Explain it for the dumb noob over here.

[b7u3angel]

Im trying to wrap my head around the ohms law/safety and I think I get it but then I realize I dont. I read some more and learn more but dont understand. Can someone explain it for the dumb noob over here? Like im thinking its this, you build your coil and it comes in at .19 I have a 3.7 volt mnke 26650 battery. Now im under the impression this is safe becouse when I bought my set up the guy tvyhe vape store built my coil for free. Well I've been reading more and now im doubting its safety. So I guess my question is this. Can someone explain it to me in layman's terms? Thanx. [emoji367] [emoji95] [emoji106] [emoji107]

 

[Katmar]

The only layman's term I can think of is that it is far from safe!!

Welcome to the forum!!!!!!!

 

[iamthevoice]

Really not a setup for you if your asking the question. Perhaps you might want to read some of the fantastic information available on the forum!

 

[tj99959]

If my coil came in at .19 I would toss it in the trash and start over.








This thread needs to be moved to the "outside, not advisable" sub forum.
(reported)

 

[rusirius]

First off understand that your 3.7 volt battery freshly charged is going to have around 4.2 volts, so that's the number you need to use in your calculations.

And no, that setup is not safe for that battery. As far as I recall that battery has a continuous current rating of 20 amp, and you really want to stay under that to be safe. So let's say you wanted to shoot for a max of 18 amps.

A resistance of .24 will give you 17.5 amps. About where you will be safe assuming it's a good battery and rated correctly.

On the other hand, with your existing setup, you're drawing 22+ amps. Exceeding your rating if it is indeed 20 amp. Now on the other hand, if it's a 30 amp battery, you're still safe.

Voltage / resistance will give you your current. And again always use 4.2 volts since that's where the battery will start...

 

[b7u3angel]

Ok. 4.2 thanks. Again im new and some things I ask is probably obvious to you but to me its important. I didn't know where to post this so I posted it here. My bad.

 

[Maurice Pudlo]

Your battery has some limits:

Brand Name: MNKE
Size: 26650
Type: Li-Mn (High Drain)
Rated Capacity: 3500mAh
Nominal Voltage: 3.7V
Peak Voltage: 4.2V
Rechargeable: Yes
Protected: No
Chemistry: Lithium manganese Dioxide (Li-Mn02)
Style: Flat Top
Color: Orange
Maximum Continuous Discharging Current: 20 A
Maximum Pulse Discharging Current: 60 A
Maximum Continuous Charging Current: 6.5 A

You want to build a coil that does not draw more than the Maximum Continuous Discharging Current (20 A for this exact battery) most people are using some margin for safety of 10% or so.

If your mod shorts out for some reason in your pocket and you built the coil to the Maximum Pulse Discharging Current (60 A for this exact battery) you would not like the result (is that a mod in your pocket melting your family jewels or are you just happy to see me?).

This calculator has a variety of interactive pages that do the math for you, one even tells you how close to a batteries limits you are.

If you see folks pushing or exceeding limits, and they say oh it's fine, just realize that it isn't.

Most ohm readers aren't very accurate this one claims "Basic accuracy is 0.15Ohm or 0.2%, whichever is larger", that's not real good if your doing some limit pushing.

Be safe and build with a bit of a margin to insure you don't exceed the limits of your battery.

Maurice

 

[K_Tech]

First off understand that your 3.7 volt battery freshly charged is going to have around 4.2 volts, so that's the number you need to use in your calculations..

Exactly. We all know that battery voltage sags (drops a little) under load, but always use 4.2 volts and you won't get into trouble.

There's a lot to Ohm's law for a beginner, but there are two important things to remember:

1 - Volts divided by resistance equals amps.
2 - Stay under (well under, for beginners) the amp rating of your battery.

That MNKE is probably rated at 20 amps continuous discharge. (I've seen some sites advertise it as a 60 amp battery, but that is its pulse rating).

 

[Baditude]

Here is possibly a simpler explanation of Ohm's Law as it applies to vaping. Ohm's Law for Dummies

​

Now, back to you coil question. NO, THAT BUILD IS NOT SAFE FOR THE BATTERY YOU ARE USING.

​

The two most important things to know when rebuilding coils is to know the amp limit of the battery you have and the resistance of your coil. This is where Ohm's Law comes into play.

List of Batteries and Amp Limits Your battery has a 20 amp continuous discharge rate.

When you build your coil and fire it on your mod, it will draw a certain current (amps) from the battery. That current must not be more than the total amps in continuous discharge rate of the battery, or very bad things could happen.




To find out what current the coil will pull, you use an Ohms Law Calculator.

You have the resistance of the coil (what you measured with your ohm meter) and the voltage (always use 4.2 volts of a fully charged battery), so type those figures into the calculator and then click calculate. The current is the amps that coil will draw from the battery. Not so hard, right?

Below calculations demonstrate that the lower you go in ohms the higher the amp requirement becomes. See how your 0.19 ohm coil will draw OVER 20 amps from your battery. 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
0.3 ohms = 14.0 amp draw
0.2 ohms = 21.0 amp draw
0.1 ohms = 42.0 amp draw
0.0 ohms = dead short = battery explosion

Sorry for the graphic photos above, 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 batteries we have can be quite safe if you use the correct batteries and do not abuse them beyond their recommended amp limit.

I personally don't believe anyone should build lower than 0.2 ohms of their battery's continuous discharge rate. This gives a tiny bit of head room should your post screws become loose and change the coil resistance. Periodically check your build's resistance to insure it doesn't fall below your target resistance.

