Battery confusion!

[quelasuerte]

Hi.

I have a smok T Priv 220w using two Samsung 25r batteries rated as 20a. I would like to know what wattage and resistance combination I can safely vape at with this set up and I don't know how to work it out. For example how do I calculate the amperage drawn from each of the two batteries if I'm vaping at 60w at 0.4ohm or 100w at 0.2ohm etc.

Thanks!

 

[Beamslider]

Ohms Law Calculator

Battery drain | Steam Engine | free vaping calculators

Try those

 

[Hawise]

120 W, although it's best to stay a bit lower so you have a margin of error. Here's how to calculate it:

Calculating battery current draw for a regulated mod | E-Cigarette Forum

You'll note that with a regulated device, resistance doesn't matter. It's all about wattage.

 

[quelasuerte]

Thanks for those!! So, if I run at 120 W and the device can go up to 9 V, the calculation per battery would be 60/4.5 = 13.33. So even if I add on the suggested 10% I would still be well under 20a. So in theory could I not go quite a bit higher than 120 W ? Not that I want to, just curious to understand it all slightly better.

 

[speedy_r6]

With a regulated mod, the resistance isn't all that important. The voltage you see on the screen is the voltage the mod is sending to the atomizer, not the voltage from the batteries. Simply put, those are 20a cells. You have two of them in the mod. You calculate for the worst case scenario of each cell at 3v(3.2v is the typical cutoff). 20 amps times 3 volts gives you 60 watts. Since you have two batteries, double that. That tells you you can output 120 watts. The batteries don't care if the chip is taking the input voltage and boosting it up or bucking it down. 8 volts at 15 amps is the same amount of power as 4 volts at 30 amps. They are both pulling 120w from the battery.

If the batteries are putting out 7.4 volts, the way to find out the amp draw is to take your wattage divided by 7.4 from the battery. That tells you how many amps you are drawing. For safety reasons, we always just use that 3v per cell mentioned earlier to make it easy since we aren't checking the individual battery voltage all the time. In your case, that would mean whatever wattage you are running divided by 6 to give you the most amps you could possibly be drawing.

 

[Izan]

Cheers
I

 

[Hawise]

Thanks for those!! So, if I run at 120 W and the device can go up to 9 V, the calculation per battery would be 60/4.5 = 13.33. So even if I add on the suggested 10% I would still be well under 20a. So in theory could I not go quite a bit higher than 120 W ? Not that I want to, just curious to understand it all slightly better.

Not quite - you've mistaken the source of your volts. While your device might be able to provide 9V to the coil, it's actually pulling energy from the batteries at a much lower voltage. The circuit board in the mod will pull extra current to boost the (lower) voltage from the batteries to the (higher) voltage going to the coil. It can also do the reverse when it needs a lower voltage than the batteries provide. When calculating amp draw from a battery, you need the battery's voltage, not the adjusted voltage provided by the device.

An 18650 is at 4.2 V at full charge. Its voltage drops as it discharges, and most mods cut it off (giving you a low battery warning) at 3.2 V. The amp draw will be highest when the voltage is lowest. That's why the calculation in the link I provided above uses 3.2 V. @speedy_r6 used 3 V, which is basically the same calculation with the 90% efficiency (actually 94%) built in.

Anyway, this gives you:

20 amps * 3.2 V * 0.9 = 57.6 W, or roughly the 60 W per 20 A battery I mentioned earlier.

I hope that was clear. If it wasn't, please keep asking until it is!

 

[suprtrkr]

Yes, I have to agree. Stop trying to equate the atomizer with draw on the batteries. The atomizer has nothing to do with the batteries. The board draws on the batteries, and then powers the atomizer. You can think of it as two separate circuits. The only thing you need concern yourself with is a) will the board fire the atomizer, and b) the set watts on the machine. So long as the atomizer falls within the parameters the board is designed to fire, it is no longer of import in the battery draw calculations. Stick with 60W per cell in good quality 20A cells and you will be fine no matter what atomizer you are using.

Welcome to the board.

 

[suprtrkr]

View attachment 691503


Cheers
I

I love the chart, Izan. Where can I get one?

 

[Izan]

The original as found:

cheers
I

 

[stols001]

The most important thing to keep in mind about your atomizer is does the resistance of the coil fall within parameters that the battery will not fire. For example, you may not be able to fire a 0.1 atomizer at 60 watts and get a satisfying vape, so the lower resistance you want to run in wattage mode, the more watts your coil may need to get a decent vape out of it. Not every coil will run well at 60 watts, for example, in which case more powerful and/or more batteries than even a two battery mod may be needed.

That's not the case for all drop in coils or builds, but it is the case for some of them?

I don't really run into this issue at my all-powerful 7--10 watts using a 120 watt "capable" mod, but I imagine some people might.

Watts is key in terms of your battery, but you do have to make sure that you have a coil that's going to be happy running at 60 watts or below. 60 watts to me is a very HIGH number, but that's not the case for everyone....??

I hope I'm getting this correct.

Anna

 

[Eskie]

@Izan , I just swiped a capture of that battery chart. That is really handy to have for a quick reference. Nice find!

 

[suprtrkr]

@Izan , I just swiped a capture of that battery chart. That is really handy to have for a quick reference. Nice find!

Ditto!

 

[quelasuerte]

Thanks everyone! I'm a lot clearer on it all than I was yesterday.

 

[BrotherBob]

Thanks everyone! I'm a lot clearer on it all than I was yesterday.

Welcome and glad you joined.
I have provided a little more information which might help evaluating batteries.
Might like to read:
18650 Battery Buying Guide for Vapor Users – Wake and Vape Blog
(9) Battery Basics for Mods; the Ultimate Battery Guide | E-Cigarette Forum
Calculating battery current draw for a regulated mod | E-Cigarette Forum
Battery Safety: Will You Marry Me? - Mt Baker Vapor
http://ecigarettereviewed.com/e-cig-charging-safety
Vaping 101: Battery Safety