Seems like I made a rather big mistake in the video. My transformer should not be switched on during the zero crossing point but at the voltage peak in order to decrease the current flow. While recording the current waveforms on the oscilloscope, everything appeared good to me and I am not sure why my circuit breaker stopped tripping when I switched at the zero crossing point. But many viewers pointed me in this direction and after doing research, it seems to be correct. Sorry about this. But if you want to build the softstarter you can still try it out whether it works for you and if not then you can always change the Arduino code in order to switch at a different time point. Sorry again for the inconvenience. I do make mistakes from time to time since this is a one man production. Stay creative :-)

@aks8403

3 жыл бұрын

Can you sir please explain me why to turn it on at the peak and not at zero crossing point?

@Sevacant

3 жыл бұрын

@@aks8403 ELI the ICE man

@greatscottlab

3 жыл бұрын

@@aks8403 You have to change the timer value OCR1B. In my case I firstly used 590 which is around 9.44ms after the zero crossing point. 625 would be 10ms. So simply use half of 625 so around 313 in order to get a 5ms value at which point a voltage peak should appear after the zero crossing point.

@BadassUchiha

3 жыл бұрын

it's ok you are a legend of electronics for me

@hefeweizen5260

3 жыл бұрын

Das war wieder ein sehr priffiges Video! Gruß aus Karlsruhe in Baden! :)

Tripping circuit breaker? Hah, I don't have such weakness with my 30-years-old house wiring. The circuit resistance is high enough to limit any inrush current.

@greatscottlab

3 жыл бұрын

Well.....that would also be a solution

@alangolab6657

3 жыл бұрын

@@403_Tuna aluminium wire and ceramic conectors and large swich board for a hause ?

@sneugler

3 жыл бұрын

My 80 year old cloth wiring has the same effect. Built in protection :)

@alangolab6657

3 жыл бұрын

@@403_Tuna the is thousands more over the world or even millions

@oniruddhoalam2039

3 жыл бұрын

@@alangolab6657 Same with our house

The current into an inductor equals the integral of the voltage accross it, in formula: i = 1/L.integral(Vdt). If you switch it on at the (rising) zero crossing the voltage remains positive for 180 degrees. This causes the magnetizing current to rise to approx. 2x its normal value. However the inductor core is not made for this 2x magnetizing current and thus the core will saturate. This causes the coil inductance to drop, which increases the current even (a lot) more. If you switch at the maximum voltage, the current also starts to rise, following the integral relation, but after 90 degrees the voltage polarity reverses and the current starts to go down again. In this way the current starts of nicely lagging the voltage by 90 degrees, as it should be in the stationary situation, with peaking and tripping the breaker. Best regards, Ben.

@Thomas72B

3 жыл бұрын

"If you switch it on at the (rising) zero crossing the voltage remains positive for 180 degrees." ....... But in normal operation, the voltage remains positive for 180 degrees and then becomes negative again for 180 degrees. What's the difference now?

@beneindhoven3424

3 жыл бұрын

@@Thomas72B The difference is exactly what you say: in normal operation a positive periode is always preceded by a negative period, and visa versa. An inductor stores current in a similar way as a capacitor stores voltage. Therefore the history is important. But at startup there is no history (current) stored in the inductor. When you then start with a full positive (or negative) period, the current becomes too high. This is only a temporary problem, after a number of periods the current normalizes, due to the series resistance of the inductor. Regards, Ben.

@Thomas72B

3 жыл бұрын

@@beneindhoven3424 Not always ! If you put the plug in the socket you cannot know where the sine curve is. 0 degrees, 130 degrees or 174 degrees you don't know .... That's why I still don't quite understand where the problem is supposed to be.

