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I used to (many years ago, use the ADCOM ACE PC. I had one stop working about the same time another one failed for a friend and took out his preamp.
I need SOMETHING and with Christmas coming the expenditure, no matter how big or small, is out of the question. There's just too many other things to buy right now.
I have the second one I'd used back then but have been wary of using it. Is there a way to test the MOVs that a brainless idiot can understand?
Although the lightning storm season is pretty much over, I'd still like to have all of the gear into one unit for ease of use and some protection. Am I safe to just go ahead and use it and simply disconnect at night?
Because of our frequent short-lasting blackouts we have to reset the clocks at least once every month, sometimes more often...we've had momentary lapses of reasonable electrical delivery 3-4 times in one day! I have everything else (The TV system upstairs and the big system downstairs) on Brickwalls. The neighbors all have asked if my power goes out as often as theirs.
Allegheny power company says there are no problems..."Is there anything else I can help you with today?"
Yes, stop lying and fix the problem!
******************************
Heck if I know! I ain't no genius.
Follow Ups:
Any Fans of Whole-House surge protection?
LInk is to the Delta site, but I've seen others. If I lived in a lightning prone area or where the power company sucked, I'd have one of them installed in a heartbeat.
Too much is never enough
On the left is a surge generator capable of applying surge pulses from 200V to 6.6kV at 1.2/50us (open circuit) and 8/20us (short circuit), as well as at 0.5us/100kHz damped oscillation, directly onto the power line to easily test for IEC, EN, Telcordia, or any custom profile.
On the right Electrical Fast Transient gererator (EFT) Burst test can test to 4.4kV, meeting and exceeding the IEC limits. This is for applying high frequency burst noise directly onto power lines or when used in conjunction with a "trench" EFT can be inductively coupled to power cords and interconnects.
If you had the test gear and the experience to be able to use it and work with AC line voltages, I could tell you a way to non-destructively test them.
BUT, given your recent posts about the state of your hobbying, I don't think it would be a good idea to try and tell you, working with the AC power line hot or "live" WITHOUT the necessary experience and caution can be DEADLY.
The simplest thing you could do is to just replace them. De-solder or cut out the old MOV's, and install some new ones from a distributor.
DigiKey carries the Littlefuse brand, and the part number V150LA20A should do the job just fine. Be sure to keep the lead lengths to an absolute minimum, dress the part out similarly to the old one, and make sure your soldering has not shorted the AC line. Of course, all the usual cautions about working with AC line items apply, so be very careful and double-check your work BEFORE you plug it back in.
Due to the reasonable voltage set point for this part, it should last a long time, even in your poor conditions.
Good luck with the power line disturbances, such frequent outages and surges can be very frustrating and costly.
Jon Risch
There are some inepensive devices on the market than have the MOV crowbar a fast acting fuse. If the fuse blows you toss the device.Would this be a reasonable strategy for a DIY device(if the fuse blows replace the MOVs)?
Edits: 11/12/10
Sure, if you use fuse protection for the input to the Surge Suppressor devices, then if a fuse blows, and replacements also blow, then replace the MOV's.
If you are asking if a MOV based SS blows a fuse once, does this mean that the MOV's should be replaced? Not necessarily, as the limiting action of the MOV's, which could have been well within their rated limits, could have blown the fuse in the first place by drawing enough current to blow the fuse during the surge.
It would be relatively cheap way to maintain both safety and positive SS action to replace the MOV's whenever a fuse blew though.
Jon Risch
At least I know all of our stuff is now required to have a fuse in series with any MOV.
I am not sure if it is a UL or CSA standard but I can ask the agency guys next time I am at the agency lab.
They also make MOV's now with integrated fuses.
My neighbor had an old Monster power strip for his video gear. The ganged MOVs blew up and took out a new dishwasher on another circuit. He asked me to take the strip apart, as he is not comfortable with electricity. The charred remains of the MOVs were an impressive sight.
"The ganged MOVs blew up and took out a new dishwasher on another circuit."
OK, I'll bite. How?
Seems more likely to me that if they are correlated at all that the same event that blew the MOV's also took out the dishwasher.
Rick
My house is on the same utility transformer and we had no indications of a problem.
I believe the MOVs shorted and the current surge on the neutral created a voltage that added to the normal line voltage on the dishwasher circuit.
Al, I've been thinking about it (always dangerous) and can't visualize how it could damage a device on another circuit.
As far as I know the neutral and safety ground are always hooked together in the breaker box (at least around here) and that node is grounded to the local ground and the common from the transformer. So what's the path through the dishwasher?
We just had to put in a new dishwasher this year as the old one could no longer hold it's water, as it were, and although a cheap one it's got a microcontroller and a sea of buttons and LED's on the front instead of a rotating timer that I could make sense out of. But it actually washes a lot better much to my surprise. Now we shall see how long it lasts...
Regards, Rick
The USA system, with a grounded center tap on the utility transformer, provides a neutral wire that is grounded at both the transformer and the panel, as you observed. The reason for the two grounds is that the earth in between is not generally a low impedance conductor.
Thus, when there is a line-to-neutral fault on one hot leg, there may be considerable voltage developed across the neutral wire (Ohm's law) until the breaker opens. This voltage is subtracted from the faulted hot leg, but adds to the opposite hot leg voltage.
Appliances should withstand voltage surges within reason. My neighbor's dishwasher should not have failed. However, it was new and the failure may have been something about to happen in any case.
OK,
Thanks for the explaination, I see what you mean. It's not something I would expect to cause problems considering the low resistances involved but who knows what the reactance looks like or the susceptibility of the dishwasher.
We are in the process of looking for a new stove and at Sears they are pushing their long-term warranty and have a controller assembly laying in front of the sign as an example of something expensive (at least it looks expensive) that is at risk. I should have looked more closely but I think it actually used mechanical relays to control the burners so that should provide pretty good isolation back to the drivers. Seems like poor marketing to me "be sure to get an extended warranty because this new model is far less reliable than the one you are replacing despite costing five times as much."
I can still get parts for he old one but they aren't cheap and I'm not sure I want to yard out the asbestos wiring which is probably getting pretty friable after forty years. Too many unknowns...
Rick
We've had numerous problems here in Vermont, but usually there are some excuses, i.e. ice storms, auto accidents, etc... It is so bad that I have a UPS with extra batteries that will run most of my computer equipment for throughout a six hour outage.
I won't buy any more electric clocks that are just "power line cycle counters". Better to have real clocks that run off of batteries, or at least have battery backup.
Tony Lauck
"Diversity is the law of nature; no two entities in this universe are uniform." - P.R. Sarkar
MOVs form conductive paths once the voltage across them reaches a certain design level, then revert to non-conducting once the surge has passed. The conductive path may be damaged by the surge event, so that there is less of the metal oxide material available for future protection. Once all the easy paths are burned out, the device either becomes useless or dies in a spectacular short-circuit. I have a neighbor who lost his new dishwasher when his old Monster surge protection power strip went out with a bang.
I don't know of any way to tell if such a device is close to failure without making it fail.
Your power situation is unacceptable. The power company needs to install an event recorder and figure out why their grid switching is causing so much trouble. I once worked for a semiconductor manufacturing company that suffered from a similar problem. Every outage cost a lot of money in scrap material. The company was quite aggressive in pursuing a fix: it turned out the power company did not even know that their own automatic switching devices were the cause.
Al, who did you work for?
I've been in the semiconductor process end as a process tech for a long time.
Western Digital? TRW? IR?
I've got an IR 'd' amp out in the garage needing a power supply. I just wanted a garage system.
Too much is never enough
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