Completely WRONG, the transformer has nothing to do with core saturation. This is completely bogus, what is happening is turning the transformer on at a peak of the AC wave form and not at a "Zero Crossing" point will always cause an inrush current. "SOFT START" circuits are usually required when the transformer and rectifier assembly is charging a high capacity filter network. Get it right guys, factual theory, CB Mentality does not cut the mustard. Respectfully & 73 Dennis, KV4WM, a US Navy Nuclear Submarine Veteran and Licensed Amateur Radio Operator.

@keithcress1335

26 күн бұрын

Sorry, you are wrong. Big CB is correct. This is a phenomenon called core remanence. Applying power at "zero-crossing" to a transformer with it's turned-off remanence near the positive peak forces further positive flux build that there is no capacity left for. This results in saturation and a LARGE magnetization inrush. Up to 17x FLC. Systems called POW or "Point On Wave" exist to avoid this. They monitor where power is lost to the core and control the power ON point of the sinewave to the same point during the next power up. To repeat, starting a transformer up at zero Crossing is worst point to do it.

@bigcbradio

24 күн бұрын

Since you threw in a dig at CB Mentality, you must also be one of the hamsters that complains people are off frequency and they should buy a better radio, even tho yours has a clarifier. Also you must be angry at CBers because you didn't fit in and had to study to be a hamster, and now all you can do is ask other hams what the weather is and then brag about your $3500 radio. How do I know you use to be a CBer and didn't fit in? Because you said "does not cut the mustard" I heard that for years on the CB, and now you bag on CBers, because you didn't fit in. Then lets top off your hamster intelligence buy you saying "factual theory" I am rolling on the floor, seriously! I passed all the hamster exams without studying and I can talk all over the world without $3500 radios and 100 foot towers. Goodbye KV4WM, but again "factual theory" Really? do you know what either of those words mean??? You are so proud to say your name and call sign and top it off with "factual theory" I Love It. ROFLMAO

@bigcbradio

24 күн бұрын

@@keithcress1335 Wow, I love it, I knew they track and/or start the wave to sync when combining or switching, but I never heard of or thought of using it for a transformer. Awesome, I love learning new stuff. I thought it was crazy when I learned how they shut off the MRI machine I was in 20 years ago. I saw inside the unit where it had this huge shunt to literally short out the massive power coming in and blow the breakers to turn it off, but you probably already knew about that. Thanks for teaching me something new, I already looking it up and reading.

@clytle374

21 күн бұрын

So completely sure of yourself. But completely ignorant on the subject too. " peak of the AC wave form and not at a "Zero Crossing" point will always cause an inrush current" Yep!, you've never been there before. I used a zero point crossing circuit once and instead of tripping the breaker 25% of the time, I got like 90% of the time.

Your highly-flammable, static-electricity-generating work surface amuses me

@bigcbradio

29 күн бұрын

Well..... I bought one of those anti static wrist straps back in the late 80's but I never used it and don't know what happened to it. I often use old towels as a work surface, it keeps things from getting scratched and also keeps screws from rolling away. The only real disadvantage is you have to be really careful about small pieces of wire getting lost in the towel, you know, like the small strands from stripping the end of a wire. When working on a live circuit board a small strand of wire in the towel could really ruin your day. Luckily for me, even after working on thousands of electronic devices over the last 50 years I have never had a problem due to static or those pesky little wire pieces, although I have let the smoke out a couple of times due to other mistakes. I am not going to mention the name of the repair shop, but there is a shop here in Southern California that has their entire work bench covered in felt. It makes me cringe when ever I go there. The felt is covered in burn marks and there are literally dozens of little pieces of wire and solder dropping stuck in it. The worst part is that almost every repair they do, they have a live circuit board laying on top of that mess. Oh well, I do know the proper way to do things, I am just too lazy to go to the effort when making these helpful (hopefully helpful) videos here on youtube. That's kinda why I mention in my "about" that these videos are not professional and I am not an expert. Also some things you see in my videos are meant to be funny, such as some of my videos will have a hammer, Elmers glue, super glue, etc.... all near what I am working on. Ok, thanks for letting me know my towel is flammable, I hadn't thought of that. I guess I have to have a fire extinguisher nearby in my future videos.

At a TV station I maintained, our soft start circuit used 2 1 ohm wire wound resistors on a Harris TV-55U 50 kw transmitter to slowly bring up the high voltage. The filaments were also soft started.

@KA9DSL

15 күн бұрын

That's 2 - I ohm 1 kw resistors, forgot to mention that.

