As basic as this seems it's still a great reminder of how to check for a voltage drop. There are guys like me who need to be reminded once in a while because we lack day to day experience. Thanks again for taking the time to teach.
I usually forget to do this because I'm in a hurry, especially when the problem is obvious like the terminals on this one. It should be the first thing I do, in addition to checking battery state of charge.
Spot on! I rarely do voltage drop. It’s a good test and CJDR recommends that over ohms testing. I generally load test and/or ohm test my circuits. I should do more voltage drop testing.
I guess im asking randomly but does any of you know a way to log back into an instagram account? I somehow lost the account password. I would love any tricks you can give me.
I would love your input, my ex wife has a 2002 Jeep Liberty with a 3.7, on cold starts you have to crank it about 2-3 times before it eventually starts. I replaced the fuelpump, has great spark and fuel pressure. When it's warm, it starts right up. I've worked on cars all my life and I can't seem to figure this out. Any help is appreciated. Thank you. You are hands down THE BEST mechanic I've seen so far on UA-cam.
Found a lot of problems over the years using voltage drop. Important to note that it will only show up when the circuit is under load. Once again, great video Eric. Thank you!
I have a stubborn no crank no start issue and every time I get stuck I find another of your videos on the issue. 3 in total have really helped me along. Good stuff!
Thank you for making videos with electrical testing and repair. I started the automotive service program at my local community college and I am having difficulty understanding it and it frustrates me and makes me want to quit and go back to warehouse work. Watching your videos are extremely helpful, encouraging, and makes me feel at ease that I have a resource for extra information. Thank you, I really appreciate all of the videos!
Do not give up. It used to be my weakest skill too. With a lot of effort and learning from pros like. Mr O, now I can diagnose with a lot more confidence and getting good results.
I'm in an automotive electrical fundamentals class in college right now and it's nice to see what we're learning being practiced on an actual vehicle! Thanks!!
Eric - Wonderful video! I learned this a long time ago when I was in the Navy in Electronics classes. Folks - understanding voltage drops is essential to your basic knowledge in my opinion. I had this very thing happen to me Memorial Day at the lake. Went to get the truck to recover the boat and it wouldn't start. Mt voltage drop was actually the ground connection on the driver's side head. Removed the bolt put it back in - whola truck cranks and starts. I used a Fluke 77 multimeter to troubleshoot. Having that meter and voltage drop knowledge has saved me lots of money and helped me fix lots of problems. Stay safe out there !
@@Lake_Lover In 2013-14 I took two semesters at a local community college in automotive electrical and engine performance . Our teacher was a 69 year old gentlemen who served 22 years in the Air Force and 20 more years teaching electrical classes . Best teacher I had in all my years . Sadly most younger men could care less about learning this field . Very challenging and rewarding if we apply our selves to it .
@@Viper81766 Wonderful ! Like I mentioned earlier I took several electronic courses in the Navy graduating an working on top secret avionics. From there, I got bit by the computer bug back in the late 80's and early 90's. For the last 26 plus years I've been doing IT work - now at a community college in east central Illinois. My father/brother and I are all mechanically inclined too. I'm very intrigued by the marrying of auto mechanics and computers in cars managing engine and other car functions. I've been subscribed to Eric's channel for a while now having watched every video he's produced. The first being the AC repair on a 02' Taurus. The first video's that I watched that had electrical/electronic troubleshooting in them really had me thinking the Eric had been in the service and went through electronic school. About the time I was going to ask him during a "what's up Wednesday" someone else had already asked and he has not been in the service. His approach and reasoning skills are so much like mine it's scary ! LOL.
Very good info for both the pros and DYI's because understanding the DC characteristics of a car circuits is usually not well known to most wrenches and can be the hardest symptom to chase down. Your explanation was very good. Dirty connections are man's worst enemy. Thanks again.
I am retired and 71 years old. I'm teaching myself to do Auto Electrical. I have watched a lot of Electrical Videos on UA-cam. But Eric O is the best teacher that I have seen on here. Learning Voltage Drop is so important. What a great channel to watch !!
Please do more voltage drop and electrical videos! As someone who is trying to grasp electrical diagnosis I’ve been trying to soak up all knowledge I can including going to training seminars, AVI training videos etc. when you do the diagnostic videos it helps me understand what to do and what not to do so something does not go wrong. Thanks Eric!
Can't believe who ever put the new batteries in didn't clean the connections. Rule number one. Was taught that back in 1969 when going through mechanics school. You have to have clean connections throughout electrical systems.
