I'm so impressed. Such a useful amount of information - just enough science to help the viewer study further, never so much as to waste any time. Great vid 5 stars!
I really appreciate your style of explaining things. From the initial setup, to the questions the viewer might think of, to the conclusion and summary, you have an excellent way of covering material. Hats off to you sir.
5:19 “…areas of corrosion are more likely to behave like a light bulb, with increasing resistance as the current increases, and the corroded area heats up.” Many thanks for this insight. I've been troubleshooting a 1HZ engine, good (new) battery relatively new starter motor (installed by others), but it still has voltage drops of 0.62-0.63V on both positive and ground sides of the starter motor. The LoadPro shows only 0.1V difference to system voltage for any test on the positive or ground sides, and this would indicate cabling and grounding are good, yet I was losing 1.25V during cranking in those same areas. Also, your graphs, especially the hyperbolic current vs resistance graph, generally loads performing work versus (essentially) signals. 6:45 “Notice how steep this part of the graph is. Which means even a couple of ohms extra circuit resistance from corrosion could be enough to dramatically reduce current and power delivery.” That's what I'm finding. The clamp meter is showing peak current anywhere from 400A onward, and small amounts of extra resistance is really impacting power delivery. I may have got there on my own, but your video has helped me get to the end of that thinking process much quicker. Thanks.
Very well done Dave and I like the usage of the graphs to illustrate your points throughout the video! Now I'm ready to see your waveform from your fuel pump :) Keep up the good work and I'm sure you'll help a lot of folks in better understanding voltage drop.
I considered myself an average intelligent person. I have an aptitude for learning and can generally excel in anything I do. However, two things have always been difficult for me. Math and electronics. Enter RUclips and great channels such as yours. Since I have been in this automotive community and have seen test lights and volt meters used correctly I am beginning to understand the process. Then there is the scope. The ability to see electricity has greatly reduced my apprehension towards electricity and the task of learning has become less daunting. Thank you for posting this video, you don't know how much this information is appreciated.
Coming from a real pro like yourself, I am humbled by your comment, thank you. This one was a little disappointing because I think it is one of my better ones, but for some reason it never gained traction in viewer counts. I assume that was because people clicked away when it got too technical, and it doesn't easily fit the search engine algorithm. Like many things in life, there is a huge disconnect between effort and outcome.
I do use the bulb method, but only on higher current supply lines of low resistance. Like testing for the fuel pump feed that has a habit of causing problems. Loading a power circuit up with a bulb is the best for ordinary circuits. But ohms law will look odd because a bulb does not have a fixed resistance, the heat of the element/resistance changes with voltage but not in a linear way. And the 21 watt indicator bulb is great for low current circuits up to 2 amps, mostly as an indicator of power for that "dodgy connection" that's hard to find, a bulb allows you to wiggle all the connectors to make the light flicker. Visual brightness feedback is so effective :-D Also if you have a fuse that keeps blowing and you cant find the short, connect a bulb across a dummy fuse and plug it in, the bulb will be bright untill you disconnect the dodgy device. Or you could just run away screaming with your arms in the air lol, Optional.
Excellent points! I made a circuit detector several years ago that plugs into the fuse box, with a light and a noise so you don't have to stare at it. It's hard to watch that old video now, information delivery is too slow. That little circuit detector is still going strong.
Sounds like a similar fuse idea as mine, but with a buzzer across the fuse holder. Perhaps using a bridge rectifier to make sure the buzzer has the correct polarity always. Thats the way i would do it, but knowing you, you have found a better way :-D Diodes and relays can also be very handy :-D
Struggling to diagnose an electrical issue on my skid steer, FSS fuse keeps blowing when key is turned on 15amp fuse it powers a handful of things, most of which ive disconnected Im wanting to have the circuit live with a bulb while i jigging wire loom and connect and disconnect things, it seems like the current circuit is almost a dead short once current is applied but was measuring 7ohms from ground to the fuse block pin earlier ill have to check and see if thats changed as the issue is sporadic and keeps evolving In guessing adding one bulb will still blow a 15amp fuse, i need to add a few?
