Naked Science Forum
General Science => General Science => Topic started by: Karen W. on 10/08/2009 08:47:24
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Well as you see this is my weed eater battery and charger, Heres a replay of 2 weeks
ago...
I have just unplugged it from the charger:
(https://www.thenakedscientists.com/forum/proxy.php?request=http%3A%2F%2Fi17.photobucket.com%2Falbums%2Fb73%2Fkarenw44%2F2009-08-09-232043.jpg&hash=696d2245aa8b0ff30fee827afc249651)
It is on the charger but not plugged in! I am very cautious.. but to be safe I removed
said battery and set it contact side up on my fireplace mantle last week so not to
overcharge it..!
like this:
(https://www.thenakedscientists.com/forum/proxy.php?request=http%3A%2F%2Fi17.photobucket.com%2Falbums%2Fb73%2Fkarenw44%2F2009-08-09-232501.jpg&hash=fc9c842222316e4e4a50a3d5e5a9c2ad)
Now later that day I go outside to say Hi to the frog family at the mailbox! Removed
said mail go in house and sort mail....
I now move to mantle to rest my daughters mail there behind my battery until she gets
home from work to pick up her dog!
So here I am reaching across said battery:
(https://www.thenakedscientists.com/forum/proxy.php?request=http%3A%2F%2Fi17.photobucket.com%2Falbums%2Fb73%2Fkarenw44%2F2009-08-09-232611.jpg&hash=81058ce6a58e82c1a56f96f7a0a5f82d)
Next thing I know I am experiencing real live pain.. and I try to move my arm and to my
dismay.. : (for recreation reasons I will substitute my pencil for my arm this time!) My
bracelet as you see below has been snagged by the metal contacts on my unplugged
removed battery!
Like this:
(https://www.thenakedscientists.com/forum/proxy.php?request=http%3A%2F%2Fi17.photobucket.com%2Falbums%2Fb73%2Fkarenw44%2F2009-08-09-232757.jpg&hash=19ead94116ec0ef7061e68908269dde4)
The battery latched hold and would not release my bracelet ..(sorry the light is
eliminating the big arch and sparks...) But they were there tonight too!
I was hollering and trying to roll the two bracelets off my arm.. one bracelet a medical
one heavy chain and the other sterling silver tiny bells.. it had both pieces in the
contacts and it heated them up so badly that it burned chain marks into my upper hand by
the thumb because the bracelets were sizzling hot it melted one link of my silver chain
off, and burning the bracelet bell off! It melted it to my arm.. minor burns, but
painful they are basically gone now this has been almost two weeks..
Now It burnt me because I could not get the bracelet off and it was so bloody hot it
burnt small burn spots into the metal contacts of the original battery...
I know a 9 volt battery will shock you if you stick your tongue across the two points as
that was how we use to test them as youngsters! LOL wet tongue on charged battery bad
news... LOL But it had never occurred to me I could get shocked and burned on an
unplugged removed rechargeable 18 volt battery!
So What have I missed I know don't put forks in toaster wires or light sockets, fingers
either, but it never occurred to me that my weed whacker battery could hurt me so
badly.. It really smarted and scared the soup right out of me!
How does that work My reflex saved me and I had to really jerk my arm back to get it
off.. Is that likely to be about the worst it could do?
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You were merely doing a bit of Welding, Karen. Once the contact had been made, the melted / vaporised metal allowed a low voltage arc to bridge the gap. Scary! A modern rechargeable can give you loads of current and your bracelet was shorting out the contacts. You have probably damaged your battery, btw.
When I was a lad, I had real fun with a thick wire coat hanger held across the terminals of an old car battery of my Dad's. Melted it a treat with a few hundred Amps.
I suggest you may have had a shock - but it wasn't an electric shock, it was probably a burning sensation! It just felt like a shock. Our brains tell us - Sparks = Shocks.
You should never wear jewelery / watches when working on high current supplies. You could burn your arm off!.
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Yes, I concur with SC. I think it quite possible that the dangers of being burnt in this way were overlooked by the designers. There is a tendancy to think low voltage is no danger and forget the high current capability can heat things up rather well.
I note that air vents in most domestic electrical equipment tend to have a fine cloth mesh across them nowadays to avoid bracelets or necklaces dangling through the gaps.
