Why I Come Down On Certain Batteries.

[Ripshod]

May 23, 2015 20:56:37 GMT monty said:

If you are using a regulated mod with Kanthal it is nearly always better not to subOhm. Put a 1.5 Ohm coil on your AWTs and you're absolutely fine at 50 Watts.

The nature of electrickery means that with a regulated mod, whether you use a 1.5ohm or 0.5ohm coil you'll still be pulling the same current from the battery at the same power, plus or minus a little bit for losses.

[monty]

Good point Ripshod. I have done a calculation below using nice round numbers and and a coil resistance that will mean that the circuitry in a mod won't have to change the voltage. I'm not saying I have this right, my brain isn't what it used to be.

IR of battery..... = 0.05 Ohms
Coil resistance. = 0.35 Ohms
Battery Voltage = 4 Volts
VW mod set to.....40 watts

Total resistance = 0.35 +0.05 = 0.4 Ohms
W = V²/R = 4²/0.4 = 16/0.4 = 40 Watts
I = V/R = 4/0.4 = 10 Amps
I = W/V = 40/4 = 10 Amps

The batteries internal resistance is one eighth of the total for the circuit and there will be heated by 5 Watts and will cause a 0.5 Volt drop. Now 5 Watts seems more than I would like heating the battery. I don't know if that is dangerous, I would guess bad but not dangerous.

[thatguy]

This is where many battery manufacurers/rewrappers fall short. Decent firms like samsung will release data sheets stating typical and worst case specs for cells.

Take the 25R for example. The typical Ri is 22.15+-2 milliohm, and the worst case is 30 milliohm.

Taking the worst case, this is 0.003 ohms internal resistance. As you can see this is a good deal less than expected of a typical cell. Most other manufacturers, if they even do release data sheets do not have this factor of safety between nominal values and worst case.

A cells Ir and a coil can for most purposes be treated as a simple voltage divider(as stated by Thevenin's theorem).

Anyways, a few people have posted about using the Ri as a value in a voltage divider circuit, but please be aware that Ri of a Lithium based cell will increase as a cell ages (via recharge cycles as some recombinations are lost each charge, an effect we have all seem with falling capacity over a cells lifetime) so if you do use Ri as a yardstick, be conservative with your estimation of the value as it will increase slightly per recharge.

To put it simply, add 5-10 milliohms to the worst case Ri rating of a cell as per datasheet, or 20 milliohms to the typical value if that is all that's stated unless you only use cells for the first score or two of charges on deep subohm builds.


Another thread of interest would be a charger thread, discussing safety, charge speed, affect on cell life and range of cells supported.

[Ripshod]

I'm glad it's not just me. May have been sounding like a fixation to other members, but as battery current goes up IR becomes more and more important.

You brought up the 25R, my spec sheet agrees, should have a an IR better than 30 milliohms. What you'd expect from a 20Amp battery right?

Then along comes the AWT claiming 35Amps with an IR of better than 80 milliohms. That is just so wrong, and in my mind bl**dy irresponsible. The two I received tested at 72 and 76 milliohms, whilst others have received samples which seem a lot more capable, but not confirmed by testing. Some kind of consistency problem there! 80 milliohms tells me they're expecting to sell poor cells, and/or they don't know where the next batch will actually be coming from.

My AWTs are now resigned to a life in the head torch.

[chykensa]

Whilst much of the physics passes way over my head, I am finding this thread fascinating reading - many thanks again to Ripshod and the other knowledgeable contributors. I am reassured that the vendors I use for batteries are confirmed by many as reliable and trustworthy ones, but I am also concerned that in striving to save a few quid, new vapers will inevitably plump for a cheaper battery from eBay and end up with a potential bomb in their hands.
I hope that this thread and the resulting pieces of work will educate and heighten the safety aspects of our hobby (can I call it that!?).
Many thanks to all - I have bookmarked this thread for reference and education

[Deleted]

Ripshod

Ecolux - one of the forums trusted battery sellers is now selling these and they have put their own test data in the listing for these AWT 40A batteries

Worth a look - www.ebay.co.uk/itm/2x-GENUINE-AWT-18650-IMR-2600mAh-3-7V-Li-Mn-40A-HIGH-DRAIN-FLAT-BATTERIES-CASE-/361259772136

[Ripshod]

So we have something solid to go on:

Continuous Discharge Current : 20A

It's a 20Amper - another rewrapper overspeccing (another of my bug-bears). Don't know about you kreed, to me they're just repeating info from elsewhere and haven't actually done any tests yet.

