Build a Simple Current Limiter for Protecting Your Electronics Projects

I'm working on electronics project (tube amp) and I needed a way to protect and test the circuit before plugging it directly into power. So, I built a current limiter with some simple off the shelf parts. I walk you through how it works, why you might need one and how I built mine.
Also, I forget to mention in the video, this could be used for all sorts of electronic repair. Mainly situations where something might "keep blowing fuses" and you want to stop throwing fuses in the garbage just to see if you fixed it or not.
Disclaimer; this project involves wiring high voltage electrical. I am not an electrician, and you should build this at you're own risk.
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[@thelowcountry2891]

Nick, you've done the impossible: made a helpful youtube video that's not even remotely annoying. thanks for sharing your time and expertise with us.

[@douglas2lee929]

What pp

[@douglas2lee929]

That is the r u fee yrnl

[@forthwithtx5852]

On his KZbin channel, Uncle Doug recommended a higher wattage bulb, like 250w. I didn’t think about the availability of incandescent bulbs. He said you could use a floodlight, if you had difficulty finding one. Great little project I’ll be taking on today.

[@nickheartrobots]

I love Uncle Doug

[@MichaelHokefromCO]

Uncle Doug suggested a high-wattage bulb because they have less resistance (meaning more current can be pulled through). He works on some high-power amps that might pull a lot of current - but a high-watt bulb will still keep a dead short from blowing the circuit breaker. I suppose you can pick your bulb wattage to allow for anticipated current draw from your (properly functioning) device?

[@MikkoRantalainen]

@@MichaelHokefromCO Flood light burning at max brightness should be pretty easy to notice, too!

[@pauldow1648]

Bulb watt rate is relative to normal watt consumption of device undertest plus some percentage extra (25 to 50 percent more ?)

[@goodun2974]

I work in an audio repair shop and the dim bulb current limiter I use has a 150 W bulb in it. This is general sufficient for most repairs and testing, ranging from a stereo 30 W solid state receiver or 30 to 40 Watt guitar amp (mono) up to a 150 watt stereo power amp. On very rare occasion I might change it to a 100 W bulb for a smaller device or a 200 W bulb for a professional high power amplifier. The lamp socket is mounted on top of my variable which also has a (current) ammeter and a voltmeter built-in, as well as a bypass switch for the bulb.

[@howardtaylor229]

GREAT VIDEO! I can't tell you how many videos I have seen about this but the videographer shows a cartoon drawing of how to do it IF they show you at all! You are the first person I have seen who actually SHOWS the real world example. You just got a new subscriber! Thanks.

[@SDsailor7]

Do you know why he cut that tab in between the two screws?

[@TheBozn]

Just an Fyi for people who are curious, U=I*R is ohm's law and for AC we mostly use U=I*Z(impedance) where Z=√(R^2+(Xl-Xc)^2) , (X = Reactance). P=U*I is generally only accurate for DC circuits and AC circuits with purely resistive loads. As soon as you have capacitive or inductive loads (like transformers or motors) you get apparent power 'S' with the equation (U*I=S) and you have to compensate for the phase angle to get the true power 'P' (P=U*I*cos v)

[@Toobzilla]

great tutorial. need to say thanks for the help, i built one today. i would however suggest that you explain your task @ 9:17- 9:21. i used the same switch/outlet combo but the the terminals are black screws on the rh side & and silver/copper colored on the lh side like yours, i thought "whatever hes doing must not apply to my outlet". i now know theres a commonizing tab between the two rh side terminals ( the one being removed @9:17-9:20).. i learned if you dont remove the tab, when you throw the switch in test mode your current limiter becomes a current remover, instantly. lol

[@devcybiko]

I'm doing smaller voltage circuits (3,3m 5, 12V) so my bulbs will be lower wattage - so the formula you gave really helps me out. Nicely done.

[@Desert-edDave]

While I do not have an electronics degree, I do understand the value of containing the magic smoke. ;) Great vid explaining simple current limiting to potentially protect projects, I liked the simple explanation of how the bulb in series limits the current for the remainder of the circuit.

[@Carlos-fu5bt]

Nicely done! Thank you! Very helpful. : )

[@MichaelHokefromCO]

BTW, thanks for posting this. I ended up building one almost exactly like yours here (I was also building a tube amp), including the same kind of box and the switch/receptacle combo. Much appreciated!

