Big Dim Bulb Tester with Variac and Isolation Transformer

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Here is a large dim bulb tester and variable AC power supply that will provide up to 240 Volts. It current limits at "Around" 1 amp at 120V, and 500mA at 240V with the bulbs switched in. This is a dangerous build. If you build this, it's at your own risk. I suggest you don't build this power supply!... Unless you know what your doing.

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28 сен 2024

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Комментарии : 289

@iainportalupi 6 лет назад

Great job! The only suggestion I have would be to replace the light switches with old knife switches to complete the old look.

@harrilumme1875 5 лет назад

Yes, we are all waiting for the Vedolyzer sequel like Christmas. Therefore I have been forced to watch reruns of all MrCLab videos. And you learn new things every time. Thanks and wish you lots of energy for the darkest weeks of the year.

@tbdc60 8 лет назад

Thanks for the time and effort you put into these very excellent videos. You're not only a first rate tech, but also a very masterful craftsman. This project is as awesomely steam punk as it is useful. Kudos comrade ! Your work is a thing of beauty.

@MrCarlsonsLab 8 лет назад

+Тимоти Блокер Thank you for the nice comment!

@garybevis8691 6 лет назад

Mr. Carlson, I recently stumbled across your channel and I have been delighted by your work, wit and ingenuity. I attended a technical school here in the states and studied digital electronics. During the first phase of the courses we learned about LCR, RF, and basic electrical circuits before we dove into logic and processors. That was back 35 years ago and my career path diverged wildly from electronics. Since a young age I experimented with electronics and your channel has renewed my interest and I am currently digging out my old power supply and test meters. Thank you for your very informative and entertaining videos. Best Regards, Gary

@MrCarlsonsLab 6 лет назад

Thanks for your kind comment Gary!

@thomaslanik7215 6 лет назад

I am thinking of rebuilding the current limiter I built yesterday adding in my variac plus a Power On lamp. Nice job, Sir.

@kevinmartin7760 4 года назад

Another way to look at he "matching" effect is that a transformer with no load is still an inductor and so will draw current. This current lags the voltage by 90 degrees of phase and so consumes no power of itself. However, any resistance in the primary circuit will consume some power, including the light bulbs.The added capacitors also draw a reactive current which *leads* the voltage by 90 degrees, so the inductive and capacitive currents are 180 degrees out of phase and cancel each other out. This nets out to no current on in the input (variac and bulbs) so the bulbs do not light.There is still a resonant current flowing between the capacitors and transformer primary so the transformer itself will still dissipate the same amount of power as heat in its primary winding due to the winding's resistance. The ideal capacitor value will indeed be the one that, with the inductance of the transformer primary, forms a circuit that resonates at the supply frequency of 60 Hz.

@klaasklapsigaar1081 4 года назад

I had some trouble understanding the inefficiencies but your explanation makes it very clear. Thank you.

@AnthonyFrancisJones 2 года назад

Kevin, excellent explanation of power factor correction - not an easy concept at all! You might like to add to what level the efficiency is raised due to there still being a resonant current and therefore iron and copper loss. The lucidity and brevity of your explanation is second to none! Many thanks!

@BoydWaters 3 года назад

It does look cool... You have developed the unconscious habits that keep you out of trouble. If I do a version of this, you bet I am using an isolated enclosure! Many thanks!

@smbrob 9 лет назад

Nice tool :-) I suddenly get the urge to yell out "it's alive it's alive"

@MrCarlsonsLab 9 лет назад

+smbrob Finally somebody yelled it, now I can release frankenstein...LOL!

@kenseastrand7428 6 лет назад

I built one kind of like that in my lab, I do have all connections covered . I used a variac, isolation transformer and a three bulb vanity fixture, so I can unscrew bulbs to lower the current, now after watching this I may revamp mine a little. great video!

