Some Questions on OHM's Law

[harriszl]

Hello, I have a couple questions about using Ohm's Law to calculate build safety.

A=V/R

1) What voltage do I use for the calculation? Do I use the Voltage printed on the side of my Sony VTC6 3.7v, the volt reading on my mod when it is sitting idle 4.7, or voltage reading on te mod while the fire button is pressed around 5.5?

2) When determining the safe amperage for my batteries, do I add the Amp rating for the two batteries together, 2x 15 amp batteries = 0A safety, the rating of only a single battery 15A, or somewhere in between.

For example: my VTC6 batteries are rated at 15 amps 3.7v. My coil is .33 ohm. The voltage on my mod reads 4.73 volts when idle, and around 5.55 when firing. Which numbers would I use for the calculation?

I have looked for around an hour this morning for these answers with no luck. I have found the Steam Engine site and watched the battery safety videos from New Amsterdam Vape, both of which were very helpful, but I couldn't find the answer to these questions.

Thank you for the help.

 

[Mattp169]

what mod are you using?
if its a VW mod then ohms law is not used. Watts law is which in this case is
wattage/current voltage of battery/eficiency of mod (most are 90%)=amp draw on battery

but in general you always use the current voltage of the battery in any calculation

if your mod is a single battery and reading 5.55 then its got something in it to boost or buck the voltage

most mods are wired in series which means you do not add the amperage of your batteries together

in a parallel mod which most are not and if you had one its more then likely advertised as a parallel mod then you can add the amperage of the batteries

 

[harriszl]

what mod are you using?
if its a VW mod then ohms law is not used. Watts law is which in this case is
wattage/current voltage of battery/eficiency of mod (most are 90%)=amp draw on battery

but in general you always use the current voltage of the battery in any calculation

if your mod is a single battery and reading 5.55 then its got something in it to boost or buck the voltage

most mods are wired in series which means you do not add the amperage of your batteries together

in a parallel mod which most are not and if you had one its more then likely advertised as a parallel mod then you can add the amperage of the batteries

Matt, than you for the response. I am using a Tesla Nano 120w in wattage mode. It has dual 15 amp 18650 batteries.

so if I understand what you are saying for my mod the calculation would be (60watts/5.55)/.90 = 12.12.

If the mod is set to 60watts and the the screen shows 5.55 volts when the fire button is pressed assuming 90% efficiency..

 

[Mattp169]

close
they are in series so add voltage together

the max they can output is 8.4v - 4.2 V per battery
so at 60 watts the minimum amps is 7.94 amps

but as the battery drains the amperage draw increases . the batteries normally cut off in many mods around 3.2v per cell so 6.4 total

so at low battery cutoff you are drawing 10.41 amps

the screen is showing something else. I am not familiar with your mod so I can't tell you what the 5.55 volts means, but ignore it for amp draw. that may be the actual volts the mod is outputting but that does not effect the amp draw on the batteries. the mod cant decide to only take 5.55 volts from the batteries, it takes the full voltage and regulates it to something else to output the wattage you want. the wattage and the current vvoltage of the batteries determines how many amps is being pulled from the battery

now if you switch to a mech mod then you use ohms law because then there is no wattage to take into account. just volts and ohms
on most online ohms law calculators there is a spot to show the wattage you would be outputting but thats more of a reference and not a variable you can change yourself

with 15 amp batteries you are safe on any dual battery mod to around 90 watts regardless of your coil
now you can push it higher and be safe, but if an accident occurs like fire button getting stuck on in your pocket etc, then there is a chance the batteries will vent
to be safe on using setting above 90 watts you should be using 20 amp batteries. Im not as familiar with sony model numbers but they make plenty of 20amp batteries and ones that can actually handle 25
other brands and models to consider are lg hg2 he2 he4 and some others
and samsung 25r and 30q

but if you are just a person who vapes below 90 watts you are more then safe with 15 amp batteries in a dual battery mod

 

[harriszl]

Thank you for taking the time for this great explanation, this really helps.