Voltage, Amps, Watts, Etc...

[Chakthi]

I recently got into RBAs, and up until tonight, I have used them exclusively with my VV devices (Vamo and Zmax). I have been reading a lot about sub-ohm coils, and how great the vape quality is. I just finished up a successful .82 ohm coil in my new AGA-S. It's a 5/6 wrap using 28 guage Kanthal. It vapes like a dream! I'm concerned about the safety of it, though as long as I don't blow myself up, it's cool as far as I'm concerned. lol I want to calculate the watts and amps that I am pushing, but there's something I don't completely understand, so maybe someone could clear it up for me.

I'm using a single Panasonic NCR18650B (3400 mah), so at full charge, it is between 4.1 and 4.2 volts. Here's the thing though, when I add the RBA to the equation, it drops to about 3.35 volts under load. I got that value by using the Voltage Indicator v2 that you can find for sale at many online sites. Could someone explain to me where I am losing almost an entire volt between the battery and the RBA? And when I calculate the amps/watts that I am pushing at a given voltage, should I use the no-load value of 4.1, or should I use the under-load value of 3.35 for the calculation?

To be as safe as I can reasonably be, I am using a Vape Safe 2 safety fuse, although the batteries themselves are unprotected. With my VV devices, I don't really consider that to be a huge issue since the device itself has protection circuitry, and I also use a Vape Safe 2 in them. I'm fully aware that there is still a chance that something could go wrong, but some protection is better than no protection imo.

There is no published max. discharge rate for the NCR18650B, but most everything I have read states that I can safely assume a safe rate of 2C, which would be 6.8amps, correct? I also calculated the amp load at 5-5.1 amps (using the no-load voltage value), so do you agree that those batteries should be sufficient? I'm sure that a high-drain battery would be better, but I'm not really concerned about battery life - when these go bad, I'll buy some new high-drain batts, but not until then.

 

[dwcraig1]

Use the under load voltage for the wattage calculation and think about using IMR batteries.
Your voltage drop is excessive, caused by possibly the battery can't do the amps or high resistance at various connection points in the mod or both.
You should expect something like 3.8v or 3.9v on a full charged battery with that load on it.
This is exactly the application where an IMR really makes a difference, I would start with replacing the battery first and going from there.

 

[Nanooks]

You are running into an amp limitation. The high MAH batterys can only pull 5 amps where the IMR can pull 10 amps. You can still use the 3100 mah you just wont get the power till you use a IMR battery. As long as the battery isnt heating up you are ok.

 

[DaveP]

That extra voltage is being dissipated as heat on the coil. Use the loaded voltage for current calculations.

You'd also be much better off using higher resistance attys with higher voltage. Run the current calculations using I=E/R.

Ex. 4 volts at 2 ohms = 2 amps. Power is E^2 /R. That same combination would get you 8 watts in a vape.


The .82 ohm coil is giving you over 13 watts at 3.35v. It's drawing a tad over 4 amps. That's way too much load to expect any kind of reasonable battery life and most of us would consider vaping at that level the same as hotboxing a cigarette. For some reason, some people like a hot, harsh vape.

Ohm's Law Calculator

 

[grindle]

You haven't stated what mod you're using. If you suspect it has chromed brass connectors, or a steel spring, these things can be fixed/replaced and you can halve the voltage drop, maybe more.

 

[Kemosabe]

he says hes using his Vamo and ZMax exclusively. my guess is that hes using his ZMax, as the Vamo wont fire anything under 1.2Ω. i didnt think the ZMax would even fire anything that low but i guess it does.

also, i was under the impression that the panny 18650s were a hybrid batt, meaning a combo of IMR and ICR. i have no idea really, but to me it seems that its an IMR batt with a protection circuit slapped on there. please add more info if you know bc i am betting there is more to this story.

 

[vapdivrr]

That extra voltage is being dissipated as heat on the coil. Use the loaded voltage for current calculations.

You'd also be much better off using higher resistance attys with higher voltage. Run the current calculations using I=E/R.

Ex. 4 volts at 2 ohms = 2 amps. Power is E^2 /R. That same combination would get you 8 watts in a vape.


The .82 ohm coil is giving you over 13 watts at 3.35v. It's drawing a tad over 4 amps. That's way too much load to expect any kind of reasonable battery life and most of us would consider vaping at that level the same as hotboxing a cigarette. For some reason, some people like a hot, harsh vape.

