Fix Electrical Problems by Understanding Voltage Drop Testing

In this video I am going to explain what is Voltage Drop, how you can perform a voltage drop test to find corroded wires or terminals, how voltage drop test is used to do a parasitic draw test on your battery, how voltage drop allows your cars computer to receive varying voltage from different sensors and how not to mistake voltage drop for measuring voltage.
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Disclaimer:
Due to factors beyond the control of Ratchets and Wrenches, it cannot guarantee against unauthorized modifications of this information, or improper use of this information. Ratchets and Wrenches assumes no liability for any property or personal damage that may arise from doing a repair on your vehicle after watching any of my repair video's. Due to factors beyond the control of Ratchets and Wrenches, no information contained in this video shall create any express or implied warranty or guarantee of any particular result. Again Any injury, damage or loss that may result from improper use of tools, equipment, or the information contained in this video is the sole responsibility of the user and not Ratchets and Wrenches.

[@ThunderbirdRocket]

I’d like to say thank you for sharing your knowledge. Great topic . We are now hitting at the gold in the mine ! Let’s get some ! Keep it coming please !!

[@lout3921]

I'm a "long" time subscriber and I'm ok fixing my own car as long a lift is not required; however, this video is for way more advanced viewers. It's something I would love to understand plus I'm very excited you're back into car repairs. Admittedly I hope you future videos are not as complicated. Keep up the great work and I appreciate what I've learned. FYI I purchased a car (2008 Honda Civic) you recommended on you older videos for my step daughter. She still has it and it runs great.

[@gusmpls]

In a series circuit the sum of all voltage drops is equal to source voltage. In series circuit the the current is the same throughout the circuit. In a parallel circuit voltage is the same but the current will be divided in each branch depending on the resistance. If all the branches have the same resistance then they would also have the same current.

[@Viper81766]

Good to see you brother. Good topic and appreciate all the work you put into the videos. 👍😁

[@myRatchets]

Much appreciated

[@GalaxybutYT]

Another great video man. Thanks for the knowledge. 👍

[@myRatchets]

Any time!

[@user-uw4cv2xb8l]

Wow, you have over a million subscribers. I'm happy for this

[@dv319]

Electricity has always confused me😣 .

[@myRatchets]

It can get complicated.

[@wyattoneable]

You were asked and you delivered!

[@CaptainVillanueva1]

Wow he helped me understand that super fast!!! Damn man your a good teacher 🤘🏽

[@nickayivor8432]

KNOWLEDGEABLE Ratchets and Wrench Outstanding tutorial stuff loved it thank you very much helpful information video Please do part 2 Voltage drop testing Please Ratchets and Wrench From start to finish loved it 🌟🌟🌟🌟🌟 Take care and have a great Evening👍👌 KNOWLEDGEABLE Ratchets and Wrench From Nick Ayivor from London England UK 🇬🇧

[@JonnyDIY]

Whoosh. Most went over my head. Electrical is definitely not my strong suit! 🤣 But you are a great teacher 👍

[@johnsee7269]

Amazing! I did not know that... Brilliant explaination!

[@myRatchets]

Glad it made sense to you, thanks for watching.

[@mayflowerlash11]

Despite having an engineering degree the use of a multimeter has always been a puzzle. The electrical course in the degree was theoretical not practical. Hopefully when I follow your instructions it will make sense to me. Thanks for the lesson.

[@myRatchets]

np, hope it helps you out. cheers

[@aaronlowman7460]

@@myRatchets BB bnhm bc CV BB BB BB mm mm mm nnmn no neenenn nnmn hmmm be nnrnnemrnrnnnene

[@markm0000]

That’s such a huge problem in society I can’t believe nothing has been done about it. There has to be a practical side to education from 1st grade up to the very top. So many people are completely oblivious to the world around them and think a fancy piece of paper is all they need in life.

[@mariogiron6120]

Great tips thanks!

[@math1412]

Very good work , im subscribe today , thx alot

[@delinquentdesign]

A lot of vehicles use ground going to the ecm to send signal to the sensors can you explain more on those?

