Is a 15 volt lab power supply safe to mess around with? - Page 1
Forum section: electronics / testgear

author: Mr D
author_rank: Regular Contributor
timestamp: May 28, 2019, 02:50:40 pm
content: Hi folks,I'm thinking of picking up a 15 volt lab supply to mess around with with my 7 year old son.I want to take some stuff apart (like an old reel to reel tape machine), and use the lab supply to trigger the motor, VU meters, lights etc.In order to pique his interest in electronics and have something fun to do with him on a rainy day (and get him off the damn iPad!)Sooooooo, my question is: how safe is it to do this with a lab power supply that can only put out 15 volts max? What if my son suddenly decides to stick his fingers into what we're messing around with? 15 volts isn't really enough to do any serious harm, right?Obviously i can tell him not to do it, but kids, right? They can be unpredictable.I was actually hoping to get a LPSU with even lower max voltage, but i haven't been able to find one as yet.Thanks in advance!

author: Kleinstein
author_rank: Super Contributor
timestamp: May 28, 2019, 03:12:17 pm
content: 15 V is usually safe unless one uses salt water or similar to get good contact. However given the right resistors there is always some danger to heat up something, so there is a chance to burn yourself slightly and there is some (though small) fire hazard, especially if not supervised.

author: DaJMasta
author_rank: Super Contributor
timestamp: May 28, 2019, 03:17:00 pm
content: The guideline for when DC voltage starts to get potentially dangerous is 40V iirc, and basically, you're trying to determine the point at which a few tens of mA flow through the body with the given DCR of the human body - for AC signals the current required to cause problems is much lower.I'd think 15V alone is pretty safe, even for a kid. If you really want low voltage supplies, I'd work off of USB based ones, batteries, or a secondary variable supply to a wall wart that only puts out 12V or 9V. Agreed that at 15V, most of any risk is going to be from heating effects, maybe a current limit would be advisable if you think that's a concern.

author: janoc
author_rank: Super Contributor
timestamp: May 28, 2019, 03:18:12 pm
content: The voltage is not a problem, usually below 30V you won't even feel it (unless you touch the bare wires to your tongue or something of the sort). However, do make sure the supply is properly insulated and enclosed, so that nothing can fall inside through the vents, for example. Kids can be rather resourceful and lab supplies are not toys designed to be kid-proof.OTOH, why to bother with a lab supply? You can do the same thing using a pack of batteries. Buy NiMH rechargeables + a charger and the kid can have fun while being safe. Keep the mains powered gear only for later when he knows how to handle it safely already.

author: janoc
author_rank: Super Contributor
timestamp: May 28, 2019, 03:21:35 pm
content: Quote from: DaJMasta on May 28, 2019, 03:17:00 pmI would rather skip those - the OP is unlikely to be knowledgeable enough to judge which one is safe and which one is not given this question. The market is flooded with dodgy ones, with some being literal deathtraps.Even USB powerbanks can be problematic - if it is not designed properly, shorting its output could blow it up. Furthermore, many have a low current cut-off, so it would be very annoying to use with e.g. LEDs and similar low power devices.

author: schmitt trigger
author_rank: Super Contributor
timestamp: May 28, 2019, 03:27:08 pm
content: Just ensure that when he makes a mistake -we ALL made mistakes when young and learning- the current is limited to a safe value.Might be worthwhile to add an output fuse.

author: Mr D
author_rank: Regular Contributor
timestamp: May 28, 2019, 03:42:30 pm
content: Thanks all!Yeah, so the reason i was thinking about a lab power supply is that it's exactly that continuous variability that would make it fun for a kid.So, dialling up the voltage will make the motor spin faster, the light to get brighter etc.It's not my intention to leave him unsupervised, but just to be sure that if he does some random thing suddenly, he won't be in danger!

author: myf
author_rank: Regular Contributor
timestamp: May 28, 2019, 04:25:15 pm
content: Hello,Some years ago one of my sons was collecting in the trash of the led lamps out of use. Remount leds and roasted them in a few seconds with a small 9V battery, or put it in a transparent waterproof bag and he plunged into the sea. He had had a lesson in school about tension and intensity, but he was not interested in keeping the leds. At 15 years old he also found funny to get warm or hot battery by short... Kid ideas are sometimes very curious, almost impossible and perhaps maybe a little dangerous. Parents try to retain such ideas but it's not always possible...At 18 or 20, I don't describe its idea to power a pyrotechnic car seat belt pretensioner. I send it very quickly to the landfill !But at 18 years old he went to a school of engineering in mechanics and electronics. Now he feels right with operational amplifier...F. from France.

