Voltage Drop, Do We Really Need To Know It!?

welcome back to the cell phone Auto Channel now that's a 2008/9 Hemi Dodge Ram 2500 with the big 6 7 in it customer complaint is it will not crank they replace both batteries and put a new starter in it and it still won't crank what it does is when you get a stick shift put a neutral push on the clutch go to start it the starter in gauges one time the engine rolls about you know up on a compression stroke on one cylinder and then it you know kicks back out and you can continually do that just you know like that that's all it does to me immediately Ralph the bat that tells me voltage drop somewheres being that the batteries are new the starters new what I've done to get it inside cuz obviously I don't want to push it I went underneath I unplugged the starter solenoid I put a jumper wire on it turn the key on jumped it across very positive cranked over it sounded like it was cranking slow to me and then I you know started up drove it inside that's as far as I've got I've printed this off a wiring diagram for the starter circuit first thing we need to do is see you know is there voltage drop a lot of potential for voltage drop in these I did another video on a I think it was a 550 we worked on a Ford that had an dual battery setup and I think it had a bad ground wire on the frame same type of symptom wouldn't crank over I believe the truck ran I can't remember the particulars but got a lot of slack in that video people saying that they would have taken jumper cables and jump from here there you know from the battery to the frame and you know stuff like that I like to use a meter lots of different ways you can do it you can do it with jumper cables and just start guessing and you know going around and you know until you get it and then fix the problem there we're gonna use a meter always lots and lots of classes we've been to on you know voltage drop voltage drop however we don't get to put it into practice a whole lot or a lot of us don't so hopefully that is the problem on this and we get to see it first off what is voltage drop well we think of our meter the easiest way to think of your volt meter is it measures difference potential difference between this point you know between Barry paws and battery negative it's going to tell you the potential difference you know twelve point six six volts on a battery now theoretically if we go from battery negative to a perfect ground with perfect wires and perfect connection the difference between here and here shouldn't be you know zero volt or darn close to it so if we just think of our meter is that just measuring the pressure difference if you will between one point and another point so that's why we can hook our meter from battery negative to ground and you know so it's you know let's just draw our meter in here because this is one test we're gonna do we're gonna go from battery negative to this left side engine compartment so I don't know if that hooks to the block I assume it does and we're gonna we're gonna stick our meter in here this is our meter and it's gonna read our voltage difference and there are there's always voltage drop in a circuit you know what would we expect to see on this big ground circuit you know maybe I'm just you know just throwing out a figure here you know 300 millivolts or you know half of all some factors in here are connections size of the you know current carrying capability of the wire you know again connections at the battery and you also have to be mindful that you can actually have voltage drop right at the battery so let's say this is our battery post and you know around it we have you know the terminal this is my best attempt at drawing a terminal comes down you know and then of course you've got your wire that goes out and then your bolt that goes through it you could have voltage drop from that battery post to that battery terminal I had a Dodge truck in one time that's where the voltage drop was it was dropping almost 11 volts between here and there well what's that mean it means you need to take a terminal off and clean it lots of potential to problems on this you know we go from battery positive battery positive but batteries are hooked in parallel so we could have voltage drop from this battery to that battery or from the battery to the starter from the starter to the engine block or from the ground side of the battery's negative side the battery to wherever these ground connections are G 100 G 111 so lots of different potentials we're going to check the easiest ones first and take it from there but hopefully that kind of sums up to you guys what voltage drop is so give you an idea here's where everything looks like there's batteries I do see some green Krusty's growing right there and this cable is the cable that runs over to this battery and according to our diagram if our diagrams right we've got this ground that goes from the battery to something I don't know if it's injured blackened to frame and then you know from battery to frame then from frame the engine block I'm not 100% sure we're not really concerned with it right now then we have the positive battery here I don't know where this goes looks like something new they added on perhaps I think the air intake heaters down there we've got a wire here that runs to the alternator we're not super concerned with that at this point but I believe this battery cable comes around goes here or around town and then just up to this battery and it you know provides it just