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Comment by pitaj | Hacker News Reader

> until I'm reminded that DC power loss over a distance can hurt bad, even 48VDC telecom power.

If you had AC to your house, then a rectifier for a 100V/200V DC circuit through your house, the losses wouldn't be any worse.

DC losses are less than AC losses at the equivalent voltage, because the resistance seen by DC is less than the AC impedance.

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Certainly at the household scale this is true. I cringe at the inefficiency of rooftop solar panels, hooked up to inverters, powering transformers that supply phones, lights, and electronics. AC in the house is great for an electric oven, vacuum cleaner, or fridge compressor, but so many modern electronic devices would be happy to run off of 5V or 12V.

Look on the bright side- in terms of real power, the electric oven, vacuum cleaner, AC compressor, and fridge compressor totally swamp the entire load, waste and all, of those 5V devices.

In a perfect world we'd have both AC & DC, and could use whichever was most appropriate. We could feed DC straight from the solar panels to the cell phone. But in terms of what consumes most of the power, in the typical home it's AC loads.

>Look on the bright side- in terms of real power, the electric oven, vacuum cleaner, AC compressor, and fridge compressor totally swamp the entire load, waste and all, of those 5V devices.

This isn't an appropriate comparison. Those appliances actually do useful things that need to get done so the energy isn't just wasted like it is with power supply inefficiency.

Sure a 12vdc circuit would be nice. It wouldn't be nice enough or efficient enough to be worth paying for.

The point is the power delivery system we have does a good job for 99% of real power consumed (or whatever the number really is).

I hate waste; my mains-connected smoke detectors (1% efficient) and garage door opener (15W standby) gnaw at my soul. But that's scope for improvement, not an efficiency crisis.

> mains-connected smoke detectors (1% efficient)

Those aren’t a waste, they are critical life safety equipment. If their 1% efficient power supply lasts the full 10 year lifespan of a smoke detector rather than 6-18 months like a typical LED lightbulb, I’d say that’s the appropriate level of reliability.

Yeah, they're important & valuable. However, battery-powered smoke detectors do it with 1% of the power.

If every home in Australia had two smoke alarms, that means 5,600 kW of continuous and largely wasted energy consumption. I don't mean wasted in purpose: smoke alarms are essential. The wasteful part is the fact that 99% of the power going into smoke alarms goes to converting AC power to DC power.

As far as I'm concerned, that's 99% scope for improvement.

https://reductionrevolution.com.au/blogs/news-reviews/584256...

That is an incredible amount of energy and I agree that it is worth trying to reduce, but I’m skeptical of adding numerous DC-DC converters to the chain. In the current state, it’s all passive devices between the turbine at the power plant and the smoke detector on the ceiling. I wouldn’t trade that reliability for power savings lightly.

A smoke detector doesn't need that much power, so efficiency of the power supply is less of a concern. You have to find a useful compromise between efficiency and use of materials. Those additional components for higher efficiency need to be produced which uses resources and energy.

Although 15W standby for a garage opener seems excessive.

In a perfect world your fridge and vacuum would use BLDC motors and be happy with whatever dc or ac voltage you give them. As my washing machine already does.

Grid-scale transformers are very efficient. The tiny pole-mounted ones used in the US and some other countries probably not so much, but everything north of 50-100 kVA gets into 99+ % efficiency.

Just because generator/machine set transformers and 380/220 kV step transformers require semi-active cooling doesn't mean they're inefficient... just means that they handle a huge amount of power (MWs), so even at very high efficiencies that translates to a lot of heat in absolute terms.

The goal in my thinking was to eliminate a complex or costly power supply at the point of consumption. Higher voltages require a beefier step down (isolation, caps, whatever) and AC requires a rectifier. I wanted to eliminate it all.

Sorry, I was being a little too loose for HN. Also, I'm not an EE but I play one on the Internet :).

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