Great demonstration here, Eric. A prime example of how voltage drop can affect any circuit. A high-amp draw circuit was the PERFECT example. What a difference in cranking RPM after ward! Could clearly hear the difference, even through the camera, across the internet, and through my speakers here. Was great to see the numbers vs. the cranking sound! 👍👍 My very first foray into this realm was with my aftermarket under-dash A/C system in my '72 El Camino, in the 110°F summer heat of Phoenix, AZ. The off/low/high switch I noticed was SUPER hot, when my finger got behind the Bakelite knob and touched the metal behind it. I could smell something burning, and the fans were real slow on high, too. Had a 5+ V drop across the switch! Wire connections were good, though - it needed a new switch (or, I could've disassembled it and cleaned inside it ... but it was all sloppy anyway). Installed the new one, and the fans blew stronger than ever. It's nice feeling 65° air when it's 114°F outside. 😁
Free tip Tuesday on a Sunday. I always spray the battery terminals of all my vehicles, atv’s, snowmobiles etc with fluid film when they are new. I live deep in the rust belt and it prevents corrosion from forming. I also spray all ground connections on the vehicle as well. Fluid film creeps into the connection and the cable strands and does a great job preventing problems. When working on someone else’s vehicle I make sure the connections are surgically clean then spray them.
I purposely searched South Main Auto Drop Testing. Thank you for sharing your knowledge. Great subject, great teacher. Thank goodness I’m not this type of mechanic having to work on vehicles with these symptoms. I believe voltage drop testing and investing in tools at this time is not necessary for me, Yet. We get our cars from dealership auction trade-ins. Occasionally public walk-in trade-ins. Either way they are picked and chosen. If an in-house loaned vehicle comes in needing voltage drop testing, I know where to come back to. The school of UA-cam, S.M.Auto. 👍🏼 👍🏼
This is good timing, my college physics 2 class is all about electricity and circuit diagrams this semester. It's cool to learn all the theory but even better to see how it applies. These videos have actually helped quite a bit in class as well as fixing my old f150, which I think is pretty cool. Keep em comin!
What great timing. My race car was running fine all day on Saturday until my 4th run, then it was dead....wouldn’t crank. Opened the battery box and found crustiest on both posts! Cleaned it up and haven’t had another issue
Got a little nervous when I caught the title of the video. Found many a bad connection using nothing more than a volt meter. Good information. Thanks for posting.
All the customer had to do was replace the alternator too and he would of had the trifecta. Good example to diagnose a problem before throwing parts at it.
Why run down a 200 mV voltage drop? Because at a modest 60 amp draw from the alternator that's 12 watts of heat on that battery post. 0.2v doesn't sound like much until you apply the current. That's like a 1 amp bulb feeding heat right into the battery plates.
I’m taking my first year heavy duty apprenticeship technical training and this video cleared up what they are trying to teach and this helped a lot with understanding voltage drop
I had what I thought was a bad starter. The battery clamps and posts looked good. But it wouldn't crank. If I had checked the voltage drop between the battery post and the terminal I would have found the problem. But like Eric said, it's better to be lucky than good. The corrosion was nearly invisible, but after cleaning the post and clamp everything worked perfectly. It'd videos like this one that made me a subscriber. Way to go Eric O!
Yay! Electrical secrets... one thing most mechanics have problems with. Ohm's Law: E=IR, or volts = amps x ohms. The more resistance, the more the voltage drops. P=EI... watts = volts x amps. Watts is what heats the connection. A volt-ohmmeter is one of the most useful things you can own.
The difference between ProMechanics and "ShadeTreeMechanics": Pros focus on the Art of the Diagnosis and ShadeTrees focus on just changing Parts. I now focus on and understand that , "The Repair is not made when you change the part. The Repair is made when you complete the Diagnosis."
And with that, Eric O. dropped the voltage and walked off the stage! Awesome video, and great examples! For as often as this gets drilled into our heads, it's not often in the real world we get to use it.
I'm with you. I use the same technique as you do.... Numbers don't lie. "jumper cables" are an in the field thing done that too. I think you did an excellent job of breaking it down makes it understandable.
Love your use of the infrared temp gauge. The more you use a temp gauge the better you get. Reflective surfaces distort infrared temp guns. As you know.
Once you understand voltage drop you've really got electrical diagnosis covered. The only thing you have to remember is that there must be current flowing during your test. Good video!
Currently learning this in class. Was having a hard time understanding voltage drop but after watching your video, I have a way better understanding of how the test works. Love your videos and keep up the good work.
You're a great teacher. I just learned how to properly do a voltage drop test and what to look out for in your videos. And learned a whole lot more. My learning has been excelled from your channel. Amazing work. And amazing craftsmanship. Thank you!
in salt water marine mechanic world we clean terminals and use corrosion grease on all connections including grounds. Road salt is the same. I am amazed how many mechanics ignore cleaning wires terminals and use greases on them. Good show
It's DAMN SAD that somebody put new batteries & left those terminals like that. JUST PLAIN LAZY IF YOU ASK ME, THANKS ERIC, VERY EDUCATIONAL AS ALWAYS. Hey you do have a remote starter, NICE, I have one from the 80"s, very nice to have, you don't have to keep running in & out to start the vehicle. As I said in an earlier vid. YOUR'E LIKE BATMAN WITH ALL THOSE WONDERFUL TOY'S.
You should work out, then work your way in. I don't know other way to find VD, but this works every time. Hey Eric, I'm glad I finally joined the club. I wasn't able to folow your videos for two long years because of my poor English, but now when that improves I know all the effort I had put into language learning, now pays off. Ivan, Paul and You are my main seminars and training sources. Although I'm professional I would be nowhere without you guys and have still much to learn. Greetings from Serbia :)
Eric, there is no question you have the knowlege here. I think you could easily be a shop teacher and instruct others as well. I realize you are doing just that with these videos, but I am specifically talking about classroom instruction at a technical school. Great video. Thanks for the time.