@beneindhoven3424

3 жыл бұрын

@@Thomas72B Yes, that’s correct, you never know where you start when you connect the plug. That’s why the circuit breaker not always trips, but only sometimes. Switching in near the zero crossing is the worst case situation. Having said that, I have to admit that I don’t understand why Great Scott’s tests at zero cross switching didn’t trip the breaker. I tried this same experiment a few months ago, and could clearly see the current peaks are maximum at the zero crossing. And minimum when switching at the voltage peaks. Regards, Ben.

@charmio

3 жыл бұрын

Ohhhh.... Brilliant comment! I think it's also just answered a question I've had about adding energy into a LC tank. Thanks for sharing the knowledge. Edit: Yes! I've been trying to get my head around this for days. You're a catylist for understanding good sir. Double thanks!

not gonna lie but this is exactly something I need to make for about 10-15 past days and here you go, guess a trip to DIY electronic store is required!

@greatscottlab

3 жыл бұрын

I hope it works for you :-) But be careful when working with mains voltage. Thanks :-)

@anonanon3066

3 жыл бұрын

don't forget to check that you have adequate mains voltage by doing the good old tongue test

Another much easier and cheaper way which I used succesfuly in the past was a 1s timed relay in parallel with a high power resistor with just enough ohms to limit the current to under 16A. Both of that in series to the load will limit the current for 1s and then the relay shorts the resistor. Worked like a charm :-)

@nicolaswannen1743

Жыл бұрын

good idea, but using an ntc instead of a power resistor is better, since it can prevent from burning down your house in case of failure of the relay/connection..

@kitecattestecke2303

Жыл бұрын

@@nicolaswannen1743 can you get ntc with lots of watt dissipating ? Better to use onetime thermal fuse on the resistors.. If relay is dead resistors heats and kills it series connection to the load by melting thermofuse once... Before the relay and resistor an inline glas tube as slow 16A is needed as well... No ntc/ptc disc that ages and sets it self on fire, just metal case grounded and fuse will do better job maybe?

@phinok.m.628

Жыл бұрын

In most cases you can also use a normal relay and connect it's coil parallel to your load. Once the current draw drops the voltage rises and the relay closes. You may have to match your resistor and relay a little. But that's probably the easiest way to limit inrush current fairly efficiently (the only power loss being the holding current of the relay).

Sorry @GreatScott!, your theory behind switching inductive loads at voltage zero crossing is wrong, it should be switched at current zero crossing (that happens at peak voltage), look around for documentations, the reason behind breaker tripping should be elsewhere. (Maybe Arduino and/or SSR are taking up time and they are switching correctly? Or is it simply because of the soft-start that it works?) Try to capture also the mains voltage with the oscilloscope in sync with the surge current and we will see. Thanks!

@greatscottlab

3 жыл бұрын

Thanks for the feedback. I just did lots of research and it seems you are right. I added a pinned comment that explains it. Sorry.

On the large DC power supplies we design at work, we just use a 20 ohm NTC inrush current limiting resistor, and a contactor that bypasses it after the main bulk caps are charged. Which could be done with an RC timer + Comparator

Great Scott, I love your videos a lot. Your content is on the point with no detours, but you still add all the background information. And I like your visualization style, with pen and paper. It gives me the feeling that I witness you developing the idea in the very moment. Please don't change too much in the future 👍

Thanks for admitting the error. Thats news to me, since I don't normally work with inductors, so zero point made sense originally. Thanks to all the Commenters for the additional explanations!

Easier and cheaper to change the breaker to type C time curve which is for high startup loads.

@greatscottlab

3 жыл бұрын

Also possible. But not always the best solution.

@cekpi7

3 жыл бұрын

That was my first thought, but i guess it isn't a viable solution if transformer shares breaker with other devices. Type C is really slow and if wires aren't properly sized it can cause all sorts of problems.