A 15A fuse should not blow with the resistance of a typical bulb, so you've probably got a parallel short, maybe upstream of the bulb. I made a little short circuit tester that plugs into the fuse box, allowing one to put the bulb and a buzzer right at the fuse box, so it has to be inline with the short. There's a really old video on my channel describing how that was done. Even a test light bridging the fuse connectors at the fuse box could be helpful. Dead shorts are a pain, it can take a long time to find the problem, especially with an intermittent. Hunt down connectors and try to divide the problem up so you can narrow down the source as much as possible, then manually trace the wire. Don't forget to look under the fuse box, too, it could be right there. If you have to you may choose to cut a wire to save yourself some time by dividing the problem in two. There are various products on the market that send an RF signal down the wire, with an inductive pickup to help in the hunt. Experienced pros are surprisingly cool to their use, they give misleading results and don't save a lot of time. I have one for 120V use but it was not very effective, too many misleading results caused by parallel wires.
For sure you could make your own, a resistor is the basic design of the LoadPro. They put a 25 ohm resistor, a fuse and a thumb switch in a wire inside the bulbous red handle of the LoadPro. The hidden internal wire connects the red lead with the black lead, so when the button is pressed you get a short between the two leads. Starting at 4:25, I've attached the LoadPro leads to a multimeter set to measure ohms. The two leads are not touching each other. Notice when I press the button I measure 25.8 ohms, with the 0.8-0.9 being a little extra line resistance. When they use is in the field, they first check resistance like I did to be sure the fuse isn't blown. Then they switch the multimeter to measure volts, put the two leads on either side of the questionable area of resistance, and press the button. You could make that with about $20 worth of parts, it would be a fun little project. That said, a light bulb gives a quick visual signal that you've got current flow, and often that's all the tech needs. It's all about time management, those guys don't want any extra steps that are distracting and cost time. The incandescent test light is good for low current applications, and the halogen headlight bulb is good for moderate current wires. For the really high current wires like the starter motor or alternator, try to use the actual device and measure current with an inductive clamp meter. Thanks for watching!
I came back to this remark because I've had that same feeling many times here on the 'net! Our amazing RUclips community is made by people of diverse backgrounds, and I can't say I've ever met somebody who didn't have something to teach me. Often it is as simple and powerful as an incentive to learn more about a new topic. For example your channel has some excellent auto repair footage. Sometimes learning a new approach to a problem takes a little work, since we all come from different places. Thanks for giving me the opportunity to give back to a community that has helped me so much through the years. I hope any extra effort people put in is worth it for them, in the end.
RUclips has been not only educational for me on many different subjects but also entertaining. The key is finding a video creator that competent. If I can broaden my horizons on a subject then it keeps my brain exercised. Keep up the good work Dave and see you on the next vid!
I took a 12 volt supply DC and placed a 2 ohm resistor on the positive side of the circuit to an empty connector. The loadpro 181 read 12.12v at the empty connector. I then pressed the loadpro button and the loadpro read 10.48v a significant drop 1.64vd. Now with the resistor removed from the circuit, the load pro read 12.12v, then pressing the button 11.43v which is .69vd
Good for you, a tradesman needs to understand his tools to have any hope of interpreting results in the real world! As you probably know, the drop in your first example should have read 11.25V, but instead it read 10.48V. ie 12.12*(25.9/(25.9+2)) = 11.25V. Two things commonly affect that. First, there may be slightly more resistance in the circuit than you account for, perhaps even in the meter wiring. I would set your meter to ohms, and without the Load Pro connected to anything else press the LoadPro button and verify that you have 25.9 ohms. That's a good test to always start out with because you want to prove your internal fuse hasn't blown before making assumptions about results. Your static resistance may be slightly more, or there may be dynamic resistance in your tool that only comes out when under load. Second, when a battery is placed under load the dynamic voltage of the battery always drops a little because of internal resistance, causing real voltage output of the battery to sag down. All of this shows that real world experience needs to account for minor resistance at connection points and battery output sag. Guys who use the LoadPro every day are more intuitive. They skip the math and look for big changes, recognizing that real world problems are usually glaring and obvious. They ignore any drop less than a volt as being insignificant. The place to watch out for are those high current wires, where the LoadPro might miss the tiny extra resistance that robs the end device of adequate power. Thanks for your comment!
