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How does temperature affect current and resistance?

ToddB64

ToddB64

Elite Member
Joined
Jan 30, 2006
Messages
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Location
Georgetown, Ohio, USA
Greetings! :tiphat:

I found the following statements related to the title on the Internet and they seem to suggest that it would be beneficial to metal detect during cool or cold weather to gain improved flow of electrical current in metals, as the inverse result of lower ohms or resistance.
I've been involved in the hobby of metal detecting for over 16 years and this is my first time to come across information leading me to this conclusion. Since I haven't been a fan of cold temperatures in my latter years, I haven't done enough metal detecting in cold weather to gauge if there is in fact a positive improvement when the ground and any metal targets in the ground are cool or cold.

Your opinions on my conclusion and/or your personal experiences of metal detecting in cold vs the warm time of year would be appreciated.

How does temperature affect current and resistance?

Temperature affects how electricity flows through an electrical circuit by changing the speed at which the electrons travel. This is due to an increase in resistance of the circuit that results from an increase in temperature.

The effect of heat on the atomic structure of a material is to make the atoms vibrate, and the higher the temperature the more violently the atoms vibrate. The more the atoms jostle around in the material, the more collisions are caused and hence the greater the resistance to current flow.

For metals, the thermal conductivity is mainly a function of the motion of free electrons. As the temperature increases, the molecular vibrations increase (in turn decreasing the mean free path of molecules). So, they obstruct the flow of free electrons, thus reducing the conductivity.

Thanks,
ToddB64
 
Last edited:
Is this April 1st already?

If it is over 80-85F, I am more RESISTANT to going outside to metal detect. If it is under 50F, I am also more RESISTANT to go metal detecting. If it is sub-freezing, I will be further RESISTANT to losing fingers to the cold and to digging through through frozen ground. Winter is almost over and I am CURRENTLY waiting for the Spring thaw. If we were to graph this, we'd get sort of a straight line at zero, followed by a nice bell curve peaking around 65-70F and back down to zero.

There's your significant effect of temperature on current and resistance.
 
TorqueMaster said:
Is this April 1st already?

If it is over 80-85F, I am more RESISTANT to going outside to metal detect. If it is under 50F, I am also more RESISTANT to go metal detecting. If it is sub-freezing, I will be further RESISTANT to losing fingers to the cold and to digging through through frozen ground. Winter is almost over and I am CURRENTLY waiting for the Spring thaw. If we were to graph this, we'd get sort of a straight line at zero, followed by a nice bell curve peaking around 65-70F and back down to zero.

There's your significant effect of temperature on current and resistance.
Click to expand...

:yes::lol:
 
TorqueMaster said:
Is this April 1st already?

If it is over 80-85F, I am more RESISTANT to going outside to metal detect. If it is under 50F, I am also more RESISTANT to go metal detecting. If it is sub-freezing, I will be further RESISTANT to losing fingers to the cold and to digging through through frozen ground. Winter is almost over and I am CURRENTLY waiting for the Spring thaw. If we were to graph this, we'd get sort of a straight line at zero, followed by a nice bell curve peaking around 65-70F and back down to zero.

There's your significant effect of temperature on current and resistance.
Click to expand...

Hi TorqueMaster ,

I like your creative way of replying and 65-70F is also my favorite temperature to metal detect. However, if cold weather means I have a better chance to find gold and silver jewelry, then I'll dress appropriately to deal with it.

I'm hoping to get some experiential reports from members regarding their success at finding more precious metal targets, or a larger volume of any kind of metal targets during periods of cold weather.

Also, is the theory that "metal detecting during periods of cold weather increases our chances of finding more and/or better precious metal targets" in agreement with the laws of science applied to metal detecting.?

ToddB64
 
I don’t know about cold temps in particular, but I think anyone who has been doing this for a certain amount of time has experienced the “zen hunt”….everything seems right, machine is stable, targets seem to be coming out of nowhere in a place that’s normally not like that…what causes this? I dunno, but I’m thinking it has more to do with EMI than temp. We have some pretty good machines out there that can tell us about ground conditions, and even if we need a frequency shift…but it would be nice to know the exact specifics at an exact time. I have experienced at least a dozen times where a hunt started great and then the signals “shut off”…or a hunt started terrible and the signals “turned on”. SOMETHING is causing this. But in these examples it wasn’t the temp. It’d be interesting to see hard data on the subject regarding detectors in particular. Because let’s face it…in this day and age where us coin hunters are scraping out the very last signals…we need EVERY advantage we can get.
 
ToddB64 said:
Greetings! :tiphat:

I found the following statements related to the title on the Internet and they seem to suggest that it would be beneficial to metal detect during cool or cold weather to gain improved flow of electrical current in metals, as the inverse result of lower ohms or resistance.
I've been involved in the hobby of metal detecting for over 16 years and this is my first time to come across information leading me to this conclusion. Since I haven't been a fan of cold temperatures in my latter years, I haven't done enough metal detecting in cold weather to gauge if there is in fact a positive improvement when the ground and any metal targets in the ground are cool or cold.

