Can Current Backflow from Powered Hub's Power Adapter & cause PC Damage?

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Old 06-13-14, 03:03 AM
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Wink Can Current Backflow from Powered Hub's Power Adapter & cause PC Damage?

Can current flow from a powered USB hub's power adapter back to computer via usb port ?
& if yes,
Can it cause damage to Computer components like mobo, etc? What should be my concerns?

Using a 2 Amp 5V Power adapter to power a 10meter Long Active Repeater USB extension cable with 4 port HUB & plugging into PC's Front port, causes the following, after PC is shut down (bit scary)

- PC Chassis fan to keep running (thought slower than regular speed)
- Front Chassis HDD & power LED to turn on (though bit dim)
- May be other things which i cant detect/see at chip level, in motherboard??

More detail :

To run 4 High power Wifi Adapters(needing >450 mAmps) , far away from PC,
Bought a 10m long Active Repeater USB Extension Cable with 4 Ports& power port at far end
33ft USB 2 0 Male to Female Extension Cable Hub Splitter Adapter with 4 USB Port | eBay (see 2nd picture for single pin adapter port on it)
& Powered it by plugging it with locally bought (medium quality) 2 Amp 240V AC to 5V DC Power Adapter

Even 4 Wifi Adapters run fine (appear to) using this setup, but running chassis fan, dimly lighted Power & HDD LED, even when PC is switched off is bit scary & surely mean 5V & some current is flowing all though that 10 meter extension cable into my USB port & powering stuff.

Can this cause damage? and what should be my concerns. Of course I can't switch off the power adapter (lying 10 meters away from PC) every time I switch off my PC to prevent this.

** PICTURE OF SETUP is attached below**
[ATTACH=CONFIG]33168[/ATTACH]
 
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Old 06-13-14, 09:11 AM
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Can current flow from a powered USB hub's power adapter back to computer via usb port ?
In your case it is. Should it ? I don't think so. I would think that that adapter should not allow 5v back into the computer. I tried to find more information on it without much luck. I would either check with the place you got it from or replace it with a different unit.
 
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Old 06-13-14, 09:33 AM
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Hard to believe there isn't a diode on the mobo or in the hub to prevent that. Have you tried a different USB port on the PC?

Yes, I think it could cause damage. I'd try another hub if switching ports doesn't help.
 
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Old 06-13-14, 03:23 PM
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Exclamation Specific question for you guys...plz help

@Pjmax
3 questions for you sir

A) when you said "adapter should not allow", i think you meant to actually name "USB HUB" ,which is actually a part of far end of 10m long active USB extension cable

Please see the exact hub here...3pictures
33ft USB 2 0 Male to Female Extension Cable Hub Splitter Adapter with 4 USB Port | eBay
This Hub has a pin port for supplying power, where i plugged in the adapter

I think you thought adapter is a part of hub, which it is not
I dont see how adapter is responsible here. i tested it with multimeter and it is giving 5V (off load; no idea about on-load) . its rated at 2amps max but i dont know how much it can give.
& whether, if it supplying >2amp is the reason for my fans/led stuff to happen 10 meters away.

B) If "USB hub cum extension cable" is low quality(probably chinese), it may have missing parts (to save costs) which prevent back flow of current along whole of that 10meter cable? is that most likely?

C) i read somewhere someone talking about disconnecting the power (5V) line cable (see the attached image; not from exact USB hub) and keep the data cables & ground cable connected to pcb of HUB. That way adapter will supply the proper power for wifi adapters and data will be properly taken of by extension cable anyway , solving this issue.
Is that right thinking?or Can i do anything else to prevent this backflow
(of course this is the only when i don't want to buy another good quality extension cable cum hub etc.....& yes i wanna save money...already costed me 25$)
[ATTACH=CONFIG]33200[/ATTACH]
@Gungguy45
Ok i think i made a mistake in picture, port is not the backend port but front end port (though i wrote so in question)
My mobo is ASUS p7h55 and asus is considered fine with quality
Can it be that front end ports are not properly shielded , even on normal to good mobo's?

So logically is this the current flow path :?
From 220v Wall port ->220-5v / 2amp Convertor Power adapter ->4Port Hub which is a part of 10m long usb extension cable ->into my front usb port -> into my mobo's port for front USB >
into the main long pin Mobo power connector -> into PSU's power supply wiring -> thus powering a simple chassis fan which is only connected to a molex psu port ??
is it?
& Similarly current reaching into mobo LED connectors and then flowing to power LED's?

That way that current should be powering almost all ports and even current must be going to my HDD's and most mobo parts (even though weak & < 5V) ???

