Parasitic Drain

[RamDiver]

Maybe I'm misunderstanding what you wrote, but you can't really measure a voltage drop across a fuse. A fuse is not a resistor, it is a conductor. It would be the same thing as trying to measure a voltage drop across 1/2 inch of a power cable.

Regards,
Dusty
2019 Ram 1500 Billet Silver Laramie Quad Cab 2WD, 5.7 Hemi, 8HP75, 3.21 axle, 33-gallon fuel tank, 18” wheels. Build Date: 3 June 2018. Now at 130131 miles.

Did you read the PDF in my post above?

Actually, a fuse does have a resistive value; there will be a voltage drop across the fuse directly related to the current and can be calculated using Ohm's law.

A fuse is basically a calibrated conductor. Different sizes of conductors will be capable of carrying a specific amount of current before they fry and cease to conduct.

We know the voltage from the measurement across the fuse, and the resistance is known from the fuse manufacturer.

I= E/R
where I=current in Amps
where E=volts
where R= resistance in ohms

The fuse voltage drop chart above was derived using the relative resistive value of various fuses, and the voltage drop was calculated based on different currents.

For instance, reading 1mV across a 1 amp fuse translates to 8mA of current flow.

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[BossHogg]

Maybe I'm misunderstanding what you wrote, but you can't really measure a voltage drop across a fuse.

Measuring the voltage drop across the fuse looking for an active circuit has been a popular way to find a parasitic loss. For a "how to" watch this video.

The BEST Way TO Perform a Parasitic Draw Test

Parasite current draw tests can be a nightmare. When a car has battery drain proper testing is vital to finding the problem. This is the best way I have foun...

www.youtube.com

 

[Dusty]

Interesting. Well, I've learned something new. Then this type of fuse must have a resistive value. I can tell you that this type is different than a non-slo-blow buss fuse.

Regards,
Dusty
2019 Ram 1500 Billet Silver Laramie Quad Cab 2WD, 5.7 Hemi, 8HP75, 3.21 axle, 33-gallon fuel tank, 18” wheels. Build Date: 3 June 2018. Now at 130202 miles.

 

[BossHogg]

Interesting. Then this type of fuse must have a resistive value. I can tell you that this type is different than a non-slo-blow buss fuse.

Regards,
Dusty
2019 Ram 1500 Billet Silver Laramie Quad Cab 2WD, 5.7 Hemi, 8HP75, 3.21 axle, 33-gallon fuel tank, 18” wheels. Build Date: 3 June 2018. Now at 130202 miles.

Any conductor will have a voltage drop over any distance proportional to the amount of current flow. No conducting material has yet been discovered that offers a free pass to elections passing through without loss.

 

[Dusty]

Any conductor will have a voltage drop over any distance proportional to the amount of current flow. No conducting material has yet been discovered that offers a free pass to elections passing through without loss.

That's true over a length of wire of some distance, but on the same wire a measurement of very short distance (ie: 1 inch) is going to be so low as to be impractical for troubleshooting purposes. I can maybe see this on a solid number 10 wire flowing 30+ amperes. I don't see this on stranded wire since current flows on the outside skin of copper wires.

Regards,
Dusty
2019 Ram 1500 Billet Silver Laramie Quad Cab 2WD, 5.7 Hemi, 8HP75, 3.21 axle, 33-gallon fuel tank, 18” wheels. Build Date: 3 June 2018. Now at 130202 miles.

 

[RamDiver]

Interesting. Well, I've learned something new. Then this type of fuse must have a resistive value. I can tell you that this type is different than a non-slo-blow buss fuse.

Regards,
Dusty
2019 Ram 1500 Billet Silver Laramie Quad Cab 2WD, 5.7 Hemi, 8HP75, 3.21 axle, 33-gallon fuel tank, 18” wheels. Build Date: 3 June 2018. Now at 130202 miles.

