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Some thoughts on how I choose my power supply
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gords1001 Offline
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Post: #1
Some thoughts on how I choose my power supply
So, I'm in another thoughtful mood.

Where is my attention?

Well, unsurprisingly its cells again.

Basically I'm becoming more aware of my personal vaping technique - long slow lung filling draw,  followed by a long exhale. I prefer a warm vape too. This is important.

How does this relate to my cells?

Well, it entirely dictates what is suitable as a cell, as well as what atomiser I choose and what resistance/power I need.

A deep lung inhale means airflow.  There are precious few tanks that can offer an unrestricted or marginally restricted airflow, off the top of my head,  fogger v4, prometheus and aqua are all that I have tried that came close to stacking up.

At the other end of the scale there are drippers with competition drip tips and massive slits - there is such a thing as too much airflow.


So where does this get us? Well, using round cells, in mechs/unregulated devices the most important limit is continuous current draw.

This absolutely cannot be exceeded by how I choose to vape - less than 3 seconds draw wont satisfy me, and given that most vapers idea of "pulse use" is utter bollocks anyway, it doesn't bare much consideration. Simple fact is,  you cannot as a vaper, make use of the pulse limits prescribed by cell manufacturers.  People get away with what they do because li ion cells sag so badly in use.


But what if what you can get out of a single li ion cell in a mech wont do it?

Well, this is where ohms law understanding comes into its own. It dictates to an extent,  your next logical step. The only other thing that does is your understanding of cell use and recharging.

You can achieve wattage in a couple of ways - draw more current or use more voltage.
More current is hit by your continuous current limits.
More voltage entails series use of cells.

You're also limited by what is a usable amount of kanthal/317/nicrome - it cannot have 0 resistance,  and measuring below .2ohm accurately is expensive.  And you need to be lab grade accurate when you are so close to a dead short.


You could try to get closer to 4.2v to your coils. Using more than 1 cell in parallel will do this as the cells share the load. Hence why parallel boxes "hit hard". But that 4.2v limit is still a boundary you cannot cross.

The next step is boosting your voltage. To do this properly, you need to start balance charging. Something I intend to go into in detail in another post.

The long and short is this, if you need to use more than 80watts, you need to balance charge cells. And if you need to balance charge cells you are more than likely looking at a box. And if you're looking at a box, why restrict yourself to li ion cells? Lithium polymer cells offer far greater current limits and far greater capacity, with the benefit that an industry has grown around their safe use and safe charging. You can buy an acceptable off the shelf charger for less than £30 and the packs come ready to be balance charged. Most lipo packs available now have a minimum 25c discharge rate.

To work out your current mah x c rate/1000 = AMPS

That tends to be between 70 (my ancient packs) and 600+amps for the latest packs with a 130c discharge rate.

The chargers can also be used, with some enginuity to balance your antiquated li ion cells.

Li polymer is for me the logical step. I cannot get close to the continuous limit of my packs - safer vaping, and because I'm drawing so little current, I get a day out of 2200mah (I do currently use 12.6v, which is imo not ideal).

If you really crave absolute power rather than the dna40 tempt control (and I still dont believe 40 watts will do me) then you need to start looking at alternative power supplies and safe ways to use them. Start to really consider ohms law and how it applys to you, with what airflow and vapour temperature is right for you.


And by all means talk about it. The whole point of forums is to share the knowledge.
26-12-2014 11:28 PM
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BOB (12-28-2014)
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Post: #2
RE: Some thoughts on how I choose my power supply
Great write-up, very informative. I have one question. I've been reading up on LiPo cells thanks to other discussions we've had, especially talking about your giggle box, and I'm just wondering why/how they have greater current limits and why they are safer. From what I've read, it seems LiPo packs are no different chemically than Li-Ion cells, so is it just the size that makes the difference? 

Here's a quote from what I've been reading:
"These cells are sometimes known as "LiPo", however, from the technological point of view, they are the same as the ones marketed simply as "Li-ion", as the underlying electrochemistry is the same." (and a link to where I read it)


I've been thinking maybe it's something about the size/shape of the packs that makes them safer and able to perform better, but please by all means correct me if I'm wrong.
27-12-2014 04:51 AM
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Don Online
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Post: #3
RE: Some thoughts on how I choose my power supply
Notice that for a given volume the round cells and lipos will have about the same capacity. Round cells by and large are optimised for capacity, but lipos aren't as much optimised for capacity as for current output - they have a massively larger area of electrodes. They are largely optimised for very high current output.

At least that's how I understand it.

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http://www.preventsuicideapp.com

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27-12-2014 09:23 AM
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Michael (12-27-2014)
gords1001 Offline
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Post: #4
RE: Some thoughts on how I choose my power supply
Its more likely increased conductor size that accounts for the increased current capability.

The safety comes from not being on the edge of the current handling of the cell. And the fact that a pack is set up for series use - balance charging is taken care of by dint of plugging the pack into the charger and running the charging program. They are just far better catered for than li ion round cells, and their intended use is very high performance.
27-12-2014 10:42 AM
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Michael (12-27-2014)
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RE: Some thoughts on how I choose my power supply
That makes a lot of sense, thanks! 
27-12-2014 07:25 PM
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Don Online
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RE: Some thoughts on how I choose my power supply
(27-12-2014 10:42 AM)gords1001 Wrote:  Its more likely increased conductor size that accounts for the increased current capability.
I think we mean the same thing there.

Ad I wholeheartedly agree with the rest of it.

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27-12-2014 07:31 PM
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Michael Offline
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RE: Some thoughts on how I choose my power supply
Graham did you ever do a write-up about how you built the giggle box? I'm tempted to try making my own, but I seem to have misplaced the thread with the information about it and I can't remember how detailed the "how-to" was. 
27-12-2014 09:38 PM
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Don Online
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Post: #8
RE: Some thoughts on how I choose my power supply
If you need detailed instructions you shouldn't build one.

First thing you need is a decent balancing charger - I'd recommend an iCharger.

Then you need suitable lipos.

then you need a box, a switch and an FET of a suitable rating to switch the many amps you will be passing.

TBH, if you have to ask, don't build one. It could be a pathway to a lot of grief. Shorting a pack capable of output in the kilowatts is no fun at all.

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27-12-2014 09:53 PM
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BOB (12-28-2014)
Michael Offline
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Post: #9
RE: Some thoughts on how I choose my power supply
Alright thanks, I'll stick to my Sigelei for now Smile

I've not done much in the way of electonics and modding and whatnot, gotta start somewhere right? Guess I'll start somewhere else lol
28-12-2014 01:30 AM
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BOB Offline
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Post: #10
RE: Some thoughts on how I choose my power supply
Michael try a parallel  box mod for your first build Good
Don that's the main reason I have not looked into lipo
I don't understand them enough to make one and know its safe to use
Gords I was just looking at your giggle box on the diy bit Good2

if at first you don't succeed ,call it version 1.0
28-12-2014 07:56 AM
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