Battery powred oscilloscope  - Page 1
Forum section: electronics / beginners

author: king129
author_rank: Contributor
timestamp: April 27, 2019, 06:06:08 pm
content: Hello i was watching Eevblogs video on how not to blow up your oscilloscope and was thinking what if I got a car battery put and converted its DC to 110 volts ac with the right amount of current and powred my oscilloscope useing that. Would I be able to put my oscilloscope anywhere in my house without worrying about it blowing up? If this would work would I be able to put my any number of my oscilloscope probes in a grounded circuit without anything bad happening? If I'm wrong please tell me why so I get this idea out of my head so I can think of something else. Thank you in advance.note the battery is not plugged in while im powering the oscilloscope.Sent from my LGMP260 using Tapatalk

author: Nusa
author_rank: Super Contributor
timestamp: April 27, 2019, 11:41:56 pm
content: A more common mistake is choosing poorly when placing your probe ground clip. No method of isolation is going to fix that. So yes, bad things can still happen.Another common mistake is trying to measure things that are not within the range of the standard probe. An obvious example would be the flyback transformer of a CRT, which is likely to be over 10 kV. That's not the only place you can find high voltage, of course. So yes, bad things can still happen.

author: Electro Detective
author_rank: Super Contributor
timestamp: April 28, 2019, 12:17:42 am
content: Well for starters:the converted DC better be putting out a proper sine wave AC into the oscilloscope, or else things will heat up fast and >do put thick rubber tubing around the BNC connectors from the probe leads, so you can grip them and turn,but never touching any metal part with your fingerskeep away from anything metal on the oscilloscopean inline fuse adapter for the croc lead with a fast blow 50ma or 100ma fuse, 'may' save your scopeand assA battery fuse and converter fuse is recommended, proper fuse values or don't bother...Protective eyewear and rubber or thin leather glovesdon't have bare knees and feet on the ground, or socksand no tacky flip flops (as featured on Youtube) whilst roaming around with this rigFigure out and plan exactly WHERE the croc clip and 10x probe go in the circuitOptions: crossed fingers, and silent prayer to Admin above(and or below) to be lenient and generous in the event of an unforeseenor dumbassdisaster(fwiw suggest to repeat this EVERY TIME you play with electronicals)

author: vk6zgo
author_rank: Super Contributor
timestamp: April 28, 2019, 12:25:01 am
content: Quote from: king129 on April 27, 2019, 06:06:08 pmIf it is a standard 'scope, the ground clip on the probe is directly connected to the "chassis" & henceallthe external metalwork of the instrument, so if you take your DMM on Ohms range you will be able to measure a very low resistance to this metalwork.This leads to several problems :-(1) Using the normal power source, if you inadvertently place the the "ground clip" on the Mains "Active" ("hot") connection, there will be a blinding flash, a Bang!, & you will, hopefully, just blow your fuse at the Mains entry point, or if you have one, drop out your RCD.If you are just unlucky, you might destroy the track on your 'scope's main board which carries the ground connection.If you are very, very, unlucky, your 'scope or probes may be destroyed, perhaps causing flying bits which may injure you.(2) If you, using two or more channels try to measure across two or more parts of a circuit where there is no common point, you will cause a nice big Bang & perhaps destroy both your 'scope & the circuit/s you are probing, as in this case you might be looking at something which isn't directly fuse or RCD protected.There are still a lot of possibilities, even if your Oscilloscope is independently supplied.(3) if you do the same thing as in (1), you will not blow the fuse or trip the RCD.Instead, you will elevate the whole Oscilloscope to the "Active" voltage.The big problem now, is that the rest of the metal things in the room are probably firmly tied to ground, so that if you measure at the power point in your kitchen, with the 'scope happily sitting on the melamine counter, & inadvertently touch the sink taps, the fridge, the microwave oven, the electric kettle, or a dozen other things whilst touching your 'scope, your Oscilloscope will soon appear on eBay as part of a "Deceased Estate".(2) will still happen!