I have not tried this on backend port yet . I cant afford losing my hardware (cost as well as other issues)


1 question for both of you guys
i kept using this setup for approx 24 hours (in divided hours) , with all wifi adapter working fine and detected by PC.
As of now, my PC has no problems (though after that period i had stopped using, until i clearly understand this)
why no damage happened all this long? or is it at micro level and would have deteriorated mobo parts etc already?


Thanks guys... but i already asked this on superuser forum and only got 1 incomplete answer.
Plz help me understand this
 
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Old 06-13-14, 03:52 PM
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disconnecting the power (5V) line cable (see the attached image; not from exact USB hub) and keep the data cables & ground cable connected to pcb of HUB. That way adapter will supply the proper power for wifi adapters and data will be properly taken of by extension cable anyway , solving this issue.
That doesn't make any sense. I think what that picture is is an UN-powered hub, since it has 4 wires and no connector for a power supply. You only have a 2 wire connection from the power supply to the board on yours. That 5V supplies power to the units plugged into the USB ports on the hub. Apparently, the port that the PC cable plugs into is just in parallel with all the device ports. Now...you might be able to disconnect the power from the port that the cable from the PC plugs into. That would eliminate any possible path for voltage FROM the hub back to the PC. That should have been done when it was designed.

I agree ASUS is a quality brand. Possibly NO mobos have diodes, since power should never come FROM any device plugged into a USB port. But using a poorly designed powered hub apparently does backfeed.

As to the current path, I think you pretty close, but I doubt the P/S is involved. More likely it is just taking different paths through all the mobo components and due to voltage drop and inadvertent circuit paths, it is supplying lower than normal voltage to the components you noticed operating. Also, if the chassis fan is a 5V item, then all those things may be on the same bus.

As to damage, no, I doubt you would see anything immediately, but low voltage on any component is bad. Fan spinning slowly may have higher than normal current and won't cool itself, leading to failure.


Hmm...another thought...do you see the same symptoms with no devices plugged into the hub? Just the P/S and the cable from the PC? That would definitely identify the hub as the problem. I'll bet if you checked everything out, you'll find all the USB ports on the hub in parallel...or at least the 5V and common/ground are.
 
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Old 06-13-14, 05:03 PM
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Lightbulb

Few things need clarification i think
I think what that picture is is an UN-powered hub, since it has 4 wires and no connector for a power supply
yes thats not my hub. I will be opening up my hub & posting pics of pcb/wires etc) soon

But i want to point here that ideally as per specifications my "hub cum active extension cable" is supposed to power 4 low power items easily on its 4 ports like KB, mouse, etc.
- The hub has power port (for a optional adapter; which i bought from some other source) for powering high power devices

The 4 wires in above picture are part of cable which plugs into PC port.
Though i am not yet sure, the same cable (10 meter long) from my hub to my PC port should also have 4 wires as its supposed to power low power items anyway.
With just 2 wires how will it power those low power usual devices?

I will still check, post pics, and confirm

Apparently, the port that the PC cable plugs into is just in parallel with all the device ports
if so, is it normal for Asus mobo's or something bad in my mobo? This mobo has some 10 USB ports @ back(fixed on mobo back end), 2 at front (connected to 1st onboard mobo connector) & another 2 (available to used by connecting to 2nd onboard USB connector)

Kindly see below my actual mobo pic and connections
[ATTACH=CONFIG]33204[/ATTACH]
As to the current path, I think you pretty close, but I doubt the P/S is involved.
But how come PSU is not involved when this simple 2 wire chassis fan (yes is of 5V) is connected to a 4 pin molex connector, which is directly coming from PC PSU only.
if fan is running (when PC is even switched off)that means reverse current has flown through mobo's USB port connector to mobo's main power connector to PSU and then into psu's other 5v rails which powers that molex connector connected to fan, HDD, etc (probably the reason HDD LED lights up too)?
do you see the same symptoms with no devices plugged into the hub? Just the P/S and the cable from the PC? That would definitely identify the hub as the problem. I'll bet if you checked everything out, you'll find all the USB ports on the hub in parallel...or at least the 5V and common/ground are.
Do you mean checking for symptoms with no wifi devices plugged to hub but everything else including hub's power adapter in place?
Haven't checked that. i will.
Just the "Hub cum extension cable" plugged to PC port of course doesn't do anything abnormal & lowe power devices run fine if attached to hub's ports. That's bound to happen as power adapter is not connected.

Are USB ports in parallel a bad/low quality thing for hubs, if its the case here? I have no idea


Thanks for your detailed reply . highly appreciate it.
Regards
 
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Old 06-13-14, 06:02 PM
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Now that you explained that your hub was an optional powered item, it makes perfect sense that all ports are wired parallel, they'd pretty much have to be for the PC to power connected devices. But since it's a cheap unit, they skimped and didn't put a blocking diode in to prevent voltage backfeed.