with with more cranking amperage and of course then we have our ground on this side which goes to you know either the frame or the engine block not sure yet at this point so that's that also I hooked us up a push button start the battery sound I mean it sounds like the cranks low to me first thing first we should do is check battery voltage technically before we're chasing down any starter circuit problems we should have fully charged batteries which they're new but it has voltage drop problems perhaps it has affected you know the way it charges also so we're just gonna go to the digital meter here let's settle it up on 20 volts and then we'll go through what's going on here we had 20 volts we are so we will see what our batteries are at currently we have 12.5 so we're close enough there let me just for grins and giggles here I'll run over I'll throw these leaves on your other battery just to see should be the same together here where do we at 12.15 technically they should be the same however if we do have a cardi connection from battery the battery we are gonna get our symptoms plus voltage differences let's just check this one again I'm checking right on the terminals you got 12.5 I need to squid sheets around because I'm gonna keep getting confused here so that is a clue in and of itself first of all to drop we can do pick your poison we can go voltage drop from negative battery to engine block where the starter is actually mounted technically we should be going from the center post on the battery not the cable with actual battery itself this is where the pixies start right to the starter case not the engine block because we could have a poor ground from the starter case to the black or we could have a poor connection between like i say the center of the battery stud and the actual cable itself so you know i'll typically start kind of broader picture will go a center center of battery stuck to engine block if you know voltage drop looks good there now i'll kind of disregard it for the time being and if i'm not finding anything yeah then i'll cron or anything go to the starter case typically you should work out and then work your way in so let's say we had three volts of voltage drop from battery negative to the starter case well now we're gonna go from battery negative to the engine block still have your voltage drop then we're gonna go from battery center battery post to actual cable so you can start any way you want most of tests are pretty quick being that we have battery voltage differential here i think the smartest thing to do in this case is to go from battery positive to battery positive just to check we got to start somewhere so that's where we're going to start and again i am going to start i'm gonna try to start in the center of the battery post if i can hopefully these are kind of shuffle enough to poke in there doesn't matter which one you use let's see if we can't do that see if we can't get that to balance in there and I'll get this one tossed over to the other side and we will go right to battery positive over there also so battery positives a battery positive I'll see if I can't get this poked in knocking our wires off here think oops try to get a good connection here for us they say resist the urge to go on actual cables and look at that so that's our difference just from battery the battery so hopefully that helps explain that we already have 300 millivolts of voltage drop from battery to battery just because of the difference in you know state of charge of the batteries so now when we crank it let's take and put this on a graph because sometimes that help represents it helps represent it a little bit better here let's see let me just change our scale let's go ten volts in case it's really bad we'll bring 20 seconds across the screen I actually will keep it out in 10 okay so now we're gonna crank it we're at point 3 volts difference because we're just measuring pressure differential or voltage differential between the two batteries butter screen refresh here and we'll crank it I don't know if you guys could see it but that was almost 4 volts that's pretty big I tell you what let's take and put this back just in digital those help us see it a little better so now we're almost at half a volt difference I'm gonna go ahead and crank it because you have to check that's the other thing with voltage drop there has to be current draw no current flow no voltage drop so our current consumer is starting motor so right there we have four volts difference between the two batteries being that we have croch and over here I'm gonna assume it's right there so let's grab our meter lead from over here tell you what we're gonna hook that this is we're gonna hook that right to that battery cable just for grins and giggles now let's see if we have the same voltage drop we have four volts so we got the same differential there and this is gonna eliminate our cable if our voltage drop is the same from here from this battery cable to that center post then we know our connection there is wow it doesn't eliminate that connection does it yes so let's see if our voltage drop is the same actually got a little works alright well yeah some days better be lucky than good right now we have a problem we have voltage drop from this cable to that center post on the battery so before we even get any further doing any more test we're gonna take this off we're gonna clean it up try to resolve the voltage drop on the positive side and then see I mean that may be