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You were merely doing a bit of Welding, Karen. Once the contact had been made, the melted / vaporised metal allowed a low voltage arc to bridge the gap. Scary! A modern rechargeable can give you loads of current and your bracelet was shorting out the contacts. You have probably damaged your battery, btw.
When I was a lad, I had real fun with a thick wire coat hanger held across the terminals of an old car battery of my Dad's. Melted it a treat with a few hundred Amps.
I suggest you may have had a shock - but it wasn't an electric shock, it was probably a burning sensation! It just felt like a shock. Our brains tell us - Sparks = Shocks.
You should never wear jewelery / watches when working on high current supplies. You could burn your arm off!.
The initial grab and arch felt like a small shock, but the remainder of time I was being bunt and yelling cause it kept burning while on my wrist after it had heated the metal to melting point!
I have learned something.. I may have hurt the battery but it seems to be holding the charge at this point.. we will see.. Thanks Sophie for explaining..
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Yes, I concur with SC. I think it quite possible that the dangers of being burnt in this way were overlooked by the designers. There is a tendency to think low voltage is no danger and forget the high current capability can heat things up rather well.
I note that air vents in most domestic electrical equipment tend to have a fine cloth mesh across them nowadays to avoid bracelets or necklaces dangling through the gaps.
There should at least be a tapped caution tab across that contact to make sure people are aware even after unplugged...I should have simply thought about it but I was not working with the battery I just reached across without thinking about it! BIG NO NO! LOL'''
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Normally you won't get an electric shock from an 18 Volt battery because the human body is quite resistive, so not much current will flow through it. But put something with a low resistance (like a metal bracelet) across the terminals of a high discharge rate battery and a very large current flows. As a result, the bracelet heats up and starts to melt very quickly. This can can result in very serious burns.
When working with any electric equipment (cars, computers, etc.) it is a very good idea to remove ALL metallic jewelery. Wedding rings and metal watch straps have led to many accidental amputations!
Although car batteries only put out twelve volts, they can be lethal. If you accidentally drop a spanner between the terminals, it may actually weld to the terminals. All the energy in the battery will then be rapidly dissipated inside the battery. The acid in the battery will start to boil from the heat produced and the case will vent and may even explode, sending a shower of hot, highly corrosive sulphuric acid over everything and everyone near by.
This is an old idea, but worth repeating: When you disconnect a car battery, ALWAYS disconnect the "earthy" terminal first (these days, that will most likely be the negative side.)
If you are disconnecting the earthy side and you accidentally allow your spanner/wrench to contact the vehicle's body or chassis, no harm is done.
If you are disconnecting the live/hot side (while the earthy side is still connected) and you accidentally allow your spanner/wrench to contact the vehicle's body or chassis, you have just applied a short circuit across the battery. Expect the spanner/wrench to get hot and, if you cannot break the circuit because the spanner/wrench has welded itself between the battery and the body/chassis, start running, and get everyone else out of the area before the battery explodes.
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I was once told by a man with a large traction engine with an attached funfair ride - producing 100V and up to 600A across open terminals - that he dropped a large spanner across the terminals, and it heated up to red heat, melted and fell between them without really slowing down.
I have a feeling that the designers of drill batteries didn't really have people wearing dangley metal jewellery in mind when they built it. They have tried to stop you shorting it by recessing the terminals in a hole, just your bracelet is ideally designed to get around the safety precautions.
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The fine manual ( as in RTFM) for my old electric drill/screwdriver started with a safety page including battery SHORT as fire or injury may result, do not put in fire,charge other than approved charger......etc.
High power, high voltage or RF are dangerous, lady engineers sometimes forget bracelets and jewellery, until you`ve made the point and then "if we are going in there you will have to take your kit off", usually handing them your watch "here`s mine"gets the message over that this isn`t a non work suggestion [;)]
You were very lucky that is all that happened, a friend of mine still has a very bad scar from a 21st birthday watch strap that shorted a truck 24v ( why get it scuffed and covered in grease and oil?).
Even innocuous things like alkaline cells have a fair amount of energy capacity, and the high current ones will get hot enough to melt plastic (60C +) if something goes wrong. I had a remote contol go saggy like a Dali due to a loose wire I only found later on 4 AAA`s.
A PP3 9v battery can weld itself to an aluminium or steel plate, that was how we selected good and bad batteries to show them when buyers took over from engineers at manglements behest in several companies, the cheap ones had high internal resistance, so your bracelet was safe there.
