:17 PM
The tablet probably charges through a micro-usb port, just like most phones do.

Yes, it'll be fine.

08-07-2014, 04:12 PM
As mentioned, if all it requires is a voltage source, then it would be fine if the plug and polarity are satisfied.
However, if it is a charger and not just a voltage source, then the battery technology should be the same in both cases, i.e. LiPo and NiMh etc require different charge techniques.

08-07-2014, 04:24 PM
One other item to be aware of. IF the voltages match, and IF the connectors match, it is okay to charge the phone from the table charger, however, IT IS NOT okay to attempt to charge the tablet from the phone charger. As stated before, MORE capacity is good, LESS is BAD.

08-07-2014, 04:28 PM
As stated above voltage and polarity matter. But your question does not ask that. It asked about current. So simply the phone battery will only consume 1000mah. Thus the power supply will only be working at half it's capacity. And that is only when the phone battery is accepting 100 percent. As the battery is charges the current into the battery, as well as the current drawn from the power supply lessens

08-07-2014, 04:34 PM
The OP mentions Charger, NOT supply, they can be two different things, especially where battery technology is concerned.

A.K. Boomer
08-07-2014, 05:41 PM
this topic kinda hits home, iv ran into a little "confusion" waking up in the morning before I have my coffee and shorting out my electric razor,,,

it's a remington and I also have norelco beard trimmer, but the two plugs are almost identical, there is a huge voltage difference and yet also their polarity is reversed, http://i146.photobucket.com/albums/r249/AK_Boomer/DSC03284_zps7d1525f9.jpg (http://s146.photobucket.com/user/AK_Boomer/media/DSC03284_zps7d1525f9.jpg.html)

http://i146.photobucket.com/albums/r249/AK_Boomer/DSC03283_zpsab4b00e7.jpg (http://s146.photobucket.com/user/AK_Boomer/media/DSC03283_zpsab4b00e7.jpg.html)

here's the thing - the norelco's plug fits into the remingtons receptacle like it's a glove...

http://i146.photobucket.com/albums/r249/AK_Boomer/DSC03285_zps3d6235b2.jpg (http://s146.photobucket.com/user/AK_Boomer/media/DSC03285_zps3d6235b2.jpg.html)

here's the other thing - and this is not a one time fluke as it's happened many a time, when my razor is running low and is on the last red increment ( there's about a half a dozen greens above it before it gets down to red) I then grab one of the two plug ins coming out of the wall socket, if not careful I forget and grab the wrong one, the split second I try to plug it into the remington hear a strange sound, disconnect and then see I grabbed the wrong plug, but get this, the remington now has what appears to be a full charge - all the lit up greens are telling me that, and,,,,,,,, the shaver acts like it, it will act like it just got a full charge within a split second of reverse polarity, and will behave as such... go figure,

overunity ??? :p

08-07-2014, 06:14 PM
overunity ??? :p Overload! :p

The Artful Bodger
08-07-2014, 08:26 PM
A.K. Boomer, you should not be shaving. It is just a waste of time amounting to more than a week over your entire life. Be a man.

08-07-2014, 08:40 PM
If it is a usb connection you can plug either device into either charger. The tablet looks for something on the data lines that tell it that a high capacity charger is attached and will charge at a high rate. if it does not see anything on the data lines it will charge at USB default of 500ma. If you plug the phone into the tablet charger it will just charge at it's standard high charge rate limited by the charging chip in get phone.

08-07-2014, 08:44 PM
If his phone is a smart phone, it should be fine although it will be charging the battery at twice the rate it is designed for, which will shorten its life somewhat. If it's a dumb phone, most likely it will simply not charge. Mine doesn't (700mA charger normally), just beeps and disconnects. Going the other way, sure you can charge a tablet with a 1000mA wall wart, if it will let you. It'll just be a lot slower. Most likely though it just wont charge - my Nexus 7 won't charge off either a 700 or 1000mA wall wart. It needs a 1.5-2A charger. It's not just charging slowly, it doesn't charge at all.

Although the voltages and plugs are the same, the current supply is designed to match the capacity of the li-ion/ li-po battery inside the device. Standard lithium batteries (high zoot RC ones and power tools excepted) don't like being charged or discharged above 1C (i.e. if it has a 2000mAh battery, don't charge or discharge it above 2000mA), which is why you have 700mA, 1000mA and 2000mA chargers, for 700mAh (dumb phones), 1000mAh (smart phones) and 2000mAh (tablets) batteries. Best to stick with the charger it came with or its equivalent.

08-07-2014, 08:49 PM
If it is a usb connection you can plug either device into either charger. The tablet looks for something on the data lines that tell it that a high capacity charger is attached and will charge at a high rate. if it does not see anything on the data lines it will charge at USB default of 500ma. If you plug the phone into the tablet charger it will just charge at it's standard high charge rate limited by the charging chip in get phone.

my experience suggests that, although that would be the right way for device makers to do it, many of them don't. I've found that iPhones charge much more quickly (not sure 2x, but noticeably faster) on 2A power supplies and the tablets (and bike lights, believe it or not) that I've tried it on aren't interested in anything under 1.5A, plus there's my crappy phone which won't even look at a 2A charger. Given that there's no guarantee that the device maker followed specs, I think it's just wiser to use the right amp charger for the device.

08-08-2014, 12:54 AM
A reply for Boomer and Magpie...

Boomer, when you plug the 12 volt, .4 amp charger into the shaver that is designed for 2.3 volt at .1 amp it is providing a huge power surge. If there is a diode bridge it will allow a .4 amp surge at 12 volts to charge the battery quickly. This will drastically decrease the lifespan of the battery.


