Question I found a 1933W monitor next to a trash bin

[adrianlicok]

It was without a power supply, and this monitor required an external power adapter. On the back of the monitor I read that it needs a 12-volt power supply. I don’t know much about watts and amps, so I looked for a power adapter for it in boxes that I had previously found in the trash, and I found a 12-volt cube-type power adapter HKA-12100EC-230.

When I connected this monitor to the computer, after a few or several seconds the image would turn off, but the LED on the monitor showed that the monitor was still on. When I turned the monitor off using the button on the monitor and then turned it on again, the monitor would turn on for a few or several seconds and then the image would turn off again, while the LED still indicated that the monitor was on. This happened at every resolution. I was already about to throw the monitor back into the trash, but then I thought that external power supplies for monitors and laptops are usually larger than these small cube-type ones and are elongated. So I decided to look for such a power adapter in the box. I searched and checked so that the adapter would be 12-volt and elongated instead of cube-type, and that the plug would fit the monitor, and I found this power adapter:


SAD04212 UV-36. I connected this power adapter to the monitor and the computer, and the image has been displayed correctly for many hours. Apparently it’s not without reason that elongated power adapters are supplied with laptops and monitors instead of cube-type ones.

Why don’t all monitors have internal power supplies installed, so that I only need to connect a cable from the wall outlet, but instead the current has to be reduced—in this case to 12 volts? When two power supplies are both 12-volt, but one is cube-type and the other is elongated, what current parameters differ in the power coming out of these adapters when they are plugged into the wall outlet? What would happen if someone made a mistake and connected an elongated power adapter to a device that requires a cube-type adapter, for example an electric shaver, but with the same voltage as the original cube-type adapter—could the device burn out even if the voltage matched, but because of different current parameters?

This monitor has the buttons ripped out:

I have to touch the metal contacts in place of these buttons with a metal screwdriver, and the monitor reacts as if I were pressing the buttons. There are also two scratches at the top of the screen.

 

[marokra]

I hope 1933W is a model number and not the power requirement!

Why don't all monitors have internal PSUs? Cost. It's way cheaper to make a monitor with a barrel jack than an integrated power supply (and all the shielding that requires), and source a dirt power brick for pennies from some high volume whitelabel manufacturer.

I don’t know much about watts and amps

Let me give you an analogy: Think of water flowing through a pipe. You have the pump generating pressure, cand causing the water to move (volts). You have the diameter of the pipe, which determines how much water can fit in the pipe (amps). Together they result in the flow rate, say meter/s (watts). If you run your pump for an hour, you can take the flow rate and multiply it with the time to get the absolute volume of water (watt hour). If you replace one segment of pipe with a narrower pipe, i.e. bring resistance into the system (ohm), you need to increase the pressure to maintain the same flow rate, i.e. higher volts to achieve the same watts.

The key thing to understand with electricity is that anything that can conduct electricity offers some resistance. That causes the conductor to generate heat. If it's too thin for the, i.e. very low thermal mass, it can't spread that heat through enough metal, and doesn't have enough surface to conduct that heat away. It gets hot, melts the insulation, shorts and burns down your house. So more amps require thicker cable. This is why the battery terminals in your car a big chunky units. They have to handle 1000-2000W at 12V to turn the engine (big old resistor, that one). And if it wasn't just used for a few seconds at a time, they'd be thicker.
Another place where you can see this principle in action is EV chargers. Big fat cable you have to plug in. On some of the faster chargers, the cable has its own liquid cooling sheath, because otherwise the cable itself would have to be much thicker (and thus much heavier). That's why we're (painfully slowly) moving from 400V to 800V, and why the Chinese are going straight to 1000V.

So to come back to my quip about 1933W being the power requirement - that would imply 161A at 12V - the cable would look like your car battery terminals.

If you google image search "volt amp watt" you'll see more analogies that help understand how they interact.

Hope this helps!

 

[TheELF]

Let me give you an analogy: Think of water flowing through a pipe. You have the pump generating pressure, cand causing the water to move (volts). You have the diameter of the pipe, which determines how much water can fit in the pipe (amps). Together they result in the flow rate, say meter/s (watts). If you run your pump for an hour, you can take the flow rate and multiply it with the time to get the absolute volume of water (watt hour). If you replace one segment of pipe with a narrower pipe, i.e. bring resistance into the system (ohm), you need to increase the pressure to maintain the same flow rate, i.e. higher volts to achieve the same watts.

The key thing to understand with electricity is that anything that can conduct electricity offers some resistance. That causes the conductor to generate heat. If it's too thin for the, i.e. very low thermal mass, it can't spread that heat through enough metal, and doesn't have enough surface to conduct that heat away. It gets hot, melts the insulation, shorts and burns down your house. So more amps require thicker cable. This is why the battery terminals in your car a big chunky units. They have to handle 1000-2000W at 12V to turn the engine (big old resistor, that one). And if it wasn't just used for a few seconds at a time, they'd be thicker.
Another place where you can see this principle in action is EV chargers. Big fat cable you have to plug in. On some of the faster chargers, the cable has its own liquid cooling sheath, because otherwise the cable itself would have to be much thicker (and thus much heavier). That's why we're (painfully slowly) moving from 400V to 800V, and why the Chinese are going straight to 1000V.

So to come back to my quip about 1933W being the power requirement - that would imply 161A at 12V - the cable would look like your car battery terminals.

If you google image search "volt amp watt" you'll see more analogies that help understand how they interact.

Hope this helps!

TL;DR
......
Match the polarity, that's the most important part.
If the brick is higher amps (elongated) then it will work on whatever device, the device will only draw as much as it needs so a low power device will be fine.
If the brick is lower amps (small) then it will do what you saw, it will not power a higher power device at all or it will shut down very fast.