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
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.
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.
As long as the cable is compatible yes. But if the charger is underpowered, and I have no idea if it is or not, it'll very likely overheat. How hot depends of how much over the charger's rating the device is ... if it is at all. Devices draw current; charges don't push current.
No its not. It is capped with an analog current limiter with a digital control. You cannot control current "digitally".
The maximum current draw is capped digitally. Call it “violating Ohm’s law” if you like. Good luck trying to get more than 1.5 A at 20 V out of the Apple 30 W charger with your MacBook, which is no problem for a good “analog” transformer and some low impedance power sink.
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.
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.)
"Devices draw current" only holds in the analog world (but actually only for an "ideal power source"), but in this age the charger is quite digital when it comes to what it will provide. In the small print on the charger you will see what voltage / current pairs the charger offers to a device and then they negotiate what will be used.
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.
Thanks ku4hx, for the quick response and useful info. Your response makes total sense.
Chargers provide a set of voltage/current pairs (e. g. 20 V & 1.5 A for the 30 W charger, but it has more) and the device and charger agree on one of those.
atthetone wrote:
"Devices draw current" only holds in the analog world
Wow, you mean that Apple has figured out how to violate Ohm's law?!
Hate to break it to you, but *everything* is analog.
+1 !
Indeed, I think this deceased equine needs no further encouragement.
Use a lower wattage charger to charge 2021 MacBook Pro?
