Battery question to experts.. I'm so confused here

[ericdjobs]

I purchased a VV boxmod.. it's on the way
It uses 2x 14500 batteries.. i'm guessing they're wired in a series to provide 7.4v and then it's just regulated down through a LDO, excess voltage passed off as heat..

Here's where I get confused..
Since the batteries are wired in a series, the 14500s are still considered 900mAh. Let's say I wanted to run a 2.5ohm carto at 5v.. or a 3ohm carto at 6v

This is an amperage draw of 2A.. this is far beyond what the 14500s can handle... so how does this work exactly? I notice the vv boxmod madvapes sells is the same exact way.. 2 14500s in a series.

How can two 14500 batteries in a series provide the discharge rate needed to power anything above 5v to begin with? This really confuses me.

* Should I change my order of 4x TrustFire protected 14500s with 4x AW IMR 14500s? It seems the AW IMRs would be the only way to ensure the batteries can handle what I'd throw at them... but they are only 600mAh compared to 900mAh.. worried about battery life, esp because of linear reg

 

[Java_Az]

First off AW gives true mah ratings , Trustfire not so much. If you did a real world test the trustfires wont get close to 900mah. You can search some flashlight forums and they do real mah tests on batteries and most of your china made companies lie about the mah.

Two batteries in series the mah stays the same the max amperage stays the same. It kinda seems like your loosing capacity by doing that. But you have to factor in the voltage change to so it makes sense. 2amps @ 3.7 volts = 7.4 watts 2 amps @ 7.4 volts = 14.8 watts. So your not really losing anything. In other words 4 amps @ 3.7 volts is the same as 2 amps @ 7.4 volts. I only using switching regulators ( because LDO linears suck at efficiency) but lets say you have the output going to the atomizer set @ 3.7 volts and it is drawing 2 amps under load. Then you take a look at the input voltage that 7.4 volts it would be drawing 1 amp on the input. Real life it would be a bit more depending on the efficiency rating of the regulator. One i am using right now can get up to 96% efficient. Anyways thats the best i can explain it tonight after drinking these samual adams.

 

[Dalton63841]

I'm thinking the OP is confusing the terms mAh with amps. The statement 900mAh is a rough estimate of how long the battery will last on a charge. They are not saying that the batteries can only output 900mA. They will handle 2amps output just fine.

 

[ericdjobs]

No.. I'm not confusing the two.

Trustfire 14500s are 900mAh. They have a max discharge rate of 1.5C (one and a half times the capacity)
This would put the max safe discharge rate at 1.35A

It would handle things fine, I'm sure.. but I'm also pretty sure there would be massive voltage sag under load (due to over stressing the batteries) and that their lifetime would be lessened from abusing them...

Maybe my understanding of how things work is off? It just doesn't seem like 14500s in a series are able to supply the amps needed to power things like a dual-coil carto at 5v

If I'm wrong, please someone let me know why... I'm honestly just trying to figure out if I should go with high-drain IMRs.. but I picked up 2 Trustfire 14500s and 2 AW IMR 14500s.. so I'll be able to find out which is better But if anyone can chime in with some information i'd appreciate it, as I'm still pretty confused.

 

[Java_Az]

The AW IMR 14500 could for sure handle it. Unlike li ions they have a max amp output of 8*C which means 4.8 amps per a single cell. But yes even with a switching reg your going to taxing the TrustFires. They could very well work fineto vape but taxing them would cut their life span down alot.

 

[ericdjobs]

The AW IMR 14500 could for sure handle it. Unlike li ions they have a max amp output of 8*C which means 4.8 amps per a single cell. But yes even with a switching reg your going to taxing the TrustFires. They could very well work fineto vape but taxing them would cut their life span down alot.

Well this is what I'm more concerned about. The person who made the mod for me told me that dual coil cartos are cutting out at around 4v, and all the regulators he has tried all do that. My theory is (And I have no formal/informal electronics training or anything like that... my interest in this started with e-cigs.. I just started learning everything 20 days ago) that the regulators have a required input voltage, and when he's trying to fire a 1.6ohm dual coil cartomizer at 4v, that requires a draw of around 2.5A.. So, because of the insane load, the voltage on the battery starts to sag really bad; below the cut-off for the regulator.

Voltage sag must get *really bad* on dual coils, because in this video, you'll see an AW IMR *18650* freshly charged sag to 3.4v firing a dual-coil carto (and you'll also notice that the kgo maintains 3.8v.. interesting battery they have there) YouTube - ‪hoosierecigsupply.com 1100mAh eGo battery whips AW 18650 IMR‬‏

I'm guessing something like this is happening and dropping the input voltage... this is something I think high-drain batteries might be able to remedy.. but then again, like I said... all of this is incredibly new to me.

*the maker did recommend I go with trustfire batteries as opposed to AW IMR high-drain cells because of the higher mAh rating, but after some research it seems they are about equal in real-life terms.

 

[Java_Az]

The Linear reg could also be thermally regulating itself and cutting out at the high amps or it could be what you posted both are feasible.

Something is wrong on that video. Seen lots of IMR's tested and they don't preform that bad. My guess is he got a bad cell or maybe something to do with the mod he slapped it in.

If it was me i would go with the Aw IMR's but i do remember there was one type of trust fires that got decent results in independent tests If memory serves correctly they are called trustfire flames but i think it was the 18650's that were preforming well.

 

[CraigHB]

You haven't said for sure what kind of regulator your mod uses. It will make a difference in current demand and run time.

The step down switching regulators don't waste much power so capacity adds (minus power lost by the regulator which is typically less than 10%). Input current is lower than output current.

For a linear regulator, capacity does not add because input current is the same as output current. A large percentage of power is wasted by the regulator as heat.

For a switched regulator at 5V with a 3Ω atomizer, input current is ~1.2 Amps at 7.4V which is within tolerance for a protected 14500. However, you could easily go over tolerance with higher voltage or lower resistance.

For a linear regulator at 5V with a 3Ω atomizer, you're looking at 1.7 Amps input current, just a little too much for an ICO 14500. Those have to be protected and the protection will likely trip.

The AW ICO 14500s (black, protected) are accurately labeled with 750mAh and have a max output of 1.5A or 2C. The TrustFire and UltraFire batts have 900mAh stamped on the battery, but it's actually a lot less. They lie about the capacity so max drain is probably not 2C. I doubt those crappy Chinese 14500s will go any higher than 1.5A, but I don't know myself, I wont touch them. I like my face the way it is.

I think most people are using AW IMR 14500s (orange, unprotected) which are high drain. As already mentioned, they're typically 8C or eight times the charge. When regulated in series, you can drive whatever you want up to 6V with those. You do give up little capacity for the high drain though, 600mAh instead of 750mAh.