@mackfisher4487 5 лет назад

Mr. Carlton’s understanding even shines through with this simple but practical test set up. It reminds me of things as seen in 1950s era popular science magazines or QST’s varnish 2X4 antenna projects. Perhaps there is an influence derived from the first Westinghouse generating station at Niagara Falls. Large knife switches meters and pilot lights, and if you’re stupid enough to put your hand on open switch or terminal you deserve a shock. (No disparity meant to lawyers) but why are instruction manuals written with 1 page of technical information and 10 pages of warnings like don't use your hairdryer in the bathtub. Thank you Mr. Carlson keep up the good work

@miniwattnetwork8204 4 года назад

amazing tool, you inspired me to build one for my own :) .... I suggest replace the on-off switch with a relay, making a 'set-reset' to bypass the lamps instead of the key, so you will never need to remember to turn of the lamp bypass switch as it will be disconnected every time you turn off the AC, putting the lamps in series...

@hestheMaster 4 года назад

Steam punk cool! One thing I would change is to turn the dual gang box 90 degrees so the outlets are up and down. Maybe omit the 220 Volt trans. unless your in Europe! Keep it safe. Cover the business below the top bulbs with a clear acrylic plastic. Awesome Paul!

@dennisa6132 2 года назад

I'm sourcing parts myself for a build like this, and an enclosed unit was always my goal. I found a tordoidal 1000VA 220-220V isolation transformer so I will need some kind of soft start or it will trip my breakers. And while I am at it, a bridge rectifier behind the variac too so I can get DC of different voltages. I am in 220V land in europe and big bulbs or lightbuls in general are getting hard to find, and with our voltage we need 2x larger ones so they become ungainly. I was instead thinking of using R7S halogen bulbs instead, a 500W one would give about two amps, and a 250 would give one amp, a 100W half an amp and so on...

@cigarboxguitar9519 8 лет назад

You could use a clear acrylic box to cover the assembly if you want the cool look but don't want the chance of an uncool e-shock from accidentally touching the live contacts. Make some cut-outs for the variac knob, switches, outlets and bulbs.

@dickchiggas1514 5 лет назад

"I am very very careful" . A common inscription on gravestones. I have worked on commercial inverters for communications in the 250 KV genre. That will peak your awareness of your surroundings!

@JurassicJenkins 2 года назад

Thanks for sharing this - I really liked the look and the schematic was a huge bonus! Off to the bench 😃 to make mine!

@pipertec 6 лет назад

Your is the best I have seen yet! Love your vids. They are very analytical and in depth! I love them👌

@MrCarlsonsLab 6 лет назад

Thanks Mark!

@graemebrumfitt6668 6 лет назад

More CRAZY STUFF!!!... Lovin it Mr C, thanks for your time :-)

@Ziplock9000 7 лет назад

People make mistakes and have accidents despite knowing what they are doing. Please cover that in clear acrylic or something if you like the aesthetic look but still be safe.

@glenwhatley4125 4 года назад

Very nice. I built a much simpler version of this that serves my purposes. I just have one bulb i can change of necessary. One suggestion i would make is to have a double pole switch for complete isolation on your primary so you don't have to unplug the DUT every time you go to solder or move things. 😊

@JurassicJenkins 2 года назад

Mr Carlson, thanks for this explanation and schematic. 😎

@realvanman1 Год назад

By having the current limiting bulbs on the input to the Variac, the value of available short circuit current on the output increases as the voltage setting is decreased. I'd put the bulbs between the Variac output and the primary of the isolation transformer.

@spudhead169 4 года назад

Variacs have always fascinated me.

@hokepoke3540 5 лет назад

I really like your design. Thank you

@bborkzilla 8 лет назад

Looks like something from the radio room from the Titanic...

@MrCarlsonsLab 8 лет назад

+hoppes9 My other half agree's.

@BruceNitroxpro 4 года назад

@@MrCarlsonsLab , Just curious... would you ever tell your viewers how to make a Power Factor meter? de KQ2E

@PeopleAlreadyDidThis 6 лет назад

I too was once perfect. Then I almost cut off my left index finger. Fortunately, I still have it, but it doesn’t work properly. I changed my attitude, realizing that I was no longer perfect. I don’t do stupid things now, and that includes exposed mains or high voltages at my bench. A nice wooden cabinet with a glass cover would provide electrocution protection and look good too.

@lwilton 8 лет назад

A very useful device to have, and a very pretty build, too! (Though I think as a practical point I would have ended up putting a bit of tape or phenolic over the bare primary screws. You might be amazed how easy it is to reach blindly for the knob while staring in a scope and miss your target by a couple of inches. Guess how I know...) BTW, that is very similar to the design of most tube testers from the 1940s and 1950s. A nice little 6.3V lamp labeled "Fuse" in the primary line.

