2450mah vs 2500mah

[Foolios]

I have a set of rechargable batteries but their milli-amp hour ratings differ. Is the mah number the amount of current that they output per hour, how much amperage they are pushing out at a given instant, or how much current they can retain? I just wanna make sure I don't over-amp my device and destroy it.

Thanks in advance

[nd4spdbh2]

the mah rating on a battery is its capacity, how long the battery will last.

The 2500mah battery will last 1 hour at a rate of discharge of 2500ma (2.5amps) thus 2500mah. A battery does not push its energy, energy is pulled from the battery only as fast as the device hooked to it wants power so running a higher mah battery wont destroy your device. A higher capacity (mah) battery will last longer than a lower capacity battery hooked to the same device.

Just make sure its the same size, voltage, and type (chemistry - NiCad NiMh, Lipo Li-ion...)

Now i would not go mixing different capacity (mah) batteries, this will cause either 1. the higher one to not be charged all the way, 2 the lower one being overcharged which is much more likely and not good at all.

Btw what device is it that you plan on replacing the batteries?

Also not all bateries are created equal. Some are ment to be in light amp draw devices, others heavy amp draw devices... the problem comes when you stick a light amp draw cell/battery into a heavy draw circuit.

[Evilsizer]

your not going to give it more amps by going with a higher MAH battery. the higher the MAH the longer it will last in your device. think of it like audio wattage, there is a MAX and RMS. the number on the side is the RMS meaning sustained AMP out put per period of time. its max rating would be for short bursts, what ever it might be, could be 2600ma or 2800ma. there is no telling without testing the battery.

DOH! beat but im also bit off i believe and ND4 is closer to what i was getting at...

[nd4spdbh2]

your not going to give it more amps by going with a higher MAH battery. the higher the MAH the longer it will last in your device. think of it like audio wattage, there is a MAX and RMS. the number on the side is the RMS meaning sustained AMP out put per period of time. its max rating would be for short bursts, what ever it might be, could be 2600ma or 2800ma. there is no telling without testing the battery.

DOH! beat but im also bit off i believe and ND4 is closer to what i was getting at...

eh close.

I have RC car batteries that are 5000mah (5amp hr), but can supply a constant 150amps of juice and have a peak of 200amps pulled from them over a 10 sec period... those things are nasty!

[Foolios]

Thanks so much for the explanations. I have a remote controlled vehicle and I'm wanting to see if I can get it take more juice so it'll run faster and/or longer.

[jstutman]

Thanks so much for the explanations. I have a remote controlled vehicle and I'm wanting to see if I can get it take more juice so it'll run faster and/or longer.

Like a wal-mart cheapo, or like a Hobby RC?

[nd4spdbh2]

Thanks so much for the explanations. I have a remote controlled vehicle and I'm wanting to see if I can get it take more juice so it'll run faster and/or longer.

OH ya big time.

Is it a standard 6 cell 7.2v pack? Do you have a NiMh charger? if so check out cheap battery packs .com (http://www.cheapbatterypacks.com/?menu=76620DD738&sid=27849)

grab 6 of the 4000 or 5000mah cells... thing will last 2x as long as it did with your 2500mah cells.

I have been into rc cars for 10 yrs now, did a lil racing at the local track awhile back, ask away and i shall give you the best info i kno!

[Foolios]

AWESOME!!! Thanks for the link!
Just junk stuff right now, I used to have a nitro powered trax truck back in the day. I'm thinking of going with something electric because my buddy showed me how fast they are nowadays.

When you say that it will pull it's energy requirement instead of it being pushed. How is that controlled? The resistance inside is preventing a full draw of total amperage right?
I just wanna make sure that I don't provide so much energy that it blows up... like if i stack too many batteries together.

For batteries in general; how come you can touch each end of the battery and yet it won't discharge through your body? And how about a car battery, why is it that you can loosen the end of one of the terminals with a wrench and not get zapped?

[nd4spdbh2]

AWESOME!!! Thanks for the link!
Just junk stuff right now, I used to have a nitro powered trax truck back in the day. I'm thinking of going with something electric because my buddy showed me how fast they are nowadays.

When you say that it will pull it's energy requirement instead of it being pushed. How is that controlled? The resistance inside is preventing a full draw of total amperage right?
I just wanna make sure that I don't provide so much energy that it blows up...

Well on an electric rc car you have the battery, the electronic speed controller, and the electric motor.

Regardless of brushed or brushless motors the motor is the determining factor of the max amps will be drawn. you buy your speed controller that will support how many turns (windings) the motor is.