@@spelunkerd Thanks for your fast reply. Could you give me an example of a circuit that I could set up at home to duplicate your following statement: "The place to watch out for are those high current wires, where the LoadPro "might" miss the tiny extra resistance that robs the end device of adequate power." I would like to duplicate that issue. Thank you very much.
@@stspringer2003 I guess if one wanted to practically duplicate that, you could introduce a resistor on the starter motor circuit, in line with the battery. If you put a 2 ohm resistor in line with the heavy starter B post wire, the resistor will drop the normal 100A spike down to slightly less than 6A (12v/2=6). Make sure your resistor is rated for the power (6X12= 72 Watts), it might get hot. If you put your multimeter on the wire between the resistor and the motor, the voltage would be dropped while current is flowing, robbing power from the motor.... Or you could replace the resistor with your test light. Even with a headlight circuit, if you put a test light in line with the headlight, the headlight won't be able to light because the test light resistance gobbles up most of the voltage drop. A headlight in line with a test light might be the bench circuit you're looking for....
@@stspringer2003 Oh, I see what you are asking. Suppose your starter motor circuit had a resistance of 0.12 ohms, giving a surge current of 100A from a 12V battery. Now add 2 ohms of resistance at the pos battery terminal. Then the drop across the 2 ohm resistor is 12*2/(2+0.12)=11.3V, leaving only 0.7 V drop across the motor! And total current is only 12/2.12 = 5.7A, not 100A. That motor won't turn, its power was robbed by the resistor. Testing with the LoadPro doesn't show the glaring abnormality, the drop across the LoadPro would be 12*(25.9/(25.9+2)= 11.1V. So, for really high current wires, it is better to test with a device that draws an equal amount of current. The easiest way to get current moving is with the device itself, if you can. If not, a headlight bulb works pretty well, drawing ~4 Amps.
so should i determine how much amperage normally would flow through that circuit and try to match a light bulb that draws the same amount?then because you now have a live circuit i can do a VD test as well thus the best way to test for a diy guy?because i dont want to buy pico scope or expensive tools as this is just my hobby this should be enough to get through most everything right?
Yes! You can easily estimate what circuits will carry based on what they drive. For most circuits a test light works fine, I would choose one with an incandescent light rather than an LED. For bigger circuits that do more physical work, like the window regulator, fuel pump, various motor drives, blower motor, door lock actuator, and even headlights, a simple headlight bulb works fine. Halogen headlight bulbs draw about 4 Amps. One of the things I most admire about Eric on the SouthMainAuto RUclips channel is the way he quickly and effortlessly uses his headlight bulb to verify the circuit can carry enough current to power a device. He proves, you don't have to be slow to do things right. If you just turn it on just for a second, it's not likely to fry anything in the circuit, but to be safe I would not test circuits ending in the computer with high current test devices. There are other methods for those. Thanks for your comment, it is nice to meet you.
@@spelunkerd perfect! i have a selection of bulbs a 0.2a 0.5a 2a 3a 4a and a monster 6a.for the starting circuit is a 6amp bulb enough?i have a few i could add together?
@@pigeonsil240sx Great. The starting circuit is a special case, because the inrush current on those motors is extraordinary, usually greater than 150 Amps. It's on such a steep part of the I/R curve that even an extra ohm of resistance can be enough to pull down the current so far that the motor won't spin. Nobody has a 150 Amp headlight! So the problem with lightbulbs is the falsely reassuring result if it glows brightly. Wiring bulbs in parallel is too much trouble, wiring in series won't work. The fast approach to the starter problem is easy enough if your starter is drawing current. Use the motor itself, rather than a headlight. If you can get to the motor connections, that is easy, clip your multimeter to the attached B+ post of the starter and run the other multimeter lead with a jumper back to the negative pole of the battery. Even with key off you should get 12 V. Then get a friend to turn the engine over with the key and watch how far the voltage sags. If it sags more than 1/2 volt, you've got excessive resistance of the line. Fix that first before condemning the starter! If nothing happens at all, move your multimeter lead to the other terminal of the battery, the trigger post that comes from the ignition relay. You should get 12 V there, only when your friend turns the key, again with minimal drop. As a final test of the wiring, you can put a 4A headlight bulb between the attached trigger post and a ground somewhere. The other tricky thing about the starter is the way you can't often tell whether the problem is the solenoid or the starter itself. Nine times out of ten it's corroded contacts of the solenoid, which can be sometimes fixed with a little effort.
