> actually, inverter limited - if I added some 48VDC loads
I know it’s only lighting as a load, but I’ve heard standard LED light bulbs will happily run as low as 36VDC, as they chop the voltage down to that level anyway.
It makes me wonder how many “120VAC” devices with switch mode power supplies could be plugged into 48VDC without any thought at all. And not just electronics like a laptop or non-plasma flatscreen, but everything is moving in this direction:
Like… what’s my Variable Frequency Drive “inverter” refrigerator motor voltage really running at? In theory it should happily run off 120VDC at least. Don’t do that, but somewhere under 110VDC should work fine. And it’s inherently soft start and easier on one’s low voltage wiring than an on/off duty cycle fridge.
Most modern switch mode power supplies will run on DC, but you really, really want to jack the input DC up high unless you're a fan of replacing bridge rectifier diodes and other input wiring.
Active power factor correction circuitry will have a fit, but... eh, whatever. It's DC now, nobody cares!
A 120VRMS AC signal peaks around 170V, and most (not all, but most...) switch mode power supplies are auto ranging, so they'll tolerate from about 100VRMS to about 250VRMS - which is near 400V peak. If you can get 300+VDC into them, they'll be quite happy, but the boost converters to do that are a pain to find, and by the time you build one, you may as well just get a 120VAC inverter and call it good.
The main thing to be concerned about, and the reason to jack the input voltages about as high as you can, is that almost every switch mode power supply has a full bridge rectifier on the input side. From an AC input source, each diode has a 50% duty cycle. Put DC on it, now two diodes are at 100% duty cycle, two are at 0% duty cycle. How much overhead was there in the system? Well... you'll find out! However, a system capable of running and not overloading the diodes at 50% duty cycle at ~100VAC should be totally fine in terms of diode heating at 300VDC - just, perhaps not at 100VDC.
I never considered the diode duty cycles. If nameplate was 120-240VAC (my TV says 120 but the p/s PCB inside says 100-240…) I’d like to think each would have the overhead to handle under 100VDC, but maybe I’m underestimating the impact of higher current. Edit: you’re right that the “hot” ones will run twice as hot with their 0.6V or whatever drop.
All I could think about was the (potential) improvements on capacitor lifespan since they won’t have to smoothen, but wasn’t sure if their electrolyte could still heat/dry if it was actually the connection to power that makes them hot.
Thinking further, an internal fuse might blow with the (expectedly) larger current draw at 48V.
And yeah on input wiring, you’re pulling more current at 48V.
Welcome to the world of powering AC equipment on DC. It can be done, surprisingly often.
But as soon as you've got some stuff that requires an inverter, you may as well just light the inverter up for everything. I've got the equipment to do a separate, lithium-backed "DC rail" in my office that would be around 40V, and then buck it down for various devices, run my routers direct on it, and... I've never gotten around to doing it, because until literally everything is on that, I'd still have to run the inverter for things like system sleep (I sleep most of my computers overnight). I'm fiddling watts around and it's just not worth it unless I can actually shut the inverter down entirely. Unfortunately, boosting up to 300VDC isn't cheap or easy.
I've wondered if you could run some of that stuff straight off solar during good sun, but I've never really wanted to subject my computers to that sort of abuse.
> I'm fiddling watts around and it's just not worth it unless I can actually shut the inverter down entirely.
That’s where I’m coming from: trying to convince a family member to setup a DC system so the inverter can stay in sleep mode during evening/overnight, because the efficiency is horrendous at small loads. it’s really academic in kWh savings per day, but it saves you the most when sunlight’s the least and reduces battery cycling. But if you’re running an office, the inverter is pretty much running a good load or off, I think.
I know it’s only lighting as a load, but I’ve heard standard LED light bulbs will happily run as low as 36VDC, as they chop the voltage down to that level anyway.
It makes me wonder how many “120VAC” devices with switch mode power supplies could be plugged into 48VDC without any thought at all. And not just electronics like a laptop or non-plasma flatscreen, but everything is moving in this direction:
Like… what’s my Variable Frequency Drive “inverter” refrigerator motor voltage really running at? In theory it should happily run off 120VDC at least. Don’t do that, but somewhere under 110VDC should work fine. And it’s inherently soft start and easier on one’s low voltage wiring than an on/off duty cycle fridge.
Of course I recommend none of this officially.