author: bitseeker
author_rank: Super Contributor
timestamp: April 28, 2019, 04:50:36 am
content: Hi king. Welcome to the forum!Bottom line: A grounded oscilloscope is not designed to be used without its ground conductor connected to earth ground. Life is better if you "get this idea out of  head," as you said in your original post.If you need a floating scope, then buy one that's designed to operate that way. If you're going to use a grounded scope, then learn how to use it as it was intended, including how to properly measure high voltages, perform differential measurements (e.g., use a differential probe), etc.

author: Shock
author_rank: Super Contributor
timestamp: April 28, 2019, 07:50:18 am
content: Quote from: king129 on April 27, 2019, 06:06:08 pmMost modern oscilloscopes specify that the oscilloscope is earthed/grounded, this is for safety reasons not to avoid blowing your oscilloscope. They state this in the manual but if not and you're uncertain assume it's the same for all. Some specific oscilloscopes have isolated channels and safety rated isolated inputs (two different things), mostly portable type battery operated oscilloscopes and ones used for mains monitoring.Otherwise use the methods outlined in the video.QuoteNo, always understand the circuit and what you are probing, this goes for multimeters as well. If you don't understand how identify the difference between AC, DC, ground referenced, floating, mains, high, low voltage circuits you're probably rushing in too fast.So start there learning to read voltages off a schematic and if it's an AC or DC type circuit, the voltage you expect and if there are parts of the circuit that will damage your gear. Never put your ground clip on a live voltage unless it's floating (no voltage in reference to earth/ground) or earthed/grounded (so no voltage potential or difference exists between your oscilloscope ground and the point you are attaching the ground clip to).

author: frobet
author_rank: Newbie
timestamp: April 30, 2019, 08:03:20 am
content: Quote from: bitseeker on April 28, 2019, 04:50:36 amI had a similar idea a couple of months back and I still recall someone told me the exact words your wrote. "Life is better if you get the idea outa ya head"

author: bitseeker
author_rank: Super Contributor
timestamp: April 30, 2019, 09:43:17 pm
content: It does seem to be a normal phase that new scope users go through.

author: schmitt trigger
author_rank: Super Contributor
timestamp: April 30, 2019, 09:54:40 pm
content: If necessary, it is far better to employ a scope that is explicitly designed to run from batteries.Not only the scope will be protected, but the operator is also fully protected. As you can see, the probe connectors are fully shrouded.Both Fluke and Tek have them, but tend to be pricey.

author: Mortymore
author_rank: Frequent Contributor
timestamp: April 30, 2019, 11:07:56 pm
content: Even cheaper brands with the inputs fully isolated they're not cheap, but for only battery powered scope some can be found at a reasonable price.Examples:Siglent,GW-instek,Micsig (isolated)andMiscig (non-isolated)

author: Zero999
author_rank: Super Contributor
timestamp: May 01, 2019, 10:56:28 am
content: There's nothing wrong with a battery powered oscilloscope, but it still shouldn't be used on mains circuits, without the usual safety precautions, unless it's specifically designed for it.The Rigol DA1054Z will run down to 36VDC, which makes it suitable for running off a 48V battery pack. Awhile ago, I considered making one, but lost interest when I bought the OWON SDS7102, with the battery.https://www.eevblog.com/forum/testgear/battery-pack-for-rigol-ds1054z/The only time I've made use of the fact the oscilloscope is floating, is when probing a signal on an earth referenced DC power supply, but I only do this with non-hazardous voltages <60V.

author: grifftech
author_rank: Frequent Contributor
timestamp: May 01, 2019, 02:07:02 pm
content: DSO138

author: jeroen79
author_rank: Frequent Contributor
timestamp: May 01, 2019, 04:26:55 pm
content: Understanding what you're doing is key.I would suggest that you first draw a basic block diagram of how you think your floating scope will look. (electrically that is)This including the power supply and inputs with their ground clips.Then we could tell you if you have made something dangerous or something safe.Things to look out for:-Don't create any shorts between different voltage levels. (usually through the ground clips)-Don't have any exposed metal parts connected to high voltages. (ie a double insulated device)Also think about why you want to do this?What exactly do you want to do?Could you accomplish it without floating the oscilloscope?

