Ohms law question

[Kajun Kevin]

OK, so i bought my first mod a couple of weeks ago. The vape shop built the mod using 22 guage a1 kanthal at 0.22 ohms of resistance. I'm trying to get a better grasp on rebuilding requirements.

My battery is a 3.7v 2500 mha VXJO 18650

As I understand it, at full charge the battery is actually 4.2 volts.

Based on ohms law, i = v/r = 4.2v/2.5a = 1.68 ohms.

My current build is 0.22 ohms...

is 1.68 ohms an ideal target, a minimum, a maximum, or am I totally turned around with all of this?

Please help!

 

[dcfluegel]

howdy, kevin - and welcome!

i don't know that 1.68 ohms would be your 'ideal targer' per se - what kind of mod are you using?

keep in mind, in this case, the variable in the equation, unless I am mistaken, would be the amps - if your v is 4.2 and your r (the ohms build you are using) is .22, then the amps when you are firing would be v (4.2)/ r (.22) or i=19.9 so your amp draw would be 19.9 - it is generally recommended to keep a buffer of about 20% on your batteries (meaning your max amp draw should only be about 80% of what battery is capable of delivering) for a safety margin

i believe you are mistaking the 2500mah rating on the battery (the milliamp hours - or how much energy it will store) and the amperage draw (amount of amperage drawn from battery to fire that coil)... check out this killer writeup from @Baditude - should help (14) Ohm's Law for Dummies (Vapers) | E-Cigarette Forum

I am betting some wiser heads will chime in on this also - but the key here is keep asking questions, do some reading and make sure you have a good grasp of battery safety, especially if you are firing that build on a mech... with a regulated mod, there are some safety features generally built into the chipset that help

 

[Kajun Kevin]

Yea, i read it right before starting this thread.

Im using an Anubis mech mod (mod & rda)

 

[IMFire3605]

VXJO???? Are you talking about the MXJO 18650 2500mah 35amp Burst Max battery, should be yellow? If that is the case, to be conservative, I am going to say going off @Mooch 's blog, that is only a 20 to 25amp continuous drain battery, though 20 to 25 amps are pushing the safe temperature levels of the battery by Mooch's data. At 0.22ohms like stated above, that is 20amps, you got no headroom of safety if there is a short. I'd bump it up to a dual coil with 24awg instead of 22awg to around 0.35ohms minimum or so, should give good performance, and give you some safety margin in case of a failure or unexpected short.

 

[Wolfenstark]

Do you mean MXJO 18650 2500 mAh ?
If so then those look to have a 20amp rating.
So myself in a mech I wouldn't go below 0.25Ω or 0.3Ω if I was new.

The resistance you want to build can depend on the atomiser and how many coils and wraps you want.

Coil wrapping | Steam Engine | free vaping calculators

Im not for 22 gauge wire, on my mech I've found 24g takes too long to heat up for the builds I like.

 

[dbrandt01]

Let's use 0.22 ohms. You're pushing about 19 amps on a 20 amp battery. Within range technically, but having a bit of wiggle room is ideal.
0.4 ohms would put you at about 10 amps which would be more ideal than what you're running. I wouldn't run 0.2 ohms on a mech mod, I have other mods for it.

This is the problem with vape shops. You're a new vaper. Bought a mech mod and they set you up with that kind of build. You're doing research on your own judging by the other post here which is great, but it's pretty sad the "clouds bro clouds" employee's at shops are building this way for beginners. Did they even explain ohms law and battery safety to you?

 

[Beastly T]

The MXJO's are rated at 20 amps continuous and 40 amps pulsing. As long as you aren't holding down that button for more than a few seconds at a time, the battery shouldn't be out of it's safety range.Download an ohm's law calculator on any smart phone and just make sure you're under the amp limit of the battery.

 

[Cullin Kin]

2500 mAh does not mean 2.5A, it means it can run 2.5A for one hour. mAh is milliampere hour. It's a measure of electric power over time. Here's a way to understand mAh... Lets say a device draws 250 mA (milliamps)... Your battery could run this device for 10 hours before being depleted in a perfect world.

Here's a little reading on it (read question 4): Battery_basics

You can always find the CDR of your battery by using its mAh rating and its C rating. mAh/1000 * C Rating = CDR of battery. The MXJO's are 8C, thus 2500mAh/1000 * 8C = 20A CDR.

