HOW TO USE A MULTIMETER to verify polarity and voltage

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” m joshua bardwell and you re gonna learn something today. We re back looking at at the multimeter you newbies out there new to the hobby don t know how what all this stuff does i m gonna show you another simple way that you can use a multimeter to do well to avoid making this magic smoke come out of your electronics. That s a pretty big deal right stay tuned in this video. We re going to talk about polarity and checking the polarity of your connectors polarity means that the positive comes out where the positive goes and the negative comes out where the negative goes.

When you get those two things backwards. The smoke comes out okay. If you ve ever accidentally wired up an esc backwards. Raise your hand everybody has done that yeah.

I ve done it too then you know and you you cannot apply reverse voltage really for any time at all without smoking things and any time you do something like this like what i ve done here is i put it this is a field charging pack. I m gonna use it to charge batteries in the field and just for funds. I put a fuse on the lappet lead how about that that s the topic of another video. I suppose.

But um. I m just gonna make sure i didn t screw anything up now as i told you in the previous video the very first step to anything like this is a physical inspection. Okay make sure that the red wire goes to the red wire goes to the red wire goes to the positive. And if you re not sure about an xt60 pull out a factory battery.

Although as i pointed out factory batteries aren t 100 guaranteed to be right. But pull out something you know is right and you can see here that the flat side of the xt60 is the red wire and the angled side of the xt60 is the black wire. We can also see it s a it s imprinted on the xt60 here. I m not gonna zoom in and show you.

But you take my word for it plus and minus. So we can take a connector. We know is correct we can plug it in and see black to black red to red. We haven t crossed our wires by accident anywhere once you ve done the basic physical inspection then we get to the multimeter now.

I m gonna put this in volts mode. You can t really put it in a continuity mode. When you have an energized circuit. So anytime.

There s an energized circuit the continuity mode is not going to work and of course. The battery is always energized what we re gonna do here though is we re going to measure voltage. So you can see here that i ve got the black wire and the red wire..


And what i m going to do is i m gonna put the black probe where the black where the negative is supposed to be i m gonna put the red probe. Where the positive is supposed to be and when i do that if everything is. Correct i should see a positive voltage 191. Volts and that means the polarity is correct when black goes to negative and red goes to positive and i see a positive voltage here that means the polarity is correct if and i m gonna reverse these but if i put black to negative and red to positive and i saw a negative voltage like so see negative nineteen point one that would mean my polarity was incorrect real quick.

I m gonna take a side trip here and just point out to you when i whenever i stick probes into things my partner gets nervous that didn t sound right whenever she sees me stick my probes into hole. I m gonna have to start over people get really nervous when they see you sticking probes into the electrical outlets and all this stuff. There s not dangerous right this the the multimeter is designed to for it to be safe to do that but you re going to want to avoid doing things like if i m sticking this in here. I don t want to accidentally short these two terminals and of course.

They re designed so that it s very difficult to short them with a straight probe. You see this little see this little tab right here. That little tab right. There.

The sticking out that is so that if i were to lay a probe across i couldn t touch both of them at the same time go get a little teeter totter action. That s a safety feature and that s very important all right so it s in this is intentionally designed to make it very hard for you to accidentally short these two. But one way you could short. It is let s say i ve got this and it s just bit let s let s try that again let s say i ve got this probe.

And it s just barely hanging on here and then i come in with this other probe and i like across the streams right no cross the streams right you don t want that if i were to cross those probes. I could i could short it and and make some sparks fly and maybe even make my battery light on fire. So beep careful when you re working not to accidentally short the probes. You just be careful fully insert the probe.

So that there s not any exposed metal for example. And then insert the other probe and just just be careful not to short. Too bad. Bad news if that happens now this is a common 55 millimeter by 21 millimeter barrel plug.

It s probably. The most common kind of barrel plug that you re going to encounter in this hobby five point five millimeter refers to the diameter of the outside and two point one millimeter refers to the diameter of the pin. That goes in the center. Another common size is five point five by two point five.

Which is the same outer diameter. But a bigger pin a thicker pin and and when you ve got something like this you might be in a situation. Where you don t know the voltage..


That it s putting out right well in my case. I have so many of these things i label them so i can just know what i m doing. But let s say you didn t have that in general with these barrel jacks or barrel plugs and and really any any plug like this the outside part is usually negative or ground and the inside part is usually positive and that reason for that is that positive if you have positive and it finds the ground somewhere else in the house somehow you can get current flow. When you don t want it so by putting like keeping the positive.

Which is the sort of more risky part on the inside. It makes it a little safer also notice that we ve got this plastic protective. Part here to again prevent you from ever accidentally touching the inside. And the outside and shorting ground to positive by accident.

Unlike with a lipo. Though if i short this the worst thing that i m going to happen is i m gonna burn out the little dc the wall wart which isn t the end of the world we re going to assume that the outside is ground. We re gonna touch ground to the outside we re going to assume that the inside is positive. We re gonna stick the red one on the inside and twelve point one six volts because i get a positive number here it means that i am correct the outside is ground and the inside is positive.

