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I am new to electronics so please forgive me.

I am looking at powering a WS2812B RGB strip. Specifically 144 LEDs/ meter. After doing some research I found that 200mA is lethal and can kill. Now, of course, the idea is to not touch the terminals but I just want to have an understanding if this strip could kill me.

I believe each led uses about 50mA and so if we do the math (50*144) that results in 7200mA. I'm not going to power all the LED's at full brightness at once and I may only end up only using around 80 LED's.

I want to use a phone brick charger to power the LED strip (5V and 2A) I understand that this will result in dimly lit LED's but my main question is: Will 5V and 2A kill me if I accidentally touch the terminals or connections?? Considering 200mA is lethal.

Melebius
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NameIsMarcus
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    It is most lethal in its fire hazard – crasic Dec 10 '19 at 05:42
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    "Dimly lit LEDs" are not the most likely outcome of grossly overloading your supply. – Spehro Pefhany Dec 10 '19 at 05:53
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    Applied **TO** the bare heart under 100 uA may kill. Sticking sharp spikes into your chest and applying 5V MAY kill you. And may not. Applying 5V to your hands will not kill you* - you will not feel it in almost all cases. I will handle up to say 24V without too much concern if conditions are dry. In the wet from say rain or a hose I'd be slightly careful. If you stand in salt water and apply 12 V between a flounder spear in your hand and the water (think 12V LED flounder fishing lantern) then you may experuience solid arm and leg muscle lock up. (A friend of mine did this). ... – Russell McMahon Dec 10 '19 at 07:12
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    ... This is still unlikely to kill you - but I'd go out of my way to avoid doing it. | I'd rate say <= 12VDC "as safe as it comes". That said - apply 12V to conductive pads on your chest across the heart location and you MAY die - long ago a volunteer did :-(. VERY unusual. || I have worked on 50V wiring frames. On a highly humid day you get small annoyance shocks across the backs of your hands from brushing the terminals. | 50 VDC is considered safe under many regulatory systems. BUT in a freak accident people have died from 36V helicopter supplies. – Russell McMahon Dec 10 '19 at 07:16
  • Moral: Consider <= 12V safe as safe - but use as much care as you sensibly can with everything electrical. – Russell McMahon Dec 10 '19 at 07:17
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    <50V is considered safe unless you stick it on an open wound or tongue. ( However in mid'90's I have been known to check modem cables with my tongue (-48V) without the 200V ringtone – Tony Stewart EE75 Dec 10 '19 at 08:06
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    Consider that a 9V battery can supply 3-4A of short-circuit current, and they sell those in stores with totally exposed terminals. As long as you don't stick the terminals straight onto your heart, you're basically safe. – J... Dec 10 '19 at 14:39
  • "I want to use a phone brick charger to power the LED strip (5v and 2A)" - don't expect 2A out of most '2A' phone 'chargers', and don't trust them not to break down and kill you https://lygte-info.dk/info/ChargerIndex%20UK.html – Bruce Abbott Dec 10 '19 at 17:29
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    The problem with questions like this is that 1) we're random people interested in electronics, not medical or safety professionals, and 2) while such low currents and voltages are _normally_ quite safe, people _have_ reportedly managed to kill themselves using surprisingly low voltages by doing weird and stupid things like sticking electrodes under their skin or triggering a spark in a room filled with explosive gas. So it's hard to give an answer like "no, 5V 2A definitely can't hurt you no matter what you do." Probably the best possible answer would be to cite some official safety regs. – Ilmari Karonen Dec 10 '19 at 17:32
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    A pencil can be lethal, but generally not so. Same with 5V and 2A. – copper.hat Dec 10 '19 at 19:04
  • @J..., Yeah, and the standard diagnostic test to determine if those 9V batteries are still good, is to touch them to your tongue. – Glen Yates Dec 10 '19 at 20:32
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    @IlmariKaronen there are plenty of professionals including safety systems professionals on here. One doesn't need to be a medical expert to identify that in terms of fatal incidents involving low voltage circuits, by far the most common reason is from fire due to electrical shorts in haphazard fixtures that are left alone for long periods of time. – crasic Dec 10 '19 at 20:52
  • Are you planning on eating it before you plug it in? Just checking, it changes the answer. :) – throx Dec 10 '19 at 22:35
  • Similar query Death by electroshock from 12V battery https://skeptics.stackexchange.com/questions/39874/death-by-electroshock-from-12v-battery/45535#45535 – bandybabboon Dec 11 '19 at 07:07
  • I have one of these strips. You will find that if you overload the power supply, the LEDs furthest from the power supply will flicker and malfunction (they won't get damaged, but they won't work properly). The power supply could also be damaged if it's low quality. You can calculate the current based on how many LEDs are on and how bright, and design your animation to keep the current less than 2A. (i.e. turn the brightness down if all the LEDs are on at the same time) – user253751 Dec 11 '19 at 09:45
  • @J... Sticking them to your tongue has interesting effects though. – Mast Dec 11 '19 at 12:52
  • I disagree with the close vote on this. Why has this been closed and marked as answered elsewhere and linked to a question that is closed due to off-topic and does not have any detailed answers. – H. Daun Dec 15 '19 at 23:54