Now you can buy batteries that will supply under what the max for the system can use but you wont get the max performance, and especially with a high rpm brushless motor setup you can easily overheat the batteries if they cant supply enough amps.

That being said IMHO there is no place any more for gas in rc cars. Considering i can make ~ 3hp and probably 10x the torque of the gas big block gas motor in my savage truck, at half the weight of just the motor... brushless motors are the way to go for sure in rc cars. U should see my lil 1/10th scale Losi buggy fly down the street... cant even hear it yet it will do easily 75mph, while leaving actual burnout marks at the start..

[cyberfish]

For batteries in general; how come you can touch each end of the battery and yet it won't discharge through your body? And how about a car battery, why is it that you can loosen the end of one of the terminals with a wrench and not get zapped?

It will discharge through your body, especially if it's wet. However, the resistance of your body is so high that negligible current will flow.

As for the car battery, since you are only touching one terminal, the circuit is not completed, and hence no current will flow. If you touch the other terminal at the same time, you'll be fried (given sufficient voltage on the battery).


When you say that it will pull it's energy requirement instead of it being pushed. How is that controlled? The resistance inside is preventing a full draw of total amperage right?
I just wanna make sure that I don't provide so much energy that it blows up... like if i stack too many batteries together.
If by stack you mean putting them in series, that's no good. You will be increasing the equivalent voltage. It will most certainly fry whatever you are trying to power.

[Foolios]

So if you are removing a car battery terminal connection and happen to hold on to a part of the engine block, you're pretty much dead then right?

I have another question. In a book I'm reading it explains that red is positive and black is negative and/or ground.
Since the negative wire is the dangerous one that current is trying to flow from, why are we color coding the positive with color? Wouldn't using black for negative and ground cause some confusion? I mean, how does one know whether the black they are looking at isn't the ground wire and they are missing the negative? Seems confusing and dangerous and I'm sure that that's prolly not the case since there's so much concern for safety.
What am I missing here?

[cyberfish]

No, you also need to be touching the other terminal of the battery.

[Evilsizer]

ground does not carry the current that would be he red one or positive. voltage is not what kills people it is the current that does. if it was voltage then people wouldnt be living after being struck by lighting...

[||Console||]

ground does not carry the current that would be he red one or positive. voltage is not what kills people it is the current that does. if it was voltage then people wouldnt be living after being struck by lighting...

it does depending on what country you live im =)

Us = Conventinal Electron Flow
Rest of world = Electron Flow From negitave to positive

[cyberfish]

Actually, it's not the current, but the power, which is I^2R. Current through a super-conductor is fine :). Electrical shock damages things (and people) by heating it up very rapidly (also causes muscle spasms in animals).

Voltage is a potential DIFFERENCE. For a battery, it's difference to negative terminal. If you only touch the +ve, the +ve side becomes the same voltage as you, and the ground will be "your voltage" - battery voltage. There is no return path to the battery, and no current will flow.

It's a different story for wall outlet (you will get a shock if you just touch the hot wire while standing on the ground) because the ground of a wall outlet is the earth ground, and the earth becomes the return path.

For a battery, the 2 terminals are not really different. If you have a 5V battery, you can equally well say the positive terminal is ground, and the negative is -5V.

By the way, electrons flow from negative to positive. "Current flow" is a concept introduced very long ago. They couldn't tell whether positive or negative charges are flowing, and guessed the positive. They were wrong. There is really no such thing as "current flow". We just continue to use the term by convention.

[Bobnova]

In most cases, what kills you is the frequency of the electricity. Not including >10000v stuff like lightning.
It just so happens that we here in the us settled on 60hz for AC, a remarkably poor choice considering that the control signal from the brain to your heart is also about 60hz. Guess what 60hz AC does? It doesn't damage much of anything, 120v isn't enough to do a very good job frying things, but it's plenty to punch through the skin and deliver the interference to the heart signal.
50hz is safer then 60, and dc 120 has a fairly low chance of killing you.

Voltage alone doesn't do it, i've gotten 10-70k quite a few times, including 70k from thumb to thumb (that, by the way, did not feel good at all).
Current can't kill you unless the voltage is high enough, so saying you need one or the other isn't really accurate. A 12v battery has hundreds and hundreds of amps of current on tap, but not enough voltage to force it through a human.
An ignition coil has plenty of voltage, but no current to speak of.

