Keyboard Shortcuts
ctrl + shift + ? :
Show all keyboard shortcuts
ctrl + g :
Navigate to a group
ctrl + shift + f :
Find
ctrl + / :
Quick actions
esc to dismiss
Likes
Search
Sort of improvised work bench
|
wn4isx
One of the members of our shortwave club lives in a small condo where space is a premium. He found this article and it works better then I'd have expected. ? https://www.stufinnis.co.uk/workbench.html ? The workbench fits on a kitchen table but could probably be used with similar tables. And forget common card tables, they are way too flimsy. I used one as my work bench when I was 12 and one afternoon a leg buckled and it was a mess. I was too busy dodging the hot soldering iron. ? Obviously you have to change the British AC outlets for American ones if you are in America, other nations will require similar adjustments. I'd add a 'ground fault interrupter' or "?"residual current device" at the workbench. A GFI has saved my rump several times. ? Take the part on isolation transformer equaling added safety with a large hunk of salt. ? Is An Isolation Transformer A Safety Measure Or Death Trap? https://sound-au.com/articles/iso-xfmr.htm ? And Variacs, variable AC power transformer, have some important issues. https://sound-au.com/articles/variac.htm Failure to place a fuse in the secondary of the Variac, a fuse in the hot/primary won't protect the secondary from an overload. ? I use a super fast magnetic breaker in series with a conventional fuse in the secondary. |
开云体育I have a 1KVA 1:1 transformer under my bench wired to a single outlet through a Variac and dim bulb limiter (with a bypass switch). ?I use this for working on old tube radios with a hot chassis. ?The idea is to prevent grounding mishaps when hooking up test equipment. ?The outlet is fused and switched independently of the rest of the bench electrical, and carries no ground. ?I only use it for hot chassis stuff.Incidentally, I started years ago with a small tabletop arrangement similar to what your article describes, and it quickly grew into a more traditional bench. ?Gotta start somewhere though. Nelson Johnsrud Manitowoc WI Nelsjohnsrud@... Sent from Apple Mail mobile? On Nov 26, 2024, at 5:38?PM, wn4isx via groups.io <wn4isx@...> wrote:
|
|
On Wed, Nov 27, 2024 at 02:38 AM, wn4isx wrote:
Is An Isolation Transformer A Safety Measure Or Death Trap?My isolation transformer (500W) was and still is indeed a safety measure for me since many decades ago. Most of my designs are related, in one way or another, to the mains voltage (220V, 50Hz). I also added a 2A fuse at its output, just in case of a short circuit.
?
The other measure of safety, I was fortunate to have (around 15 years ago), is a digital scope whose two channel grounds are isolated.??
? |
|
On Tuesday 26 November 2024 06:38:14 pm wn4isx via groups.io wrote:
One of the members of our shortwave club lives in a small condo where space is a premium.I am currently using such a table for a workbench. There's another bench, 3 by 8 feet, that we built some years back but the surface needs to be replaced, and it's currently in a disassembled state and in storage. I couldn't deal with having to set something over the kitchen table (which is round, anyway, and not near a wall) as my current bench is *way* too cluttered and the shelf at the back of it has way too much in the way of test equipment on it. And forget common card tables, they are way too flimsy. I used one as my work bench when I was 12 and one afternoon a leg buckled and it was a mess. I was too busy dodging the hot soldering iron.When I build a bench I like at least 2x4s for the legs, maybe even bigger... Obviously you have to change the British AC outlets for American ones if you are in America, other nations will require similar adjustments.I picked one of those up that's on a short cord, with outlet, etc. but the test button doesn't seem to do anything. I have yet to investigate that... Take the part on isolation transformer equaling added safety with a large hunk of salt.I have one, and use it seldom. I forget what it's rated at, I'm going to have to look into that. The subject came up in another list (HPAK or maybe Tekscopes?) in the contest of repairing a switching power supply, and I suggested that it might be a good idea. If nothing else, use a pair of similar transformers connected secondary-to-secondary. I have a pile of UPSs to scrap that are probably going to supply some good candidates for this. Or for buck transformers to drop the voltage down a bit for vintage equipment. Right now the voltage here is sitting at 125V, which seems to be pretty typical, sometimes I've