@MrCarlsonsLab 8 лет назад

+l wilton Thanks for your comment!

@davecc0000 8 лет назад

Mr. C, I've got all the components to make one and I've been procrastinating. Will also have 240 output to drive some industrial electtonics I repair.

@MrUbiquitousTech 7 лет назад

Nicely done, I like the looks of it too.

@totbenru 9 лет назад

Hi Mr. Carlson. Channel subscriber here from the Philippines. You talked about improving the efficiency of the variac to isolation transformer coupling by adding a capacitor in parallel. How exactly does this work? By adding a capacitor to the transformer, are you resonating it (LC) to 50hz? Thanks

@MrCarlsonsLab 9 лет назад

Ben's BatCave Hi there! We have 60cy electricity over here. Yes, by the addition of a capacitor, you create an LC network that better "tunes" the circuit. Thanks for the sub Ben!

@BruceNitroxpro 5 лет назад

@@MrCarlsonsLab, Especially when you are "out in the sticks," the amount of motors and inductive loads makes the power factor less than 1. If you add some capacitance with an AC RATED AND OVER VOLTAGE CAPACITOR DESIGNED FOR PF CORRECTION, you can return the power factor to closer to or equal to one. Ask your local power company to tell you what the power factor is at your home. They may add a PF correction cap free of charge!

@pepe6666 5 лет назад

i have seen a whoollle bunch of mr carleson videos where ya mention this power supply and i finally got to see it. i was always curious about what ya were referring to.

@RocRizzo 5 лет назад

Not a new one, but necessary. Should be at the top of anyone's list for their shop if they are working on tube projects. Nice that that transformer has 220 volts as well. You can work on European stuff too!

@totallysmooth1203 Год назад

My question is where did you get those neat bulbs? I'm presently building mine. But frost bulbs just don't cut the mustard.

@rickkennard8027 4 года назад

What did you tie the earth ground on the equipment side to?

@jimthesoundman8641 3 года назад

I don't think you can tie it to anything, otherwise you lose the isolation factor.

@mkepler5861 Месяц назад

so a standard isolation transformer would suffice? sounds like it would do the same thing.

@windward2818 8 лет назад

Paul, I am also designing an AC power supply for troubleshooting (120VAC only). I thought perhaps you could comment on equipment AC leakage current tests as part of the repair process (Final outgoing test). Take a look at the B&K 1655A user manual for leakage tests, as proposed by B&K. For 120VAC three prong grounded plug, I plan on using a GFCI self testing receptacle as my first screening device (5mA). Also of note, is in the possible need for low pass filters when testing for leakage on switching supplies.

@alexwade9921 3 года назад

Paul. Why do you put the variac on the line side and the isolation transformer downstream? Why not the other way around? Is there a reason to choose one way or the other?

@cranegantry868 Год назад

An isolation transformer also needs low capacitance between pri. and sec. Iso-transformers for safety use are purpose built. A 240 to 240 ordinary trans. is not an iso-trans.

@travised Год назад

I would like to know on the schematic,where you place the capacitors?

@peteb2 7 лет назад

I've chosen to make the same rig for my repair bench. Sadly with 230Vac and 50Hz (the Mains in my country) and the fact I need a few Amps, my Variac is 9.7kVA meaning it weighs in at 16kgs (~35 pounds) and the isolation transformer the same order of magnitude in mass.... making it all real hard to bolt up and mount as a wall panel!

@MrCarlsonsLab 7 лет назад

Yikes!

@voxpathfinder15r 4 года назад

A good philosophy to have for bench equipment is not protecting yourself, but making sure there is no way it can fry your pet cat! I am cool with the high voltage, but I do everything to the nth degree to make sure a loved pet doesn’t become an unwilling victim

@migsvensurfing6310 3 года назад

Hotcat, not hotdog... love it.

@SilverCoreLabs 9 лет назад

Very cool. I have a separate section in my lab that is HV, Variacs, 10KV Hipot, 2KV DC Supply and etc. I like to keep all the HV isolated to it's own circuit and bench. Cool build!