10 Answers10

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200mA is lethal (actually much much less is lethal) and can kill, but only it if gets inside you. For it to get into you, it needs enough voltage behind it to push into you. If there is enough voltage to push a lethal level of current into you, and enough of that current is actually available to push then it is lethal.

Think about a bullet. It's a little piece of lead and is lethal right? Well, it's only lethal if it gets inside you. For it to get inside you, something has to be behind it to push it hard enough to get inside you. So a lead ball the size of your first is even more lethal right? After all, it's even more of the deadly stuff a bullet is made of. Again, only if it gets inside you so something has to be pushing it hard enough to get inside you.

On the opposite end is static electricity which actually does have a high enough voltage to push those lethal level of currents inside you...but static electricity doesn't have enough power behind it to produce that current so it doesn't kill you. It's like shooting a grain of sand at you at high speed. It has the push, but it's not pushing "enough stuff into you" to do any damage

Then there is something like a lightning bolt which has both the voltages to push those currents into you AND the power to produce those currents, and those can definitely kill.

DKNguyen
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    Thank you for your comment. That does make a lot of sense but.. can 5V and 2A kill me? Is that enough?? – NameIsMarcus Dec 10 '19 at 05:32
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    @NameIsMarcus 5V is not enough. 50V isn't enough either unless you go out of your way to stick needles under your skin (your insides are much more conductive than your skin and so less voltage is required to push current). – DKNguyen Dec 10 '19 at 05:32
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    @DKNguyen I thought static discharge had enough current and voltage to potentially be lethal, however the time of exposure is so small it doesn't matter. Correct me if this is wrong. – Sorenp Dec 10 '19 at 06:23
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    I loved the analogy presented here, to explain voltage, current electricity all at once!!! – AKR Dec 10 '19 at 07:58
  • @Sorenp I'm not sure about that. Can't comment. – DKNguyen Dec 10 '19 at 14:23
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    @Sorenp But there isn’t enough energy (read: number of electrons) behind it to deliver that current for a sustained period of time. – Jonas Schäfer Dec 10 '19 at 14:45
  • Just to give a general idea of the voltage scale that might be dangerous: German regulations define voltages above 50V AC and 120V DC as dangerous. – Nefrin Dec 10 '19 at 15:51
  • @Nefrin That's RMS for the AC right? So 71V peak? Personally, I would start being wary at above 70VDC. – DKNguyen Dec 10 '19 at 15:53
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    @DKNguyen yes you are right. The Voltage in the regualtion is 50V RMS – Nefrin Dec 10 '19 at 15:58
  • I think there's an unstated assumption here about the bullet entering violently through the skin. It might not be that lethal if you eat it. Lead poisoning might be an issue there, but that's nothing to do with pushing the bullet through. – ilkkachu Dec 10 '19 at 21:14
  • @ilkkachu Then let's replace lead with gold bullets and fist sized balls, – DKNguyen Dec 11 '19 at 03:54
  • @DKNguyen It looks like 9V is enough if you stick needles under your skin... at least if you believe this story to be true: https://darwinawards.com/darwin/darwin1999-50.html (Someone tried to measure his own _internal resistance_ and killed himself with the probe voltage of a multimeter). – orithena Dec 11 '19 at 11:51
  • This post is a helpful analogy, but it doesn't fully explain why the power supply isn't capable of killing someone. Maybe you could include a brief scientific explanation of resistance, voltage and current. – ConcernedHobbit Dec 11 '19 at 16:30
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To make it easy:

1- Car battery 12V (hundreds of Amps) will not kill you. Laptop charger 20V 7A will not kill you. Therefore, the 5V 2A will not kill you also.

Most of power sources you will see are voltage source. Therefore, the current will follow the voltage (by other way the current is dependent on the voltage ) and the impedance (your impedance here) by ohms law. If you touch both ends of the battery which is 12V, assume your impedance is 100k ohm. You will only draw 0.012 mA which is safe (IEC 60479-1). Current source are rare for normal user to find and they are extremely dangerous.

Unless the voltage become very high enough to enter the zones in the picture it will be safe. your impedance is not fixed and depend on many condition. to sum up, I believe any thing below 40V is safe for human. enter image description here 2- Phone charger will not kill you if you use it to charge your phone and to light your LED.