seen it go even higher. And Variacs, variable AC power transformer, have some important issues.I built a box to enclose a panel mount unit some years back, which includes a double-pole on-off switch, another switch to select normal or "boost" if I want higher voltage, and a third switch that gives me the option to place a light bulb or a meter to monitor current in series with the output. Only use I've ever found for those DPDT center off switches that were all over the place some years back. Neon indicators show me when power is on and when I've blown the fuse. :-) That variac is only rated to about 2.5A or so. I acquired another one a while back, rated at 4A I think, and the knob that's on it is one that I've seen installed in the wall in some places, used as a light dimmer. I've had some thoughts about putting that in another box with a meter built into it, since I have some meters on hand here, but I haven't gotten motivated enough to move forward on that project. Failure to place a fuse in the secondary of the Variac, a fuse in the hot/primary won't protect the secondary from an overload.Super fast? But they seem to be okay with brief overloads according to what Rod had to say about it... -- Member of the toughest, meanest, deadliest, most unrelenting -- and ablest -- form of life in this section of space, ?a critter that can be killed but can't be tamed. ?--Robert A. Heinlein, "The Puppet Masters" - Information is more dangerous than cannon to a society ruled by lies. --James M Dakin |
开云体育Hi group,
About an hear ago, I saw a portable (battery operated) 2 channel scope for approx $120-$200 (depending on max bandwidth) and bought one. ? While I never work on mains voltage, I figured it would be nice to have such unit just in case I ever get
the urge (to probe a 120v device). ?And sure enough I later decided I want to see the voltage wave form out of my battery backup UPS device.
But …. What is the industry opinion on using a portable ?/ floating (DMM style) scopes on mains voltage ?? ? Is it considered just as safe as using HV differential probes ??
Jong?
P.s. ? about my battery backup UPS - crappy waveform output. ?Luckily all my devices connected to it uses some form of switching power supply, so I’m hoping that’s good enough to undo the evils of “modified” sine wave?
On Nov 26, 2024, at 8:10 PM, Kerim via groups.io <ahumanbeing2000@...> wrote:
|
|
On Mon, Dec 9, 2024 at 12:58 PM, jong kung wrote:
That seems like a very VERY bad idea!? As in, a severe safety hazard.
?
But I may not fully understand what you are asking.
?
To me, DMM style implies having no metal on the instrument'that the user can touch.? That is probably OK.? Does your battery-operated scope have any touchable metal, anywhere?? If yes, then it's a hazard.? The scope's common could be 'hot'.
?
Or are you suggesting letting the scope's common float (literally not connected to anything) and just connecting the two channel's inputs as if they were one differential input, letting the scope perform a subtraction?? That might work in theory, but I would not expect good results.? OTOH, safety-wise it is not good because there is capacitance from both inputs to scope common, and this makes the scope's metal float at 0.5 * the mains voltage.? NOT good.
?
Andy
?
?
|
|
wn4isx
A few comments on taking measurements on AC Mains. ? With the exception of rated battery operated DVMs or neon testers, don't unless you know exactly what you are doing, what you are measuring, why you are measuring it. ? AC Mains waveforms are boring, do you have a good reason to look at them? ? ? You want a safe work station with an obvious power off switch that does not take down the room lights. ? You want someone there who knows how to do CPR and a working telephone. ? I've played with direct mains powered devices since I was 8, I'm 73, and I've been knocked silly more times then I can count. ? I am extremely lucky, care to try your luck? ? Over 400 people are electrocuted in the US every year, better them 1 a day, 4000 are injured, more then 10 a day, feel lucky? ? Ground fault interrupters (residual current device in Great Britain) can help but also make you careless. Properly used isolation transformers can also help but again can make you careless. ? Ask yourself, is this project work dying over? |
开云体育Andy,
It’s this model (excstly) :
Originally they came with just one probe and nothing else. ?Now they include second probe as well as few other accessories. ? Those other accessories doesn’t have insulated plastic cover over the BNC twist cover. ? That seems to be a weak point
(having metal exposed for operator’s touch).
