Solved Charger query

Not Windows 11 related but I hope experts on here can help. I am ignorant regarding how electric devices draw power from chargers and I don’t want to damage my devices hence my query.

We have two smartphones. A Xiaomi model with a charger (22.5W maximum) and a Motorola with a charger (68.2W maximum). Both chargers and phones have USB-C 2.0 connection.

To save space and reduce cable clutter I was hoping to use only the Motorola charger for both phones in the hope that the device will only draw charge at a rate that it demands instead of the charger pushing more charge than the phone can take.

I see that charger output has several V x A output ‘modes’ as shown on photos. The Xiaomi charger has four modes and the Motorola charger has 5 modes but the two chargers only have the 5V 3A output mode in common.

Xiaomi charger supports wattage outputs of 5V 3A ¦ 9V 2.3A ¦ 12V 1.67A ¦ 10V 2.25A so maximum output is 22.5W

Motorola charger supports wattage outputs of 5V 3A ¦ 9V 3.0A ¦ 15V 3.0A ¦ 20V 3.4A ¦ 11V 6.2A so maximum output is 68.2W.

Question 1: Does this mean I can safely use the Motorola charger with the Xiaomi phone and it will auto-select the 5V 3A (15W) mode as the only compatible option?

Question 2: If the answer is ‘Yes’ then am I right that the only downside of a 15W output is a slower charge than using the 20W Xiaomi charger could deliver?

If it is not safe to do this then I am able to keep both chargers. It is just a preference if I could manage with just one charger for both phones.

As far as I have been reading about those chargers, they are developed according 'new' standards for USB-C, called USB-PD (Power Delivery).

They use the normal 5V output to feed the connected device and then communicate over USB-C connection for other voltages.
That would mean, that the charger never can overload the connected device.

You can learn a lot about it, when you search with your favorite search engine for: USB-PD standard.

And by the way: if you connect a charger that has 5 Volts, it will deliver the current the connected device needs. A device consuming (example) max. 0,5 A never can be overloaded by a charger that can deliver 3 A. That already was so with 'dumn' chargers and stays so with these more sophisticated chargers. The amperage is only indicating the maximum current the charger can deliver, if the device takes less it will not force a higher current to flow.

Edit: So this would mean you can use both chargers for both devices, just as you wish. The voltage will be chosen by USB communication between charger and device. The current that will flow will depend on the characteristics of the connected device. So the charging speed will not be predictable without knowing what the device does under what circumstances. But a charger that can deliver more Watts will be able to charge faster, if the device is able to use that extra power.

Kees said:

Edit: So this would mean you can use both chargers for both devices, just as you wish.

Click to expand...

Thank you. Now that you have pointed it out I remember that some smartphones (Examples: Samsung Galaxy and Google Pixel phones) no longer come with chargers and you are free to use your own charger as long as it is the correct USB connection.

Your post and remembering about this modern practice assures me that it is okay to use one charger for both phones. It will be less cable tangle and clutter for me to look at.

I'll call this 'Solved'.

There are some different standards, but for the most part phones and laptops using USB-C use the PD (Power Delivery) standard as was noted previously. PD is a protocol whereby the phone and charger actually negotiate an acceptable voltage for use with the device.

Having more capacity will not hurt. It simply means that your charger can delivery more power than your device needs, but the device will not draw power than it needs. The only real reasons to go with a lower capacity charger are:

1) They generally cost less.
2) They are often smaller in size.

As an example, I have 3 laptops. one of them wants 100W of power, one only needs 65W, and yet another only needs 45W. I also have a Samsung smart phone which draws less than that (not sure of the exact rating on the phone). I have a 100W charger and it will work with any of those devices flawlessly.

There is one practical reason for enabling a higher voltage:
If a 100 Watt USB charger would deliver that power at 5 Volt, it would mean that the cable and the USB-connector has to withstand a current of 20 A (Ohm's law). And that while the cable and the contact are rather thin.

By raising the maximum voltage, the current will be much less. At 20 V it would be 5 A, which is much more acceptable.

Kees said:

There is one practical reason for enabling a higher voltage:
If a 100 Watt USB charger would deliver that power at 5 Volt, it would mean that the cable and the USB-connector has to withstand a current of 20 A (Ohm's law). And that while the cable and the contact are rather thin.

By raising the maximum voltage, the current will be much less. At 20 V it would be 5 A, which is much more acceptable.

Click to expand...

That is true, however the point about having a higher wattage rating than necessary still stands, namely that it will work even with a device that requires a lower wattage output.

