A good demonstration. Not just switchgear, though; I've got a solar PV setup in my house, and on the inverter there is a warning label: "DO NOT disconnect DC plugs and sockets under load - turn off AC supply first." There is a pair of switches for disconnecting both ends, but it's wise to switch out the AC end first (then the inverter shuts down internally). Of course, those who are used to DC electrified railways will be familiar with what happens from time to time!
me too pdgeman, really annoying, sticking etc! mine is ancient big and heavy and a load of rods probably older than me, but it was cheap (free from a friend actually)
Well I have hardly ever heard it referred to as anything other than stick over det hundreds of welding videos I have watched. But in the age of brunel I guess it was. JK
I've only ever seen one other video like this before and this one does a better job of displaying the difference. Great video and thank you for showing everyone this important switching concept!
so I have a ryobi compound miter saw that was given to me. was told the switch is bad. it runs of a 120 volt 15 amp DC brushed electric motor. I took the switch out after a failed continuity test and cleaned the contacts along with removing the brushes and sprucing them up as well. then I noticed the armature assembly needed a good cleaning so I did that as well. put everything back together and sure enough ran great. long story short my brother said he had the correct new brushes and a new switch so I let him take it and put them in. he did not have the brushes and his DPST 6 pin toggle switch... blew a fusible link with the field. my question is can I wire in a DPST 4 pin that I have now that I have the field back to working order and if so can you help me out with the correct wiring schematic if I was to send pictures and or video. I really need this saw have 4" baseboard to cut and install l. thanks for the video as well very informative
Thank you sir! As an electrician in Europe I found this very informative and helpful as well very well presented. It is very easy to understand. I have some advice or a challenge for you. Please do the same or similar video with name and tags about photovoltaic, solar cells so it will reach more people and bring you many new views also. There were 6 roof fires in my near area just this year, just because of photovoltaic. As I heard news from investigators recently, there was probably combustion because of an arc.
Would be interesting to repeat the experiment using 12v DC at different current ratings. I am using standard mains 10a light switches for a 12v DC solar installation running some 12v 10w LED floodlights.
I've always known the difference between AC & DC, but never made the connection (no pun intended) as to why a spark with AC is much smaller. Brilliant explanation, thank you for appearing randomly in my recommended feed!
Nice demo of how conductive air becomes once it turns to a plasma. Fixing small powerful magnets in the correct orientation close to the contacts can "throw" the arc out in a curve and help to snub it for DC. It works for AC too but the arc goes in two directions so positioning can be tricky. Heavy duty DC contactors sometimes have them built in. Viewers, don't make the mistake of choosing "gold contacts" thinking they are better. Silver is best for DC even at the small scale. Choose gas envelope enclosed contact relays if possible, the ones opened by a rotating armature are faster, if you can get them big enough. I have long been puzzled by the regs quoting higher safe voltages for DC. Crunching your muscles in one direction rather than making them "ripple" they are a lot more painful, or so I assumed, and seeing it happen to others that conclusion seems safe.
You can't really use a "snubber" here, because there isn't much of a large change in current or voltage, but rather a continuation of conduction through air instead of wire, so "arc-quenching" techniques need to be used.
Brilliant demo as usual thank you. I wish other electronic experts were more approachable I’ve been trying to ask electronics user groups etc for a solution to my problem but it seems too simple for them to even reply? Thanks for sharing your considerable knowledge, I’m sure many appreciate it as I do.
I'll use my 3500V series mosfet switch to show the difference between positive and negative DC sparks. difference in heat, color, and sensitivity to magnetic fields. there are a few major differences...
I've experimented a bit myself with arcs in a magnetic field. A decently strong magnetic field changes the way an arc behaves - makes it much harder to strike, shorter-lived and shorter in length. It also melted my copper wires with ease once inside the field, so I suspect hotter.
The one issue i found with this demonstration is DC voltage, multimeters usually show RMS of AC voltage and not peak voltage, so if you use 240V AC, the DC voltage should be around 340V and not 240V.
