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Post by leonski on Jul 21, 2022 14:37:39 GMT -5
I'm hoping that a powerful amp with LOTS of current will make the KEFs as dynamic at low volumes as the Klipsches. Maybe - But maybe not... When I first saw them at an audio show.....they were being shown with Parasound amps......FWIW? I think it was the A23, which is 125x2 @8, not the bigger A21 or heaven forbid, the JC-1...... |
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Post by housetech on Jul 21, 2022 16:27:29 GMT -5
Thanks for posting your Generac story Boom.
When I was looking at generators, I thought "why are gas tanks mounted above the engine and not below?"
If I saw 'gasoline bubbling' I would have crapped my drawers. lol
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KeithL
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Post by KeithL on Jul 21, 2022 16:42:30 GMT -5
The only thing I have that uses one of those is a Blu-Ray writer ... All of the USB 3.0 hard drives I have use a USB-3 A-to-micro-B ...  I rather prefer the larger connector... but it does take up a lot of panel space. What kind of equipment do you use that accepts the 3 type B out of curiosity? |
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KeithL
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Post by KeithL on Jul 21, 2022 17:08:57 GMT -5
An MOV is connected ACROSS the power lines... and is normally open. When the voltage across the MOV exceeds its clamping voltage it starts to conduct. (So it "clamps the surge at its clamping voltage - or close to it".) The clamping voltage is the voltage at which the MOV starts to conduct. The peak current is the maximum amount of current it can accept, for a very short period of time, without blowing up. A Joule is an amount of energy - basically 1 watt for one second. The Joule rating is the amount of energy an MOV can absorb for a relatively short amount of time without overheating. If you look at a typical MOV in a surge suppressor it is a small disc that looks like a disc capacitor. When you exceed its threshold voltage it can conduct a relatively large amount of current for a relatively short time. Too much current and it will literally be blown apart (they pop quite impressively). Too much current for too long and it will overheat and burn up (remember that it's only about the size of a quarter). This works well for moderate surges - which are usually a moderate amount of current for a VERY short amount of time. If you actually overload an MOV they will generally blow themselves apart - all you find is two legs and some little pieces of epoxy... The way they degrade is that, after "activating" multiple times, their clamping voltage starts to gradually creep lower... At some point they eventually start to conduct at the normal peak line voltage... And, once that happens, they overheat and die quite quickly... At which point they pop... WikiPedia has a pretty good page on them... en.wikipedia.org/wiki/Varistor#:~:text=Multi%2Dlayer%20varistor%20(MLV),from%200.05%20to%202.5%20joules. (the proper name for an MOV is "metal oxide varistor") Note that an MOV must be rated for the PEAK voltage of the AC line.... And they usually use one rated somewhat higher to provide some safety margin after some degradation... So an MOV around 250V for a 120 VAC line. (Most electronic gear can tolerate a short peak of up to around 400V without damage.) It's also worth mentioning that MOV-based surge suppressors RELY ON a good solid ground.. because they operate by shunting current to ground. (Series mode surge suppressors do not do this.... since they block the surge rather than shunt it.) Keith? How come MOVs are rated in volts? (as well as an energy product.....Joules)? |
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Post by leonski on Jul 21, 2022 22:25:18 GMT -5
Yes.....Anyone buying into MOV should be aware it is is sacrificial device. Big enough surge and it's plastered all over the inside of the enclosure.
But for sub-critical hits? They'll last quite a while. Here in SoCal, for example, we don't have much in the line of big zaps, except maybe up in the
mountains or out in the deserts.....
For those actually interested in how they work? Look at the link I provided for a Good, simple explanation.
And since they are 'commodity cheap'? You may be able to use them in a DIY fashion?
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Post by Boomzilla on Jul 23, 2022 10:34:36 GMT -5
Lightning storm this past week caused one fire that destroyed the gym of a local school and blew a hole in the roof of a local house. TV news was touting the installation of lightning rods as a protection measure. Worth bothering with?