our only problem I don't know a lot of you guys are pretty technical probably called me out on it technically we should have taken a voltage drop measurement also from this cable to this outer terminal because that would tell us definitively you know because potentially we could have a problem from this terminal to the battery's center post we can add a great connection from here to here which I highly doubt this based on the looks of it but technically to chase it out further to determine is it this connection or is it from the terminal to here that's at a certain point it gets kind of redundant because it only takes you know a few extra seconds to just you know take care of both connections while you're in here which is what I'm do I've got this cable off I did not hook the other battery but you can see how crappy this is this should have been cleaned up when they put new batteries and perhaps it would have solved all their problems and perhaps it was the original problem I'm gonna work on I gotta grab this a pair of vise grips we're gonna take this battery bowl out we're going to clean up this positive connection we're gonna clean this up I'm gonna leave the rest of the stuff as cruddy as it is just so we can see was this our only problem and yes I know visual inspection we have to pull out a meter chances are this is our problem but I like for you guys to see what voltage drop looks like you know let's say these connections look beautiful and you're like oh yeah I know it's not my battery connections they look good they look clean well how can we tell for sure where's our voltage drop play well the only way to do it this actually put it into practice so the battery terminal has been removed I cleaned inside the terminal I cleaned the post use the wizard wheel we cleaned off the copper lug from that battery over to this battery everything has been put back now of course it took the bolt out we clean that off so you got to have super clean connections fresh lead you know clean LED against LED you know let oxide can sometimes have voltage drop you know as I've mentioned sound like a broken record but right from the terminal to that post it seems ridiculous but it can so now we're gonna rerun the same test we're just gonna do it from here we're gonna hook right on to the battery cable from that battery and then we're gonna go right into the center post of this battery and we can see we have about 10 millivolts I guess we can probably change our scale because I'm assuming it's going to be a lot less go down to let's say a to bowl scale crank it 30 millivolts battery the battery and we can hear I don't know if you guys can tell but the engine cranks much much better all from just one cruddy connection battery the battery chances are I hook the terminal back to the starter this thing will start under its own power for what it's worth we can do a quick voltage drop from the negative side to the engine block just to see for example over at so we're gonna switch our lead over here the battery negative let me get my other clamp here and like I'd say technically we should be going to the starter case if you want to do this 100 percent properly it should be going to the starter case the starter is brand new I'm gonna make an assumption which I shouldn't I'm gonna assume it's clean and bolted to the block you know as it should be a huge assumption so I'm gonna go right hook right here - what's like where the EGR used to be something to the center battery stud and you can see we're about 30 millivolts let's crank it our voltage drop there is fine we can also go from negative battery to negative battery based on just the way it sounds I'm sure we have this vehicle fit that's just I'm gonna crawl on in there we're gonna hook the starter back up the way it should be let's start under its own power 258 that was mal than the old Dodge now she cranks like a chant back and say help overall some coal baby funny lights on II guess like well that's it that was easy alright folks so that's it that was the problem with this one or the biggest problem is voltage drop from battery to battery the battery over here over on the one that we fixed security connection on was eel technically the only one hooked to the starter circuit so it drew so much amperage drop voltage so low the ECM would you know kick out and that was it because these newer cars I don't know if it a lot of you guys in training you have experienced you know low voltage conditions later batteries only got 11 volts you know an old-school starter you had crank the engine slow enough and you know it fired right up with these new cars they dropped down below let's say 9 volts cranking ECM you know kicks out and that's it because they are a electronically or ECM controlled starter in a sense that that's what turns out to start a relay so I guess that's it now technically I should go through and you know voltage drop the rest of the circuit I know that's the main problem you can use voltage drop for testing any circuit with a load on it and that's what I wanted to kind of use this video to show you yeah that term rose green and crusty we couldn't took a big fat guess but I wanted to use it as an opportunity to show you you know what's voltage drop look like we always hear about it we don't often see it we get to see a lot of good stuff so I mean you can voltage drop test or you should voltage drop test you know fuel pumps I mean if you got dim headlights you know anytime on any video where we found you know Chrysler