@@LeeCookson partially yes, when there is no load applied to DC power supply, the voltage is almost perfectly flat, but when load is applied, the voltage starts to look more bumpy, the more current is drew from power supply, the bumpier it gets due to capacitors not storing enough charge and since most multimeters measure only RMS voltage, it is showed as big voltage drop, while peak voltage drops only by a small amount. Another reason for bigger voltage drop is introduction of additional elements (diodes) adding more resistance into the circuit reducing overall max current the power supply can deliver.
Yes, I learned this as an undergraduate trainee trying to break a 60Vdc supply with a relay. It melted! Eventually got away with a bigger relay and snubber across it, but these days prefer solid state solutions.
It would be great if you covered the construction of DC switches and showed them in operation. I noticed that some people insist that DC is an overall better system because of the efficiency you get with UHV transmission. I won't get into a debate on whether AC or DC is superior, but I will say that it looks like AC is more practical in the home so you can use higher voltages to use cheaper, thinner wires to distribute power while using more cheaply made switches. It doesn't look like you could use a 120-240 volt thermostat very reliably on DC without the added complexity of arc suppression. Certainly it would seem that you would want AC during a malfunction so the arc could much more dependably snuff itself out to help prevent a house fire. On a side note, I notice that your voice seems to drop in intensity in the middle of your sentences, and it becomes harder to hear you. Usually, I have the auto volume on with my television to help deal with the large variances in volume level on RU-vid between channels. I prefer to turn in off when I play music. Anyway, most people likely don't have a volume compressor on their audio. Perhaps you need a lapel microphone? You can get them rather cheaply on eBay if your camera can use an external microphone. Many people are just using their smartphones these days also so I don't know what you are using. Anyway, it should help boost your subscriber count to help normalize your audio pickup.
Be nice to see some differing types of anti spark and quenching methods used over the years in relays and fuses and then force a mosfet switch to spark.
+John Ward What about wiring the DC//AC 240v heater through the CLIX 15A socket without back, and a suitable plug, if clamped down in place should be easy to press the big white button etc... Both contacts clearly visible on camera would be good!.
You know... I just read the title and was thinking for a moment ~aww... shit~ but then I realized my switch will be just fine. :)) I'm using a 20A 240Vac switch on a 48V battery that powers an ebike. But for me it's all well and dandy as when I operate the switch there is never a load on the battery, there is no current flowing so there is no arching.
Why is the voltage drop so much more significant in the DC setup? During the AC test at about 4:20 it fell by just a couple of volts, but during the DC test at around 5:40 it was around 50.
With no load, the capacitors are fully charged 100% of the time and the voltage is the same as the peak of the AC input. With a load connected, the capacitors charge and discharge on each cycle and the voltage is nearer to the RMS value of the AC input.
Yes, something like 340V. Well spotted - I shouldn't have said "voltage drop" which has a more technical meaning. What I meant was the amount (or, better still, proportion) that the voltage decreased.
John, another very instructive video. How about a video on relay switching of AC induction electrical motors. This could cover inrush currents and inductive spikes when switching inductive loads and explain how these are dealt, I.e. by relay current rating and an RC snubber, for example. Perhaps show a typical relay data sheet and explain about life of relay varies with kW (or horsepower) of motor. Perhaps cover concepts on LRA and FLA.