@MrCarlsonsLab 9 лет назад

That's a safe thing too do (separate bench). I'm running out of room.... Now using wall space :^/ Thanks for the comment Eric!

@AdamJPollockLiveProd 6 лет назад

Hi Mr Carlson. Your videos are excellent! I completed an Associate Diploma over 20 years ago. Plus I’ve had a couple of years worth of some tech bench experience a number of years ago. You’re videos have inspired me to really get back into this field of work. Thank you. I have a few questions. My country’s power is 240V. I want to repair SMPS for pro Audio equipment and tube/Transistor amps. I understand the current from our mains here would be approximately half of your 120V is the US for the same amount of output power to the device. I’m not 100% sure if what current sharing globes to use. I’m assuming to match 1 amp I would simply use 2 x 120Watt globes in series. Some guitar amps draw 2 or even 3 amps. More for big 1000W pro Audio power amps. Thanks heaps in advance.

@nazgullinux6601 Год назад

So I know this video is quite old, but I have been trying to find a variac in that compact formfactor but best I can locate is Staco brand and those things are stupidly expensive. Where can I find a small variac such as that?

@TheOzzimadman 6 лет назад

Hi if i had a home made dim bulb tester and shop brought isolation transformer and Variac unit, in what order should i have the 3 items thanks

@SciPunk215 8 лет назад

So the 1-1 ratio windings which take us from 120V to 120V isolated, those windings are physically on the same side of the transformer, sort of stacked on top of each other? I always thought a transformer works by having the windings opposite each other, or sort of facing each other.

@MrCarlsonsLab 8 лет назад

+SciPunk215 They are just wound on top of each other in phase. The windings are spaced apart with paper and varnish.

@AC9BXEric 6 лет назад

Just be sure the windings are indeed separate and not a center tap primary. Using a second primary winding as a secondary isn't all that uncommon. I've done that for isolation or to get a high voltage output from a transformer that doesn't offer one. Say you want 6 volts for filaments and 170V for the plate of a tube and you don't have the right size transformer around or don't have one with the secondaries you want. You shouldn't expect it to pass a 3000V hipot test. But at a few hundred volts it's fine.

@dakata2416 7 месяцев назад

How long do the light bulbs last?

@robertskolnick8162 5 лет назад

can the isolation transformer go before the variac... or does it have to go after it?

@jamesharrison2041 Год назад

Hey paul''''''''''i have a idea that i put to use & i want too know what you think'''' good or bad''''''i finally built my bim bulb tester'''''''what i did was i used 2 (150 watt) light bulbs'''' i put a switch on it so i can select 150 watt or 300 watts to take a bulb out of the circuit or put both bulbs online''''''this a my idea of a current limiter controller'''''not trying to out do anybody'''''''just trying to make it a efficient as i can & utilize any practical additional controls.... also change to different wattage of bulbs but then id have to change the Labels to project that'''''ha''ha''ha'''''''thanks paul.

@johnmcgiv1 3 года назад

Great video, using the variac would this not cause the under/over voltage protection to kick in? Many thanks.

@repairfreak Год назад

Hello, I have questions. With your 2 bulb system you said it limits to about 1 amp. How would this be useful to see if a larger device that works normally at say 4 amps? A higher current device would light your bulbs bright every time making a person think there was a dead short when there wasn’t. How would a person go about calculating what wattage bulb to use to allow a current limit to just a bit below that of say a mainline power fuse wired to a power transformers primary? In other words calculate a wattage of bulb to only limit or light brightly at just under main power fuse blow point with say the device under test using either a delay blow, or norm blow type of fuses. Or would a better approach be to note from device label the input wattage of the device under test, under its normal stated operating voltage, and then somehow select a proper wattage bulb that just starts to glow dimly at this point? Thanks for any insight you can provide.

@raygosper1656 Год назад

Hi, just for interest, as it is impossible to obtain incandescent light bulbs these days, can the light bulbs be replaced with current limiting resistors?

@BijuKumar-kj7qr Год назад

What is the power of this Isolation transformer ?.

@iamhe999 3 года назад

I just designed my unit and came here to see how I did in relation to Mr Carlson's design... I put the bulbs and by pass switch on the output of the isolation transformer, I wired in the Variac output to the isolation transformer primary and it's secondary to the bulbs and on to the load.. appreciate any thoughts.. Did I miss something?

