Don't forget about Watts Law

[Douggro]

You are perfectly correct you must always concern yourself with the amp draw on your batteries. The thing about the resistance is the batteries can't "see" it. It's downstream of the board. The board sees resistance, yes, and adjusts it's output voltage to make the set watts. But that doesn't mean anything to the batteries. Upstream of the board is the batteries, and they don't care what the board does on the other side. Upstream, voltage is fixed (sort of, it varies with battery charge) and watts are always watts. If the board is outputting X watts, then it must draw X watts plus board losses from the batteries and it must take it at whatever voltage the batteries are supplying at that charge state. Thus, to hold watts constant, if voltage is fixed, it is current that must vary. Nothing else can as resistance is also fixed by the wire size connecting the board to the batteries. Varying the resistance on the other side of the board is not meaningful. Watts is Watts, and they stay the same.

Right. Board says "I need to make X watts" and pulls as much amperage from the battery as needed to make it, as long as there is sufficient voltage in the charge-state of the battery to make it. That's why the CDR of batteries is important relative to the wattage being used, since over-drawing amperage at lower charge-states is what stresses and overloads the batteries. The battery in a low-charge state is being asked to do something that it really can't - but the battery doesn't know how to say "NO!"

 

[WharfRat1976]

Everyone is so concerned about ohms law that I'm scared they only preach it because they were told they should know about it. The only time ohms law is even relevant is in a mech mod, if you're using a regulated mod it's watts law you need to deal with, instead of preaching ohms law we should be preaching basic DC circuits and understanding when it's necessary to use which law.

Too funny. Speechless.

 

[sonicbomb]

Whether it's Watts law or Oms law is of significantly less importance than the maths and the rules as they apply to safe battery use.
In terms of pulling safe amp levels from a battery in a regulated mod, the coil resistance is of no consequence.
I we can all agree that Lars knows what he's talking about. Click on the 'How it works' link in the bottom left corner of this page.
Battery drain

OP started this thread accusing people preaching secondhand misinformation, but has only muddied the water for you average vaper with no electrical engineering background.

 

[WharfRat1976]

Cosidering the average vaper and 80% of vape shop employees do not know what 3mg nic means in a bottle of eliquid, muddied waters regarding battery saftey is fairly moot.

 

[Ryedan]

Everyone is so concerned about ohms law that I'm scared they only preach it because they were told they should know about it. The only time ohms law is even relevant is in a mech mod, if you're using a regulated mod it's watts law you need to deal with, instead of preaching ohms law we should be preaching basic DC circuits and understanding when it's necessary to use which law.

Good point and an issue that could cause problems for someone with a VW mod, but you left out variable voltage mods. They are also ruled by Ohm's law similar to mech's in that load resistance affects battery current draw similarly. OTOH there are not many VV mods in the vape community any more

When VW became mainstream for vaping a lot of folks thought atty resistance and battery amp draw had the same relationship with them as in mechs and VV mods. That is still all too common, but I think the word is getting out. Also, not everyone understands the relationship between battery voltage and battery amp draw in these different types of mods, but one thing at a time

It's changing as the word gets out and threads like this one help so thanks for that. People geting exposure to how things actually work is great and the more folks that understand the quicker the knowledge spreads.

 

[suprtrkr]

Good point and an issue that could cause problems for someone with a VW mod, but you left out variable voltage mods. They are also ruled by Ohm's law similar to mech's in that load resistance affects battery current draw similarly. OTOH there are not many VV mods in the vape community any more

When VW became mainstream for vaping a lot of folks thought atty resistance and battery amp draw had the same relationship with them as in mechs and VV mods. That is still all too common, but I think the word is getting out. Also, not everyone understands the relationship between battery voltage and battery amp draw in these different types of mods, but one thing at a time

It's changing as the word gets out and threads like this one help so thanks for that. People geting exposure to how things actually work is great and the more folks that understand the quicker the knowledge spreads.

I had not considered that. Indeed, you are correct: the danger lies in too little knowledge. Anyone with no or small knowkedge of the interconnected nature of Ohm's Law, and how Watt's Law relates the three Ohm variables to applied power, who has read this thread all the way through may still lack complete or perfect knowledge, but they must surely know more than when they started. At the minimum, they will see calculating battery draw on regulated mods is different in practice from that of mech mods. That is, as I observed, my actual purpose. It's better, of course, they understand these matters as thoroughly and intuitively as the participants of this thread, but "better" can easily be the enemy of "good enough." It is enough to avoid, or at least attenuate the frequency of, catastrophe for such persons to know there are things they don't know, that it can be dangerous, and to seek wiser counsel when required. Far above I took OP to task for muddying already murky waters, but in so doing I forgot the basic purpose is to get them to stop and think; to not assume the teenager at the vape shop who blows cloud and is (temporarily) still alive knows what he's talking about. You are right about this, and I was wrong.