Hello. Thanks for the informative video. I would like to ask you a question. I have an issue with my car that I can't understand. My left headlight is not working. When I check with multimeter the voltage is 12V. The moment I connect a bulb, the voltage drops to 0 and the bulb doesn't light up. I've tried with 3 different bulbs. Do you think that this is an issue with the car wiring?
Excellent question. Yes, you likely have a source of resistance between the battery and the bulb. A very common cause is the connector, so look for clues like “green crusties” and overheating. For more info, search “voltage drop testing”.
Sitting by the fireside, ready to pour a nice wee drop of mountain dew, listening attentively when you decided to take your leave. Now, to me, that's bad manners. Would have offered yourself a drop if you weren't in such a big hurry. Now I'm left wondering about the bleedin pump and the amp display. Life ain't easy for a boy named Sue.
I'm so impressed. Such a useful amount of information - just enough science to help the viewer study further, never so much as to waste any time. Great vid 5 stars!
I really appreciate your style of explaining things. From the initial setup, to the questions the viewer might think of, to the conclusion and summary, you have an excellent way of covering material. Hats off to you sir.
Thanks, man!
5:19 “…areas of corrosion are more likely to behave like a light bulb, with increasing resistance as the current increases, and the corroded area heats up.” Many thanks for this insight. I've been troubleshooting a 1HZ engine, good (new) battery relatively new starter motor (installed by others), but it still has voltage drops of 0.62-0.63V on both positive and ground sides of the starter motor. The LoadPro shows only 0.1V difference to system voltage for any test on the positive or ground sides, and this would indicate cabling and grounding are good, yet I was losing 1.25V during cranking in those same areas.
Also, your graphs, especially the hyperbolic current vs resistance graph, generally loads performing work versus (essentially) signals.
6:45 “Notice how steep this part of the graph is. Which means even a couple of ohms extra circuit resistance from corrosion could be enough to dramatically reduce current and power delivery.” That's what I'm finding. The clamp meter is showing peak current anywhere from 400A onward, and small amounts of extra resistance is really impacting power delivery. I may have got there on my own, but your video has helped me get to the end of that thinking process much quicker. Thanks.
Very well explained! Looking forward to that fuel pump current video with the PicoScope! Thank you for sharing.
Very well done Dave and I like the usage of the graphs to illustrate your points throughout the video! Now I'm ready to see your waveform from your fuel pump :) Keep up the good work and I'm sure you'll help a lot of folks in better understanding voltage drop.
stuzman!
Ozzstar yes Glen! I see that you get around. 😀👍
I considered myself an average intelligent person. I have an aptitude for learning and can generally excel in anything I do. However, two things have always been difficult for me. Math and electronics. Enter RUclips and great channels such as yours. Since I have been in this automotive community and have seen test lights and volt meters used correctly I am beginning to understand the process. Then there is the scope. The ability to see electricity has greatly reduced my apprehension towards electricity and the task of learning has become less daunting. Thank you for posting this video, you don't know how much this information is appreciated.
r/iamverysmart
Very well explained, I also like the explanation of how subjective gauging voltage drop via bulbs can be. Thanks for sharing.
Thanks!
Well done. Nice to see good diagnostics rather than throwing parts at it.
Very well explained. Now I understand the light bulb theory. Thanks......
I use this method all the time. Really narrow down the diagnostic for me
so awesome. adequate depth and breath, nicely sequenced and well narrated. thx.
Thank you!
Great info! Thanks
Great job on explaining , You got great skills .
Coming from a real pro like yourself, I am humbled by your comment, thank you. This one was a little disappointing because I think it is one of my better ones, but for some reason it never gained traction in viewer counts. I assume that was because people clicked away when it got too technical, and it doesn't easily fit the search engine algorithm. Like many things in life, there is a huge disconnect between effort and outcome.
excellent video and explanation. Thank you for taking the time to share.👍👍👍
I do use the bulb method, but only on higher current supply lines of low resistance.