The rating of the charger is the max that it will provide if the cell phone or tablet tries to suck that much current from it. An ipad will charge faster on a 2000ma charger than it will on a 1000ma charger, but it will charge from both if it's not running an app that is eating up all the power. The amount of current that is drawn from the charger is dependent on the load that the tablet presents to the charger.


08-08-2014, 06:57 AM
My daughter's tablet, if connected to a normal micro usb connector, will run normal even if it's battery is low but won't charge. For this it needs the original charger that has a dual voltage output (5/18V). When you connect it, I suppose, the tablet "negotiates" the correct voltage and gets it from the charger.
Mini usb plugs have 5 contacts, one with a resistor that informs the device of the available current. I had to build a special cable with a 18Kohm resistor in the plug to be able to charge my Garmin GPS from a 5v 1000mA generic charger. (this is the required current for the device)

J Tiers
08-08-2014, 08:43 AM
The difference between "maintaining" and "charging" from USB is very likely determined by the capacity of the USB.... Some are older and have a much lower current limit. Newer ones seem to have higher limits, ever-increasing as time goes on.... and devices get more power-hungry.

The charger cannot pull more than is available.

As for the charge rate etc vs "capability".... A 120V (or 230V) outlet can run a reasonably powerful machine.... but it can also operate a low power pilot light.... The power draw is determined by the load. A 40W bulb or a 150W bulb plug in the same place, and draw according to their resistance, NOT the capability of the outlet.

Joe Rogers
08-08-2014, 08:43 AM
I have a Nikon digial camera that uses a USB cable to transfer data and charge the battery. If it is plugged into a standard USB socket it won't charge unless you "tell" the camera this is happening. If you plug the cable into the Nikon wall plug charging adapter it charges fine.

Jay Fleming
08-08-2014, 09:06 AM
I think computer USB ports are rated at 500 mA. My guess is the camera either knows it's a data connection and doesn't bother charging or sees the USB power supply as underrated (not sure of charging capacity of camera charger) and deems it insufficient to charge, thus turning off the charging circuit.

A.K. Boomer
08-08-2014, 09:13 AM
A reply for Boomer and Magpie...

Boomer, when you plug the 12 volt, .4 amp charger into the shaver that is designed for 2.3 volt at .1 amp it is providing a huge power surge. If there is a diode bridge it will allow a .4 amp surge at 12 volts to charge the battery quickly. This will drastically decrease the lifespan of the battery.


Dan --- that's what's weird - the shaver is the 12 volt,,, this is something that does not make any sense at all to me and yet it's happened quite a few times...

im plugging the beard trimmer's 2.3 volt charger into the shavers 12 volt receptacle, so not only is it way lower voltage - the polarity is also reversed,,, the charge led's on the shaver then totally freak out for a split second then all the sudden settle way higher off the last red increment that it was displaying a split second before,,, about half way charged, the shaver then acts normal and lasts for days and the green increment scale gradually goes down to the red again before it gets too low and needs another charge... I never repeated the process twice in a row to see what would happen as I was just glad I did not blow up my shaver.

I have no explanation except maybe it "shocks" the battery and does something to it to get more residual power that it was holding in it, or maybe there's a reserve cap that it triggers or something... ?

A.K. Boomer
08-08-2014, 10:06 AM
In the name of electronics science I have an update, went to shave this morning and as luck would have it the shaver needed a charge - it was on the last increment which is red,

you know how I stated the norelco plug fit's like a glove? it doesn't -- but it does connect, if you look at the pics of the plugs it's the one with the connectors right at the edge of the plugs end,,,

so - I did this AFTER drinking my morning coffee and took notes, the norelco plug actually connects in both directions I think due to the leads almost hanging out of the end of it,,, but it will not physically go in fully either way, nothing seems to happen in the normal direction with the center groove cut out on one side aligned with the male piece in the shaver (which would put the polarity in reverse)

yet when I went to put it in the opposite direction the led's on the shaver all lit up, this was just a split second,,,

I then quickly disconnected and there it is plain as day the shaver it not half charged - it's instantly fully charged.

this is a 2.3v 100ma charger being hooked up to the 12v 400ma shaver and it is in the correct polarity as the plugs are reversed yet I was hooking it up backwards so the polarity is the same...

go figure,,,

then I plug the remingtons charger into the remingtons shaver and it shows full charge but the last green increment is blinking - which means almost fully charged...

Edit; I stated I heard a strange sound in my first post but did not hear anything this time,,, I may have equated the visual of the lights doing different things and remembered it differently - it was going off of memory of being half awake,,,

this time it's different as I was fully awake and took notes... does anyone have an explanation?

Jay Fleming
08-08-2014, 12:09 PM
I'm not intimately familiar with appliance chargers but I think I may understand what is happening. First, would it be possible to take two small wires strands (thin paperclips would be ideal but may be too thick) and stick these in the charger when it is connected to the shaver. Use a multimeter to check the output voltage. Also check the voltage with the charger disconnected from the shaver. All electrical generating devices have a higher open circuit voltage than the nominal output voltage. Imagine an auto battery charger running but disconnected from a battery. It will probably put out 14 volts. Connect it to the battery and the indicated voltage drops. Depending on the circuit inside the 2.3V charger, the OCV could be 12 volts. This charger may depend more on the appropriate shaver's charging circuit to regulate the inrush so the OCV doesn't damage the shaver. The 12V shaver probably has a lower impedance thus allowing the 2.3V charger to deliver the OCV for some amount of time longer than it would with the 2.3V shaver. I know this doesn't explain what the 2.3V charger does differently than the 12V charger, but it may be a start.

If I'm completely blowing smoke, someone please correct me.

08-08-2014, 01:14 PM
I quit shaving about 11 years ago, just trim once a month and life has been much better since.

Boomer, paint the end of one cord, and the socket on the matching device.