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0 pointsbryanlarsen3y ago0 comments

We've had 2 standard DC outlets for a while now: 12V cigarette lighter and 5V USB. You do often see them in odd places. But the voltage and wattage of those specs is too low to be useful, so they haven't evolved into DC power distribution.

USB-C PD is at a useful voltage & wattage level, and so is Ethernet POE. I wouldn't be surprised to see them start to be used for general power distribution in niche applications, like RV's and off-grid cabins.

I don't think we're going to ever get a bulb standard, though.

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zaroth3y ago

Cars are starting to move to 48V DC. My under cabinet lighting in the kitchen are powered by DC from a power supply in the basement.

I could definitely see this becoming more common. Powering the ~100 watts of fixed lighting spread across my whole house on ten different 15A 120v circuits, each with their own arcfault breaker and 12 gauge copper electrical lines running back to the panel is fabulously expensive for what could be done with a bunch of CAT5 in each floor running to some conveniently located “POE injector” type devices.

You would want to be able to take a standard fixture and just push DC through it and use special bulbs with a standard A19 base, but that’s problematic when the next owner tries to screw in a standard bulb - what happens when it sees 48V DC?

I would guess if for safety reasons it has to be a non-A19 connector, then your light fixture choices get cut down to almost nothing and no one will make the switch?

It’s really interesting to think about, most everything I’m plugging into AC outlets in my house, the first step is converting it to DC. A lot of my outlets I’ve switched to include USB ports so I don’t need the wall warts. If you have solar and battery backup even more-so you start to question why we are wasting so much money moving everything back and forth between DC/AC/DC within a house.

azernik3y ago

If you're introducing electrical incompatibility, why on Earth would you try to preserve mechanical compatibility?

Tsiklon3y ago

This is a fair point, breaking mechanical compatibility will at least stop any electrically exciting goofs from occurring from plugging a low voltage DC lamp into a (comparatively) high voltage AC socket.

pwg3y ago

> but that’s problematic when the next owner tries to screw in a standard bulb - what happens when it sees 48V DC?

If by "standard" you mean a incandescent tungsten filament bulb, nothing at all.

For a true LED driver power supply, it would be constant current, so the tungsten filament would see 25mA (or whatever the constant current is set for) of DC, and nothing bad would happen (the filament also would not likely illuminate either).

Screwing in an LED bulb with integrated power supply, the external supply will still feed the constant current value, so what happens depends upon the design of the LED bulb's integrated power supply. If 25mA is enough to drive everything, the LED bulb might light up. If 25mA is not enough to drive everything, most likely nothing lights up.

Dylan168073y ago

48V without a current limit shouldn't be nothing, but you should expect less than 10% brightness.

For constant current, you'd need to drive at least 9 watts so it would be more like 250mA if not higher.

A 1600 lumen LED module might take as much or more current than a 60w incandescent. If your constant current supply can output between 0 volts and input volts, and it's set for a bulb with such a module, it would be able to power an incandescent bulb.

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garaetjjte3y ago

>screw in a standard bulb - what happens when it sees 48V DC?

Either it lights up or not? I don't see a problem here.

But I'm not sure moving part of power supply elsewhere will help that much, it needs current driver electronics anyway.

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