When you use your charger which is connected to the mains. you will be concerned about the mains voltage (110~ or 230~ depend in your country). These chargers has double insulation. Which means that the input (mains) is isolated from the output by transformer. The casing is also plastic which is not a conductor.

Ashraf Almubarak
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The power source you are looking into is a voltage source (like 99% of the power sources you interact with in your daily life). This means that 2A is the maximum it is designed to supply, but it will try to keep a steady 5V. Thus, the current is determined by the electrical resistance between the terminals.

It can't kill you because your body electrical resistance is too high for 5V to be able to drive a lethal current through your skin (let alone through some vital organ).

lvella
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Short answer No,

Long answer, The confusion here comes from a few common misconceptions/misunderstandings.

First being, "Current kills, not voltage" or similar.

Yes, it is the amount of current that determines how much damage is caused. However it is the voltage that determines how much current can flow.

Ohms law states V=IR and therefore I=V/R.

A human tongue is on average around 7000 Ohms.

By this, 5V / 7000 Ohms = 0.0007A or 0.7 mA. At these levels you wouldn't even feel the electricity so that voltage is safe for a human. Now obviously you won't be touching the 5V power supply with your tongue, and instead with your fingers likely. Skin has an even higher resistance of around ~100kOhm when dry which decreases when wet.

The second misconception is how power supplies work.

Often people will see a power supply that is marked as 5V 2A or 5V 10A and be worried that it may break their device or hurt them, i.e. their device may say 5V 0.5A on it.

The rating of the power supply is the Voltage and Maximum current at that voltage it can supply. Due to ohms law, even though the power supply can supply that much current, the 0.5A device will not draw that much current due to its effective resistance which would in this case be 10 Ohms.

H. Daun
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Just to add two aspects not mentioned before: a 2A load can badly burn a (DC) cable and burn down your house, this could even kill you in your sleep, so always be careful.

Also, bad (cheap) power supplies with missing ground connection or poor (transformer) isolation between primary and secondary stages are not unheared of. This can either cause fire or result in dangerously high potentials on wires or enclosures.

So even if 5V is harmless with most skin contacts, you should not touch it intentionally and install it without considering the implications.

eckes
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  1. Your skin is the body's largest organ.
  2. It is a fairly good insulator but your internals (muscles, bones etc) is more like a fairly good conductor.
  3. The skin is able to withstand 5V (and even more up so 50 V is deemed as safe, I work with equipment there upto 48 V can be expected , and well everything have wiring posts which isn't insulated so it exists a fair risk of small shocks.)
  4. Large voltage will easier push thru insulation material so 180V AC is deadly i.e. the voltage (or we could call it intensity) is what decides the insulation and your skin won't keep its insulating properties to protect you i.e. the skin will begin to burn and when that happens the flowing current will increase (while the skin is intact the current will be low ie a fair bit below 30 mA.)

I have a computer supply which can feed 100 Amps at 5 V, what do that says : on the inside of it I expect voltages around 500 V or to be present. getting a shock from something which can provide 100A at 5V is unpleasant but: DON'T short the terminals .... depending on what you short them with that thing will burn.

Electric_90
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Stefan Skoglund
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  • 180V is about as deadly as driving your car at 20mph without a seat belt. People do die from that, but a very large majority gets away with a scare. The point where death becomes a not unlikely outcome is higher than 180V by some hundred volts. – Stian Dec 11 '19 at 13:31
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5V and 2A is not lethal itself. 5V and 2A also won't power a load that needs 5V 7.2A, so perhaps only less than 40 LEDs can be fully on at one given time.

Justme
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It won't kill you if you accidently touch the terminals as others already pointed out, but: 2A and 5V make a power of 10W, which can be quiet a lot if concentrated on a small volume, i.e. you definetly can burn yourself, but in most cases this will not leave any lasting physical damage.

yar
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You can take any multi-meter with range above 1 megohm and measure resistance of your body -- it should come in a few megohms.

Your power supply is regulated voltage source of 5V. Divide 5V by your body resistance/impedance -- result is a current which will flow through your body.

For example if I take leads of multi-meter with my fingers of both hands impedance of my body is around 2.4 megohm then through my body will flow

I = 5/(2.4*10^6) = 2*10^-6 = 2μA [around 2 microamperes]

This magnitude of the current is absolutely safe for human body.

Elliot Alderson
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Andrew
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60v-70v is the highest safe DC voltage for bare hands according to IEEE and similar groups.

Very rarely poeple electrocute themselves on a car battery if there is water and a cut and a gold ring involved... no deaths afaik. capacitors take many more lives.

bandybabboon
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