I felt a small shock when I touched the USB connector from the Canon Pixma IP1500 printer and the grounded PC case at the same time. It's not a 60hz AC type of shock but is felt as very brief pulses of approximately 2-3 pulses per second when printer is in off mode. These pulses are faster if the printer is turned on. I put a neon tester between the USB cable and the PC ground and it glew continuously but could not see the pulses on the neon tester. Although the neon tester glew continuously, why did I only feel a series of short pulses about 2-3 times per second. The shock feels like a couple of milliamps through the finger.
Yikes! I suspect a defect in the power supplies of the PC or the printer or the wiring of the outlets they are plugged into.
I DO NOT THINK IT IS SAFE TO CONNECT THEM TOGETHER. Please don't.
I'm guessing they both have 3-wire power cords and are plugged into different outlets, and one of the outlets is not grounded properly. Is that the case?
Or the printer has a 2-wire power cord and has a defect in its power supply. Again, one of the outlets is probably not wired properly.
You can get a little tester with 3 neon lamps in it which you plug into an outlet to check that the correct side is grounded. I urge you to do so.
The computer is grounded but the printer is not. The printer has a non-polarized plug. I tried reversing the printer plug and the result was the same. Both the computer and printer is plugged into the UPS unit which has a built-in building wiring fault light but this light is off. The computer has the third prong intact. The outlet tester indicates correct polarity. Many SMPS have the ground side connected through a small capacitor to the negative DC side of the AC line rectifier. I have the printer connected to the computer and am able to print without any trouble. There is only a tiny spark when touching the USB cable to the PC case.
----- Original Message ----- From: "Michael A. Covington" Newsgroups: sci.electronics.misc Sent: Saturday, September 11, 2004 2:38 PM Subject: Re: Shock from USB printer cable
Any continuous potential, i.e., not static electricity, difference you can feel with dry skin is definitely too much from a safety standpoint. Have you tried measuring the voltage with a voltmeter?
In any case it's time to contact the printer manufacturer's help line and ask them what they are going to do about replacing your defective printer or power module before some one gets hurt using it.
The USB cable sends periodic pulses to the PC even when off and this is what is actually felt. It's not a standard 60hz shock like from a wall outlet which would be much worse than a shock from the USB connection. Do you have any USB printer and have you gotten the same shock from the USB connection?
To feel a shock you need about 25 volts. Something seems to be wrong. My next move would be to use a voltmeter to measure the pulses. I think there's some kind of leakage in the power supply of either the printer or the computer.
The movement of the voltmeter isn't fast enough to measure short pulses. The neon tester glew dimly when placed between USB connector and PC ground but there isn't enough current to feel it except for the short pulses. The neon tester goes out with even a very light touch between the USB connector and the PC ground. The slight shock is felt only if I touch the USB connector and PC case firmly, not if I touch it lightly. There isn't enough current to cause a spark when connecting the USB connector to the PC.
"Keith Weisshar" schreef in bericht news:ryb1d.6770$sX2.4401@trndny09...
pulses.
this
wrong.
printer
Keith,
You need to kow:
- To feel a shock requires some tens of volts and some milli amperes of current albeit for a very short time.
- To ignite a common neon bulb requires about 90V and it extinguishes below some 60V. Current in the micro ampere range.
- To measure voltages you need an electronic instrument with a high resistance (>10MOhm). This is because you're dealing with high impedances (otherwise you'd been dead already.) Check for AC *and* DC voltages.
- Equipment with a two pin mains connector are - or should be - "double insulated". That's to say none of the metalic parts you can touch has a galvanic connection with the mains or the ground. They're floating.
Assuming your mains installation is OK and following the discussion so far the only thing I can imagine the cause of your shocking experiences is a leaky power supply of the printer. That leak can be capacitive i.e. the parasetic capacity of the transformer and/or a deliberately placed capacitor meant for decoupling. They are not necessarily defective but I can't see that on this distance. It is also possible that these - or other components lost a part of their insulation resistance and became leaky.
It's hard to proceed without some electronic skills and equipment. You can try another power supply or printer of the same type and look for differences. I'd try an insulating transformer to do the same. A good one is shielded inside and has very low parasetic capacity to the mains. Even a less professional one may solve your problem... if you can find one.
petrus bitbyter
--
Outgoing mail is certified Virus Free.
Checked by AVG anti-virus system (http://www.grisoft.com).
Version: 6.0.754 / Virus Database: 504 - Release Date: 6-9-2004
It's not a linear power supply. It's a switch-mode power supply in a rectangular box mounted to the bottom of the printer with a screw. The label on the black box says AC adapter and has 120-220VAC input and a 24VDC output.
"Keith Weisshar" schreef in bericht news:juo1d.13904$z_3.10759@trndny07...
PC
USB
impedances
far
can
one
24VDC
It nevertheless contains a transformer to separate the mains from the printer. These type of power supplies use to run on >25kHz and needs much smaller a transformer then the ones that run on 50/60Hz. The transformer core is a ferrite instead of iron. But it is a transformer. There even may be a second, much smaller, transformer used for the feedback although most of the times a opto coupler is used for it these days.
petrus bitbyter
--
Outgoing mail is certified Virus Free.
Checked by AVG anti-virus system (http://www.grisoft.com).
Version: 6.0.754 / Virus Database: 504 - Release Date: 7-9-2004
I have many iron transformer based UL listed AC adapters and none of them cause a shock to ground and they don't light the neon bulb either. The capacitive leakage between primary to secondary is too small to be felt from normal adapters. Do switch-mode adapters have higher leakage currents than normal adapters? Normal adapters don't have any y capacitors between primary and secondary unlike switch-mode ones. Y capacitors are used to suppress EMI but are only found in SMPS.
I have contacted Canon tech support and they transferred me to consumer relations department and they said there is current going through the USB cable and I asked how much current and they said up to 10 milliamps. Canon just gave a warning over the phone to be careful never to touch the metal part of the USB cable and any grounded objects at the same time.
Well, that's a great warning. I could have said that myself. You also could as you found it out the hard way.
Wonder whether this printer(s power supply) meets the local (and/or national) safety regulations.
The 10mA they mentioned looks very strange to me. Can't imagine they're right. I have my doubts about the technical skills of that consumer relations department personal. Most of the time they repair clients and never printers.
petrus bitbyter
"Keith Weisshar" schreef in bericht news:6Y12d.19382$z_3.18711@trndny07...
--
Outgoing mail is certified Virus Free.
Checked by AVG anti-virus system (http://www.grisoft.com).
Version: 6.0.754 / Virus Database: 504 - Release Date: 7-9-2004
There is even a slight buzzing sensation when rubbing a finger across the USB connection with just a very light touch and it goes away when the printer is unplugged. Have you had this happen with your printer?
ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here.
All logos and trade names are the property of their respective owners.