Don't forget about Watts Law

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crxess

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Will the mod tell you that the 10 amp battery you put in isn't safe to run at 50w? Actually asking, like I said, I don't use regulated mods.

I cannot speak to All Regulated mods, but the 8 different models I have will either:
Recycle power
Not fire
Stop firing
or Shut down, if Draw is higher than programmed.
I'm not an Electronics student, so don't ask proper terminology, the Mods I own all have safety features to prevent over taxing a cell.
A feature none of my Mechanical Mods can provide.
 
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Ryedan

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Rather than Watts Law vs. Ohms Law

Why precisely is Watts Law so important to the Average Vaper?

That's both a very good question and a very good point, which I believe Lessifer covered with his post:

Just want to see if I understand.

On a variable wattage mod, to calculate the amp load from the battery(at a basic level):
Watts / battery voltage / number of batteries (not accounting for board inefficiency)

So if you have a 50 watt mod that uses a single 18650
at full charge it's 50/4.2/1 = 11.9 amp
at low voltage(more important) it's 50/3.2/1 = 15.6 amp

Is that right?

That is correct Lessifer. Yes, it leaves out regulator inefficiency but that's typically between 90-95% loss causing a 5-10% more battery draw to cover it, which I don't consider critical. If you want to take that into account you can just add '/ 0.9' to your formula creating this: Watts / battery voltage / number of batteries / 0.9 and it will be exact at 90%.

If anyone missed it, note that atty resistance is not in the formula. It's irrelevant other than it changes regulator efficiency a bit, but we're really not worried about the last few percent in accuracy anyway.

Here's another way of looking at it that might be even simpler.

Using Lessifer's formula, 1W with a battery voltage of 3V and a regulator efficiency of 90% added in, needs 0.3704A from a one battery mod. Let's round that down further to 0.37A which is still quite accurate for our needs.

Now we get this formula for maximum battery amp draw in a VW mod:

watts * 0.37 / number of batteries (so with a one battery mod it's just watts * 0.37)

Both formulas work, but if anyone finds this is a bit easier to remember then it will have done its job :)
 

Dlmdavid

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I cannot speak to All Regulated Mods, but the 8 different models I have will either:
Recycle power
Not fire
Stop firing
or Shut down, if Draw is higher than programmed.
I'm not an Electronics student, so don't ask proper terminology, the Mods I own all have safety features to prevent over taxing a cell.
A feature none of my Mechanical Mods can provide.
A mod can't tell if the battery you put in it is rated to discharge 5 amps continuously or 25 amps, it sees the required voltage it needs to output the power and draws whatever current it needs, the safety features in it will keep the device itself from drawing more than it is capable of but if you throw a 4 amp rated flashlight battery in there, there is a very good chance of explosion, best case scenario is it will drain the battery fast enough before it vents, but no matter what whether it be regulated or mech, user discretion needs to be used in every case
 

suprtrkr

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Just want to see if I understand.

On a variable wattage mod, to calculate the amp load from the battery(at a basic level):
Watts / battery voltage / number of batteries (not accounting for board inefficiency)

So if you have a 50 watt mod that uses a single 18650
at full charge it's 50/4.2/1 = 11.9 amp
at low voltage(more important) it's 50/3.2/1 = 15.6 amp

Is that right?

Just exactly so. I tend to work the equation by adding the "discharge volts"-- the point the mod stops working because the batteries are too low-- together before dividing this into set watts as it eliminates dividing by the number of batteries. 50/3.2/2 = 7.8125, and 50/6.4 = 7.8125 But you can see it yields the same answer.

Well, I will admit that I did not know that there was a different equation to find the amp draw on a battery when using a VW mod, as opposed to when using a mech. It's an important distinction, if I were ever to choose to use a VW mod. Although it seems like you should be pretty good using a 20amp or more battery, as long as the mod's chip itself doesn't try to go higher than the number of batteries can support.

A good rule of thumb I often post is, using a name brand 20A battery in top condition, 60 watts on 1 battery; 100 watts on 2 batteries. If you want more than that, you need better batteries.

Will the mod tell you that the 10 amp battery you put in isn't safe to run at 50w? Actually asking, like I said, I don't use regulated mods.

It will not. It will, however, happily vent or flame out that battery that shouldn't be in there if you crank it up too high.
 