The BNC connector on the scope itself is recessed so that if 2 probes are connected, then it’s actually harder to touch the exposed metal connector.
?= ?= ?= ?= ?= ?=?
What do you think about them as test devices for mains voltage ?
Jong?
On Dec 9, 2024, at 11:21 AM, Andy via groups.io <ai.egrps@...> wrote:
|
开云体育And eliminating all the tracking nonsense: Please be aware that [often/usually] everything including and
following the '?' is information that web spyware use to track
your usage. Try cutting off that crap and protect your privacy a
little. (N.B. EVERYTHING utm* is spying on you. utm is the
"Universal Tracking Module" and it IS universal. It tracks your
web browsing wherever utm* element is appended to a link.) Donald. On 12/9/24 18:29, jong kung via
groups.io wrote:
[snip] |
|
On Mon, Dec 9, 2024 at 06:03 PM, wn4isx wrote:
I don't know if this is still taught, but in vacuum tube days, where lethal voltages were often exposed, they used to say to have a walking-cane nearby.? It must be wood.? And with the curved handle.? The cane is used to pull someone's arm or torso away from a "hot" circuit without becoming part of the circuit yourself.? Wood is a pretty good insulator when not wet.
?
And from first-hand experience, the cane also comes in handy for daily exercises if someone is getting shoulder-related PT.? :-)? Or if you have trouble walking and actually need one to safely walk, as we get old.? :-(
?
The last time I checked, a couple years ago, ordinary wooden walking-canes were still available at the local drug store chain.? Alas, checking just now at cvs.com, they no longer have the old traditional cane with the nicely rounded handle.? You need that so you can hook around someone's arm and pull.? Another drug store chain has them, about $15 online.? In-store prices are highly marked up by the likes of CVS so better bought online.
?
Please don't take this safety stuff as if it doesn't matter.
?
Andy
? |
|
In that same vein, my electronics lab had several features I added after working on OH and CH downhole tools. Fashioned a Deadman Pedal that had to keep pressed to energize tool with 200-400vdc @ 2-5amps from a Sorensen supply.
Not quite related but shows spontaneous hazards... The tools would sometimes leak but not quite flood. Normally is just a PITA to clean up. Then I ran into my first Salt Water Saturation tool (used a 40curie Cesium source) that had H2S inside. Knocked me on the floor and was unconscious for several minutes. Regained consciousness in the back of an ambulance. Answer to that scenario was a klaxon wired to 30sec delay. Would turn it on when opening all tools coming back from sour wells. If reset wasn't hit after 30 seconds, sonalert would fire for 15 seconds, if that timer expired, very loud and irritating klaxon would sound off. All in shop trained what that sound meant, and would respond in SCBA (no 'U') gear. Needed that response twice. My battery Tek TDS2024 scope was a strange bird. No idea what option (attached to front) it had, but it had an input tolerance to 10kvpk with Tek probes, 1000vpk using typical X1/X10/X100 probes. Burned up so many Tek probes while probing HV that ended up buying by the dozen. Of course, this was when running on battery. Plugged in, I think was derated to 600vrms or similar. Spare batteries littered my lab. Incidentally, burned up the GPIB on day 2 due to static discharge, I think. Sign on exterior door " Danger! 10,000 ohms in use" kept a lot of looky-loos out. The braver visitors were usually turned back an over-driven GM tube. That just plain went *NUTS* several days after Fukushima! ~SD |
|
Many decades ago, while working at Motorola, one of the engineering workbenches gave me a very slight tingle.