 

[frjaldomr]

In my opinion, taking pulse ratings into account, is a bad idea.
CDR or continuous discharge rate is the only thing I consider.
All the batteries I own are 20A CDR.
So, everything I build nowadays is between .27 and .3
This gives me about a 25% safety margin.
OP: I would strongly suggest you gain a solid understanding of ohms law, and how to use an ohms law calculator, before proceeding with a mech.

 

[Bunnykiller]

I cant believe that the vape shop set you up with 22 ga wire at .22 ohms.... for your first mech... how expensive are thier batteries they sell? maybe they were expecting return business for battery sales...

 

[Kajun Kevin]

Yea, its a mxjo battery.

Actually, i got a good deal, I think. $70 for mod kit, build, battery, and 30 ml of juice.

I think i'm getting a much better grasp on the topic now, but it leaves one last question i'm still a little fuzzy on. So I definitely don't want to go under the ohms calculation. That makes the calculation a minimum ohms, right? If i'm a bit over its still perfectly safe?!

I'll be rebuilding my mod later today. All I have is 100ft of 22 gauge (minus a couple feet), so ill stick with it for now, but I do have a dvom so Ill pay close attention to the ohms. I'll also be ordering some smaller wire for the next rebuild.

 

[Kajun Kevin]

And thanks everyone for the input.

 

[dbrandt01]

If you're higher, like 0.4 or 0.6 ohms, that's safer. The problem with 22g, I'm trying to figure out how he built it?
I've never worked with 22g, but looking at a calculator online. To get to 0.5 ohms with a 2.5mm diameter for example. Assuming you wanted dual coils, you would need 18 wraps per coil. I don't see that fitting well. However, if you did a single coil, you would need only 9 wraps. Make sure you check the resistance without AND with the top cap on. A short could happen when the top cap is on, but a lot of builder just starting out, don't seem to check it twice.

 

[edyle]

Yea, its a mxjo battery.

Actually, i got a good deal, I think. $70 for mod kit, build, battery, and 30 ml of juice.

I think i'm getting a much better grasp on the topic now, but it leaves one last question i'm still a little fuzzy on. So I definitely don't want to go under the ohms calculation. That makes the calculation a minimum ohms, right? If i'm a bit over its still perfectly safe?!

I'll be rebuilding my mod later today. All I have is 100ft of 22 gauge (minus a couple feet), so ill stick with it for now, but I do have a dvom so Ill pay close attention to the ohms. I'll also be ordering some smaller wire for the next rebuild.

I'd suggest you get some 28 gauge and build a 1 ohm single coil.

totally inexperienced new vapers shouldn't be messing around with mech mods and such low ohms.

I've been vaping 2 years now and while i do have and use mechs, i use them with kick modules, and my coils are all over 1 ohm; most are 2 ohm; the coil I'm vaping on right now is about 2.5 ohm 28 gauge in a 3D rtda on a nemesis mech truehybrid, with a vv kick module at 4.8 volts



but then again i'm 50+ so i don't feel the need for the adventure

 

[suprtrkr]

Deal me in. I personally wouldn't go .22 on a one-battery mech mod. There's no safety margin at all. Perhaps I am more conservative than others here-- okay, *definitely* I am more conservative than others here-- but I like to keep builds on one-battery tube mods to .5 or higher. That's in the neighborhood of a 50% safety margin; I like that a lot better than 25% or 0%. Honestly, I find better vape in the .5 to .7 range which, depending on battery state and build value, fluxes watts between 15 and 30. I get good cloud and great flavor like that. I'm running a Dark Horse built .67 dual Kanthal right now, on either a Smok Magneto V1 or Nemesis-- I forget which-- and it won't win a competition, but 3 or 4 puffs on a fresh battery fogs out my bedroom so bad I can't see the screen. And flavor? Lol, make your eyes water ;-)

I'd also like to suggest you never put any battery in a mech that isn't a Sony VTC4. Regulateds are different. But on a mech, I like the thicker safety margin. Be sure you get authentic ones, meaning buy them from RTDVapor, Orbtronic or Illumn. +1 on thinner wire being easier to heat; it also helps conserve battery. I build my mechs exclusively with 28 or 32, or 32 twists, or 28/32 Claptons. Finally, let me say I don't think much about your vape shop. Handing you that mod, that battery and that build-- to somebody who doesn't understand to boot-- in my mind approaches criminal irresponsibility.

 

[Baditude]

Battery Basics for Mods

Explain It To The Noob: Ohm's Law Calculations

Information Resources for Your First RBA