Ahh...didn't realize the fan was powered from P/S, those I've worked on normally connected to the mobo somewhere, sometimes with 4 pin, sometimes with 2. If 4, the additional lines are normally for control/data reporting, ie...fan speed/failure.

Yes, I meant disconnect all the wifi devices on the hubs output ports. Doubt it will really matter now that I have more info.

I doubt there is anything wrong with your mobo, but trying a different port should verify. The mobo was designed to a higher standard than the hub...as in...no power should be coming in, just out.
 
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Old 06-13-14, 06:26 PM
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In order to run heavy drain devices from the hub you would have to use the plug-in wall adapter. That plug in adapter's power should be for powering only the items plugged in at the hub.

In my opinion..... that voltage should not be getting back to the computer and can be harmful to your computer.
 
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Old 06-13-14, 07:00 PM
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I was just looking over the specifications for your motherboard here Motherboards - P7H55 - ASUS . According to the specifications you have plenty of USB hubs on the back of your computer and at least two places inside of the computer where you can connect further hubs on the front of the computer. I have a powered hub myself but don't like buying them from e-bay many of those you buy on e-bay can come from China and are cheaply made. I would buy from Newegg or Tiger direct.

I also like to stick to the highest rated hubs like the ones I found on this page from newegg Newegg.com - usb powered hub or from Tiger direct Search Results for usb powered hub at TigerDirect.com .

I am not saying buy any of these in particular but like these two websites for buying things like this as they rate the products. You still might find something made in China but to a higher standard than what you would find on e-bay.

The really good hubs though are those you connect onto your motherboard like those hubs with card readers. I have one of those on one of my desktops and may get another one just like it for my other desktop. They certainly prevent feedback issues from the power supply on some of those powered hubs and will supply more than enough power.
 
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Old 06-23-14, 06:47 AM
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Check images plz

Sorry guys.... power crisis in my area and i was away from home.

Now that you explained that your hub was an optional powered item, it makes perfect sense that all ports are wired parallel, they'd pretty much have to be for the PC to power connected devices. But since it's a cheap unit, they skimped and didn't put a blocking diode in to prevent voltage backfeed.
Are usual hubs not in parallel? Anyway I opened the hub and clicked photos. Attached below.

Ahh...didn't realize the fan was powered from P/S, those I've worked on normally connected to the mobo somewhere, sometimes with 4 pin, sometimes with 2. If 4, the additional lines are normally for control/data reporting, ie...fan speed/failure.
The fan concerned here is a chassis fan. Though my mobo does have a CHASSIS fan connector, this fanh came with Cabinet & has larger molex type 2 wire connector(no speed/PWM feedback) . So i connected it to PSU connector itself .
Yes, I meant disconnect all the wifi devices on the hubs output ports. Doubt it will really matter now that I have more info.
anyway i tried...and doing that too, still causes same symptoms when PC is switched off.

[ATTACH=CONFIG]33633[/ATTACH]
[ATTACH=CONFIG]33634[/ATTACH]
[ATTACH=CONFIG]33635[/ATTACH]
HIGH QUALITY PICS as forums causing resizing ->
imgur: the simple image sharer
imgur: the simple image sharer
imgur: the simple image sharer


So seeing the pics, how do find it?
Well doesn't appear to me too bad .
You can see the power adapter plug too.
Is there any diode there?
& not sure what are those nude twisted wires close to end (no i didnt twist the hub to do such damage if its some damage(unlikely))

Coming to the wires solution:
So i was correct, that actually has 4 wires going back all throughout those 10 meters back to PC.
That was obvious actually given the fact that this Repeater Cable cum Hub is supposed to run low power devices anyway , without any need for power adapter.

So , can i trim the connections of 2 non data wires GROUND and 5V or just the 5V wire and prevent this backflow from happening? or may be find some diode locally (a time consuming process to find for sure) and then put somewhere where you guys tell me? (yea i have a solder at home and do a bit of soldering myself)
if both these ways will solve the issue, i think 2nd would be better as that will ensure Repater cable cum hub will work for low power devices too , when adapter is not plugged in) as cutting that 5V cable connection from PC will mean there is no power & without adapter repeater cable cum hub would be useless

Please help guys.
 
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Old 06-23-14, 06:51 AM
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@hedgeclippers
I was just looking over the specifications for your motherboard here Motherboards - P7H55 - ASUS . According to the specifications you have plenty of USB hubs on the back of your computer and at least two places inside of the computer where you can connect further hubs on the front of the computer.
Well if you see the detailed picture of my setup, in which i posted the mobo picture too....i actually pointed the same that this front usb panel is actually connected to those one of the 2 USB points on mobo, you are referring to.

The really good hubs though are those you connect onto your motherboard like those hubs with card readers. I have one of those on one of my desktops and may get another one just like it for my other desktop. They certainly prevent feedback issues from the power supply on some of those powered hubs and will supply more than enough power.
Well those wont solve my requirement because i bough this 10meter long Active repeater cable cum hub (see 1st post for details) to run wifi adapters far away from PC. the hubs you are talking are limited in distance to Cabinet only.
 