I traced down the reason: The hot wire was interchanged with the ground wire! As a result, the workbench ground and all the test equipment were continuous at 120VAC. It had been that way for a long time. By luck there was no other grounded object within reach. Bertho |
开云体育I had a PDP8I in a 19" 6ft high rack and when we moved in to a new house it occupied the spare bedroom. The mains is 240v in the uk. I would feel a "tingle" when I brushed my hand over the frame. Never had that in the previous home. On investigation
I found that the 3 pin wall socket had earth and neutral reversed. I checked every socket and foud one where live and neutral were reversed and 2 had the earth folded back also lots of loose screws.
Dave
Get
On 10 Dec 2024, at 12:19, Bertho <boman33@...> wrote:
Many decades ago, while working at Motorola, one of the engineering workbenches gave me a very slight tingle. |
|
wn4isx
I'm going to borrow your deadman peddle idea.
?
I seldom work on tube/valve equipment today, everything is 5 or 12V.
?
Which is safer in one way because I'm not constantly poking around in 300V circuits, dangerous in others because I've grown careless and have to really keep thinking "This will knock the pee out of you if you aren't careful" when working with tubes/valves. A GFI isn't of any use on the output of a transformer HV power supply.?
?
I have this nice foot peddle I bought with the idea of a stomp to transmit for my ham radio, since I seldom play ham, so it was never used.
?
A friend is bringing a Fender tube/valve amp over later this week, and, if I can get my pain meds straightened out so I can sleep, I'll be working on it. A "Keep your foot on this peddle or the power goes away" is a nice safety feather. A full nights sleep is another!
?
It is DPDT, so I'll wire the contacts in series down closed, that way a single contact failure welded shut won't defeat the safety and I'll control a nice small STDP 50A contactor, energise to close contacts.
?
I wish I knew why electricians insist on calling large relays contactors. One of life's mysteries.
?
--------------------
My wife has her great-grandfather's wooden cane, complete with curved handle like a Shepard's crook. I shared "And you can use it to pull be free if I really mess up." She moved it from her art room to my electronics / radio room hanging it on the wall next to the emergency "kill the AC to the work bench" switch.
?
You cannot have too many safety steps.
?
?
? |
|
On Tuesday 10 December 2024 07:03:45 am Bertho wrote:
Many decades ago, while working at Motorola, one of the engineering workbenches gave me a very slight tingle.This reminds me of one place where I used to live. We were in the upstairs apartment, and them downstairs mentioned getting a tingle from the washer or the dryer, I forget which. So I put a meter between them, and found 120V. Eventually I traced this problem to the breaker box in the basement, where someone had switched around the red and white wires for the dryer outlet, making the dryer shell live at 120V all the time. That didn't take long to fix, but I've often wondered who the hell did that... -- Member of the toughest, meanest, deadliest, most unrelenting -- and ablest -- form of life in this section of space, ?a critter that can be killed but can't be tamed. ?--Robert A. Heinlein, "The Puppet Masters" - Information is more dangerous than cannon to a society ruled by lies. --James M Dakin |
|
wn4isx
On Tue, Dec 10, 2024 at 11:35 AM, Roy J. Tellason, Sr. wrote:
but I've often wondered who the hell did that...Some highly paid electrician. ?
I've seen more miswired AC Mains outlets in my life then I can count.
Reversed hot neutral, reversed neutral ground, reversed hot ground.
?
And the NEC requires the neutral and ground only be bonded at the entry breaker panel/
I worked in a place with about 18 sub panels, every one of them had the neutral ground jumper in place.
?
That place also had at least a dozen outlets with H and N reversed.?
?
I'm still amazed it passed inspection. Oh wait, inspection in most cities in KY is by firemen, whom I'm sure know how to fight fires, not sure they know a volt from an amp....
?
A friend worked in a local hospitlal the new wing had all the 120V outlets Hots miswired to 240.
All of them.
?
Heads rolled in that mess.