@AJMjazz 6 лет назад

A "must have" on any bench. Almost 40 years ago in my electrical engineering classes, we always used 1:1 iso-xformers when working on AA5 radios and similar to avoid a hot chassis. But recently, I read someone using a couple of 2A step-down xformers wired: 120V||24V => 24V||120V as a "cobbed" iso-xformer. Theoretically, it might work. I'm a bit suspect of the safety of such a set up - current draw on the 2nd xformer; might be dangerous. Agree?

@aliadnan4906 4 года назад

i buy in working condition but now on few days it is not working i didnt understand whats problem going with receiver

@amado1957 8 лет назад

Paul, thank you for this video, very informative ..

@MrCarlsonsLab 8 лет назад

Your welcome Amado!

@ddom678 2 года назад

Am I mistaken? Are the light bulbs (the current limiter) on the primary side of the transformer? Why not have the light bulbs on the secondary side (the isolated circuit/test side)?

@bobkins270 9 лет назад

Cool! I like that Frankenstien look.

@MrCarlsonsLab 9 лет назад

Funny thing is... People come to visit, I have a lab full of complex test gear, and that dim bulb tester almost always gets the first comment.

@johnbedell2376 6 лет назад

I have a Variac brand autotransformer, a topaz isolation transformer and I’m going to build the light bulb current limiter device this weekend. Is there a difference on where the isolation transformer is placed in the chain? Mr. Carlson has it placed last in this video, but could one place it at the front of the chain - that is, at the wall outlet - and then the variac, light bulbs, and DUT last?

@cvetomircvetkov5670 6 лет назад

Is touching any of the wires after the insulation transformer going to electrocute you, since there is insulation between the grid and the potential of the wires?

@robertcalkjr.8325 9 лет назад

Nice video, thanks. I need to build myself one of those so I can have 2 isolation transformers. I'll run the ground to a copper rod in the ground outside so they will have separate ground planes. My Tenma variable isolation transformer uses the house ground.

@MrCarlsonsLab 9 лет назад

Hi Robert. The whole idea of the isolation transformer is to isolate you from the existing system. I have never heard of a variable isolation transformer. I know of "autotransformers" and Variacs, but they have no isolation. There should be no connection between the primary and secondary of any isolation transformer. This can be tested with your ohm meter, if there is any continuity between the two, there is no isolation. Be careful with the ground connection! Remember the ground is tied to neutral in your main breaker panel. If this is connected along side the secondary of the isolation transformer, again you have no isolation.

@robertcalkjr.8325 9 лет назад

Mr Carlson's Lab It's variable because you can adjust the voltage. It is an isolation transformer but the ground on the output is the same as the input. Having another isolation transformer on a different ground plane I can power the device with one and my soldering iron with the other one.

@MrCarlsonsLab 9 лет назад

Robert Calk Jr. Very interesting! I have never seen a variable isolation transformer. I would like to see that. Do you have a model number and name? The concept makes total sense, That's why I built one :^) On another note, be careful about running another detached ground rod! Due to ground conductance, that may also pose a shock hazard. Ground conductance will carry current to the neutral side of your house supply.... And every one else's too. Just think of it this way, Think of all the ground rods connected to the neutral side, from the connection in the breaker box in everyone's house. This planet is a pin cushion for one side of the hydro line! I will do a video on this one day.

@robertcalkjr.8325 9 лет назад

Mr Carlson's Lab It's a Tenma 72-1097. You can see it here: www.element14.com/community/search.jspa?q=tenma+72-1097 I will be glad to see that video. I changed the memory backup battery in my Tek 2465A DV myself. Alan at w2aew and some commenters reminded me about using my DC power supply for a temporary power source to keep from losing the memory while my soldering iron was on the same ground plane. So I used batteries, which was easier anyway. It worked great.

@MrCarlsonsLab 9 лет назад

Robert Calk Jr. That Tenma Is a neat device.... Sure does have isolation..... aside from carrying the neutral wire through the ground pin. I guess for regulations, that needs to exist... but still scary! Good on you for changing that memory battery, that's risky business as well. It's no fun when parameters go missing!