Ohm's Law Calculator

i find it the opposite, i have vaped higher resistant coils and found them to be much hotter and harsher. its funny because when i did try out a high resistant coil i did think to myself that it did remind me of hot boxing a cigarette. a lower resistant coil uses a thicker wire, i have found this wire covers more wick at the contact point compared to a thinner wire, i have always thought that being it covers a larger space, that space is actually cooler. i believe a low resistace coil is much smoother and slightly cooler. and i believe that lower volts also plays a part in a smoother, less harsh vape. as for the better option for cheap batterys, then a higher resistance is probably better. my thoughts are why would you opt for a worst vape just because of your batterys, just invest a few dollars and have a great vape at low resistance.

 

[DaveP]

i find it the opposite, i have vaped higher resistant coils and found them to be much hotter and harsher. its funny because when i did try out a high resistant coil i did think to myself that it did remind me of hot boxing a cigarette. a lower resistant coil uses a thicker wire, i have found this wire covers more wick at the contact point compared to a thinner wire, i have always thought that being it covers a larger space, that space is actually cooler. i believe a low resistace coil is much smoother and slightly cooler. and i believe that lower volts also plays a part in a smoother, less harsh vape. as for the better option for cheap batterys, then a higher resistance is probably better. my thoughts are why would you opt for a worst vape just because of your batterys, just invest a few dollars and have a great vape at low resistance.

I've tried 1.6 ohm coils and found them good at really low voltages. I prefer a 2.8 ohm coil at around 3.7v or a 3 ohm coil at 4.2v. That's just me though. I like a barely noticeable warmth level. Much higher and like you said, it's hotboxing and I never enjoyed that kind of heat while smoking or vaping. If there's too much warmth in the vape, I eventually start to get throat irritation.

To me, it's all about a smooth vape with good taste. One of my favorite vapes is a Smoktech dual coil carto tank. They are just finicky to carry around in a jeans pocket. The tank tends to slide up during carry. I've found that a Vivi Nova is just right and pretty trouble free once you find the mods that make it work well. That, and a 2.8 ohm SS Boge carto are my main vapes.

 

[Nanooks]

To be as safe as I can reasonably be, I am using a Vape Safe 2 safety fuse, although the batteries themselves are unprotected. With my VV devices, I don't really consider that to be a huge issue since the device itself has protection circuitry, and I also use a Vape Safe 2 in them.

I just reread this. My previous suggestion of IMR batterys applies. Any safety fuse albeit the Vape Safe or protected battery reduces the amp capability of said battery. The Vape Safe products can rob 2 amps plus. So your Panasonic is now a 3 amp battery. Protected batterys are personal choice when using sub ohm. I rock .7 to .9 and I have 1 protected IMR battery and 3 unprotected IMRs. the Vape Safe with any IMR will get you plenty of power, just remember 18350 normally is 7 to 8 amps. If you are looking for a protected IMR:

Here is where I got mine. Even with this it is not 10 amps but 7 to 8 amps.

 

[WillyB]

You are running into an amp limitation. The high MAH batterys can only pull 5 amps where the IMR can pull 10 amps.

True IMRs can do much more that 10A.

From Mr AW's sales thread.

IMR18490 Specifications :

Nominal Voltage : 3.7V
Capacity : 1100mAH
Lowest Discharge Voltage : 2.50V
Standard Charge : CC/CV ( max. charging rate 3A )
Cycle Life : > 500 cycles
Max. continuous discharge rate : 15C
Operating Discharge Temperature : -10 - 60 Degree Celsius


IMR18650-1600 Specifications :

Nominal Voltage : 3.7V
Capacity : 1600mAH
Lowest Discharge Voltage : 2.50V
Standard Charge : CC/CV ( max. charging rate 4.5A )
Cycle Life : > 500 cycles
Max. continuous discharge rate : 15C
Operating Discharge Temperature : -10 - 60 Degree Celsius

15C means the 18490 can handle 16.5A and the 18650 a whopping 24A Max continuous discharge rate.

 

[eehtpc]

Great information! Learn so much here!

 

[Chakthi]

Use the under load voltage for the wattage calculation and think about using IMR batteries.
Your voltage drop is excessive, caused by possibly the battery can't do the amps or high resistance at various connection points in the mod or both.
You should expect something like 3.8v or 3.9v on a full charged battery with that load on it.
This is exactly the application where an IMR really makes a difference, I would start with replacing the battery first and going from there.