[@raymondmenard5444]

Hey man, thank you for sharing this, been looking for days to find a good tutorial on the matter that actually showed how to do the wiring. I'll admit i would not have thought of ripping the copper jointer between the 2 sections if i hadn't seen you do it. I built my own last night following along on my computer and it works as expected. I needed this Dim Bulb Tester in order to start working on restoring an 1937 Vacuum Tube radio, (RCA-Victor 87-K 7tube console), wish me luck i'll need it...

[@test-rj2vl]

Instead of hardwired lamp I made mine with just 2 sockets in series. That way I have unlimited customization options. For example I can add power strip and plug in combination of different bulbs. Or electric kettle if I want bigger limits. I also added volt-amp-watt meter to both sockets. And the switch on my enclosure cuts both neutral and and live so that it does not matter which way I plug it in, I can always be sure that off means off (I live in europe where you can plug AC wall sockets with any polarity).

[@ekbanjosworld4926]

Nice build on the amp ! 👍 I'm getting ready to build a combo isolation transformer/variac/DBT. I'm gonna run 3X 40w bulbs parallel in series with the switch. The last two bulbs on toggle switches to keep from having to screw in bulbs. Good video ! Now do one showing that awesome variac you built !😊

[@thesongtowoody]

Nick, thanks for the video. Excellent. Can i make a few observations? helpful criticisms? maybe? ok. So, I blew two house fuses! The bit where you snip the hot and neutral on the one side with pliers, the video speed is speeded up and its there but i thought you could have highlighted the great importance of this step either in words on and in the video or at some point verbally in the video. It went by so fast i hadnt noticed it? secondly, for inept electrical persons like me and to folk who are brand new, if there is a problem with the device you are testing the bulb will glow "bright" ! this might seem simple or obvious, but it wasnt to me, who am brand new to this whole diy tool. No one told me what good or bad should look like. I thought you could have included this too. great video. Kind regards. woody.

[@josephnavarro3620]

Great video I hope more people get a chance to see it!

[@santiagomoreno696]

Thanks, I just built one and your diagram was useful.

[@07standard]

Good morning Nick. Thank you for sharing the video. Please let me know in the series connection what wire needs to be cut off from the receptacle.

[@georgeschaefer3712]

Nick! Thanks very much for your help! Great instruction.

[@uptownphotography]

Well done and very well explained. Thanks for doing it. Phil NYC Area

[@WorksbySolo]

Good job! You’re a natural! Nice clean video and audio. Clear instruction, with some well played humor. Looking forward to seeing more of your projects.

[@nickheartrobots]

Thank you. That means a lot coming from you!

[@markjohnson8645]

Agreed!

[@benjamintmehaffey]

Hey Nick. Great tutorial, id love to see how you built your isolation transformer! Thanks

[@gladstonefuller953]

Hi, thank you for this video! I am a hobbyist and I think your work is very neat and inspiring to me. I have subscribed and of course, I gave a like. I will be searching for more of your videos. Regards!

[@TheStimpy60]

Nice, thanks. I watch a lot of Uncle Doug and love his stuff. I had gathered everything to build his when I found yours, which is a bit neater and better enclosed, so I will do something more like this. That dang music tho, gonna be stuck in my head for a while now 😆

[@tagztv1970]

Great idea thanks for sharing sir

[@frankstone919]

Even with a Variac using a limiter in between the Variac and the amp is not bad idea. A safe way to test the limiter , plug a lamp into the outlet with a higher wattage bulb. A 250 watt heat lamp bulb , will make my 100 watt limiter bulb shine pretty bright. I was using the 250 watt heat lamp bulb in the limiter for bigger amps. A couple amps I have built will make that heat lamp glow a little bit but , you have to look at it dead on. Reflector bulbs are not the best but , if that's all you can get.

[@AlejandroGomez-yx1sg]

Great vide and explanation! Thanks.

[@ShopperPlug]

Excellent explanation

[@juanmf]

came here looking for a chocke coil but still good info LOL

[@hksunchaser1]

Good work!

[@nirolfaciram]

Thank you!

[@thorinbane]

Thanks very useful. Mine worked but the bulb doesn't glow when I first turn on the amp. It is a 100 watt bulb though. It does turn on when I short it out.

