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Author Topic: AC voltage between CM15A and PC  (Read 8425 times)

bri-ko

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AC voltage between CM15A and PC
« on: March 13, 2006, 11:20:35 PM »

Recently my PC has been powering off apparently all by itself!!  I started checking around and found that there was about 10volts AC between the usb cable from the CM15A and my PC (I used a DVM and measured between the rectangular metal housing on the usb cable connected to the CM15A and the matching metal usb connector on my PC).  This is AC and is associated with the connection of the CM15A to the wall outlet - when I remove it from the wall the reading drops.  Has anyone else experienced similar situations i.e. unexplained computer powering down or crashes?  I actually think that this was the reason for a recent failed disk drive :o  Anyone have any suggestions ???
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Dan Lawrence

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Re: AC voltage between CM15A and PC
« Reply #1 on: March 14, 2006, 11:22:07 AM »

Sounds like it's your PC, rather than anything the CM15A is doing.  USB cables and ports do transmit power to devices, but the CM15A gets its AC power from the outlet it's plugged into.  The USB port is sending the power, but the 15 doesn't use it.  It sends the timer data to X10 Network Services, which loads with Windows and is supposed to update module status in AHP, but there are problems that X10 is aware of and a correction is due in the next update.

As to the shutting off of the PC, check the power status in the Control Panel and make sure the Power Scheme is set to "Always on" and the monitor and hard disk(s) are set to never turn off.

Hard disks are known to fail, so it's aways a good idea to back up data from programs frequently.
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bri-ko

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Re: AC voltage between CM15A and PC
« Reply #2 on: March 14, 2006, 11:58:56 AM »

Dan,
TNX for the reply, gave me some food for thought.
I didn't think it was my computer but I decided to test your theory.

I placed my DVM between the CM15A and the house ground,
with no computer involved, and get the same 10VAC reading.

Also, with the computer shutting down; it happens when I
plug the USB connector from the CM15A into the USB jack
on the computer, nothing to do with the power settings.
 
Could there be a faulty component in the CM15A leaking the
voltage back to the USB connector?

If this were the case do you think it could be a potential hazzard?

Appreciate your thoughts
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dave w

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Re: AC voltage between CM15A and PC
« Reply #3 on: March 14, 2006, 12:35:44 PM »

Bri-ko

It doesn't seem like the 10VAC should be present on the shroud of the CM15A USB. Since your computer is grounded (usually) your computer shroud is at ground and your CM15A shroud is at 10VAC (correct?). There has got to be some current flow. Have you tried to measure any possible AC current between CM15A shroud and ground? Although the leakage might cause the re-booting (I have had computer re-boot when accidently shorting USB out) I doubt it could cause HD failure. (humble opinion only).
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bri-ko

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Re: AC voltage between CM15A and PC
« Reply #4 on: March 14, 2006, 12:53:33 PM »

Dave w,

Thanks for the reply.

I did isolate the CM15A from the computer.
I measured directly from the CM15A USB cable to the
ground for my house wiring and did, in fact,
measure the same voltage.  This I think proves
that 1) my computer is grounded properly and
2) there is a 10volt AC potential difference
between the CM15A and the power system ground.

I did try plugging the CM15A into a GFCI outlet
to see if it would trip the circuit but it didn't.
This isn't too supprising as the CM15A does not
have a grounded connection.

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ka0wph

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Re: AC voltage between CM15A and PC
« Reply #5 on: March 16, 2006, 10:14:14 AM »

Have you tried the CM15 in another outlet?  My experience with differential voltage between two devices has shown that the is a bad connection in the outlet you are plugged into.  I have had as much as 60VAC between the shield of twinax cable coming from one system and the case of the terminal/pc that's attached at the other end, due to a bad outlet.
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Mystyx

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Re: AC voltage between CM15A and PC
« Reply #6 on: March 18, 2006, 01:43:25 PM »

Just to throw a couple things out there....

a Longer USB cable will draw more current from the PC, my friend had tried to add a USB cable to his living room and its power draw increased FRYING his USB connector ON the mother board.

