Link to ohms law calculator

[Bazz_74]

Just going to post up this link for anyone who needs an easy to use ohms law calculator, just remember to use 4.2v for all single battery and parallel mods and 8.4v for any series mods.

http://www.ohmslawcalculator.com/ohms-law-calculator

 

[Andii]

the only page you ever need guys.........as old as vaping
http://www.steam-engine.org/

 

[Lazydrippin]

There’s this app as well which has helped me so much in the past

 

[Narkis]

I’ve never dipped my toe into Mechs, Been wanting to try the Bonza for a long time now and always put myself off because of the horror story’s etc,

so I have a little question if I went out and got a Bonza would I then do the calculations before buying battery or do the calculations with the battery I have?

also I’ve heard it’s best to calculate from 3.7v instead of 4.2v

also would I do the calculations from the battery to work out what ohms I should be using or the volts and ohms,

I get that I’m a noob with all this so
I’m not going out to buy a mech till I’m fully confident about using them and making sure I’m as safe as I can be because of the horror story’s I’ve heard,

Last question what battery’s do people use for the bonza I’ve seen it can take 18650/20700/21700

sorry if this is the wrong place to post this

 

[Deleted member 58360]

also I’ve heard it’s best to calculate from 3.7v instead of 4.2v

For a mech, do it from 4.2 - fully charged cell.

That's when the current draw will be highest.



On a regulated device, do it from the cutoff or 3.7 if you must if using wattage - because the current draw goes up as the voltage drops to maintain the wattage.

 

[Deleted member 58360]

also would I do the calculations from the battery to work out what ohms I should be using or the volts and ohms,

I don't really know what you're on about here...

 

[Narkis]

I don't really know what you're on about here...

So when you have a mech and your working out the calculations do you do it from the Volts and Amps and get your ohms from there or do you do volts and ohms etc I’m a complete noob and ohms law kinda goes over my head which is why I’ve never had a mech

this maybe a very stupid question I really don’t know anything

 

[Mr Ripple]

So when you have a mech and your working out the calculations do you do it from the Volts and Amps and get your ohms from there or do you do volts and ohms etc I’m a complete noob and ohms law kinda goes over my head which is why I’ve never had a mech

this maybe a very stupid question I really don’t know anything

I'm not really a mech user but the basic principles are never draw more amps from your battery than it can offer with a margin for error included in your calculations.
And just as important maintain your kit in tip top condition for safety not just performance.
You need to know or have a basic understanding of ohms law or learn to use an ohms law calculator so you can work out how many amps your coil will ask the battery for.

 

[Deleted member 58360]

So when you have a mech and your working out the calculations do you do it from the Volts and Amps and get your ohms from there or do you do volts and ohms etc I’m a complete noob and ohms law kinda goes over my head which is why I’ve never had a mech

this maybe a very stupid question I really don’t know anything

Depends what you're wanting.

If you know you have a 20A cell and want to go as low as possible while keeping within that spec, then:

4.2v/20A = 0.21 ohms. Shouldn't build below 0.21 ohms.

Alternatively, you have a coil built (say it's 0.18 ohms) and want to check your cell can handle it:

4.2v/0.18 = 23.3A. You'll be needing a 25A cell.



Always a good idea to allow some overhead in that.


It's also best to know your build and how it reacts to different voltages - there's nothing on a mech to tell you that your cell is getting flat, and overdischarging a li-ion is a Bad Idea.

 

[speedfreek67]

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.