You can grab both terminals of a car battery and get absolutely nothing. You could even lick 'em and you'd get about the same result as on a 9 volt battery (but moreso, plus some lead poisoning).

[cyberfish]

In most cases, what kills you is the frequency of the electricity. Not including >10000v stuff like lightning.
It just so happens that we here in the us settled on 60hz for AC, a remarkably poor choice considering that the control signal from the brain to your heart is also about 60hz. Guess what 60hz AC does? It doesn't damage much of anything, 120v isn't enough to do a very good job frying things, but it's plenty to punch through the skin and deliver the interference to the heart signal.
50hz is safer then 60, and dc 120 has a fairly low chance of killing you.
Interesting, that I didn't know. Do you have any references?


Voltage alone doesn't do it, i've gotten 10-70k quite a few times, including 70k from thumb to thumb (that, by the way, did not feel good at all).
Current can't kill you unless the voltage is high enough, so saying you need one or the other isn't really accurate. A 12v battery has hundreds and hundreds of amps of current on tap, but not enough voltage to force it through a human.
An ignition coil has plenty of voltage, but no current to speak of.

Ohms Law. V = IR. The load draws the current from the source. The source doesn't just "have" some current to "push" through things. It will supply as much current as necessary to maintain the voltage (Kirchoff's voltage law), or until it breaks down.

The damage done (if we ignore the effect of nerve disruption for now) is also to do with total energy delivered, which is the time integral of power. If the power drops rapidly (due to a rapid drop of voltage), as in the case of static discharge (even from a van der graaf generator), very little energy would have transferred despite high voltage, and little damage will be done.


You can grab both terminals of a car battery and get absolutely nothing. You could even lick 'em and you'd get about the same result as on a 9 volt battery (but moreso, plus some lead poisoning).

I wouldn't try that...
Probably safe if your body is dry. Definitely not lick.

[Bobnova]

Done it tons of times dry, i'm an auto mechanic :P

[cyberfish]

I happen to be a soon-to-be electrical/computer engineer, in 2 or 3 years :D. When we are not producing the magic blue smoke in the labs, we play with the DC power supplies, too. I think we tried 35V (the highest it will give us) and didn't feel anything. The mechanical pencil lead certainly did, though.
http://www.youtube.com/watch?v=caEBBYjIJ54
(I'm not in the video, those are my group members)

But let's not mislead other people :). It can be dangerous if you are wet (or using your tongue...).

[Bobnova]

I doubt the tunguw test would be pleasant, that's for sure.
I also doubt it would do damage (unless you left it on for a long time i suppose).

I'll give 12v a while with a wet hand on monday (i don't work fridays) just for giggles.
Having worked in the rain on batteries without issue i doubt it'll do anything.

They certainly make for a hell of a show when you accidentally short 'em with your wrench though!

I'm going to see if i can find references for the heart control signal bit too, i read it a long long time ago somewhere.

[cyberfish]

I would guess saliva has very low resistance (since it probably has more ions than regular water), meaning a huge current will flow (like a short circuit). Exactly how huge would depend on how much the battery can supply. I am not familiar with the v-i characteristics of lead acid batteries so I don't know. Entirely possible that it will burn a huge hole on the tongue in very short time. Probably won't kill you, though, unless the bleeding is that bad.

[Bobnova]

Automotive batteries are happy to put out 200-300 amps, that usually drops 'em to around 10.5 volts or so (starter draw).
A straight up short i don't know, lots i would imagine.

[noxqzs]

I would guess saliva has very low resistance (since it probably has more ions than regular water)....

If we use water as an example, less ions equals a higher resistance. For example, de-ionized water usually has resistance in the mega-ohms.

[Bobnova]

I know, i'll grab a hotdog or something and try that with saliva.

[jstutman]

I know, i'll grab a hotdog or something and try that with saliva.

All I can imagine is you having a hotdog in your mouth, while being electrocuted. All for the name of science? :confused:

[Bobnova]

rofl. That'd be a darwin award winner for sure.

Thinking about electrocuting meat products reminded me of something i read a while ago, this:
http://www.evilmadscientist.com/article.php/hotdogs

Now tongues are shorter then hotdogs (and hence lower resistance, assuming the meat has the same resistance per inch), and still having blood in 'em (one hopes) are probably lower still in resistance. However that is 120v rather then 12v.


Anybody have a bright idea as to what i could use to simulate a tongue? I'm curious now. Maybe just a really short hotdog chunk?


(Disclaimer: I don't recommend hazardous activities.

