Which Voltage reading do you input for Ohm's Law?

[Binigo]

Hello ECF, love the amount of information you can find here, I've been going through so many threads the past few weeks about anything. But I wasn't able to find a specific answer to this question, just a lot of info about how it works etc.

My question: Take for example a fresh battery. When deciding which voltage to input into Ohm's Law Calc to gauge how safe your batteries are in your mech, do you use the 4.2 V reading off a freshly charged battery? Or will you use the Volt reading of the same battery under load inside the mod with X.X Ohm Coil? I.E. 3.9V Reading?

Also is the 3.9V reading the true value determining how many watts the coils are receiving?

Same question would go for the 3.6 / 3.7 V's people say is the moment they remove and charge their batteries. When people say they take their batteries out and charge them at 3.7V, are they referring to the battery's under load reading?

This is unclear to me b/c I can't imagine people keeping a multimeter in their pockets, taking their batters in and out at work or elsewhere and testing this constantly.

I don't have a mech mod nor do I build sub ohm coils, I've just been reading a lot on it lately out of curiosity. Thanks in advance ECF.

 

[Bunnykiller]

you use the voltage that the battery is supplying before you push the power button. Once you push the button a voltage drop occurs due to the work occuring.

 

[bacc.vap]

Yeah, actual battery voltage is usually used(4.2v) as a safety factor. The actual wattage will be lower do to voltage drop under load, and yes, most people are giving the actual batt voltage when replacing their batteries, not the under load voltage.

 

[cthulhufan]

Yes and also use the value measured right off the charger (for me that is 4.25 V) when determining safety.

 

[Baditude]

Use the voltage of a fully charged battery: 4.2 volts.

 

[WarHawk-AVG]

Fully charged Li Ion battery is 4.2vdc, in a true "mechanical" what is in the battery is what goes to the coil (minus minor losses due to resistances in the springs and connections but aren't usually an issue) so you always start at 4.2vdc, on other rigs that have circuits in them, they regulate the 4.2vdc to a set voltage, like eGo, they push 3.7vdc on a full charge, but as the battery depletes from 4.2vdc to 3.7vdc the voltage stays the same, so the vape stays the same, only when the battery discharges below the regulated voltage point will the vape get weaker.

I hope that helped

 

[dice57]

For safety sake and an extra buffer margin, I use the 4.2 voltage for my calculation of amps drawn. For my .3 ohm build that puts me at 14 watts draw. Since I use 30 amp continuous batteries, I know I have a double buffer. Actual amps drawn will be more like 13 since under load I'll lose .3 volts or more, depending on my build and which mechanical I am using. The bigger the buffer, the better and safer one is. Even though the max a .3 ohm build would draw is 14 amps, I wouldn't use my 16 amp batteries, because that is pushing the limit to close for my liking.

For true watts, the actual voltage delivered under load is what is used as the starting point, but one has to also take in consideration that the measured ohms at room temp is not the same once the coil and at operating temperature. I find that the resistance will drop by .03 ohms or so once the coil is hot. This is another reason to have as big of safety buffer as possible, and why one shouldn't push up to the max continuous amp rating of the battery, because things change.

To complicate things even further, when I wrap a coil, mount it, then measure the ohms, I will get one reading, say .29 ohm. I use mainly micro coils, so once I mount and measure the ohms, I then put it on the mech, heat the coil to red hot and the pinch the coils tight together with needle nose pliers. Usually do this several times, till the coils are set, and glowing evenly, and heating up from the center out, then I'll check my ohms again, and they will be different, say .32 ohms. Now I'll wick the coil, either through the coil or wrapped around it, depending on the build and the atomizer, saturate with juice, test fire, then check the ohms again, and it has changed, usually it is higher.

To be safe, one has to check the ohms along every step of the build so that you know for sure what is going on, and are aware of the risks being taken. Every time I re-wick and dry burn my build I'll check the ohms again, to see how it is fairing.

 

[tj99959]

Depends on what you are looking to understand.

If you want to know the watts you are actually vaping at, you need to know the "under load" voltage.
If you want to know the safety factors of the battery to resistance, you want to know the battery voltage fresh off the charger