[dBe]

This is a place where a lot of the discussion will center around power.  It may be in the form of balanced 220/240VAC step down balanced transformers or it could be in the form of 3.3VDC inside of a computer. Stop and think:

    (An aside.  I always get a kick out of that phrase - "stop and think."  What if you never started again?)

Back to the topic:  What does electricity do?  It powers our lives, lights our world, makes everything MUCH easier.  It also eliminates crazed murderers and other dregs of humanity in an awful display of searing, smoking finality.  It is absolutely imperative that we approach electricity with an almost religious reverence and fear, or at least a healthy respect.  In short, doing anything stupid can get you killed.  We don't want that. 

When working around AC power in particular, safety precautions must be taken.  Make sure that you are absolutely comfortable in taking your life in your own hands before starting and project that deals with powerline level voltage.  Do all of the standard things: make sure appropriate circuit breakers and/or switches are in the OFF position;  TEST THOSE CIRCUITS to make sure they are off;  make sure that storage circuits are properly and completely discharged; wear insulating gloves if at all possible;  wear rubber soled shoes; use caution at all times and think about what you are doing.  The thing that injures or kills most weekend warriors is simple inattention or being distracted.  The best place to start is to make sure that every circuit in your home is properly wired.  Your friend is a simple circuit tester available at any Lowes, Menards, Home Depot or my favorite place for these things - Harbor Freight.  I now include a Harbor Freight circuit tester with all of my power products.

     http://www.harborfreight.com/electric-receptacle-tester-32906.html

or

     http://www.harborfreight.com/electrical-receptacle-tester-with-gfci-diagnosis-32907.html

A special note about DC power: just because it is 12VDC don't think that you are in the safety zone.

My Dad was a lifelong electrician that worked everything from house current to 77KV.  He had an exemplary service record and was an apprentice's dream to train under.  He never got rattled and always stressed safety as THE most important aspect of an electrician's job.  One day Dad and I were working on my '57 Chevy (sigh) and we were trying to track down an under-dash rattle.  I was pounding on the top of the dash and Dad reached under the dash to put his hand around a bundle of wire to see if the rattle was related to that bundle.  The key was off.  Instantly, I smelled burned flesh as his gold wedding ring completed a circuit somewhere under the dash.  His injuries were such that he almost lost his finger from the ring becoming a glowing circle of pain and he had a deep gash close to the radial artery in his wrist from trying to tear the dash out of the car as he yanked his arm out of that closed space.

A 12V battery can wreak your day in a heartbeat.  You ain't lived until you see one short.  It can be a 1AH or a 100AH like I have for my system.  A battery is an instantaneous source of pain for those that are inattentive or ignorant.  Be extremely careful when working around DC, especially because we tend to think of it as safe.  A direct short is to be avoided at all costs.  Always disconnect the battery's cables and it is a good idea to put an insulating sleeve around the positive (+) terminal.  A battery can turn a screwdriver into a branding iron in an instant and most batteries don't have circuit breaker protection.  Consider yourself warned.

Vacuum tube gear:  so much has been written about tube safety that I'll just refer you to here:

http://www.aikenamps.com/SafetyTips.html

Almost everything Randall discusses here is a demonstration of common sense.  READ IT!!!

The bottom line here is that if you are not experienced, comfortable with or are leery of working with something that can kill you, hire a trained and competent professional.  I heartily recommend that you check with friends or Angie's List to find a good one.  There are a lot of charlatans in the trades, especially now that the economy has tanked.  Electricians and plumbers - everyone needs to know at least one good one.

I don't mean to scare anyone off of what can be a place (power) where it is possible to reap huge improvements in SQ for your system.  It is simply that one must have a healthy respect for what you are doing and pay attention.  When I was in the semiconductor industry I was a line technician on high energy ion implanters.  When people asked what I did for a living I told explained that I worked on a death ray.  Imagine, if you will, a tool the size of a single car garage that has these attributes:  vacuums to the -8 torr; high energy ion beam generators and accellerators; ionizing radiation; intense magnetic fields; poisonous gasses and solids; cryogenic temperatures; source currents of ~250A; voltages to 500KV and total energy in the 1-2Meg electron volt range.  Best of all?  We wore conductive soled shoes in the FAB for static dissappation.  I simply paid attention and was good at what I was doing.

Let's make a pact:  ask if you don't know, OK?

Have a safe and fun time in your journey.

Dave

 

[srb]

A special note about DC power: just because it is 12VDC don't think that you are in the safety zone.

I have to agree about distraction and inattention.  I was cleaning my car's engine bay and at the end decided to spray the battery terminals with some aerosol white lithium grease.
 
I carefully took my left hand with paper towell cupped around the post to catch overspray and sprayed the negative terminal with my right hand.  But when I went to spray the positive terminal, the bottom of the can touched the fender and the electrically conductive spray stream completed the circuit to the positive terminal.
 