P.S. Be sure to read the comments at the bottom of that page.

[cyberfish]

I am going to try something tonight when I get home - use a multimeter to measure the resistance of my tongue, and the rest can be done in calculations.

200-300A is certainly way more than enough power. At 10V, that's 2000-3000W. That's almost twice the maximum power your 110V wall outlet can put out without blowing the fuse.

[cyberfish]

hahahahaha the link is too funny. I need to try this some time.

Resistance is directly proportional to length. If 120V supplies that much current to the hotdog, 12V can supply the same current to 1/10 the hotdog. A hotdog is also wider, though, which decreases resistance (think of it as parallel resistors).

[Bobnova]

I hate my multimeter. I was in the process of trying to figure out what it was telling me ($7 harbor freight, it's vague about units) when my 15 month old saw it and stole it, or more specifically started cranking the dial around. Not wanting to get to the capacitor test section with my tongue stuck to it, testing has been delayed.



OK, looks like 70-80kohms. When they first touch down it's in the 50k range then climbs to 70 and stays in the 75-80k. The ramp up may just be the multimeter being silly.
On the 20k range it reads as infinite.
I'll be interested to see what your (no doubt vastly superior!) multimeter says.

EDIT:
I'm tempted to start measuring resistance in hotdog-inches.

[Foolios]

Ok, so conventional flow is why red is positive. It was thought that the positive was the side that needed special attention right?

But for electron flow theory, current actually travel from the negative side. This is A/C we're talking right? Just in case there's a difference between A/C and D/C when making these references that I'm not aware of.

I think the two theories are causing confusion in getting to the answer.

So, if we need to be concerned about the negative side(electron flow theory), the black wires, why are they a neutral color? Why aren't they flourescent orange to denote that it's a live wire.
Unless I am getting this all wrong, positive wiring doesn't carry the current right? I mean, if you take the positive to ground that's not going to give you any juice right?

Anyways, why the heck is this negative and ground relationship so seemingly ambiguous?
In the real physical sense it's the negative wiring that has the current that wants to find a return right? It would just love to be grounded no?

[Bobnova]

AC switches current flow direction constantly, 60 times per second here in the US for 110.
It has one wire for source voltage (regardless of whether it's positive voltage or negative voltage) and the other for return.
On the positive swing, electrons flow from the return line to the source line, on the negative swing they flow from the source line to the return line.

DC voltage doesn't switch, it always flows from negative to positive.

In a DC circuit the only reason you have to pay more attention to one is that the other is everywhere. In a computer situation negative is ground, which means that the entire case and such is just waiting for an opportunity to supply some electrons, and if you give it a path for them via the positive wires, ZZZT!
In some older british cars the used positive for ground (probably because they wanted electron return via ground, but who knows with the british), so the chassies and such was just waiting to return some electrons.
Either way, the wires that aren't ground are the ones you have to be careful with.

On house AC there is a ground wire (literally, it goes to a big copper stick sunk into the ground) and a neutral, the neutral is essentially another ground wire, though it often heads off through the power poles to the power plant directly (not always, some systems use ground return).
Seeing as you're standing on the ground, you're grounded. This means you're part of a potential circuit returning (or sourcing) electrons to (or from) the power plant, all you have to do is touch the other half of the circuit, in this case the "live" (source, black) wire.

USA 220v is a different story, it also has three wires but they are black (live), red (live) and green (ground, still a stick in the ground). The red and black wires hook up like the black and white ones, except that the red wire isn't neutral, it's a second live wire. It's AC sine wave (positive to negative to positive etc) is 180* out from the black one, so when the black wire is at +110 the red wire is at -110, for a total of 220 (note: AC is actually higher, the peak is 160something for "110" volts).
Because both wires are live, either one can short to ground, OR they can go to eachother.
If you grab one red and one black you're in for a really fun time of it (and likely dead, really).

Both wires carry current, the electrons can't just disappear :D
110ac using the earth as a return path makes things more confusing.
If you have a battery (doesn't matter how many volts, really) you can grab one post with no issue, as long as you aren't connected to the other post, the electrons in the battery have no path to get back to the battery (not that the individual ones do, anyway, but that's a different mess. They have to pretend that they can).

