Ohm's Law: How safe am I?

[Viper_SA]

Hi all,

So recently I got a Dead Rabbit RTA as part of a trade. It had dual coils pre-installed that came to 0.08 Ohm. Running it at 100W in an Augvape V200 (dual battery 200W mod) I began to do the calculations. I was firing at 2.9V, but still drawing in the region of 36A. Batteries started giving "low power" messages at around 3.96V. So I rebuilt with some other pre-made coil;s coming to 0.14 Ohm for the dual coils. But, firing at 3.6V this still puts me at 25A current draw.

Got me thinking about how safe these dual battery mods are that can fire up to 200W in series.
I'm using Samsung 25Rs and don't feel particularly safe vaping the coils as they are now. Am I missing something, or is this dangerously close to the limits?

 

[Silver]

Hi @Viper_SA

For your first 0.08 ohm coil, you are right, you are drawing about 35 amps at 100W
I=sqrt(P/R)

I think the Samsung 25 R has a CDR of 20 A, so its not something I would do with those batteries.

For your second coil, i assume you made a typo and its 0.14 ohms not 0.014 ohms
At 0.14 ohms I get 27 A at 100W
Still above the Samsung 25R CDR I think

Many folk think that regulated mods are safe and wont let you fire into the danger zone. Yes they may have short circuit protection but they dont know what battery you put inside so it still helps to understand ohms law and build for the battery you are using.

 

[Viper_SA]

Hi @Viper_SA

For your first 0.08 ohm coil, you are right, you are drawing about 35 amps at 100W
I=sqrt(P/R)

I think the Samsung 25 R has a CDR of 20 A, so its not something I would do with those batteries.

For your second coil, i assume you made a typo and its 0.14 ohms not 0.014 ohms
At 0.14 ohms I get 27 A at 100W
Still above the Samsung 25R CDR I think

Many folk think that regulated mods are safe and wont let you fire into the danger zone. Yes they may have short circuit protection but they dont know what battery you put inside so it still helps to understand ohms law and build for the battery you are using.

Thanks @Silver, corrected my typo.

 

[Silver]

I just checked Mooch's battery table
Samsung 25R does have a 20A CDR

To get 20A with 100W you would need a coil of 0.25 ohms
But to be safer at 18A - coil would be 0.3ohms

Id say at 100W you shouldnt go much lower than 0.3 ohms with those batts

 

[Viper_SA]

Just got me thinking that many new vapers indeed rely on regulated mods to keep them safe, when indeed you can still get into trouble.

 

[Silver]

Just for the sake of clarity here

The CDR is the conitnuous discharge rating of a battery
It is the amps the battery can push contionuously without problems or getting too hot.

Batteries may be able to pulse for short periods of time (like we vape) at higher than the CDR but the reason its not safe to do that is if your mod gets stuck in an autofiring position in your pocket or your bag, then the battery could get hot and vent - which can be dangerous.

 

[Silver]

Just got me thinking that many new vapers indeed rely on regulated mods to keep them safe, when indeed you can still get into trouble.

Agreed 100%

Especially if they buy cheaper 15A batteries and want to build very low ohms on their new setup!!
I think these mods usually have a 35A limit or something like that but they have no way of knowing the limits of the battery you are using. Some user manuals say you need to use an appropriate high drain battery but thats not very helpful to a newer vaper.

This battery safety topic is very important and all we can try do here is help vapers understand the issues and the potential dangers so they can make better choices to stay safer.

 

[CTRiaan]

On a regulated mod the resistance of your coil/s does not matter when in power mode.

100 W dual battery is 50 W per battery.
50 W/3.2(lowest voltage example)/0.9(efficiency example)=17.36 Amp per battery which means 25R batteries are fine.

Note that the voltage displayed on your mod is output voltage, not input which starts off at about 4.2V and decreases with use.

 

[Silver]

Thanks @CTRiaan

That mod @Viper_SA is using is a 200W mod
So using your example above, it would mean 100W per battery or 34A per battery?

does that sound correct?

 

[Raindance]

Regulated mods have a max amp draw they will allow. Depends on the mod but the DNA boards limit this to just under 20 amps from what I have seen (75 and 250 monochrome boards) so the low battery warning probably means the power you selected is out of reach of the board with the limits set on it.

Generally a 25 Amp CDR cell would mean you are relatively safe. Depends on the board though so do not take that for granted.

Regards

 

[CTRiaan]

Thanks @CTRiaan

That mod @Viper_SA is using is a 200W mod
So using your example above, it would mean 100W per battery or 34A per battery?

does that sound correct?

If he fires it at 100 W it would be as per my example and at 200 W it would be 34 A per battery.

 

[Silver]

If he fires it at 100 W it would be as per my example and at 200 W it would be 34 A per battery.

Ok thanks

@Viper_SA
My mistake - i forgot to share the power you dial in between the two batteries.

Same principle though - if you fire at higher than the batteries can handle - then even though its a regulated mod, you could be in a dangerous zone for the battery. I.e. if you fired at 200W, you would be going way higher than those 25Rs are rated for.

 

[CTRiaan]

Minding Your mAhs – Ep3 – Battery current and batteries for regulated mods

 

[CTRiaan]

Ok thanks

@Viper_SA
My mistake - i forgot to share the power you dial in between the two batteries.

