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I recently watched a video on Youtube which claims you may charge your Mac through an adjustable power supply, by setting its output voltage on 18.5 and connecting your MacBook adapter’s wire (the one connected to the MagSafe connector) to the power supply. The circuitry at the top of the MagSafe connector determines how much power your mac is going to draw from the power supply, so even if the power supply supplies more voltage and/or amperage, your mac would not be allowed to draw more than the required power from the power supply.

Now, I just want to know your ideas on this video and if you consider it safe? Does higher voltage, say, 20 v. hurt the chip located at the MagSafe connector or my MacBook’s logic board? And based on all this, may I use a different adaptor instead of my original mackbook MagSafe charger? An adapter like the following HP charger:

HP PPP016H 18.5V 6.5A Laptop Charger

The link to the YouTube video: https://www.youtube.com/watch?v=B3w8nwyrdYw

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    Is it worth it, on two grand's worth of laptop? Mismatched amperage is 'safe' but mismatched voltage is not.
    – Tetsujin
    Commented Feb 13, 2019 at 13:06
  • I'm not sure about using an adjustable power supply. Anecdote: I did buy an off brand ac adapter to replace my fraying original adapter and it worked for a few years until one day it just melted. I went ahead and replaced that one with on from Apple.
    – dwightk
    Commented Feb 13, 2019 at 13:34
  • I re-purpose adaptors for many things - even to make an electrolysis bath... BUT I will always buy Apple chargers for the Apple laptop - and I have 2 macbook pro....
    – Solar Mike
    Commented Feb 13, 2019 at 13:37
  • @dwightk You mean you used the off brand ac adapter instead of the mac adapter? If so, please let me know which brand?
    – user321044
    Commented Feb 13, 2019 at 14:28
  • Yes. I ran my 2012 MacBook Pro for several years with a boost DC converter from a solar-powered car battery.
    – n1000
    Commented Feb 13, 2019 at 16:51

1 Answer 1

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Let's start off by addressing the video you linked to....

It's a video by Louis Rossman of The Rossman Group the owner of a laptop repair facility that specializes in component level repair (repairing logic boards). In it, he explains why he uses a bench top power supply to deliver exactly 18.5V; so he can monitor the amperage draw. Suffice to say, it's not a "wall wart" he is using.

The MagSafe Adapter.

The MagSafe power adapter can supply voltages from 14.5V to 20VDC. However, it's not the "brick" that determines if it can charge or not, it's the actual MagSafe adapter that actually determines whether or not it will interface with your Mac. The brick just supplies the power.

The connector end is what communicates with your laptop and tells the brick how much power to supply. Basically, the way it works is that it that it identifies the power supply as having so much capacity (wattage). If it's enough, it will charge/power the laptop. If not, it won't accept the voltage.

This is why you could use a 90W adapter on a Mac that came with a 40W but couldn't use a 40W adapter on a Mac that needed a 90W. This is true with all other power supplies except Apple added some logic into their connector.

Is it safe to Use a 3rd party power supply?

If you know what you're doing, then yes, it is.

Will the 18.5V, 6.5A charger work?

It should because it's supplying 120 watts of power (18.5V * 6.5A = 120W; more than enough to satisfy any Mac.

TL;DR

Yes, based on the info you supplied that power adapter will work. Whether it's safe or not depends on your skills with DC power supplies and electrical circuits.

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  • It's an AC power supply
    – Allan
    Commented Feb 13, 2019 at 16:17
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    I used a 60W brick for several years on my 15 inch 2012 MacBook Pro, which comes with a 85W brick. So lower wattage actually works. However, communication between the Mac and the MagSafe connector seems to matter. Some people cover the center pin of the MagSafe cable to prevent charging the Mac's battery. I ran my MacBook with a simple boost DC converter from a solar-powered 12V car battery for years and it worked fine. However, I used an original Apple MagSafe cable, which I bought on eBay.
    – n1000
    Commented Feb 13, 2019 at 17:13
  • @n1000 - If your MBP never drew more than 60W, then it's not a problem. It may charge or power it, but not both. Given that you link to that exact scenario by isolating the center pin, confirms this. Car batteries typically supply 40-50A per hour so at 12V you're talking 600W meaning that DC converter was easily able to step up the voltage to the necessary 14.5, 16.5, 18.5 or 20V.
    – Allan
    Commented Feb 13, 2019 at 17:20
  • In the case of the under-powered brick, the battery would slowly discharge in peak load situations, but charge again when load was lower. Fun fact: Even the 85W and 90W bricks are underpowered and are not able to provide enough power under continued maximum load conditions. apple.stackexchange.com/q/130972/45492
    – n1000
    Commented Feb 13, 2019 at 17:26

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