 

[b7u3angel]

Exactly. We all know that battery voltage sags (drops a little) under load, but always use 4.2 volts and you won't get into trouble.

There's a lot to Ohm's law for a beginner, but there are two important things to remember:

1 - Volts divided by resistance equals amps.
2 - Stay under (well under, for beginners) the amp rating of your battery.

That MNKE is probably rated at 20 amps continuous discharge. (I've seen some sites advertise it as a 60 amp battery, but that is its pulse rating).

Ok so thats the main number to use the rating? Keep under that

 

[b7u3angel]

to give you an actual answer: The safety of your build does not only depend on the voltage, also the amperage rating of your battery. basically you want to make sure your amp output with the coil you build does not exceed the rating of the battery. to figure out how many amps your build is putting out, divide voltage x resistance. this is how many amps your build is putting out. if this number is higher than your batteries continuous discharge, you need to rebuild at a higher resistance. for example, my build at the moment is a .41 and im using a sony vtc5 which is 30A. 3.7 / .41 = 9 amps. well within my batteries 30A capabilities.
note that it is best to multiply 4.2V for your battery, because this is the voltage of your battery straight off the charger.

hope this helps

Thank you that made alot of sense. Basically stay below the rating. Much appreciated.

 

[b7u3angel]

Ok thanks this was all very helpful and insightful. So basically I NEED to get rid of the build the store guy put in for me and rebuild it at around .4-.6
I wonder why he built it so low knowingly what I had battery wise. O well I know now and that's what matters. Also Ive not been useing it. Since I got it and doing the reading I had doubted the safety. Again THANK YOU ALL.

 

[Maurice Pudlo]

20 A x 10% = 2 A

20 A - 2 A = 18 A

0.2333 ohm + .15 ohm = 0.3833 ohm (the .14 ohm is the meter accuracy)

So 0.38 is about the lowest I would call SAFE on your battery with normal equipment that we all use to check ohms.

0.38 ohm on a 4.2 volt battery will draw 10.96 A
0.23 ohm on a 4.2 volt battery will draw 18.00 A

Because your meter has that +/-0.15 ohm accuracy error, assume the lower of the two is the reality in your device.

That's plenty low enough

Maurice

 

[Baditude]

Ok thanks this was all very helpful and insightful. So basically I NEED to get rid of the build the store guy put in for me and rebuild it at around .4-.6
I wonder why he built it so low knowingly what I had battery wise. O well I know now and that's what matters. Also Ive not been useing it. Since I got it and doing the reading I had doubted the safety. Again THANK YOU ALL.

Unfortunately, we are seeing more and more vape shops making unsafe builds for complete novices to mechanical mods and RBA users and not providing any education. Not all of them do that. The shop that I go to has a strict policy of not making a build less than 1 ohm for any customer and attempts to give some education, but adequate research falls upon the users themselves. That is in everyone's best interest as safety should always be the first priority.

 

[b7u3angel]

Unfortunately, we are seeing more and more vape shops making unsafe builds for complete novices to mechanical mods and RBA users and not providing any education. Not all of them do that. The shop that I go to has a strict policy of not making a build less than 1 ohm for any customer and attempt to give some education, but adequate research falls upon the users themselves. That is in everyone's best interest as safety should always be the first priority.

Yea that makes sense and I know it falls on me. Thats why when I put it on my meter and seen the number I thought that it was way to low so I didnt fire it up so I started googling and trying to find some answers. And it always led me here so I figured why not join and ask the questions directly. I know im probably making alot of peaple laugh at my inexperience but I felt like this was important. Turns out it was and I now have a better understanding. Thank you.

 

[Maurice Pudlo]

I myself prefer a 0.5 ohm build, while I've tried out the 0.3 range it just doesn't appeal to me in most all situations. From a safety point of view I use 30 A 18650 batteries for the fact they provide much more margin than the 20 A 26650 ones.

Super sub ohm builds are like racecars, all out to the very edge of the limits where control is as much hope as it is understanding of what's going on.

Maurice

 

[carrielsal]

Check out this online calculator, Ohm's law | Steam Engine | free vaping calculators.

 

[b7u3angel]

I myself prefer a 0.5 ohm build, while I've tried out the 0.3 range it just doesn't appeal to me in most all situations. From a safety point of view I use 30 A 18650 batteries for the fact they provide much more margin than the 20 A 26650 ones.

Super sub ohm builds are like racecars, all out to the very edge of the limits where control is as much hope as it is understanding of what's going on.

Maurice

That made alot of sense to me. I never told the guy I wanted super sub ohm. I asked him for a build that gave flavor mild heat with a good vape cloud.

 

[pwheeler]

At full charge, 4.2 volts you would be dangerously vaping at 92 watts at 22 amps! Even though the MNKE 26650 is rated for 30 amps the maximum continuous discharge is 20 amps. You would be pushing the limits of the battery, and that's assuming you have a brand new authentic battery. Why even take the risk?

 

[b7u3angel]

20 A x 10% = 2 A

20 A - 2 A = 18 A

0.2333 ohm + .15 ohm = 0.3833 ohm (the .14 ohm is the meter accuracy)

So 0.38 is about the lowest I would call SAFE on your battery with normal equipment that we all use to check ohms.

0.38 ohm on a 4.2 volt battery will draw 10.96 A
0.23 ohm on a 4.2 volt battery will draw 18.00 A

Because your meter has that +/-0.15 ohm accuracy error, assume the lower of the two is the reality in your device.

That's plenty low enough

Maurice

So aim for around that then? Gotcha. Thank you.