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Use a lower wattage charger to charge 2021 MacBook Pro?

Can I use the 61 watt charger that came with my 2017 13" MacBook Pro to charge my new 2021 16" MacBook Pro? I know I'll need to use the USB-C to MagSafe 3 cable instead of the cable that came with the 2017 MacBook. My guess is that the new laptop will just charge more slowly with a lower wattage charger, but I want to be sure.


Thanks.

MacBook Pro 16″, macOS 12.0

Posted on Dec 6, 2021 4:18 AM

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Posted on Dec 9, 2021 12:52 PM

For light CPU loads, it will charge very slowly with 18W, and will charge visibly with a 30W charger. When you are not stressing out the CPUs, the MacBook Pro will be using between 5W and 15W. The command line program 'powermetrics' will often show significantly less than 5W for the 'package' (CPU etc.) when not doing any heavy lifting, so just add some watts for the screen and you get a rough idea of the power consumption. The charger won't "overheat", but it will, of course, run at "full power" longer than it would for, say, the M1 MacBook Air it was created for, so you have to decide for yourself if you think that might damage the charger.

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Dec 9, 2021 12:52 PM in response to Sonicray

For light CPU loads, it will charge very slowly with 18W, and will charge visibly with a 30W charger. When you are not stressing out the CPUs, the MacBook Pro will be using between 5W and 15W. The command line program 'powermetrics' will often show significantly less than 5W for the 'package' (CPU etc.) when not doing any heavy lifting, so just add some watts for the screen and you get a rough idea of the power consumption. The charger won't "overheat", but it will, of course, run at "full power" longer than it would for, say, the M1 MacBook Air it was created for, so you have to decide for yourself if you think that might damage the charger.

Dec 9, 2021 11:58 AM in response to T_Lynch4

Quote: “2021 16" MacBook Pro? “

Hi,

Your 16 inch requires at least 67 - 97W via USB-C. If you want to use the Magsafe3 adapter, you should use the 140W brick. The 61W brick might be too low for the 16 inch. (but it doesn’t hurt to try… worst case, it will not charge…)


I’m currently using an Apple 87W brick via USB-C and it works fantastically well…(I do have the 140W in another room.)

Dec 10, 2021 10:03 AM in response to atthetone

Ok, let's say I'm totally wrong in my original comment ... Devices do in fact accept current and chargers push current, or electricity or however you choose to say it. It's one way or the other ... no middle ground.


Most service drops into homes that are not "mansion" in size are usually 200 Amps or thereabouts. IF electricity is pushed, that would mean every device in your house or apartment is exposed to 200 Amps and 110 or 220 volts. You'd have some more pretty tough Macs there. Not talking about step-down transformers, or any other kind of intermediary devices, strictly the "draw/push" proposition.


Typically, appliances, to include Mac chargers (and we're still strictly talking "draw/push"), are NOT exposed to full 200 Amp service because it's not pushed, it's drawn. But if they were to have "full power" pushed onto them, and the voltage and phase matched, they'd be enormous! You'd have to have a forklift to move your charger around.


You guys can continue on if you wish, I got a MacBook to charge and I got to move the charger.

Dec 10, 2021 10:25 AM in response to ku4hx

Yes, it is “drawn”, let’s leave it at that. I just hope the takeaway for anyone reading this is that it is not drawn without limit: the current is capped (the technical term is “limited”, as Keith Barkley writes) and your MacBook won’t draw more current than the charger was designed for, just for longer. (I’ve been doing this for years and with many Apple devices without any issues.)


Enough said, you have a point, so let’s all go do some charging 😊 I personally just make sure that I pick a power supply that can cover both the current power usage of the device and still charge the battery; I don’t want the battery “discharging and being charged at the same time” (I hope you get what I mean). But that’s a different story.

Use a lower wattage charger to charge 2021 MacBook Pro?

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