with a bad ground yeah well we'll load the circuit grounds missing if we did a voltage drop test it would be you know whatever battery voltages because the difference between this point and that point is going to be you know your voltage drop so think of your meter as a pressure tester how much pressure do I have here and how much do I have here and you know it depends on the circuit you're testing ball the voltage should be consumed across the load so do some look and do some research on it and you know use that method but always remember that you cannot voltage drop test a circuit unless it's loaded you know example the starter motors cranking if your voltage drop testing the alternator circuit you know the thing has to be on it has to be charging you're gonna check the difference between that all day our battery all dater positive and the battery positive what's the difference is there some corrosion we've done some videos on that I think it was a Ford Ford Explorer that we did where there was you know several volts of voltage drop from the alternator to the battery positive all mater's putting out 14 volts batteries only has you know 12.2 or whatever the case was it can be caused from corrosion under sized wires that can't carry current and there are voltage drops that are acceptable anytime there's a connection anytime there's a relay there's gonna be some loss of voltage across those contacts so keep that in mind do a little research you'll find out what is acceptable or do some testing on circuits that don't have problems and you'll see you know kind of get a good feel for it it's good to know what's good before you start trying to figure out what's bad you know a case like this you know clearly four volts is too much so anyhow go down I know it's a lot of rambling leave any questions comments or concerns in the comment box below try to answer them other folks in the cell phone auto youtube comment community can also help answer those questions and while you're down there click subscribe ring the bell all that stuff and those from our viewers if I can do it you can do it thanks for watching [Music] the other side this is where the old a rough I just wanted to do I like to say I like to keep in practice yeah I know that connection what's cruddy is it you know they just look bad or is it really bad he's up for it located over Center coat battery cable that runs backside No here that goes then take Peter which isn't even drawing current now we just this table we've got 120 millivolts the difference hey Gary there's gonna be a whole different 120 millivolts in deciding to draw I'm gonna try to get on to see all there I can do that just the island of y'all the battery terminal for 20 millivolts for t-mobile range right here my thermal imager I mean regular temperature gun because I don't have one you see the ferry itself is sixty eight point two degrees Fahrenheit back style at 146 degrees so whole distractions create resistance resistance create a hospital many times 160 degrees that could be another clue for a dog in this mess let me see nobody's back that all day when we drain to the stud on the elevator we'll see what the difference will see their total voltage drop circuit perhaps including this in the regular course side of y'all later we'll go right through the center we should have at least 100 there's our total voltage drop on that circuit - the wolf glances difference between charging 240 volts or 13.8 you start more load on that you create more heat both drop actually increases so I'll show you the other way that you can see that at might help might help you what their voltage drop - point - okay all later 40.8 hole we check the battery we're going to be about fourteen point set 14.8 there we've got over fourteen point six so we're missing that you testable Kleenex let's check the same circuit again everybody please why you're here where we were it goes music here your battery terminal and now we're down around ten the alternator riders about portifino go right onto the back of that all there now this is where there's going to be some acceptable voltage drop I'm going to assume we've got a small gauge wire from the all-day there is going to be something back doll about 70 millivolts that's perfectly acceptable I have all the loads of the vehicle turn on headlights are on lower side so if you're going to see some holes in 60 millivolts not conservative so you'll see our turning voltage of the battery to go 14 points you know small numbers now we're gonna be all there's going to be like the 14.6 beyond phone numbers somebody might ask why did why why did I chase down 120 millivolts simply because I mean that's pretty significant given what the where the voltage drop was occurring you know right there at the battery stun plus it was getting hot and I have seen in cases where you start to build heat from corrosion and the voltage drop gets worse very very quickly so keep that in mind

Channel: South Main Auto LLC

Views: 157,634

Keywords: voltage drop, voltage, voltage drop test, drop, what is voltage drop, voltage drop calculation, how to calculate voltage drop, voltage drop formula, voltage drop explained, voltage drop across resistor, voltage drop calculation in hindi, voltage drop calculation for cables, voltage drop %, voltage (literature subject), voltage drop urdu, basic voltage drop, voltage drop hindi, voltage drop in urdu, voltage drop in wire

Id: 3xjLtg3FLoA

Length: 26min 57sec (1617 seconds)

Published: Sun Nov 11 2018