The Do-it-Yourself Thread: A Home for Handymen and Artisans - General

Decided to take my subwoofer out of my car since E46 have pretty nice default speakers anyway and to save battery power, decided to install it in my room instead. With bit of help from facepunch it's kind of working: [video=youtube;1U9zBBmiUg4]http://www.youtube.com/watch?v=1U9zBBmiUg4&feature=youtu.be[/video] Requirement: 300-350W power to function fully with full bass. What I provided: 2-3W from my old damaged server PSU, but hey, it works, just a matter of getting some second hand 400W PSU from internet and ready to go.

[QUOTE=Legend286;40781751]Go lick a car battery and tell me it wasn't painful. 12V from a few AA batteries attached together isn't shit, it won't hurt you if you lick it (like a 9v battery doesn't...) Yeah you can say licking it is different to touching it, but it's nothing to do with voltage. It's a combination of both voltage and amps that can make something dangerous, a thousand volts at 0.01 amps isn't gonna hurt you.[/QUOTE] All that matters is having enough voltage to pass a lethal or painful current through you. If you lick a 12 volt car battery it will probably kill you because your mouth is very conductive, if you touch it nothing with happen.

There seems to be a general forgetting of how electricity works in this thread. A battery is a voltage source not a current source, so you get 12v of potential between the terminals (assuming for a moment that are battery is ideal and in perfect condition, otherwise it may be a little less than that especially if you draw a large current from it), it all comes back to basic ohms law, V=IR (since its DC we can assume the human body is purely resistive). If you connect a terminal to either hand, the path taken by the current is going to have to travel up on arm and down the other which is potentially of the order of 2m and whilst it's difficult to exactly quantise the resitivity of the body because its made of so many different things, it's still bloody high. Your tongue is wet and the distance across it compared with the length of your arms is very very small, added to which it's a rather sensitive object to enable you to taste. This is why you can feel it when you put it across your tongue you know about it. Finally, I suspect even if your tongue was long enough to lick both terminals on a 12v battery it's unlikely to kill you, just be incredibly unpleasant since the current isnt going near your heart (to which you actually only need to apply a few milliamps to to cause damage)

[QUOTE=metallics;40785197]There seems to be a general forgetting of how electricity works in this thread. A battery is a voltage source not a current source, so you get 12v of potential between the terminals (assuming for a moment that are battery is ideal and in perfect condition, otherwise it may be a little less than that especially if you draw a large current from it), it all comes back to basic ohms law, V=IR (since its DC we can assume the human body is purely resistive). If you connect a terminal to either hand, the path taken by the current is going to have to travel up on arm and down the other which is potentially of the order of 2m and whilst it's difficult to exactly quantise the resitivity of the body because its made of so many different things, it's still bloody high. Your tongue is wet and the distance across it compared with the length of your arms is very very small, added to which it's a rather sensitive object to enable you to taste. This is why you can feel it when you put it across your tongue you know about it. Finally, I suspect even if your tongue was long enough to lick both terminals on a 12v battery it's unlikely to kill you, just be incredibly unpleasant since the current isnt going near your heart (to which you actually only need to apply a few milliamps to to cause damage)[/QUOTE] Say that again when the amount of current a car battery is capable of dumping causes massive burns to your tongue, mouth and face

[QUOTE=download;40785388]Say that again when the amount of current a car battery is capable of dumping causes massive burns to your tongue, mouth and face[/QUOTE] ... It can't bend the laws of physics. I never said it was sensible but it definitely wont kill you and the burns would be localised to your tongue, it's not going to take a wander around the back of your head because it fancies it.

[QUOTE=metallics;40786633]... It can't bend the laws of physics. I never said it was sensible but it definitely wont kill you and the burns would be localised to your tongue, it's not going to take a wander around the back of your head because it fancies it.[/QUOTE] I don't think you appreciate how hot arcs are and how deadly head burns are

[QUOTE=download;40787336]I don't think you appreciate how hot arcs are and how deadly head burns are[/QUOTE] It's not going to create an arc though? You need more than 12v to create an arc of any significance...

Metallics is right your not going to kill yourself by putting 12V across your tongue although it will hurt, I've actually tested this myself with a variable power supply and can quite easily withstand up to 20V before it gets too painful. Worst case current at such low voltages is a mere couple of mA which is unlikely to cause any sort of burns. Shorting it out is a much more significant danger with high capacity batteries.

Sorry for dumb question but: In what units is car battery charge measured? I mean if it's say car battery 12V, and it is drained, would it show 8V? Because yesterday my car battery went flat and on board diagnostics shown 11.0V which wasn't enough to start ignition.

