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Comment by yazaddaruvala | Hacker News Reader

I'm just talking about DC inside the home. To the meter it should still be AC, then pushed into a battery bank. The house should only use the battery bank (i.e. different battery packs that are dedicated for different parts of the house - like the breaker box - the battery packs exchange power between each other and the grid as needed.

This way DC -> DC fast charging could be a thing, also my DC -> DC oven could pull a lot more Amps and pre-heat very quickly.

Inputs:

- Solar Panels -> Battery Bank

- Grid <-Inverter-> Battery Bank

Outputs:

- Battery Bank -> Washing Machine

- Battery Bank -> Lights

- Battery Bank -> Induction Stove

- Battery Bank -> USC-C to charge devices (my devices could charge so fast!)

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Why do you think DC to DC fast charging will be better than AC to DC fast charging? Both involve voltage conversion and the conversion has about the same efficiency. The one advantage is that could choose higher DC voltage, like 480V, and send more power on same wires. But that won't get you DC fast charging, will still take a couple hours to charge.

A lot of the things you are talking about will require conversion. LEDs will still need conversion from line voltage. Any incandescent lights will need AC conversion. The USB-C adapter will still exist, and there would no effect on charging speeds.

You can get most of the benefit by having DC power cables between the battery, solar panels, and inverter.

https://www.noodoe.com/blog/what-is-dc-fast-charging-and-how...

Most certainly DC to DC is faster. It is only limited by the local infrastructure. i.e. want to charge faster? own a bigger / better battery bank, with bigger charging cables and a better car.

DC -> DC (with some PWM / battery management) can also be slowed down (or use reduced amps) to best suit the moment. So if versatility is better, then DC to DC is again "better".

This is the scaled up equivalent of an external laptop AC/DC power brick. It’s faster because it’s supplying much, much more power. Multiple homes worth.

Batteries need DC to charge and putting the transformer in the external fast charger means the one in the car itself only needs to be sized for lower power domestic charging.

I think you’re underestimating the resistive losses at lower voltage. For the same amount of power (volts x amps) resistive losses are inverse square to the voltage so losses are 100x greater at 10V x 10A than at 100V x 1A.

Resistance is inverse to the cross sectional area of the wire so to compensate you need thicker wire, 10x the diameter (100x the area) for 1/10th the voltage x 10x the current. That’s why the wire that connects to your car battery is so much thicker than the mains wire in your home.

You could have high voltage DC in your home but then you still need the transformer so I’m not sure it really buys you anything.

Have you ever had an issue with the resistive losses in your long ethernet cords?

If you're prefer you can think of it as: each room gets its own Tesla powerwall, and therefore the battery to wall socket resistive losses are negligible.

Power over Ethernet usually supplies milliamps of current. Resistive losses are proportional to the square of the amps so they’re not a big problem for most things you power over PoE.

Latest standards seem to max out at 90W. https://www.analog.com/en/technical-articles/ltpoe-extends-p...

Over the 100M max cable length voltage will drop 25% from 56V input to 48V output. http://poe-world.com/Calculator/

For the same power draw, losses are 4x as high as at 110V, and 16x as high as at 220V. DC/DC power adapters are more efficient at low power (a few watts), so PoE might conceivably be marginal efficiency win for powering a bunch of low power VoIP phones. But as soon as you want to do something like power a laptop or even fast charge a mobile phone, you’re going to be better off plugging it into the mains with a modern AC/DC adapter that can be 95% efficient.

It’s not that AC is better than DC, it’s that higher voltages are far more efficient than lower voltages as soon as you need even moderate amounts of power over moderate distances.

You can currently use most appliances with switching power supplies on DC, but you need at least 100V.

100V doesn't cut it, we need them to work off USB-C. The current generation of appliances is a bit too old, and should soon be phased out. It has already begun, but the next generation of appliances all have built in battery and capacitor banks. Batteries are trickle charged through USB-C (i.e. like phones and laptops).

e.g. cordless vacuums / lawn equipment with swappable batteries.

e.g. water proof electric shavers, toothbrushes, blow dryers.

Likely soon induction stoves, air fryers (for instant pre-heat), heat pumps (including the fridge / freezer), blenders, etc. If it can run on USB-C, off the wall cool. If it can't add a battery.

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