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I have a 2015 MacBook Pro with a MagSafe 2 charging cable. My wife has a new MacBook Pro from 2016 with USB-C. I was wondering whether I could technically (in the matter of electronic feasability) use her charging cable on my MacBook and vice versa with some sort of adapter / dongle, and, if so, where I would get one?

LinusGeffarth
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  • Is the focus of the question on "is it electrically feasible" or on "where to I get an adapter"? The second one would be off-topic, please edit your question to indicate what you are looking for. – nohillside Feb 25 '18 at 19:25
  • I'm trying to figure out the same. I've found these two options so far but not sure if they are reliable: https://www.ebay.co.uk/itm/Type-C-USB-C-to-Magsafe2-Cable-Charger-MacBook-computer-with-USB-C-Power-Adapter/183440998614 https://www.ebay.co.uk/itm/163153641220 – szerte Feb 28 '19 at 00:30
  • @szerte Sadly, they don't seem to be compatible with USB-C powerbanks, which is what I'm after. – Agent_L Apr 13 '19 at 17:09
  • I can confirm both of the above works. More detail : https://discussions.apple.com/thread/250197308?answerId=250435831022#250435831022 – szerte Apr 14 '19 at 21:52
  • https://www.amazon.com/dp/B07G95NSC9 does what you want (with the extra magsafe 1->2 passive adapter from Apple). Who knows how safe it is, of course. – Rehan Jul 11 '19 at 23:22

5 Answers5

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You don't want to mix those two.

Why?

Because the USB-C port conforms to the USB 3.1 Power Delivery Specification whereas the Magsafe charger does not. Part of that specification includes the negotiation of delivered power. The Magsafe will not negotiate how much power is supplied. What it's looking for is the presence of the 1 wire charging circuit before it begins charging.

There may be adapters/converters on the market that will convert one interface to the other and vice versa, but (IMO) those cheap adapters are not worth the risk of sending the wrong voltage to your very expensive MacBook Pro.

Bottom line, use the genuine adapters built and designed for your MacBook Pro.

Allan
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    If that "cheap adapter" didn't actually act as a step-up/step-down converter to the voltage it negotiated with the MBP, I'm hard-pressed to see how it would work at all. – Charles Duffy Feb 24 '18 at 16:58
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    @CharlesDuffy: There are some amazingly bad USB-C products on the market. – Kevin Feb 24 '18 at 16:59
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    @Allan, what do you think about Charles' answer? – LinusGeffarth Feb 24 '18 at 18:02
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    "The Magsafe will not negotiate how much power is supplied." Why does that matter? It won't supply more than is needed. – Isvara Feb 24 '18 at 18:19
  • This is one of those types of adapters I referenced in my answer. Maybe it works (and looks innovative), but I, personally am not willing to put a $2700USD MacBook Pro at risk for a $25 adapter. That said...if you have Apple Care.... For me, the cost of the MBP and the cost of being without it while it gets fixed isn't worth the $50 I'll save on buying a new charger. – Allan Feb 24 '18 at 18:20
  • @DanEllis - It's in reference to USB-C power delivery - it can't negotiate. – Allan Feb 24 '18 at 18:20
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    @DanEllis Computers will draw as much current as it needs, but the USB-C standard can provide multiple voltages. If the wrong voltage gets to your computer, it's bad. Also, the USB-C standard negotiates the maximum power (current) the computer can draw, if it tries to draw too much, you'll fry the supply. With the MagSafe adapter, the computer doesn't know how much is too much. – jkd Feb 24 '18 at 19:47
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    Who says a hypothetical adapter doesn't contain a chip to handshake and set the powersupply to give the voltage mag safe expects? – Alexander Feb 24 '18 at 22:42
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    @Alexander They probably do. Allan is just saying that he won't trust the cheap adapter to protect his expensive MacBook. Also, that doesn't protect against the computer overdrawing. – jkd Feb 25 '18 at 03:59
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    USB PD is a bit of a standard, and you can buy perfectly good third party adaptors that won't blow up your system – Journeyman Geek Feb 25 '18 at 07:39
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    There's no reason the adapter itself couldn't perform the USB-PD voltage negotiation. For example: when the Magsafe end is plugged into the computer, the adapter listens on the center pin for the requested voltage, then requests the same voltage using USB Power Delivery on the other end. With a careful design there's no risk of damaging the computer. – rspeed Feb 23 '19 at 00:59
  • Magsafe negotiates voltage pretty well. From few volts of presence signal, to 16V of 60W power and then fine granulation up to 20V to deliver 85W. The problem is that it's completely different, analog protocol. USB-PD 1&2 can't even do what Magsafe requires. Only PD3.0 can achieve required voltages. – Agent_L Feb 05 '20 at 20:33
  • MagSafe negotiates nothing, @Agent_L the chip in the MagSafe adapter is only for identification by the MacBook being charged. It does not regulate voltage. – Allan Feb 05 '20 at 21:13
  • @Allan You're right about the chip, but I said nothing about it. The negotiation is analog, on power lines. – Agent_L Feb 06 '20 at 08:33
  • I don’t know from where you’re getting this idea of “analog negotiation,” @Agent_L; there’s no such thing. A load will only draw what it needs which is why the MagSafe has an id chip. You don’t want your Mac drawing more than the adapter can supply. See https://apple.stackexchange.com/questions/271793/danger-of-damaging-13-macbook-pro-by-charging-it-with-85w-charger/271794#271794 for more details. – Allan Feb 06 '20 at 09:12
  • @Allan I'm getting it from observing the behaviour. I'm talking about changing supplied voltage from few V (I forgot the exact value) to 16.5V and then up to 20V. It appears that you believe that a fully compliant Magsafe brick delivers constant voltage. In that case you're mistaken. Knockoffs do that, that's why they throw sparks on a misplaced coin. – Agent_L Feb 06 '20 at 09:28
  • @Allan We all here agree that USB-C to MagSafe is infeasible - and yet: https://www.amazon.de/Salcar-Magsafe-Netzteil-Versionen-Niedriger/dp/B07CH12XP5 (Probably that's a custom extension to USB-C and won't work with any other USB-C brick) – Agent_L Feb 10 '20 at 09:11
19