author: Jan Audio
author_rank: Frequent Contributor
timestamp: May 28, 2019, 04:28:17 pm
content: I would not buy a Korad PSU.

author: SparkyFX
author_rank: Frequent Contributor
timestamp: May 28, 2019, 04:42:07 pm
content: Lab power supply is usually a good choice.Low voltage is defined as < 50VAC/120VDC, under 25VAC/60VDC personnel protection insulation can be omitted.For kids toys however, according to 2009/48/EG, maximum is 24VDC nominal.I mean, working from batteries can produce shorts and people weld wrenches to 12V battery terminals - at welding temperatures, so what counts is the energy provided. Voltage limits at least provide safety when getting in contact to the voltage source.

author: janoc
author_rank: Super Contributor
timestamp: May 28, 2019, 04:49:09 pm
content: Quote from: SparkyFX on May 28, 2019, 04:42:07 pmYou don't give kids a car battery to play with, obviously!

author: shakalnokturn
author_rank: Super Contributor
timestamp: May 28, 2019, 04:52:48 pm
content: It looks like most risks have been mentioned here already. Well closed power supply, limited voltage, limited current...Despite that even with limited power with some imagination the right thing will heat. (As a kid I enjoyed getting pencil "leads" red to white just playing on contact resistance. enough to start a fire.)Then even with limited voltage and current, with a little more imagination (I.e: relay as an oscillator, diode, capacitor...) you can reach dangerous voltages.I think it's important even at a young age to try to make the dangers clear, even if that can involve a small capacitor tingle across a finger...Never underestimate curiosity.

author: ralphrmartin
author_rank: Frequent Contributor
timestamp: May 28, 2019, 07:31:00 pm
content: When I was a kid, I had great fun with a (large) lighting starter coil and 1.5v battery. The back EMF could make sparks perhaps 1 cm long, and my younger brother jump several inches into the air....I also electrolysed water using old carbon - zinc battery insides as electrodes. Collect the gas, use the coil...Even low voltage stuff can have serious consequences.On the other hand, it's stuff like this that gets kids really interested in science, not a bunch of switches and lights.

author: David Hess
author_rank: Super Contributor
timestamp: May 28, 2019, 08:27:47 pm
content: If it is current limited, then it will be very safe.

author: xavier60
author_rank: Super Contributor
timestamp: May 28, 2019, 10:15:55 pm
content: The kid should be encouraged to wear eye protection. I have seen near misses from exploding electrolytic capacitors.

author: SparkyFX
author_rank: Frequent Contributor
timestamp: May 28, 2019, 10:42:45 pm
content: Yeah, when i was a kid i also got curious why wires heat up when the 4.5V battery is shorted by it. Got no explanation back then, but was forbidden to use any of it again.

author: Old Printer
author_rank: Frequent Contributor
timestamp: May 28, 2019, 11:18:17 pm
content: As a youngster in the late fifties I got a nasty burn from a 6 volt lantern battery and some telephone wire donated by a well meaning ham friend of my father. Batteries can deliver a large amount of current, and without a low amp fuse can light up a piece of 24 ga wire red hot. A 7 year olds curiosity will be around when you are not there, it takes a very crafty adult to out smart a youngster with a lot of time on his hands.

author: Jan Audio
author_rank: Frequent Contributor
timestamp: May 29, 2019, 01:37:38 pm
content: Quote from: xavier60 on May 28, 2019, 10:15:55 pmI did not have that before, also with 15 volts ?Electrolytic is no tantalum.

author: CatalinaWOW
author_rank: Super Contributor
timestamp: May 29, 2019, 02:01:42 pm
content: Yes that would be a good choice, and safe enough. Nothing is totally safe. So to satisfy the danger mavens the risks of strangulation from the various cords should be mentioned, the dangers of generating poisonous substances though electro chemistry, tripping hazards from the wires, the risk of dropping a heavy supply on a toe, outgassing from plastic materials and the possibility of disease and other biocontamination on used equipment. Relax and get him the supply.

author: Ice-Tea
author_rank: Super Contributor
timestamp: May 29, 2019, 02:41:27 pm
content: Pointing out the obvious: there are some pretty cool kits out there that are gear especially to get kids interested. Why not start there?

