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Old 1st September 2010, 04:42 AM   #31
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Originally Posted by TechGuy View Post
Fuses have limited voltage flash over arcing. A big voltage spike will vaporize the fuse filmament and turn it into ionized gas that conducts current. Breakers are even worse, and have very slow switching times. Thermal breakers take a couple of seconds, a Magnetic breaker is around 500 ms.
agreed.

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They rely on the tower to take the bulk of the lighning strike. They usually protect the attenna and isolate the coax cable from the tower. Gas Discharge tubes are used to divert any surges that are conducted into the coax cable.

<snip>
Afaik this is NOT how it is done. The feedline is BONDED to the base of the tower, and the transmitter building is also bonded to the tower's ground system often via a radial.

You can read online what the major commercial transmitter mfrs say about this...

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Old 1st September 2010, 06:31 PM   #32
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Originally Posted by Andrew Eckhardt View Post
Bear, Dratt! 8.0 works in linux. I'll post in pdf soon.
A "real" MOV can handle 20kA pulses with 200J energy for under 5 bucks.
But only once. In an average device with MOV protection, the MOV are frequently tripped as induction loads (refridge, AC, etc) during the day. Each time the MOV trips it degrades reducing the maximum energy and current it can clamp. Lets say you install a new MOV in a device, then two years later after it's degraded big surge hits. it fails and permits the bulk of the surge to pass through. There could also be instance where multiple rapid surges happen, such as tree branch during a storm striking multiple arc a the pole.

Here's just an example.

Digi-Key - 495-3647-ND (Manufacturer - ETFV25K130E4)

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You probably couldn't find any glass if an AGC fuse had to try pushing that into it, about the same energy as a small handgun. The fuses would more than share the energy dissipation (that's the point of blowing a fuse with an MOV, anything to keep the pulse from getting out of the clamp and into the equipment), a sacrifical part anyway, may as well go out with a bang.
When fuses blow the filament, the metal vaporizes and creates an plasma cloud that conducts electricity. Most AGC fuses have limited voltages within a few hundred volts. a Lightning strike can cause line voltages above 6KV.

A device protected with a single MOV does protect against common mode surges, and MOVs that divert surges to ground can also cause problems as the surge flow from ground into the device and out any other external connections (ie phone line, data cables, etc).

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MOVs are sort of like lamp filaments. Several times below their max ratings they can run for a very long time, over the spec kiss it goodbye.
More like a device with thousands of tiny filaments. each time a spike triggers a group the tiny filaments are destroyed, leaving less and less current capacity. The problem with MOVs is that the don't blow like fuses. The can look fine until they suddenly fail. MOV's are inexpensive solution to a difficult problem. They are cost cutting devices to save money, over more traditional surge protection systems.
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Old 1st September 2010, 07:02 PM   #33
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MOVs aren't cost saving devices in any other sense than they protect against more expensive failure than their own. It's only when you try to cut cost on the cost cutting that you develop problems.

There must be dozens of papers out there that can help you choose an appropriate rating for the MTBF you want.

The OP asked for a line conditioner design, and I just wanted him to be sure he needed a line conditioner, because if he wants very high energy surge protection most line conditioners fall back on transient absorbers of one kind or another anyway, because beyond certain high voltages and energies no amount of insulation or electromagnetic/electronic dynamic headroom is going to hold it back better. Even most battery / continuous inverter systems have MOVs in them somewhere. Different, sometimes necessary jobs.

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Old 14th September 2010, 10:58 PM   #34
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Default idealistic tech guy