The ElecJet Anywatt One fills this need, for the purpose of powering a USB-C device from a MagSafe power supply.

From the product page:

Anywatt built-in self-developed LDR6032 smart chip supports the latest USB C Power Delivery & PPS protocol, Automatically recognize the end device needed power and adapt the voltage and current to best suit the end device charging purpose, range from 5V@3A 9V@3A 12V@3A 15V@3A 20V@2.25A and PPS 3-12V@3A MAX.

It is not licensed by Apple. That said, I own one and have been using it without incident to connect my 2016 MacBook Pro (87W) to my Thunderbolt Display; it can't provide the full 87W, so the battery charges somewhat more slowly than it would if I had the big charger with me, but it's been fully adequate in practice.

Charles Duffy
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    Well, it costs $24 while the same site sells complete mains charger for $25. So the adapter is rather limited to niche applications, eg when you can't plug in your charger, but the place provides MagSafe cables. – Agent_L Feb 25 '18 at 10:47
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    @Agent_L, yup. In my case, I have a Thunderbolt Display in storage at my coworking space -- with the AnyWatt, I only need the one plug (out of three per shared desk) for both monitor and laptop, as the monitor provides MagSafe output; with a separate adapter, I'm using 2/3, limiting whoever is on the other side of said desk to one. – Charles Duffy Feb 25 '18 at 17:30
  • For what it’s worth, I bought one of these and it works fine with a normal MagSafe charger but won’t negotiate with my Thunderbolt Display: just flashes the green light on the cable once every second and a half or so, and makes an audible click every time. – Robin Whittleton Sep 10 '19 at 15:06
  • Interesting. I gave my Thunderbolt Display away to a friend on getting a replacement (a modern Samsung w/ native USB-C/Thunderbolt support), so I'm not in a place to try to find an exact model number or such to share, to try to determine the difference. – Charles Duffy Sep 10 '19 at 16:20
  • Is this out of stock item the one you have working ? https://elecjet.com/products/anywatt-magsafe I would love to see how efficient it is (say if you have 85/60/45w MagSafe 2 chargers, how much USB charge is delivered). – bmike Mar 13 '24 at 18:28
  • @bmike, ...that looks like the right device (I wonder if they rebranded it). Moreover, I happen to have a tool for measuring USB-C PD voltage/wattage/amperage; but as I no longer have the Thunderbolt Display (or, that I know of, the ElecJet device -- assuming it went to the friend I gave the display to), I'm not in a place to do any measurements here. – Charles Duffy Mar 13 '24 at 20:04
  • I should send you a few old MagSafe I have idle “for science” – bmike Mar 13 '24 at 20:11
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You can buy adapters (dongle) that converts USC-C PD signals to Magsafe1 and 2 (and in fact to any needed voltage to any old laptop). There also the inverse adapters that converts from a Magsafe 1 or 2 chargers to USB-C output to charge a modern computer although less useful.