One might think water has zero resistance, but everything has a defined resistive value, including water and air. Maybe, everything but an insulator has resistance.

The Resistivity Of Water Explained | Atlas Scientific

The resistivity of water is a fascinating concept that is directly determined by the concentration of dissolved salts found within the water. This means that water with a higher concentration of…

atlas-scientific.com

Air Gap Resistance Calculator & Formula Online Calculator Ultra

Air gap resistance is a critical factor in electrical systems where insulation properties are essential. This calculator allows you to compute the resistan

www.calculatorultra.com

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[RamDiver]

That's true over a length of wire of some distance, but on the same wire a measurement of very short distance (ie: 1 inch) is going to be so low as to be impractical for troubleshooting purposes. I can maybe see this on a solid number 10 wire flowing 30+ amperes. I don't see this on stranded wire since current flows on the outside skin of copper wires.

Regards,
Dusty
2019 Ram 1500 Billet Silver Laramie Quad Cab 2WD, 5.7 Hemi, 8HP75, 3.21 axle, 33-gallon fuel tank, 18” wheels. Build Date: 3 June 2018. Now at 130202 miles.

Look at the PDF and decide on the functionality of measuring voltage drops on fuses.

It does work.

The concept is well presented in the video Boss Hogg posted above.

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[BossHogg]

That's true over a length of wire of some distance, but on the same wire a measurement of very short distance (ie: 1 inch) is going to be so low as to be impractical for troubleshooting purposes. I can maybe see this on a solid number 10 wire flowing 30+ amperes. I don't see this on stranded wire since current flows on the outside skin of copper wires.

Regards,
Dusty
2019 Ram 1500 Billet Silver Laramie Quad Cab 2WD, 5.7 Hemi, 8HP75, 3.21 axle, 33-gallon fuel tank, 18” wheels. Build Date: 3 June 2018. Now at 130202 miles.

Define "some distance". You are making something that isn't, difficult. Simply watch the video I linked as well as the voltage drop article I linked. Even as resistant as you are to learning, you can not change the properties of physics.

 

[Dean2]

Boss and Ram are correct. It can be done that way. It is an alternative to measuring Milliamps or Amps on the negative post and pulling each fuse until the amperage draw drops.

Speaking of electrical stuff that isn't well known, stick your black ground lead off you Voltmeter into the dirt and measure how many volts that are present by touching the red lead to any metal pipe going into your house.

Some examples of readings I have taken.

Earth to my gas meter 0.395 VAC
Earth to the ring on my meter socket - 0.488 VAC
Earth to my neighbours gas meter - 0.298 VAC.

 

[Dusty]

Define "some distance". You are making something that isn't, difficult. Simply watch the video I linked as well as the voltage drop article I linked. Even as resistant as you are to learning, you can not change the properties of physics.

Excuse me but I am not opposed to learning. Did you read my previous post? I accept the process as valid. I'm not questioning electron theory, either. All electrical conductors have loss. Now does this make you happy?

"Any conductor will have a voltage drop over any distance proportional to the amount of current flow. No conducting material has yet been discovered that offers a free pass to elections passing through without loss."

True.

Technically, it doesn't matter how long a wire is, if you can measure the voltage drop of 1 inch along the same wire in a low current circuit it will be so low that the reading will likely be beyond the sensitivity of all but the most expensive laboratory equipment. That's all. Sure, in 1 mm there's a drop, but is that practical in troubleshooting?

Most auto technicians I've known don't know how to work Ohms Law, and using tables may seem inconvenient to others. Disconnecting a battery and measuring current flow directly or interrupting a circuit by pulling a fuse will seem much more practical. Some of the available DVOMs will float between .1 to .3 volts with the meter leads shorted together, so i wouldn't trust the subject method in all cases.

Regards,
Dusty
2019 Ram 1500 Billet Silver Laramie Quad Cab 2WD, 5.7 Hemi, 8HP75, 3.21 axle, 33-gallon fuel tank, 18” wheels. Build Date: 3 June 2018. Now at 130202 miles.

