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Worried!
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Don Offline
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Post: #1
Worried!
I find it rather alarming that there are a whole bunch of regulated mods running at up to 200W and fuelled by two 18650 cells. There is no such thing on the market as a pair of 18650s that can be used safely at 200W - this is taking the cells way, way beyond the rated spec.

If you use 200W you need at least three 18650s to be borderline safe. Any 200W mod really ought to be using Lipos rated at (minimally) 80A for a single cell, 40A for 2S and 28A for 3S. These aren't just 200W divided by 3.6V (Essentially the end point of usable charge in IMR cells at these loads) as there is no such thing as a 100% efficient regulator out there.

With two cells, this is out of spec on ANY 18650. With three cells it is out of spec for anything other than Sony VTC3 cells - which are going to last about ten minutes at 200W.

TVF tested battery info to be found here

http://www.preventsuicideapp.com

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04-12-2015 04:31 PM
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gentlydoingit* Offline
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Post: #2
RE: Worried!
Wouldn't two cells hit 8.4 series? At .25 it's 25a with voltage to spare, doesn't seem too dangerous to me..  With on board regulators, stabilisers overload and thermal cutout protection.

My snow wolf pulses the power if it's set over 150w, pulse loading the batteries safely.

Don't forget to apply for the freecycle section!
http://www.thevapingforum.com/Forum-FreeCycle--191
(This post was last modified: 04-12-2015 05:03 PM by gentlydoingit*.)
04-12-2015 04:45 PM
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BOB Offline
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Post: #3
RE: Worried!
could I ask why the high powered mods are not using lipo from the factory
I don't really understand lipos,I know they vent violently but surely they could safely be used as a power source for vaping

if at first you don't succeed ,call it version 1.0
04-12-2015 04:52 PM
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gentlydoingit* Offline
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Post: #4
RE: Worried!
They're catching on but the mah sucks with them. They charge quicker than lithium but even so, who wants to put their vape down for even 5 mins. Now a switchable battery would be great, shame they need special care while charging

Don't forget to apply for the freecycle section!
http://www.thevapingforum.com/Forum-FreeCycle--191
04-12-2015 05:00 PM
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Don Offline
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Post: #5
RE: Worried!
(04-12-2015 04:45 PM)gentlydoingit* Wrote:  Wouldn't two cells hit 8.4 series? At .25 it's 25a with voltage to spare, doesn't seem too dangerous to me..  With on board regulators, stabilisers overload and thermal cutout protection.
They'll only be at 8.4V till you put a load on them. You need to look at the current draw when they are at 3.6V each under load - most of the higher powered mods seem to cut off at around 3.75/7.5V under load. But no regulator is all that efficient so you need to add that.

200W at 7.5V is 27A before regulator losses are taken into account. With a cheap chipset the efficiency might well be 50%. 

There is also the issue of the cells getting out of balance. This can rapidly become dangerous.

In my experience of cells going bad, by the time you notice it getting warmer than it should, thermal runaway has already started. It is already too late.

TVF tested battery info to be found here

http://www.preventsuicideapp.com

[Image: 24291313393_16615b20b2_m.jpg]
04-12-2015 05:12 PM
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Don Offline
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Post: #6
RE: Worried!
(04-12-2015 05:00 PM)gentlydoingit* Wrote:  They're catching on but the mah sucks with them. They charge quicker than lithium but even so, who wants to put their vape down for even 5 mins. Now a switchable battery would be great, shame they need special care while charging

It isn't quite that simple. Under heavy loads, the typical 18650 is way, way down on capacity. In practice a 900mAh 12.6V (Sometimes called 10.8 or 11.1V) Lipo designed for the current required will actually give more usable capacity than three 2500mAh 18650's.

TVF tested battery info to be found here

http://www.preventsuicideapp.com

[Image: 24291313393_16615b20b2_m.jpg]
04-12-2015 05:25 PM
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gentlydoingit* Offline
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Post: #7
RE: Worried!
(04-12-2015 05:12 PM)Don Wrote:  
(04-12-2015 04:45 PM)gentlydoingit* Wrote:  Wouldn't two cells hit 8.4 series? At .25 it's 25a with voltage to spare, doesn't seem too dangerous to me..  With on board regulators, stabilisers overload and thermal cutout protection.
They'll only be at 8.4V till you put a load on them. You need to look at the current draw when they are at 3.6V each under load - most of the higher powered mods seem to cut off at around 3.75/7.5V under load. But no regulator is all that efficient so you need to add that.

200W at 7.5V is 27A before regulator losses are taken into account. With a cheap chipset the efficiency might well be 50%. 

There is also the issue of the cells getting out of balance. This can rapidly become dangerous.

In my experience of cells going bad, by the time you notice it getting warmer than it should, thermal runaway has already started. It is already too late.

Sorry to keep referring to the snow wolf but it's the only 200 I have atm.
It won't let me fire at full wattage if the battery is around quarter % on the readout, so I'd assume higher wattage is present only while the battery has higher voltage than you've listed, though I couldn't define how much it differs.
You've educated me on some math there though Wink

Where do you stand on pulse versus continuous discharge? I can't help but assume the way vapers use batteries falls into the pulse category and the amp drain available is at the highest end of the stated battery capacity, giving enough room to play the odds comfortably?.

On the lifepo's. . I had a vapourshark dna for a few days and I had to charge it twice a day, I don't mean to say that the mah isn't adequate, as I change li-ons as regular, I mean that you can't use the device while it charges and you wait a good while for the next vaping frenzy, if it lasted longer it'd be worth while hence the mah sucking remark.
(This post was last modified: 04-12-2015 06:58 PM by gentlydoingit*.)
04-12-2015 05:59 PM
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Don Offline
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Post: #8
RE: Worried!
I'm not a fan of using pulse ratings. The manufacturer's data sheets will give details but in general I'd use the continuous rating and not exceed it.

It depends a lot on the Lipo. You can get the things in all sorts of shapes and sizes. Often it is possible to fit a higher capacity pack of a suitable rating in the mod. Obviously the cheapest ones are unlikely to be the best.

TVF tested battery info to be found here

http://www.preventsuicideapp.com

[Image: 24291313393_16615b20b2_m.jpg]
04-12-2015 06:05 PM
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ecignut Offline
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Post: #9
RE: Worried!
Wow - I'm lost with all this 200W stuff - indeed I'm lost when it comes to batteries - I think I will stick to my 8.9W for my Nautilus on my rechargable Wismec and Isticks[Image: smile.gif].
04-12-2015 06:16 PM
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BOB (12-04-2015)
gentlydoingit* Offline
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Post: #10
RE: Worried!
Randomly dropping a question in here, you clearly have a handle on batteries Don. How long is a 'pulse' officially? I've always taken it as 3 seconds, 1.5 to heat the cell up 1.5 at normal working temp. 

Don't forget to apply for the freecycle section!
http://www.thevapingforum.com/Forum-FreeCycle--191
(This post was last modified: 04-12-2015 07:03 PM by gentlydoingit*.)
04-12-2015 06:19 PM
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