Voltage Loss or Voltage Drop, That Is The Question?

We hear the terms “Voltage Loss” and “Voltage Drop” test frequently in the Automotive industry.  But most refer to it as what’s is really a Voltage “Drop” test.  This is incorrect, these are two separate test with two separate purposes – however, many-times the same failure result can be determined with both test.  So what is the difference between the two test, and why do we perform them?

Well, it’s actually what it states:

A Voltage Loss test is testing for a voltage “loss” across one or more connections or components.  This test is performed on “one” side of the circuit at a time – meaning to test the Positive side of the circuit, and / or then test the negative side of the circuit. 

A Voltage Drop test is to test for a voltage “drop” across one or more connections and components.  This test is performed across both sides of the circuit and requires a component – meaning to test from the positive side of the circuit to the negative side of the circuit.  This requires some sort of resistance through a load component like a light bulb or resistor, etc…

The below circuit examples shows a voltage loss test.  This test is typically not performed across a component – although you can in some cases.  It is typically used to test circuit hard wire connections – like a starter cable, or for a lose ground with lights flickering or dim on one side.  A “General” rule is 0.5 volt allowance across each connection.  If you are testing across several connections, it would be 0.5 Volts “per connection.”  Three connections would be 0.5 Volts X (3) Connections = 1.5 Volts loss allowance.  Now this is a general rule, realistically it would be typically in the 0.35 to 0.37 volt range depending on wire length, gauge, number of connections, quality of connection, number of components and the resistance or voltage loss value of each component (any resistance equates to a volt loss value).  I will not be going into formulas, however below is a link to a great site that explains Ohms law and formulas.

See This Site on Ohms Law

Volt Loss Examples (Click Examples to View Full Size):

voltagelossexmp1.jpg  Example 1 checks volt loss from the battery terminal to the fuse power input.  With the positive volt meter lead on the actual battery post, you will test for a loss of the terminal, wire, and connection to the fuse.

voltagelossexmp2.jpg  Example 2 checks volt loss across the power input and output of the fuse.  A poor connection to the fuse or open fuse would be the result.

voltagelossexmp3.jpg  Example 3 checks volt loss from the fuse power output to the positive lead of the light bulb.  The result of this test would indicate a bad wire or terminal /connection for the fuse / bulb.

voltagelossexmp4.jpg  Example 4 checks volt loss on the ground side of the circuit after the components (the light bulb in this case).  The fail result of this test would indicate a bad battery terminal, wire, terminal/connection to the light bulb.

Keep in mind that all of the above tests are assuming that battery voltage is being applied to the circuit in the first place.  If there in no (“0 Volts”)battery voltage (12 volts normal in this case) test results of a voltage loss test will test OK on all connections.  So be sure to check basics first…

The next four examples are demonstrating a Voltage Drop test.  The same rule applies, but instead of a 0.5 volt loss per connection (general rule again) you are allowed a 0.5 volt drop per connection.  So if your battery voltage is 12 volts, your allowable voltage would be 11.5 volts – 11 volts for 1 connection would indicate a problem.  Also, you are checking the circuit under load from the connection back to the battery, not across the component as it may appear in the examples (the light bulb in this case).

Voltage Drop Test Examples (Click Examples to View Full Size):

voltagedropexmp1.jpg  Example 1 checks volt drop across the two battery terminals, if the test leads are actually on the terminals.  If the test leads are on the actual batter posts, then all you are checking is initial battery voltage.  The failed result (possible 11 volts or less for two connections based on the general rule), if leads are on the battery terminals, would be bad, corroded or poor connection of the battery terminals – assuming battery voltage is 12 volts to start with.

voltagedropexmp2.jpg  Example 2 checks volt drop from the battery terminal to the input lead of the fuse.  The failed result (possible 10.5 or less voltage for 3 connections), would be a battery terminal, wire or fuse connection (if checking on the fuse itself). 

voltagedropexmp3.jpg  Example 3 checks volt drop from the battery terminal to the output lead of the fuse.  The failed result (possible 10 volts or less for 4 connections), would be a fuse, terminal, wire or battery terminal.

voltagedropexmp4.jpg  Example 4 checks volts drop from the battery terminal to the power lead of the component (the light bulb in this case).  The failed result (possible 9.5 volts or less for 5 connections), would be a light bulb connection, fuse, terminal (s), wires (2 possible) or a battery terminal.  Note:  if you were to now put the positive volt lead on the ground side of the bulb, you would be performing a voltage “loss” test and not a voltage “drop” test.

