Hi all, hope everyone is keeping well and your all enjoying your 4th July, I recently bought 3 rda’s for flavour testing and some pre built coils, now I’m struggling to figure out at what wattage to use them at, used to just buying coils from my local shop, have looked into ohms law hut just can’t seem to get my head around it, have never used voltage mode or anything on my mod
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Don’t over think it if your on a regulated mod your safe to a point down load steam engine on your phone .( I keep a tab open on my opening page ) it’s battery draw you want never go over your battery amps.regard the wattage 3.7 volt is where a mech works most if it’s to hot turn it down and as they say adjust to taste.single coil I’m usually at .25/.30 ohm 35/45 watts
Think that should help
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You can use an online calculator, just search “Ohm’s Law calculator” and you will find several. I use the one from the Android app Vape Tool. Screen shot is shown below.
There are two primary things I use it for. I check to ensure I can’t exceed the max current listed for the batteries I’m using. I also calculate a good starting point to set my Wattage(or Voltage) when using a new coil.
It can also be used to decide a good target resistance when building a new coil or selecting a pre-built coil.
The Ohm’s Law math formula is:
E = I × R.
E is Volts
I is current(Amps)
R is Resistance (Ohm’s).
In a single battery mod, or dual parallel battery mod, the max voltage the battery can supply is 4.2V. Some chipped mods can boost above 4.2V but you don’t need to think or worry about that. If they can boost above 4.2 V they also have you covered for safety.
Series battery mods Voltage will be 4.2V times the number of cells used, so for a two battery series mod it’s 4.2V × 2 = 8.4V. So 8.4V max.
When you know the max Volts you put that in the Ohm’s Law calculator. The calculator must have two values given and it will output the third value. You have the Voltage, now you can input either the current to find the Resistance in Ohm’s, or the Resistance in Ohm’s to find the resulting current.
When I’m using Ohm’s Law for a safety check I input 4.2V (single or parallel battery) because it’s the maximum Voltage the batteries are capable of providing. Then input the Resistance of a coil in Ohm’s to find if the resulting current is within the bounds for the battery you are using. The Max current is usually listed on the battery, if not look it up from the manufacturer. If you have a battery that is a 20Amp max battery and the calculator comes back with 22.6 Amps you don’t want to vape that coil as it could break the battery causing instant discharge and fire. If the result is 20 or less, you should be good to go. A word of caution, there are counterfeit batteries being sold so always buy your batteries from a reputable seller. You can search the Forum here for that info. A counterfeit battery my have 35Amps listed on the wrapper but in reality it may only be a 15 Amp battery under that fake wrapper.
Using Ohm’s Law to select a coil, or find the desired target resistance to build a coil, you input the Max Voltage and then input a Resistance. Repeat using different Resistance values to get an idea of how much you would demand of your batteries. You can target so your battery will last a long time if your going out, or you can target for a max performance for cloud chucking, or somewhere in between.
Using Ohm’s Law to set my initial variable mod setting I usually punch in 3.9 V because that’s about what your battery will supply most of the time during use. A fully charged battery may start able to supply 4.2 V but very quickly it will only provide around 3.9 V and that will decrease slowly over time till a point where it drops off quickly and you need to recharge. I have a screen shot below showing 3.9 V with a 0.23 Ohm coil. I will set my mod for 66 Watts. As you vape away the Voltage will drop and so will the max currant draw so if you start in a safe range for you batteries, you will remain in a safe range throughout unless you change coils.
ALWAYS use Ohm’s Law for safety if you plan to vape using a series battery mod. A two battery series mod using a 0.23 Ohm’s or less coil will exceed the max Current of possibly all batteries currently made and is very easy to build or buy a 0.23 Ohm or less coil.
It is my hope that I was able to show the usefulness of Ohm’s Law without overcomplicating it. It’s simple if you use an online or app Ohm’s Law calculator. The math can be confusing and prone to error if you don’t use an Ohm’s Law calculator.