Also, I had problems with my old power in this house, I had phase balance issues with my breakers, one breaker was loaded and caused power to spike on the opposite phase and it got bad one day when upstairs cleaning (dishwasher was on, vacuum going plus other things and blew up my M.B., CDRW, Router within 2 PCs which wasn't on a surge protector.
Does your lights dim at certain times (peak dinner time? peak evening?) it could be power company, as my area has had several multi family houses being built and could be overloading their transformer. or have disrupted the wire connections can cause phase issues. may need to just be tightened.
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Brian H

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Re: AC voltage between CM15A and PC
« Reply #7 on: March 18, 2006, 04:55:09 PM »

Mystyx; Most motherboard USB ports should shut down on an overload; that said I will add your data to my collection of problems.
Sounds like your Neutral power wires is poor. Loads on one phase should not effect the other drastically. Though my friend lost his neutral at the pole and fried just about everything in the home on the phase that went high due to unbalanced loads.
Been doing electronics long enough to say theory and what happens sometinmes are not the same. ::)
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Mystyx

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Re: AC voltage between CM15A and PC
« Reply #8 on: March 19, 2006, 12:35:01 AM »

yea, cameras have seen the hydro guys 3 times in 2 months... not my call, but I wonder if I should complain :)
maybe get some cash back on equipment if my house turns out ok ;)
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dave w

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Re: AC voltage between CM15A and PC
« Reply #9 on: March 20, 2006, 12:06:33 PM »

Mystyx

Brian is right, Loads on one phase will not cause spikes or variations on the other phases UNLESS the neutral is bad, or pole transfromer is bad. Either situation can be very dangerous ( also amusing...we had an underground neutral line to our house corrode open and the house became "haunted". Turning on light in bathroom would cause outside lights to come on dim, etc. All the lights in the house shimmered and danced, light switches turned on completely unrelated lights...and then we smelled the smoke.

If you are still having probelms like you describe, have power company come out and check the neutral....today.
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Mystyx

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Re: AC voltage between CM15A and PC
« Reply #10 on: March 20, 2006, 12:59:46 PM »

I havent seen the fluctuation much since the last time the cameras saw them, but I did change some things around inside to make sure I didnt have any single circuit more then 1600 watts and found maybe during the summer with fans going it could have been higher. so I am still in the process of wondering if its my house or power company.
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billy

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Re: AC voltage between CM15A and PC
« Reply #11 on: March 20, 2006, 08:42:29 PM »

bri-Ko,

I just measured the voltages of my CM15A/PC.

1. Line voltage = 125 vac
2. Neutral to ground measured = .525 vac
3. USB shield of CM15A to ground (not connected to PC = 6.93 vac
4. USB shield of PC to ground (not connected to CM15A = 0 vac
5. USB shield to ground (CMA15A connected to PC) = .001 vac  I will call that 0 vac

Measurements taken with a Fluke 77 DMM.

Have not look at the schematic yet, but it looks like the Vdd/Vss float from the isolation xformer.
So it looks like a common voltage your seeing.
Whether connecting and disconnecting the PC and grounding this voltage potential cause problems is another thing.

Regards,
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roger1818

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Re: AC voltage between CM15A and PC
« Reply #12 on: March 30, 2006, 11:55:21 AM »

3. USB shield of CM15A to ground (not connected to PC = 6.93 vac
4. USB shield of PC to ground (not connected to CM15A = 0 vac
5. USB shield to ground (CMA15A connected to PC) = .001 vac  I will call that 0 vac

Measurements taken with a Fluke 77 DMM.

Have not look at the schematic yet, but it looks like the Vdd/Vss float from the isolation xformer.

Interesting.  I have noticed that if I have left my CM15A disconected from my PC for an extended period of time (a month or more typically), when I do connect it to my PC, the CM15A locks up (and sometimes my PC starts to go crazy to).  I wonder if the Vdd/Vss float gradually increases over time and if it is too big when it is connected, a glitch occures.  Decoupling caps should protect the chips from this, but for some reason X10 didn't put any on the CM15A.  One person here (Andre I think) said that adding them fixed his reliability problems.  I have been meaning to add them to mine, but haven't gotten around to it yet.
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