Doodoo Posted April 3, 2014 Share Posted April 3, 2014 Hi, I've just built a new system with an RM 650 power supply, and something does not quite work as expected. I've got a multi-card reader with a USB port solely dedicated to charging (it does not actually work as a proper USB port). Naively I thought the USB charging port would be active all the time, including when the PC is turned off (it has a dedicated connection to the power supply, with a 4-pin molex). However that is not the case, which reduces the interest of the charging port a lot.... Is this normal ? Is it somehow related to the missing 5V connection in some RM650 ? (which, I understand, should be on all the time, even when the PC is turned off). Or do I need to connect my USB card reader to a specific port of the power supply, which is constantly on ? Thanks for your help, David. Link to comment Share on other sites More sharing options...
Corsair Employee jonnyguru Posted April 3, 2014 Corsair Employee Share Posted April 3, 2014 When the PC is off, only the +5VSB is live. +5V is one rail and +5VSB is another. A 4-pin Molex has a +5V lead, but it DOES NOT have a lead to the +5VSB. There's only one +5VSB wire on any power supply and that wire is on the 24-pin connector. Link to comment Share on other sites More sharing options...
Doodoo Posted April 3, 2014 Author Share Posted April 3, 2014 A 4-pin Molex has a +5V lead, but it DOES NOT have a lead to the +5VSB. There's only one +5VSB wire on any power supply and that wire is on the 24-pin connector. Right, so that means there is no hope to have this USB charging port active when the PC is turned off ? My motherboard actually has one (and only one) USB port which is powered all the time (so on the +5VSB, whereas the others are on the +5V I suppose), but it is at the back of the PC which is not terribly handy. Is there any way I can get the +5VSB from this USB port and route it back to the inside of the PC to connect to the card reader with the molex connector ? The spec of the card reader says "USB 2.0 charging port, 5 V / 2.4 A (Meets new USB battery charging BC 1.2 specification)". How much current can safely be drawn on the +5VSB ? I suspect a last resort would be to tap directly off the 24-pin connector (see this pic), but that's very ugly, isn't it ? Link to comment Share on other sites More sharing options...
Corsair Employee jonnyguru Posted April 3, 2014 Corsair Employee Share Posted April 3, 2014 The spec for the +5VSB load is on every PSU label. For the RM650, the +5VSB is 3A. And keep in mind that if you tap into your 24-pin cable, you void the warranty. Certainly your motherboard has more than one USB port that uses +5VSB? None of the internal ports? Setting in the BIOS? Link to comment Share on other sites More sharing options...
Doodoo Posted April 4, 2014 Author Share Posted April 4, 2014 For the RM650, the +5VSB is 3A. That's good news.... more than enough (I think) for one charging port :-) And keep in mind that if you tap into your 24-pin cable, you void the warranty. I know, and I certainly will not try it ! Certainly your motherboard has more than one USB port that uses +5VSB? None of the internal ports? Setting in the BIOS? I need to double-check, but I am pretty sure only one USB port at the back is on the +5VSB. I have an Asus Z87-Pro and Asus refer to this feature called USB Power+ which lets you charge devices even when the PC is off (see page 2-14 in the manual) but that is only for one specific port. Funnily enough in the entire manual there is only one reference to +5VSB, which is to enable power-on from keyboard: [Power Key] Sets Power key on the PS/2 keyboard to turn on the system. This feature requires an ATX power supply that provides at least 1A on the +5VSB lead I couldn't find any info about the internal USB pin headers. I suspect that the only way to find out if they're on the +5VSB or not is to try..... Link to comment Share on other sites More sharing options...
Doodoo Posted April 5, 2014 Author Share Posted April 5, 2014 I need to double-check, but I am pretty sure only one USB port at the back is on the +5VSB. I have an Asus Z87-Pro and Asus refer to this feature called USB Power+ which lets you charge devices even when the PC is off (see page 2-14 in the manual) but that is only for one specific port. I was actually wrong all the way. This Asus stuff is really confusing I think. In fact this feature only allows (supposedly) faster charging. However all ports (back and internal pin headers) seem to be on the +5VSB, because some devices (e.g. my mobile phone) appear to be charging ok when the PC is off. But some other devices (e.g. my camera) will only charge from that specific port at the back, and when the USB Power+ feature is enabled. Link to comment Share on other sites More sharing options...
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