?
? |
|
On Tuesday 10 December 2024 11:58:38 am wn4isx via groups.io wrote:
On Tue, Dec 10, 2024 at 11:35 AM, Roy J. Tellason, Sr. wrote:Not necessarily. I've been doing AC wiring for a long time. Helped the landlord with outlets and lighting as he finished his basement, an electrician was called in to inspect afterwards, no problems. This was in NYC, which has some pretty strict licensing requirements. I have had a number of occasions where people mentioned the "need" for a licensed electrician, but PA has no such requirement, excepting the city of Harrisburg as far as I know. And I've seen some crazy shit. In one place I lived there was a box with a switch at the top of the basement stairs, for the basement lights. Wires coming out of that box was not romex or anything similar, just single conductor black, held down with staples. In this 100 year old house all of the outlets are of the grounded variety, I'm sure that somebody did that for convenience of plugging things in without the need to use an adapter. My handy outlet tester shows no ground on several of them. A complete survey is on my list.but I've often wondered who the hell did that...Some highly paid electrician. One of the things I did a fair amount of before I retired from running those service calls was a lot of "low voltage" wiring. Phone, network, RF -- I still have boxes of cable and jacks and wall plates and such that used to live in my car. My service area used to include MD, but then I bumped into a licensing requirement in Harford County. Inquiring, I was told that the way to get a license there was to get into a 3 year apprenticeship. Not gonna happen! I just love it when some trade decides to protect themselves with crap like this. (...) And the NEC requires the neutral and ground only be bonded at the entry breaker panel/If they really want people to conform to the NEC then they should make it more easily available. Like downloadable or similar. But no, they see that as a money making source, so they don't. (...) A friend worked in a local hospitlal the new wing had all the 120V outlets Hots miswired to 240.As it should be. Several years back we were buying a trailer. Got a site, and had the guy bring it up there and hook it up. I had to borrow a truck and go and get a fuel tank for the furnace and install it. Then fix it when the lack of a filter started causing me some problems. I learned much more than I wanted to know about oil furnaces back then. The guy hooked up the three wires for the electrical service wrong. Turning on some lights caused them to blow immediately, and another casualty was the element in the water heater, which in trailers is 120V, not 240, so when it got 240 it wasn't real happy. At that point in time I was lucky enough to know a contractor that had the special wrench to swap that thing out, too. Yep, carpentry and electrical work can get real interesting here in PA... -- Member of the toughest, meanest, deadliest, most unrelenting -- and ablest -- form of life in this section of space, ?a critter that can be killed but can't be tamed. ?--Robert A. Heinlein, "The Puppet Masters" - Information is more dangerous than cannon to a society ruled by lies. --James M Dakin |
|
wn4isx
On Tue, Dec 10, 2024 at 02:08 PM, Roy J. Tellason, Sr. wrote:
If they really want people to conform to the NEC then they should make it more easily available. Like downloadable or similar. But no, they see that as a money making source, so they don't.Please don't get me started on the NEC or 'adopted by reference" to avoid complying with "laws can't be copyrighted." It is my favorite rant, outshining religion, politicians, economics or healthcare.
?
I f-ing hate the National Fire Protection morons, the US, ANSI, SAE, IEEE (although to be fair the IEEE isn't used to make laws...I think.]
If I have to comply with a law, that law should be readily available.
Argh!!!!!!!!!!!!!!!!!!!!!!!
? |
|
On Tuesday 10 December 2024 02:16:47 pm wn4isx via groups.io wrote:
If I have to comply with a law, that law should be readily available.Yup! -- Member of the toughest, meanest, deadliest, most unrelenting -- and ablest -- form of life in this section of space, ?a critter that can be killed but can't be tamed. ?--Robert A. Heinlein, "The Puppet Masters" - Information is more dangerous than cannon to a society ruled by lies. --James M Dakin |
Nelson Johnsrud
Bertho
to navigate to use esc to dismiss