Same principle though - if you fire at higher than the batteries can handle - then even though its a regulated mod, you could be in a dangerous zone for the battery. I.e. if you fired at 200W, you would be going way higher than those 25Rs are rated for.

Yes, about double.

 

[Silver]

Regulated mods have a max amp draw they will allow. Depends on the mod but the DNA boards limit this to just under 20 amps from what I have seen (75 and 250 monochrome boards) so the low battery warning probably means the power you selected is out of reach of the board with the limits set on it.

Generally a 25 Amp CDR cell would mean you are relatively safe. Depends on the board though so do not take that for granted.

Regards

Thanks @Raindance
So a 25A battery is mostly fine
However, these Samsung 25Rs are 20A

And the issue I am harping on about here is that if you somehow get a 15A battery (maybe a fake or a low rated battery) - you could be in for some trouble - trying to fire a big wattage on your new gear.

Not directed at @Viper_SA but just making the point. Many vapers know that mechs are dangerous but I have seen vapers that think regulated mods are 100% safe. However, one still needs to know what the battery limits are and whether you are overstressing them or not.

 

[Raindance]

Minding Your mAhs – Ep3 – Battery current and batteries for regulated mods

Stated this before many times but seems people are under the impression that a 200 (or whatever) mod will fire at the selected wattage whatever you dial in. Not true. In truth your mod will only allow that power level as long as it does not need more amps than the pre-programmed cut off. Most to not publish this cut off as it is easier to sell that way. the fact that your 250W V@0d#@0d mod only fires at that level at a coil resistance between 0.15 and 0.19 Ohms would not be something promoting sales at all.

Regards

 

[Raindance]

Thanks @Raindance
So a 25A battery is mostly fine
However, these Samsung 25Rs are 20A

And the issue I am harping on about here is that if you somehow get a 15A battery (maybe a fake or a low rated battery) - you could be in for some trouble - trying to fire a big wattage on your new gear.

Not directed at @Viper_SA but just making the point. Many vapers know that mechs are dangerous but I have seen vapers that think regulated mods are 100% safe. However, one still needs to know what the battery limits are and whether you are overstressing them or not.

True @Silver , what really P's me off is that most product manufacturers state the need for a high amp draw cell but do not state what that level is. I mean what is high? 5 amps? 150 amps? Seriously? why not just state the level they set their mods at?

Regards

 

[Silver]

True @Silver , what really P's me off is that most product manufacturers state the need for a high amp draw cell but do not state what that level is. I mean what is high? 5 amps? 150 amps? Seriously? why not just state the level they set their mods at?

Regards

Agreed, I said a similar thing above - asking for a high drain cell is hardly helpful to a new vaper
The other complication of course is finding out the true CDR of each cell.
Thank goodness for Mooch's battery tests - but a new vaper would probably not think about that.

 

[Viper_SA]

On a regulated mod the resistance of your coil/s does not matter when in power mode.

100 W dual battery is 50 W per battery.
50 W/3.2(lowest voltage example)/0.9(efficiency example)=17.36 Amp per battery which means 25R batteries are fine.

Note that the voltage displayed on your mod is output voltage, not input which starts off at about 4.2V and decreases with use.

Could you elaborate on this some more please @CTRiaan?

 

[CaliGuy]

I use this as a guideline, easy to use and helpful.

 

[Viper_SA]

I use this as a guideline, easy to use and helpful.

View attachment 154039

Yeah, it's much more clear-cut with mechs. My question was more how to treat the voltage in a series regulated mod. I used the formula: I=V/R

 

[CTRiaan]

Could you elaborate on this some more please @CTRiaan?

Which part?

Have a look at the Mooch's video. He explains it very well.

NB. The video is for regulated mods.

 

[Viper_SA]

Which part?

Have a look at the Mooch's video. He explains it very well.

NB. The video is for regulated mods.

On a regulated mod the resistance of your coil/s does not matter when in power mode.

100 W dual battery is 50 W per battery.
50 W/3.2(lowest voltage example)/0.9(efficiency example)=17.36 Amp per battery which means 25R batteries are fine.

Note that the voltage displayed on your mod is output voltage, not input which starts off at about 4.2V and decreases with use.

Just that last "note" has me confused by exactly what you mean.

 

[Cynarius]

On a regulated mod the circuit board pulls the selected wattage from the battery then transfers it to the coils. Thus you should work on the formula that @CTRiaan and mooch give, amps=watts/volts/power factor

Amps = total power drawn if you have multiple batteries divide it by the total number of batteries to get power per battery

Watts is what ever you have set your mod too

Volts = the lowest voltage your average battery will fire at for 18650's that's about 3.2 volt

Power factor is accounting for any power loss or volt drop caused by your mod which the average to work with is about 10% loss hence 0.9

As for pulse current that should never be used in vaping always stick to the cdr. Very few manufacturers give a pulse rating and if they do remember the 18650, 20700 or 21700 where never designed for vaping they where designed for battery packs in industrial sectors thus they give a pulse rating so that external protection can be set up properly.

In electricity a pulse is milliseconds not a 3 second pull.

 

[CTRiaan]

Just that last "note" has me confused by exactly what you mean.

What @Cynarius said and also the input is what is drawn from the battery and regulated output is what is sent to the coil by the chip.