I work in the Refrigeration industry and work on my own vehicles. Did just this recently on one of my Ice boxes. Checking the time clock for continuity while it was still connected to the wall. Pulled the neutral wire to the timer motor and connected the meter in voltage between the neutral and the terminal on the time clock. Had voltage and I knew that the clock was still operating short of a mechanical binding in the clock. If there was no voltage then I would know there is a bad time clock winding. Another example of voltage drop in application. My final outcome on this box was the defrost wire was disconnected at a connection point. Thus causing the cooling coil to turn into an ice block.
What surprised me most about relearning ohm's law was the hyperbolic shape of the current/resistance curve for a fixed voltage. Effectively that means a nearly vertical downward slope for low resistance circuits that rely on high current. So, those high current circuits suffer a HUGE compromise of power delivery from even an ohm or two of corrosion. Minor circuits don't even notice a little extra corrosion, they work on the flat part of the graph where you need a big change in resistance to have any effect on power delivery.
Resistance is critical for automotive circuits. With just 12 volts (or 14 or so with engine running), you need 10 times as much current for a given amount of power as you would for 120 volt household electricity. That means anything that draws a significant amount of power has low resistance, and will only work if the wiring supplying it has very low resistance.
I'm surprised people question your methods, your approach is perfect! I was going to say something more but am in the middle of a huge brain fart, so you'll excuse me if I just add thanks for the video and good job as usual! I will say though, I always liked starting with the hardest first so I can ramp into easy as the day progressed..... I can't believe they went through all those steps of replacing batteries and starter and didn't clean the terminals, are they brain dead?
U should be teaching your way of explaining is the best I have seen í am an older tech in nz re training to keep up b the influence of having a family support you is great to see keep on trucking thanks for another awesome video
As someone who is still learning to work with voltage drops and electrical gremlins videos like this really help specially when you get ahold of vehicles that act crazy got an 89 mustang that tries to start and will start on its on as soon as the key hits on it just randomly quit happening still an unsolved mystery lol
As a new subscriber and a A.S.E. diesel d&r certified tech. I love the diesel tips, because even I forget the simple stuff. At the beginning my first diagnosis was a bad ground, thinking that it was a rusty frame. I've seen worse terminals on big trucks, but wow that was a lot of crud.
When I bought my brand new 1994 GMC 6.5 Diesel Suburban, 25 Years ago, about 1 year later, I had a slow crank "problem" that was developing. Like this Diesel Dodge, it too has 2 -12 volt batteries and an inter connection. I am surprised that ANY manufacturer would make a connection under the battery cable clamp clamping bolt.... just asking for trouble. GM connected the Positive Posts on the side terminal batteries together on the Left Battery Positive Post with a slightly longer bolt. Even though the Side Post batteries are quite a bit less suceptible to acid corrosion, I found that the bolt did not provide a lot of clamping force and some "Fretting Corrosion" (black areas) had built up. I installed an insulated 3/8" NF Marine Stud Connection on each inner fender within about 8" from each battery, made up a new crimped and soldered inter-connect cable and moved ALL positive connections to these terminals. New clean connections with silicone grease and torqued to about 30 Ft Pounds, then new short positive battery cables. Each Negative Connection went directly to the engine block with a smaller gauge wire to the body. The engine also has a bradded cable to the frame rail. 24 Years and 420,000 Kms later these connections are still good and the truck is going strong. I also agree...... who in their right mind installed 2 new batteries without cleaning these connections. GREAT LESSON IN BASICS!
I've heard a lot about voltage drop, but this is the first time I see it explained and demonstrated. It sure looks like a handy process to keep in mind. Thanks Eric!!
Another thing to watch out for are those lead battery terminals. Had to change a few because of voltage drop between the terminal and the cable coming out of it. Love your videos, keep em coming.
Thank you, this is the type of thing I try to tell people who want to know. You tell it very well. I'm going to use some of your expressions to improve my description.
You chased the drop because it was a detail that was just OK. And, the old saw is correct: the devil is in the details. Also, 100mV here, a 100mV there, pretty soon your 12 V circuit is 11. As usual, another great job. Thank you, Eric.
Nice job of explaining voltage drop and multimeter use....great job!! In addition, it shows how pretty simple preventative maintenance can prevent major issues......
Very well done! A resistance on the alternator output cable where it meets the battery positive will cause the alternator regulator circuit to put more voltage on the alternator field to the point that it can't maintain the desired regulated battery voltage and the connection as you showed will get hot, get more resistance and get hotter, loads then start to deplete the battery. A vehicle battery is only to start the engine, the vehicle runs on the alternator. Gotta love it.
I tell my customers all the time these meters are a potential difference device and with 10 million ohms of input impedance they will not load the circuit enough to perform voltage drop with just the meter. Like you said no current flow not voltage drop! 👍Relays can give you fits so I like to load those circuits and see my drop across the relay. Great Sunday morning video! Thanks!
