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Charge laptop directly from solar panel?
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Charge laptop directly from solar panel?

by jonsleepy on Thu Jul 16, 2020 1:05 pm

Hi all,

I'm an Adafruit user from back in the MintyBoost days :)

I want to charge my MacBook Pro from the sun. I like a 60W solar panel with a couple of lowish-power 5V USB out ports, and a 19V DC jack, which I imagine can push 3A in full sun. Adafruit sells DC to MagSafe adapters (I'll link it below). I'm sure an adapter like that is typically used from a proper DC power or voltage source that will reliably push out what the MacBook is looking for. Is it a bad or good idea to wire a MacBook directly to the 19V output from the solar panel, without something like a battery and/or inverter in the middle? I imagine the current would fluctuate if a cloud passes by (and maybe the voltage, too), but I would like to believe that the MacBooks probably have sophisticated charging circuitry that can handle some fluctuations. Any thoughts on charging directly from a solar panel to a MacBook? I have a later model that charges from a USB-C cable, so I'd use a different adapter, but the same idea applies. Links below. Thank you!

Link to an example of DC to MagSafe adapter: https://www.adafruit.com/product/3547
Link to panel: https://www.amazon.com/gp/product/B0879F33KW/.
jonsleepy
 
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Re: Charge laptop directly from solar panel?

by jonsleepy on Thu Jul 16, 2020 9:22 pm

In doing a bit more research, I found this video, which I think is an important clue:
https://www.youtube.com/watch?v=gud5jHHa3Fg

If I find more info or have more idea's, I'll post again. Still happy to hear any advice from you all, of course.
jonsleepy
 
Posts: 13
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Re: Charge laptop directly from solar panel?

by adafruit_support_bill on Fri Jul 17, 2020 5:45 am

Looks like he's using a 24v panel and a 12 buck converter. That difference in input vs output voltage should give him enough headroom to get a steady voltage output over a range of solar conditions. I don't know what the tolerances of the MacBook charging system are, but some charge controllers (like the one on my old iPhone) do not handle fluctuating input voltage very well.

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Re: Charge laptop directly from solar panel?

by jonsleepy on Fri Jul 17, 2020 8:53 pm

Just want to follow up that I've done more research. Looks like it's not enough just to provide a stable 19V to the laptop. The protocol of interest here is USB-Type C Power Delivery (PD). It requires a chipset both on the source and the sink. When a connection is made using a compatible cable, they negotiate the voltage (and maybe the current?) at pre-approved voltage levels. So this means at a minimum I need to pass the DC 19V out from the panel into a PD-compliant chipset. There appear to be a couple of products out there and I will try and find an appropriate one. Then the only remaining question will be whether the fluctuations due to sun/cloud cover will cause any issues, or if we can keep a steady voltage and ramp the current up and down with the sun without affecting charging.
jonsleepy
 
Posts: 13
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Re: Charge laptop directly from solar panel?

by jonsleepy on Sat Jul 18, 2020 3:41 pm

Here's a good article explaining more about USB-C Power Delivery:
https://www.androidauthority.com/usb-po ... ry-806266/

The newest flavor apparently offers more voltage possibilities than just the ones listed in the article, but the rest of it still applies.

As it turns out, there's a couple of panels out there at 100 or 120 watts that come with built-in USB-type-C Power Delivery ports (one of them is at 45 watts and the other at 60 watts). I'm not sure why they would take a 100 Watt solar panel and only utilize 45 watts for charging, especially if they could set the voltage to 20V and let the current fluctuate with the sun up to the max it could create. My MacBook Pro 15" comes with a 86W charger, which is still between the panel's rating of 100W so I'm unclear on why they would've chosen to "throttle" the panel's output below it's capability. But I suppose it's a "safe" bet that if you buy one of these panels, it's likely you'll get a reliable 45 watts (or 60 watts) of USB-C charging, so it seems reasonable to just get one of these. They're bigger, bulkier, and more expensive than the 60W panel I was originally looking at, but I bet they'd keep my laptop charged when it's sunny!
jonsleepy
 
Posts: 13
Joined: Sun Dec 16, 2012 2:55 pm

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