@erin19030 2 года назад

I built mine open frame, but stopped using the bulbs.I found them a waste of time and money. Instead I use an isolation transformer and a Variac tied to a metering system and the outlets are GFI types.

8 месяцев назад

If i understoold right you raise the voltage with the variac and watch the ammeter? What difference it makes when the isolation transformer is at the output side like he did or at the input side? IF you have a video or schematics that can help a lot also.

@RC-Flight 6 лет назад

I recently made one of these with two transformers back to back 120/24 volt This created the isolation. Mine is wired much like yours power switch fuse auto transformer two parallel series lamps then the transformer. The circuit puts out 135 volts. If I put a 1.3 amp 160 watt load the 135 volts drops down to almost 80 volts. The auto transformer and the two step down transformers are rated for 4 amps I’m assuming this is due to the voltage drop created by the light bulbs?

@harrilumme1875 5 лет назад

Hi Paul. Is there any particular reason to have the variac first and the Olsen after it? Here in Scandinavia the plugs are not polarized and a variac becomes even more unsafe. Therefore I have used my variac after the isolation transformer (which is of course just 1:1, no extra windings).

@hoochharp Год назад

I recently inherited an old sola constant voltage transformer model 72104 95-130v in, 115-120v out. Can these be used as an isolation transformer. From what I can find out they seem like they have the windings isolated . I got bitten by the "ground on oscilloscope" monster (didn't get hurt) and want to make sure it never happens again.

@LifeBloodMarketing Год назад

No, CVTs are not isolated. I wondered the same thing sometime ago as I have a few as well.

@arthureschner9319 3 года назад

I was planning to put my variac and current limiting bulbs, on the output (secondary) side of my transformer, then I saw this video. If this was a normal 1:1 isolation transformer, would there be any benefit to which side (input / output) of the transformer you place the variac?

@TheOpenAirGarage 7 лет назад

So the Variac needs to always go in front of the isolation transformer.

@larrybud 2 года назад

I would put this in an clear acrylic box, it would look even cooler!

@InsideOfMyOwnMind 8 лет назад

I should know the answer to this but at the moment I'm being a bit lazy. If you connected the two 240v windings in parallel (in phase lol) first most obviously you would dispense with the 480v hazard but how if at all would that effect the power factor compensation that you demonstrated with the capacitors? You might find that standard cap values may get you closer to the ideal config. Or the reverse. Worth a try? It may even serve as a place to actually do your PF comp. Feel free to shoot me down.

@petersullivan8513 2 года назад

Hi Mr Carlson, love your stuff. I’ve learned a great deal from you and admire your professionalism. I thought you might like to see my effort at current limiting. What do you think?

@wesrichards6168 4 года назад

I'm seeing some complacency on this one, becoming to familiar with dangerous things gets people killed... as you are warning us, remember to protect yourself.. cover those transformer lugs.

@bertconvey3881 3 года назад

Your right it only takes once, I vision Paul stretching for something above it loosing his balance zap : (

@georgek2734 Год назад

My Question for you is, what would be a good watt size for a isolation setup ?

@chuck7494 6 лет назад

Hi Paul... Very nice design! It looks really cool too, although a bit scary with the exposed circuitry. I restore vintage radios as a hobby and built a small one for testing them. It's only a five amp system and I designed it a little differently than yours, whereas I have the dim bulb on the output side of the variac rather than on the line the way you have it. Although it appears to work fine, I am wondering if my design is in fact safe? if you are interested in seeing it, I could upload the schematic. Your evaluation would be much appreciated.

@lesjohnson9740 8 лет назад

Who needs to pay Mega money for a ITr. you are quite correct, interesting.. Les again.

@MrCarlsonsLab 8 лет назад

+Les Johnson Thanks Les!

@barbara217 6 лет назад

Great tool! I have to build one! THX

@Cleofizoid 2 года назад

It's my understanding that incadescent bulbs in the US may be become unobtanium soon. If I wanted to build my bench test set today (iso xfmr, variac, "dim bulb limiter") without worry of finding replacement light bulbs, what would you recommend to replace the dim bulb current limiter?

@ekbanjosworld4926 Год назад

Appliance oven light bulbs 60w three in series... That's what I'm doing...