[@walkernottexasranger7565]

I had a coolant temp sensor fail on a later model Jeep Wrangler a while ago. I was doing my due diligence and testing the circuit and I noticed the 5v wire went from something like 2v to 5v when I unplugged it. I'm guessing this is super similar to what you were explaining in the video with the 5v circuit going to 12v. But if you could explain this clearly I'd be grateful. Great video thanks !

[@myRatchets]

I will try to make more videos like this, but I think I need to split things up and be more thorough :)

[@walkernottexasranger7565]

@@myRatchets it might be cool to do a video on diagnosis of 5v sensor circuits. I would definitely be interested in learning more about that

[@matt_b...]

Man, lots of new videos lately. That new garage ain't gonna pay for itself!

[@myRatchets]

thats right lol

[@siko1101]

What would you recommend (tune-up wise) on a car that's been inactive for 5+ yrs? Thanks and love the content!

[@jduda1127]

Id first and most put some oil down each cylinder before turning it over. I would also disconnect fuel and spark to build up oil pressure. Everything is dry as a bone. full brakes, calipers, brake lines, air filter, cabin filter, oil change, fuel filter, trans fluid change, coolant flush ugh just redo it all. Sitting inside and outside plays a role.

[@warner1600]

Hi, I have. problem with dodge caravan. I changed the alternator and the battery was tested it is working, however. There is a sharp rapid drop in voltage after I turn the engine off. does within seconds from 12 to 9 volts. I have to jump start every single time I turn it off and even for gas filling at the pump. Do you have any suggestions on what that might be?

[@ceciliovillalobos2964]

Love it , are you located in Los Angeles

[@davidg5704]

This was a great video explaining circuits, resistance, electrical theory. I've taught myself how to read wiring diagrams to to the level of adding heated seats and power windows in a manual window car. Everything worked 100%. A great sense of accomplishment for me. Toyota dealer was impressed because I designed circuits to bypass bcm with stand alone harnesses. Excellent content made perfect sense.🙏

[@ninjarider2941]

The two resistors in series form a voltage divider circuit. When the connector gets disconnected @16:00 and you read 12V instead of 5V, the resistor in the ECM is acting something like a pull-up resistor found in digital circuits.

[@myRatchets]

ah makes sense, thanks for your comment.

[@shortydancer]

Holy crap I forgot everything from my electrical class. I need to get back to understanding these.

[@markbrzezinski8889]

Thankyou, that was the bit I was confused about.

[@mbs5328]

I love the Ratchets and Wrenches channel, but I didn't seem to get much out of this video.

[@myRatchets]

I should have split this one up into a few different videos.

[@tasanijanus7092]

@@myRatchets I think it had a good flow

[@daltonlawrence3690]

Thank you man

[@georgesmith37]

Can you help me I have a Mazda mpv and it will idle when I unplug mas but when I plug it back in van dies

[@ajanderson8434]

I LOVE the new way he says, hey hey how is it going Do.. it your... sulfers.

[@tetttettamilli6761]

@R&W - Just two questions (1.) In most shop manuals, you'll read, in bold print -"Do Not Test Grounds Using Vehicle Ground" (or something to that effect); I guess there's fear of errant 12V running thru the ECU. Is this the case? (2.) And I've seen old school techs test an alternator by quickly removing the neg. battery terminal, and watching the stall and/or hesitation - can this actually damage the vehicle's electronics?

[@bernardaflores1720]

old school techs test an alternator by quickly removing the neg connection, not good for modern cars because they have computers.

[@myRatchets]

That is not a good way to test an alternator, modern cars will stop running regardless of a good alternator or not, also you'll lose all setting and not safe for your ECUs etc. sorry not sure I understand the first part of your question.

[@catfeline1530]

If we can expect to see a voltage drop of no more than .5 between positive bat and stud of alternator, what is the benchmark voltage drop we are looking for between the housing of altenator and negative bat?

[@myRatchets]

no more than .5v total. You rarely have a problem on negative side without other electrical circuits not working right.

[@bradpyron8928]

New battery and new OEM Alternator been replaced couple of days ago, all interior exterior light more brighter, but when I depress the gas pedal with no significant load expect vehicle interior light on the light gets brighter for half a second and the volt gauge on the dash still shows drop on voltage, any idea why I still have volt drop please?

