Thread: Help with 12V to 5V step down converter.

OK, really odd issue that I need advice on! I connected the step down to a 350 watt PSU to test. Everything comes on and works nicely. Now here is the issue, when the converter comes on, I notice that all USB devices and hubs come on, but so does the Mobo for the multizone system. What I mean by that is that it seems like 5V power is being run through the setup. One hub is powered, when I plug the plug into the hub, all hubs connected to the PC come on. None of the devices attached to the PC come on, so im guessing they wait for the PC to activate them? Also the LAN lights come on. It seems almost like some type of wake feature is being powered by the 5V converter. Im just worried that if I power on the PC something will blow. I wanted to see if maybe it was the converter, but if I remove it from the hub, then plug in the wall adapter that came with the USB hub, all hubs once again come on, also LAN, but it looks like a dead battery almost, the lights on the hub are very dim. Is this normal?

Here is the unit installed: http://www.mp3car.com/worklogs/14375...-remix-33.html

It sounds like the Hub is not isolating the +5v standby line coming from the PC and the +5V power coming from the Hub’s externally supply. If the PC is in sleep mode, applying power to the HUB, and therefore to the +5v Standby line going to the PC, will bring the PC out of sleep.

The adaptor for the Hub, most likely, cannot supply enough power to supply all devices and therefore behaves differently to the High power 5v inverter.

I had a similar problem and the fix is easy. But you need to verify if this is the problem.

Originally Posted by Mickz

It sounds like the Hub is not isolating the +5v standby line coming from the PC and the +5V power coming from the Hub’s externally supply. If the PC is in sleep mode, applying power to the HUB, and therefore to the +5v Standby line going to the PC, will bring the PC out of sleep.

The adaptor for the Hub, most likely, cannot supply enough power to supply all devices and therefore behaves differently to the High power 5v inverter.

I had a similar problem and the fix is easy. But you need to verify if this is the problem.

How do I fix this? Do I turn off some option in the BIOS? The DZ setup doesnt seem to have this issue.

I assume that you checked all power on triggers are disabled in the Bios.

I am going to retract that simple solution as in my case it was simple because as I was powering the HUBS differently. However it depends on how you control it.

I will have a similar problem when I change over to one of these devices.

What I intend to do is switch the power to the 5v inverter with a relay that’s controlled from the +12v PSU output rail. When the PSU is powered on the HUBS are then powered by the inverter. When PC shuts down, the inverter is switched off.

As you are trying to control two PC’s and you may want the HUBS powered when the one of the PC’s is off so I’m unsure if this is what you want to happen.

the other option would be to clip the power wires in the usb cable going to the hub-- assuming it can work with 0 power from the host pc(some hubs won't)

Another problem could be if you wanted to use sleep mode. If you do, you may have to provide external power to the hubs for the duration of sleep mode.

Well the main PC will use hybrid sleep, but since it doesnt seem to be affected by this issue, im not going to worry. The MZ setup is cold boot all the time. The DZ and MZ setups both control the 5v Step down converter. Now what I could do, which is what I am thinking, is power the only powered hub on the MZ system via the PSU. I know for a fact that the PSU is only using about 440 watts, and the PSU is 550 watts, so it should be able to handle powering the one hub on the 5V rail. Then all the other USB devices on the other PC will be powered via the step down.

As soundman98 says, cut the red wire in the USB cable going to the hub, or maybe even put a diode in that line.
I'll need to do the same thing, as my PCB leaves the USB power turned on when it is in sleep mode, which is a waste of power. My hub pulls power from the USB line or the plug in, so even if I drop power to the plug the USB line keeps everything alive and drawing power.

I fixed it. Since the MZ controls its inverter and cuts all power, it doesnt matter. There is never any power when the setup is off. I did rewire that one hub though. I ran it to the PSU of the MZ and all is ok. What worries me though is hybrid mode on the DZ system. All the 5V hubs run off the step down converter. So when the system sleeps the 12V rail cuts off. Will that affect when the system comes back on, or is that dependant on the mobo?