Your opinions on my conclusion and/or your personal experiences of metal detecting in cold vs the warm time of year would be appreciated.

How does temperature affect current and resistance?

Temperature affects how electricity flows through an electrical circuit by changing the speed at which the electrons travel. This is due to an increase in resistance of the circuit that results from an increase in temperature.

The effect of heat on the atomic structure of a material is to make the atoms vibrate, and the higher the temperature the more violently the atoms vibrate. The more the atoms jostle around in the material, the more collisions are caused and hence the greater the resistance to current flow.

For metals, the thermal conductivity is mainly a function of the motion of free electrons. As the temperature increases, the molecular vibrations increase (in turn decreasing the mean free path of molecules). So, they obstruct the flow of free electrons, thus reducing the conductivity.

Thanks,
ToddB64
Click to expand...

Todd,

You are correct, most metals have a positive temperature coefficient of resistance, so their resistance decreases as their temperature is lowered from the reference temperature (reference temperature is usually taken to be 20 degrees Celsius). However, some metals (alloys) have a negative temperature coefficient, for example, Manganin and Constantan.

Having said all that, for the temperature extremes that individuals are comfortable with, say a range from 0 Celsiue (32 F) to 35 Celsius (95 F), the change in resistance is too small to make a large difference.

For example, Copper has a thermal coefficient of resistance of 0.004041 per degree Celsium. If you have a pure copper target that measure 1.0 Ω at 20 Celsius and you re-measure it at 0 Celsium, its would measure 0.92 Ω, not a very dramatic difference (8%).
 
believe it or not when my wife and I lived off grid we used solar as our only source of electricity we did have a generator as back up though, summertime was the worst time charging the batteries the best time is when the temps were in the 70s the way it was explained to me is because the higher temps affected the resistance of the solar panels and wire to carry the charge from the solar panels to the batteries, the person that told me this was a electrical engineer, and all I can tell you is when the temps were up around 100 degrees my batteries seemed to work less efficient, I do not know if the same thing applies to metal detecting or not but by what the person told me it did apply to solar systems from what I seen
 
You lost me at

"The effect of heat on the atomic structure of a material is to make the atoms vibrate, and the higher the temperature the more violently the atoms vibrate."
 
ToddB64 said:
Hi TorqueMaster ,

I like your creative way of replying and 65-70F is also my favorite temperature to metal detect. However, if cold weather means I have a better chance to find gold and silver jewelry, then I'll dress appropriately to deal with it.

I'm hoping to get some experiential reports from members regarding their success at finding more precious metal targets, or a larger volume of any kind of metal targets during periods of cold weather.

Also, is the theory that "metal detecting during periods of cold weather increases our chances of finding more and/or better precious metal targets" in agreement with the laws of science applied to metal detecting.?

ToddB64
Click to expand...

That was just my tongue-in-cheek way of saying what Rudy pretty much said -- negligible effect. To targets, to detector performance.

Seems like anecdotally, conditions / detector "deepness" get better after it rains... I've read that a lot. Others can chime in. In my case, I'm more likely to go digging if the dirt isn't rock hard, so after a rain is frequently more successful...
 
I would think the effect of temperature on the performance of hobby level detectors,say 2000.00 and less is so small as to be unquantifiable, to wit,other factors probably have a greater effect,if any.Just an opinion,I have no solid evidence.
 
Phew lot of stuff going on in here...

OP your hypothesis about electrical resistance is all sound but I really don't think it comes in to play with detecting.

First and foremost most of are using VLF which uses magnetic field detection:

https://electronics.howstuffworks.c...metal detector,thousands of times each second.

We are getting in to some heavy science beyond what I've already pointed out. Old Google says that temperatur had no affect on magnetic fields themselves... but I'm not going to read the scientific what paper or even link it here.

The objects we detect and their magnetic field response is a different topic all together and one that I'm no where near we'll enough versed to begin to speak on. Maybe someone else here has some input.

I'm going to say that the biggest impact heat would have on detecting would come down to electrical efficiency of our machines but the voltages we are dealing with in the coil and control boxes is micro voltage. My Garrett machine is what a 6v system... the deus 2 has button cell batteries to drive the coil field. These run at every lower power. Anyway time for another cup of coffee.

Sent from my SM-F926U using Tapatalk
 
kazacomy said:
Phew lot of stuff going on in here...

OP your hypothesis about electrical resistance is all sound but I really don't think it comes in to play with detecting.

First and foremost most of are using VLF which uses magnetic field detection:
Click to expand...

Sorry, but the magnetic field the VLF detector is sensing from the target, is caused by Eddy Currents induced in the target by the detector's transmit field.

The amount of Eddy Current induced in the target is inversely proportional to the target's resistance.
 
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