Ryedan

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I cannot speak to All Regulated Mods, but the 8 different models I have will either:
Recycle power
Not fire
Stop firing
or Shut down, if Draw is higher than programmed.
I'm not an Electronics student, so don't ask proper terminology, the Mods I own all have safety features to prevent over taxing a cell.
A feature none of my Mechanical Mods can provide.

I think most mods will shut down or adjust max power for low battery voltage under load and I think that's what you're describing. Please correct me if I got that wrong.

That's why I like to use 3V as a minimum even if they come out and meter 3.4V, because I know how much battery voltage drop under load can be from my mech mod years, specially with older batteries.

That could be pretty good protection as most batteries will suffer a lot of voltage drop under load when you draw too much power from them, but I don't know if this is a good enough safety 'feature' to count on with all batteries in all mods. Ultimately, the mod will pull the watts asked for until it decides to stop, so until I know for sure that this works universally I will not advise anyone that the mod will take care of it.
 

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mcclintock

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    Even with mechs, there seemed to be an impression that the resistance number told a lot about the coil, when actually it was basically a way to say how much power you are running, assuming the normal range of battery voltage. Only by inference did it say much about the coil -- if it draws more power, it better be able to handle it, if it draws less, it better work better that way. Then along comes regulated and people are suddenly saying stuff like "50 watts at .3 ohms" and the only reason that's not completely redundant is that with regulated, the resistance tells you even less than it did before. You need at least one other piece of info, such as wire gauge, to be able to calculate additional parameters of the coil.

    As to having a current readout on regulated mods with replaceable batteries, it would seem better to me to have a settable current limit. This would allow using lower current batteries, although you would still prefer a safe chemistry. As it is, the current limit is preset and you must use batteries to match. The mod could also sense battery temperature and cut signal on a sudden rise.
     

    WattWick

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    Then along comes regulated and people are suddenly saying stuff like "50 watts at .3 ohms" and the only reason that's not completely redundant is that with regulated, the resistance tells you even less than it did before.

    This is a pet peeve of mine. An extension of that peeve: Many seem to believe that electric energy applied to a coil instantly and directly translates to heat energy emitted from a coil. Just as resistance tells next to nothing about how a coil performs - wattage applied to the coil is equally nondescript.

    The mod could also sense battery temperature and cut signal on a sudden rise.

    Some mods do this, if I'm not entirely mistaken. On the other hand, just like a coil, the heat energy has to be distributed throughout a mass (the battery) to reach those sensors. By the time the outer casing gets hot, you may already have an unstoppable thermal runaway chain reaction going on inside the battery.
     

    VNeil

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    This is a pet peeve of mine. An extension of that peeve: Many seem to believe that electric energy applied to a coil instantly and directly translates to heat energy emitted from a coil. Just as resistance tells next to nothing about how a coil performs - wattage applied to the coil is equally nondescript.
    Actually it does. Watts is a measure of power and power is dissipated as heat, light, radio waves, or mechanical movement (and maybe a couple other possible but irrelevant etc's here). Unless the coil glows red there is no light emitted. NMo mechanical energy and no radio waves, being DC. So in a vape coil virtually all the power should dissipate as heat. So any coil dissipating 50W for example should dissipate the same heat (lets leave out ramp-up effect).

    What varies is the amount of vapor emitted from the coil/wick and two coils dissipating the same heat could generate different amounts of vapor depending on coil surface area and wicking and some other etc's.
     
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    skoony

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    o any coil dissipating 50W for example should dissipate the same heat (lets leave out ramp-up effect)
    This is what every one gets wrong. Coils of different resistances can dissipate
    the same amount of power but, not necessarily the same amount of heat.
    Aa 0.3 ohm resistance at 50W of power requires 3.87 volts and produces
    12.9 amps of current.
    A 2.5 ohm resistance at 50W of power requires 11.18 volts and produces
    4.7 amps of current.
    Now you tell me which one is hotter? Time's up. The 0.3 ohm coil dissipates
    almost 3 x the heat as it has almost 3 x the amperage minus the power needed
    to push the amperage through the resistance.
    The 2.5 ohm coil needs over 2 x the voltage to push a measly 4.7 amps
    through the resistance.
    The higher the resistance the more force needed and power lost doing
    the work of pushing the current through the resistance. The power lost
    is not available to produce heat.
    Regards
    Mike
     

    crxess

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    That could be pretty good protection as most batteries will suffer a lot of voltage drop under load when you draw too much power from them, but I don't know if this is a good enough safety 'feature' to count on with all batteries in all mods. Ultimately, the mod will pull the watts asked for until it decides to stop, so until I know for sure that this works universally I will not advise anyone that the mod will take care of it.