author: L_Euler
author_rank: Regular Contributor
timestamp: May 01, 2019, 04:45:52 pm
content: Quote from: Nusa on April 27, 2019, 11:41:56 pmI actually did that when I was much younger and dumber. Touched my heathkit scope probe to a TV flyback. Scope no more.

author: bc888
author_rank: Regular Contributor
timestamp: May 01, 2019, 05:23:59 pm
content: Threads like this scare the crap out of me. I did by Micsig differential probes in the hope that as I still do not know what I'm doing, it's better than nothing. Lordy lordy.Oh, also, thank you all for sharing, I don't post nearly as much as I read and I try to read all pertinent threads. THANK YOU!

author: DMack
author_rank: Newbie
timestamp: January 18, 2021, 03:56:42 pm
content: Quote from: bc888 on May 01, 2019, 05:23:59 pmHey bc888 – how are those differential probes working out? I'm another scope newbie who's not using my device because I've read too many horror stories about things going badly. I understand that I can use an oscilloscope safely if my circuit is battery-powered and not connected to USB and/or mains power. However, I prefer to use bench power instead of batteries, and I'm considering the MicSig differential probes you got to minimize any catastrophes. Have you found that they are worth the investment?Thanks much.

author: fordem
author_rank: Regular Contributor
timestamp: January 18, 2021, 06:14:58 pm
content: Quote from: DMack on January 18, 2021, 03:56:42 pmNot necessarily - you can still destroy a scope using battery powered equipment - hook a scope up to the high voltage circuit of an old battery powered TV and you'll get the chance to see it smoke, and the only connections will be to the scope - the key lies in understanding what you're attempting to doQuoteThis can also be done safely - as before the key is understanding what you're attempting to do.If you're going to use a scope that is designed to be grounded on equipment that has a potential between ground and the "ground reference" you plan to use - you're going to get a spark and destroy something - it was very common with television sets before CRTs were replaced with LCDs, to have approximately 60V between the TV chassis & ground - it never prevented techs from using scopes to diagnose the problem, they simply powered the television set via an isolation transformer.Most bench power supplies have the outputs floating with respect to ground, and include a third binding post on the output so that you can ground either voltage rail if you need to.

author: rstofer
author_rank: Super Contributor
timestamp: January 18, 2021, 07:18:14 pm
content: Quote from: bc888 on May 01, 2019, 05:23:59 pmAnd they scare me too! What is so fascinating about mains power that people simply feel compelled to probe it?There should be a rule: You must own a signal generator before you're allowed to buy a scope. Then you have something to look at. In general, there isn't much you can do about mains trash so why bother looking at it?In 62 years of using a scope, I haven't blown one up. Yet... But it's still early.I don't work on mains (anything) and most everything I do is at 12V or less. The exception is some op amp stuff at +-15V but that is low energy.There is a very long threadhttps://www.eevblog.com/forum/beginners/what-an-oscilloscope-recommended-for-a-woman-passionate-about-electronics/150/and the link starts on page 7 where CharlotteSwiss buys a new Siglent scope. There was a lot of build-up to the purchase that might be worth skimming but we get serious at Reply 150.We spend the next 40+ replies on "Don't Probe Mains" and start to get serious around Reply 193 and by Reply 224, she has the probes compensated. Measurements start around Reply 251 and it gets more interesting from here.We play with nearly ALL of the functions over the next pages. By Reply 753, we are playing with Sqrt() which I had never used before. Somewhere, we play with the Integral function, another feature of the modern DSO.It is an epic thread in how to use a scope and the fun that can be had with just the compensation signal. However, epic threads take a long time to read.Still, highly recommended!

author: rstofer
author_rank: Super Contributor
timestamp: January 18, 2021, 07:31:21 pm
content: There are references, here and there, about Micsig differential probes. I haven't studied the issue, I don't know anything about the product but I did notice that they are in stock at Amazon. The link is for the 1300V version. There is a 5600V version as well.https://www.amazon.com/Micsig-DP10013-Differential-Attenuation-Tektronix/dp/B074K4XPW3The kit further down has a couple of differential probes (1300V and 5600V) plus a 100:1 HV probeHere's a link to more items:https://www.amazon.com/s?k=dp20003It would be worth comparing price and specs to Dave's differential probe:https://www.eevblog.com/product/hvp70/This whole topic needs more research. Maybe spend time searching the Test Equipment forum for 'micsig differential'. There are quite a few threads which I didn't read.