@fabianmayer

3 жыл бұрын

@@cekpi7 true in some cases, but if IK is in the right range, it shoul‘d be ok

@robertwillemsen368

3 жыл бұрын

Might be true. But less fun😜

@ebhhon7826

3 жыл бұрын

@@greatscottlab Yes, why do it simple when you can make it complicated 🤔

I rly wanna thank you for everything!!! I learned so much from your Videos! I started watching your Videos like back in 2017 and learned almost everything about Electronics including English. Please never stop making Videos☺️☺️

@greatscottlab

3 жыл бұрын

Thanks for the feedback :-) I am glad that I could help you :-)

I had a similar issue with a 3000 watt transformer for reducing power from 220 to 120 volts. I later learned that the type of circuit breaker used makes a difference. There are some breakers rated for inductive loads and some for resistive loads. Most home breakers are of the resistive loads found in most homes. Replace breaker with an inductive rated breaker. Did this and no problems now.

Thanks so much for posting this! I've needed an AC soft starter for quite some time but was hesitant to spend the $300+ that most places want for a decent one. Thought for sure the circuit would be much more complicated than it is! I'll be using it for an air conditioner instead of an autotransformer.

May I suggest that you add a relay to bypass the triac after completion of the load soft starting in order to limit the power loss in triac and saving it from overheating. And you might want to add a variable resistor to enable the user to set the soft starting phase duration. Great job

Thermistor with relay latching. Monitor voltage drop across thermistor and latch when it falls low enough. Your solution of course works and is very creative.

I have a 15A variac behind a 15A capable isolation transformer (isolated and adjustable voltage is sometimes handy). All in parallel with a second lower power isolation transformer. I use a high power resistor and a timer relay. The inrush current is limited by a simple resistor in series on the mains side and after a second or two, the resistor is bypassed by a timer relay. Works a treat.

Great project! For softstart I used a "Finder DPDT Multi Function Timer Relay" set to 1 second with a thermistor over the "off" position. The first second you power up the thermistor heats up then the relay clicks to the "on" position so the attached device is powered directly. The switching time seems fast enough so far.

@gblargg

3 жыл бұрын

There are NTC thermistors that have an initial resistance then heat up quickly and lower the resistance, made just for this task of soft-starting.

@o0arend0o

3 жыл бұрын

@@gblargg yes but they will become very hot, not ideal for long-term use. Also when you switch off and on before the ntc had time to cool off the resistance is still too low. This is why I used a time relay in combination with an ntc.

@gblargg

3 жыл бұрын

@@o0arend0o Good points. They're probably used for lower-current devices like switching supplies.

@muthumanikya1847

Жыл бұрын

​@@o0arend0o this solution still has the lingering heat from previous on time. Unless chosing time delay longer allowing ntc to cool down enough to make a difference.

@o0arend0o

Жыл бұрын

@@muthumanikya1847 the ntc only heats up for less then a second when power is switched on for first time. The rest of the time the ntc cools off while the device is on.

You know the day is gonna be great when GreatScott uploads

@greatscottlab

3 жыл бұрын

Ohhh stop it you ;-)

I'd been pondering a soft start circuit for DIY audio amp builds and I think you've nailed it, really nicely done! Thanks!

@fransdebruijn6763

3 жыл бұрын

most of those just use a large current limiting resistor in series with the transformer and a relay on a short timer that shorts the resistor.

As you mentioned, even a zero volt point initial turn-on is not always curing the problem. The reason is the remanent magnetism in the transformer core. If the magnetism left in the core at previous turn-off matches the direction of the start time voltage growth slope, there still is a big inrush. The theoretical analysis considers the fact that there is a 90 degree phase shift between the voltage and the current (on the primary). So, at the positive going zero crossing of the voltage, the usual transformer operation condition would have actually the negative peak current at this moment. You don't have that, if you make the primary connection at the voltage zero crossing moment. Your gradual increase of the voltage is indeed the way to prevent the breaker popping inrush. As funny as it may sound, if the transformer was turned OFF gradually, you would get near zero remanence and then the optimum time to turn it again on would be near the voltage peak (either positive or negative) !!! Too bad, you generally cannot know the state of the remanence, nor force it to any known state. I hope this explanation can serve other people who may suffer from the same issue and are wondering why.

i'm always amazed by your penmanship

Your programming has become much better over the years. You started off writing terrible code and now your code looks quite nice. I'm glad to see you improving that skill!