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Thank you ever so much for all the information it’s appreciated, has made more sense now, just trying to find my battery max current because i’m using a Geekvape M100 AIO so has built in battery
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I forget about the built in battery mods. They usually don’t list that most important value. Instead they say to use the one or two coils they want you to buy from them. I think most of them have built in safety smarts though. If they provide a 510 connection they cannot control what the user does with it. If it’s a coil cartridge there is usually an aftermarket rebuildable available to buy.
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Thank you once again, yeah I can’t seem to find it anywhere, I never vape that high wattage and my lowest coil is a 0.50Ω mtl staple coil, so mainly trying to find the best wattage for each coil, was easy with commercial coils as it tells you on the bottom
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I found many commercial coils overstate the Wattage they can handle. They sell more coils if you burn them up quicker. That’s how I moved away from pre-built coil cartridges and started building my own. That and every n’th cartridge would be a dud from the factory. Not to mention supply issues.
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I found a review of the M100 online:
In it they have this power chart, that might give you some starting points for current drawn, for various resistances.
Maybe that’ll help a little.
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I want to move away from commercial coils myself but just not quiet ready to build them myself as yet so thought I would try out some pre built ones ended up getting some Wotofo Ni80 0.90, Coil Art Kanthal 24ga 1.0 and a Coilology mtl 4 in Kit to try out
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You don’t have to learn how to make coils there is loads of good coils pre made that are perfectly good for what we vape if you want really good coils check out some of the hand made ones but don’t be put off with the price a good coil/coils will last you ages I’m still using a pair I paid 15quid a year on
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Your doing good. It’s all part of the process. I think it’s a fun hobby and not just a way to stay off the stinky ciggs.
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Thanks, these was just quick and easy to get hold of, I have ordered some hand made ones from my local shop and will order some more hand made once I know what type of wire I prefer etc, wanted some Aliens but most seemed a little too low ohms for me, already getting Nic rush from my 12mg nic since changing to a RDA lol
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Thank you, just been reading thru the review and it says it’s a 29 amps max so was of great help
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Ha ha nooooo drop your nic on low ohm to 3 mlg your blow ya head off 
The more vape The lower The mlg
Mtl i vape 12 in a pod 9 in a tank .8/1.0 ohm
Restricted Dl 6 mlg
Duel coil .1to 0.12. 3 mlg
Single coil as well
No wonder you got a nic rush
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Just stay above .18 ohms on a mech and you have nothing to worry about with a 18650 battery. On reg mods there really isnt a spot to use it at. Not like manufacturers coils that state best wattage( which is not really correct. Crank the watts up till it tastes right to you and blast away
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Thanks, I’m more scared of burning my coils out then anything else so didn’t want the wattage to be too high for the coil
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I struggle with this too that’s why I have multiple rda’s Rta’s I just don’t use. As when I have built on (without knowing my ohms law) they always either under burn or I think im too high when it spits hot liquid in my mouth and I always open my air right up because im a DL person. (Everything everywhere else goes the hot liquid.) But why does that chart have 4 different answers to the same resistance coils? I don’t get that part.
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Shit mabye that’s been my issue this whole time. All I’ve been using for any of these rebuildable tanks are commercial mods like vandy vape guar 21 or geek vape ageis. But my mesh profile works great on them. Mabye im not at all vaping at the right watts? See this is exactly what happens when we don’t know our ohms laws. We guess and hope for the best and get hot liquid everywhere.
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Im scared of anymore hot damn liquid in my mouth or on my arms or anywhere else.lol!.it hurts!. And turns me off anything but mesh.
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Lol yeah I think it would put me off too, luckily I haven’t had that happen yet… Yet been the word lol I think there is four different results for each resistance to show it at different wattage settings, does seem a bit easier using a ohms calculator and following what Jim20 advised, you can use a coil build calculator if you know what wire and how many wraps etc but I haven’t a clue to what half of them are as yet lol is so many different types and combinations, so not sure if you have to have a different wattage for each different type of wire
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