12v DC to 110v power inverter doing the impossible?

realflow100

Joined Apr 17, 2016
16
Ok so I have a power supply at 12v 2A (with safety overcurrent cut-off) to test a car inverter

the strange thing is. I have a monitor/pc screen that takes 163w of power to run
and at 12v 2A theres no way to get 163w of power.
yet the monitor turns on just fine! i'm so confused how its possible the inverter has over 100% efficiency or something?
It was a cheap 300w 23$inverter off amazon for use in emergencies if the power goes out. yet it somehow steps up 2A 12v 20W to over 160w 110v? The weird thing is it's incapable of lighting a 20w fluorescent bulb (power supply cuts out from over-current protection.) I dont know how its able to run a 100W+ monitor yet not run a 20w bulb. I just don't get it. it doesnt look possible but somehow its capable of doing so. tcmtech Joined Nov 4, 2013 2,867 Pictures and links to the exact devices being used so we can see their specs would be helpful. ronv Joined Nov 12, 2008 3,770 Ok so I have a power supply at 12v 2A (with safety overcurrent cut-off) to test a car inverter the strange thing is. I have a monitor/pc screen that takes 163w of power to run and at 12v 2A theres no way to get 163w of power. yet the monitor turns on just fine! i'm so confused how its possible the inverter has over 100% efficiency or something? It was a cheap 300w 23$ inverter off amazon for use in emergencies if the power goes out. yet it somehow steps up 2A 12v 20W to over 160w 110v?

The weird thing is it's incapable of lighting a 20w fluorescent bulb (power supply cuts out from over-current protection.)
I dont know how its able to run a 100W+ monitor yet not run a 20w bulb.
I just don't get it. it doesnt look possible but somehow its capable of doing so.
163 watts is a lot for a monitor. Maybe 16.3???

BR-549

Joined Sep 22, 2013
4,938
Wow, the price of inverters is coming down. And a lot are advertised as true sine.

realflow100

Joined Apr 17, 2016
16
the back of the monitor lists 100-240v 1.6A 163W on the label.
also tested with a different LCD monitor that runs from a 19v laptop-type PSU rather than wall plug. and it also works.

also when i went to plug in a usb charger cord to a usb port on the inverter i heard a loud pop after 2 seconds and now the usb port is dead

it still has 3.4v but only supplies a max of 5-10mA!? its supposed to be 5v 2.4A
I checked on the circuit board but couldn't find any burnt out components near the usb port. (There was an enormous inductor toroid near it but it was fine.)

The wall plugs at least still work... it sucks that the usb charging ports died from some kind of defect. guess i have to get a power strip and put some kind of usb charging adapter on it.

BR-549

Joined Sep 22, 2013
4,938
Can you measure the AC current going to the monitor?

tsan

Joined Sep 6, 2014
116
If you have a multimeter you can measure dc current while supplying the monitor. Then it is easy to calculate power consumption.

Dodgydave

Joined Jun 22, 2012
10,088
Measure the current input and output, then you will know what's going on.

realflow100

Joined Apr 17, 2016
16
Where would I measure the current output? at the wall outlet of the inverter or at the 12v power supply going to the inverter?

tcmtech

Joined Nov 4, 2013
2,867
Both.

Dr.killjoy

Joined Apr 28, 2013
1,196
I have to agree with Ronv here with something miss read cause my big flat screen are only 160w-200w depending on the model and your talking about the same power for a screen 1/6 th the size..

tcmtech

Joined Nov 4, 2013
2,867
See post 2 again.

realflow100

Joined Apr 17, 2016
16
It's a 1440x900 dell E1709Wc screen with 100-240v 1.6A on the back label of it.
but also works with a 1920x1080 17" Acer LED tv that im currently using.

I'm confused how 20w can translate to even more than 20w on the output?? it should actually be limited to lower than 20w even because of losses in the inverter and wires themselves.

The inverter is an SNAN 300w car power inverter
The test power supply is an enercell 3-12v power supply rated 2 amps maximum. with safety overcurrent protection (cuts off if anything draws over 2A)

Last edited:

BR-549

Joined Sep 22, 2013
4,938
You got two choices.

You can keep telling everyone that you have a new power source..............

OR you can take some measurements.

You decide.

realflow100

Joined Apr 17, 2016
16
I read on the website the monitor takes 25w power running.
but the power supply is actually 11.5v on the output checked with a multimeter. with a very sharp 2A current cut-off (test with a DC motor and slowing it down while testing current. and the instant it got past 1.9A it cut off.)
so it gives out even less than 25W maximum.

tcmtech

Joined Nov 4, 2013
2,867
The 1.6 Amps is its maximum draw not it's continuous which means that if the backlighting is turned down (primary power user on flatscreens) the actual running wattage could be well under 20 watts.

If you really are putting out more wattage than you are putting in you should be able to run the system off of 12 volt battery to get things running and then have the power supply plugged into the inverters output and have that feedback to the battery and inverters input and see the battery voltage start going up rather than down or be able to remove the battery altogether.

If you can't do that then obviously you're not putting out more power than you are putting in.

BobaMosfet

Joined Jul 1, 2009
1,898
Ok so I have a power supply at 12v 2A (with safety overcurrent cut-off) to test a car inverter

the strange thing is. I have a monitor/pc screen that takes 163w of power to run
and at 12v 2A theres no way to get 163w of power.
yet the monitor turns on just fine! i'm so confused how its possible the inverter has over 100% efficiency or something?
It was a cheap 300w 23\$ inverter off amazon for use in emergencies if the power goes out. yet it somehow steps up 2A 12v 20W to over 160w 110v?

The weird thing is it's incapable of lighting a 20w fluorescent bulb (power supply cuts out from over-current protection.)
I dont know how its able to run a 100W+ monitor yet not run a 20w bulb.
I just don't get it. it doesnt look possible but somehow its capable of doing so.
Don't confuse power ratings with actual power consumption. A sticker has a rating. No monitor that you describe actually requires 100-240VAC potential-- it regulates that down to a much much lower voltage. Your supply is providing more than the maximum current draw that the monitor claims it can draw (depending on what it's doing) and apparently your supply is providing enough voltage to satisfy regulation in the monitor itself.

Until you actually determine the current draw and the voltage potential being used by the monitor, you cannot know exactly what it's doing, other than it is able to manage it.