I`ve seen the molten remains of a spanner fell down a riser onto a telco 50v busbar, 2 small pits and 3 blobs,one had CHR van...... written on it one of the others was just the jaws of one end. 40-45V is about when you will notice dc as a tickle depending on your personal moistness, I measure 22-28Kohm as a very dry person, I have been told 30V can tingle, not for me though.
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I had a remote control go saggy like a Dali ...
[:D]
[ Invalid Attachment ]
http://en.wikipedia.org/wiki/The_Persistence_of_Memory
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Yes, high current (even at low voltage) is quite dangerous because of the heat/welding you can get from short-circuits.
While it doesn't seem so far-fetched that a car-battery can be dangerous, people used to relatively harmless alkaline batteries don't realise just how much energy (and how much current can be drawn from) domestic rechargeables.
(You should also be careful with the innards of modern computers and their power supplies as these can often supply tens of amps, albeit at 3.3V or less.)
Many consumer rechargeable battery packs these days have overcurrent protection built in, in the form of "PTC" (positive temperature coefficient) devices which go almost open-circuit when overloaded (and reset after a few 10s seconds). Others have an inbuilt transistor switch connected to an overload sensor. Such devices are extremely cheap ($0.20 or something).
It is rather scary that a battery of the size you show in the photo does not appear to have such a safety-feature. In the UK (where we have a quite strict safety regime) you would probably have grounds to take the problem up with our Trading Standards body who are supposed to ensure that consumer goods are safe.
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You were merely doing a bit of Welding, Karen. Once the contact had been made, the melted / vaporised metal allowed a low voltage arc to bridge the gap. Scary! A modern rechargeable can give you loads of current and your bracelet was shorting out the contacts. You have probably damaged your battery, btw.
When I was a lad, I had real fun with a thick wire coat hanger held across the terminals of an old car battery of my Dad's. Melted it a treat with a few hundred Amps.
I suggest you may have had a shock - but it wasn't an electric shock, it was probably a burning sensation! It just felt like a shock. Our brains tell us - Sparks = Shocks.
You should never wear jewelery / watches when working on high current supplies. You could burn your arm off!.
yes indeed I cant believe it melted that bracelet section and burned so bloody bad... Now I am worried bout my lap top battery taking it out and putting it back on!
I wondered if it could hurt the battery!
Man Sophie those old hangers were pretty hefty wire back then.. Glad you were ok!
Well the burning did not come till after.. what I felt that got my attention felt like a big zap of power then boom the heat became very intense quickly getting hotter as I tried to remove the bracelets.. I did not see the sparks on the original zap my sister did ... I wasa two busy yelling cause it grabbed my bracelet and I was getting shocked.. definitely felt a shock.. thats how I new I was stuck in the battery....
The burning came after the metal had heated the shock came before..
Yes I have learned a valuable lesson!
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Normally you won't get an electric shock from an 18 Volt battery because the human body is quite resistive, so not much current will flow through it. But put something with a low resistance (like a metal bracelet) across the terminals of a high discharge rate battery and a very large current flows. As a result, the bracelet heats up and starts to melt very quickly. This can can result in very serious burns.
When working with any electric equipment (cars, computers, etc.) it is a very good idea to remove ALL metallic jewelery. Wedding rings and metal watch straps have led to many accidental amputations!
Although car batteries only put out twelve volts, they can be lethal. If you accidentally drop a spanner between the terminals, it may actually weld to the terminals. All the energy in the battery will then be rapidly dissipated inside the battery. The acid in the battery will start to boil from the heat produced and the case will vent and may even explode, sending a shower of hot, highly corrosive sulphuric acid over everything and everyone near by.
This is an old idea, but worth repeating: When you disconnect a car battery, ALWAYS disconnect the "earthy" terminal first (these days, that will most likely be the negative side.)
If you are disconnecting the earthy side and you accidentally allow your spanner/wrench to contact the vehicle's body or chassis, no harm is done.
If you are disconnecting the live/hot side (while the earthy side is still connected) and you accidentally allow your spanner/wrench to contact the vehicle's body or chassis, you have just applied a short circuit across the battery. Expect the spanner/wrench to get hot and, if you cannot break the circuit because the spanner/wrench has welded itself between the battery and the body/chassis, start running, and get everyone else out of the area before the battery explodes.
Boy I hear that!
I have always disconnected the battery terminals when dealing with car stuff!