[@myRatchets]

You have to measure for voltage drop you could have excessive corrosion on one of the terminals. Also its not unheard of to have weaker than normal new oem alternators. gl

[@majorkin19]

Amps is the lazy one that doesn't go anywhere unless theres a clear path to ground Voltage is the active one thats always on the go, until something get in its way or send it on a detour, for example A break in a wire is like a bridge that would've carried you on foot straight home had it not been blocked by cops all of a sudden , now you have to detour a much longer way which will then drain some energy from you by the time you reach the other side, that blockade can be one of 2 things, a switch that will drain a required amount of volts which is normal or resistance thats contributing to more than normal voltage drop, bad switch, break in the wire, rust corrosion etc

[@robmut1357]

Kirchhoff’s voltage law baby!

[@aymenmohamed1134]

Awesome

[@CarlosContreras-gk9gp]

Love it !

[@myRatchets]

glad to hear.

[@StickNclutch]

Can you explain why a brand new battery forms acid around the terminals? I've replaced my car battery twice with new interstate battery, and still continues to build up acid.

[@kennethwatt3491]

Maybe the Car is over charging ? Have You had that checked ?

[@k9under]

Clean your battery terminals then put some silicone paste on them.

[@myRatchets]

yes check the alternator to see if its overcharging the battery.

[@markm0000]

@@k9under You can put anything on there. I’ve used just basic chassis grease and it works fine. Some people periodically add engine oil off the dip stick and that works fine. If you’re real fancy you can buy a tube of dielectric grease and feel good about yourself.

[@k9under]

@@markm0000 Yes sir back in the 1970 i use to put vaseline on battery cable.

[@ManWander]

thank you

[@myRatchets]

You're welcome

[@dr.mohamedaboomar3031]

Thanks 🙏

[@myRatchets]

You’re welcome 😊

[@ifell3]

The alternator isn't going to try to charge the battery from that test wire, is it? Just wondering if it tries to send 10 amps through my multimeter?

[@myRatchets]

no you're just measuring for voltage basically. No current it flowing through your multimeter unlike when you test for amps.

[@ifell3]

@@myRatchets But what if the multimeter is the path of least resistance, or does it not work like that. Sorry, I've managed to short a multimeter before. But that was at 230v and I really cant remember what it was I was doing. All I can remember was there was a massive spark and my wires blew aha

[@noonday8240]

Can you explain how to use a voltmeter

[@noonday8240]

It's the most important step

[@myRatchets]

I've done a video in the past, I'll see if I can do a new one.

[@bwest-yq3uc]

Would have been more informative, if we had a vehicle that would start and run to do the test on. It would have been more clear to me and others. Maybe have a re-run of this video with a good vehicle.Thanks for the video.

[@myRatchets]

I'll do a re do of this or just the voltage drop procedure.

[@shortydancer]

I miss you homie

[@elitedelta9001]

Early Gang crew reporting for duty

[@ese3v]

Voltage drop is king

[@myRatchets]

thats right

[@jum5238]

I don't think this was explained well. Made it too complicated. You're trying to work with a voltage divider circuit and using that to detect the state of the device that is dropping voltage (presumably for a position that correlates to a changing resistance level of a variable resistor). The end comment about 12 v. when unplugged is also confusing. There are voltage grounded circuits, where the 12 volts is being supplied by one wire, then going through the device, and then back out to a PCM with a circuit that has internal resistance, and possibly a transistor circuit for bias (switching), and is grounded. The resistance outside the PCM, along with the resistance inside the PCM provide a voltage divider circuit, and affect what is sensed inside the PCM for decision making elsewhere. The sidetrack onto voltage drop across fuses was also confusing. Basically too many concepts/examples across too little time while jumping around the engine bay also contributed to the confusion.

[@8gomerpyle22]

Where is your automotive school at? I need to attend that.

[@situationmoney]

So, the test light was using 7.6 volts and fuel float was using 4.3 volts. That would be 11.9 volts total. Supplied voltage from the battery was 12.3 volts. This would tell us that 0.4 volts was being used from another source, which most likely was from the wires connected to the battery or the battery terminal connections. So, the complete circuit would have 0.4 volts of resistance?????

[@jpol3808]

He said 12.06 or 12.07 v with the light on.

[@jpol3808]

The drop would be the difference between 12.6 and the 11.9 which would be .7

[@jpol3808]

You should always measure the bat voltage without anything in the car on first! That is your reference voltage. Then test for voltage drops.