author: DMack
author_rank: Newbie
timestamp: January 18, 2021, 09:29:59 pm
content: Quote from: fordem on January 18, 2021, 06:14:58 pmThanks for the info fordem. So I have a basic bench supply (TekPower TP1803D) that is grounded with the 3-prong plug, but only has binding posts for positive and negative. Assuming my circuits won't have any USB connections, can I still get into a dangerous situation if I connect my scope to it a circuit that is powered from this supply? From what I've been reading, it's the power supplies that have the ground binding post that can cause this situation. I did a continuity test from both of the bench supply's probes to its ground prong and there was no continuity. I'm thinking that indicates that its voltage is floating and should be fairly safe, but I could be wrong.

author: ledtester
author_rank: Super Contributor
timestamp: January 18, 2021, 09:44:48 pm
content: QuoteWhere have you read this?A ground post on a power supply is usually provided as a convenience. This is especially useful for floating power supplies since it gives you an easy way to ground the supply if you want to.That said, the absence of a ground terminal doesn't not necessarily mean that the supply is grounded. It could just be a cost saving measure.QuoteI would perform a resistance test -- meters have variable standards for what constitutes continuity.You should get "overload" when measuring resistance on your meter's highest setting. That, combined with the fact that the supply is a linear supply would be a good indication that the supply is floating.

author: bob91343
author_rank: Super Contributor
timestamp: January 18, 2021, 09:46:05 pm
content: That's correct. The power supply is indeed floating. However, there is a limit as to how much voltage it is safe to apply between the output terminals and the ground. The ground is connected to the mains ground. The only thing between that and the output terminals is the insulation of its transformer. If that breaks down, you have disaster of one sort or another.

author: DMack
author_rank: Newbie
timestamp: January 18, 2021, 09:47:46 pm
content: Quote from: rstofer on January 18, 2021, 07:18:14 pmThanks for replying rstofer. I have zero fascination with mains power; I'm just interested in using bench power instead of constantly buying batteries to power my little newbie circuits. You know – blinking LEDs, simple logic ICs, and the like. However, since the bench supply is connected to mains power, I want to be sure I know what to avoid when I bring an oscilloscope into the mix. When I got my first multimeter, I blew the fuse because I measured voltage when I mistakenly had the meter set to measure current (classic rookie error, I know). I don't want a repeat of that with my new scope where I could potentially destroy much more than a fuse with an accidental connection.

author: S. Petrukhin
author_rank: Super Contributor
timestamp: January 18, 2021, 10:11:09 pm
content: Quote from: Mortymore on April 30, 2019, 11:07:56 pmI use this toy as an isolated oscilloscope sometimes in power supplies.https://aliexpress.ru/item/32967348583.html

author: rstofer
author_rank: Super Contributor
timestamp: January 18, 2021, 10:16:23 pm
content: The output of your bench supply, if it's a decent unit, is probably floating. As a result, your project will be floating and if you happen to interject an earth ground with the probe grounding clip, nothing will happen. I do this all the time because essentially everything I work on is a 5V give or take.If you want to guarantee your project is grounded and your PS has a ground terminal, you can add a jumper between the black and green jacks. Then you can probe at modest frequencies without even connecting the probe grounding clip. Remove it completely. All measurements will be relative to the ground established at the PS. Modest frequencies... If the waveform looks like trash, try using the grounding jumper at the probe and connect it to the 'black' side of the PS input to your project.When you get to three output power supplies like the Rigol DP832, things get a little more involved, particularly when you want +-15V and +5V output simultaneously. This is a case where it is important to RTFM. You can still put an earth ground jumper at the center point of the +-15V supply and the black side of the 5V supply (if you want +5V) but the +- supplies have to be stacked in a non-intuitive manner. It becomes intuitive upon some amount of reflection. And RTFMing...I keep my probes set to X10 as this adds a lot of impedance to the signal entering the scope. Besides, the frequency response is much higher. In fact, for my Analog Discovery 2, I bought a pair of ProbeMaster FIXED X10 probes because the allowable input voltage is quite low. A switch that doesn't exist can't be set to the wrong position.Sometimes, even most times, my needs are simple and a 5V 2A wall wart will do the job. This turns out to be a lot more handy than using my bench supply. I have no objection to using rechargeable batteries. They don't take up much bench space and they are usually sitting right next to the project board.High energy sources, like car batteries or industrial batteries are a different thing. There's a reason I know that MOSFETs will explode when things go wrong on a 24V speed control using 4 6V floor polisher batteries. Violently!