I had no Idea how badly one could get hurt dealing with batteries.. thats really terribly scary and they should mention the jewelry warnings on the contact points in the operating manual and have a warning on the battery itself!
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I was once told by a man with a large traction engine with an attached funfair ride - producing 100V and up to 600A across open terminals - that he dropped a large spanner across the terminals, and it heated up to red heat, melted and fell between them without really slowing down.
I have a feeling that the designers of drill batteries didn't really have people wearing dangley metal jewellery in mind when they built it. They have tried to stop you shorting it by recessing the terminals in a hole, just your bracelet is ideally designed to get around the safety precautions.
Wholly smokes that is a lot of volts... That would kill you in a big hurry!
I never noticed the recessed prongs and would not have thought about it like that! I bet you are right Dave... I should write them a letter and tell them what I did! LOL...
Maybe they can add a warning to the battery!
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quote Edster
You were very lucky that is all that happened, a friend of mine still has a very bad scar from a 21st birthday watch strap that shorted a truck 24v ( why get it scuffed and covered in grease and oil?).
Wow thats terrible and I am understanding more about why mechanics do not wear jewelry.
That makes perfect sense to me now,, some before but I did not realize the extent of danger involved!
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I had a remote control go saggy like a Dali ...
[:D]
[ Invalid Attachment ]
http://en.wikipedia.org/wiki/The_Persistence_of_Memory
Great piccy RD.. A remote control??? How?
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Yes, high current (even at low voltage) is quite dangerous because of the heat/welding you can get from short-circuits.
While it doesn't seem so far-fetched that a car-battery can be dangerous, people used to relatively harmless alkaline batteries don't realise just how much energy (and how much current can be drawn from) domestic rechargeables.
(You should also be careful with the innards of modern computers and their power supplies as these can often supply tens of amps, albeit at 3.3V or less.)
Many consumer rechargeable battery packs these days have overcurrent protection built in, in the form of "PTC" (positive temperature coefficient) devices which go almost open-circuit when overloaded (and reset after a few 10s seconds). Others have an inbuilt transistor switch connected to an overload sensor. Such devices are extremely cheap ($0.20 or something).
It is rather scary that a battery of the size you show in the photo does not appear to have such a safety-feature. In the UK (where we have a quite strict safety regime) you would probably have grounds to take the problem up with our Trading Standards body who are supposed to ensure that consumer goods are safe.
Thanks Techmind I agree with that. I found no safty feature except as Dave pointed out about the recessed contacts... Thats interesting.. maybe I just do not know what to look for!
Good information and I feel very lucky to have gotten off so lightly ! Thank goodness!
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Re the saggy remote, as said there was a "loose" as in badly soldered wire inside from the battery terminals to circuit board.
It was very cheap and a replacement until the real one emerged from the sofa( yes it had fallen through).
It had become intermittent, but if you slapped it it worked, so I assumed it was battery contact. I slapped it one time too many and it got hot in my hand, I threw it in the kitchen sink and turned the tap on, when it emerged the battery end was at about 20-30deg sag to its former plane with the rest of it. ( the water didn`t get in for several seconds)
Curious me opened it up and one battery wire had detached and stuck on a component, the insulation had melted off both wires to the battery compartment and shorted everthing in sight.
I`d got a staff shop deal on industrial alkalines so we are talking over 1 A/hr energy capacity ( domestics about 500ma/H) at 6v for 4 being limited only by the wire as a short and the internal resistance, say 0.5R, or less, so 10 watts heat easily. A lot of heat in a small space!
Alkaline batteries have something like "do not short, heat in fire or..... risk of fire....." in the pack warning.
I must dispute tech mind`s assertion that alkaline`s are harmless, perhaps 20 years ago that was valid, but the technology has moved on. Any examination of stated capacity and internal resistance from manufacturers suggests that they are now just as dangerous in short circuit as many of the rechargeable options.
Zinc carbon primary`s are safe ( unles you short a special "flag" cell as used by railways and telco`s) as they have high internal resistance, which limits the current. A flag cell is (was?) the size of a bucket.
Care very befull!
Edit:http://www.cellpacksolutions.com/Search_Data_Sheet.asp?ID=LR40
The flag cell is now even more dangerous! Alkaline 40Ah!
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Thanks Edster that is an amazing heat that built up in that remote control.. I know my arm had several burns in the shape of the medical bracelet which was just burning the crud out of my skin!
Thank you for your most informative information on the different batteries!