PC getting power from hdmi switch?

F

Foz2001

[H]ard|Gawd
Joined
Aug 25, 2001
Messages
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Hi guys


I have an hdmi switch with a cable box and PC hooked up to the inputs. The cable box is always on (dvr) and it is powering lights on my fans, and even slightly rotating some fans on the PC. The hdmi is plugged into my vid card. Do I have any options here besides unplugging the PCs hdmi cable? Is this harmful for the PC?

Thanks.
 
That's just... bizarre. Do you have a battery backup? I mean, you seem like you are sure where the power is coming from, so you've unplugged the computer completely from the power source, and everything else, except the hdmi out to the DVR box and your fans are spinng even with the motherboard lights off? Power supply flipped off even?
 
I believe it goes without saying, but this should not be happening.

That being said, HDMI does technically include a 5V power source via one of its pins (pin 18, I believe), albeit one with only 50mA of current. You're not going to power much with 50mA, but a few LEDs may be able to make use of it assuming your motherboard is somehow wired to make use of the 5V pin to begin with.

And as you are using an HDMI switch, it is possible, I suppose, that the switch is amplifying the signal and potentially dumping more current onto the 5V pin in the process.
 
It is 100% coming from the HDMI cable via the cable box, as I unplugged everything else. The HDMI switch does not actually have any power adapter.

So the power is running through the video card, into the motherboard, and to the fans....
 
If that is indeed the only connected cable, then it must be, odd as it may seem.
 
Do you think I should be concerned with this damaging any components?
 
It wont cause any harm, it will just be a nuisance.
The supplies are limited to around 50mA current so there is no chance of fire/heat damage due to 2 supplies competing with each other.

There was another thread made a month or 2 ago where someones case fans came on if he plugged another PC into the same monitor.

I have an HDMI switch that has its own power supply, but without it plugged in, it will also accept power from any of the HDMI in or out ports.
There doesnt appear to be any standard for restriction on what can supply power and to where.
 
I guess it should also be noted that 50mA is the maximum 5V current according to the HDMI specification, but some devices can output several times that amount of current. Even so, you're still looking at a small fraction of an amp. E.g. nothing to worry about.

Its only purpose is to allow for reading EDID tags when a display or other connected device is powered off.
 
Last edited:
TESLA said:
I guess it should also be noted that 50mA is the minimum 5V current according to the HDMI specification, some devices can output several times that amount of current. Even so, you're still looking at a small fraction of an amp. E.g. nothing to worry about.

Its only purpose is to allow for reading EDID tags when a display or other connected device is powered off.
Click to expand...
50mA max, not minimum.

http://en.wikipedia.org/wiki/HDMI
Pin 18 +5 V (max 0.05 Amp)
Click to expand...

http://en.wikipedia.org/wiki/Display_Data_Channel
+5V DC power up to 50mA
Click to expand...
 
Supposedly it is a max, but in practice I believe it's a bit inconsistent:

http://www.hdmi.org/learningcenter/kb.aspx?c=13#42

Though I suppose my statement should be amended to:
I guess it should also be noted that 50mA is the maximum 5V current according to the HDMI specification, but some devices can output several times...
 
Lol, both specs fly in the face of each other.
Strange that it can be so specific yet blatantly overridden.
The cable can handle say 200mA, but with no formal barrier on how much could be supplied, multiple PSUs feeding power on the same rail could cause problems.
 
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