[@blackforestgifts]

Good Job will wait for more.

[@hughbetcha436]

Thanks bro!

[@cmguitar50]

Nice video, good music. Call me paranoid, but I'd have a ground to one of the boxes :) This Old Tony - great stuff, too! I like the variac - do you have plans?

[@EddieLeeFunn]

Ohm's law is E=IR, what you are showing is what I like to call Watts' Conundrum! ;)

[@danc2014]

Appliance like ovens and fridges work best with the old bulbs but tend to be 40 W. I have seen the Dollar store also sells leftover bulbs 75W up. An alternate solution may be to wire 2 bulbs in parallel. 2X 40w S = become 80W?

[@derekec]

Question. My 200W bulb will light gently on startup of course but again when I increase volume to a more substantial amount. No one talks of this - I assume it's normal as I generate more current (and voltage?) by volume knob reaching the bulb's threshold. But I don't really know and now I'm afraid to run my amp. Help?

[@michaelureste2763]

Yes sir

[@manujasiriwardhana]

I need to test my new fan motor. If I install this part, can I protect my motor even if a short circuit happens?

[@shabazan]

Not sure if this applies... I'm charging a battery (EcoFlow 1260) with an ALP 1000 (800w continuous) 120V generator. The generator overloads & recycles when the EF 'requests' more than 1000w. It tops out at >1000w if on standard house current. If I use a 500w bulb, can this device limit the wattage to the battery to 500 watts? Thus not overloading the generator.

[@Softwaremaker]

This should work the same as well if we use the neutral wire passing through the lamp instead of the hot live wire right ?

[@nickheartrobots]

Yep! Should work exactly the same. Because its an AC circuit it doesn't matter which side you put the lamp or switch on.

[@greanjeans31]

Why is it OK if the bulb lights at all when you turn the amp on?

[@jakeblanton6853]

Depending upon the power being used by the device you plug into the outlet, it is possible that you might get a bit of a light from the bulb. You could easily illustrate this by using another incandescent bulb to replace the tube amp as the "load:... If you use a low wattage bulb as the "load", the current limiter bulb will either not be lit or be dimmer than if you used a high wattage bulb as the "load".

[@stevepatin9540]

Why does the radio turn on and off with the switch ?

[@morganwheeler7417]

Luv it.

[@stevepatin9540]

Hey...I need help...Can you help me

[@c_b5060]

Those few bars of music were real nice at first. But after about the tenth time through, the repetition became annoying. It was like listening to a kid's toy playing the same simple few notes over and over and over and over and over. (If the music volume level was lower, that might not be the case.) But I did give you a thumbs up.

[@nickheartrobots]

I agree!

[@josephnavarro3620]

​​@@nickheartrobotsI hope this idiot isn't the reason you haven't made more videos.. I bet his videos are awesome since he's such an expert 😂😂😂. Anyway I was wondering why this video didn't have more views because it's good, and it's because you've only put out one video. You're good at this. Put out some more videos and you'll see. Maybe show your tools and bench setup. You have a lot of information to share with people.

[@thebighat99]

You need to GROUND those metal boxes . if not and a fault happens and bare wire hits the box you touch it and its goodnight Irene.

[@jwingo7257]

Yup, place a pigtail wire attached to a green grounding screw to one of the holes already in each metal box (designed for this) on each box and use a wire nut to then connect the green ground wire and pigtail wire along with another pigtail wire with a Shepard’s hook to the outlet/switch device. The same goes for the 4x4 metal box and mud plate housing the lamp.

[@AudioNote]

Please hurry up and update the video of autotransformer

[@rul1175]

You should ground those boxes or u will get a nasty surprise. Two ground screw and u will get good.

[@kaybhee6]

isnt this a 0.5A big fuse

[@nickheartrobots]

It's not just a fuse, but I can see why you'd make that association. A fuse is rated to blow or create an open circuit at a specific current and has very low resistance. A PTC fuse will heat up and then the resistance will effectively go to infinity. A light bulb has an impedance and as your circuit draws more current the light bulb's impedance goes up until it effectively hits an equilibrium thus limiting the current flow, not creating an open circuit.

[@qddk9545]

Eh, eh, eh, and then we will, eh, eh, eh, finding eh, ah, eh. Yes, very annoying.