Apple magsafe power brick - Page 1
Forum section: electronics / projects

author: Harvs
author_rank: Super Contributor
timestamp: April 17, 2014, 08:58:11 am
content: So I've been playing around with my new eload, and one of thing this I wanted to do was re-purpose an old magsafe laptop charger. So I did some investigation into it.Anyway I thought I'd share on here because I think the way they've implemented the dual voltage level vs current demand is quite neat. Something I hadn't seen before.http://www.electronicsinoz.info/85w-magsafe-power-adapter-repurpose/

author: con-f-use
author_rank: Unknown
timestamp: April 17, 2014, 10:14:37 am
content: Thanks for sharing. Nice solution!I had to improvise a new supply when my GF broke her MacBook Pro power brick over the holydays. This helped alot:Teardown and exploration of Apple's Magsafe connectorI hate Apple for the general design of it. It was a pain in the ass. Then I had to install a Linux on her Mac alongside OSX because it was required for her class. That was even more painful. Why do they have to make it so difficult?

author: Harvs
author_rank: Super Contributor
timestamp: April 17, 2014, 11:18:18 am
content: That was one of first links I looked at. There's a few pages around with various bits of information about the Magsafe connector.But I didn't find anywhere that answered that question of how to get 18.5V out it. It was really just by chance that I found it by winding up the load on it, I was actually expecting to find the current limit so I was kind of surprised when the voltage jumped!

author: turbo!
author_rank: Regular Contributor
timestamp: April 17, 2014, 12:38:51 pm
content: I do recall some older adapter rated 6/12v with just two wires. I haven't figured out how the two coordinates. DC-DC converter in a laptop is usually a buck regulator using SMPS topology. So, if the load power is increased and the power supply voltage steps up, the current will drop, which then causes the adapter to lower the voltage, which in turn raises the current. If the dead-band is not set right, it will hunt back and forth.Quote from: con-f-use on April 17, 2014, 10:14:37 amI fail to see a technical merit in this just like their Lightning connector. I think this is Apple being Apple as usual and turd polishing prior inventions so they can get patents, claim exclusivity and use the legal arm to keep out the production of aftermarket accessories. Magnetically held connectors that pop off has been used for decades on portable cooking equipment and hot water pots so you don't get doused in hot water if you were to trip over the cord.

author: Harvs
author_rank: Super Contributor
timestamp: April 17, 2014, 01:09:25 pm
content: Quote from: turbo! on April 17, 2014, 12:38:51 pmIt's not a two level switch in this case. It's a linear ramp up of voltage over 3/4 amp, so there will be no hunting with a buck converter on it as long as their control loops are compensated correctly.

author: Jarrod Roberson
author_rank: Regular Contributor
timestamp: April 17, 2014, 02:02:16 pm
content: I run Linux, Windows, Solaris and older version of OSX on OSX in virtual machines all the time with no trouble. Dual Booting is a PITA no matter what the "native" host system is considered to be.Virtual Machines are the way to go.

author: Aigars
author_rank: Regular Contributor
timestamp: April 17, 2014, 04:05:59 pm
content: i put may mac in to lab power suplay and its works fine. just need know corect voltage and amps.

author: amyk
author_rank: Super Contributor
timestamp: April 17, 2014, 07:16:06 pm
content: Quote from: turbo! on April 17, 2014, 12:38:51 pmI agree. This weird dual-voltage (and only ~2V difference, or roughly a bit over 10%!) doesn't appear to have any real purpose beyond making things more complex. I can see the "soft-start" load sensing being perhaps a safety feature because the pins on the magsafe connector are tiny and easy to short out accidentally, but if they just wanted to minimise resistive losses, wouldn't keeping the voltage at 18.5V (or 20V as some other laptops do) already keep the current to a minimum?

author: Len
author_rank: Frequent Contributor
timestamp: April 17, 2014, 09:29:24 pm
content: Quote from: amyk on April 17, 2014, 07:16:06 pmWhat they wanted is for the newer AC adapters to supply a higher voltage for new laptops, but still work with older models too. 18.5V is too much for the older laptops to handle.

author: Aigars
author_rank: Regular Contributor
timestamp: April 18, 2014, 07:00:59 am
content: for macbook need 16,5 volts and 3,65 amps. dont gou ower this, its will born ys mac, if u gou ower.

author: Aigars
author_rank: Regular Contributor
timestamp: April 18, 2014, 07:01:59 am
content: for macbook air 14,5v 3,1 amp

author: Aigars
author_rank: Regular Contributor
timestamp: April 18, 2014, 07:03:21 am
content: macbook pro retina 20v 4,25amp

author: Harvs
author_rank: Super Contributor
timestamp: April 18, 2014, 08:29:59 am
content: Quote from: Aigars on April 17, 2014, 04:05:59 pmWill it actually charge though? My limited understanding of them, is if the Mac can't get a response on the center pin of the magsafe connector (which is connected to the 1-wire IC), it will only power itself off the voltage on the pins and won't charge the battery.I have to say what makes them a PITA is also kind of clever, in that you can plug any magsafe adapter into any macbook (note magsafe 2 and magsafe are not compatible, dam you!), the macbook will read out the code in the IC and know what the maximum power rating the adapter is. Then it will pull up to the max power of the adapter to charge itself. E.g. I've plugged a 45W adapter into my macbook pro before and it just charges slowly, but no other ill effects.

author: amyk
author_rank: Super Contributor
timestamp: April 18, 2014, 01:17:35 pm
content: Quote from: Len on April 17, 2014, 09:29:24 pmSorry, but I have pretty definitive evidence that you're wrong. All of the Macbook family were designed with 18.5V input. Here's the Macbook Air (A1304/M96) mentioned above, which is supplied with a 14.xV adapter:Why would 18.5V be "too much" anyway? The input is only directly connected to buck converters and filter caps. The former are usually rated for much higher voltage. E.g. the A1304 has only an ISL6258 (appears to be some proprietary Apple part but the '57 is similar) with a 25V max input voltage, and an LT3470A - 40V(!) max input. The filter caps are 25V. Thus, you should be fine with running a Macbook from as high as 20V (I disclaim all responsibility, etc...)(Some smaller laptops with 9-12V adapters will have 16V caps instead, and the safe input voltage on those is more like 9-13V. The next common value is 25V so that's what created the two ranges.)