@bigcbradio

15 күн бұрын

@@KA9DSL I figured they were BIG resistors since you were working with 50KW.. LOL. Sounds like a fun job. I only work with small stuff, like 1000 watts. I was only mentioning the soft start in this video regarding the kick from the magnetic field, but yes, as you mention, it is a good idea also for charging capacitors and filaments also. Thanks for the comments.

@KA9DSL

15 күн бұрын

@@bigcbradio Thank you, by the way, the xfmr and rectifiers were all in a big tub of mineral oil for cooling. And the beam voltage was 32kv. Very dangerous to work on, even when it's off.

@bigcbradio

15 күн бұрын

@@KA9DSL Dangerous is an understatement at those voltages. I have been zapped many times, everything from your ordinary car ignition coil to 240ac house, but the worst ever was from a capacitor in an old ceiling fan that had been removed from the ceiling for a month! As crazy as that sounds, I was taking the fan apart for who knows what now, but as I took it apart the capacitor got me from hand to hand thru both arms and across the chest. Seems silly since the cap was about the size of a D battery and it was just a 110v fan, but my muscles were sore for a week. It was one heck of a firm contraction. I was holding the fan up with my left hand and had the wire cutters in my right, and when I cut into a wire..... Snap! Since that day I don't mess around with anything without thinking first.

I hadn't considered this. I have a bench supply I use on occasion when I need big power. It has twin secondaries 20.5vac @ 30a. I did put a soft start on the secondary side to limit the inrush to the 4 x 60,000uF filter caps because the thing used to pull the lights down on power on. Good vid! I'll make another modification next time I dust old Bertha off. Cheers.

@bigcbradio

Ай бұрын

Yes, and if you do just a little testing you can come up with a resistance and an amount of time needed on the primary side and you won't need it on either of your secondaries. These soft start mods not only stop the thump, and in your case stop the lights dimming, it also protects your capacitors. Have fun.

Good presentation. I've known about the concept of inrush currents and all that for sometime. I have built circuits using quick duration timers and a resister for a couple of my high powered audio amplifiers (vintage that used big iron transformers). Makes a huge difference. SMP (switching) power supplies are no exception! They surge too. What I didn't know, however, was the relationship between the static magnetic "charge" left over from the last shutdown and the position of the AC wave when it hits the transformer! That's cool. Now add all the stuff on the secondary side that is sucking hard for power like big filter capacitors in amplifiers. On all the mods I made to amplifiers, I chose to limit the inrush current ONLY to the high rail B+/- power windings but leaving the transformers still intact to line (mains). Just doing that allows amp to fire up and NOT have my room light flicker! Modern home theater type receivers sometimes use 2 power transformers! One is the big heavy one to power the amplifier stages, but use a tiny doorbell size transformer that's on 24/7 for the memory and some other low current circuits. In tht case, limiting inrush current to the high power transformer is a good idea.

@bigcbradio

29 күн бұрын

Now you know... LOL. I didn't figure out that "static magnetic "charge" left over" on my own. I read it somewhere 25 years ago or more. I don't remember where I read it, but I am glad I ran across it back then. One of the easiest ways to demonstrate that static magnetic state it is by pulling that trigger on your Weller soldering gun a bunch of times. They make a pretty good clunk sometimes. I was going to use my Weller to make the video, but then I remembered I had this power supply that the cover has just enough clearance that is make that loud ringing sound. I am really glad you picked up on that static magnetic state rather than just the basic inrush. Have fun and thanks for watching and commenting.

Luckily, my 20 amp isolation transformer has dual primaries, so I run it from 240 VAC, instead of 120, and that keeps the breaker from popping. It's enough current to make the wires rattle inside the conduit. Transformers, even with no load, appear as a series R-L circuit, and there is a startup transient. You can even model it in SPICE and see for yourself that several cycles are required to reach steady-state.

@bigcbradio

6 күн бұрын

Rattle in the conduit..... sounds like you could use some soft start there

My suggestion, use a time-delay relay. Connect the value of the resistor needed to stop the surge in series with transformer primary. Connect NO contacts of timer across resistor. When timer activates, say 1 second, contacts close and take resistor out of the circuit.

@bigcbradio

14 күн бұрын

Yes, that is the correct way to do it. I'm cheap though, I just use a switch and I'm the timer and by the time I switch it, it's ready. LOL

There is a special thermistor called an inrush current limiter.....High resistance when cold, low when hot. These are made in a variety of current ratings. They are commonly used with switching type power supplies. I bought a bunch of these years ago and add them to any gear which i wish to protect. The ones i have were made by Keystone.

