That's the thing: even expensive Fluke or Agilent meters still have a degree of accuracy that's +/- a couple percentage points. With resistance this low, that's a huge deal (especially when that thing you're measuring is right next to your face.) Another thing to note is that, when it comes to measuring Ohms, multimeters are usually less accurate the lower the resistance is. My meter's resistance accuracy is +/- 1% PLUS 2 least significant digits (meaning I could measure a 0.13 Ohm coil and, since 3 is the least significant digit, it might actually only be an 0.11 Ohm coil!) And did the OP take into account his meter's internal resistance? Mine has an internal resistance of .01 Ohms; if I didn't REL that out before I measured such a low-ohm coil, I could basically just be winding a deal short and not even realize it. This is on my $60 Amprobe meter, and cheaper ones are typically even less accurate (and even $200 Flukes aren't much better.) There's a reason electrical engineers use $5000 scopes and meters to accurately measure things like this; the stuff we typically have easy access to isn't all that accurate in the grand scheme of things.
Battery amp advice
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That's the thing: even expensive Fluke or Agilent meters still have a degree of accuracy that's +/- a couple percentage points. With resistance this low, that's a huge deal (especially when that thing you're measuring is right next to your face.) Another thing to note is that, when it comes to measuring Ohms, multimeters are usually less accurate the lower the resistance is. My meter's resistance accuracy is +/- 1% PLUS 2 least significant digits (meaning I could measure a 0.13 Ohm coil and, since 3 is the least significant digit, it might actually only be an 0.11 Ohm coil!) And did the OP take into account his meter's internal resistance? Mine has an internal resistance of .01 Ohms; if I didn't REL that out before I measured such a low-ohm coil, I could basically just be winding a deal short and not even realize it. This is on my $60 Amprobe meter, and cheaper ones are typically even less accurate (and even $200 Flukes aren't much better.) There's a reason electrical engineers use $5000 scopes and meters to accurately measure things like this; the stuff we typically have easy access to isn't all that accurate in the grand scheme of things.
Your meter reading of 0.13 ohms is unlikely to be completely accurate. Even expensive meters reading resistance this low need to be calibrated. So if your coil is actually 0.09 ohms you're vaping at 46 amps with a fresh cell in there.
If you have a coil short at half of its length you will go from 0.13 ohms to 0.065 ohms, 65A. If the coil was really 0.09 ohms, your at 93A. If you were using a 0.2 ohm coil in this situation you be at 42A.
VTC5s or any good IMR or hybrid battery should not burn or explode if you get them too hot and they vent.
I still will not go past the continuous amp draw my cells are rated for, taking possible meter inaccuracy into account. If I wanted to go lower than 0.3 ohms I would do what I needed to do to calibrate my meter first. I also have a reasonably good DMM, a Klein MM1000.
jbish86, you're probably just fine, but you're taking on more risk than I'm willing to.
Vape safe
Well said. I'm using a cheap 20 dollar meter and it works fine for my needs. But I don't dip down to the danger zone, so I'm comfortable. I would like a fancy meter, but I'm saving for a shiny new provari v3...
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That was an ICR cell. The ones we all (I hope) tell people not to vape because they burn when they vent. These cells usually have protection boards on them, but that's what happens if the board fails and you get a short. IMR and hybrids don't do that if all is well.
Here's a video of a Panasonic NCR and a AW 18650 being shorted. Still a lot of heat but the process is much safer than a shorted ICR cell that burns. I still don't want that happening beside my face, but with IMR and hybrids it's a risk I take in using mechanical mods because I know these cells are pretty safe, I leave 'head room' in my builds and I maintain my gear as well as I can minimizing the chance of a short.
It's also what can happen when the current limit is exceeded. It's why batteries have a rating. Considering that the 30 amp limit is generous and talking about going to 32 amps is reckless, IMO.
Absolutely. It's why I choose LiMn lMR cells instead of Li-ion. I've lived a long time with my face. I want it to remain static until the last heartbeat.
Live long and leave a pretty corpse. People will walk by and view it the day after.
And if its a good mfg'er, a generous amount of 'fudge factor' in the headroom...
Hopefully they do. That, or the End User Should to be Safe.
Because if I Sample 100 Batteries and 50 are 25A and 50 are 35A, then I could say that Statistically, they are 30A Batteries.
