[mythtv-users] HDPVR problems - power supply again?

Keith Pyle kpyle at austin.rr.com
Wed Aug 14 16:14:14 UTC 2019

On 08/14/19 07:00, Stephen Worthington wrote:
> On Tue, 13 Aug 2019 20:39:24 -0700, you wrote:
>>>   Has anyone ever hooked up an ammeter to see what the HDPVR actually
>>> draws?  I
>>> wonder if it is close to the 2 AMP rating of the PS, so just stresses it
>>> out,
>>> causing earlier failures.
>> I had the same thought last time mine crapped out. Instead of doing the
>> science as you propose, I replaced with an over capacity wall wart (3-4A I
>> think) and that's the one that just failed.
>> I don't know enough about PS electronics to say if anything other than
>> over-drawing current could stress the PS.
>> It also makes me worry about getting power from the USB of the Myth box.
>> It's one thing to kill a $15 wall wart and another to kill a $100 PC power
>> supply.
> PC power supplies are usually very robust, and typically are running
> well below their rated capacity.  If you buy expensive ones, they
> usually have a list of the protections they provide (over voltage,
> over current and so on).  USB ports have limits in their circuits to
> prevent anything from drawing too much power - that is part of the USB
> standard.  So the real problem with using a PC power supply only comes
> if you connect the HDPVR to a standard power connector (ether Molex or
> SATA) and do not have any current limiting in the connection you use
> (such as a properly rated fuse or circuit breaker).  The PC power
> supply can then supply a great many amps into the HDPVR, and if the
> HDPVR has a fault that draws huge current, that can cause a fire.

I just checked AC input current for an HD-PVR PS since I could do it quickly.  My ammeter has a display to .01 A. 

HD-PVR off                      0.00 A @ 120VAC

HD-PVR on, not capturing        0.00-0.01 A

HD-PVR capturing 1080p input    0.01-0.02 A

This isn't great data since it's near the meter's measurement limit, but it suggests that the output current demand could be close to 2 A and maybe a bit over at times.  It would be better to check the output of the PS, but I didn't have the connectors handy to interpose the ammeter there.


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