@Kelpie26 5 лет назад

Hi Mr. Carlson, always looking forward to learning from your videos. I was wondering if the variac could be substituted with a rheostat set up as a voltage divider? I have a 500ohm 250W toroidal rheostat which I'd like to use, but I'm having second thoughts wether such a low-ohm device would just present a constant load and send the whole thing straight to brightly current limit. Any help/comment will be greatly appreciated.

@noelconway2589 2 года назад

Don't use it. A rheostat is resistive in nature while a variac is inductive.

@captainmother1268 3 года назад

Pilot light still ON after fuse blows....that is good and bad. Add second pilot lamp to show fuse is closed.

@LitchfieldCountyComputer 4 года назад

Would it be better to put the fuse before the main power switch?

@thomaslanik7215 6 лет назад

Any reason there is no line GROUND to the source?

@doogie812 5 лет назад

Dude most variacs I have used were autotransformers. They went up to 140 VAC.

@quadplay2591 5 лет назад

Add a double throw knife switch just for the looks

@voxpathfinder15r 4 года назад

Didn’t you say the two bulbs are in series? In the schematic they are in parallel

@pb7379-j2k 4 года назад

He meant the pair is in series with the rest of the circuit

@packratswhatif.3990 2 года назад

Excellent !

@jamespaterson7597 9 лет назад

Hi Mr Carlson could you please explain how I can identify the line and the neutral from the isolation transformer regards James

@MrCarlsonsLab 9 лет назад

James Paterson Hi James, the whole idea of an isolation transformer is to isolate you from that system. Line and Neutral are on the primary side of the isolation transformer. The secondary side isolates you from that (so called) polarity. (There is no connection between primary and secondary windings in a true isolation transformer) Many store bought isolation transformers carry the safety ground wire (green) through from the wall side to the secondary side outlet on the isolation transformer. One needs to keep in mind that the safety ground wire and neutral wire are tied at the breaker box in your house. Since these two wires are tied at the breaker box, there is a direct connection to neutral carried through to the secondary side outlet (by the ground wire) on some of these store bought isolation transformers. (This is not truly isolated from this stand point.)

@sethlavinder 6 лет назад

I totally need this in my shop! Where can I find a good isolation transformer? I have done similar to this on DC stuff with an old car light bulb one of the square bulbs like in an old pickup truck. The bulb would catch me if I screwed up rather than blowing parts off the project I was working on. Trick an old EE friend taught me 73 de Seth - W8FG

@rayislooking2 8 лет назад

hi, I love your Videos I learn so much. I want to build one of these can you please tell me where and which transformer to buy for this project. I only need 120v to 120v. Thanks for your time.

@BruceNitroxpro 4 года назад

Just1ofMany , Look for a medical isolation transformer, but don't USE it until you remove the ground terminal by replacing the output power socket with a two wire socket. Or, make your own by disconnecting the ground lead from the normal, polarized socket from the output side. Watch out that you don't accidentally connect different sides of the output of the transformer to two loads which might touch each other. In other words, use only ONE item at a time on the isolated winding (safest way) by only connecting one output socket. A medical grade transformer usually has lower coupling of transients because it has a very effective shield between its windings.

@ddom678 2 года назад

Great video in any event

@carlubambi5541 Год назад

Complacency is dangerous in any electrical or electronics trade .when you get too comfortable is when accidents happen .I know I survived getting a poke from 600/347 V lighting control circuit ..Let's just say it sounded like a shotgun going off by your head and being kicked by a horse

@Justin-vn8to 9 лет назад

I have a 1947/48 Brunswick BJ-6836 AM radio that use to be my grandparents that I am attempting to repair. I just got it out of the cabinet and ordered the Photofact Folder off eBay. It claims its rated at .900A @ 117V. Im far from the point of powering it on. Still need to recap it. But when I do get to that point I want to build this. Is there a ratio to the current the lightbulbs limit to the current your load can take. If the radio where to draw 900mA (I doubt that is its normal steady state current but thats the only figure I have to go off of) the bulbs would be 90% lit. I would be within the 1A current limiting but wouldn't the bulbs be dropping a significant amount of voltage preventing the radio from working?

@MrCarlsonsLab 9 лет назад

+Justin Derleth You are correct. You would need to use higher wattage bulbs, or parallel them. You can use a modern current meter to measure the line current as well.