author: DMack
author_rank: Newbie
timestamp: January 18, 2021, 10:20:30 pm
content: Thanks S. Petrukhin. You know, I'm starting to think a battery powered scope might be the best solution for my situation. It sounds like they're a bit slower and less accurate, but a safer bet for beginners. Do you know anything about the Seeed Studios DSO Nano V3?https://www.amazon.com/Handheld-Oscilloscopes-DSO-Nano-V3/dp/B015X6LZFO/ref=sr_1_1?dchild=1&keywords=DSO150+15001K+Fully+Assembled+Digital+Oscilloscope%2C+DIY+Kit+with+Carrying+Case%2C+Digital+Oscilloscope&qid=1611008009&sr=8-1

author: S. Petrukhin
author_rank: Super Contributor
timestamp: January 18, 2021, 10:33:16 pm
content: Quote from: DMack on January 18, 2021, 10:20:30 pmYes, it's just a toy of the sound range and the only trigger on the front. sampling is performed by the built-in STM32F103C8 ADC. But it can be powered by powerbank and not be afraid of grounding. Most often, you need to look at the passage of the signal and roughly its shape.For serious research, of course, it is necessary to use a normal oscilloscope and a differential probe. I have an MSO5074, but no differential probe yet. Therefore, I do not throw out the DSO150.I can't say anything for sure about the option you indicated, but I think it's $100 thrown away.

author: rstofer
author_rank: Super Contributor
timestamp: January 18, 2021, 10:35:07 pm
content: Quote from: S. Petrukhin on January 18, 2021, 10:11:09 pmI ordered one! There are times where using my bench scope is awkward and a little low bandwidth scope is all I need. My AD2 will often do the job but this looks a little more convenient.I won't see it any time soon, shipping is 20-40 days.

author: rstofer
author_rank: Super Contributor
timestamp: January 18, 2021, 10:49:22 pm
content: Quote from: DMack on January 18, 2021, 09:29:59 pmIf the output of the supply is floating, and it probably is, you have no issues connecting the scope ground clip to the black output (assuming you want a +5V supply). The supply doesn't have a ground jack next to the black jack, that is regrettable.Use a DMM to measure voltage between the output jacks and the scope BNC connectors (which should be earth ground through the scope power cord). There shouldn't be any. If there is and it's on the red output while the black shows nothing to ground, that's probably ok. It just means the black jack is probably grounded. In the circuit, connect the probe ground to the black wire or somewhere connected to black.Draw a picture and ask before guessing.I wouldn't use those banana plugs on a bet (or dare)! All exposed non-current carrying metallic surfaces are to be grounded. That's why the scope BNC connectors are grounded. Here we have the voltage on a screw that the user is bound to touch. A really poor banana plug! Hopefully there is no high voltage feeding back toward the power supply.

author: DMack
author_rank: Newbie
timestamp: January 18, 2021, 10:58:53 pm
content: Quote from: rstofer on January 18, 2021, 10:49:22 pmI agree that my cheap power supply's design isn't ideal, and potentially even dangerous. However, I've been using it for years for my relatively low-powered circuits. Some day I will upgrade to something better/safer ...