author: bob91343
author_rank: Super Contributor
timestamp: May 29, 2019, 03:35:05 pm
content: Most of these warnings are pretty obvious. Such as, don't put the power supply in the sink and turn on the water.For the most part I wouldn't worry. I think back on the stuff I have done over the years and it's remarkable that I am still alive. But the human body is very resilient and these worries are largely overkill.I recall my son, as a tot, pushing scissors into a wall socket. Come to think of it, as a kid myself I cut a power cord with scissors and burned a big hole in the metal.So worrying about a 15 Volt lab supply seems rather trivial. I recently acquired, for almost no money, a small lab supply capable of 50V and 500 mA. I wouldn't hesitate allowing a kid to play with it. Sure, it puts out 25 Watts maximum and that is as much as a small soldering iron. But if he managed to find a way to get that much out of it, he'd quickly learn that one can get burned, and would probably not do it again.I think it's comparable to allowing him to cut vegetables. Knives can kill but I doubt a kid would kill himself with a kitchen knife. You can also fall off a bicycle or push a toothbrush into your eye.Overprotection is a poor idea; it inhibits learning.Back to the point the OP was trying to make, the short answer is that it's harmless.

author: radiolistener
author_rank: Super Contributor
timestamp: May 29, 2019, 09:56:57 pm
content: it depends on the max current which your power supply can provide. For example if your power supply provides 40 Ampers 15 Volts, it means that it can provide 600 W power. Such power can easily make barbecue from you.Even 1.5 V battery can easily provide enough energy for death, all depends on your brains and knowledge. So, learn first and make sure, you're well understand what you're doing

author: Neomys Sapiens
author_rank: Super Contributor
timestamp: May 30, 2019, 12:51:28 am
content: Quote from: Jan Audio on May 29, 2019, 01:37:38 pmNot in the fiery/fire-y form like tantalums, but like the cup detaching and bouncing through the lab like a lower energy form of that gizmo in 'Men in Black'.>pchoot-ting-ping-ting-dingaling-donk...mooo!<

author: Brumby
author_rank: Unknown
timestamp: May 30, 2019, 02:46:06 am
content: Quote from: Neomys Sapiens on May 30, 2019, 12:51:28 amIndeed. Lower voltagedoesn'tmean youcan'thave an electrolytic perform calisthenics - it just may take a bit longer* 15V is not a worry in itself* High current capability has the potential for thermal dangers - which can lead to explosive failure in some circumstances. Learn to use the current limiting at the very beginning - and show the youngster why that's a good idea for protecting the circuit and themself.* Supervision...... and all the usual cautions when using mains powered gear.

author: Fungus
author_rank: Super Contributor
timestamp: May 30, 2019, 05:48:28 am
content: Quote from: xavier60 on May 28, 2019, 10:15:55 pm<eye roll>Oh, sure, a kid's going to wear eye protection when you're not around.The best thing to do is explode a few capacitors so he sees the problem for himself. You might need more than 15V though, try it first to make sure you don't end up with egg on your face.(and learns that electrolyte can be nasty stuff)

author: james_s
author_rank: Super Contributor
timestamp: May 30, 2019, 05:50:16 am
content: There's no real danger, but a lot of reel to reel tape decks are somewhat valuable collectibles so you'll want to make sure you don't have a desirable classic before you tear it apart.

author: Fungus
author_rank: Super Contributor
timestamp: May 30, 2019, 05:52:14 am
content: Quote from: bob91343 on May 29, 2019, 03:35:05 pmThis. 15V is a safe place to experiment in a world full of AC mains.

author: bob91343
author_rank: Super Contributor
timestamp: May 30, 2019, 05:09:12 pm
content: Even seeing it as collectible, there remains the problem of finding a buyer for my old stuff. And yes a 15 V supply is relatively benign compared to some alternatives.

author: james_s
author_rank: Super Contributor
timestamp: May 31, 2019, 06:19:50 pm
content: Finding a buyer is easy between ebay and places like this forum. The difficulty can be packing and shipping but since it's free to list and takes only a few minutes I at least try selling anything I'm tempted to scrap that may possibly have value to someone. A few times I've been surprised and got far more than I was expecting. Other times I broke even and was happy to have something go to a new home.

author: bob91343
author_rank: Super Contributor
timestamp: May 31, 2019, 09:41:23 pm
content: Yes I have a garage full of antiquated electronics. I would love to see it go to a good home.Even some 15V power supplies, signal generators, oscillators, voltmeters, much more.