 

[RamDiver]

Excuse me but I am not opposed to learning. Did you read my previous post? I accept the process as valid. I'm not questioning electron theory, either. All electrical conductors have loss. Now does this make you happy?

"Any conductor will have a voltage drop over any distance proportional to the amount of current flow. No conducting material has yet been discovered that offers a free pass to elections passing through without loss."

True.

Technically, it doesn't matter how long a wire is, if you can measure the voltage drop of 1 inch along the same wire in a low current circuit it will be so low that the reading will likely be beyond the sensitivity of all but the most expensive laboratory equipment. That's all. Sure, in 1 mm there's a drop, but is that practical in troubleshooting?

Most auto technicians I've known don't know how to work Ohms Law, and using tables may seem inconvenient to others. Disconnecting a battery and measuring current flow directly or interrupting a circuit by pulling a fuse will seem much more practical. Some of the available DVOMs will float between .1 to .3 volts with the meter leads shorted together, so i wouldn't trust the subject method in all cases.

Agreed, measuring voltage drops does have some limitations and may not be practical for every scenario. The smaller currents are much more of a PITA.

With most of my experience chasing gremlins in automotive, the current rate is a couple of amps, which makes it easier to find.

By far, the majority of my pursuit of electrical gremlins has been working in Telecom, but I have chased a few of the automotive variety.

I would bet @Sherman Bird knows his way around Ohm's law, and any of the recently minted automotive techs had best be fluent in basic electronics, given the vehicles of today.

Then again, Sherman is by no means the usual automotive tech.

When you say some of the DVOMs float between .1 & .3 volts with the meter leads shorted together, are you possibly thinking of when the meter is set to resistance and attaining zero ohms is near impossible?

When measuring resistance on a smaller scale, zero ohms will never happen due to meter lead resistance and marginal contact of the probe ends.

I would bet that some of the very inexpensive DMMs are just that, cheap and incapable of the smaller mV measurements.

Just for fun, I tested my DMM on the 200mV scale. The first picture is open leads, the second is leads shorted together.





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[62Blazer]

Maybe I'm misunderstanding what you wrote, but you can't really measure a voltage drop across a fuse. A fuse is not a resistor, it is a conductor. It would be the same thing as trying to measure a voltage drop across 1/2 inch of a power cable.

Regards,
Dusty
2019 Ram 1500 Billet Silver Laramie Quad Cab 2WD, 5.7 Hemi, 8HP75, 3.21 axle, 33-gallon fuel tank, 18” wheels. Build Date: 3 June 2018. Now at 130131 miles.

This has been an industry standard check for parasitic draw since fuses were invented. There are hundreds of articles on the web and YouTube videos showing people doing this. It's not complicated by any means and can be done with a standard voltmeter/multimeter. If there is no power flowing through the circuit the voltage drop will be zero. If there is power (amperage) being pulled in that circuit you will see a voltage drop, and you are talking maybe .2-.4 mV.

 

[Dusty]

Agreed, measuring voltage drops does have some limitations and may not be practical for every scenario. The smaller currents are much more of a PITA.

With most of my experience chasing gremlins in automotive, the current rate is a couple of amps, which makes it easier to find.

By far, the majority of my pursuit of electrical gremlins has been working in Telecom, but I have chased a few of the automotive variety.

I would bet @Sherman Bird knows his way around Ohm's law, and any of the recently minted automotive techs had best be fluent in basic electronics, given the vehicles of today.

Then again, Sherman is by no means the usual automotive tech.

When you say some of the DVOMs float between .1 & .3 volts with the meter leads shorted together, are you possibly thinking of when the meter is set to resistance and attaining zero ohms is near impossible?

When measuring resistance on a smaller scale, zero ohms will never happen due to meter lead resistance and marginal contact of the probe ends.

I would bet that some of the very inexpensive DMMs are just that, cheap and incapable of the smaller mV measurements.