Tested Capacity : N/A mAh , 5A CC Discharge test ,% of Claimed Capacity ECOLUXSHOP UK® testng in progress

Tells me the same thing - zero results, we're still testing. I'll be watching this, but I've got a feeling they may be 'cherry picking' for some decent results.

Summary : Excellent High Drain Battery with real tested capacity

A lie, they've already stated they haven't tested capacity yet.

You know the more I look at ecolux the less I'm liking them. No disrespect but to put contradicting information like that is a massive boo-boo!

[Deleted]

I agree - but my point here is that a forum recommended "TRUSTED" seller is selling them ..........and before completing the testing.

Bit of a worry ain't it?

[Ripshod]

Added to my post above, you  'd me kreed

[Deleted]

[Ripshod]

We have to resign ourselves to the fact that wrappers and vendors are going to continue quoting the peak current - cos high numbers sell. That will never change.

So long as we help peeps understand that then we're doing the right thing. Obviously there will always be those that ignore the free advice, wanting to trust the vendors because 'they know more about the batteries they're selling than a few enthusiastic battery users'. That's the way it should be - in an ideal world.

Peeps new to vaping don't appreciate that the battery is potentially the most dangerous piece of kit most of them will ever hold in their hand

[Deleted]

Ripshod - I sent Ecolux a message asking about the testing results for those batteries - got a really quick reply:

Hi Kevin , yes will do within 2-3 days.
i couldnt get replacement fuse to my testing machine ,
but got lucky yesterday so start testing again.
By first test the AWT 2600 , im sure this is not 40A CC battery , max 20Amp CC .
the pur[ple version is already done , you can see in listing , yesllow will be same or similar.
The efest 2800 35A is already done check in listing , its really surprise even less then AWT 2600 purple.
Has excelelnmt results from AWT 3000 red already in listing ,
and new Samsung 30Q as well already in listing ( looks built in the AWT 3000. )
so give me pls 2-3 days.
best regards , Norb

[Deleted]

And another:

Hi Kevin , forgot ,
the AWT 2500 its definitely better battery compare to the awt 2600 ,
im sure the 2500 is one of the LGs inside HE2 or HE4
but nobody know whats inside the efest 2800 and awt2600
and first test doesnt look very well to be honest .
please text me to email address showing in my contact details :
ampreiumebay......
i can upload the graphs and result direct there and you can use and publish .
regards , Norb

[Ripshod]

So for the 35Amp they tested:

Internal Resistance : 0.04-0.05 Ohm

A lot better than the result I had, but still a lot higher than I'd expect for a 22Amp battery. Worst case would be 1.1Watts of heat inside the cell @ 22 Amps.

I'm still not convinced. That's not a 'dangerous' battery. But I won't be using these I have for sure.

There's still a chance someone could buy a 35 with an IR of 0.075 Ohms (within the spec) and expect to be safe using it at 35Amps.

Sorry Norbert, there's the chance of an accident here. Things were good at the start, the everyone started competing with the numbers.

[Deleted]

May 24, 2015 2:40:59 GMT thatguy said:

 please be aware that Ri of a Lithium based cell will increase as a cell ages (via recharge cycles as some recombinations are lost each charge, an effect we have all seem with falling capacity over a cells lifetime) so if you do use Ri as a yardstick, be conservative with your estimation of the value as it will increase slightly per recharge.

To put it simply, add 5-10 milliohms to the worst case Ri rating of a cell as per datasheet, or 20 milliohms to the typical value if that is all that's stated unless you only use cells for the first score or two of charges on deep subohm builds.


Another thread of interest would be a charger thread, discussing safety, charge speed, affect on cell life and range of cells supported.

I've taken the liberty of editing the post from thatguy to the bit about battery life.

The possible folly of chasing the cheapest batteries has been mentioned, but what are the effects on the specs with regard to safety after prolonged use?

I date all my batteries and try to rotate them but that's not always practical. I don't have any equipment to test them so after 1yr they get replaced. I have read of people still using batteries after 2 1/2 yrs.

Any thoughts on the changes that take place and best practice regarding this, cheers.