Hi all

I have a little project going at the moment and i am mystified by a reading i am seeing. I have a 43 inch LCD monitor, originally powered by an AC to DC converter box. There are 2 PSU's inside the box, one to power the backlights at 24v, the other to power the AD Board at 12v.

My goal is to run this monitor in remote locations off a lithium battery pack. To get an idea of the sort of battery capacity i would need i measured the current draw whilst using the AC/DC inverter box. This is a high brightness display (2500 nits) so don't be alarmed by the results.

That said, from the AC/DC output on the 24v line, the current draw was 8.68 amps. The 12v line pulled 0.74 amps. Which was what i expected as the manufacturer of the panel stated it required roughly 225 watts of power.

This is where it gets confusing. As the circuit boards in all monitors are DC, i decided to create my own PSU that i connect to the 24v lithium battery. To keep a stable voltage (due to the varied states of charge of the battery) for the LCD panel, i have 2 buck converters (manufactured by Drok). One for the 24v line, and one for the 12v line. The 12v line is pulling around 0.7 amps, however, the 24v line that powers the backlight is now only pulling 2.08 amps???

Can anyone explain the difference? I understand there is some loss in efficiency on the AC/DC inverter, roughly 12% to produce 24v, for information purposes, the AC/DC inverter provided is a Meanwell LRS-350-24, but my results are massively different! There is no noticeable difference in brightness on the panel, i checked this just incase the Drok DC/DC converter, even though rated at 10 amps was faulty.

Don't get me wrong, i am happy with the result, i just wondered if anyone could give an explanation??

Many thanks in advance

John

 

Not offhand.
Are all the current measurements for the current into the TV?
If it seems to work okay, then I wouldn't sweat it.

 

Yes, all the current measurements were from the output. So DC side of the AC/DC inverter, so the DC current draw to the TV circuitry and on the DC/DC setup, the output side again.

Like i said, i'm happy with the result as it means i don't need a battery with anything near the capacity i was expecting, i just find it very strange and like anything, there must be a reason?

Thanks for your response