[@eduardopemex7435]

Hey hey

[@QBRX]

It kinda made sense, but only kinda.

[@myRatchets]

haha I understand.

[@pete4866]

Wow, suddenly now you increased subscribers to 1 million,what did you do?

[@myRatchets]

I don't know but its taken a while :)

[@Mr.Unacceptable]

I have been trying to learn this but nobody has explained to to me that makes sense. Still makes no sense. Less words more demonstration.

[@spelunkerd]

Imagine two lakes at different heights, with a dam between the two not allowing water to flow down a dry stream bed between each lake. The difference in elevation between the two lakes is analogous the voltage difference between the two lakes, what we call voltage drop across the entire line. Now imagine the tech lowers the dam to allow water to begin spilling down the creek bed between the two lakes. Water cascades down in a series of little waterfalls, with a small "voltage drop" across each little waterfall of the stream. The sum of all the small waterfall drops has to be equal to the total height difference between the two lakes. Now think of an extension cord with a bad spot in it, with frayed, corroded wires. When you measure voltage at the end of the cord, voltage is 120V when the cord is not plugged in. But then you try to run your table saw with it, and you notice the saw won't work. Then you measure voltage right at the saw while the saw motor is turned on, and to your surprise the voltage is not 120 V, it is only 40V. The upstream resistance in the wire caused a voltage drop in the wire, much like an upstream waterfall. That voltage drop in the wire is robbing power from your downstream saw. It's only visible when you get electrons moving....

[@mikepettengill2706]

"I dare you! Ask me more questions!" I thought that you did a good job explaining this concept in the context of working on a vehicle. I would like to see you do this to check the WIRES to the O2 sensors on a chevy Silverado, preverably as it applies to the 2000 models. (mine's a 1500 ;) )

[@markhb3346]

Unless you’re referring to heater circuit of the O2 sensor this really doesn’t apply . O2 sensor generate a voltage that ranges from 0-1V , that voltage is only capable of pushing at best maybe 1 or 2 mili amps .. The best way to test is with using live date on a scan tool or a lab scope .

[@df4480]

I got lost when you tried to explain it maybe I’m not advanced.

[@jameschavez3780]

You talk about the alternator, but not explain which cable is positive and the. Negative to find out voltage drop 12:48

[@mariogiron6120]

Only commenting for the algorithm

[@MrZimmaframe]

"Hey hey hey do it yourselfers" reminds me of the scene in Scary Movie 2 when the disabled guy is being seduced by the big boobed brunette, and he says "hey hey hey I can do it myself" 🤣

[@christen1075]

When you do a formula and then simply wing it, without putting up any real numbers, you simply will lose an audience who is trying to grapple with the concept of electricity and that’s difficult enough. A formula without a number and example based on a real world demonstration, just causes people to shrug their shoulders and basically say “I don’t understand.“ And that was me who kind of dropped off about five minutes into this. Sadly.

[@nguyennt99]

He had me at voltage drop. Lol. Alot of confusion

[@angelsaucedo2231]

Gotta say this was very confusing. I think you failed to explain to someone who doesnt really know the basics. In your first example youre measuring the voltage drop clipping on the positive side coming into the needle part of the bulb tester and the ground on the battery. Then in your alternator example you talk about measuring first the positive side voltage drop then the negative side. I saw other videos so I get what youre doing but this one just felt like one of those videos where you skip details because you know what youre saying, but its a little too vauge for someone who doesnt know. But thats just me. The comments are divided between people who got it, people who were confused, and people asking for unrelated advice. Also examples are always helpful. Maybe wait till youre ready to provide an example of your concepts. Thanks for your videos though. They have been helpful.

[@kamalabbady6778]

Good video but I didn't understand sh***t. Electricity always been so complicated to understand.

[@jennysmith3224]

I’m dizzy

[@Zparker31]

Not a good video for the average person....much easier way to explain it

[@moonpeach4684]

🤡👍🏼

[@rayhope7957]

Knowing where to set the meter helps low iq like me.

[@chiefdenis]

Afraid to say, i didn't understand a thing

[@JCGible]

Didn't understand a single word you said.

[@electricblue8707]

Poorly explained to be honest