Hacker News Reader

Comment by Scoundreller | Hacker News Reader

One cool thing I like about the USB-C Macs (at least the MacBook Airs, but probably the rest too) is that they'll even happily take 5V from USB-C. May not get enough amperage to actually charge while in operation, but will extend internal battery lifetime. They'll also take 12V. And probably 9V, 15V and 20V.

I always wondered if they can accept any voltage over the range. Can I just plug in a solar panel and it will happily charge even as it cuts in and out at low voltages?

View on HN

Unless your Macbook negotiates USB-PD, or USB-C standard 5V mode, it won't charge. There's a USB-PD controller in front of all the USB ports, so they will not pass any current in unless it gets the right signaling.

If you just try to trick it, there's over- and under-voltage protections built-in, so it should shut off if you just let the voltage float around.

Stick with something in-between to handle the solar.

That is so refreshing, yeah the lenovo P series just ignores USB-PD inputs as it nominally wants 135W external power minimum. The kicker is it rarely ever draws more than 90w

My P1 (G4) gladly accepts power over USB-C, depending on what I'm doing the 80W my monitor supplies are not enough and it slowly discharges, but it's enough to keep it going for a day's worth of work and recharge over night.

Except that it does not unlock full power unless the slim-tip is there. It is a bit slower but on the plus side it is dead quiet and runs a lot cooler.

My ROG Zephyrus M15 only supports up to 65W in through the Thunderbolt port, even though it's a 230W laptop. Two hundred and thirty watts, and they couldn't even accept 100W over USB-C PD, they had to limit it to 65W.

I'm in the process of replacing the crappy thing with a proper desktop.

Personally, I wouldn't. An external battery is cheap; Macbook Air logic board replacements are actually free if you have AppleCare+, but then you lose your laptop for days while it's being repaired. I'd just have the solar panel just charge a (small, portable) battery and use that battery to charge the laptop, with bonus points for not having to have your laptop tethered to the solar panel if you want to use it while the sun is out.

As far as the Macbook air goes, the official chargers will do 5V, 9V, 15V and 20V output, so yeah, no probably; it supports those.

> logic board replacements are actually free if you have AppleCare+

They aren't if you fried the board by connecting an aftermarket (or makeshift) charger.

I tried feeding my ASUS Zephyrus G15 (GA503QM) 5V over USB-C once. It discharged faster, because it decided “hey, I’m plugged in, I can consume more power”, and even my attempts to reduce it by controlling the CPU’s power limits (which absolutely reduces its consumption when unplugged) didn’t make it discharge more slowly than not being plugged in.

I think I estimated it was getting around 1.5W (by putting it to sleep for hours and comparing the small amount it had filled by with the drain of a similar period unplugged), though the wall adapter is rated for 11.5W (5V/2.3A), and certainly charges a phone at about that.

A "12v" solar panel typically has an open-circuit voltage around 22v, which is probably fine, but I don't know how Macs are made. You might want to exercise it a little with a benchtop PSU and some instrumentation first.

I wonder if any laptop power-input circuits are agile enough to perform MPPT and extract a bit more juice out of a panel thus provided...

My Lenovo also takes 5v from usb-c. Doesn't do too much but it extends the lifetime a bit.

Reply on news.ycombinator.com