The irrational claims of how a computer or a charger could be fried is just a old wives fable. You cannot over draw current for a USB-C PD charger because it will shut down. The charger cannot provide more than its design capacity nor provide more current than the load needs!

The reverse of charger providing "too much" of something or another that could fry a computer is also untrue. No computer use the direct charger input for operating the computer or charging the battery. The voltage is regulated by a DC-DC converter to generate the needed voltages. If the provided voltage too low, it will not charger; if the voltage is too high, the charging circuit will shut down.

Hamdi El-Sissi
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  • Hm, thanks for your thoughts. I'm not really down to testing this with my Mac, though, ha! Sorry! – LinusGeffarth Jul 19 '18 at 06:47
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    Like the irrational claims of a Google engineer who actually bricked his Pixel with a faulty USB-C cable? `Not only did the cable kill the analyser, though, but it also fried both USB Type-C ports on Leung's Chromebook Pixel: "Neither would charge or act as a host when I plugged in a USB device such as an ethernet adapter."

    Upon further analysis, Leung found that the cable had killed the Chromebook's embedded controller` https://arstechnica.com/gadgets/2016/02/google-engineer-finds-usb-type-c-cable-thats-so-bad-it-fried-his-chromebook-pixel/

     – clacke Jan 24 '19 at 03:29
  • Maybe it shouldn't be possible, and ports should be buffered against faulty inputs. In practice though, apparently you can fry computers and possibly power supplies too, if you give them inputs the manufacturer didn't account for. – clacke Jan 24 '19 at 03:30
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    @clacke That's mostly irrelevant. The concern here is whether the laptop might draw too much current from the charger. The cable in Benson's review had the polarity of the positive and negative voltage lines swapped; protecting against swapped power rails would require a different type of protection circuit than overcurrent protection would. Also, note that he didn't say that it damaged the power supply! :) Personally, I would avoid trying to charge the laptop from another computer, but a dedicated charger should be fine. – dlitz Feb 09 '19 at 21:47
  • @dlitz Heh. Yes, maybe the charger should be safe. But I'd say that a claim that bad cables or other equipment can fry your computer ports has been clearly shown to be more than myth. – clacke Feb 12 '19 at 15:01
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    @clacke That's not what was being claimed at all. – rspeed Feb 23 '19 at 01:20
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Electrically, it is possible to go from either direction, it just requires a computer (microprocessor, etc) in between to do the USB-C PD negotiation. As people have noted, there are plenty of MagSafe2 → USB-C PD options.

There are only 3 wattages for MagSafe2[1] chargers and they have well known voltage / currents. The MacBook knows what the max wattage for the charger is by getting the id of the charger from the MagSafe2 plug itself. It won't draw more current than the charger will allow because it knows which charger is plugged in. Any USB-C → MagSafe2 dongle would essentially ensure the wattage via USB is available and emulate the correct MagSafe2 charger ID.

There does not seem to be a USB-C PD → MagSafe2 option, possibly because it would require a charger that supports enough wattage to both power the MacBook (45W/65W/80W) and the dongle itself. So at a minimum, ~50W to supply 45W (which is only enough for a MBAir and not enough for a Pro).

[1] http://www.righto.com/2013/06/teardown-and-exploration-of-magsafe.html

yincrash
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  • so, having a USB c power bank to feed an old magsafe MacBook air is probably impossible? i can't, at least, seem to find any conversor that would do the trick. – cregox Mar 30 '20 at 11:31
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As others have said, the standards being different makes this kind of dangerous if you're not careful what you're buying.

But if you only want the magnetic connector (so that it doesn't pull the laptop with it when tripped and such, you could try one of these options to convert the USB-C connector to a magnetic one.

Bogdan Marius Calapod
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