I think Tesla's way was right given the choice, A.C. has it's issues. But D.C. issues tend to be more destructive, as Well as the arcing john has shown, electrolytic action can effectively plate contact areas effectively forming dissimilar materials at junctions, The whole basis for metal plating, but sometimes it's an effect that will not be required and then it becomes a maintenance issue, it just pays to do research on these matters!
i found a street light in malaysia and this is so common where they still dont use circuit breakers (some of them does) but a lot of light poles still uses fuses or some of them are just like bypassed with a wire. well come to malaysia and look at the street poles you can see a lot of street lights cover opened with some black overhead cable.... some of then were taken action by the goverment and they put some metal plates to cover it but most of them are real crap. i touched one of the black overhead cables near the "protected wiring circuit". and most of our street lights are 260+ because the voltage on these lights arent balanced. the reason why they use those overhead black cables on the light poles because the armoured cable inside the road is not working anymore. now if you touched those cables going to the light poles most of the time they will spark if youre really lucky it wouldnt spark at all. well one day i was at a clothing shop there was this not turned on street light with its black overhead cables coming to provide power to light because the inroad cables are broken i touched the live wire and "BZZZZZZZ SPARKSSSSSS BZZZZZZZZZZZ *and then light turns on*" theres some people in malaysia who's almost killed by a lamppost because at some state theres a problem where the live has leaked to the metal body, and most of the times when you ground it, theres not gonna be a RCD nearby
Good demonstration, but what was missing (for me) was an explanation for why the arcing condition is so destructive..? Would it be something to do with oxygen burning thus acting in a similar way to a blow torch..?
On a related note, isnt there something called the skin effect which means the higher the frequency the more the current 'clings' to the outer part of the conductor, therefore for AC you need a thicker guage for any given current than you do for DC?
Skin effect is a thing, but it's not significant in normal AC circuits - at 50Hz in copper, skin depth is about 10mm, so is not a factor until you have copper conductors over about 300mm².
John Ward fair enough cheers for the response. Could I ask you maybe in an upcoming video to do this experiment with your Welder on the high current setting on a 6A AC MCB? I think that would wicked. Reason I ask is that I was once fixing an installation were by a 50A AC MCB was used on a battery disconnect for a solar installation.... lol. I’d like to see how the MCB reacts as all I saw was a burnt out thing that I then changed for the correct device. :) Kyle
Voltage was lower - it was set with no load which was nearer the peak of the AC, and voltage dropped when the load was applied. You can see the voltage drop on the multimeter when the switch is closed.
a frend from "elektronik mal einfach " make a similar vid! With a 1000 watt halite lamp a 25A relais manuell switcht is after first try with dc melt together! but you realy had to say that the same problem with fuse is!
foufou33g Maybe its because the resistance changed because DC doesnt has to push against the magnetic field. That could end with more power and the Variation in the voltage(because its not pure DC) would make the sound. Its only a theory. It all depends on what kind of resistance this heater is. But that would make this test useless. I mean 1A 240VAC vs. 10A 240VDC wouldn't show the difference between AC and DC.
very good demo, Thank you. What if I used a SPST AC Toggle switch to switch on and off a 12v DC Circuit that carries no load while switch is thrown? lets say I have a 12v dc cigar male one end and female other end with the SPST AC toggle switch (10amp at 220V AC) between the male and female point (Im using a cigar lighter extension cable with the AC toggle switch as a simple on off switch, If I only switch the toggle on and off with no load or very little like a 2 amp usb phone charger, and digital volt meter, would it still be as bad? I mean I can always throw the switch first and then only plug in the load, then you may ask what the point of the switch... the point of the switch is that always connected to the other end of the cigar cable extension (Female side) is a little digital volt meter to show the volts and amp drawn. I do want to switch this off, the vehicle that it is in, only gets used on weekends and the Digital Volt and Amp meters lit up display will drain power during the week, unnecessary
Very very good John well done hey how about doing experiments with capacitive loads, inductive loads as well as the resistive you've just shown Kind regards Warren
Warren Gray this is an inductive load. Huge voltage spikes on disconnect indicate that, but JW hasn't got his meter across the heater he's got it across the supply so it's not shown. The heater he's used is basically a huge coil of thin gauge wire, which has inductance as well as resistance.
burgersnchips Hi there, I am not sure that the fact that the load is a coiled wire and therefore inductive, I think it will play a part in the energy discharge, but I reckon the huge reservoir capacitors on John's test rig would cause it regardless of load as they have a low internal resistance and therefore can supply massive amounts of Q in one burst, Load is not the main factor in what was shown, But it is a good point that you have raised!