When doing a voltage drop test, the assumption is that the component (light bulb in this case) is good and drawing a load on the system (load meaning an “Amperage” draw).  You would not normally test for a drop across a component unless you knew the actual volt drop value of the component – referring to ohms law again and determining the formula for the draw and volt drop.  If there is no load on the circuit when doing the volt drop test, result will show system or battery voltage – test OK.  Check the resistance of the component, the bulb, or incorporating the use of an amp meter when performing this test would verify appropriate system load.

On a realistic note on the above tests, drop and loss tests, typically a good system under normal load, will only show a max of 1 volt loss across all connections – unless you have a lot of connections and components on one circuit, or have really lengthy wiring, or a really heavy load like a starter circuit drawing 200 and 300 amps with sub-standard gauge wire.  If I see more than a 1 volt loss or drop, I’m going to investigate the circuit further to see if there might be a problem.  Many time this results in a loose bolt, slightly corroded or contaminated terminal, etc…

You see many technicians waisting unnecessary and valuable time testing specific components in a circuit.  By performing the voltage loss and drop test, you can accurately diagnose a circuit at easy access locations to determine if further specific test are needed based on your result.  Thus, hours saved with unnecessary component testing by removing hard to get panels and parts.

– Jack Miller (Click to View Business Card)

Advertisements

19 responses to “Voltage Loss or Voltage Drop, That Is The Question?

  1. Excellent! This is where everyone should start any electrical troubleshooting.
    Thank you for your efforts in posting this.

  2. it is a very good site and its knowledgeable

  3. I’m pretty pleased to find this website. I want to to thank you for ones time for this fantastic read!! I definitely appreciated every little bit of it and i also have you bookmarked to see new stuff in your site.

    May I just say what a comfort to uncover someone that actually understands what they’re talking about online. You certainly understand how to bring an issue to light and make it important. More and more people really need to read this and understand this side of your story. I was surprised you’re not more popular given that you certainly have the gift.

    Very nice blog post. I absolutely love this website. Keep it up!

    It’s hard to find well-informed people for this subject, however, you sound like you know what you’re talking about! Thanks

    You should take part in a contest for one of the finest blogs on the internet. I most certainly will highly recommend this site!

    A fascinating discussion is worth comment. I do believe that you ought to write more on this subject, it may not be a taboo subject but generally people do not discuss such issues. To the next! Many thanks!!

    Hey there! I simply would like to give you a huge thumbs up for the excellent info you have here on this post. I am coming back to your website for more soon.

    After I initially commented I appear to have clicked on the -Notify me when new comments are added- checkbox and from now on whenever a comment is added I get 4 emails with the same comment. Perhaps there is a way you can remove me from that service? Thanks!

    The next time I read a blog, Hopefully it won’t fail me as much as this particular one. I mean, I know it was my choice to read, nonetheless I truly thought you would have something helpful to say. All I hear is a bunch of moaning about something that you could possibly fix if you weren’t too busy looking for attention.

    Spot on with this write-up, I actually feel this web site needs far more attention. I’ll probably be back again to read more, thanks for the information!

    You’re so awesome! I don’t believe I’ve truly read through something like this before. So wonderful to find another person with unique thoughts on this issue. Really.. thanks for starting this up. This site is one thing that is needed on the internet, someone with a bit of originality!

    I love reading an article that will make men and women think. Also, thank you for allowing for me to comment!

    Right here is the perfect blog for anybody who wishes to understand this topic. You know so much its almost hard to argue with you (not that I actually would want to…HaHa). You certainly put a brand new spin on a subject which has been written about for decades. Wonderful stuff, just wonderful!