All the stuff South Main Auto demonstrates / teaches is GREAT STUFF 👍😊 YOU have many , many years of PROVEN EXPERIENCE and vehicle repair knowledge and when I watch you make repairs and you say - if I can do it - you can do it - I'm STOKED 😊 Again - GREAT INSTRUCTION , I learn something from every video you make - MANY , MANY THANKS and , no doubt , if I lived near you - I would surely bring my vehicles to your shop for repair and ABSOLUTELY REST ASSURED - knowing you would repair it properly. ✌️✌️✌️
A lot of people also forget that the starter can be used as a great load to test the batteries and main wiring. I’ve seen people overlook wiring because it shows good with a resistance test and unloaded voltage test. But, when cranking the starter is usually the biggest single load. So, run the voltage drop test when cranking, or trying to and you’ll see what it does under load.
Just another outstanding video, Eric O. And, inside my head, the puzzle pieces make total sense. Thanks and please don’t stop. These videos are just like master mechanics classes. You da best!!!
258000 miles on a northern car,I thought all those northern car rusted and fell apart right after 100000 miles But love your Channel keep up the good work and yeah you might make a good teacher probably easier on that old back and more money
I've always been more prone to ohm testing a cable/connection vs volt drop. I would have been interested in seeing the resistance difference in before and after compared to your voltage drop test results. I do understand though that a circuit can show low resistance but not be capable of carrying a load or have voltage drop. Or both. Good video. Enjoy your veterans day weekend.
Oooo!!! Nice lesson, Erick!!! I wouldn't have thought voltage drop from center of post to battery clamp would be that significant, but you just proved it is. Lesson learned is a clean battery post and clamp are a must to get proper voltage to the user item ( aka starter). Thanks for sharing Erick.....
Since I don’t have all the fancy equipment you have, I would have used a ohmmeter to test for a zero ohm connection between the post and battery terminal. Since resistance causes voltage drops and also heat, I probably would have come to the same conclusion. I do however appreciate the alternative way to skin a cat. You are the best.
Back in the old days the rule was 0.1 volt drop for every foot of cable (while cranking) provided the starter isn't drawing excessive amperage. One time I diagnosed a car with a bad battery, customer said price was too high (Ford Dealership, so...) Took the car and replaced the battery, had it towed back to the Dealership mad as hell because the battery didn't fix it and we diagnosed it wrong. I went out to the car to test their new battery only to find they had not removed the plastic protector caps and installed the terminal ends over them. I removed the plastic caps and installed their battery terminals at no charge. :)
As basic as this seems it's still a great reminder of how to check for a voltage drop. There are guys like me who need to be reminded once in a while because we lack day to day experience. Thanks again for taking the time to teach.
Sooo true,me included
I usually forget to do this because I'm in a hurry, especially when the problem is obvious like the terminals on this one. It should be the first thing I do, in addition to checking battery state of charge.
Spot on! I rarely do voltage drop. It’s a good test and CJDR recommends that over ohms testing. I generally load test and/or ohm test my circuits. I should do more voltage drop testing.
I guess im asking randomly but does any of you know a way to log back into an instagram account?
I somehow lost the account password. I would love any tricks you can give me.
@Cohen Jadiel Instablaster =)
Also, my 6 year old son loves your videos, I'm glad you keep it family friendly :) "Is that what you do at your work Daddy?" "Yep, sure is bud".
😂
This is twice this video has fixed my car. Great explanation of voltage drop.
Fantastic information. Definitely saving this episode.
One of the best UA-cam channels ever. I've been watching older videos back-to-back all afternoon 👍
Not "one of",..."The best" channel.
@@FortyTwoAnswerToEverything I stand corrected 😉
I concur.
Ian Fahlman-Morgan Me too. It’s like a very satisfying “This how you do it” drug. 😂😂😂😂
@@BigDaddy_MRI exactly! I diy all my volvo "projects" and Eric does a great job of confirming my suspicions when diagnosing
Thank you Eric for all time and effort you put in your channel. Truly outstanding work. Cheers👍
I would love your input, my ex wife has a 2002 Jeep Liberty with a 3.7, on cold starts you have to crank it about 2-3 times before it eventually starts. I replaced the fuelpump, has great spark and fuel pressure. When it's warm, it starts right up. I've worked on cars all my life and I can't seem to figure this out. Any help is appreciated. Thank you. You are hands down THE BEST mechanic I've seen so far on UA-cam.
Found a lot of problems over the years using voltage drop. Important to note that it will only show up when the circuit is under load. Once again, great video Eric. Thank you!
Eric. O would make a awesome Auto Tech class instructor.
I was just thinking the same thing.
These videos are a gold mine for the guy that cares about his car and would like to work on it himself. Thanks for making them Mr. O.
I have a stubborn no crank no start issue and every time I get stuck I find another of your videos on the issue. 3 in total have really helped me along. Good stuff!
Thank you for making videos with electrical testing and repair. I started the automotive service program at my local community college and I am having difficulty understanding it and it frustrates me and makes me want to quit and go back to warehouse work. Watching your videos are extremely helpful, encouraging, and makes me feel at ease that I have a resource for extra information. Thank you, I really appreciate all of the videos!