This is exacly what I needed 4 years ago :D

That was very cool that the SSR has a zero crossing bult-in, however make sense when you think about what it does. Very cool solution.

Nice video! One recommendation, make sure your diy pcb can handle up to 3000 watt or preferred 3600 watt. The small screw connectors are not designed for this loads.

This is absolutely a project that I am going to build. I have a table saw that shakes the whole thing and makes this horrible sound that makes me cringe every time I use it. This project is perfect, and add always, ein weiteres herausragendes Video

Note that an autotransformer is just one with a single shared winding, yours is a variable autotransformer. Also, the input voltage is only across part of the winding, which is what gives it the ability to output a higher voltage than the input.

Hi, I have an old tube clock which I turn on only when I'm in my workshop (to save the tube lifespan and to save electricity). Would such soft start device make sense to spare the squishy bits inside the clock from the often turning on and off? Or would the the relay you mentioned do the trick? Or is it completely unnecessary and I'm just over thinking it?

I’ve faced the same problem with my 10Kw Variac, I’ll try your solutions ASAP, Thanks 🙏

I have seen a simular control in high end, hi power stereo receivers..soft start off the mains before the amplifier comes to full power reducing in- rush current to other components..on a failure to soft start, I experience a corona in the cabinet, finding the regulators themselves burned along with local components damaged beyond recognition. Thank you friend for sharing .. Oh and see my suggestion on your generator project..👍

Outstanding project Scott! You are a very talented!

I had a similar problem 20 years ago. Solved with a 2kW heater in series with the transformer that was shorted by a relay. It takes some tens of ms for the relay to close the contacts and this time is enough to limit current surge

Only feedback I'd have for you would be to move those LEDs, put the red one near the back, as it indicates power in, move the other one to out outlet side and make it light up red when the button is pushed and go green when the sequence is done (those looked to be three or 4 legged LEDs, so either dual color or maybe RGB?). This way it is much easy to know what the state of the thing is by a quick visual glance, and therefore a bit safer to use.

Yet another great video. Most circuit breakers have a time delay trip to allow for inrush from motor starting. Maybe there is one with a longer delay available? When transformers are turned off the core steel will stay magnetized in the direction of the polarity at that exact moment north and south. When you energize it again, if the polarity is opposite at that instant, there will be a longer inrush time to correct it. Using the SCR relay seemed to be a great solution switching at current zero. The soft start would be great for tungsten light bulb filaments too.

Thanks for this, always wondered what soft starters were for. This was a great explanation!

You know what you need to make? An infinite-loop, programmable, loss-suppressing contest repeater tuned for an MSO ScopeNmultimeter that's compatible with a pre-century reserved shelf-gap filled with transient notta-waves that keeps inducing negative optical feedback?

@greatscottlab

3 жыл бұрын

I love it :-)

@greatscottlab

3 жыл бұрын

I am on it ;-)

@moonmatthew

3 жыл бұрын

Cool

@segwaydave

3 жыл бұрын

Bazinga!

@seizes4936

3 жыл бұрын

Brain hurty

i didnt think about that in first place i have something does kick braker n i did upgrade braker so doesnt kick braker aging i notice ur video n watch it so that got me learn something new i think it was spike voltage n cause kick back "fire back voltage" to braker that cant handle it but wasnt i see it now ty inform useful things u make is awesome jobs greatscott

Previously you have mase video on soft starter for solar mppt and that was functionaly same as in this video. Am I right? If yes then why one should go for this complex design accept controllable phase? And another question was if I had to drive 3 phase water pump of my home then shall I need triac control on all three phase, (all phase had different control or same)?

