Build a Simple Current Limiter for Protecting Your Electronics Projects

[Music] hey everyone i'm working on building this little guitar tube amp and i needed a way of testing it without letting it go boom boom so i decided to make a current limiter and i'm going to show you how it works and how to build one so why do we need a current limiter well in this case with a hand wired guitar amp build a lot of things can go wrong mainly we're testing for a bad wiring job i could have wired the power transformer wrong or the output tube wrong anything that would cause potentially a dead short on the primary side or the secondary side of the power transformer with any good electrical project it's important to have four main things something old something new something borrowed and something there are other ways that i could test this other than a current limiter in this case i have a variac that i built a few years ago it has a built-in voltage and current meter and i could plug in the guitar amp and slowly raise up the voltage here just monitoring the current to make sure that we're not drawing uh more current than we would expect to be for such low voltages this is a much more expensive option the current limiter is cheap and easy to make and it's going to serve our purposes just fine one quick disclaimer i am not an electrician i do have an electronics degree um but not the same as being a licensed electrician so if you do want to work on this project please do so at your own risk so let's take a look at a typical circuit so we have um our source which in this case is going to be a plug that we're going to plug into another outlet in our wall um normally this would be connected to a circuit breaker in your circuit panel uh you know with the conduit going to your uh going to an outlet in the wall um in our case here just going to be using a plug so a typical circuit is this any of the loads here would be in parallel um so they happen to be terminated uh through this receptacle so hot gets uh passed through uh this junction here and goes up to our load in this case a light bulb so anything here being plugged into this receptacle would be acting as a load as well as the light itself and we have a switch here which is in series with the light so if we close the switch current is allowed to flow through the lights if we open it current can't flow so our circuit's going to be a little bit different we have a source plugged into an outlet same as the other one the difference here is our load is going to be the receptacle and the light bulb is going to be in series with our load so over here if you ignore the switch the the light bulb and the receptacle are both getting uh 120 volts through the hot neutral um they're both in parallel in our case here our light bulb is going to be in series with not only the switch but also whatever is plugged into the receptacle so if you can imagine we have electricity coming in uh it's current is going to be flowing through the hot through the switch through the light bulb and through the the hot terminal on our receptacle through our device whatever's plugged in completing the circuit back to the the neutral side and then um going back to the source so everything here will be in series with uh each other instead of in this case in parallel so what this allows us to do is um when when we have current flowing through this circuit it's never going to be more than the current that is allowed to flow through that light bulb so in this case i'm going to be using a 40 watt light bulb and uh so we're going to be limited by the amount of current that can flow through this circuit um by whatever that 40 watt light bulb wants to draw so we're no matter what we plug into here we're never gonna get more current flowing through this circuit than what normally would be flowing through this 40 watt light bulb so we can use ohm's law here to figure out what the max current would be through our circuit with a 40 watt light bulb so we can use this equation which is watts is equal to volts times amps and if we set our equation where we have 40 watt bulb um equal to the 120 volts coming from our outlet and then we have to solve for current so if we divide both sides by 120 volts that leaves us with current is equal to 40 watts divided by 120 volts which gives us current uh the max current that could flow through this circuit um with our ideal light bulb here is .33 amps or 330 milliamps so i'm going to start with two used junction boxes obviously you can go buy new ones these i probably ripped out of a friend's house while helping them or i don't know maybe my own house who knows who knows really we have no idea these probably never existed at all but in this case i'm going to have one for my light switch and my outlet and the other for my light itself so i'm going to first join these two together with one of these couplings you see when i put my light switch in here i don't really have a lot of clearance so i've got the nut backed pretty far all the way to one side so that as i put it in here there's just enough to get the other side of the nut on and we still have enough clearance once i tighten down those those terminals [Music] the next thing i'm going to do is wire up the light socket so the probably easiest thing to do is just cut a section of wire wire it up and run it through and then we'll terminate everything on this side for the light switch but i got this mud ring here and i'm gonna basically just use this to raise up the the light socket as well as uh allow me to kind of clear this other switch plate here it's gonna make it a little bit easier so i gotta knock these inner screws out and then we should be good to go [Music] do do [Music] do [Music] do [Music] [Music] do [Music] do [Music] do [Music] do [Music] so let's take a closer look at how this is wired we have our neutral coming from our power cord that's going to the neutral side of the receptacle the other side of the power cord the hot is going to our switch so that switch is going to deliver voltage from here across the switch when it's turned on through into our light bulb through our light bulb and then back what would be this neutral wire into the positive side of our receptacle so that's how we're completing our [Music] circuit [Music] do [Music] do [Music] honestly the hardest part about this whole build is finding an incandescent light bulb uh in 2020 uh these things are pretty much extinct i think they might even be illegal so uh if you're gonna do this probably don't post a youtube video advocating illegal incandescent light bulbs in the year 2020. in all seriousness i did find this light bulb at the specialty section of my hardware store under appliance bulbs so this would be something that would go in like a range hood apparently led technology hasn't gotten that far yet i've got this plugged in and theoretically if we wired it correctly turning this on will not do anything the light bulb should stay off because there's nothing in series with it here to complete the circuit the next thing we can do is we can test it by shorting across the hot neutral here so all this should do is complete our circuit uh because this outlet is in series with our light bulb so it is unplugged from the wall don't do this while it's plugged in [Music] okay we're plugged back in we've got the receptacle shorted and now if i flip the switch it should be simply just a regular light bulb all right so let me talk about the setup i've got my amplifier plugged into the current limiter it's currently turned off as well as my amplifier i also have a dummy 8 ohm load here in lieu of a speaker so what i'm going to do is turn on my current limiter completing the circuit from power here through the light bulb through the amplifier and then i can turn on my amp so what we should expect to see is hopefully something uneventful maybe a little glow here through the light bulb but certainly not any full brightness coming out of that thing so i'm going to turn on the amp and let's see what happens this was super easy to build and could potentially save you a big headache having to rewire something that you just put together if you got any value out of this uh please consider leaving a like otherwise leave a question or comment down below um and uh keep an eye out hopefully i'll be making some project videos here soon and uh yeah [Music] you

Channel: nickheartrobots

Views: 21,030

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Id: NoqivJhQhU8

Length: 15min 4sec (904 seconds)

Published: Wed Jul 15 2020