Stay with it Severo it takes a good teacher sometimes and you may have to do your own digging on youtube to find one.
Do not give up. It used to be my weakest skill too. With a lot of effort and learning from pros like. Mr O, now I can diagnose with a lot more confidence and getting good results.
I’m currently learning voltage drop at my training for my dealership and this is such a great way for me to see a real world scenario
I'm in an automotive electrical fundamentals class in college right now and it's nice to see what we're learning being practiced on an actual vehicle! Thanks!!
Watch scanner danner, he is the electrical GOD! I'm subscribed to his premium channel and it's packed with years worth of info.
Most thorough voltage drop test I have seen on internet that I have seen. I watched the video to the end. I learned a lot. Thanks.
Eric - Wonderful video! I learned this a long time ago when I was in the Navy in Electronics classes. Folks - understanding voltage drops is essential to your basic knowledge in my opinion. I had this very thing happen to me Memorial Day at the lake. Went to get the truck to recover the boat and it wouldn't start. Mt voltage drop was actually the ground connection on the driver's side head. Removed the bolt put it back in - whola truck cranks and starts. I used a Fluke 77 multimeter to troubleshoot. Having that meter and voltage drop knowledge has saved me lots of money and helped me fix lots of problems. Stay safe out there !
Amen brother :-)
And thank you for your service 😀
@@Viper81766 thank you Robert.
@@Lake_Lover In 2013-14 I took two semesters at a local community college in automotive electrical and engine performance . Our teacher was a 69 year old gentlemen who served 22 years in the Air Force and 20 more years teaching electrical classes . Best teacher I had in all my years . Sadly most younger men could care less about learning this field . Very challenging and rewarding if we apply our selves to it .
@@Viper81766 Wonderful ! Like I mentioned earlier I took several electronic courses in the Navy graduating an working on top secret avionics. From there, I got bit by the computer bug back in the late 80's and early 90's. For the last 26 plus years I've been doing IT work - now at a community college in east central Illinois. My father/brother and I are all mechanically inclined too. I'm very intrigued by the marrying of auto mechanics and computers in cars managing engine and other car functions. I've been subscribed to Eric's channel for a while now having watched every video he's produced. The first being the AC repair on a 02' Taurus. The first video's that I watched that had electrical/electronic troubleshooting in them really had me thinking the Eric had been in the service and went through electronic school. About the time I was going to ask him during a "what's up Wednesday" someone else had already asked and he has not been in the service. His approach and reasoning skills are so much like mine it's scary ! LOL.
You can definitely hear the difference in cranking after just cleaning the one terminal & cable.
Back to the basics :)
Very good info for both the pros and DYI's because understanding the DC characteristics of a car circuits is usually not well known to most wrenches and can be the hardest symptom to chase down. Your explanation was very good. Dirty connections are man's worst enemy.
Thanks again.
Thanks for sharing real voltage drop testing diagnosing. Your passion for fixing vehicles is awesome !
I am retired and 71 years old. I'm teaching myself to do Auto Electrical. I have watched a lot of Electrical Videos on UA-cam. But Eric O is the best teacher that I have seen on here. Learning Voltage Drop is so important. What a great channel to watch !!
Please do more voltage drop and electrical videos! As someone who is trying to grasp electrical diagnosis I’ve been trying to soak up all knowledge I can including going to training seminars, AVI training videos etc. when you do the diagnostic videos it helps me understand what to do and what not to do so something does not go wrong. Thanks Eric!
Can't believe who ever put the new batteries in didn't clean the connections. Rule number one. Was taught that back in 1969 when going through mechanics school. You have to have clean connections throughout electrical systems.
Your advice saved me a $1000 repair on my corvette. Thankyou.
Great demonstration here, Eric. A prime example of how voltage drop can affect any circuit. A high-amp draw circuit was the PERFECT example. What a difference in cranking RPM after ward! Could clearly hear the difference, even through the camera, across the internet, and through my speakers here. Was great to see the numbers vs. the cranking sound! 👍👍
My very first foray into this realm was with my aftermarket under-dash A/C system in my '72 El Camino, in the 110°F summer heat of Phoenix, AZ. The off/low/high switch I noticed was SUPER hot, when my finger got behind the Bakelite knob and touched the metal behind it. I could smell something burning, and the fans were real slow on high, too. Had a 5+ V drop across the switch! Wire connections were good, though - it needed a new switch (or, I could've disassembled it and cleaned inside it ... but it was all sloppy anyway). Installed the new one, and the fans blew stronger than ever. It's nice feeling 65° air when it's 114°F outside. 😁
Free tip Tuesday on a Sunday. I always spray the battery terminals of all my vehicles, atv’s, snowmobiles etc with fluid film when they are new. I live deep in the rust belt and it prevents corrosion from forming. I also spray all ground connections on the vehicle as well. Fluid film creeps into the connection and the cable strands and does a great job preventing problems. When working on someone else’s vehicle I make sure the connections are surgically clean then spray them.
