Author Options:

Mains supply to wireless charger UK Answered

Hello everyone.

Hobbyist here. I had the idea of building a desk lamp with wireless charging in the base. The led light comes from the mains supply. I wanted to split the power into two feeds. One for the light and the other for the wireless charging base. I was going to put a resistor in between the charger and the wireless base to bring it down to 5v.

My question is - Does what i want to do sound right? I am still at the researching and planning part, so was hoping to get some advice from somebody more knowledgable than myself.

Thanks in advance for taking the time to help me out. I really appreciate it


The forums are retiring in 2021 and are now closed for new topics and comments.
Jack A Lopez
Jack A Lopez

11 months ago

I do not think there is anything wrong with the want, the desire, to have a desk lamp with a wireless charging gizmo as a part of it.

However the way, the method you are contemplating for doing it, seems wrong, especially this sentence:

"I was going to put a resistor in between the charger and the wireless base to bring it down to 5v."

Which part is the "charger?" Is that the power converter that supplies power to the LED desk lamp?

Also is the "wireless charging base" expecting, wanting, a 5 volt DC supply of some kind? If so, why not use a 5 volt DC supply, or "charger," or black brick, or "adapter," or whatever word we are using for the converter that changes mains power into the kind of power at lower voltage, usually DC voltage, wanted by some particular device.

I mean, why not use two power adapters? One for the LED lamp. And another for the wireless charger gizmo.

I think the goal in powering multiple devices at once, is essentially, to give each device the kind of power it wants.

If a device wants a constant 5 volts DC, then the way to do that is to come up with something that can supply a constant 5 volts DC, independent of how much current the device wants.

A resistor can give a voltage drop, but it is kind of drop that depends on current, not independent of it.

For example if a resistor R has voltage Vin on one side, and Vout on the other, and current I flowing through it, the equation relating these variables is:

Vout = Vin - I*R

That is something different from:

Vout = constant

By the way, devices that do supply constant voltage, over a wide varying range of current, are said to have "regulated voltage" or "constant voltage." Moreover the art of building such power converters, is complicated enough, that it is almost always easier to buy a mains powered adapter, or DC-to-DC converter, in the case where the power you are using as input, is already DC, like from a battery, or a car's battery, or something like this.


11 months ago

If you mean converting some lamp that uses a mains powered LED bulb then you will fail.
Here is my suggestion:
Get a dedicated LED light that runs off USB power.
Like some small cob light with good brightness.
Add a USB charging circuit with protection - easy and cheap to find in the usual online markets.
These circuits combine what you need in a small pack.
USB input, 3.7V battery connection and a 5V step-up converter for the USB output.
Or if you need a battery anyway go for a cheap USB power bank.
Like that you can use a normal USB charger and cable to power it.