Twelve point one six volts great what if you got an oddball like this what is this this is the charging adapter for my lenovo laptop and it is a weird one. But it s not too different from the barrel plug that i just showed you let s assume that the outside is ground okay. And if you look on the inside. If you look very carefully you can see there s a pin in there um.

It s a little might be hard for you to see. But there s also metal on the inside of the sidewall. So we got something a little strange here and it s it s we kind of got a wonder what s what in there is normally. I would expect that the center pin would be positive and the outside would be negative.

But if i try to test that by the way this is live so i m gonna be real careful. When i m sticking my probes in here not to touch. But one metal thing at a time so for example this little the sidewall has a little bit of metal on it and i ve got this pin in the center. I m being real careful not to touch those at the same time in case.

One is ground and one is positive. I would short it and you can see we ve got this yellow plastic here which is designed to prevent you from touching two things at once so i m just gonna go in and i m gonna touch that pin very carefully and the multimeter is gonna read zero volts now since there s zero volts between them that suggests that they are both they should both have continuity. But it will tell you that when i run this continuity test. I do not get continuity between them.

And what that tells me is that they re both grounded. But for some reason. We can t get current flow between them that s kind of weird..


I m not really sure maybe. There s a diode that only lets electricity go one way and not the other i really don t know. But we can say for sure that that center pin is not positive. So it must mean then that this metal on the side wall is positive again.

I m going to test that by touching the outside with black which i presume to be negative ground. I m touching the inside to the side wall. I m gonna be careful not to touch the pin again just in case. The pin is grounded.

I don t want to short it. But i m going to come in from the side and twenty point two volts okay so i got twenty two point two volts between the outside and the side wall on the inside. Frankly i think it s really unlikely that this center pin is grounded and the reason for that is that it would be really poor designed to put ground and positive so close together with nothing in between them. If anything were to bend or break this pin sideways.

We would have a short and it would destroy the power supply. So i think that pin is there for support for just physical support maybe it definitely has zero volts to ground. But it doesn t actually have any ability for current to flow so maybe again maybe there s a diode or something protecting it i really don t know exactly what the reason is for the design. But we ve verified then where ground is and where positive is positive on the inside sidewall ground is here.

What i ve got is this now. This is an xt 62. Lenovo adapter and what i m gonna use that for is this is a 5s battery. If you do the math on 5s you ll see it goes from about 21 volts down to about 18 in change.

That s within the safe range that lenovo adapter put out twenty point five volts dad s i can charge my laptop up off of this thing when i m out and doing a site survey of them so that s why i built this so let s do our little tests and checks on this adapter. Now. Let s let s just set aside. I ve done let s presume that i ve done the physical inspection already so i should have continuity from negative to the outside right.

So let s do our continuity test first remember that i remember that negative is the the vent one and positive is the flat one i could double check that if i wasn t sure when doing continuity it usually doesn t matter whether you re using red or black. Which one goes where usually if electricity flows one way it ll flow the other way so i m gonna touch a negative pin here. I m gonna touch the outside there bingo got it yes continuity that s what one just for funds. Let s touch.

The touch that inner pin and see if there s continuity. There as well. I don t think there is yeah so weird zero volts between them..


But no continuity does it and i know there s not a diode in here this is just there s no dots or a diode in the connector. If there was a diode then i would get a beep d. One way. But not the other let s try that and see if anything happens no i don t get a beep either way i cannot figure out what s going on with that pin how can you have no continuity.

But zero volts. I don t really know joshua from the future here while editing this video. I think i did figure out what i m overlooking here. What i did wrong with my multimeter that caused me to get what seemed like a bogus result.

I m not gonna tell you the answer because it s not really relevant to this video. And it would require a lot more explanation to then this video calls for and also if i don t give you the answer then those of you who can figure it out for yourself will get to feel super smart and clever and and have a great day and smile and be nice as a result so if you think you know the answer put it down in the comments and if you don t know the answer don t worry it doesn t really freakin matter. So now we ll check positive. I ll touch the positive pin.

And i ll touch the side wall of lenovo connector on the inside. So okay. So this is wired up correctly and then the next thing i ll check is i ll check up we ll go ahead and i ll plug it into the battery. And i want to check that the voltage that i see here is the same as the voltage that i saw from the factory adapter and i m gonna double check that like five times because if i screw this up and i plug this into my computer boom.

I destroy well is probably repairable. But jake s bad news right so negative on the outside we re gonna go to dc volts negative on the outside positive to the side wall and nineteen point two volts see black to where i think negative is red to where i think positive is i see a positive voltage that means i ve done it right and in fact i can tell you i have plugged this into my computer. And the magic smoke did not come out we there you go. That s gonna bring us to the end of this one that is how you check the the polarity of a connector sure.

But also if you re gonna build your own connectors or adapters that is how you verify what the polarity and the voltage. And the pin out of the the connector is and that it s a very basic thing get yourself a handful of this kind of thing. This is five point five by two point went one millimeter. But pigtailed.

I guess you could call it get yourself a handful of these and you can just make whatever your world is your oyster. So next t 60 s. Etc. Just make up any kind of adapters you want there you go thanks.

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