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Old 06-23-14, 09:33 AM
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I don't see any diodes, though possibly the IC could perform that function, but apparently it isn't.

Just looking at the quality of the soldering, it looks like it was made a by a team of monkeys with no thumbs. Sorry, I'd send it back or trash it and buy a quality name brand item.
 
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Old 06-23-14, 10:22 AM
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Since the computer supplies 5vdc..... you couldn't have a regular diode to block reverse flow as that junction drops .7v Even a low loss diode would have some drop and the hub wouldn't be AT 5vdc.

It would seem that a relay would almost be needed that would activate when the power supply was plugged into the hub.

If I was experimenting.... I would try disconnecting the red 5v+ wire that goes to computer to see what happens. If that gives the desired effect then you should dedicate that hub to be powered or not. Not both.
 
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Old 06-23-14, 11:36 AM
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I would try disconnecting the red 5v+ wire that goes to computer to see what happens.
Thats what I said back in post 5. That would completely eliminate any path for power back to the PC from the hub. Since it's going to have some relatively high draw devices (assuming they aren't powered separately), the hub should be powered anyway.

It would seem that a relay would almost be needed that would activate when the power supply was plugged into the hub.
Or one of those connectors on the board for the external power that would disconnect the 5V line from the PC. Like they do for battery powered devices that can also use an external supply.
 
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Old 06-23-14, 11:41 AM
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Or one of those connectors on the board for the external power that would disconnect the 5V line from the PC. Like they do for battery powered devices that can also use an external supply
Exactly right ,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,
 
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Old 06-23-14, 01:07 PM
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Alright guys, thanks for reply ....but lets clear the chaff
Here are a few things:
- i cant return the item. lets not go onto those lines
A) Gunguy...can you explain a bit more on this
"Since it's going to have some relatively high draw devices (assuming they aren't powered separately), the hub should be powered anyway."
the high draw devices (high amp i mean) are the wifi adapters i use and as they need atleast 460mA each , that was the reason i needed a powered USB hub as no USB hubs provide 500mA per port(USB 2.0 Specification) without having a power adapter. They ofcourse are being powered by the 2Amp power adapter i have. Otherwise, without power adapter, when i add >1 such wifi to this HUB, they dont get properly detected
B) As i explained in last post, i preferably want it Repeater Cable cum Hub to work as OPTIONAL powered hub (both unpowered and powered with adapter).
So 1st option
i search, get & solder that relay thingy pjmax also talked about, which will disconnect the circuit of the 5V Cable (colored red in above pictures) when it detects current in Power adapter port
Q's what kind of relay is that? any specifications so that i can ask electronic store
how big it can be? will it fit on that hub PCB? i think relays are mechanical. if so, will it be quick enough for switching 5V line off? Ofcourse short bursts of current flowing back are equally bad for mobo in long run.

2nd option
I simply cut that 5V off hub's PCB and thus this item will become a "mandatory" powered hub cum repeater cable (and ofc low draw devices like KB/Mouse etc will not operate without adapter...in case i want to use this long cable cum hub for other purposes)

Any other option?

C) I asked this before too....are those nude wires in zoomed picture below normal?
[ATTACH=CONFIG]33662[/ATTACH]
is that part of ground wire out of total 4 wires? i hope i dont need to fiddle with this GND wire, if i employ 2nd option above??
 
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Old 06-23-14, 01:20 PM
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Those strands are just shielding, no electrical connection, though normally they are grounded at one end or the other or both. Thats another indication of a cheap manufacturer, IMO. The condition of the shield I mean. I didn't know which wires you meant in the other pics.

Right, if you cut the red power wire, the hub will always need the transformer to work. I mean, the thing costs less than $20. If you want the unpowered option available for the future, just buy another. I guess you could carefully wire a mini switch in the red wire path so you could have it on or off, assuming there is room in/on the case to mount it.

This is kind of you wanting to have your cake and eat it too, lol. I'd be concerned about what it may mess up in your PC more than the possibility of using it unpowered in the future.
 

Last edited by Gunguy45; 06-23-14 at 03:46 PM.
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Old 06-23-14, 01:38 PM
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haha
Alright... so as per you the "relay" route is also bid dodgy
well shipping adds..costed me some 30+.Anyway

Ok then i would go by route of cutting 5v wire and adding a switch( preferably outside the hub case...something like http://www.robotroom.com/PCB/Color-P...-small-PCB.jpg or something like push button)

now i just that wish that hub's electronic components work properly without that 5v line .

Thanks guys.thanks for tolerating me :P
I will also post the outcome , even if the mod worked
 
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