Why the live wire is black i have no idea, bright red or fluorescent orange makes more sense to me.
In cars, black is ground (negative), red is B+ (12v, unless it's a big truck then it'll be 24v), yellow is the airbag detonation circuit (don't muck with it) and orange is HIGH voltage HIGH amp power for hybrid car's electric motors. Don't muck with that one, either.
The other two won't hurt you directly, but secondary effects (sparks of the chunks-o-metal type, UV radiation from electrical sparks) can do a number on you. Plus if you do a good enough job shorting the posts together it may well explode rather impressively and spray sulphuric acid everywhere. (What air space there is inside the battery case is filled with a lovely stoichiometric mixture of hydrogen and oxygen. When burnt in the proper ratio (stoich.) their flame front is greater then the speed of sound, making them a high explosive. Too much current through the battery gets things hot, to where they eventually melt and spark, then BOOM! Fun stuff, don't try it at home, or anywhere else)


EDIT:
Wow that was longer then intended.

[Foolios]

Either way, the wires that aren't ground are the ones you have to be careful with.

Ok, you're say in respect to damaging computer equipment.
But in D/C if I touch the positive with my hand nothing happens right? But if I touch the negative with my hand, then I'm gonna get hurt right?

[Bobnova]

You have to touch both, just touching one does nothing, you have to complete a circuit (or be dealing with hundreds of thousands of volts, like the half million volt inter-state power lines) to get hurt.

Wall AC hurts because you're standing on the other post of the battery, so to speak.

[Foolios]

Regarding A/C and the way that current travels back and forth, saying that voltage becomes positive and negative in it's 60hz cycle.

Ex: the two wires going to a light within the ceiling in my room. The one is the black, and the other wire is the neutral(white). (I'm not sure, I'm guessing with my limited knowledge, feel free to correct me)

Q: Which wire is the positive and which is the negative in this case? Is there such a labeling in house wiring or is it just that one line is called live and the other a return?

Touching either of them could kill you?

[Foolios]

You have to touch both, just touching one does nothing, you have to complete a circuit (or be dealing with hundreds of thousands of volts, like the half million volt inter-state power lines) to get hurt.

Wall AC hurts because you're standing on the other post of the battery, so to speak.

Sorry, I should have added, AND if I was touching the case or some other metal object that was grounded...

[Foolios]

You know, I was watching a video about Google Waves and it showed how your google e-Mail also functions as a chat in that it's threaded and typing is shown in real time.

Isn't there a forum with this technology in place yet?

[cyberfish]

A voltage is a difference in potential. You cannot talk about the voltage of a point alone. It's always the difference between 2 points. When we talk about the voltage of a point (eg, the hot wire of wall outlet to be at 110V), we mean the voltage relative to some chosen "ground". There are actually 2 meanings of the word "ground" in common usage. First is the earth ground. It's the potential of the earth. It's unambiguous because we can assume the earth to have a constant potential everywhere. Things get complicated when we talk about things like a battery, because if both terminals of the battery are not connected to the earth ground, talking about the voltages of the 2 terminals relative to the earth ground becomes pointless. The 2 voltages are "floating". They can be anything, as long as "V+" - "V-" is the voltage of the battery. A 12V battery can be at 100-112V, or -1000 to -988V. The battery couldn't care less. That's why, for an ungrounded (to earth ground) circuits, we just pick an arbitrary ground to make calculations easier. By convention, we pick the negative terminal of the battery. We can also pick the positive terminal, or any other point in the circuit for that matter.

Think of a voltage source (wall or battery, AC or DC, doesn't matter) as a force that always tries to keep its 2 terminals at the specified voltage difference (constant for DC, amplitude*sin(2*pi*frequency) for AC).

But there is a difference between touching the positive terminal of a battery and touching the hot wire, because the neutral wire of the outlet is always connected to earth ground. That means, the hot wire is always 110V ABOVE earth ground (or oscillating between 110 and -110 RMS in the case of AC). And if you touch it while you are grounded... in order to force a 110V difference between the wire and the earth, it will have to run a current through you (by Ohm's law, V = IR, where V = 110V, R is fixed). Current only flows when there is a voltage (difference). Therefore, touching the neutral wire is ok (because it's at the same potential as you). It really has nothing to do with which way electricity flows.

Touching the battery is a different story, because, say if you touch the positive terminal of a 12V ungrounded battery, you will bring the positive terminal to earth ground, and the negative terminal will become -12V (relative to earth ground). No current will flow.

If you touch both terminals, though, you are essentially trying to ground both ends of the battery, and the battery doesn't like that. It will run a current through you to maintain its voltage.

That's why if you are hanging off a power line (not touching ground), you will never get hurt. And birds can stand on power lines even if they are bare conductors.