Like testing for the fuel pump feed that has a habit of causing problems.
Loading a power circuit up with a bulb is the best for ordinary circuits.
But ohms law will look odd because a bulb does not have a fixed resistance, the heat of the element/resistance changes with voltage but not in a linear way.
And the 21 watt indicator bulb is great for low current circuits up to 2 amps, mostly as an indicator of power for that "dodgy connection" that's hard to find, a bulb allows you to wiggle all the connectors to make the light flicker.
Visual brightness feedback is so effective :-D
Also if you have a fuse that keeps blowing and you cant find the short, connect a bulb across a dummy fuse and plug it in, the bulb will be bright untill you disconnect the dodgy device.
Or you could just run away screaming with your arms in the air lol, Optional.
Excellent points! I made a circuit detector several years ago that plugs into the fuse box, with a light and a noise so you don't have to stare at it. It's hard to watch that old video now, information delivery is too slow. That little circuit detector is still going strong.
Sounds like a similar fuse idea as mine, but with a buzzer across the fuse holder.
Perhaps using a bridge rectifier to make sure the buzzer has the correct polarity always.
Thats the way i would do it, but knowing you, you have found a better way :-D
Diodes and relays can also be very handy :-D
Good thought about correct polarity, you always add remarks that raise the bar.
nice
Struggling to diagnose an electrical issue on my skid steer, FSS fuse keeps blowing when key is turned on 15amp fuse it powers a handful of things, most of which ive disconnected
Im wanting to have the circuit live with a bulb while i jigging wire loom and connect and disconnect things, it seems like the current circuit is almost a dead short once current is applied but was measuring 7ohms from ground to the fuse block pin earlier ill have to check and see if thats changed as the issue is sporadic and keeps evolving
In guessing adding one bulb will still blow a 15amp fuse, i need to add a few?
A 15A fuse should not blow with the resistance of a typical bulb, so you've probably got a parallel short, maybe upstream of the bulb. I made a little short circuit tester that plugs into the fuse box, allowing one to put the bulb and a buzzer right at the fuse box, so it has to be inline with the short. There's a really old video on my channel describing how that was done. Even a test light bridging the fuse connectors at the fuse box could be helpful. Dead shorts are a pain, it can take a long time to find the problem, especially with an intermittent. Hunt down connectors and try to divide the problem up so you can narrow down the source as much as possible, then manually trace the wire. Don't forget to look under the fuse box, too, it could be right there. If you have to you may choose to cut a wire to save yourself some time by dividing the problem in two. There are various products on the market that send an RF signal down the wire, with an inductive pickup to help in the hunt. Experienced pros are surprisingly cool to their use, they give misleading results and don't save a lot of time. I have one for 120V use but it was not very effective, too many misleading results caused by parallel wires.
Good video
great smile
Thanks for sharing your knowledge. Can we use a load resistor as a fixed resistor instead of bulb when doing voltage drop test?
For sure you could make your own, a resistor is the basic design of the LoadPro. They put a 25 ohm resistor, a fuse and a thumb switch in a wire inside the bulbous red handle of the LoadPro. The hidden internal wire connects the red lead with the black lead, so when the button is pressed you get a short between the two leads. Starting at 4:25, I've attached the LoadPro leads to a multimeter set to measure ohms. The two leads are not touching each other. Notice when I press the button I measure 25.8 ohms, with the 0.8-0.9 being a little extra line resistance. When they use is in the field, they first check resistance like I did to be sure the fuse isn't blown. Then they switch the multimeter to measure volts, put the two leads on either side of the questionable area of resistance, and press the button. You could make that with about $20 worth of parts, it would be a fun little project. That said, a light bulb gives a quick visual signal that you've got current flow, and often that's all the tech needs. It's all about time management, those guys don't want any extra steps that are distracting and cost time. The incandescent test light is good for low current applications, and the halogen headlight bulb is good for moderate current wires. For the really high current wires like the starter motor or alternator, try to use the actual device and measure current with an inductive clamp meter. Thanks for watching!
spelunkerd Thanks you sir. that was very useful for me.