    Aw, this was an extremely nice post. Taking a few minutes and actual effort to make a great article… but what can I say… I hesitate a whole lot and don’t seem to get nearly anything done.

    I’m amazed, I must say. Seldom do I encounter a blog that’s equally educative and interesting, and without a doubt, you’ve hit the nail on the head. The issue is an issue that not enough people are speaking intelligently about. I am very happy I found this in my hunt for something concerning this.

    Oh my goodness! Amazing article dude! Many thanks, However I am going through issues with your RSS. I don’t know the reason why I am unable to subscribe to it. Is there anybody having similar RSS problems? Anybody who knows the solution can you kindly respond? Thanx!!

    An outstanding share! I’ve just forwarded this onto a co-worker who has been doing a little research on this. And he actually bought me lunch simply because I discovered it for him… lol. So let me reword this…. Thanks for the meal!! But yeah, thanks for spending the time to discuss this subject here on your website.

    After checking out a few of the blog articles on your site, I truly appreciate your technique of writing a blog. I saved as a favorite it to my bookmark website list and will be checking back in the near future. Take a look at my web site as well and let me know what you think.

    This website truly has all the info I wanted concerning this subject and didn’t know who to ask.

    There’s definately a great deal to learn about this issue. I like all of the points you made.

    You made some really good points there. I looked on the internet for more information about the issue and found most individuals will go along with your views on this website.

    Good post. I learn something new and challenging on websites I stumbleupon on a daily basis. It will always be interesting to read through content from other authors and practice something from their sites.

    I blog frequently and I really appreciate your information. This great article has truly peaked my interest. I’m going to bookmark your blog and keep checking for new details about once per week. I subscribed to your RSS feed too.

    Pretty! This was an extremely wonderful post. Thank you for providing this information.

    Greetings! Very helpful advice within this post! It’s the little changes that will make the greatest changes. Many thanks for sharing!

    Hi there! This blog post could not be written much better! Going through this article reminds me of my previous roommate! He continually kept preaching about this. I’ll forward this post to him. Pretty sure he will have a good read. Thank you for sharing!

    Hello there, I think your website could possibly be having internet browser compatibility issues. Whenever I take a look at your site in Safari, it looks fine however, if opening in I.E., it’s got some overlapping issues. I simply wanted to provide you with a quick heads up! Aside from that, wonderful blog!

    Having read this I believed it was extremely enlightening. I appreciate you finding the time and energy to put this content together. I once again find myself personally spending a lot of time both reading and commenting. But so what, it was still worthwhile!

    Hi! I could have sworn I’ve visited this blog before but after browsing through many of the articles I realized it’s new to me. Anyways, I’m certainly delighted I discovered it and I’ll be bookmarking it and checking back often!

    I want to to thank you for this great read!! I absolutely loved every little bit of it. I’ve got you saved as a favorite to look at new things you post…

    Hi, I do believe this is a great blog. I stumbledupon it 😉 I am going to come back once again since I book-marked it. Money and freedom is the best way to change, may you be rich and continue to guide other people.

    Your style is really unique in comparison to other folks I’ve read stuff from. I appreciate you for posting when you’ve got the opportunity, Guess I’ll just bookmark this page.

    I used to be able to find good info from your blog articles.

    Wonderful article! We are linking to this great article on our website. Keep up the good writing.

    This is a great tip especially to those fresh to the blogosphere. Simple but very accurate info… Thanks for sharing this one. A must read article!

    I could not resist commenting. Very well written!

    bookmarked!!, I really like your website!

    Very good post. I am dealing with many of these issues as well..

    Way cool! Some extremely valid points! I appreciate you writing this article and also the rest of the site is also really good.

    Excellent blog you’ve got here.. It’s difficult to find high quality writing like yours these days. I truly appreciate individuals like you! Take care!!

    This is a topic which is near to my heart… Take care! Exactly where are your contact details though?

    I absolutely love your website.. Pleasant colors & theme. Did you make this web site yourself? Please reply back as I’m wanting to create my very own blog and would love to find out where you got this from or exactly what the theme is named. Cheers!

