Voltage Drop Test

[Matt Brandsema]

Hey Everyone,

In the past I have had people tell me that they do not understand voltage drop testing. So I made a little video explaining the concept (Using a very basic, and intuitive approach).

[video]http://www.youtube.com/watch?v=R6Z-hWzIgDY[/video]

I am not sure if I am allowed to post links to my YouTube Channel, if not then just delete the thread.

EDIT: Interesting.. The video embed doesn’t seem to be working. Here is the link..

Topic

[twiggy]

Good job. This should help a,lot of people.

[EricTheCarGuy]

It’s totally cool that you post your own videos, in fact, it’s encouraged.

I think your explanation is a little off however. Yes, lots of people use the ‘pressure’ analogy when talking about electricity but I think in this case it would have been better to go at it using Ohm’s Law rather than spending so much time on the pressure analogy. A circuit uses ALL of it’s voltage in the circuit. So if you start with 12v by the time you reach the end of the circuit you’ll have 0v. This is the voltage drop. If you find that you have substantially less than 12v before the load, then you’ve found your resistance. Of corse you’ll loose a little voltage through the circuit but not nearly as much as you would loose passing through the load. After the load in a normal circuit, you will have lost most of your voltage due to ohms law and how the circuit works.

I just wrote an article on this that will be out with the new website. I go into a more detailed explanation there. I also hope to make my own video on this topic at some point.

I appreciate your contribution. Thanks for the post.

[dave]

It’s important to realize why you are doing a voltage drop test….

A: to check for ‘unwanted’ resistance.

The unwanted resistance can appear in the following forms:

• quality of connection
• material of the conductor
• thickness of the conductor
• temperature
• corrosion
• physical damage

Learn how to look for and find that bad case of VD. B)

(awesome vid btw)

[Dustin Hicks]

realfixesrealfast has a four part video on voltage drop testing that can be useful. In part four, he demonstrates a powerprobe 3.

part 1
[video]http://www.youtube.com/watch?v=6Sqk_Gai59I&feature=player_detailpage[/video]
part 2
[video]http://www.youtube.com/watch?v=a1vR2BxJ9jQ&feature=player_detailpage[/video]
part 3
[video]http://www.youtube.com/watch?v=WONhgSxeZ2s&feature=player_detailpage[/video]
part 4
[video]http://www.youtube.com/watch?v=H8rl5w51fNo&feature=player_detailpage[/video]

here’s one I really like though:
[video]http://www.youtube.com/watch?v=ggKnH-95ty0&feature=player_detailpage&list=TLV9wFR1HamNo[/video]
the lead he uses on the positive lead of the dvom is a load pro.

[Travis]

The best place to learn about anything electrical is by scannerdanner. You can also buy his book. Look him up on YouTube. He is a friend of Eric’s also. His book is amazing and so are his tutorials

[Kevin Criswell]

[quote=”bdazsvt03″ post=76848]The best place to learn about anything electrical is by scannerdanner. You can also buy his book. Look him up on YouTube. He is a friend of Eric’s also. His book is amazing and so are his tutorials[/quote]

Yeah, I love his videos, he does a pretty good job of explaining electrical issues.

[Matt]

Scannerdanner is the guy you want to work besides in a shop for those “please help me i cant for the life of me figure it out situations” when it comes to hardcore drivability and electrical work. Yes I just went way off topic but his videos are very complex if your just a DIY.

[Kevin Criswell]

That load pro is pretty slick, I am going to have to check one out.

[Julian]

I’m still having a hard time understanding Voltage Drop even after watching a bunch of videos.
BTW, I liked this series:

http://www.youtube.com/watch?v=4f-vWFOYmxI

I get the main 2 points:

1. Current has to be flowing
2. At the end of the circuit, all the voltage supplied to it needs to be used up.

However, what I’m having a hard time with is the car circuits are made up of many components each adding it’s own load (resistance) right? So how do you make sure the value you’re reading on the meter is the correct value? How do you actually go about testing each in the car? What’s the general rule? Do you always have one lead on the battery and use the other lead to check the drops? All the examples in the video deal with one load.

Also, I think the name Voltage Drop is kinda misleading. I initially thought it’s a test too see how much Voltage “Drops”, but it actually is a test to see how much Voltage Remains 🙂 since in theory– all of it has to drop.

[twiggy]

[quote=”juels98″ post=79598]I’m still having a hard time understanding Voltage Drop even after watching a bunch of videos.
BTW, I liked this series:

http://www.youtube.com/watch?v=4f-vWFOYmxI

I get the main 2 points:

1. Current has to be flowing
2. At the end of the circuit, all the voltage supplied to it needs to be used up.

However, what I’m having a hard time with is the car circuits are made up of many components each adding it’s own load (resistance) right? So how do you make sure the value you’re reading on the meter is the correct value? How do you actually go about testing each in the car? What’s the general rule? Do you always have one lead on the battery and use the other lead to check the drops? All the examples in the video deal with one load.

Also, I think the name Voltage Drop is kinda misleading. I initially thought it’s a test too see how much Voltage “Drops”, but it actually is a test to see how much Voltage Remains 🙂 since in theory– all of it
has to drop.[/quote]

You seem to understand it based on your post above. There really isn’t much more to it. Your statement above that “2. At the end of the circuit, all the voltage supplied to it needs to be used up.” is true and it’s actually called “Kirchhoff’s voltage law” which states that the sum of voltages going around any loop must add to zero. This only makes sense when you realize that current flow inside the battery is negative because there it flows negative to positive so we define that as a negative voltage.

Power is required to run any motor and is defined as (Voltage * current), so if you need 100 amps to run a starter motor, the resistance of the wires has to be very small or ohms law kick in causing voltage drop/reduced current before the starter. This is no different than having a kinked garden hose.

[Author]

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