Well said I had to google a lot of big words to know what they mean
Thanks for putting in the effort, I tried to avoid difficult jargon as much as I could.
I came back to this remark because I've had that same feeling many times here on the 'net! Our amazing RUclips community is made by people of diverse backgrounds, and I can't say I've ever met somebody who didn't have something to teach me. Often it is as simple and powerful as an incentive to learn more about a new topic. For example your channel has some excellent auto repair footage. Sometimes learning a new approach to a problem takes a little work, since we all come from different places. Thanks for giving me the opportunity to give back to a community that has helped me so much through the years. I hope any extra effort people put in is worth it for them, in the end.
RUclips has been not only educational for me on many different subjects but also entertaining. The key is finding a video creator that competent. If I can broaden my horizons on a subject then it keeps my brain exercised. Keep up the good work Dave and see you on the next vid!
Excellent video, I fix cars and boats.
Nice to meet you, I'm headed out to the boat today to do a furling roller video.
excelent work
Thanks!
I took a 12 volt supply DC and placed a 2 ohm resistor on the positive side of the circuit to an empty connector. The loadpro 181 read 12.12v at the empty connector. I then pressed the loadpro button and the loadpro read 10.48v a significant drop 1.64vd. Now with the resistor removed from the circuit, the load pro read 12.12v, then pressing the button 11.43v which is .69vd
Good for you, a tradesman needs to understand his tools to have any hope of interpreting results in the real world! As you probably know, the drop in your first example should have read 11.25V, but instead it read 10.48V. ie 12.12*(25.9/(25.9+2)) = 11.25V. Two things commonly affect that. First, there may be slightly more resistance in the circuit than you account for, perhaps even in the meter wiring. I would set your meter to ohms, and without the Load Pro connected to anything else press the LoadPro button and verify that you have 25.9 ohms. That's a good test to always start out with because you want to prove your internal fuse hasn't blown before making assumptions about results. Your static resistance may be slightly more, or there may be dynamic resistance in your tool that only comes out when under load. Second, when a battery is placed under load the dynamic voltage of the battery always drops a little because of internal resistance, causing real voltage output of the battery to sag down. All of this shows that real world experience needs to account for minor resistance at connection points and battery output sag. Guys who use the LoadPro every day are more intuitive. They skip the math and look for big changes, recognizing that real world problems are usually glaring and obvious. They ignore any drop less than a volt as being insignificant. The place to watch out for are those high current wires, where the LoadPro might miss the tiny extra resistance that robs the end device of adequate power. Thanks for your comment!
@@spelunkerd Thanks for your fast reply. Could you give me an example of a circuit that I could set up at home to duplicate your following statement: "The place to watch out for are those high current wires, where the LoadPro "might" miss the tiny extra resistance that robs the end device of adequate power." I would like to duplicate that issue. Thank you very much.
@@stspringer2003 I guess if one wanted to practically duplicate that, you could introduce a resistor on the starter motor circuit, in line with the battery. If you put a 2 ohm resistor in line with the heavy starter B post wire, the resistor will drop the normal 100A spike down to slightly less than 6A (12v/2=6). Make sure your resistor is rated for the power (6X12= 72 Watts), it might get hot. If you put your multimeter on the wire between the resistor and the motor, the voltage would be dropped while current is flowing, robbing power from the motor.... Or you could replace the resistor with your test light. Even with a headlight circuit, if you put a test light in line with the headlight, the headlight won't be able to light because the test light resistance gobbles up most of the voltage drop. A headlight in line with a test light might be the bench circuit you're looking for....
@@spelunkerd I am confused. Wouldn't the loadPro pick up a voltage drop on a 2-ohm resistor in line with the B+ battery line?