I purposely searched South Main Auto Drop Testing. Thank you for sharing your knowledge. Great subject, great teacher. Thank goodness I’m not this type of mechanic having to work on vehicles with these symptoms. I believe voltage drop testing and investing in tools at this time is not necessary for me, Yet. We get our cars from dealership auction trade-ins. Occasionally public walk-in trade-ins. Either way they are picked and chosen. If an in-house loaned vehicle comes in needing voltage drop testing, I know where to come back to. The school of UA-cam, S.M.Auto. 👍🏼 👍🏼
This is good timing, my college physics 2 class is all about electricity and circuit diagrams this semester. It's cool to learn all the theory but even better to see how it applies. These videos have actually helped quite a bit in class as well as fixing my old f150, which I think is pretty cool. Keep em comin!
Never had a problem with left battery that does the starting if facing truck only on cold days. Keep up the good work
What great timing. My race car was running fine all day on Saturday until my 4th run, then it was dead....wouldn’t crank. Opened the battery box and found crustiest on both posts! Cleaned it up and haven’t had another issue
Got a little nervous when I caught the title of the video. Found many a bad connection using nothing more than a volt meter. Good information. Thanks for posting.
Every automotive student needs to watch and learn!
#566 belive it or not I am learning new things every time I watch your videos . Don't change and keep your feet grounded
All the customer had to do was replace the alternator too and he would of had the trifecta.
Good example to diagnose a problem before throwing parts at it.
well at 250K miles.....battery and starter can be justified in replacement. but not as a diagnostic method.
Why run down a 200 mV voltage drop? Because at a modest 60 amp draw from the alternator that's 12 watts of heat on that battery post. 0.2v doesn't sound like much until you apply the current. That's like a 1 amp bulb feeding heat right into the battery plates.
Very true. Also the heat exacerbates the corrosion development and wiring degradation.
Of the 12,415 voltage drop videos on UA-cam, this is the best.
Best video on voltage drop in action on the Internet. Thanks so much
I’m taking my first year heavy duty apprenticeship technical training and this video cleared up what they are trying to teach and this helped a lot with understanding voltage drop
Been a subscriber over a year, still can't believe you give this away. Thank you
I had what I thought was a bad starter. The battery clamps and posts looked good. But it wouldn't crank. If I had checked the voltage drop between the battery post and the terminal I would have found the problem. But like Eric said, it's better to be lucky than good. The corrosion was nearly invisible, but after cleaning the post and clamp everything worked perfectly. It'd videos like this one that made me a subscriber. Way to go Eric O!
Yay! Electrical secrets... one thing most mechanics have problems with. Ohm's Law: E=IR, or volts = amps x ohms. The more resistance, the more the voltage drops. P=EI... watts = volts x amps. Watts is what heats the connection. A volt-ohmmeter is one of the most useful things you can own.
totally agree !
in what country is E the symbol for voltage?
Ever country... that is how it is representative in ohms law, Voltage is E for Energy. Use E or V whichever works for you. 👍
@@skee0310 Voltage and energy are different - the E comes from "emf" - electromotive force
@@skee0310 E actually stands for "Electromotive Force" as is measured in Volts. Energy is power over time and measured in Watt Hours.
The difference between ProMechanics and "ShadeTreeMechanics": Pros focus on the Art of the Diagnosis and ShadeTrees focus on just changing Parts. I now focus on and understand that , "The Repair is not made when you change the part. The Repair is made when you complete the Diagnosis."
And with that, Eric O. dropped the voltage and walked off the stage!
Awesome video, and great examples! For as often as this gets drilled into our heads, it's not often in the real world we get to use it.
Great practical example of the effects of voltage drop. Thanks for taking the time to explain it so well.
Be it a liquid, gas, photons or electrons- you can't find a leak until it's under pressure.
Unbelievable!! New batteries, new starter and the problem was VISIBLE green crusties, Great video Eric.
Best auto diagnostics channel on UA-cam Thanks Eric👍
I'm with you. I use the same technique as you do.... Numbers don't lie. "jumper cables" are an in the field thing done that too. I think you did an excellent job of breaking it down makes it understandable.
Sir, You are an awesome teacher. No ifs and or buts. Just awesome.
Love your use of the infrared temp gauge. The more you use a temp gauge the better you get. Reflective surfaces distort infrared temp guns. As you know.
Once you understand voltage drop you've really got electrical diagnosis covered. The only thing you have to remember is that there must be current flowing during your test. Good video!
Currently learning this in class. Was having a hard time understanding voltage drop but after watching your video, I have a way better understanding of how the test works. Love your videos and keep up the good work.
You're a great teacher. I just learned how to properly do a voltage drop test and what to look out for in your videos. And learned a whole lot more. My learning has been excelled from your channel. Amazing work. And amazing craftsmanship. Thank you!
in salt water marine mechanic world we clean terminals and use corrosion grease on all connections including grounds.
Road salt is the same. I am amazed how many mechanics ignore cleaning wires terminals and use greases on them. Good show
It's DAMN SAD that somebody put new batteries & left those terminals like that. JUST PLAIN LAZY IF YOU ASK ME, THANKS ERIC, VERY EDUCATIONAL AS ALWAYS. Hey you do have a remote starter, NICE, I have one from the 80"s, very nice to have, you don't have to keep running in & out to start the vehicle. As I said in an earlier vid. YOUR'E LIKE BATMAN WITH ALL THOSE WONDERFUL TOY'S.