@LitchfieldCountyComputer 4 года назад

also, what's a good source for that transformer?

@kgsalvage6306 5 лет назад

I don't know if I missed it but what is the wattage rating on the bulbs. Is there a reason that you used two?

@retrohipster994 5 лет назад

As light bulbs are really just resistive elements, using two 60-watt bulbs in parallel means that you are dropping the resistance they pose on your test circuit by half. I believe he just used two Bob's because there was Symmetry and it looked cool. Most people just use one Higher wattage bulb like a 150 or 250 watt bulb since it would pose less resistance then a lower wattage bulb like a 60 watt bulb. A 60-watt bulb would only be able to Source 500 milliamps instead of one Watt.

@NourMuhammad 5 лет назад

Come on guys, he knows what he is doing, he is very safe around 7000V so 120 V would make nothing to him, would just tickle his feet :lol

@jackallen6261 4 года назад

There is a lot of truth to that statement, I have worked industrial Maint for over 20 years and been shocked by 120 more times than I can count after a while you just get to the point where it's like "Yep, that's hot" lol. 220 hurts more and yes a single leg of 480 (277 volts) hurts a lot more, lol. I highly recommend not trying it at home, lol.

@AThreeDogNight 5 лет назад

I finally found it, thank you.

@rentacowisgoogle 3 года назад

I want to power up a 1946 radio that i just re-capped and checked all the connections with the schematic. Would it be safe enough to put it back in its case and then bring it up slowly using only a variac and no isolation transformer? So long as i don't go probing around with a voltmeter or anything. Should I use a high voltage insulated screwdriver to operate the controls, just to be extra safe?

@redemptusrenatus5336 2 года назад

I know this is a late reply but someone else might find it useful: One issue, not related to your safety, but that of the radio, is that without the current limiting (dim-bulb portion) you could still have a short that will source the maximum current available which could burn out your variac or worse still, the parts in the radio. The isolation transformer is normally for your safety when working on equipment that has no ground such as an old 1946 radio or the typical two-prong CRT TV. The isolation transformer would of course remove the connection to earth ground so that if your device's chassis is connected to the hot side of the cord, you won't get shocked if you come in contact with it. I wouldn't work on equipment without an isolation transformer, at least, not without someone around to call the paramedics and/or cut the power. As for the controls on the radio, I'd put the knobs back on if possible and be careful that way as they should be insulated unless someone decided to put metal knobs on the thing.

@rentacowisgoogle 2 года назад

Thanks and no worries! I made a dim bulb tester and brought it up slow. It works and even sounds great! It's a transformer type so unless it develops a fault, i checked and it's nicely isolated. Plus now with a modern safety cap. The knobs are all factory originals i think. bakelite with no set screws

@findleyjohn2486 8 лет назад

Hi - I use a Sencore PR57 isolation Transformer that I plug my variac into. What do you think of that procedure?? Thanks, John

@MrCarlsonsLab 8 лет назад

+Findley John Hi John, Without knowing the way it's wired (first hand) I'm reluctant to give an opinion.

@LitchfieldCountyComputer 4 года назад

do you have a schematic for this? I would like to build a safer and more compact version of this.

@klaasklapsigaar1081 4 года назад

15:00

@Skilldibop 6 лет назад

I'd probably also add voltmeters to each outlet so the voltage is easily readable rather than having to do maths :) Also getting incandescent bulbs in the UK is awkward, are there any other options you could use? I'd imagine CCFL energy saving ones won't work right.

@schsch2390 8 месяцев назад

Incandescent bulbs have a positive temperature coefficient of resistance, with ~15x increase in resistance from cold to fully lit which gives that protection in case of short circuit in the device under test which is mostly what a dim bulb source does, (ie protect against short circuits). One substitute would be a line voltage rated polyfuse.

@toltec13 8 лет назад

Greetings, I'm interested in purchasing an isolation transformer. What advice can you give me? I see some on ebay that are literally a transformer with a plug in cord on the back of the transformer and the front has the socket connection for a tube radio. I also see isolated transformer what are enclosed with an on/off switch. Do I take in consideration the amperage limitation of an isolation transformer? I work on All American Five radios as well as 10 tube radio consoles. I do have a variac and I realize I need am iso-transformer.