Narkis
Initiate
- Joined
- May 17, 2017
- Messages
- 42
Okay, so...
For safe use of the chosen battery, you don't want to exceed the Constant Discharge Rate (CDR) of the battery. This is the current the battery can safely output, and is measured in amps.
Your battery has a charge of 4.2 volts, when fully charged.
You need to use
Volts/Resistance = Amps.
So, lets stick to single battery mechs for simplicity, and let's say your battery has a CDR of 20 amps (Samsung 25r, for instance).
4.2/0.21 = 20 amps
Therefore, on a fully charged battery, a 0.21 resistance will pull 20 amps from that battery. That's your *lowest* resistance to use with a 20 amp battery - 0.21 ohms. That's the limit you don't want to go below.
If you used a 0.17 ohm coil...
4.2/0.17 = 24.7 amps
...you would need a 25 amp battery (Sony VTC5A, Molicel P26A etc).
So thats how to calculate the minimum resistance to build to, for safety. You might want to build higher, to extend the time between battery swaps, or to not push your batteries too hard, but you shouldn't build lower.
Now for the 3.7 volt thing...
When you complete the circuit in your mod/atty combination by pressing the button, you won't actually get 4.2 volts out of the battery. These batteries might have a resting voltage of 4.2 volts when fully charged, but under load they output around 3.7 volts.
Basically, the voltage coming from your battery drops as soon as you make it work hard!
This doesn't mean you are pulling less amps however (which is why we use 4.2 volts for the safety calculation), it means that various factors like the internal resistance of the battery itself conspire to make sure only 3.7 volts reaches your atty.
So, when using a coil calculator like https://www.steam-engine.org/coil to calculate a good coil for a mech, for the warmth of vape you like, you want it to work at around 3.7 volts or a little less.
This is a good starter build for a dual coil mech:
https://www.steam-engine.org/coil?mat=n80&s=dp&r=0.24&awg=24&id=3
Even though it pulls a little less than 20 amps, I would use a 25 amp battery for better safety and battery life.
Notice how the heat flux is a warm vape (not too hot and firey, but not too cool and limp) at 200 mW/mm^2 (don't worry about these figures and units, just keep the heat flux at 200) and how the mod setting is 3.7 volts.
This means I get a nice vape because the coil is optimised for 3.7 volts, which is around the voltage that actually reaches my coils.
I use this build on all my mechs pretty much. 24 gauge Nichrome, 7 wraps 0.48 ohms per coil. Under 20 amps dual, under 10 amps single coil, works great at 3.7 volts.
Have a play with the resistance in that calculator and see how it changes the number of wraps, the heat flux and the voltage required.
this is amazing thank you really helps,
