iMac Power Cable - anything unusual about it?

jaymenon

Is there anything unusual about an iMac IEC power cable?

My iMac developed a fault at the internal power supply - my local computer shop fixed it.

They however, told me not to use the same power cable again.

The iMac works fine with an ordinary kettle IEC lead - which makes me wonder:

 is there anything unusual about the Apple Original power cable?

Surely if all three contacts have continuity with the electrical plug and no shorts between them, it should be fine?

unless the cable is ‘chipped’ by Apple in some way?

robinbowes

I don't think that is anything other than a regular IEC lead, with a specially-shaped end to look neat in the back of the iMac.

Unless it's damaged in some way it should work just fine.

Funkfingers

Did the shop provide any details of the damage to the iMac power transformer? 

Do you have surge protection where the iMac normally plugs into the mains electricity supply?

TTony

Ask the shop what their reasoning is.

We'd just be guessing!

Kittyfrisk

I'm certain iMac's use an IEC 320 C13/C14 'kettle lead'  without any additional Apple circuitry but with a cosmetic plastic surround.

thermionic

There is something strange about them. When my 2009 iMac was new, the plug fit snugly in the socket and you had to put some effort into pulling it out. Later on it became very loose, so much so that sometimes an accidental bump of the desk was enough to dislodge it and cut power to the computer. Exactly the same thing happened to a 2011 model. I thought maybe some kind of non-standard anchoring tab had worn away but I haven’t been able to figure it out. Maybe that’s what the shop was referring to - they become so loose the power to the computer becomes unreliable.

Danny1969

It's a standard Kettle lead in design but low profile in design, I've never seen one fail BUT sometimes jigging the cable in that area with jiggle the headers that plug into the PSU and that might convince a shop the problem was the mains cable. In our community thread I show the header that can come loose which  leads to no power in the iMac

JayGee

Does the big collar thingy on the official Apple lead sit right up against the back panel of the Mac when it’s plugged in?

I’m wonder if the socket on the Mac isn’t quite as mechanically well supported as it might be, needs a little extra stress/strain relief to keep things stable, and Bad Things happen when it wobbles… 

thermionic

JayGee said:

Does the big collar thingy on the official Apple lead sit right up against the back panel of the Mac when it’s plugged in?

I’m wonder if the socket on the Mac isn’t quite as mechanically well supported as it might be, needs a little extra stress/strain relief to keep things stable, and Bad Things happen when it wobbles… 

It does when it’s new….

On reflection, I suspect now that the problem is with the socket rather than the plug. I still have my old 2011 21.5” but couldn’t find out what was wrong with it. 

Danny1969

That plastic bit pulls off ...it's only held on with 2 clips 

jaymenon

Thanks guys

I needed to change the 10amp fuse in the plug. I then tested the mains cable with a multimeter and it seemed fine. Reconnected everything and it is working perfectly. You chaps saved me £10 and a wasted cable

Kittyfrisk

Glad you got back up & running.
Not sure why Apple ships iMacs with 10 Amp fuses as standard, as none of the devices use more than 400W max. CPU.
 https://support.apple.com/en-us/109513
 A rule of thumb guide to selecting the correct fuse: 3 Amp fuse for appliances up to 700 Watts, 5 Amp fuse for appliances ranging from 700 to 1000 Watts,13 Amp fuse for appliances over 1000 Watts.
10 Amp fuses are available (as are 7 Amp) but are not standard in the UK.
I used 3 Amp mains fuses for iMacs, even in rooms full of them in educational settings 

robinbowes

Kittyfrisk said:

Glad you got back up & running.
Not sure why Apple ships iMacs with 10 Amp fuses as standard, as none of the devices use more than 400W max. CPU.
 https://support.apple.com/en-us/109513
 A rule of thumb guide to selecting the correct fuse: 3 Amp fuse for appliances up to 700 Watts, 5 Amp fuse for appliances ranging from 700 to 1000 Watts,13 Amp fuse for appliances over 1000 Watts.
10 Amp fuses are available (as are 7 Amp) but are not standard in the UK.
I used 3 Amp mains fuses for iMacs, even in rooms full of them in educational settings 

I too raised an eyebrow at the 10A fuse.

As you say, 3A should be fine.

R.

jaymenon

I wondered about that too. However, it actually says 10 A on the iec13 connector plug…

all things considered (and particularly since I was reusing the cable against the explicit advice of my computer repair man), I thought discretion would be the better part of valour, and I went with Apple’s recommended fuse value

robinbowes

jaymenon said:

I wondered about that too. However, it actually says 10 A on the iec13 connector plug…

all things considered (and particularly since I was reusing the cable against the explicit advice of my computer repair man), I thought discretion would be the better part of valour, and I went with Apple’s recommended fuse value

The fuse is essentially protecting the cable (there will be another fuse inside the device itself).

You really should use a 3A.

Danny1969

It’s a little trickier rating what fuse with a SMPS as the inrush current is quite large even with a MOV fitted to tame it down. Once the large caps are charged it no longer pulls that current .. so if left plugged in it’s not an issue but it’s possible if plugged in from cold certain very short term conditions could overload a 3 amp 

Kittyfrisk

Danny1969 said:

It’s a little trickier rating what fuse with a SMPS as the inrush current is quite large even with a MOV fitted to tame it down. Once the large caps are charged it no longer pulls that current .. so if left plugged in it’s not an issue but it’s possible if plugged in from cold certain very short term conditions could overload a 3 amp 

Granted, under those conditions a 3A might blow, but better that than having a 10 Amp fuse not blowing before damage could occur.
Playing it on the overspecced but stil cautious side, a 5 Amp (or possibly 7 if you can't get a 5) fuse should do the job.

Danny1969

5 amp be a good choice

The PSU is essentially split into 2 parts. The first part is very simple, The mains is rectified and connected to the primary of a transformer via a MOSFET. There are other components related to power factoring and suppression but that’s essentially it for the high side. 

This is the part that is being protected by the fuse in the mains cable

The low side, the part which actually runs the iMac has all kinds of clever protection built-in and will refuse to pulse and thus start the power supply if any abnormal loads are detected from the computer.