    I like it when people get together and share opinions. Great blog, keep it up!

    Great info. Lucky me I discovered your site by accident (stumbleupon). I have saved as a favorite for later!

    This website was… how do you say it? Relevant!! Finally I’ve found something that helped me. Thanks a lot!

    Everything is very open with a clear explanation of the issues. It was definitely informative. Your site is very useful. Thank you for sharing!

    I would like to thank you for the efforts you’ve put in writing this blog. I really hope to see the same high-grade content by you later on as well. In fact, your creative writing abilities has encouraged me to get my own, personal blog now 😉

  4. Hello Dear, are you truly visiting this site
    on a regular basis, if so after that you will definitely
    obtain fastidious knowledge.

  5. Much last year’s Basketball 2K12, fans should expect the latest and in addition greatest from Nike to be effortlessly 2K13 via down loadable updates on the same day the actual pumps drop. High heel sandals like the Nike LeBron 10, the entire Nike Zoom Kobe 8 and most of the Nike Zoom KD V were one of those mentioned in the press release. Nike+ Basketball can also get a presence amongst players as players who wear the Nike+ Hyperdunk 2012 (and possibly the Nike+ LeBron 10) if it becomes available the actual planet game) will have the ability to see stats on their dunks during replays.

  6. My developer is trying to persuade me to move to
    .net from PHP. I have always disliked the idea because of the expenses.

    But he’s tryiong none the less. I’ve been using Movable-type on a number of websites for
    about a year and am concerned about switching to another platform.
    I have heard good things about blogengine.net. Is there a way I can transfer all my wordpress
    posts into it? Any help would be greatly appreciated!

  7. “Voltage Loss or Voltage Drop, That Is The Question?
    | Applied Auto Weblog” truly enables myself contemplate a small bit extra.
    I actually admired every individual part of this post.
    I appreciate it ,Luigi

  8. Hey there! I simply wish to offer you a big thumbs up for the great info you have got right here on this post.
    I am returning to your web site for more soon.

  9. Hello friends, pleasant article and fastidious arguments commented at
    this place, I am genuinely enjoying by these.

  10. Having the great health and financial resources to travel with my wife as much as possible, to see more in the world and meet more of its folks.

  11. of their many go sic a itu these programs sonsg ndwe sosial perspecti

  12. Just wanted to say keep up the great

  13. the way it stands is possible to be literally secure in the next years. Cote d’Ivoire could be the logical area for freestaking.com to be accepted

  14. The ability to think like that shows you’re an expert in buying a used car!

  15. En motores de 2 hp lleva dos capacitores, 1 de arranque de 590-708, 110 v, de trabajo de 60 mf 230v siemens. En Motores de 3 hp lleva dos capacitores, 1 de arranque de 590- 708, 110 v, uno de trabajo de 75 mf 230 v siemens. Primero hay que saber qué factor de potencia tienen en toda la alimentación, este dato si no tienen medidor, viene en el recibo de CFE ó Iberdrola, y se trabaja en base a este dato para la corrección del Factor de Potencia, ahí se ve si se requiere corregir con filtros sólo capacitores.

  16. Ofrecemos un servicio técnico Westinghouse de calidad y con garantías, siempre esforzándonos al máximo en cada reparación, satisfaciendo las expectativas que nuestros clientes ponen en nuestra empresa, aunque no seamos el servicio técnico oficial de la marca Westinghouse. La reparación y el mantenimiento de sus electrodomésticos Westinghouse es muy importante para garantizar la vida útil de su electrodoméstico así como para ofrecer un rendimiento óptimo en el uso del electrodoméstico en el día a día. Nuestras reparaciones en Madrid están garantizadas por escrito en los materiales empleados como en la mano de obra.

  17. Thanks for sharing such great article about cats. The social adaptations of cats and humans are similar enough that dogs can live perfectly happy lives surrounded by humans and vice versa. Dogs are pampered with the best of treat and medical care, frequently have a rest in their owners’ comfortable beds.

  18. Excellent blog post . I absolutely like this website. Continue the good work!

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s