I've never been involved in manufacturing batteries, but I was involved in a production engineering capacity in making limit switches that shut down oil fired residential furnaces if the burner didn't shutdown when it was supposed to. This was the last thing that would stop the furnace from starting a fire in a house.
I can assure you the scenario you describe above was not how we determined product quality. Any company who would use statistics in this manner for any high risk product would be out of business very quickly.
That doesn't mean mistakes never happen. It's almost impossible to cover every design, manufacturing and end user scenario 100% of the time, but large companies are quite risk averse and do everything they can to cover themselves against law suits by making sure their products are safe to the best of their ability.
The Dreamliner li-ion battery fires is a case where something was overlooked. Probably doesn't have anything to do with the cells themselves or I think someone would have found the problem. I suspect a lot of complexity in the electronic battery control system and a lot of other electronics close by too. AFAIK they still haven't figured out what happened, or been able to recreate the problem. I don't envy the people working on this one
Battery manufacturers list whatever battery specs they wish to. Some companies understate their specs, some overstate their specs.
For instance, Efest lists their purple 18650 2500mah battery as a 35 amp battery. Tear the purple wrapper off and the cell says it is a re-wrapped LG18650HE2 battery -- LG lists the same cell as only a 20 amp battery. So who are you going to believe? The company who actually makes the cell, or the company who is just rebranding it? For people who are doing extreme sub-ohm vaping, those missing 15 amps could be critical.
Efest 30 & 35 amp batteries
Quoting Dampfakkus.de:
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I've never been involved in manufacturing batteries, but I was involved in a production engineering capacity in making limit switches that shut down oil fired residential furnaces if the burner didn't shutdown when it was supposed to. This was the last thing that would stop the furnace from starting a fire in a house.
I can assure you the scenario you describe above was not how we determined product quality. Any company who would use statistics in this manner for any high risk product would be out of business very quickly.
That doesn't mean mistakes never happen. It's almost impossible to cover every design, manufacturing and end user scenario 100% of the time, but large companies are quite risk averse and do everything they can to cover themselves against law suits by making sure their products are safe to the best of their ability.
The Dreamliner li-ion battery fires is a case where something was overlooked. Probably doesn't have anything to do with the cells themselves or I think someone would have found the problem. I suspect a lot of complexity in the electronic battery control system and a lot of other electronics close by too. AFAIK they still haven't figured out what happened, or been able to recreate the problem. I don't envy the people working on this one
I have Worked in Manufacturing for Most of my career. And have seen Many Specs that were based Statistically on Least Case Scenarios. But I have Also seen some that were Questionable at best for Drawing a Line on Minimum Performance.
When someone Doesn't Tell You how a Statistical Result has been derived, they haven't told you Much.
The Point I was trying to make is that it, to Me, it is Up to the End User to build in there Own Safety Factors.
This is what I find somewhat Troubling about Batteries.
I seem to be able to buy Cells from OEM's and then and my own PCB Protection and then Band them with what ever Specs I feel are Reasonable.
Perhaps I might Take 10 Battery Assemblies and if 80% of them can Perform >30A and No Battery is <20A I might decide to call them a 30A Battery.
Fine for the people who get the >30A Ones. But perhaps Problematic for the 2 out of 10 who get the Other Ones.
Also, How many People who sell Batteries do any Independent Testing of what they Sell? Verses trusting what a Battery Rep or Wholesaler says they Should Do. Or even, what they Should Be.
Yes, twice as bad, you're not looking at it with a relative comparative, it's not '.13 is only .12 lower then .25', it's '.12 is half the resistance of .25'
I'm not familiar with the term 'least case scenario' (and Google didn't help much). In my experience it all depends on what your FMEA's turned up and how much importance company management puts on mitigating the risks.
I've never worked for a company that I felt was making something that was dangerous through negligence and I never will.
Agreed. And the case of the re-wrapped LG18650HE2 that Baditude pointed out is definitely troubling. The difference between 20A and 35A is huge. I don't buy Efest because I feel they have inferior batteries. After hearing about this example I also have doubts about their ethics, but I'm not convinced either way on it yet.
I don't think max battery amp numbers are an exact science, but it would be nice if we knew how those numbers were derived. And then again, maybe not. I can see a scenario where it might make some people less careful rather than more.
Yup, that's what I do too
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