Got my 1st mech mod from my local B&M the other day. I've got an MXJO 18650 2500mah 3.7v battery. After looking around online, the general consensus is that this battery is just a re-wrap of the lg 18650 he2. Had I known that I probly wouldn't have bought it.. but I'm new to this and I had no idea. Now I'm going to spout off what I think I know and you tell me if I'm right or not. Since it's just a rewrapped lg 18650 he 2, the actual continuous amperage is 20a. I was told somewhere that it's not a good idea to make a build that uses more than 60-70% of your amp rating. So, erring on the side of caution, 60% of my 20a is 12. So, .35ohm setup is the lowest I can safely go... Right?
Lowest ohms I can safely vape on my battery
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Steam engine lists that battery:
Battery drain | Steam Engine | free vaping calculators
Battery drain | Steam Engine | free vaping calculators
It says 1.8ohm atomizer resistance. Does that mean I can that 1.8 is the lowest I'm supposed to go? I find that hard to believe.
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That's MFGs data as collected by Steam Engine creator, @Dampmaskin... better to review, most current and actual vaping practice objective test data... as conducted by ECF resident battery maven, @Mooch.
Somebody please just tell me what is the lowest ohm I can safely use for this battery. Don't point me to some complex crap that I won't be able to understand. I'm new to mechs and I've been reading up on it. But for now, all I need is a simple answer to keep me safe until I learn all the technical stuff.
change the 1.8 to your desired .35ohm, to see the specs.
I'm not qualified to give a safe answer (new to this also)
Mooch or State O' Flux will be able to give better info.
Assuming it's an HE2 (which it might not be)...
0.35 ohms = should be safe. It will keep the battery running cool (extending its life) and you won't boil the battery if your button gets stuck on or breaks.
As you learn all the technical stuff you'll be able to work out if you can push that battery any further.
Assuming its a rewrapped he2, stay above .25 on that battery and you'll be safe. .20 if you're feeling particularly brazen, but that's pushing it.
If you want to go lower, get a box mod with 2 18650's wired in parallel or a regulated mod.
Fwiw, lower ohm's on a mech isn't necessarily "better". Many experienced mech/rda users find their sweet spot to be between .3-.4, usually closer to .4.
If you want to go lower, get a box mod with 2 18650's wired in parallel or a regulated mod.
Fwiw, lower ohm's on a mech isn't necessarily "better". Many experienced mech/rda users find their sweet spot to be between .3-.4, usually closer to .4.
Not trying to be a snob, but you really shouldn't be building that low when you first start to rebuild. Keep it simple and safe at the beginning. Try 1.0 ohm initially.
This is not rocket science, but you MUST understand the basics before sub-ohming. There are no short cuts in this realm of vaping. Below is a blog post which explains in relatively simple terms how to figure what resistance coils you can build with a battery as long as you know its true amp limit. If you're not willing to put in the time to learn this, you have no business doing it.
Explain it to the Dumb Noob: Ohm's Law Calculations
The below calculations demonstrate that the lower you go in ohms the higher the amp requirement becomes. You are also putting a lot of faith into a cheap ohm reader in being precisely accurate to the tenth/hundreth of an ohm. Always tend to err on the side of safety when you make your builds by allowing some safety head room.
1.0 ohm = 4.2 amp draw
0.9 ohm = 4.6 amp draw
0.8 ohm = 5.2 amp draw
0.7 ohms = 6 amp draw
0.6 ohms = 7 amp draw
0.5 ohms = 8.4 amp draw
0.4 ohms = 10.5 amp draw <--- safe head room for a 20 amp battery
0.3 ohms = 14.0 amp draw
0.2 ohms = 21.0 amp draw <--- over the 20 amp limit
0.1 ohms = 42.0 amp draw
0.0 ohms = dead short = battery goes into thermal runaway
0.9 ohm = 4.6 amp draw
0.8 ohm = 5.2 amp draw
0.7 ohms = 6 amp draw
0.6 ohms = 7 amp draw
0.5 ohms = 8.4 amp draw
0.4 ohms = 10.5 amp draw <--- safe head room for a 20 amp battery
0.3 ohms = 14.0 amp draw
0.2 ohms = 21.0 amp draw <--- over the 20 amp limit
0.1 ohms = 42.0 amp draw
0.0 ohms = dead short = battery goes into thermal runaway
Everyone is free to set their own parameters, and I can only say what mine are.
I try to never exceed 50% of the CDR (continuous discharge rating) of a fully charged battery (4.2v). So with a 20A batteries, that would be 10A. The above Ohm's Law Calculator tells me that a 0.4 ohm build is as low as I would want to use by leaving me reasonably safe headroom.