    Well said. Nor will I as I simply refuse to play around with - Can I get away with this - when it comes to my safety.
    I will do things others may not, vape or non-vape related, but only after careful consideration.

    * I also consider Regulated max output much like a Speedometer - Just because there is a Top end, does not mean it's smart to push to it.;)
     

    VNeil

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    This is what every one gets wrong. Coils of different resistances can dissipate
    the same amount of power but, not necessarily the same amount of heat.
    Aa 0.3 ohm resistance at 50W of power requires 3.87 volts and produces
    12.9 amps of current.
    A 2.5 ohm resistance at 50W of power requires 11.18 volts and produces
    4.7 amps of current.
    Now you tell me which one is hotter? Time's up. The 0.3 ohm coil dissipates
    almost 3 x the heat as it has almost 3 x the amperage minus the power needed
    to push the amperage through the resistance.
    The 2.5 ohm coil needs over 2 x the voltage to push a measly 4.7 amps
    through the resistance.
    The higher the resistance the more force needed and power lost doing
    the work of pushing the current through the resistance. The power lost
    is not available to produce heat.
    Regards
    Mike
    A watt is a measurement of energy (rate). All the energy is dissipated in some way. Here, either light or heat (leaving out mechanical energy or radio waves). 50W is 50W regardless of the current. Electrical energy is the sum of volts and current. A 50W lightbulb will create the same amount of light + heat, regardless of voltage. Different lightbulbs of the same wattage might deliver varying amounts of light, but the total light + heat will be identical. A 50W lightbulb driven from a 12V source will deliver the same light+heat as a 50W lightbulb driven from a 125V source. The 125V lightbulb will NOT deliver 10x the light + heat.
     

    WattWick

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    (lets leave out ramp-up effect)

    I could indeed have phrased it better.

    On the other hand, let's not leave out ramp-up effect. Are you saying that a heating element fed 100 watt of electrical energy for 60 seconds - that takes 30 seconds to reach peak/steady temperature - emits the exact same amount of heat energy - every individual second during that 60 second period?
     

    skoony

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    50W lightbulb will create the same amount of light + heat, regardless of voltage.
    A 50 W light bulb will dissipate 50 Watts of power at the voltage it is rated
    at.
    A watt is a measurement of energy (rate). All the energy is dissipated in some way. Here, either light or heat (leaving out mechanical energy or radio waves).
    The voltage is the force needed to provide the circuit with enough current to
    do what it was designed to do. Using this force requires power. The power lost
    using the force of voltage to supply the circuit with enough current to accomplish
    its work is not available to be radiated as heat.
    The higher the resistance the more force(voltage) necessary to dissipate the
    same amount of power. The extra force required comes with a price tag.
    The use of more power. Watt = force + work done + loss.
    Regards
    Mike
     

    VNeil

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    I could indeed have phrased it better.

    On the other hand, let's not leave out ramp-up effect. Are you saying that a heating element fed 100 watt of electrical energy for 60 seconds - that takes 30 seconds to reach peak/steady temperature - emits the exact same amount of heat energy - every individual second during that 60 second period?
    Yes it does but the heating element itself acts like a heat sink. It takes some time for the initial heat to actually radiate out of the coil- AKA ramp up time to most people here.

    This is basic Ohm's Law and what some call Watts Law here. A watt is one joule of energy for one second. Your 100 watt heating element is generating 100 joules of energy per second starting with the first second. That 100 joules of energy dissipated in the first second is just as "potent" as the 100 joules radiated on the 60th second.

    Consider the use of heat sinks in electrical circuits. The coil or heating element itself is a rather modest heat sink. I'm not sure the electrical heat sink is a good analogy because it is doing other things too, after it reaches thermal equilibrium. But if you put a huge heat sink on a heated coil it will take much longer to reach thermal equilibrium, as well as allow the coil to dissipate more power than it otherwise could without melting down.

