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I have a PC w/ a great processing-to-power-consumption ratio, however its idle consumption and power-off power draw (phantom load) is far from ideal. I could use an external switch to manually toggle the VAC to its power brick but doing so would negate any legitimate use of auto-hibernation, so I figure, why not use a relay in conjunction with a spare USB port in order to switch the relay off when the USB 5 volts is no longer present (as the computer is off)? The issue is turning the PC back on. I could easily use a separate USB charger's 5 volts with a momentary switch to flip the relay (& auto power-on the PC w/ a bios option) until the PC brings its own USB port's 5 volts on, thus keeping the relay in the on position but I know that combining separate DC sources is a no-no.

After googling for a couple hours I found that I could probably manage this setup by use of two solid-state relays (SSR), each having its separate DC source (external USB charger and PC USB port) while switching the same AC line.

from online.visual-paradigm.com (the only free one I could find with SSR

(Please excuse the rudimentary circuit diagram. I could only find one free one w/ SSRs)

I think I'm okay with going further and buying the parts however before I do I would like to ask the community for approval or suggestions. From what I've found, its going to cost $28 for a dual input SSR, or $12 for 2 separate (cheap) SSRs.

Is this the best way of doing this? The cheapest? Safest? Is it possible to just use 1 relay? Should I use coil relays? I'm open to all ideas.

Also I would imagine that this sort of setup could be practical for similar uses. Anything with a high phantom load could make use of this solution by taking an appliance's internal voltage and externalizing it to keep the the relay on during use until it sleeps/hibernates thus shutting off the relay and cutting all possible current draw.

I'm trying to cut down on idle electrical use, and hopefully a solution will allow many others to do the same.

Thanks!

FOR THE RECORD: the PC has a REAL phantom load that cannot be turned off. the power brick ALSO has a phantom load (much lower though) and would be much more expensive to replace. the PC USB ports CAN be configured to SHUT OFF during HIBERNATE (confirmed with USB LIGHT). Hibernate saves all the ram to the disk and can allow for PC power to be removed. I am VERY confident about working with DC and mains but NOT confident about brainstorming a particular circuitry.

abc
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  • As you are making a device intended to be connected with live mains voltage, how confident you are making a safe and reliable mains connected device while you seem very unconfident with the non-mains part already? Not all PCs cut USB power in standby as they support waking up via keyboard or mouse. How about just getting a new power supply that has less power draw when PC is shut down? – Justme Oct 16 '21 at 21:22
  • The only thing that would affect its power consumption when turned off is the PSU; have you considered replacing that with one that doesn't have such high idle load? Sure, a good ATX power supply can cost a fair bit, but it would probably be similarly expensive to develop this relay system. And swapping out a computer PSU is a hell of a lot safer than trying to design mains-connected circuitry yourself; I do this for a job and I'd still take that route. – Hearth Oct 16 '21 at 21:43
  • for the record it is NOT the power brick. the pc literally consumes anywhere from 5-17 watts while OFF. the power brick consumes 3 watts with NO load. – abc Oct 16 '21 at 21:54
  • Let me add to the suggestions of replacing your supply; this is one of these cases that if you even have to ask for help, you probably should not be trying to do this on your own. – Yiannis Oct 16 '21 at 21:55
  • @abc 5-17W when off, 3W just for the suppy? It means the supply is garbage and something else inside the computer is consuming 2-14W of power in standby. Modern power supplies are required by legislation to consume 0.5W. – Justme Oct 16 '21 at 22:19
  • Maybe consider a battery or USB charger powered microcontroller that communicates with an off the shelf wifi smart outlet. – Passerby Oct 16 '21 at 23:12
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    @justme, thats not a helpful answer. saying something is garbage and avoiding the whole electrical engineering aspect and $$ factor is not cool. It would definitely cost more to replace the THREE AMP power supply. – abc Oct 16 '21 at 23:29
  • @Hearth I've worked with AC mains before. I know what I'm doing. correction: the psu only consumes .5 watts, but the pc does have a phantom load of 5-17 watts and I cannot do anything to reduce that. – abc Oct 17 '21 at 00:26
  • @abc Does the PC not send a proper shutdown command to the PSU? I'm pretty sure ATX motherboards are supposed to send a shutdown signal to the power supply to turn off everything but what it needs for the power button. – Hearth Oct 17 '21 at 00:27

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First, please clarify what is "far from ideal"? *

  • "however its idle consumption and power-off power draw (phantom load) is far from ideal"

To come at your goal another way, check if you have an "always on" USB with something plugged into that USB port that might draw current. You can either check your bios or owners manual to see if one or more of your USB ports are "always on". Some have a little battery symbol next to the USB symbol to indicate always on (especially Lenovo).

If that option doesn't work and you still need an electrical disconnection, your method appears on paper to work, but, check the SSR datasheet to make sure you can directly connect to the "coil" or if you need a current limiting resistor in series.

Example of a bios setting to turn off always on feature... https://pcsupport.lenovo.com/us/en/products/laptops-and-netbooks/yoga-series/yoga-500-14ibd/solutions/ht503671-how-to-configure-the-system-to-charge-devices-over-usb-port-when-it-is-off-ideapad

GT Electronics
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  • you're right about a current limiting resistor. for example a dual channel ssr i'm looking at says the control current needs to be under or equal to 20mA. If I use a 500/1000 mA 5 volt usb charger, what kind of current limiting resistors in series will I need? – abc Oct 17 '21 at 01:24
  • I feel like we are solving your solution (relays), not your problem (high phantom load). There are ways to track down what is causing the high current load while hibernating. – GT Electronics Oct 17 '21 at 01:56