28g single coil is a heat flux of 1500, HOT HOT HOT. Dual coil at 377 still hottish but would be vapable. Try adding a wrap or 2, or maybe some try 24-26awg wire.
Unregulated Box Mod
- Thread starter rangerrobin
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Got .3 on my second build. Working well. Thanks everyone who contributed!
Two cells in parallel actually gives you about 70% of the combined CDR as I understand from several reliable sources. So with VTC4s thats about 45 amps.
Your reliable sources are wrong. This is basic electrical principles. Here is a link to batteryuniversity.com, where there is a good intro to series and parallel battery circuits:
Serial and Parallel Battery Configurations and Information
ETA: I am not advocating that OP do a build that draws 60 amps... its not a beginner build. I am just saying that the batteries (which will be drawing 30 amp each) are tested to handle continuous drain at this amperage safely for the entire charge cycle without issue.
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In my experience current sharing is usually within a few percent, if not tighter, for new cells. The factors that are usually present include the slightly different cell capacities, cell internal resistances (IR), and any slight difference in the contact/wiring resistance of the battery holder. Decent quality cells typically have a very small spread of IR values when new.
However, the IR in some cells increases a lot faster, or the capacity decreases a lot faster, over time than others. This can lead to worse and worse current sharing in paralleled cells. The rule of thumb I've used is to assume about a 15%-20% mismatch in sharing to cover any aging issues that might pop up over time. Depends a lot on the product life expectancy and temperatures/abuse the cells will see. I've never seen it that bad though. Usually the capacity has dropped far enough to retire the cells before the IR differences cause any problems.
I can easily see 30% being used as a number to cover any possible worst case mismatch issues that might arise over time with vapers though. Especially with box modders modifying sled contacts, having varying degrees of soldering skill, etc. Or with less-than-stellar design and soldering of the lower price mods that are so popular. But for new cells in decent holders, wired/soldered well, the sharing is much, much tighter.
Right, any extra percentage tacked on to 0 is an error margin, put there to cover for stupid user mistakes, mismatched cells, a single failing battery, a wired mod with poorly soldered battery terminals, or a user who forgot to insert one of the batteries. It is kind of like teaching someone that 2 + 2 = 3, just because you are afraid that, if they do something stupid, they going to be disappointed when they expected 4 and didn't quite get it because they didn't add one of the 2s correctly. We shouldn't be altering the technically correct numbers to quietly save users from mistakes.
It is OK to use a safeguard if, for example, you want to assume that any 20A CDR battery is perfectly capable at 10A, or any 30A battery is definitely going to be fine at 15A... essentially using half the rated CDR... a lot of people do this. But that doesn't mean that a 20A CDR battery is technically 10A CDR. That would be wrong.
Instead, lets just help people to build their atomizers correctly, measure resistances, clean their mech mods, use good batteries, and understand how their devices work. While, at the same time, using the correct math to explain that 2 married batteries in a parallel configuration output the same voltage with double the mAh and current handling capacity.
It is OK to use a safeguard if, for example, you want to assume that any 20A CDR battery is perfectly capable at 10A, or any 30A battery is definitely going to be fine at 15A... essentially using half the rated CDR... a lot of people do this. But that doesn't mean that a 20A CDR battery is technically 10A CDR. That would be wrong.
Instead, lets just help people to build their atomizers correctly, measure resistances, clean their mech mods, use good batteries, and understand how their devices work. While, at the same time, using the correct math to explain that 2 married batteries in a parallel configuration output the same voltage with double the mAh and current handling capacity.
I agree with you regarding helping others to learn how their gear works along with the proper techniques and maintenance procedures, etc.
But I'm not sure if we should ignore the possible several percent imbalance in current though. It usually only gets worse over time. And I have no idea of how large the possible imbalance is between lower quality cells. This complicates what needs to be learned, but not any more so than a lot of other things they should know.
No need to involve math or to unnecessarily complicate things. A person would just need to know that the sharing isn't perfect and that if they are pushing their cells hard that they might be overstressing one cell more than they should.
What Mooch and myself are saying is that under perfect circumstances the combined amperage is equal. In reality it is likely to be significantly less, and as most people don't have the time, equipment or experience to test each setup. Factoring it at 70% of the combined values is a practical workaround.
But we aren't talking about a practical workaround for the overly cautious. We are talking about the rated CDR of batteries in parallel, which is exactly double. And Mooch just said that it is not significantly less, even in a less than ideal scenario. Although he does occasionally use 15 to 20% sometimes as a margin of error, it never even comes close to this, even with major discrepancies. In real world, it is a difference of a few percentage points.
Lets not spread around misinformation to the point where other people start repeating it as fact, saying they heard it from credible sources.
ETA: The whole point of this is that OP is worried about doing a .2 build on a dual parallel mech mod. This is a build that is going to use 20 amps, less than half of the rated CDR of both of those batteries. So it is safe. He just needs to build it right and measure it and make sure he puts the batteries in the mod correctly. There is nothing complicated here. OP does not need to be uneasy for a normal build that many people do every day.
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The truth is though by figuring at 100% when without all the proper equipment, one may not be at 100% from the very beginning.
Just like the advice that a .5 build is too high. That's odd .5 on a single battery mod works fine for me. No one asked him what type of coil he was using to get .5. For all anyone knew he could have had too high a wire gauge and dual 13 wrap coils.
I see it perfectly acceptable to give the caution amount over the data sheet. How many times have we seen if you don't know, or have to ask, you're not qualified to use it. Giving a safe level amount and saying research your batteries and etc is a better route. It gets someone going, safely and then they look up the info needed. Most remember what they have to look/work for for than what is easily given.
Just like the advice that a .5 build is too high. That's odd .5 on a single battery mod works fine for me. No one asked him what type of coil he was using to get .5. For all anyone knew he could have had too high a wire gauge and dual 13 wrap coils.
I see it perfectly acceptable to give the caution amount over the data sheet. How many times have we seen if you don't know, or have to ask, you're not qualified to use it. Giving a safe level amount and saying research your batteries and etc is a better route. It gets someone going, safely and then they look up the info needed. Most remember what they have to look/work for for than what is easily given.
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