Not lazy , STUPID IDIOT !
You should work out, then work your way in. I don't know other way to find VD, but this works every time.
Hey Eric, I'm glad I finally joined the club. I wasn't able to folow your videos for two long years because of my poor English, but now when that improves I know all the effort I had put into language learning, now pays off. Ivan, Paul and You are my main seminars and training sources. Although I'm professional I would be nowhere without you guys and have still much to learn.
Greetings from Serbia :)
Eric, there is no question you have the knowlege here. I think you could easily be a shop teacher and instruct others as well. I realize you are doing just that with these videos, but I am specifically talking about classroom instruction at a technical school. Great video. Thanks for the time.
I work in the Refrigeration industry and work on my own vehicles. Did just this recently on one of my Ice boxes. Checking the time clock for continuity while it was still connected to the wall. Pulled the neutral wire to the timer motor and connected the meter in voltage between the neutral and the terminal on the time clock. Had voltage and I knew that the clock was still operating short of a mechanical binding in the clock. If there was no voltage then I would know there is a bad time clock winding. Another example of voltage drop in application. My final outcome on this box was the defrost wire was disconnected at a connection point. Thus causing the cooling coil to turn into an ice block.
One of the most important tools in my tool box the knowledge and the meters
Your channel is unbelievable. Thanks for all your effort and knowledge with these videos.
What surprised me most about relearning ohm's law was the hyperbolic shape of the current/resistance curve for a fixed voltage. Effectively that means a nearly vertical downward slope for low resistance circuits that rely on high current. So, those high current circuits suffer a HUGE compromise of power delivery from even an ohm or two of corrosion. Minor circuits don't even notice a little extra corrosion, they work on the flat part of the graph where you need a big change in resistance to have any effect on power delivery.
Resistance is critical for automotive circuits. With just 12 volts (or 14 or so with engine running), you need 10 times as much current for a given amount of power as you would for 120 volt household electricity. That means anything that draws a significant amount of power has low resistance, and will only work if the wiring supplying it has very low resistance.
Tech tip: Feel the terminals after cranking. The terminal that feels hot is the bad one. Nice voltage drop tutorial.
I vote for bonus footage on all future episodes of SMA....
Very informative.
Ive always been interested in how voltage drop works in a practical situation and your explanation was perfect
Few years on and still the ONLY channel I'm subscribed too!
You need to watch more youtube there are many guys and gals like Eric out there.
Impressive dedication!
Such as the other Eric!
Very well explained. Love voltage drop for parasitic draw testing across fuses.
I'm surprised people question your methods, your approach is perfect! I was going to say something more but am in the middle of a huge brain fart, so you'll excuse me if I just add thanks for the video and good job as usual! I will say though, I always liked starting with the hardest first so I can ramp into easy as the day progressed..... I can't believe they went through all those steps of replacing batteries and starter and didn't clean the terminals, are they brain dead?
If a shop did that , I wouldn't let him clean a toilet !
U should be teaching your way of explaining is the best I have seen í am an older tech in nz re training to keep up b the influence of having a family support you is great to see keep on trucking thanks for another awesome video
As someone who is still learning to work with voltage drops and electrical gremlins videos like this really help specially when you get ahold of vehicles that act crazy got an 89 mustang that tries to start and will start on its on as soon as the key hits on it just randomly quit happening still an unsolved mystery lol
Sound like a defective key switch.
As a new subscriber and a A.S.E. diesel d&r certified tech. I love the diesel tips, because even I forget the simple stuff. At the beginning my first diagnosis was a bad ground, thinking that it was a rusty frame. I've seen worse terminals on big trucks, but wow that was a lot of crud.
Great explanation of voltage drop. Now I feel the need to check my vehicles.
When I bought my brand new 1994 GMC 6.5 Diesel Suburban, 25 Years ago, about 1 year later, I had a slow crank "problem" that was developing. Like this Diesel Dodge, it too has 2 -12 volt batteries and an inter connection. I am surprised that ANY manufacturer would make a connection under the battery cable clamp clamping bolt.... just asking for trouble. GM connected the Positive Posts on the side terminal batteries together on the Left Battery Positive Post with a slightly longer bolt. Even though the Side Post batteries are quite a bit less suceptible to acid corrosion, I found that the bolt did not provide a lot of clamping force and some "Fretting Corrosion" (black areas) had built up. I installed an insulated 3/8" NF Marine Stud Connection on each inner fender within about 8" from each battery, made up a new crimped and soldered inter-connect cable and moved ALL positive connections to these terminals. New clean connections with silicone grease and torqued to about 30 Ft Pounds, then new short positive battery cables. Each Negative Connection went directly to the engine block with a smaller gauge wire to the body. The engine also has a bradded cable to the frame rail. 24 Years and 420,000 Kms later these connections are still good and the truck is going strong. I also agree...... who in their right mind installed 2 new batteries without cleaning these connections. GREAT LESSON IN BASICS!