    I really wanted to leave out ramp up just so we could focus on the basic concept that watts = heat in a vaping coil application... but it might help clarify things for some.
     

    fenderstrat

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    Im glad some of you guys dont fly rc helis.My 600 size heli runs a 12s set up.2 6s lipos run in series.50.4 volts fully charged and capable of 195 amp bursts.you want to see some fireworks you shoud see when someone puts one in nose first as they have soft cases.

    Andria d....just curious,why do you only use half of your available battery power?
     
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    VNeil

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    A 50 W light bulb will dissipate 50 Watts of power at the voltage it is rated
    at.

    The voltage is the force needed to provide the circuit with enough current to
    do what it was designed to do. Using this force requires power. The power lost
    using the force of voltage to supply the circuit with enough current to accomplish
    its work is not available to be radiated as heat.
    The higher the resistance the more force(voltage) necessary to dissipate the
    same amount of power. The extra force required comes with a price tag.
    The use of more power. Watt = force + work done + loss.
    Regards
    Mike
    Let me try another angle. Consider a basic electrical resistor. And there are wire wound resistors that electrically and mechanically are essentially identical to our atomizer coils, except they have some potting material around them to keep them mechanically stable.

    Resistors have two basic specs: resistance and max power dissipation. A class of resistors with varying resistances will have the same power dissipation. In my example, let's use a 1 watt resistor.

    If you put 1 volt across a 1 ohm resistor then 1 amp of current flows, and the resistor will dissipate one watt.

    If you put 10 volts across the same *CLASS*resistor, then only 0.1 amp flows through it. But the resistor will dissipate the same one watt. And if you put your finger on both resistors they will be identically hot.

    In terms of power dissipation the resistor does not care how many volts are across it or how many amps. It only cares that the sum product of the voltage and current is less than one. Otherwise it burns up.

    This applies similarly to vape coils. I have built two coils for two subtank minis. I built one to 0.5 ohms and the other to about 1.5 ohms. As far as I was concerned they performed nearly identically, as they should. But I did try to configure them with similar turns and diameter (same wire length), trying to make them as similar as possible, it being impossible to make them "identical" of course. One might have ramped up a bit quicker than the other. So I am convinced that the basic Ohm's Law/Watt's Law equivalence actually can carry through even when considering the fluid dynamics and thermodynamic complexities are are added into the mix when trying trying to compare the actual vape performance of dissimilar coils dissipating the same power.


    (eta: in the above comparison I vaped both coils at the same power level. Different volts and amps but same power level)

    Please also read what I said to @WattWick above. Look at any definition of a watt. It is one joule of energy dissipated for one second. Or one joule per second if you like. A watt does not care how much voltage or how much current, it only cares about the product of the two. A watt is a watt, regardless of the resistance of the coil.

    "Watt = force + work done + loss."

    In the above you are over complicating things. There is no "work done" here, in the context of mechanical work (could be if this were a motor but it isn't). All the power is "lost" here, to the extent that effectively all the power is dissipated as heat through the coil. Assuming no power is dissipated via light, which it is effectively not.
     
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    VNeil

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    This is what every one gets wrong. Coils of different resistances can dissipate
    the same amount of power but, not necessarily the same amount of heat.
    Consider this link: How is the measurement Watts related to temperature in terms of energy?

    It indicates that one calorie of heat is generated by 4.184 joules of electrical power. So 4.184 watts of power will generate one calorie of heat per second. And it does not matter what the resistance of the wire is, or the gauge, or the voltage, or the current or the surface area. The amount of heat is purely dictated by the power level in watts (or total power over time measured in joules)

    Thus confirming what I am trying to say... when it comes to dissipating electrical power across a simple resistor, watts = heat.
     

    WattWick

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    Im glad some of you guys dont fly rc helis.My 600 size heli runs a 12s set up.2 6s lipos run in series.50.4 volts fully charged and capable of 195 amp bursts.you want to see some fireworks you shoud see when someone puts one in nose first as they have soft cases.

    Eeek...! Hope that's not aimed at me as I actually do fly RC helicopters :lol:

    (Far from one of those awe-inspiring 3D pilots, mind you. And I lack the courage/funds to fly anything bigger than a 500.)
     
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