This wouldn't be inductive, otherwise it would completely destroy everything it's connected to. It is probably coiled, but the wire is folded in half before coiling so that any magnetic field would cancel itself out instantly, destroying the chance of being an inductor even worth worrying about
Very interesting demo, I didn't think it would ark that bad. Question though, would it be fine to use a normal house switch (AC 120v) on a 12v DC system?
Bille747 - my advice would be to derate the current rating of the switch by 50% minimum. So for a 5A switch, don't switch a 12V load greater than 2.5A. The lifetime of the switch will be even greater with even less current flow.
Mike EL - i don't know if i agree. this demonstration utilized high voltage dc, and thats the significant difference. high current dc loads (30-50 amps) at low voltage are very easily handled by standard 5 pin relays, take one apart and you will see the gap between the contacts is not very large. there is a point at which dc becomes dangerous to touch (as in touch ur 12 or 24 volt car battery terminals and nothing happens) i think its about 60 volts or so and that is probably the point where using an ac switch for dc becomes a liability.
Mark 1024MAK - generic 5 pin automotive relays rated at 50 amps in either 24 or 12 volt varieties have contacts whose size is less than 4 mm and their gap is around 3 mm when open so ur recommendation is wrong.
Bille747 - dc is lik ac it can be whatever voltage it needs to be i have a few low voltage (12 volt) ac power adaptors its the same as low voltage dc if you touch the output it won't do anything to you. electric cars as far as i know are high voltage dc. they just put the batteries in series.
Twig depends on the motor, for standard squirrel cage and universal motors their stator magnetic field is also generated using the line voltage, so it flips exactly as does the rotor field allowing it to continue to rotate. Universal motors can be used on both AC and DC and are actually more efficient on DC I believe
i had a idea of using a solar panel to rotate a wind turbine induction motor, it should theoretically generate more electricity than the solar panel would provide 🤔🤷♂️
JW; you're claiming the heater is a resistive load. It's clearly an inductive load! Where else is all that increased voltage coming from to form those sparks? Your heater is effectively a huge coil of thin gauge wire, which provides resistance and inductance. It's an interesting test but please repeat it using a genuinely resistive load.
Very informative video, but still missing one important aspect - the case when DC is just rectified AC i.e. current flows in one direction but voltage reaching zero at double AC frequency. Will it be sufficient to suppress excessive arcing or not?
John I have a gsm switch thats rated to switch 240v ac at 2 amps. Would it be ok to get it to switch 12v dc, if I used an automotive 12v relay? Current to switch the relay would be probably be something like 300 milliamps.
The video intro is a bit misleading. This doesn't show _why_ we don't use DC, it just shows why it's a bad idea to use AC switches for DC applications.
You disappoint me Mr.Ward... You need to subject an ordinary AC switch to the test, film the result & show the charred mass which will be the result! Thank you.
the ordinary AC switch would be the one on the side of the heater which has switched it on and off since it was made and that thing looks ancient, its got to be 40 or 50 years old
Who said to use the heaters' own on-board switch? I suspect that John would rather prefer to keep that functioning as it was designed to do, as he clearly values the appliance. There are such things as adding another switch in-line, and destroying that with arcs instead, much in fact as was demonstrated in this video. As for the age of the appliance, I've just installed, for actual use, not just display, two wall mounted fan heaters, each 3 kw, each works beautifully, each has passed every electrical test I can throw at them, and each is at least 50 years old. 'Ancient' doesn't automatically equal crap, useless, or worn out.
yeah no I misunderstood 6A8Gs comment completely. but Johns reason for doing it this way was so we could see the arc and what was going on, what he made from a pipe clip and screws is essentially an ordinary AC switch, two contacts that are brought together then spring apart.
John, Thanks for the video. Would it be a good idea to have a capacitor across the contacts when switching DC like on old car contact breakers in a distributor?