Would this implementation switching at peak or zero? be suitable as a soft start for a 500VA toroidal transformer in an amplifier or would just a series resistor and relay to bypass it be a better solution?

I solved this very same issue with my variac with a beefy enough inrush current limiter (NTC thermistor) in series with mains input. Much simpler and immediate than a whole softstarter

@greatscottlab

3 жыл бұрын

Also a solution :-)

I had the same problem and I built a "dim bulb tester", basically I start the transformer with 2 40 watts lamps in series with the load and I added a switch to bypass the lamps once the transformer is powered on. Maybe this helps somebody that wants to make this really cheap and easy. Great idea and video as always btw

Schöne Schaltung! Ich hatte mir vor Jahren einen Sanftstart mit einem 5Ohm Lastwiderstand gebaut. Dieser wird nach 1s durch ein Solid State Relais überbrückt. Als Zeitgeber dient ein Ne555. Ich benötige die Schaltung für leistungsstarke PA Endstufen. Der reine Nulldurchgang hat alleine nicht gereicht, hatte immer noch Peakströme größer 90A. Du hast echt klasse Ideen, weiter so!

hey great scott, a few minior problems here, the initial current flow is only depending on resistance? where is the time constant of the RL circuit? also transformer powerup neasr zero-crossing is more or less the worst that can happen (highest current because of the field requiered to build up (integral from halfwave))

You may want to add a reverse diode in parallel to the zero crossing detection optocoupler. Otherwise, the LED inside might get destroyed by overvoltage while in reverse. Since practically no current is flowing no voltage is dropped over the current limiting resistor and the optocoupler LED sees the full reverse voltage.

Hi great scott, another amazing video !! Just a little question, at the middle of your paper schematic i have noticed u wrote 325V ... that's confusing me ... if we have 230-240 V AC isnt the max value +- 230 V ? why 325 ? could be a refuse thinking on a 3 phase system, where u have such voltrage between phases ?

Been thinking about a DC spark prevention with an NTC, with some sort of bypass, is there a common way to do that? Would be nice to have that built into a switch that first contacts with a higher resistance before pushing on to the main connection. Or like a preload button. Need to switch 100 amps.

Getting better and better. It's explained well, and the whole lesson is demonstrated by a working device. I also like how this guy goes to great lengths to show the flow between the problem and the solution. I mean he hauled a big and heavy electric motor just to show that it applies to them as well. Well worth the subscription. P.S. What I don't like is the fact that he doesn't want to admit that he took the "Great Scott" name from the movie "Back to the future" (the mad scientist). Yet, I figured it out! Got him!

@greatscottlab

3 жыл бұрын

Haha thanks for the feedback :-) And yes, my name is from Back to the future :-) My favourite movie

@liviuconstantin9960

3 жыл бұрын

@@greatscottlab You should also get into AI (i.e Jetson Nano, Jetson Xavier). It's the future, herr professor !!! ;-)

If you need to start a high inrush transformer -for example the type used in industry for 240 v to 120 v centre tap for use for industrial site safety. the simple way to "soft start" it is pulg it into a standard 15 to 25 metre 13 to 16 amp extension lead, which slows down the initial rush . The alternative is a C type rather than B type circuit breaker but in some -particularly domestic sytems it is not allowed - but would be on most PME systems.

An old TV mechanic I knew had a soft start circuit made with 200W light bulb and a switch 😀

@WalterKnox

3 жыл бұрын

ah, the old "dim bulb" great for slowly powering up something like an old radio or TV that has wax caps in them. light bulb lights up brightly you shut it the hell off.

I have a single phase 220v Table saw that starts too aggressively. looking at customizing this circuit for that. what would you recommend to integrate it with the existing magnetic switch?

I've got a 4kVA variac, if I switch it on it's 50:50 whether it'll trip the breaker or not. I use a big 7kVA mains conditioner which soft-starts it and prevents tripping.