I saw an arc, heard a loud pop, and simultaneously dove to the ground, hands over my head and curled up in a ball.  At first I wasn't sure if I had been impaled with aerosol can shrapnel.  Not knowing if there would be a secondary explosion, I stayed in that position while hearing a continuous shhhhhhhh.
 
Good news was there was only a small hole burned into the can, no "explosion".  Minor bad news was the can, laying on the ground, had it's hole aimed perfectly at the side of the car and emptied it's entire contents of grease on the doors and windows.
 
Whew!  Close call!  I'm a lot more careful now around a battery that can instantaneously discharge 400-600 amps when shorted.
 
Steve

[dBe]

I have to agree about distraction and inattention.  I was cleaning my car's engine bay and at the end decided to spray the battery terminals with some aerosol white lithium grease.
 
I carefully took my left hand with paper towell cupped around the post to catch overspray and sprayed the negative terminal with my right hand.  But when I went to spray the positive terminal, the bottom of the can touched the fender and the electrically conductive spray stream completed the circuit to the positive terminal.
 
I saw an arc, heard a loud pop, and simultaneously dove to the ground, hands over my head and curled up in a ball.  At first I wasn't sure if I had been impaled with aerosol can shrapnel.  Not knowing if there would be a secondary explosion, I stayed in that position while hearing a continuous shhhhhhhh.
 
Good news was there was only a small hole burned into the can, no "explosion".  Minor bad news was the can, laying on the ground, had it's hole aimed perfectly at the side of the car and emptied it's entire contents of grease on the doors and windows.
 
Whew!  Close call!  I'm a lot more careful now around a battery that can instantaneously discharge 400-600 amps when shorted.
 
Steve

Steve, 

Not to make light of a potentially fatal home/auto related chore, BUT I would almost pay good money to be able to watch that in person.    

I think we all have those "HOLY CRAP!!!" moments that makes us much more observant in our lives.  If not, then we could wake up dead, eh?  I'm just glad you are OK and can take the time to post here about the dangers of batteries.

Dave

[werd]

Don't play the game "Operation" with feeding live wires. turn the main box off. 



 

[Demarche]

This is always a great reminder,  as a lot of people here are working & tinkering with some potentially dangerous stuff.

As the saying goes, "volts thrill, amps kill" and it doesn't take much.


Effects of current size

1 rnA -       Just perceptible
Up to 10 rnA -    Tingling sensation
15 mA -    Muscular contraction in-ability to ‘let go’
15-100 mA -    Pain. Perhaps fainting. Difficulty with breathing
100-500 mA -    Ventricular fibrillation
Above 500 mA - Heart restarts when current stops
6 A -       Sustained muscular contraction of the heart
Above 6 A -    Temporary respiratory paralysis. Serious burns

[DDF]

I watched a favorite screwdriver tip disapear in a blinding arc as I "taught" my wife some basic electrical repair on her motorcycle.  Couple that with the 35mA that makes my right foot involuntarily contract during physio, and its pretty amazing the power of power!

While I'm no Elmer the safety elephant, I think this is a wise start to the group.

Congrats on the circle Dave, and God-speed!

Dave

[dBe]

I watched a favorite screwdriver tip disapear in a blinding arc as I "taught" my wife some basic electrical repair on her motorcycle.  Couple that with the 35mA that makes my right foot involuntarily contract during physio, and its pretty amazing the power of power!

While I'm no Elmer the safety elephant, I think this is a wise start to the group.

Congrats on the circle Dave, and God-speed!

Dave

Hey, Dave.  It is really great to see you here.  I hope that work lets you drop in fairly often, but feeding the ladies comes first.  Tell your brother to drop by, too.

Batteries can be the insidious little culprits that lead to pain.  Knew a guy once that put a 'AA' battery in his pocket with car keys and change.  Man, did that hurt!   

Dave

[jules]

Useful thread, thanks Dave and congratulations for bringing this circle into existence.

Like many others here I haven't had any electronics training though I've DIYed several amps and various other bits and pieces. Many basic mistakes we can make aren't immediately obvious. The gold ring one is a great example ... who'd have thunk it? The same goes for the lithium grease spray surprise. I guess anyone who's done an apprenticeship would pick up stuff like this very early on but maybe this thread can include "surprises" that are easy to make if you haven't been specifically made aware of them. I nominate ...

CENTRAL MOUNTING BOLTS ON TOROIDAL TRANSFORMERS: making a conducting link between the top of this bolt and a metal case [or other earthed component] with a screwdriver, or maybe the lid of the case, can result in an almighty and damaging high current, low voltage surge of electricity with massive spark and even welding potential. The logic isn't immediately obvious but what's been created is a single "turn" around the core of the transformer in a world where many turns = higher voltage and lower current while fewer turns = lower voltage and higher current. It might be interesting to do a calculation for the current flow and voltage through a single turn ... quite alarming for many trafos I imagine 

jules

[Photon46]

You are so right about the potential dangers in a 12 volt battery. I had a Mitsubishi van years ago that wouldn't start. I opened the hood and heard a ticking noise from a relay in the battery box area. I put my head nearer to the source of the noise to try and determine the source and at that moment the battery shorted and blew apart like a hand grenade. I was stunned and knocked to the ground in an incoherent daze. When I came around, I was covered in battery acid and had a large piece of battery container buried in the middle of my forehead. Luckily, my glasses protected my eyes. A co-worker took me to emergency care and I got a shower, checked over, and my hearing tested ( I was nearly deaf from the blast for at least 15 minutes.) All was well, but it sure scared the crap out of me.

