Hmm, Maybe Evidence for Unseen Intelligence

This is the place for any magazine-related discussions that don't fit in any of the column discussion boards below.
rshayes
Posts: 1286
Joined: Tue Mar 04, 2003 1:01 am
Contact:

Post by rshayes » Sat Sep 08, 2007 5:43 am

The base-emitter junction of a transistor is fairly easy to damage with reverse voltage. The breakdown voltage is usually in the 5 to 7 volt range. The 2N5088 has high gain at low currents and low output capacitance, which may imply a small junction area combined with a thin base region. This might cause it to be exceptionally sensitive to damage compared to other transistors.

With 120 volts available, a resistance of 12 K would allow 10 milliamps to flow, which might be enough to cause damage to a sensitive device. The resistance of the rebar is far below this, and I wouldn't be very suprised if the resistance of the wood beam is below this also.

User avatar
Joseph
Posts: 681
Joined: Mon Dec 10, 2001 1:01 am
Location: USA,World
Contact:

Post by Joseph » Sat Sep 08, 2007 5:59 am

Dyarker, nah, I am good at these things. I have decades of experience. There is no high voltage potential exposed anywhere.

But a good general warning!

User avatar
Joseph
Posts: 681
Joined: Mon Dec 10, 2001 1:01 am
Location: USA,World
Contact:

Post by Joseph » Sat Sep 08, 2007 6:35 am

If the base emitter junction had shorted, it would just have disabled the circuit operation without any other problems.

Wood and vinyl are both considered good insulators. Their resistances both must be in the hundreds of megaohms. The good conductor short steel piece of wire was insulated.

User avatar
Joseph
Posts: 681
Joined: Mon Dec 10, 2001 1:01 am
Location: USA,World
Contact:

Post by Joseph » Sat Sep 08, 2007 6:45 am

I still don't see any plausible explanation other than either what we have called spiritual intervention or high RF energy from somewhere. The possibility of the former being the case is what intrigued me. But sometimes there could be scientific reasons which go beyond known physics.

Robert Reed
Posts: 2276
Joined: Wed Nov 24, 2004 1:01 am
Location: ASHTABULA,OHIO
Contact:

Post by Robert Reed » Sat Sep 08, 2007 8:39 am

Joseph
Very mysterious! Two things come to mind though. One, if this is an aftermarket router speed control, it has no common other tha the neutral (white wire). Since your diagram shows the temp. sens. going into that unit - does it also derive power from that same AC source - as a floating low voltage DC supply configured between the mains? Two, and not to question your electrical experience here, but is it possible that the long cable could have shorted while being moved and that bumping the hose was just coincidental at the time of damage?

User avatar
Joseph
Posts: 681
Joined: Mon Dec 10, 2001 1:01 am
Location: USA,World
Contact:

Post by Joseph » Sun Sep 09, 2007 12:22 am

Hi Robert,
There is a pair of tiny transformers which are powered by AC components having the fastest rates of change through a .22uF film capacitor. The output of those transformers is rectified to provide 6vdc referenced to the neutral.

The cable going to the temperature sensor very unlikely had any shorts. The failure mode of the unit is still an unsolved mystery. I have decided that under almost perfect circumstances which I do not believe were present, the 4 foot section of wire, insulated from all other conductors, which the emitter of the transistor at neutral potential touched could acquire an appreciable static charge.

Robert Reed
Posts: 2276
Joined: Wed Nov 24, 2004 1:01 am
Location: ASHTABULA,OHIO
Contact:

Post by Robert Reed » Sun Sep 09, 2007 9:52 am

So, if I understand correctly your DC circuits are 6 volts and common to the AC line neutral. You said that the 6volts was obtained from a transformer- in series with an 0.22 Mf to the high side of the line? - this would indicate you are intentionally dropping voltage to the trannys primary. If so, what is the primary rated at. I may be misinterpreting what you said and this is where a print clears up a lot of confusion. It sounds strange the way you described it.
I know you don,t want to be blowing up circuits without knowing what caused it as this leaves a low level of confidence in replacing with an identical circuit (not to mention cost and time), but I keep coming back to power interconnections on this one.
If you suspect static on that hanging wire, I was wondering if you could measure a voltage ( referenced to ground) on it that may again have built up. I have never tried to measure a static charge as the testing device would have to be of an extremely high input impedance, but you might try a 100 megohm resistor in series with your 10 meg DVM and see if you could obtain a reading ( 1/11 of actual voltage). This may not work as even this high of a resistance may bleed the charge to rapidly to get a reading.
I guess if no definate conclusion is ever reached, you will just have to put in the category of "Murphys Law" - and we all understand that
:grin: .

User avatar
Joseph
Posts: 681
Joined: Mon Dec 10, 2001 1:01 am
Location: USA,World
Contact:

Post by Joseph » Sun Sep 09, 2007 10:53 am

The little trannies are little signal isolation transformers. They have a lot of galvanic isolation between windings. I decided to press the into use for something since they were cheaply priced and I have not been happy using them in MOSFET drive.

The transformers are rated something like 1000 ohms at 1khz. I had to attenuate the low frequency AC components to them with the series capacitor. Two primaries from two transformers are in series while those transformers' secondaries are in parallel.

A detached observer might tend to draw that conclusion about the isolation aspect. However isolation/non both follow all the physical laws. A spark jumped from the neutral to a short piece of unconnected and isolated-by-high-resistance wire. (Cue music.)

I could touch the sink water faucet at any given time along with that little piece of rebar wire, simultaneously, and not ever be surprised.