Or if you are sleeping in a car while a hot power line falls on you, don't try to get off the car by walking out. You should hop out. Never touch the ground and the car at the same time. And after you get off the car, don't take big strides. Preferably hop away from the car with both feet together, this is because the powerline will give your car, and hence the ground below it, some voltage. And there will be a circular voltage gradient centered at your car (voltage is proportional to distance from your car). So if your car is at 1000V, and 1 meter from it is 800V, 2 meters from it will be 600V. If you take a 1 meter stride, you will have 200V across you, and electricity will flow into your leg, through your private parts, and out the other leg. But if your 2 legs are always at the same potential (same distance from car), nothing will happen.

There was this story that there were once a few cows centered around a tree, and a lightning strike hit the tree, killing half the cows - the cows that were facing the tree. I have no idea if that's true, but it's theoretically sound.

[cyberfish]

I just put my multimeter to my tongue, and had a few discoveries.

1. my multimeter leads taste really bad
2. I see about 20ohm minimum resistance across 1cm, if I press hard. It jumps around quite a bit, though.

If you assume 20 ohms, the current will be 12V/20ohm = 0.6A. Power dissipation will be 12V*0.6A = 7.2W. Which is quite a bit.

[Bobnova]

That's an excellent explanation.

My multimeter doesn't taste real great either, reminds me of 9v batteries, really.
7.2w would be highly unpleasant and not something you'd want heating your tongue for too long i suspect. Shouldn't blow chunks out of it though.

[cyberfish]

I think I actually felt a bit of tickling when I put both leads on my tongue. Could just be placebo effect.

Or maybe the multimeter measures resistance by pushing a constant current through the leads then measure the voltage. Which makes sense.

edit - I think I was right

A more accurate type of ohmmeter has an electronic circuit that passes a constant current (I) through the resistance, and another circuit that measures the voltage (V) across the resistance. According to the following equation, derived from Ohm's Law, the value of the resistance (R) is given by...

[freeagent]

OH ya big time.

Is it a standard 6 cell 7.2v pack? Do you have a NiMh charger? if so check out cheap battery packs .com (http://www.cheapbatterypacks.com/?menu=76620DD738&sid=27849)

grab 6 of the 4000 or 5000mah cells... thing will last 2x as long as it did with your 2500mah cells.

I have been into rc cars for 10 yrs now, did a lil racing at the local track awhile back, ask away and i shall give you the best info i kno!

I knew Id see some r/c goodness here :D

These look tasty, for use in my erevo heh :beer:

http://www.allerc.com/product_info.php?cPath=3_4_93&products_id=4708

[Foolios]

Thanks for the explanations. I will keep thinking upon them and ask more questions as I have them.

[Foolios]

Either way, the wires that aren't ground are the ones you have to be careful with.

Ok, you're say in respect to damaging computer equipment.
But in D/C if I touch the positive with my hand nothing happens right? But if I touch the negative with my hand, then I'm gonna get hurt right?

The other + goes to ground, - becomes the negative rail.

The ground is going to supply electrons...
So, if you take a positively charged side of a battery and connect it to anything metal, whether the metal has a surplus of electrons or not, the positive terminal of the battery wanting some electrons will draw current from the metal. Is that it?

[Bobnova]

I think I actually felt a bit of tickling when I put both leads on my tongue. Could just be placebo effect.

Or maybe the multimeter measures resistance by pushing a constant current through the leads then measure the voltage. Which makes sense.

edit - I think I was right

Yupyup, that's what all the ohm meters i've run into do. Can't think of another way to do it, really.

I'm tempted to measure the voltage the ohm meter puts out on a volt meter.

[cyberfish]

The ground is going to supply electrons...
So, if you take a positively charged side of a battery and connect it to anything metal, whether the metal has a surplus of electrons or not, the positive terminal of the battery wanting some electrons will draw current from the metal. Is that it?
The "positive" side of the battery is only positive relative to the negative terminal. If you just put it to some random metal, without connecting the other side, the "positive" end will move to the same voltage as the metal, and nothing will happen. The same can be said for the negative terminal.


Yupyup, that's what all the ohm meters i've run into do. Can't think of another way to do it, really.

Another way would be to supply a constant voltage and measure the current. Voltage and current are duals of each other. In fact, it can be proven that a voltage source with a resistance can always be replaced with a (constant) current source with a resistance in parallel. That's the Thevenin/Norton theorem


I'm tempted to measure the voltage the ohm meter puts out on a volt meter.

It will be directly proportional to the resistance.