author: S. Petrukhin
author_rank: Super Contributor
timestamp: January 18, 2021, 11:02:55 pm
content: Quote from: rstofer on January 18, 2021, 10:35:07 pmThere is a free space inside the case, where you can put a flat battery, a charge board and a converter.But it is more convenient for me to connect powerbank through the converter wire 5V->9V. This toy still works after triple power conversion.Inside, the LCD backlight is powered via a resistor from 9V input voltage, then an LDO of 3.3 V for the processor and a capacitor-forming chip of +/- 9V for powering the op-amp. Maybe I have already forgotten a little and do not describe it exactly. The scheme of this oscilloscope is available on the Internet.Be careful when connecting the boards, if you disassemble them. I have an old version, where the MSU outputs do not have protective resistors and an offset of 1 pin (which easily occurs - there is no key) burns out several MCU outputs.

author: DMack
author_rank: Newbie
timestamp: January 19, 2021, 10:46:53 pm
content: Thanks everyone for your responses. Not to oversimplify things, but is it safe to say that if I make sure to never connect the scope probe's ground clip to anything other than the negative rail in my circuit – which is actually ground if I use bench power, I should be okay, or am I still missing something important?

author: ledtester
author_rank: Super Contributor
timestamp: January 20, 2021, 01:23:31 am
content: I just want to nitpick on the way you worded this...Quote from: DMack on January 19, 2021, 10:46:53 pmSimply connecting the oscilloscope's ground clip to the negative rail in your circuit will cause it to be connected to earth ground - regardless of what power supply you are using. I.e., even if you are using batteries.From what you have said about your Tekpower 1803D it appears it is a floating supply. Therefore, using it to power your circuit will not ground reference it. The words above in bold make it sound like your circuit will be earth grounded if you use the Tekpower, and I don't think that will be the case.

author: DMack
author_rank: Newbie
timestamp: January 20, 2021, 02:01:09 am
content: Thank you ledtester, you made a good point. If I omit that part, does the basic premise still hold together as a general rule of thumb?:“If I make sure to never connect the scope probe's ground clip to anything other than the negative rail on my circuit, I should be fine.”

author: ledtester
author_rank: Super Contributor
timestamp: January 20, 2021, 02:24:39 am
content: It all depends on your power supply's relationship to earth ground.If you use a floating supply -- batteries or a floating bench supply -- you are safe to connect the ground clip to anywhere in your circuit.If your power supply is referenced to earth ground then there will be nodes in your circuit which are at earth ground, and you should only connect the ground clip at those nodes.For instance, there are some power supplies where the positive terminal is at earth ground. In that case the oscilloscope ground clip should only be connected to the positive rail of a circuit powered by that supply.Perhaps until you're more comfortable using your scope and power supplies, just power your circuits with batteries / a floating linear power supply.Update:Besides your power supply's relationship to earth ground, you also need to consider your circuit's relationship to earth ground. For instance, if your circuit has a wire extending out to a water pipe, or if it sitting on and touching a metal desk which is grounded, etc. then there will be nodes in your circuit which will be referenced to ground and you have to be careful where you put your ground clip.

author: DMack
author_rank: Newbie
timestamp: January 20, 2021, 02:49:31 am
content: Will do ledtester. I’ll stick with testing battery-powered circuits. I had no idea how complex this subject was when I first posted. Hoping I’ll start understanding with more experience. Thanks for the info.

author: rstofer
author_rank: Super Contributor
timestamp: January 20, 2021, 03:08:27 am
content: Quote from: DMack on January 20, 2021, 02:01:09 amUnfortunately, this 'rule' won't work either. There are circuits, like op amp designs, that use both a +15V and -15V power rail. Grounding the -15V rail might be bad if the center of the voltage rails is already considered a system ground which it usually is.It's really difficult to sit thousands of miles away and propose solutions of a general nature that apply in all conditions. At some point, you just have to know what the circuit does.One thing that might be true: We can measure the voltage between the BNC ground and the point in our circuit where we propose to put the ground clip. If it is 0V, good to go! If not, we would need to find a better point. If our op amp PS doesn't have an earth ground, clipping to the -15V supply wouldn't really hurt anything but the waveforms would be bizarre.I like the idea of testing with a DMM.

author: rstofer
author_rank: Super Contributor
timestamp: January 20, 2021, 03:12:21 am
content: In the real world, this kind of problem just doesn't show up all that often. We 'know' where to put the ground clip and we 'know' where to probe. Why wouldn't we? We just designed the thing...Where it might be a problem is in the repair business when schematics aren't available. I remember when I was a kid, around '60 or so, we could buy schematics for the TV sets we wanted to play with. They even had sample waveforms and lots of voltage test points. Today? Not so much...

