3 ms·
No you are completely 100% wrong. This was one that came with a MacBook Pro from the Apple Store actually in the sealed box when I bought it. Don't assume I'm s
by cjsuk 9y ago
No you are completely 100% wrong. This was one that came with a MacBook Pro from the Apple Store actually in the sealed box when I bought it. Don't assume I'm stupid. I'm actually a qualified electrical engineer and I know switching power supply topologies and design very well.
Don't assume that because 90% of the charger is well designed, the rest of the 10% is.
There is no or insufficient inrush protection in the charger. This results in a hefty current flowing the charge the primary DC cap in the switching power supply when you plug it into the wall (step response of a capacitor at DC is high instantaneous current if the source impedance is low such as rectified AC - derived from I=C(dV/dt), dv=350, dt -> 0, C~10mF, I->infinity in an idea model ignoring parasitics and series resistance of capacitor). This damages the pins and stresses the diodes terribly reducing the time to failure. Google inrush current protection.
You do NOT get this on decent industrial switching power supplies that actually cost less. They either have NTCs or pre-charge.
The Chinese ones are a whole different story. Some of those are absolutely abysmal and are in no way even comparable to the Apple ones.
The Apple ones certainly don't rank that high really in the scale of things, regardless of all the love spread over the Internet. If you're comparing them to a lowest bidding turd from China, then of course they're going to look good.
Here's a picture of the burn marks on the pins: https://i.imgur.com/aaHV1kX.jpg https://i.imgur.com/aaHV1kX.jpg
I'm not going to even go into the three left IO boards I've replaced on MBP's where the magsafe connector has burned out.
- abritinthebay 9y agoI stand corrected sir! It did sound a lot like you were describing the common issues with the knock offs though - however with the extra detail it really cleared it up, thanks for that.
- ianhowson 9y ago> There is no or insufficient inrush protection in the charger There's at least a PFC chopper and fuse. I'd be surprised if there were no series inductors, though I can't spot them on http://www.righto.com/2015/11/macbook-charger-teardown-surprising.html http://www.righto.com/2015/11/macbook-charger-teardown-surpr... It's a reasonably complex pre-rectification stage for a consumer device. It's certainly not AC->rectifier->DC cap. I can't explain the burn marks in the image -- stunning for a British plug. None of mine with Australian or European plugs show any significant burns. I see sparking when I plug it in, but that's standard for pretty much any SMPS.
- cjsuk 9y agoPFC is required under EU law and is a good idea anyway from an efficiency and harmonic reduction POV. It doesn’t however establish or change startup currents. There’s sparking when you plug it in and there’s this which is like a small explosion. Either way the sparking is entirely avoidable as well with a trivial. Little startup circuit or a couple of NTCs. I’ve tried it on a sample of three chargers now (we have three MBPs in the house of differing ages and original chargers) and they all have it. I’ve got a Lamba 12v 5A unit here as well which isn’t much bigger with a chopped off IEC lead on it. Nothing when you plug it in at all.