Boom
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Post by leonski on Jul 24, 2022 1:59:37 GMT -5
Lightning storm this past week caused one fire that destroyed the gym of a local school and blew a hole in the roof of a local house. TV news was touting the installation of lightning rods as a protection measure. Worth bothering with? Boom Frequency of such storms? Cost to install / ground? Isolation from your home electrics? ANY insurance break? (They'd know risk) Nearby tall trees? House backs up to a slope? I don't know that I'd 'invite' a direct hit? When I was a kid in the far South out of Chicago? One fall, a big storm blew thru and disappeared the 'air supported gym' at the local HS. We called it 'The Bubble'. Held 6 or 8 Volleyball courts for winter gym class. Found! Reassembled! NEXT time it blew away, it was never found...... |
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Post by Boomzilla on Jul 24, 2022 6:58:29 GMT -5
Frequency - ~ fifteen per year (but in 30 years at this location, no direct strikes). Trees - Seven that are taller than the house within 100 yards Insurance - Don’t know but I’ll check this coming week Cost - ditto Terrain - Louisiana is all flat alluvial soil - no slope or hill is proximate. Connectivity - during half of the close strikes, the house is connected to the grid. During the other half, a hurricane is blowing, and we’re on our own portable generator. Both air conditioner compressors are protected by their own surge suppressors, but the house circuitry has no “ whole house” protector. The A/C protectors are inline MOV units. |
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Post by leonski on Jul 24, 2022 13:04:55 GMT -5
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Post by Boomzilla on Jul 24, 2022 16:19:45 GMT -5
Since I couldn't sink a lightning rod through the center of my house, I'd need multiple, interlocking "cones of protection" from lightning rods. Overall, I think I may not want them. There are lots of higher structures and trees that will attract lightning away from my house. Otherwise, I could build a decoy trailer park down the road to attract both lightning AND tornados...
The units on the air conditioners are self-monitoring and have a bright external LED that will change color if the unit is damaged.
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Post by DavidR on Jul 24, 2022 20:08:57 GMT -5
The height of nearby structures has nothing to do where the lightning strikes. What attracts a lightning bolt is what is called a feeler. The feeler is a stream of electricity reaching up from objects on the ground. What causes feelers to be produced in some objects and not others is not fully understood. However, the bolt from the sky influences the feelers opposite charge as the lightning bolt searches for a path to ground.
There are other videos on feelers.
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Post by leonski on Jul 24, 2022 20:29:34 GMT -5
Which seems to be statistically related to height.
That's why they telll you NOT to stand under a tree during a lightning storm.
Even your image is of a tall object being the 'end point' of a streamer.....and the target, if you will.....
I lived for years in a tornado zone. THAT's worse, IMO. Neighbor came out one morning and had a New TREE in the front yard.
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Post by DavidR on Jul 24, 2022 21:02:44 GMT -5
I've never run across any information or suggestion that height is related to feelers.
We used to have a house on Lake Winnipesaukee and lightning bolts would frequently strike the water missing all those houses and trees on the mountain.
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Post by Boomzilla on Jul 24, 2022 21:18:44 GMT -5
I've seen lightning strike the ocean while fishing offshore. Fish jumped out of the water near the strike!