Just for fun, I tested my DMM on the 200mV scale. The first picture is open leads, the second is leads shorted together.

View attachment 565228

View attachment 565229

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The 8026 is a true RMS meter. they are nice. I cannot say I've ever seen a true RMS meter in the hands of an auto tech., at least the yellow series.

My experience has been mostly in the RF field, but done a fair amount of automotive electrical troubleshoot.

My meter reference was regarding meters in the dCV range. My garage meter is famous for this.

Regards,
Dusty
2019 Ram 1500 Billet Silver Laramie Quad Cab 2WD, 5.7 Hemi, 8HP75, 3.21 axle, 33-gallon fuel tank, 18” wheels. Build Date: 3 June 2018. Now at 130202 miles.

 

[Dusty]

This has been an industry standard check for parasitic draw since fuses were invented. There are hundreds of articles on the web and YouTube videos showing people doing this. It's not complicated by any means and can be done with a standard voltmeter/multimeter. If there is no power flowing through the circuit the voltage drop will be zero. If there is power (amperage) being pulled in that circuit you will see a voltage drop, and you are talking maybe .2-.4 mV.

Of course my automotive training occurred when vehicles still had points and a condenser (capacitor), and I've used the voltage drop method on battery to ground and starter circuits. I am familiar with automotive and business machine service manuals and I've never observed the fuse as a way to check for a voltage drop. Would I use this method when checking for low current circuit draws? I don't know. Maybe. In the past it didn't bother me to remove a battery cable or disconnect a connector.

The one good point I got from the video that was posted is that sometimes just pulling a fuse could stop the problem by remove voltage from the gate of the driver. This can happen.

Regards,
Dusty
2019 Ram 1500 Billet Silver Laramie Quad Cab 2WD, 5.7 Hemi, 8HP75, 3.21 axle, 33-gallon fuel tank, 18” wheels. Build Date: 3 June 2018. Now at 130202 miles.

 

[BossHogg]

The 8026 is a true RMS meter. they are nice. I cannot say I've ever seen a true RMS meter in the hands of an auto tech., at least the yellow series.

Most auto technicians I've known don't know how to work Ohms Law

I've never observed the fuse as a way to check for a voltage drop. Would I use this method when checking for low current circuit draws? I don't know. Maybe. In the past it didn't bother me to remove a battery cable or disconnect a connector.

That is because RMS, and with your experience in radio frequency, should know that RMS is used to find the DC equivalent voltage of an AC circuit. I believe most, if not all, late-model digital volt meters include true RMS measurements since a computer already controls them. RMS is a mathematical calculation of an AC waveform.

You don't even need to know Ohm's law exists to measure a voltage drop across a conductor. Then, you can use the reading to reference a table to find the current flow.

If you were looking for a parasitic current draw in a modern vehicle, one with dozens of computers and individual circuits, you would be. Removing the battery cable or breaking a connector would cause some number of vehicle computers to wake. It takes considerable time for the vehicle's computers to fall asleep and then go into a deep sleep. I don't know any tech that has that time to waste. This is why measuring voltage drop across a fuse is so popular and a fast way to isolate current-carrying circuits.

 

[aszumilo]

Another thing to check is the alternator. Modern alts have the regulator built in. After some time, the diodes start to weaken and can drain off the battery. My mom's car would occasionally kill the battery overnight. It was intermittent, so, it took a bit to chase it down. Started getting weird symptoms, like the dash lights flickering, then the voltage gauge started to act odd, sometimes would read fine, sometimes read high, sometimes read low. Alt was still putting out 14v +/-. Replaced it and all the symptoms went away and never drained the battery again in the 2 years after replacement.

 

[rzr6-4]

 

[RamDiver]

I included a few details above about Ohm's law and how the fuse voltage drops were derived for those who might care to know more.

If you can use a multimeter and interpret the fuse voltage drop chart, you're good to go.

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