I just got a multimeter to test things with. I took the spring from the mod in question out and tested it. Putting a lead on each end result in a 1.1 ohm reading. So, I took the spring from the extra end-cap of my Zmax and measured the resistance on it, and it gave a reading of 0.9 ohms. I swapped the springs out, put it all together, and there's no doubt in my mind that more voltage is getting to where it's supposed to be than there was before. I also purchased a pair of Panasonic CGR18650CH high-drain IMR batts which also seem to be making a difference. I'll test the actual under-load voltage soon, maybe even this evening. Thanks very much for the reply. I would have responded sooner, but I forgot about the post, and wasn't receiving any notifications that there was activity on the post.

 

[Chakthi]

You haven't stated what mod you're using. If you suspect it has chromed brass connectors, or a steel spring, these things can be fixed/replaced and you can halve the voltage drop, maybe more.

It's just a generic 18650 mod that I paid 20 bucks for. The spring is/was steel, but I swapped the spring from my extra Zmax end-cap which I believe is a hot-spring. What I know for sure about it is that it creates less resistance than the spring that came in the mod. Where is a good place to purchase springs? Would a Vamo replacement spring like (I believe) Avid Vapers sells be sufficient, or is there something even better?

 

[Chakthi]

he says hes using his Vamo and ZMax exclusively. my guess is that hes using his ZMax, as the Vamo wont fire anything under 1.2Ω. i didnt think the ZMax would even fire anything that low but i guess it does.

also, i was under the impression that the panny 18650s were a hybrid batt, meaning a combo of IMR and ICR. i have no idea really, but to me it seems that its an IMR batt with a protection circuit slapped on there. please add more info if you know bc i am betting there is more to this story.

It's a mechanical mod, not my Vamo or Zmax, though I am now using a borrowed spring from the Zmax. As for the NCR18650A/B batts, I'm nearly certain those are Lithium-Cobalt batts, neither IMR nor hybrid. I got a couple of CGR18650CH Pannys though that are definitely IMR, and are definitely giving me much better performance.

 

[Chakthi]

i find it the opposite, i have vaped higher resistant coils and found them to be much hotter and harsher. its funny because when i did try out a high resistant coil i did think to myself that it did remind me of hot boxing a cigarette. a lower resistant coil uses a thicker wire, i have found this wire covers more wick at the contact point compared to a thinner wire, i have always thought that being it covers a larger space, that space is actually cooler. i believe a low resistace coil is much smoother and slightly cooler. and i believe that lower volts also plays a part in a smoother, less harsh vape. as for the better option for cheap batterys, then a higher resistance is probably better. my thoughts are why would you opt for a worst vape just because of your batterys, just invest a few dollars and have a great vape at low resistance.

I definitely enjoy low-voltage vaping versus the alternative. As for the batts, I got some good IMRs now. I wasn't in a big hurry because I primarily use my Vamo and Zmax, and to the poster above btw that mentioned the Zmax, the lowest my Zmax will fire is 1.3 ohms, the Vamo in comparison works at 1.2 ohms. BTW vapdivrr, I enjoyed watching a couple of your videos on YouTube, especially one on ceramic wicks. Thanks for posting them!

 

[Chakthi]

I just reread this. My previous suggestion of IMR batterys applies. Any safety fuse albeit the Vape Safe or protected battery reduces the amp capability of said battery. The Vape Safe products can rob 2 amps plus. So your Panasonic is now a 3 amp battery. Protected batterys are personal choice when using sub ohm. I rock .7 to .9 and I have 1 protected IMR battery and 3 unprotected IMRs. the Vape Safe with any IMR will get you plenty of power, just remember 18350 normally is 7 to 8 amps. If you are looking for a protected IMR:

Here is where I got mine. Even with this it is not 10 amps but 7 to 8 amps.

Hmmm... how would a Vape Safe rob amps? Sure, it will kick in if it senses 6-7 amps or more for too long, but I checked it with my meter, and it doesn't even read as having any resistance. While I am certainly no expert in these things, it seems to me that the worst thing that anything between the battery and your mod could do is add to the resistance in the circuit. Is that not correct?

 

[Chakthi]

Again, I apologize for all the consecutive posts. I didn't know that anyone had replied to my post, and had quite forgotten about it. I'm on it now!