The reason that I place a 50% limit is because as a battery ages the mAh of the battery degrades, as the mAh degrades so does the batteries c rating (amp limit). So down the road, your 20A battery may only be a 10A battery.
Sorry for the graphic photo below, but I believe its important to get the point across that you should not mess with Ohm's Law when it comes to batteries. The below pic is an extreme example, but I believe you'll agree that you don't want that to happen to you.
The batteries we have can be quite safe if you use the correct batteries and do not abuse them beyond their recommended amp limit. Most battery incidents result from user error or wrong calculations, or ignoring safe battery practices.
A battery venting in thermal runaway will release extremely hot gas, toxic chemicals, and possibly flames. Once this chemical reaction begins, there is no stopping it. The gas can build up inside a mod, and if there is inadequate venting the mod becomes a little pipe bomb.
I personally don't believe anyone should build lower than 0.2 ohms over their battery's maximum continuous discharge rate. This gives a tiny bit of head room should your post screws become loose which can change the coil resistance, and also accounts for some error in your Ohm reader.
Periodically recheck your build's resistance to insure it doesn't unknowingly fall below your target resistance. I recently re-checked my typical 0.6 ohm build and it was off by 0.5 ohms (0.1 ohms) because of a loose positive post scew. I consider myself to be extremely lucky that I found this.
Also know there are two amp ratings: Continuous and pulse (burst) discharge rating. I prefer using the continuous discharge rating over the pulse discharge rating. Pulse ratings are always higher than the continuous, and are not as reliable as the continuous rating.
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If you want to stay safe, while still new to mechs, stay over 1 ohm.
Gonna depend on the wire he's using though. 1 ohm coils and 22ga wire aren't exactly a match made in heaven, especially on a mech.
Thanks everyone. You're so very helpful. It warms my soul.
Is there some sort of chart/guide you could point me to? Appropriate gauge wire for your target ohm?
No chart that I'm aware of, but as you begin to learn how to use steam engine it will all come together for you. A lot of it comes down to the heat flux, which steam engine will show for any particular build. The numbers themselves might not mean much, but once you start building and get an idea of what a particular heat flux feels and vapes like, you'll get an idea of where you want to go with your builds.
For example, a 30 gauge single coil with a 3mm inner diameter at 1ohm target resistance is a HOT 356 mm/mW. This number means nothing to you, but if you were to build that coil you would find that it will heat up pretty much instantly when you press the button, and it will likely be an extremely hot and dry vape.
Conversely, a 22 gauge single coil with a 3mm inner diameter at 1 ohm target resistance is a cold 22mm/mW. If you were to build that coil you would find that it takes about 10 seconds of holding the button to produce any vapor, and when it does it will be a cold unproductive vape.
Neither of those two builds would be an ideal vape, but it's somewhere in the middle that you'll find your bliss. The only way to know where your taste and style fit is to start building and get an idea of what you like, what you don't, and tailor the vape experience to suit yourself.
For example, a 30 gauge single coil with a 3mm inner diameter at 1ohm target resistance is a HOT 356 mm/mW. This number means nothing to you, but if you were to build that coil you would find that it will heat up pretty much instantly when you press the button, and it will likely be an extremely hot and dry vape.
Conversely, a 22 gauge single coil with a 3mm inner diameter at 1 ohm target resistance is a cold 22mm/mW. If you were to build that coil you would find that it takes about 10 seconds of holding the button to produce any vapor, and when it does it will be a cold unproductive vape.
Neither of those two builds would be an ideal vape, but it's somewhere in the middle that you'll find your bliss. The only way to know where your taste and style fit is to start building and get an idea of what you like, what you don't, and tailor the vape experience to suit yourself.
One last thing. I'm building my first dual coil setup as I type this and I can't seem to get the two to be identical. They are the same number of wraps with identical diameter. One is .93 and the other is .84 Are these close enough? Tweaking the two repeatedly is very tedious. Just the act of putting it on the rda changes the readout. Then you take it off. Put the other coil on there and measure it. Tweak it. Rinse and repeat.
Don't try mounting and measuring the coils independently, you'll probably never get them both to read exactly the same.
If they're the same number of wraps, with the same inner diameter, with the same length legs you should be good to go. Mount them both, check it on your meter to be sure its safe, then put it on your mod and and dry fire it a few times. You'll have to poke and prod the coils a bit to get them heating simultaneously but you should be able to get it.
Once they glow evenly from the inside out, wick, juice er up, and vape.
If they're the same number of wraps, with the same inner diameter, with the same length legs you should be good to go. Mount them both, check it on your meter to be sure its safe, then put it on your mod and and dry fire it a few times. You'll have to poke and prod the coils a bit to get them heating simultaneously but you should be able to get it.
Once they glow evenly from the inside out, wick, juice er up, and vape.
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