However, while we are on the topic - what you bring up here is exactly how PD 3.1 works. PD 3.1 raises the maximum amount of power that a USB-C cable can carry from 100W to 240W. A USB-C cable is limited to 5 Amps of current. To go any higher would require a thicker cable and there simply is no room for that with a tiny USB-C connector. Since the highest voltage supplied by PD 3.0 is 20V and since power in Watts is equal to voltage x current (in Amps), 20V x 5A = 100W maximum power. To work around this, the new PD 3.1 standard adds several more voltages, topping out at 48V. Since the maximum current is still 5A, 48V x 5A = 240W. Note that for anything above a 100W, a special PD 3.1 capable cable is needed, and as with PD 3.0, some cables will limit the max current to less than 5A. As an example, 120W cables are common.

In fact, this concept of increasing the voltage to carry more power is exactly how electrical transmission lines work. Here in the United States, the voltage over transmission lines is typically 345,000V. That's how they can carry so much power over what is still a relatively thin cable.

hsehestedt said:

That is true, however the point about having a higher wattage rating than necessary still stands, namely that it will work even with a device that requires a lower wattage output.

However, while we are on the topic - what you bring up here is exactly how PD 3.1 works. PD 3.1 raises the maximum amount of power that a USB-C cable can carry from 100W to 240W. A USB-C cable is limited to 5 Amps of current. To go any higher would require a thicker cable and there simply is no room for that with a tiny USB-C connector. Since the highest voltage supplied by PD 3.0 is 20V and since power in Watts is equal to voltage x current (in Amps), 20V x 5A = 100W maximum power. To work around this, the new PD 3.1 standard adds several more voltages, topping out at 48V. Since the maximum current is still 5A, 48V x 5A = 240W. Note that for anything above a 100W, a special PD 3.1 capable cable is needed, and as with PD 3.0, some cables will limit the max current to less than 5A. As an example, 120W cables are common.

In fact, this concept of increasing the voltage to carry more power is exactly how electrical transmission lines work. Here in the United States, the voltage over transmission lines is typically 345,000V. That's how they can carry so much power over what is still a relatively thin cable.

Click to expand...

In simple terms (this is a simplification but close enough to understand principle)


Power = current x volts

Power loss equals current squared x resistance

Reduce the current, reduce power loss.

That is why transmission lines operate at high voltage, low current.

However, the power company needs a network of transformers to convert the high voltage & low current to low voltage & high current

When it comes to mobile power supplies (which are transformers), they use even lower voltages, so power loss is proportionally higher.

In general, thin lines have a higher resistance than thick.

Power loss is basically dissipated as heat.

I had 12 volt lighting in one house (already installed) and according to advertising this is much safer as you cannot be electrocuted.

However, the power loss is high (see above equations), so costing more in electricity and the consequence is these run extremely hot to the point, the plastic electrical connectors used to melt. There is also a hugely increased risk of fire.

The hot temperatures were exacerbated by loft insulation preventing the heat dissipating.

I went into the loft and cut holes in the insulation over each light and used a pringles tube to create a small chimney to help heat dissipate.

After that I had no problems with heat.

The crucial point is power supplies can run warm and poorer designs can overheat.

So ventilation is important in where you put power supplies.

I no longer use power supplies but I use conventional extension sockets with usb ports. These never run hot, and you can usually connect 2-4 devices.

These (imo) are the best way to reduce clutter and is safer than conventional chargers.

Most new houses come with dual usb/mains power sockets nowadays to avoid extension leads.

cereberus said:

I no longer use power supplies but I use conventional extension sockets with usb ports.

Click to expand...

Good point. Very interesting. I will look into replacing my current (pun) extension socket for one with USB ports. It will reduce clutter and look neater due to not having a charger block plugged-in.

wiganken said:

Good point. Very interesting. I will look into replacing my current (pun) extension socket for one with USB ports. It will reduce clutter and look neater due to not having a charger block plugged-in.

Click to expand...

and safer.

cereberus said:

and safer.

Click to expand...

I ordered one with both USB-A and USB-C ports. Thanks for the pointer.

wiganken said:

I ordered one with both USB-A and USB-C ports.

Click to expand...

For most applications these multi-port USB units are fine. Where they are not so great is for anything without a battery backup. The reason for this is that they periodically reshuffle how much power is allocated to any one given port especially when you plug in another device into one of the other ports. That operation causes power to be lost to the device.

As an example, if you are charging a laptop, tablet, or phone, no problem. For the brief second or two that those devices lose power from the charger they simply switch to their internal battery and the user will likely never even realize that anything happened. However, let's say that you are powering some other kind of device like a Mini PC that has no battery backup. That brief disruption in power causes the Mini PC to crash.

In fact, in a lot of chargers (Anker is especially bad with this), even if you plug in no other device, it will drop the power momentarily to the single device plugged into it after one minute. So, again using the example of a Mini PC, you turn it on, it boots, after one minute it crashes.

The solution in those cases is to use a USB-C power supply that has only a single output.

hsehestedt said:

The solution in those cases is to use a USB-C power supply that has only a single output

Click to expand...

Thanks. In my case only the USB-C port will be used. We do not have multiple devices. Just two smartphones and only one will be on charge at any one time so I think we should be okay.