I love all of your videos they are so informational. I was wondering why you did not make the final product using JLC PCB sense they are your sponsor? I thought that would have been a perfect opportunity to show how their products can be used. Much love

Good stuff as usual, I have build a pellet burner which it's heating up my house for a couple of years with no major issues, i am still implementing more functions to it, the controller in an arduino micro, a question for you since i can't find any relevant answers on the internet, pin 2 and pin 3 of the arduino micro are the interrupt pins, which are also SDA and SCL used by the i2c bus, on those pins i have a 20x4 screen and a rtc 1307, will the dimming feature work for the zero cross...

Informative video. I didn't realize that Solid State Relays have a zero crossing circuit. This should fix my Siglent Bench PS from tripping the UPS on my router.

Greatscott " warning do not touch its high voltage " Electroboom " Hmm this is high voltage wire 🎆 yeeeeaaawoooouch fu** fu** fu** I am an idiot "

@ek8710

3 жыл бұрын

I saw he made use of a FOOL BRIDGEE RECITFYERRRR >:U

@petermuller608

3 жыл бұрын

Electroboom would also try to lick the transformer xD

Will this soft starter work for a solar setup? Starting a motor running off an inverter and solar panels, the startup current is too high and trips the inverter.

Just saw this...very useful. I am going to try on a few things. Gemutlichkeit!

Great job! Only question is what is the motor jump at 11:17. Just at the button push there is a jump and than slow speed up. Looks like a short maximum peak at the initial. It shoudn't be. Am I right? Did you fix it?

Hi Scott, I need to add an isolation transformer to a solar inverter 5.5Kw AC output. I'm scared the inrush current of a big transformer might damage the inverter. Does 0 cross offer enough protection you think?

Will this soft starter work on a motor pump too? I wanted to reduce the “current spike” when the pool motor pump starts :)

I did have that same issue with the tripping circuit breaker, but it was with my power supply(it has a 270uF cap) I solved it with an NTC placed in series with the live wire. I did think about making a soft starter, but then there would be a delay when powering up the PSU.

Nice project I have a couple questions. Does this work for 120V? I've seen a couple other soft start projects which claim that a relay is a more reliable long term solution than a triac? Also would like to see a soft start which starts up automatically when the load device is powered on. Thanks.

hi scott do ur slow/smoth start work with switch mode power sub. like psu for pc etc? have a sub woffer runing of a psu 1600w to a 2000w amp and it wtrip my breaker 90% of the time 75% one at the time( yes they have BIG capasitor in them) thx for reply ps have 20 amp plugs and 220v ac

Great video. I need to make a soft start for a circular saw that's 240v and 1400w, could I use the same setup?

Where can I found the schematic? I'm very interesting in build something like that to controll my saw.

I have a motor for a water pump very similar (by appearances) to the blue motor that you connected to the soft starter. If I remember correctly, it stopped working because the motor won’t start, but spins freely. Would this work to possibly use this motor again??

Many Auto transformers don't have the primary not across the entire coil, but tapping at a 90% or so. The wiper however does extend across the entire coil, permitting the output to actually be higher than the input voltage. Eddie Van Halen used to use an auto transformer to lower the line voltage to his guitar tube amplifiers, for what guitarists call the brown sound. Sorry if this is a duplicate comment. Thanks for Colorado.

Hi @GreatScott, I have two questions please. 1) Why is the optocoupler's anode connected via two parallel resistors (R6 and R2) both 220k. Would just one 110k not work? 2) Is the black filament the galaxy black from Devil Design :-) ?

How would I go to... instead of a push button, use the thermostat of the ac unit make on and off... So instead of a momentary switch have it for a toggle switch at line voltage ? Great work thanks !!!