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Post by leonski on Jul 25, 2022 1:13:28 GMT -5
I've never run across any information or suggestion that height is related to feelers. We used to have a house on Lake Winnipesaukee and lightning bolts would frequently strike the water missing all those houses and trees on the mountain. Water.....both fresh and salt.....is conductive to a degree. Maybe more so than surrounding soil? We had a device that I've mentioined before which ran at 10kv. The cooling circuits required deionixed water, above some specified resistivity. Device was an electron beam power supply, used for 'evaporation' of metals to coat semiconductors.... I doubt a lake would attract lighning if, in the VERY unlikely event, it was filled with deionized water! |
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Post by KeithL on Jul 25, 2022 9:43:05 GMT -5
Fresh water itself is a very poor conductor... but lake water would likely contain mineral and organic contaminants. However most types of rock are also relatively poor conductors so a solid mountain may be less conductive than a lake (ceramic insulators are basically rocks). And the lake is "connected to ground water which is grounded". However, in fact, lightning generally strikes UPWARDS... Electrons build up a charge at the point on the ground closest to the clouds... That charge is focused at the point of some high object - like a tree.... And the electrons "spray" upwards... providing an ionized path for the main strike to follow. (I would also suspect that the lightning is striking debris in the water and not the water itself.) I've never run across any information or suggestion that height is related to feelers. We used to have a house on Lake Winnipesaukee and lightning bolts would frequently strike the water missing all those houses and trees on the mountain. Water.....both fresh and salt.....is conductive to a degree. Maybe more so than surrounding soil? We had a device that I've mentioined before which ran at 10kv. The cooling circuits required deionixed water, above some specified resistivity. Device was an electron beam power supply, used for 'evaporation' of metals to coat semiconductors.... I doubt a lake would attract lighning if, in the VERY unlikely event, it was filled with deionized water! |
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Post by KeithL on Jul 25, 2022 9:48:26 GMT -5
In general lightning will strike the highest point. If you have a house on the top of a hill then your house is that point. And, in that case, a lightning rod sounds like a good idea. Also note that a lot has to do with the conductivity of the path to ground. So, if there is a tall tree next to the house, then the tree will be more likely to be hit. But, if the tree is the same height as the house, the metal wiring in the walls of the house make it the more likely target. A lightning rod is going to increase the likelihood of a hit... But a PROPERLY DESIGNED AND GROUNDED lightning rod should be able to absorb that hit with minimal damage. (But a poorly designed or insufficiently grounded lightning rod will almost certainly increase the risk.) Lightning storm this past week caused one fire that destroyed the gym of a local school and blew a hole in the roof of a local house. TV news was touting the installation of lightning rods as a protection measure. Worth bothering with? Boom |
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Post by KeithL on Jul 25, 2022 10:18:57 GMT -5
Just a note for anyone considering doing anything DIY with MOVs. Remember that an MOV does NOT "magically eat the surge".... When the MOV "activates" it simply short circuits the surge to ground for a split second. And, in order to do this, the ground connection it's connected to must be able to handle that current. Therefore it is critical that the other end of that MOV have a REALLY SOLID connection to a REALLY SOLID ground. The protection you get from the MOV is only as good as the ground it is connected to.(Remember that what you call "ground" is simply a wire connected to "ground".) If your ground is not solid... For example if you use a cute little ground terminal... Or a thin ground wire... Or if the ground on your circuit breaker panel is weak... Then your GROUND may jump up to a VERY DANGEROUSLY HIGH potential... (You can actually get a dangerous surge in the ground connection itself.) So it's very important that you make sure your ground connections are tight and properly maintained. (That's one of the benefits of series-mode protectors... they don't rely on being able to safely dump lots of current to ground.) And, yes, as Leonski said, when an MOV does fail, they tend to explode into little burnt pieces... Often to the accompaniment of quite a bit of smoke and even a risk of actual fire... (MOVs are considered to pose a fire risk - so they should always be used in at least a fire-resistant enclosure... ) Yes.....Anyone buying into MOV should be aware it is is sacrificial device. Big enough surge and it's plastered all over the inside of the enclosure. But for sub-critical hits? They'll last quite a while. Here in SoCal, for example, we don't have much in the line of big zaps, except maybe up in the mountains or out in the deserts..... For those actually interested in how they work? Look at the link I provided for a Good, simple explanation. And since they are 'commodity cheap'? You may be able to use them in a DIY fashion? |
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Post by Boomzilla on Jul 25, 2022 11:59:07 GMT -5
I’ve had two MOV failures in surge suppressor strips. As KeithL says, both were pretty spectacular failures with significant smoke and charring of the enclosure. I couldn’t buy a robust enclosure and a MOV for the price of a surge strip with one included (economy of scale at work). But don’t keep loose papers or other combustibles in close proximity to your surge strip! |
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Post by garbulky on Jul 25, 2022 12:34:29 GMT -5
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