 

[fenderstrat]

I have been saying this(watts law) since the day I joined and all it does is get me into arguments
I have no idea why people with reg mods are so fixated on ohms and actually once had someone who had been a memeber for quite a while ask me what you need watts law for...so the question gained from this is....how have people with reg mods been calculating amp draw on their batts???

 

[ReigntheGamer]

I have been saying this(watts law) since the day I joined and all it does is get me into arguments
I have no idea why people with reg mods are so fixated on ohms and actually once had someone who had been a memeber for quite a while ask me what you need watts law for...so the question gained from this is....how have people with reg mods been calculating amp draw on their batts???

Honestly, your average vaper doesn't calculate anything. They buy a tank, mod, coils, batteries, and juice then slap it all together and vape.

 

[suprtrkr]

Honestly, your average vaper doesn't calculate anything. They buy a tank, mod, coils, batteries, and juice then slap it all together and vape.

some of them live.

 

[ReigntheGamer]

some of them live.

So far they've all lived just some now vape through the drip tip shaped hole in their teeth.

 

[skoony]

If I put a .3 ohm coil on my Sigelei and run it at 50w, I'm gonna draw the exact same current as a 1 ohm coil at 50w assuming the voltage on my batteries stays constant.

Just to be clear the voltage at the battery is isolated from the coil by
the regulation circuit. The voltage from the circuit would have to adjust to the different
loads in order to maintain 50W.
Regards
Mike

 

[sonicbomb]

..how have people with reg mods been calculating amp draw on their batts???

Incorrectly mostly, or in a state of ignorant bliss. It took me a while, and some educating on here to get it.

I=P/V (- mod inefficiency, 10% as an average)

Charged ~ 50w / 4.2v / 0.9 = 13.22a
Discharged ~ 50w / 3.2v / 0.9 = 17.33a

With multi battery devices, calculate the amp draw then divide by the number of batteries.

 

[Dlmdavid]

Incorrectly mostly, or in a state of ignorant bliss. It took me a while, and some educating on here to get it.

I=P/V (- mod inefficiency, 10% as an average)

Charged ~ 50w / 4.2v / 0.9 = 13.22a
Discharged ~ 50w / 3.2v / 0.9 = 17.33a

With multi battery devices, calculate the amp draw then divide by the number of batteries.

In series that would work as the total voltage will be the sum of your batteries, but in parallel it only works as long as the batteries are married and have the same nominal voltage on them, I know most people are diligent about that but I'm sure there's some guys that pay no attention and throw a fully charged battery in with one that is almost dead, they would have different discharge currents on each battery

 

[Robert Cromwell]

Lets just call the whole relationship of Watts, Ohms, voltage and current. Fred's Law?

 

[sonicbomb]

Fred works

 

[edyle]

Everyone is so concerned about ohms law that I'm scared they only preach it because they were told they should know about it. The only time ohms law is even relevant is in a mech mod, if you're using a regulated mod it's watts law you need to deal with, instead of preaching ohms law we should be preaching basic DC circuits and understanding when it's necessary to use which law.

If you're using a regulated mod, and your batteries are rated in Watts, then ...................

but...., the batteries are rated in amps.

 

[suprtrkr]

Lets just call the whole relationship of Watts, Ohms, voltage and current. Fred's Law?

"The" Law...

 

[edyle]

I still don't see the correlation.

If a regulated mod does not require the resistance to pull X amount of power, why does my istick30 die after 2 tanks at 30w on .6 resistance coils but can last as far as 8 tanks at the same wattage?

I really don't understand

Because the istick30 can deliver 30 watts to a 0.6 ohm coil,
but if you look at the graph, if you put maybe a 0.41 ohm it can't deliver 30 watts.
similarly if you put a 2.5 ohm coil, it can't deliver 30 watts.

check the graph under 'mod range' in steam-engine.org

 

[beckdg]

I disagree with OP, although he is correct on the technical side. In point of fact, in a regulated mod, the coil resistance is meaningless to the load on the cell so long as it falls within the parameters of the board so it fires at all. The cell can't "see" the atty resistance; it's downstream of the board. What matters to the cell is the load placed on it by the board. That is set watts, plus board efficiency losses, divided by battery voltage.

And cell voltage.

In mechs we calculate with a full battery to determine the load.

In regulated, the highest amp load will be on a near empty cell.

Tapatyped

 

[beckdg]

Yes it does, as watts is set, the voltage to make up the watts is decided by the ohms of the coil

Absolutely not.

The circuitry can buck or boost the voltage output through it while only getting the voltage provided from the cell. This skews the resistance seen by the battery to a resistance determined by the completed circuit. The whole circuit resistance will differ from the coil resistance nearly 100% of the time in a regulated device.

Tapatyped