transformer for wall charger, not required?

[DNSB]

Originally Posted by Lynx-lynx

Okay, I'm going to go around this question another way, why is a transformer required?

Compared to say the complexity of a current model mobile phone or tablet, which doesn't require a wall transformer (well Android in any event), why does a rather simple (in comparison) ebook reader?

Are you saying you have an Android mobile phone that you plug directly to an AC outlet to charge? Or are you talking about needing a stepdown transformer to convert the local mains voltage to a voltage the charger will handle? Looking at the wall wart you posted a picture of, you will notice that it will handle 100V-240V 50/60Hz AC input and outputs 5V, 1.0A which will charge most USB connected devices.

[Semwize]

Originally Posted by DNSB

Are you saying you have an Android mobile phone that you plug directly to an AC outlet to charge? I look at the latest Android devices I've handled and they either need a USB port with appropriate cable or a wireless charger.

USB ports have been built into wall sockets for a long time. Something like this, but it's quite primitive...

[DNSB]

Originally Posted by Semwize

USB ports have been built into wall sockets for a long time. Something like this, but it's quite primitive...

Plugging into one of the USB ports on the outlet panel is not quite the same as feeding 100-240V 50/60Hz directly into the trusting guts of your device.

I must admit your definition of a long time and mine are slightly different. The first one I installed was in 2014. That one is long gone and I'm looking at updating a couple of the existing ones to USB-C.

[Semwize]

Originally Posted by DNSB

The first one I installed was in 2014. That one is long gone and I'm looking at updating a couple of the existing ones to USB-C.

This is a variant of just 2012 somewhere)) Maybe a little later. Now need to put something like this:

[Lynx-lynx]

Okay, here are the photos of 2 Samsung wall chargers I use. From what has been said in this thread it will be no problem to charge my forma using these, or similar.

[davidfor]

Originally Posted by Lynx-lynx

Okay, here are the photos of 2 Samsung wall chargers I use. From what has been said in this thread it will be no problem to charge my forma using these, or similar.

No, there will be absolutely no problem using them or anything similar.

[frostschutz]

According to the label on my Kobo Libra 2, it supports 5V DC - 2.0A. This label is printed on the bottom (charging port side) of the device. On my Aura H2O it says 5V - 0.8A. So it seems like the Libra 2 might be able to charge faster than the Aura H2O, but I haven't tested it.

If you want to make extra sure, use a wall charger that meets these exact specifications... 5V output only (no other voltage level) with up to 2A.

That said even if you use a charger that supports other voltages (like the one in your picture that supports both 5V and 9V output) there is a charging protocol involved so the 9V level (which would like as not fry the Kobo) should be inactive.

As long as it's USB(-C) it's supposed to be safe to use. But there have been cases where this didn't work out, like 3rd party chargers/docks frying the Nintendo Switch due to not switching voltages properly.

[Lynx-lynx]

Okay, that's on the side of my forma. First time I've looked for it, and first time I've noticed it.

Thank you @frostschutz for pointing out to me something I should have taken notice of, and for some reason it didn't dawn on me, lol.

[Lynx-lynx]

Originally Posted by davidfor

No, there will be absolutely no problem using them or anything similar.

Thanks David, I'm aware that both of those plugs provide for variable charging according to the device being charged eg phone is different to ear buds is different to tablet etc
So I feel more confident now in plugging in my forma

[kacir]

Originally Posted by Lynx-lynx

Are the transformers still required for wall charging?

What do you mean by that question?

To charge a reader or a phone or any piece of small electronics nowadays you usually require 5V Direct Current, usually written 5V DC.
Socket on the wall has Alternating Current AC, usually 230V or 110V nowadays.

In the "Goode Olde Dayes" you needed a transformer, a rectifier (four diodes) and a capacitor to smooth the current out. In a typical transformer, running of the mains with 50 or 60Hz frequency you had to have a number of windings in a primary and secondary coil in the same ratio as the input output voltage. Sometimes you had transformers that had a switch attached that allowed you to select output voltage by engaging additional windings in secondary. Sometimes you had a switch between 110 and 230V that would select two different primary windings. (220V would use the whole primary, 110V position would use just half the windings).

Nowadays, we have switching supplies. They contain a transformer too, but the transformer is much smaller and we do not switch between different number of windings to select (or regulate) output voltage. The primary of that transformer is fed by electronics that rectifies and smoothes the input voltage and then feeds a high-frequency pulses. The output of the transformer is measured and the feedback is used by that switching circuit to make the pulses that feed the primary wider of narrower. The result is that the modern power supplies are much, much lighter and can produce exact 5V (or any other arbitrary value) even with widely changing input. That is why you need just a simple wall socket interface and the power source for your mobile phone of a reader or a notebook can work with any mains voltage and frequency in the world. The transformer inside can be much, much smaller (reducing the amount of iron for core and amount of ever-more-expensive copper). You can see the difference best with the new "inverter" welders. Old ones were difficult to lift by a strong man, new ones are unbelievably light. The transformer can be smaller, because it works on much higher frequency.