I've heard a lot about voltage drop, but this is the first time I see it explained and demonstrated. It sure looks like a handy process to keep in mind. Thanks Eric!!
these reminders are so good glad you took the time to show
Another thing to watch out for are those lead battery terminals. Had to change a few because of voltage drop between the terminal and the cable coming out of it. Love your videos, keep em coming.
Yes, I've seen the cable corride inside the lead terminal too. And everyone of them looked fine visually.
My favorite video so far. I was not aware of this voltage drop method. Thanks!
Thank you, this is the type of thing I try to tell people who want to know.
You tell it very well. I'm going to use some of your expressions to improve my description.
You chased the drop because it was a detail that was just OK. And, the old saw is correct: the devil is in the details. Also, 100mV here, a 100mV there, pretty soon your 12 V circuit is 11. As usual, another great job. Thank you, Eric.
Nice job of explaining voltage drop and multimeter use....great job!! In addition, it shows how pretty simple preventative maintenance can prevent major issues......
Very well done! A resistance on the alternator output cable where it meets the battery positive will cause the alternator regulator circuit to put more voltage on the alternator field to the point that it can't maintain the desired regulated battery voltage and the connection as you showed will get hot, get more resistance and get hotter, loads then start to deplete the battery. A vehicle battery is only to start the engine, the vehicle runs on the alternator.
Gotta love it.
That's only true if the alternator has remote voltage sensing for regulation such as the #2 terminal on the DelcoRemy's
I tell my customers all the time these meters are a potential difference device and with 10 million ohms of input impedance they will not load the circuit enough to perform voltage drop with just the meter. Like you said no current flow not voltage drop! 👍Relays can give you fits so I like to load those circuits and see my drop across the relay. Great Sunday morning video! Thanks!
All the stuff South Main Auto demonstrates / teaches is GREAT STUFF 👍😊 YOU have many , many years of PROVEN EXPERIENCE and vehicle repair knowledge and when I watch you make repairs and you say - if I can do it - you can do it - I'm STOKED 😊 Again - GREAT INSTRUCTION , I learn something from every video you make - MANY , MANY THANKS and , no doubt , if I lived near you - I would surely bring my vehicles to your shop for repair and ABSOLUTELY REST ASSURED - knowing you would repair it properly. ✌️✌️✌️
Treat 'em and street 'em! Way to go Eric O!
Nice demonstration on how and why you should carry out a voltage drop. 👍
A lot of people also forget that the starter can be used as a great load to test the batteries and main wiring. I’ve seen people overlook wiring because it shows good with a resistance test and unloaded voltage test. But, when cranking the starter is usually the biggest single load. So, run the voltage drop test when cranking, or trying to and you’ll see what it does under load.
Just another outstanding video, Eric O. And, inside my head, the puzzle pieces make total sense. Thanks and please don’t stop. These videos are just like master mechanics classes. You da best!!!
258000 miles on a northern car,I thought all those northern car rusted and fell apart right after 100000 miles
But love your Channel keep up the good work and yeah you might make a good teacher probably easier on that old back and more money
I've always been more prone to ohm testing a cable/connection vs volt drop. I would have been interested in seeing the resistance difference in before and after compared to your voltage drop test results. I do understand though that a circuit can show low resistance but not be capable of carrying a load or have voltage drop. Or both. Good video. Enjoy your veterans day weekend.
Eric O love your process using the basics, you slow down to go fast.
Oooo!!! Nice lesson, Erick!!! I wouldn't have thought voltage drop from center of post to battery clamp would be that significant, but you just proved it is. Lesson learned is a clean battery post and clamp are a must to get proper voltage to the user item ( aka starter). Thanks for sharing Erick.....
That’s what I’m talking about! Good job Mr. O!!
Since I don’t have all the fancy equipment you have, I would have used a ohmmeter to test for a zero ohm connection between the post and battery terminal. Since resistance causes voltage drops and also heat, I probably would have come to the same conclusion. I do however appreciate the alternative way to skin a cat. You are the best.
You're churning these videos out like the Chinese parts you're so fond of!
hes changed his name to dorman
Back in the old days the rule was 0.1 volt drop for every foot of cable (while cranking) provided the starter isn't drawing excessive amperage. One time I diagnosed a car with a bad battery, customer said price was too high (Ford Dealership, so...) Took the car and replaced the battery, had it towed back to the Dealership mad as hell because the battery didn't fix it and we diagnosed it wrong. I went out to the car to test their new battery only to find they had not removed the plastic protector caps and installed the terminal ends over them. I removed the plastic caps and installed their battery terminals at no charge. :)
Really like these diagnosis and voltage drop/ parasitic draw videos. You have the best videos put there.....
Another great job explaining voltage drop testing. Keep making these videos!
Resistance and heat just get worse one adds to the other..
Great demo on voltage drop thank you Brother for sharing.
Great video as always and a good reminder of checking voltage drop on any circuit thats not operating as designed.
To measure is to know.
And pro's want to know.
I love how you term electricity to plumbing terms! Good Job!
I love your way of explaining your approach. Clear and to the point. I also appreciate you using a diagram. Great work! Subscribed and liked!