[srb]

Wow!  That's not at all humorous like my auto battery story.  The skin can tolerate some battery acid, but I'm not so sure the eyes can.  You sure were lucky that they were protected by glasses.
 
I have heard of auto batteries exploding before.  For those who use an AGM auto battery to power audio equipment inside the home, can those type of batteries explode?  They don't have liquid battery acid to disburse as it is contained within the absorbent glass mat, but is there still any possibility of explosion under the correct adverse conditions?
 
Steve

[jtwrace]

but is there still any possibility of explosion under the correct adverse conditions?
 
Steve

Yes there is.  There's always a possiblity if you do something wrong. 

Could be worse, you could be driving a "green" car with them.   

[Johnny2Bad]

Conventional automotive batteries (Lead-Acid) store and can deliver a staggering amount of current. As an example, a typical Group Size 26 battery (not a large battery by any means ... it's used in cars with 4-cylinder engines) has an RCM rating of 81 minutes.


Think about that for a moment ... the RCM (Reserve Capacity Minutes) specification requires continuously delivering 25 Amps @ 80F/27C before voltage (on a 12V battery) drops to 10.5V. There is still plenty of stored energy available at 10.5 volts, by the way; note that the specification doesn't mean that it is not able to continue to deliver 25 A after the rating time period expires, it just means the voltage has fallen below a set point.


So, a moderately sized lead-acid battery can deliver 25 amps non-stop for more than one hour. A direct short on a fully charged battery will deliver a whopping amount of current, nolo problemo.


As for explosion potential, every charging event (and driving the car is a charging event) creates both Hydrogen Gas and Oxygen inside the battery; the battery has tiny vents to safely handle the pressure of this gas. If those vents are plugged, say, by a dirty battery, it has nowhere to go. A Hydrogen Gas/Oxygen mix is highly explosive ... makes gasoline look safe in comparison.


If your car battery is swelled at all, there's a big clue the vents are not working, or your car is overcharging the battery. Fix the problem, whatever it is.  A sealed lead-acid battery is not significantly different than one you an add water to, so treat it the same.


With most cars (negative ground) always remove the negative cable first, and attach it last. You can't create sparks by shorting the negative cable to the frame of the vehicle with your tool. You can only do that if you take the positive cable off first, or attach the positive cable last. It's a very, very good idea to detach the negative cable anytime you work on the vehicle.


If you're using a lead-acid battery in your home, for some reason, be careful. especially with charging. You probably should consider charging it outside the home.

[dBe]

Conventional automotive batteries (Lead-Acid) store and can deliver a staggering amount of current. As an example, a typical Group Size 26 battery (not a large battery by any means ... it's used in cars with 4-cylinder engines) has an RCM rating of 81 minutes.

Think about that for a moment ... the RCM (Reserve Capacity Minutes) specification requires continuously delivering 25 Amps @ 80F/27C before voltage (on a 12V battery) drops to 10.5V. There is still plenty of stored energy available at 10.5 volts, by the way; note that the specification doesn't mean that it is not able to continue to deliver 25 A after the rating time period expires, it just means the voltage has fallen below a set point.

So, a moderately sized lead-acid battery can deliver 25 amps non-stop for more than one hour. A direct short on a fully charged battery will deliver a whopping amount of current, nolo problemo.

As for explosion potential, every charging event (and driving the car is a charging event) creates both Hydrogen Gas and Oxygen inside the battery; the battery has tiny vents to safely handle the pressure of this gas. If those vents are plugged, say, by a dirty battery, it has nowhere to go. A Hydrogen Gas/Oxygen mix is highly explosive ... makes gasoline look safe in comparison.

If your car battery is swelled at all, there's a big clue the vents are not working, or your car is overcharging the battery. Fix the problem, whatever it is.  A sealed lead-acid battery is not significantly different than one you an add water to, so treat it the same.

Always remove the negative cable first, and attach it last. You can't create sparks by shorting the negative cable to the frame of the vehicle with your tool. You can only do that if you take the positive cable off first, or attach the positive cable last. It's a very, very good idea to detach the negative cable anytime you work on the vehicle.

I really like it when people add to this thread.  As guy that has worked around very high continuous DC currents, I'm acutely aware of just how much damage can be done by the DC V/A combination.  Thanks for your input and the safety bump.

 

Dave