[QUOTE=arleitiss;40788559]Sorry for dumb question but: In what units is car battery charge measured? I mean if it's say car battery 12V, and it is drained, would it show 8V? Because yesterday my car battery went flat and on board diagnostics shown 11.0V which wasn't enough to start ignition.[/QUOTE] Charge is not very straightforward to measure since it can only really be measured while under load, open circuit voltage usually remains quite close to normal unless you've really discharged it for a long period, discharge curves are also non-linear. [img]http://frittliv.autonomtech.se/HintsKnowhow/Mobile12V/DischargeCurvesLeadAcidBattery_2.jpg[/img] The amount of charge is usually measured by drawing a fixed current from the battery and measuring the voltage, as a battery discharges the internal resistance increases which means the voltage will decrease under load. Generally for lead acid if the voltage is 0.5V to 1V below the normal ratings it needs a charge. Battery capacity is commonly measured in Amp-Hours which indicates how many amps of current it can supply continuously in a 1 hour period before needing a charge.

[QUOTE=download;40784435]All that matters is having enough voltage to pass a lethal or painful current through you. If you lick a 12 volt car battery it will probably kill you because your mouth is very conductive, if you touch it nothing with happen.[/QUOTE] Point is saying 12 volts isn't harmful is dumb, sure it can be but voltage can be misleading and just because its low doesn't make it safe.

[QUOTE=download;40787336]I don't think you appreciate how hot arcs are and how deadly head burns are[/QUOTE] a 12 volt arc flash? highly doubtful.

[QUOTE=Legend286;40789412]Point is saying 12 volts isn't harmful is dumb, sure it can be but voltage can be misleading and just because its low doesn't make it safe.[/QUOTE] How is 12V misleading ? 12V isn't harmful unless you're a total idiot.

I understand that not everyone knows that much about electricity, but I don't see why it happens to be the one subject everyone thinks they're an expert on and decide to put forward their bullshit ideas as the truth. You would have to do something really stupid to cause any real damage with a 12v potential. As for arcs, the breakdown voltage for air as around 30Kv/cm. Good luck with your 0.00004cm long arcs of death.

On a related note, I took the cord from an old mouse and an extra case fan I had lying around and made a USB powered fan. [t]https://dl.dropboxusercontent.com/u/13781308/iamyourbiggestfan.jpg[/t] It needs 12v but the USB only puts out 5v. Is it possible to increase the voltage somehow? [editline]edit[/editline] How well do transformers scale? Would I be able to make a tiny step-up transformer? The USB puts out 500mA and I have a fan that only needs 200mA.

[QUOTE=Pelf;40793375]On a related note, I took the cord from an old mouse and an extra case fan I had lying around and made a USB powered fan. [t]https://dl.dropboxusercontent.com/u/13781308/iamyourbiggestfan.jpg[/t] It needs 12v but the USB only puts out 5v. Is it possible to increase the voltage somehow? [editline]edit[/editline] How well do transformers scale? Would I be able to make a tiny step-up transformer? The USB puts out 500mA and I have a fan that only needs 200mA.[/QUOTE] Transformer don't run on DC so there are two main options, use a inverter to convert the DC into AC which can be fed into a transformer (preferably a high frequency transformer) or build a boost converter which can directly convert the low voltage up to a higher voltage using a few simple components. Since your current requirements are not that high I recommend the latter approach, how you want to do it is up to you, there are ICs that can do practically the entire job such as the MAX1771 or LT3433 or you can do it with a dozen or fewer simple components. If that's too much effort you can probably get something off of ebay or dealextreme to do the job. You could also route the 12V supply out of your case.

[QUOTE=chaz13;40793017]I understand that not everyone knows that much about electricity, but I don't see why it happens to be the one subject everyone thinks they're an expect on and decide to put forward their bullshit ideas as the truth. You would have to do something really stupid to cause any real damage with a 12v potential. As for arcs, the breakdown voltage for air as around 30Kv/cm. Good luck with your 0.00004cm long arcs of death.[/QUOTE] Arcs can be drawn out if there is a load however.. You can draw arcs with 36 volts. But the electrodes have to be touching, and slowly drawn out. Highly unlikely to happen unless you are purposefully doing it. I tried drawing arcs with a car battery and haven't had any luck. Lowest voltage I can manage is about 36 volts, and even then I used carbon electrodes, low wind, and the distance was tiny ~1cm. Once it vaporizes the conductors though it extinguishes itself quite quickly. So even if you wanted to it's quite unlikely to cause much damage.

