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Comment by tenacious_tuna | Hacker News Reader

I think it's less that 12 or 24 is more efficient than mains, but rather that not having to convert DC -> AC -> DC and also not having to step the voltage up and back down is more efficient. That's 2x 'rounds' of conversion you don't have to do anymore.

(though I'm not an electrician, I'm just guessing)

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does someone actually make an compressor that runs off DC directly? It'd have to be a universal motor from what I understand. That seems really unreliable.

https://www.hotspotenergy.com/DC-air-conditioner/ for example

the spec sheet for that says "Panasonic BLDC" which is just an induction motor with an inverter making AC from DC power

At the scale used for building AC? Probably but I wouldn't know where to even look.

At smaller scales? Absolutely. You'll find them in almost every enclosed vehicle in the USA at various sizes.

I believe most vehicle AC compressors run directly off of the serpentine belt (12v power comes from the engine anyway, why send it through the alternator and battery?) or, in the case of electric cars, off of the ~400v traction battery. The compressor draws around 1-2kW at full tilt, so in all cases it's best to run it directly off of the main power source with as few intermediate conversions as possible.

Ok, I was basing this on searching for DC air conditioning compressors with results that referenced automotive and mobile uses. Possibly what I was seeing were retrofit kits?

While I think Teslas somehow drive the compressor via an electric motor, it's almost certainly brushless.

In traditional ICE cars it's belt driven off the engine. There is no electricity e involved to rotate it, just to engage a small clutch.

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