Hi fellow apes, recently I have noticed a lot of people, mainly new vapers, asking if their build is safe on their regulated mod, and some confusion amongst the answers.
Skip to the end for a simple explanation of maximum wattage to use as a rough guide if you just want to know if you are in a safe zone or not.
I thought I would write a little guide to try and help here, and let everyone that uses a regulated mod know if they are within safe limits, or actually think they are safe, but in fact maybe not.
The main issue is a lot of people still calculate as if they are using a mech, using standard Ohms law calculations at full charge voltage. With a regulated mod, what hits your atomiser follows the standard Ohms law calculations, this is the output of the board.
This is not helped by the fact mods display the output amp load and voltage, leading to more confusion as people think as their mod shows the amp load, it must be what is being drawn from their batteries. It isn't. It is the output of the board.
What you really want to know though, for battery safety, is what is happening at the INPUT of the board.
This works out as P(watts)/V(cut off voltage)=I(amps)
The full calculation is Watts used/Minimum single battery voltage/number of batteries/Mod Efficiency.
I will use a few examples here, to show you the difference between a single, dual and triple 18650 device, and the amp load that is being asked from your batteries at a given wattage.
I will use 75W in all examples, as this seems to be an average maximum for a single 18650 mod, and also will show how as input voltage increases with more cells, amp load decreases- which is how mods with more batteries in series can offer higher power levels safely.
Lets use a single battery mod first, at 75W.
The calculation here, assuming a 3.1V cut off, and also an efficiency of 85% (I am using this as it is the efficiency of the DNA75 and its efficiency is shown in the datasheet) is-
75/3.1=24.19 Divide the answer by 0.85 for 85% efficiency, and this leaves you at 28.46A- far over a 20A cells CDR. I did not have to include the number of batteries part of the calculation due to there being just one cell.
Now, for a dual 18650 device.
The calculation here is, assuming 90% efficiency this time-
75/3.1/2=12.09A. Divide your answer by 0.9 for the 90% efficiency and this leaves you at 13.44A. As you can see, you are now within a 20A batteries CDR, even at cut off where amp load is highest.
Now, the final one, a triple 18650 device. I will again use 90% efficiency.
75/3.1/3=8.06A. Divide by 0.9 for the efficiency, and you are left at 8.96A.
So, you can see in each instance the amp load decreases as the battery number increases- this is due to the higher input voltage. A regulated mod will draw less amps from its battery/batteries at full charge vs cut off voltage, which is why it is safest to use cut off voltage.
Now, you may be thinking what about resistance? This is where the mistake usually happens- with a regulated mod, this effects output voltage and amp level, but NOT the input amp load!
To hit high power levels,you may need to build within a certain resistance band so you don't hit output voltage and amp limits, but it is how a mod like the DNA200 has a fuse that blows on the input side at 25A, but can output 50A constant/55A burst and 200W of power!
Here is the page on steam engine that can be used to work out what is bring drawn from your batteries- as you can see, what is pulled from your batteries is very different to what hits your atomizer
http://www.steam-engine.org/batt.asp , this is handy to double check your calculations or even to use quickly to check you are safe.
TL,DR- Just divide your watts used, by the input voltage, followed by mod efficiency to give you a correct figure regarding amp load on your batteries. A regulated mod CAN push more watts safely while the battery puts out more volts- near full charge in easy terms.
Safe wattages for each mod with a 20A CDR (Constant/Continuos Discharge rating- how many amps your battery can put out safely, and continuously till the end of its charge. This is the rating you want to know, ignore pulse ratings as these are pushing past a batteries design, although as you learn more you may feel comfortable doing so).
This is highly dependant on your mods cut off, and is a rough guide!
Using 90% efficiency at 3.1V cut off per cell-
Single 18650- 55 Watts. At cutoff, this would give you 19.71A, very close to a 20A CDR battery.
Dual 18650- 110W. At a cutoff of 6.2V, or 3.1V per cell, this again leaves you at 19.71A.
Triple 18650- 162W.
This is assuming a cut off of 9V, which is the lowest I personally know of triple 18650 mods cutting off, so 3V per cell.
This will be drawing 20A, dead on a 20A CDR.
These are all at CUT OFF, higher wattage can be achieved at full charge of your batteries, this is the MAXIMUM amp load possible.
If you are using batteries such as LG HD4's or Sony VTC5A's, with a 25A CDR, or even 30A cells such as LG HB6's, you will be able to achieve higher wattages safely using the calculations I provided.