Love the project with a practical example built right in

hi , i tried it but i have a problem ... when i didn't connect the output to anything ( or to a small lamp less than 5 w) the voltage is going up gradually as it should. but when i connect a single phase motor or a 100w lamp the voltage jump from 0 to 220 in one step like an on-off switch . do you know were the problem?

I think a SSR may be a good idea for my well pump, I just want something to take the brunt of the starting current off my inverter! A NTC, with SSR should do fine, then I can use 12-24vdc on the pressure switch, maybe at low voltage/current it will nearly last forever! The pump is 120vac, abd is about a 7 amp peak load, it's in a shallow well, and has a easy job! It isn't worked hard! I just don't want it to possibly blow gets in my inverter if it's bear full output, and the pump comes on at the peak of the sinewave! Great video!

Amazing!!!!!! As was looking for this for a long time!!! Great video and Project!.

This is just what I need in my workshop, my circular saw is very spark in the start. But at the end of the video the motor start with a jump, stops and start again. What's happening? Because I thought it will start slowly and gentile, until get the full power. Thank you for share this project, I really wish to build one.

can we use a power resistor for soft starting and a triac to short the resistor after soft start?

Did a similar thing for the mystrey rating variable voltage transformer I got. Unknown what the ratings are, but it seems fine to handle 15A output current. Just used a high power resistor in the input line, 4 10R 10W in parallel, and with a 100C thermal fuse between them, with a relay fed from a simple resistor, bridge rectifier and capacitor smoothing, so the relay turns on around 5 cycles after switch on and shorts out the resistors. Also used a winding tap that gave 60VAC (lowest one on it) that fed a half wave rectifier, smoothing capacitor, and then a 47V zener regulator, that in turn feeds a 33V zener regulator, providing power to a LM723 set to provide an output of 6V, that can sink 10mA if needed. This is the one side of a simple voltmeter, so that the scale starts at 60VAC, and goes all the way to 360VAC, which is the range of the output at maximum. All made using parts either repurposed or lying around, including the box, which was the case the variable voltage transformer came in, just with a coat of paint, and the assorted outlet sockets attached. 60VAC to 360VAC because the surplus meter I had came with a 1mA FSD coil, and was marked with 0 to 30 already, so quick to simply use a black drawing pen to relabel the numbers, after a painting over of the originals.

Looks bit complicated this softstarter. In a PA amplifier, they use also a big coil and everytime my circuitbreaker pops also. But i fixed it easly whit just 2 NTC resistors in serie in one of the two wire to my amplifier. When the NTC getting hot the resistance is dropping to 0 en the amplifier works than correclty. Even there is a softstart whit 10resistors to lower the inrush current and after some seconds a relais kicks in to bypass the resisstors. Mayby idea for video to see whitch kind of softstart there are and whitch one is the best. Because i am curious what is the best solution.

Thanks so much for your efforts in teaching us for free (I´m going to design one of this for my grinder!) Stay teachly!

I got a 3 kw one too, but haven't had any problems with a breaker triggering. Maybe it's because my mains voltage is 120?

Hi Scott, where can I get digital AC voltmeter that starts from 0V? They typically start from measuring 70V or 80V.

Voll gut, dass du das thema mal behandelst. Allgemein cooler channel. Creative buils.

I’ve been looking for something like this, but for 12v DC - my doorbell always startles me by suddenly ringing obnoxiously loud, a slow build up would be great. I can’t just increase the resistance or muffle the bell as it needs to get to its loudest to be heard in the workshop.

Always add extra bypass relay for post soft start bypassing to prevent lose while system is running at full Walt.

Nice job. I had a similar problem with many switching power supplys on one breaker. Here the problem is the capacitive load and MeanWell has a DIN rail module to softstart these. Maybe a good topic for DIJ or Buy?

This one of your best works. Kudos. I've learned a lot.

Nice idea, i would like to ask if this soft starter has a power limit? Because you might use all 3kw of the transformer? I am asking because I think about a soft start for a Compressor...~10kw Thank you.