I'm not interested in flaming, but I'm not sure how much experience tech guy has with real life lightning events. I've found an exploded cap across the power switch of the PAS2, an exploded neon bulb in the power switch of the ST120, and seen plasma jump out of the front adjustments door of my television during a strike. I had a PC take a hit probably through the phone line, and despite Tech Guy's mumbling, the power supply and CPU did not go out, only the modem and PCI slot. Southern indiana is proof against earthquakes and wildfires, has few tornadoes and limited sensitivity to hurricanes, but we are a proving groud for lightning strikes. I have well used factory equipment (years of life), variable frequency motor drives, that have S14 500v MOS suppressors at the input of the 3 phase bridge. I have a dead 50V dc power supply, after 5 years life, from an ishida scale, that has MOS suppressors. All these suppressors read 9999 meg ohms, and some them I have reused. Ishida and Allen Bradley and TB Woods have major reliability reputations to protect, and all use S14 MOS suppressor on their inputs.
Direct strikes on home electronics, not bridged by the refrigerator compressor, AC compressor or blower, are rare.Blowing the fuse is my idea, instead of blowing the expensive or impossible to replace power transformer. As most transformers in the tube age were wound with 600 V rated wire, I feel justified in putting 500V MOS suppressors (salvaged from the motor drives) from case to neutral and from neutral to hot on the imputs of the dynaco equipment. These won't be reacting to nuisance surges from the A/C or refrigerator. I might point out the motor drive suppressors withstood years of on-off surges from parallel non-speed controlled motors, and lightning strikes which took out building power numerous times, without shorting across.
If you're designing a system to stand in the middle of a field with no motors around to take most of the strike energy, I supposed it would pay to be as worried about lightning as tech guy is. In a home environment, a couple of free salvaged MOS suppressor shouldn't hurt anything and may save trashing a historic piece of audio gear and replacing it with something new that might last less than a year, like all these dead PC switching power supplies I have piled up for suppressor and current limiter salvage. In no case are these PC power supplies showing damage near the fuse/input area, all the burned spots seem to be tiny components near the switching controls or lands leading to the switching transistors..
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Last edited by indianajo; 14th September 2010 at 11:00 PM.
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Old 18th September 2010, 09:58 AM   #35
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hi, this is my home built power conditioner i posted in this forum....
WiredState Audio Community &bull; View topic - DIY Line Conditioner, rig your own
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Old 18th September 2010, 10:23 AM   #36
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I don't like the look of this. Doesn't a common mode choke need capacitance to ground ?

This project looks like someone just threw together a random collection of chokes they had lying around. Not a well thought out design.
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Old 18th September 2010, 10:32 AM   #37
AndrewT is online now AndrewT  Scotland
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the advantage of Tony's interference suppressor is that it does not increase the leakage to earth.

Caps to Earth do increase leakage to earth.
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Old 18th September 2010, 09:02 PM   #38
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the advantage of Tony's interference suppressor is that it does not increase the leakage to earth.

Caps to Earth do increase leakage to earth.
And the disadvantage is any noise common to Live and Neutral isn't filtered.

---

I'm throwing together an RF filter too.

All the RF EMI filters I've seen in PC PSU (switch mode) design and general RF suppression have at least one set of Y caps. Y1 and Y2 compliant capacitor's have an absolute max leakage specified by electricity authority regulations (various compliance logos are awarded per country, obviously, as regulations differ between them) such that they will not turn the device into a personal hazard, will be efficient and 'green' (more or less) and will not trip residual current safety devices.

That whole project is massively over-engineered (me LIKES massively over-engineered!!!) - dual (or triple) filter stages are for switch mode supplies that require a huge amount of decoupling in the RF band to stop the house's power lines being used as giant broadcast antenna: Something that never happens with transformer based PSUs.

It's only barely a 'power conditioner' in terms I'm familiar with. It's a line noise suppressor. For that full rich creamy conditioner feeling, a complex [AC-rectified-to-DC] -> [filter] -> [buffer] (capacitor or battery) -> [sine-wave-inverter] (with over-current and short monitoring) is ideal. And it's going to be much much harder and more expensive for a DIY fan to build than buying a suitabe VA rated model of computer uninterrupted power supply made in China. Depressing, really.

Be careful with 1uF or larger X capacitors: X caps will always alter the power factor of the power supply. Usually for the better but some measurements and sums are needed to be sure large values are not making things worse (that is, even worse).

Many electricity authorities specify approved filter designs must have a drain resistor across L & N. A good idea if there's a chance the amp PSU will be disconnected while the filter is still connected. Schematics I've seen vary between 250K and 1M. Use cement or fire/flame-proof resistors when using them in the mains AC area.

Sorry, that was all a bit lofty and proselytizing in tone. Hate that.
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Old 18th September 2010, 09:15 PM   #39
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Quote:
Originally Posted by pjp View Post
I don't like the look of this. Doesn't a common mode choke need capacitance to ground ?

This project looks like someone just threw together a random collection of chokes they had lying around. Not a well thought out design.
yes...indeed.....earthing is a joke in my country....

anyways, the design objectives were:

line isolation,
surge protection,
emi/rfi filtering, those inductors capacitor filters surely present a ver very low impedance for higher frequescies...

my contraption works.....and i use it for my pc....
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Old 19th September 2010, 10:13 AM   #40
AJT is offline AJT  Philippines
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Not a well thought out design.
right again....with parts that i have, and the transformer building skill that i have.....it did not take me a few seconds to cook up this project....

making a write-up for posting in the net took me week however....
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