@bigcbradio

29 күн бұрын

Thermistors do have their place, and even tho they market some as inrush current limiters, I will stick to this type of example in this video. Why? For example, if you were to switch a device off and then immediately back on, the thermistor will still be warm an offer no protection, or if the area around the thermistor is still warm, again, no protection. Also thermistors characteristics change over time and use "they age" and the specs change, additionally, they are affected by ambient temperature. But, everyone can research all the different ways and test and decide for themselves. Thanks for the idea.

@clytle374

21 күн бұрын

They also don't like greatly varying loads. Easy to design a with an ICL and find out it's shutting down when the system is idle and 'soft starting' your circuit when the current requirement jumps up. Trying to find one with the cold R high enough, and the other specs is a pain.

@gregebert5544

5 күн бұрын

I looked into these before, but the ratio of cold vs hot resistance was too low (I recall around 4 to 5) to make enough of a difference for me, and also the hot resistance was too high because it was going to overheat from the 5-10 amp load.

Nice

@bigcbradio

Ай бұрын

thanks

I would argue that Residual magnetism is only one factor in this. I installed at 1.5KW torrid transformer at my test bench for isolating a DUT. It was my first rodeo with large inrush currents, torrids are worse. I would pop the fuse, or blow the 20A breaker 25% of the time. At first I installed a zero point crossing circuit, and it blew about 90% of the time. I did some reading and studying, and even worked up a current clamp to my scope to measure current and voltages. I went full Obsessive Compulsive on it, lol I think you stated it wrong about the residual magnetism. Best case is the polarity of the field left in the core is against what is incoming when the switch is closed, hence bucking the current. If it is aligned with the incoming current then it doesn't buck the incoming current, and you might start off on the edge of saturation. This will leave the current limited by only the DC resistance of the primary winding. Now if you turn on at zero point crossing, even without a residual field, then you have nearly a full 180 degs for current to build. This only gets you the first cycle, as the next cycle DOES HAVE a heavy residual magnetic field bucking the current this leaves little current in the primary, unless the secondary is eating the field up as a load. I demagnetized the core in a few tests and that made the problem better, but not fixed. Here is a ugly, or genius, way I used to fix the problem. My output was 120V, so I used a power relay that had a 120VAC coil. I wish I could include a sketch. The relay coil was driven off the OUTPUT of the transformer. The output of the transformer went through one set of NO contacts so the output couldn't be loaded until the replay closed. The input of the transformer went through one set of NO contacts powered from the existing power switch. Then a resistor(iirc 12 ohm 2W surge rated) was put across the NO primary relay contacts. Now when the switch is turned on the resistor limits the current, the voltage in the secondary doesn't come up if the core is saturated so it is limited for a time. Once the output voltage is up the relay closes bypassing the resistor and connecting the output.

@bigcbradio

18 күн бұрын

Seems like genius and maybe over engineered, but who am I to judge, mine is just a resistor and a switch, but I didn't actually show mine, it was just a demo to give people the idea. Whatever solves the problem right? You are definitely are putting some thought into it.

Goes without saying. "Switch to safety"

Everything is better with softstart.... ;)

@bigcbradio

Ай бұрын

Yep

@ketas

29 күн бұрын

even sex

@bigcbradio

24 күн бұрын

@@ketas LOL, made me laugh

All these bare wires!!!

@volvo09

Ай бұрын

Well he's not touching them...

@bigcbradio

Ай бұрын

Yes, it makes it exciting, and if you look at the tip of the alligator clip on the yellow wire, and look at the spade lug right next to it, you may notice I had a little excitement just before I started recording. LOL. The other option was to make a professional looking setup that would take some time and effort. I don't have much time left and I hate effort. Hopefully someone learned something from this video and they can make their soft start as safe and as pretty and professional as they want. Thanks for watching and commenting.

@bigcbradio

Ай бұрын

@@volvo09 I try not to touch em, LOL. I will mess around like this with 120ac, but I don't fool around when I'm in there with higher voltage. There are some videos I have with the cover off of some high voltage stuff, and in the videos it may look like I'm close, but I'm not, and I even double check the area where I will be walking around when recording so I don't trip/slip/stumble and fall face first into something that will burn my face off and kill me. I am even afraid of DC of 48v or more. DC is way more dangerous than AC in my opinion. I designed and installed my own Solar and it is around 500v DC and that is no joke. You won't see a video of me playing with that.

@makerjeff86

20 күн бұрын

Meh, I've done sketchier and lived to tell about it. I really freaked out a neon sign repairman once when I bypassed a 120v photocell with an alligator jumper to turn the sign on at work.

@bigcbradio

20 күн бұрын

@@makerjeff86 Lots of fun. I had to do some emergency repair one night and all I had for lighting to see what I was doing was scratching the wires (120ac) together to get some sparks.