author: Ian.M
author_rank: Super Contributor
timestamp: January 20, 2021, 07:31:51 am
content: If you get into MCUs and programmable digital stuff, even at as basic a level as using an Arduino, you also need to be aware that almost invariably whenever you connect your circuit to a desktop PC or to many laptops, no matter whether its via a serial or USB lead or a programmer or debugger, it grounds the 0V rail of your circuit via the PC.Exceptions that don't introduce a ground: Connections via a USB isolator (which usually limits the max USB speed), Non PoE at both ends RJ45 Ethernet, orspecifically isolatedprogrammer/debugger and USB UART cables.Grounds introduced via USB are particularly problematic because if you goof and blow up your scope it will almost certainly take out the PC as well, so you've probably doubled the cost of the lesson!Another thing to be concerned about is ground loop currents. These can become high enough to do damage if there is significant potential difference between supply grounds, or between supply ground and true earth ground.e.g. if you are working on a radio receiver connected to an external antenna and ground rod, and your mains supply isTN-C-S, which uses a single conductor for both Ground and Neutral (aka: PEN or CNE conductor) upstream of the customer's utility meter, there can be enough voltage difference at a low enough impedance between your scope grounded to supply ground and the receiver chassis grounded to the ground rod to melt your scope probe leads! Its also very dangerous as you have introduced a non-bonded grounded object into your electrical installation's equipotential zone, and if the PEN conductor gets broken you could get full mains voltage between the chassis of any grounded equipment on your bench and the radio ground. It only takes ONE idiot with a backhoe half a mile away to kill you! If you have a TN-C-S supply, seek qualified expert advice before introducing *ANY* other ground to your bench.Other ground loop problems can occur due to voltage drops in high current DC circuits. They are rarely dangerous to you, but can be very destructive to equipment.

author: DMack
author_rank: Newbie
timestamp: January 21, 2021, 12:30:03 am
content: Quote from: rstofer on January 20, 2021, 03:08:27 amThis sounds like a promising solution for my situation rstofer. Thanks!

author: Ian.M
author_rank: Super Contributor
timestamp: January 21, 2021, 01:00:10 am
content: Unfortunately, due to the Y capacitor in non-grounded SMPSUs, you get a relatively high mains supply (line) frequency leakage current of up to 0.75mA with a driving potential of approx half the mains supply voltage. A normal 10Meg input impedance DMM will thus show approx half the mains voltage between the scope ground and any point (that isn't very high impedance) in an ungrounded crcuit fed by such a SMPSU. To know whether or not its safe to connect the scope ground to a node, you can't just check voltage. 0V is *always* safe to connect but 120V AC may be either 'will blow up your scope' or a phantom voltage that will vanish as soon as you load it down a little. A 3W 10K wirewound resistor connected to insulated test prods is a useful thing to have. Touch it between the suspect voltage and probe ground, and if the voltage drops to under 7.5V RMS, 0V DC, you know its only Y capacitor leakage current and is safe to ground. Worst case, assuming a 5:1 pulse overload rating, the resistor will survive for one second connected across the primary side DC bus of a 240V mains SMPSU.

author: wizard69
author_rank: Super Contributor
timestamp: January 21, 2021, 11:11:02 pm
content: As others have said posts like this scare me seriously. This is the first post that sums up my feelings.I'd go even a bit further and say don't even plug in the scope until you understand how it works and how the circuit you intend to work on functions. Work on the right equipment and you can blow up even an isolated scope.Interestingly; briefly after reading the title for this thread I immediately thought about the AC batter operated power source that Sportsman Warehouse had on display that I saw on a visit yesterday. Such a unit would certainly power a small scope and might be useful for field use. However after reading the post starting this thread alarm bells, whistles and sirens went off in my head. Somebody is fixing to kill them selves if they don't take the time to learn what is going on with respect to connecting test gear of any type frankly.Quote from: bitseeker on April 28, 2019, 04:50:36 am