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Years ago, at my previous job, my boss came into the office and asked a group of us if we had a spare cellphone charger. As everyone scrambled to help the boss out by offering their own cellphone charger, I pondered for a moment how odd it was that no one was bothering to ask him what model of phone he was using.

I was deep in the middle of a project, so didn’t pay too much attention to what was going on, but I do recall seeing my boss take the charger that one guy handed to him, compare the connector with the port on his phone, and satisfied, took the charger into his office.

About ten minutes later, the boss came back into our office area and sheepishly informed us that the charger had completely fried his phone. “I forgot to check the voltage of the charger” was his explanation.

Up until a few years ago, the mish-mosh of assorted chargers and connectors led to this problem more often than people realize. The general assumption by many people was that if the connector fit perfectly into the phone’s power jack, then it should be sufficient to charge the phone. This wasn’t the case at all. In the best of cases, the charger simply wouldn’t do anything. In the worst, it would fry the phone’s circuits and damage it permanently.

Thanks to the advent of USB, that all changed. However, there are still some important things you should keep in mind when you’re looking for a quick, temporary charger to get your phone or tablet’s battery charge back up.

Not All Chargers Are Created Equal

Here at MakeUseOf, we’ve tried to help out readers with a number of charger issues through the years. Matt provided 5 ways you can charge your phone in an emergency 5 Ways To Charge Your Phone In An Emergency 5 Ways To Charge Your Phone In An Emergency Smartphones can be important tools in an emergency. Besides providing the chance to call for help, a phone can act as a flashlight, compass and GPS. But all of a phone’s functions rely on the... Read More , and he also described how wireless charging works What Is Wireless Charging & How Exactly Does It Work? [MakeUseOf Explains] What Is Wireless Charging & How Exactly Does It Work? [MakeUseOf Explains] We live in a wireless world. Except we don’t. Sure, we can send huge amounts of information across the airwaves, but the devices capable of sending and receiving it are tied down to power cords.... Read More . Christian provided a few tips on how to troubleshoot when your HP TouchPad isn’t charging HP TouchPad Not Charging? Don't Worry, It's Probably Not Bricked! HP TouchPad Not Charging? Don't Worry, It's Probably Not Bricked! The HP TouchPad is a remarkable piece of kit. This tablet computer with its dual core CPU was released with a buggy version of the webOS operating system back in mid-2011 and failed to capture... Read More . There are a lot of times when it would be good to understand just exactly how charging actually works.


So, just as a quick exercise, let’s do a quick test. Go around your house and collect as many of those newer style USB chargers that you might have. Some might be some form of mini-USB, or you might have those USB chargers for your tablet. Maybe you have a few of those “smart chargers” that you can disconnect the cord from and insert other USB cords into it. Gather those all up and then bring them back here.

Now, before I have you look at the actual numbers on these things, I’m going to describe what we’re looking at. Years ago, there was a much larger variety of chargers that went along with Nokia, Motorola and all other brands of phones. Everyone had their own proprietary connector that you had to purchase special if you ever wanted to replace it. Hopefully, you had a phone that was common enough that you could find the charger in a regular big-box store.

charge multiple gadgets

Each one of these had its own voltage and current rating, based on the phone manufacturer’s specs. USB changed everything, because manufacturers finally standardized on two or three mini-USB jacks, as well as the typical 30 pin tablet heads.

Those newer USB chargers all carry a standard output voltage spec of 5V. This is great, because now no one should be able to plug in a phone with a lower voltage demand and fry the phone, because the phone – if it’s newer – is likely manufactured based on that 5V input voltage.  However, not all is right with the world just yet. Every device has its own special current demands – so the current ratings for many of the manufacturer chargers still varies.

To show why this matters, take a look at the diagram below.

how chargers work

These aren’t your standard electrical symbols. I’ve taken the liberty of creating my own symbols to make visualizing what’s going on a little easier. Picture the “Amps” circle as a sort of a power generator that only works as hard as it has to in order to provide the amount of “energy” that your device needs at any given moment. Picture the “Volts” as a constant waterfall of energy that never changes.  Now, let’s take a look at those chargers you’ve collected.

Take a look at the labels on them and look for the “OUTPUT” section. Log the different numbers you see. Here are three chargers that I collected from around my house:

Samsung – 5 Volts, 0.7 Amps
Motorola – 5.1 Volts, 0.850 Amps
Asus – 5 Volts, 2 Amps

As you can see, with modern chargers, the waterfall never changes, but the capacity of each engine is different. Some chargers can only put out 0.5 amps. Others can put out 2 amps or more.

In the old style chargers where you might accidentally plug a charger rated with a large voltage into a phone with a small voltage requirement, it would be like trying to shove way too much energy through a very small hole.

how chargers work

That mass of energy would blow apart the hole – basically overcharge the circuit and fry it. Now that everything is based on 5V, what’s the problem? Why can’t we now swap around power chargers? Well, if you’ve ever tried plugging in a larger smartphone with a USB charger from a smaller phone, you probably know that the smartphone won’t work if you try to use it while charging. This is because that smaller 0.7 Amp charger just doesn’t have an “Amp” engine powerful enough to provide the energy needed by a 1.2 amp device in full use.

However, you could definitely take the 2 Amp charger for the larger device and use it for a smaller device that only needs 0.7 Amps, because that larger charger has an engine that’s powerful enough to feed all of the needs of that device.

how chargers work

This is the main difference between voltage and current in chargers. When that rating label shows a voltage that’s higher than the phone’s rating, it’s going to provide that voltage no matter what – and you’re going to destroy the device. However, when that rating shows an amperage that higher than the phone’s rating, nothing is going to go wrong. This is because the device “draws out” the amps from the charger that it needs – the charger will not pump the maximum rated amperage into that phone.

So, as long as your tablet charger is rated with the same voltage as your smartphone (these days, that’ll be 5 volts), then go ahead and charge your smartphone with it.

charge multiple gadgets

Keep in mind that the cable matters too. That USB cables that came with your phone may plug into your tablet’s interchangeable charger, but that USB cable will limit the current to between 1 and 1.5 amps.  Meaning – if you try to use your phone’s USB cable to charge your tablet or large smartphone, it may not work. Especially if you’re doing something with the smartphone that forces it to require a greater current draw.

Another mistake people make – assuming anything can be plugged into the computer USB port and charge. The reality is that a standard USB on a laptop is approximately 0.5 amps max. So, many devices will actually use up the same (or more) charge than the USB port can supply, never charging the battery at all.

The world of electric power can be a little complicated. The relationship between current and voltage isn’t always obvious, and sometimes people get tripped up when using certain chargers that have no business being plugged into those larger electronic devices. Hopefully this explanation provided you with a better understanding of what to look for when you’re trying to match up that charger with a device, or at least now you have a way to try and troubleshoot problems.

Have you ever had any odd charger issues? Every fry a device by plugging in charger that was too large? Share your thoughts and experiences in the comments section below!

Image Credits: Burning Cellphone Via Shutterstock, Power Up Via Shutterstock, Smart Phone Via Shutterstock

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