@@stspringer2003 Oh, I see what you are asking. Suppose your starter motor circuit had a resistance of 0.12 ohms, giving a surge current of 100A from a 12V battery. Now add 2 ohms of resistance at the pos battery terminal. Then the drop across the 2 ohm resistor is 12*2/(2+0.12)=11.3V, leaving only 0.7 V drop across the motor! And total current is only 12/2.12 = 5.7A, not 100A. That motor won't turn, its power was robbed by the resistor. Testing with the LoadPro doesn't show the glaring abnormality, the drop across the LoadPro would be 12*(25.9/(25.9+2)= 11.1V. So, for really high current wires, it is better to test with a device that draws an equal amount of current. The easiest way to get current moving is with the device itself, if you can. If not, a headlight bulb works pretty well, drawing ~4 Amps.
so should i determine how much amperage normally would flow through that circuit and try to match a light bulb that draws the same amount?then because you now have a live circuit i can do a VD test as well thus the best way to test for a diy guy?because i dont want to buy pico scope or expensive tools as this is just my hobby this should be enough to get through most everything right?
Yes! You can easily estimate what circuits will carry based on what they drive. For most circuits a test light works fine, I would choose one with an incandescent light rather than an LED. For bigger circuits that do more physical work, like the window regulator, fuel pump, various motor drives, blower motor, door lock actuator, and even headlights, a simple headlight bulb works fine. Halogen headlight bulbs draw about 4 Amps. One of the things I most admire about Eric on the SouthMainAuto RUclips channel is the way he quickly and effortlessly uses his headlight bulb to verify the circuit can carry enough current to power a device. He proves, you don't have to be slow to do things right. If you just turn it on just for a second, it's not likely to fry anything in the circuit, but to be safe I would not test circuits ending in the computer with high current test devices. There are other methods for those. Thanks for your comment, it is nice to meet you.
@@spelunkerd perfect! i have a selection of bulbs a
0.2a
0.5a
2a
3a
4a
and a monster 6a.for the starting circuit is a 6amp bulb enough?i have a few i could add together?
@@pigeonsil240sx Great. The starting circuit is a special case, because the inrush current on those motors is extraordinary, usually greater than 150 Amps. It's on such a steep part of the I/R curve that even an extra ohm of resistance can be enough to pull down the current so far that the motor won't spin. Nobody has a 150 Amp headlight! So the problem with lightbulbs is the falsely reassuring result if it glows brightly. Wiring bulbs in parallel is too much trouble, wiring in series won't work. The fast approach to the starter problem is easy enough if your starter is drawing current. Use the motor itself, rather than a headlight. If you can get to the motor connections, that is easy, clip your multimeter to the attached B+ post of the starter and run the other multimeter lead with a jumper back to the negative pole of the battery. Even with key off you should get 12 V. Then get a friend to turn the engine over with the key and watch how far the voltage sags. If it sags more than 1/2 volt, you've got excessive resistance of the line. Fix that first before condemning the starter! If nothing happens at all, move your multimeter lead to the other terminal of the battery, the trigger post that comes from the ignition relay. You should get 12 V there, only when your friend turns the key, again with minimal drop. As a final test of the wiring, you can put a 4A headlight bulb between the attached trigger post and a ground somewhere. The other tricky thing about the starter is the way you can't often tell whether the problem is the solenoid or the starter itself. Nine times out of ten it's corroded contacts of the solenoid, which can be sometimes fixed with a little effort.
Hello. Thanks for the informative video. I would like to ask you a question. I have an issue with my car that I can't understand. My left headlight is not working. When I check with multimeter the voltage is 12V. The moment I connect a bulb, the voltage drops to 0 and the bulb doesn't light up. I've tried with 3 different bulbs. Do you think that this is an issue with the car wiring?
Excellent question. Yes, you likely have a source of resistance between the battery and the bulb. A very common cause is the connector, so look for clues like “green crusties” and overheating. For more info, search “voltage drop testing”.
@@spelunkerd Thank you very much.
smart i always though of using a cpu fan or a heating element
Good point, there are many options. In the end, you just need to have enough experience with the tool to understand what its telling you.
Sitting by the fireside, ready to pour a nice wee drop of mountain dew, listening attentively when you decided to take your leave. Now, to me, that's bad manners. Would have offered yourself a drop if you weren't in such a big hurry. Now I'm left wondering about the bleedin pump and the amp display. Life ain't easy for a boy named Sue.
Ha ha, Tom. Thanks to my friend from Galway for dropping by.