High-Power Box Mod Battery Requirements

[Senze]

My girlfriend pre-ordered a sigelei 100w box mod for my birthday and when I looked at the requirements it stated that the mod needs 30amp batteries. I could be wrong here but it seems like they are "requiring" 30amp batteries simply because it's possible that a build could require that amperage, but at the same time other builds may not, and therefore a 20amp battery could potentially suffice. For instance, if the resistance of my build was 1ohm, and I ran it at 100W, it wouldn't pull anywhere near 30 amps, or even 20 for that matter. Yes, I realize the Sigelei has a voltage limit and wouldn't actually be able to run a 1ohm coil at 100W, but even a .5ohm build at 98w wouldn't require over 20 amps.

Am I right here or is my understanding of Ohm's law completely out of whack? Are they "requiring" 30amp batteries simply to cover their .... (not that I blame them), and would 20amp batteries be perfectly safe as long as the build doesn't require more than 20 amps?

 

[Papa_Lazarou]

Yep - they are "requiring" you to be safe at any potential setting of the device, given any potential usable build. The device won't not work with bats of lower r ratings, but safety is of paramount concern.

Note that you should factor in head room on your amp calcs - a lot of peeps use 20% as a guideline (i.e., add 20% to the amp calc to determine minimum bat requirement).

Oh, and use 4.2 volts in your calculations, and use the continuous fire rating of the battery (not the pulse rating).

 

[Senze]

Yep - they are "requiring" you to be safe at any potential setting of the device, given any potential usable build. The device won't not work with bats of lower r ratings, but safety is of paramount concern.

Note that you should factor in head room on your amp calcs - a lot of peeps use 20% as a guideline (i.e., add 20% to the amp calc to determine minimum bat requirement).

Oh, and use 4.2 volts in your calculations, and use the continuous fire rating of the battery (not the pulse rating).

Cool, thanks for the confirmation that I'm not out in left field somewhere. However, you mentioned using 4.2v in my calculations and I have always done that in the past, but this will be my first dual battery mod so I'm unsure if that still applies. I've read that the Sigelei has a voltage limit of 7v, so wouldn't I need take that into consideration?

 

[Papa_Lazarou]

Cool, thanks for the confirmation that I'm not out in left field somewhere. However, you mentioned using 4.2v in my calculations and I have always done that in the past, but this will be my first dual battery mod so I'm unsure if that still applies. I've read that the Sigelei has a voltage limit of 7v, so wouldn't I need take that into consideration?

Yes, it's late - the 4.2 V thing is for a single bat.

 

[Ryedan]

My girlfriend pre-ordered a Sigelei 100w box mod for my birthday and when I looked at the requirements it stated that the mod needs 30amp batteries. I could be wrong here but it seems like they are "requiring" 30amp batteries simply because it's possible that a build could require that amperage, but at the same time other builds may not, and therefore a 20amp battery could potentially suffice. For instance, if the resistance of my build was 1ohm, and I ran it at 100W, it wouldn't pull anywhere near 30 amps, or even 20 for that matter. Yes, I realize the Sigelei has a voltage limit and wouldn't actually be able to run a 1ohm coil at 100W, but even a .5ohm build at 98w wouldn't require over 20 amps.

Am I right here or is my understanding of Ohm's law completely out of whack? Are they "requiring" 30amp batteries simply to cover their .... (not that I blame them), and would 20amp batteries be perfectly safe as long as the build doesn't require more than 20 amps?

Coil resistance does not matter here. 100 watts is 100 watts with a 2 ohm coil and also 100 watts with a 0.5 ohm coil. That means the amp draw on the batteries will be the same, except for differences in regulator efficiency at different output voltages.

100 watts at 3.3 volts (it will be more amps at lower voltage to keep making 100 watts through the regulator) requires about 30 amps. If your regulator is 75% efficient that becomes 37.5A. Split that between 2 cells and you need 18.75A from each. If you use 20A batteries you're right on the edge. I believe this would work out about the same if you consider the cells in series.

I know Sony VTC batteries are pretty much impossible to get right now. I honestly don't know what I would do in this case.

 

[Baditude]

The purple Efest 18650 2100 mah battery is a 30 amp battery (actually a re-wrapped Sony VTC4 battery). The purple Efest 2500 mah battery says 35 amps but is actually 20 amps (re-wrapped LG18650HE2 2500 mah). The purple Efest 3100 mah (20 amps advertised) is actually only 6 amps. Purple Efest Batteries Not As Advertised

Orbtronics sells an 18650 2100 mah battery also 30 amps. (may be the same re-wrapped Sony VTC4)

If you can't get those, I'd go with either the Samsung INR18650-25R 2500mAh 20A or LG18650HE2 2500 mah 20 amp.

 

[dice57]

any of the one's bad listed will work fine, and have the usable amps to push them, anything less will not provide as much run time when pushing the high watts. A VTC 4 or 5 would also be more than adequate, maybe a tad over kill, but will work fine none the less.

 

[Senze]

Thanks for all the info guys. I have a brand new set of LGHE2's already, so I think I'll use those and limit the wattage until I can track down a set of legit VTC5's. I appreciate the assistance.