At least I have found some mechanical thermostats which I intend to use now since I don't see the need or have time left to build a new circuit like that one. It would have been interesting, though to be able to fine tune the operation of the compressor to suit my needs. I don't expect such good results from the mechanical one since it probably won't have nearly the thermal sensitivity as a small silicon junction.

User avatar
haklesup
Posts: 3048
Joined: Thu Aug 01, 2002 1:01 am
Location: San Jose CA
Contact:

Post by haklesup » Sun Sep 09, 2007 9:54 pm

I'm not going to guess at the failure mode again as failure analysis from afar would require at least a schematic, a list of damaged components and which pins were shorted/open and ideally a photo clearly depicting construction details. As they say on CSI "It's the Evidence" with all due respect to your eye witness account.

BTW, one would use an electrostatic field meter to measure an ESD charge. It is a non contact instrument. A DMM has sufficient parasitic capacitance in the test leads to absorb the charge before it can be measured so you get nothing. A better way is to hold a hair (or similar lightweight plastic object) near the object and see if it is attracted or repeled. Its not qauantitative but it proves the possibility of charging.

User avatar
Joseph
Posts: 681
Joined: Mon Dec 10, 2001 1:01 am
Location: USA,World
Contact:

Post by Joseph » Mon Sep 10, 2007 5:14 am

I talked to my brother-in-law about it last night. He thought it was more likely that something was already weak in the circuit and the minuscule spike involved in touching the steel wire was all it took to make it fail. Then, once it failed the power surge caused an EMP to be radiated by the wire, indicated by the spark. I thought it could be either that way, or a very strong radio wave came in from the wire. The first is the most likely, I'd say.

It cannot really be determined with much certainty since experimentation with the scientific method would be necessary to do tests and establish repeatability. Since the item is destroyed, this option is gone. I am working on my 60hz transformer PWM instead.

User avatar
haklesup
Posts: 3048
Joined: Thu Aug 01, 2002 1:01 am
Location: San Jose CA
Contact:

Post by haklesup » Mon Sep 10, 2007 9:37 pm

That's the thing about cascade failures (chain reaction). A tiny initial failure can cause the next part to go then the next until you reach your highest voltage source in the circuit then forms a short that runs back and damages stuff even more.

Even though the transistor in question had low design current or voltage, if multiple parts shorted, it may have experienced more. All the way up to the highest wattage source in the circuit.

That was a generalization not another guess :)

Another possibility is that the spark you saw was a round trip event, two seperate but simultanious sparks from the closely spaced leads. That would explain a circuit without requiring the wire to be not isolated or making a claim for a very large ESD event or likewise EMP Now thats a guess. An Arc with sufficient current would have left a microscopic pit on the wire but ESD events lack the power.

User avatar
Joseph
Posts: 681
Joined: Mon Dec 10, 2001 1:01 am
Location: USA,World
Contact:

Post by Joseph » Wed Sep 12, 2007 3:57 am

Since my eyes were a couple feet away from the spark, I recall pretty clearly that the emitter (at power neutral potential, nominally, at least) was what touched and gave the spark. The three leads of the transistor are in a row. making only one of them touching likely, too. I wouldn't say that it could have been a spark between two leads. I tend to think that EMP is the only explanation for a power spike intense enough to pass appreciable current to such a short piece of wire.

For long conductors, the story is different. I recall mention from somewhere that linemen are instructed to discharge long, dead power wires before touching them. Someone gets a thank you for mentioning it. It is good to know.

Robert Reed
Posts: 2276
Joined: Wed Nov 24, 2004 1:01 am
Location: ASHTABULA,OHIO
Contact:

Post by Robert Reed » Wed Sep 12, 2007 8:36 am

Joseph

"For long conductors, the story is different. I recall mention from somewhere that linemen are instructed to discharge long, dead power wires before touching them."

These are usually looonnngg lines (miles) where even though the line has been deenergized, it may still hold a small charge, but more importantly these wires may still be parrelling live circuits that can inductively couple a large voltage over that distance. This is usually problematic at 13.2 KV and above.
A bolt down ground is required before work proceeds and is not removed until work is completed. For lower voltages and shorter runs the concern would be energy storage in deenergized but still connected equipment such as transformers,VAR correcting devices and so on that could retain some charge. Usually a short dischage period is all that is required here.
Your short peice of wire wouldn't be subject to these conditions and any RF pickup induced into it to be able to cause significant damage to your circuit would have had to be coupled from a very strong and nearby (couple of feet) RF feild. Again,I am just guessing, but it seems more likely that damage was done by its own internal power.

User avatar
Joseph
Posts: 681
Joined: Mon Dec 10, 2001 1:01 am
Location: USA,World
Contact:

Post by Joseph » Thu Sep 13, 2007 6:15 am

Robert,
that is very useful information. Some day in the future the population could have been decimated somehow, and those folks having read that may be able to continue to survive with electric power.

I tend to think something similar about the failure mode of the router. It seems most likely to me the spark visible was from a power surge during failure. That spark would have been evidence of a strong EMP signal going out, using the wire as an antenna.

That failure possibility is pretty much like one of the ones haklesup gave, I think.

jjdraw
Posts: 1
Joined: Fri Mar 02, 2007 10:31 am
Location: Muskegon MI
Contact:

Post by jjdraw » Thu Sep 13, 2007 11:16 am

ESD is my vote..
Here at work, we get ESD all over.
We heavily protect for ESD with transorbs, caps, and ferrite beads.
We have ESD discharge guns to test PCBs and we commonly design and test at 30,000 volts human and machine discharge arrays. We have observed clouds of 3 inch 'parks' coming off plastic balls rolling along wood tracks.

Post Reply

Who is online

Users browsing this forum: No registered users and 41 guests