Clarification on Mechanicals and Battery Amp Limits

[DaveHolland]

So I see everyone is still talking about ohms law and referencing amp draws with super sub ohm coils (0.05 Ohm). Lets look into a few things here, if a battery is only capable of supplying 35 amps (LG and MXJO) will it be able to supply the full 84 amps required at 4.2 volts??

The answer is no, in the real world with battery powered devices we have what is called voltage drop. If you cannot supply the 84 watts you will sag voltage and continue to supply 35 watts so in reality on a mechanical you fire a 0.05 ohm coil and it sags to around 2 volts under full load. In this process you are running the batteries at the limit and they will start to get hot before thermal runway occurs. You will notice it because you will feel a burn in your hand before it becomes unmanageable.

The real danger to mechanical vaping is a hard short where it will instantly overload the battery and cause thermal reactions. The main take away is though, when you place exceeding loads on the battery it will only supply what it can and no more, at that point the voltage will drop. Voltage drop occurs at all levels of load also, so at no point in vaping a mechanical will you ever get 4.2 volts to the coil.

Sure, how do I know, well because I have run different coils on a mechanical and measured the actual voltage under load. At no time have I seen above 3.7v to the coild on anything below 0.5 Ohm. I find that on 0.09 Ohm coils I am actually running around 2.70v for an acutal wattage of 81 and 30 amps. That is well within the limits of my battery but if you think its 4.2v you would think you are pulling 46 amps which is 11 amps above my limit.

So as you can see, sub ohm vaping is not as dangerous as you think it is if you have the proper battery. Where it was dangerous in the beginning is all of the low quality batteries that were being pulled too hard. With todays batteries just make sure you have a quality brand and you will be fine. Dont fire it for 2 minutes and allow a cool off if it becomes warm in your hand. This of course does not take into account defective batteries.

 

[Froth]

You seem to be confusing battery sag and voltage drop, two different terms. Battery sag is when the voltage coming out of the battery drops down under high load where as voltage drop would be the loss of voltage AFTER the battery due to conductive losses in the mod itself.

If you've never seen over 3.7v to the coils with a build under .5 ohm then you're not using very conductive mods IMO, My Copper SMPL drops down to 3.66V from 4.2V with a 0.15 ohm coil, with a .20 ohm coil it does not drop below 3.70v, Battery being used was a Samsung 25R.

 

[supertrunker]

Why is a hard short only a danger to mechs? what does one do to regulated devices?

The reason we build to nominal values is to build in some margin of safety - i don't for one moment think my perfect mod delivers all the power to my coil and even batteries themselves have an internal resistance. Rather, i think they are a reference number we can all relate to, in much the same way that we insist on using continuous discharge ratings for batteries over nebulous 'pulse' ones.

T

 

[DaveHolland]

A hard short is dangerous because it will essentially zero out the Ohm and allow the electrons from the battery to continue to run through it repetively speeding up each time until its out of contol and will vent the battery.

I guess I also forgot that over discharge will cause venting too so monitor the battery.

In regulated mods if you short it just wont fire. That is the ptrotection and also why they have a minimum ohm that can be run.

Essentially its not as dangerous as madenout to be. If you have a proper coil with shorts and a brand battery it will not vent. There will be many signs of inconsistent firing and a heat build up before it ever gets to grenade status. Keep in mind that there are defective batteries such as the cell phones that explode but nothing can prevent that battery from failing except for not using it. It will also have signs though, again in the form of heat.

Yes I do not run copper mods as they start to get oretty nasty after a lot of handling. The main point though is that our batteries will sag the voltage on an over amp situation. They cannot manufacture amps that they cannot supply. As long as you dont fire it for 2 minutes in that situation it will not vent.

On.a daily basis I work with much more power and high voltage applications. The ecig is fairly safe even in its mechanical state, just a few things to look out for. Obviously using an old Blue EH that was never rated for any amp draw will not sustain. A battery rated for 2c being ran at 20c will heat and vent quickly, but the sag will also effectively kill it. Now the standard batteries designed to be run at 14c and have a load of 20c will still sag but will take much longer to heat and vent.

I do ot all the time as the electronics load up much more than the battery is capable but the battery will hit its limit and hold a certain amperage. The way we increase performance is to get higher amp limit batteries. Which applies to mechanicals. You can fire it all day on a 0.02 ohm build but you wont get the performance of that coil until they come out with an 80 amp battery.

This information is derrived from actual personal tests and electronics experience. Not from a quick glace on wiki.

Nominal voltage of 3.7v and 35 amp limit is 129 watts. You will not get more than that out of these batteries. Stacked to 7.4v you can push 259 watts. Though again sag under load will lower the numbers in real world applications. If you exceed the load the battey will get warm then hot and eventually vent, its not a fast process unless you load it demanding 1kw. If you are holding the mechanical it will become uncomfortably hot in your hand before it starts to vent, thus built in safety.