I took some pictures with my late great uncle's old Minolta today... First time working with film. Does that count as DIY?

In the wake of making my house the way I freaking want it now, i tore down my rasterbated picture of a b-17 flying over the golden gate, and in its place, a b-17 will be flying over the golden gate possibly post-apocalyptic style. This is all going to be painted in 1shot oil base. First black backgrounds [URL=http://s43.photobucket.com/user/serj22/media/CAM00819_zps184b5bec.jpg.html][IMG]http://i43.photobucket.com/albums/e356/serj22/CAM00819_zps184b5bec.jpg[/IMG][/URL] Then some chrome, and some tan, and some green, and some black, mixed accordingly... and red fields [URL=http://s43.photobucket.com/user/serj22/media/CAM00836_zpsfee80af1.jpg.html][IMG]http://i43.photobucket.com/albums/e356/serj22/CAM00836_zpsfee80af1.jpg[/IMG][/URL] Still a lot more coloring and blending on the plane, which is still at underpaint phase, then on to the golden gate... and some water... And its upside down. Even though photobucket shows it right side up... well hell.

[QUOTE=Chryseus;40791394]How is 12V misleading ? 12V isn't harmful unless you're a total idiot.[/QUOTE] Car batteries can actually be a bit harmful. I havent personally been shocked, but not too long ago I was tightening down a ground wire and dropped my wrench. It fell, landed on my positive starter wire, and grounded that to the block. It pretty much tried to weld my wrench to the block, and started melting the wrench.

That's what they're saying, though. Car batteries are freaking dangerous, if you're made of metal. The high resistance in the human body makes the 12V voltage in car batteries safe.

Pickguard attempt #6. This is the one I'm sticking with. I've taken this guitar part and carved and changed it for the last 7 years. I think I'm finally happy. It only has finish on it to keep the wood from expanding or contracting, which causes the layers to seperate. That did happen like 4 years ago. I got wise to it, so any time I sand or carve, I clear it immediately after. Fun times... [URL=http://s43.photobucket.com/user/serj22/media/CAM00844_zps1aeff7e2.jpg.html][IMG]http://i43.photobucket.com/albums/e356/serj22/CAM00844_zps1aeff7e2.jpg[/IMG][/URL]

Just to bring a little closure to the electricity debate; Unless you attach the electrodes DIRECTLY to your heart, nothing under 30 volts is even remotely close to lethal under any other circumstances and you need up to double or even tripple that before there's any risk. Even then that's not particularly lethal under most circumstances. That said to stay safe anything near or above 100 volts should be treated with respect, as if it could kill you.

Anyone have any good ideas for a relatively small Arduino project? Summer break hit and I have absolutely loads of time and I should probably make use of it.

[QUOTE=TheCube;40837579]Anyone have any good ideas for a relatively small Arduino project? Summer break hit and I have absolutely loads of time and I should probably make use of it.[/QUOTE] Get a small LCD display for it and play around with that, they're rather good fun. I got one of these: [url]http://www.adafruit.com/products/358[/url] And have been tinkering with getting it to display various things. The most recent thing was I got a real time clock module picked up an old temperature sensor I had kicking around and made it into an alarm clock with temperature display. [t]https://dl.dropboxusercontent.com/u/3798635/2012-12-24%2014.02.34.jpg[/t] But you can quite a few cool things just with drawing graphics and making user interfaces on a screen.

Made some butterknives from a piece of juniper wood. Came out pretty nice. Carved, sanded and then oiled with paraffin oil. [t]https://dl.dropboxusercontent.com/u/5342745/sm%C3%B6rknivar.jpg[/t]

I guess my woodworking thing's not as good as Armandur's... Because those are just beautiful... But I painted a door red to use as a desk surface. [t]http://i.imgur.com/MEjQV06.jpg[/t] Two more coats, a stain around the edges, and a poly... And I'll have the best dang bear pong table a broke college student could wish for. (Yes, I know I painted over the sides on that side... I'll sand that off before I stain the edges.)

Bear pong?

[QUOTE=SomeENG;40850401]Bear pong?[/QUOTE] he meant what he said. The most hardcore of pongs. That's why he needed a fire door mounted on the table. To support the bears.

[QUOTE=chipset;40825141]Just to bring a little closure to the electricity debate; Unless you attach the electrodes DIRECTLY to your heart, nothing under 30 volts is even remotely close to lethal under any other circumstances and you need up to double or even tripple that before there's any risk. Even then that's not particularly lethal under most circumstances. That said to stay safe anything near or above 100 volts should be treated with respect, as if it could kill you.[/QUOTE] One volt would kill you with enough current behind it.