I really love your content. It's fun learning for me.

I like how it's 2021 and he's still using torn pieces of paper to annotate things in real life. Cheers.

Great video Sir! I watch all Your video's, to learn and also just informative entertainment. If I may ask, will this circuit be suitable to soft start and, effectively, control a resistive load such as an electric geyser element, or must the components be adjusted to handle greater current for longer period? Those elements are usually rated at around 3 Kilo Watt on a 220V, 50 Hz single phase supply in my country. I apologies If I am asking something you already answered. Thanks in any case. Once again, Great channel!!

soft start circuits a class to have for loads of projects. power tools especially.

Got a link to where you bought the 3kw auto transformer? My 500w one is a little weak.

So why did the motor at the end jump and then soft start? Was it to do with the pinned comment? Did you switch to current zero switching afterwards?

Could this be used for simple ac loads like a non computerized refrigerator? My fridge has a terrible surge on it. 2200 watts, makes my inverter flip out and the lights dim.

Circuit was already assembled and seams to work with test bulb. Strange thing is that bulb blinks once when I turn AC IN and stays off till I press the button. Then it starts to increase brightness softly as expected. What can be a reason for the initial blink?

Hi G.S., I had the same problem with a 30KVA autotransformer and the simplest solution was to turn on the circuit with a load applied to the output of the secondary: the large initial current is due to the magnetization current of the primary which is not reabsorbed by the current magnetization of the secondary (output circuit) due to the absence of load. This suggestion was given to me by my service manager (I worked in ENEL) who had worked in a company with a large transformer cabin and who had the same problem, when the softstarters could not be used due to the load (> 4 MVA at 15 KV) and possibly triac, mosfet and arduino did not exist. Try to apply a load to the output (one ohm resistance is fine too: you adjust the output voltage so as not to let it exceed its power) and then power it up: you should no longer fail a ignition P.S. of course the resistor is used only for switching on and must not remain active for all use of the variac. Thanks anyway for sharing the design of a softstarter. P.S. there are modules for universal electric motors, up to 2KWp, very compact (with three wires and automatic, to be inserted in the casings of power tools) on the market, but you would not have made the video :-)

Large transformers are always a problem for standard house breakers, if permanently installed the type of breaker can be changed to a C or even D, but then the tripping time has to be correlated with local disconnection times as dictated by local law. If the appliance is portable, then a soft start (cheaper than a full inverted) can be used to reduce the inrush, many are available commercially and are mainly used for motors. I am a little concerned that the motor jumps into life at the button press then returns to slowly accelerating, not something one would expect from an off the shelf solution!

Nice video! I really enjoy all of your videos, but I miss the big projects, with a lot of electronics. Is there any of that type of video coming up soon?

One super simple solution I seen used in an 40amp Isolation transformer was just a contactor that had a power resistor over it, the contactor was wired in wit the feed power. Now the time that takes for the contactor to pull, the transformer will start true the resistor. It was actually working great, with no output loud the transformer started even with 10A fuse!!! A super simple solution that just works! I got my hands on something like 4 or 5 off those transformers. Back then I gave them all away for other hobbies, but played around with one off them for a while. I ewen had small plans to make a 700A 12v charger / start jumper. But never got around it and just decided it's better served with someone who has "reall needs" for one phase 40A isolators. I think some of them went to a both harbor for feeding aluminum bouts

I'm currently looking for a softstarter for my 1HP well pump, and came across your video (even though I've already been a long time subscriber, I hadn't seen this one yet). Softstarting doesn't seem to be an overly complex issue - so why is the cheapest softstarter on Amazon more than 100$, with most of them costing more than 300$? Is there another name for a basic thing that makes motors start up a bit more gradually?

Err.. we used to do this for big ham amp power supplies with a resistor and a time delay relay. Cheap simple potter and brumfield socket relays set to 3 sec or something like that. Those were supplies with big caps to charge though.