Battery testing - choices for series circuits

Discussion in 'Technical Research' started by rolygate, Mar 1, 2012.

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  1. rolygate

    rolygate Forum Manager Admin Verified Member ECF Veteran

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    A thread for discussion of makes & models for use in 'stacked battery' mods.


    ____________________________________

    The goal of this debate would ideally be the ability for ECF to say:

    "ECF believes that for 6v use (2 x 3v) the best options are:
    Smith 16340 Li-Mn 3.2v model XYZ123
    Jones Li-FeO4 3.2v model XYZ456

    For 7.4v use (2 x 3.7v) the best options are:
    Smith 16340 Li-Mn 3.7v model ABC123
    Jones Li-XxXx 3.7v model XYZ789.

    ECF gives this advice based on safety, not performance."


    We needed a simple, straightforward answer for the best single-cell configuration battery, and the answer we decided on in the end was the AW IMR 18650. It isn't right for all circumstances but it is an all-round safe choice, with the benefit of being a simple answer. There is a huge benefit to having a simple answer even if it isn't always perfect.

    The end result here, for 2-cell configurations, needs to be a simple answer if possible - a 6v and 7.4v result where we can keep people safe. That is the main consideration. Ultimate performance under differing duty regimes is not a consideration here.

    As before, there is no liability for testers, as in the end the advice will come from ECF. We need safe choices above all else. Ultimate performance is not the issue here. For example, using a pair of a certain make of unprotected Li-ion cells might give easily the best performance - but we could never recommend that under any circumstances. We need safe.

    To go forward, how about if people post their nominations for batteries that could be considered. Let's just throw in all the names and not worry at this stage about the finer details, all that can be worked out later. The only thing I would ask at this point is: please don't suggest unprotected Li-ions since even if they will potentially run a space station for ten years, we won't be recommending them.

    There are many questions to be asked, such as: what about protected Li-ions? And: I really like Tenergy Li-FePo4 even though they are only 50c each on Alibaba? Good - just chuck it all in please :)

    ____________________________________
     
  2. Rocketman

    Rocketman Ultra Member ECF Veteran

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    Unless you don't think this fits here (which I will gladly delete, no harm, no foul ::), I would like to point out the importance of the USER knowing how to IDENTIFY protected cells. Stacked protected cells may not fit in many mods, but falsely labeled unprotected ones probably will. Purchasing is a gamble, but once received all cells should be looked at closely. Any anomalies such as wrapper color, imprinted text should be investigated before actually putting the cells into service.

    Identifying IMR vs. unprotected may be tough. Identifying protected vs unprotected is not. Then worry about stacking them.
     
  3. rolygate

    rolygate Forum Manager Admin Verified Member ECF Veteran

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    Yes. If we determine that 2 x protected Li-ion cells will fit in some/all metal tube mods that take an 18650, then maybe we can get into how to ID the PCB etc. But at this stage I don't know if it is possible to use them, due to the length, and also the trip-out factor.

    It might be easier in the end to avoid them. I have no idea, that's what this thread is for :)
     
  4. AriM

    AriM Registered Supplier ECF Veteran

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    +1. Couldn't agree more
     
  5. AriM

    AriM Registered Supplier ECF Veteran

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    I think it is also important to note diameter of the cell. As an "IMR" 18350 stack will fit in an 18650 tube mode, and so will a 16340/123a, but for example....neither will work in a mantis, without first wrapping the cells in tape....to keep them from binding in the case.

    Also this is important for safety in a tube mod, as loose cells can dead short against the case and positive terminal connection....

    [​IMG]

    [​IMG]

    [​IMG]
     
  6. AriM

    AriM Registered Supplier ECF Veteran

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    Also some flat top cells can make contact with BOTH terminals in a rough stack and cause it to fire continuously in someones pocket (ask me how I know). Which is very dangerous with an unprotected cell

    I wrap all of my stacked cells in tape before installing them in ANY mod (unless it's a side by side pack....

    [​IMG]

    [​IMG]
     
  7. AriM

    AriM Registered Supplier ECF Veteran

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    I nominate the following

    Tenergy LiFepo4 rcr123a 3.2v
    AW LiFepo4 r123a 3.2v
    AW IC ICR123 protected 3.7v
    AW IMR 16340 unprotected 3.7v
    AW IMR 18350 unprotected 3.7v

    should we be including 14500's and other 2 cell configurations in this as well?
     
  8. Rocketman

    Rocketman Ultra Member ECF Veteran

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    That would eliminate the user putting what he thinks are protected cells into a stacked battery mod.

    Just because one vaper gets better life from his Brand Y protected short cells doesn't mean you will get the same life, or even the same cells when you order. Counterfeit wrappers, several shades of blue or green, or red, need to be addressed or anything deemed safe will be counterfeited and show up in the market. Granted, the AW line of cells is respected and IMR chemistry has a better chance of surviving with a "Heavy Vaper" (what ever that means) but trip points designed into a protection circuit should represent cell capabilities, and when used within these limits should show the user he just tried to do something wrong. Thus the posts "my Brand Z mod trips out when I go over X volts". If the trip point on a small protected cell is not high enough for you, you picked the wrong cell. If your stacked battery mod also has a trip point, how can you tell which caused the trip?

    When using smaller cells, like the 16340 and 18350, the protection circuit takes up valuable space in the overall package. Many complain about the protection circuit, how many understand what it is doing? How many know the actual overcurrent trip point of their protected cells?

    I expect to see reports of unprotected cells sold as protected, or protected small, over stressed cells not living up to the load of a heavy vaper. Until a user can determine what level of stress and load he is putting on his stacked cells he is probably better off with the biggest meanest cells available, damn the torpedoes, full steam ahead :)
     
  9. Rocketman

    Rocketman Ultra Member ECF Veteran

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    Not familiar with all the 'stacked battery tube mods', but don't some use 18350 cells?
     
  10. rolygate

    rolygate Forum Manager Admin Verified Member ECF Veteran

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    Mainly this is for tube mods (at first). I think that puts us in the RC123 / 16340 / 18350 sort of size (length is the thing here).

    I don't know of any tube mods that take 2 x 14500 cells, but we should look at that later for the boxmods.

    Yeah I should have said: tube mod batts first please :)
     
  11. rolygate

    rolygate Forum Manager Admin Verified Member ECF Veteran

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    OK here are some I found that look the right size:


    AW IMR 18350 700mAh Li-Mn Rechargeable
    Nominal Voltage : 3.7V
    Capacity : 700mAH
    Lowest Discharge Voltage : 2.50V
    Standard Charge : CC/CV ( max. charging rate 1.5A )
    Cycle Life : > 500 cycles
    Max. continuous discharge rate : 8C
    AW IMR 18350 700mAh LiMN Rechargeable Lithium Battery


    AW IMR16340 550 mAh IMR CR123 size Li-Mn Rechargeable
    Nominal Voltage : 3.7V
    Capacity : 550mAH
    Lowest Discharge Voltage : 2.50V
    Standard Charge : CC/CV ( max. charging rate 1.5A )
    Cycle Life : > 500 cycles
    Max. continuous discharge rate : 8C
    AW IMR16340 550 mAh IMR CR123 size LiMN Rechargeable Lithium Battery


    AW Li-FePo4 3 Volt Lithium Rechargeable
    Nominal Voltage : 3.2V
    Capacity : 500mAH
    Lowest Discharge Voltage : 2.0V
    Standard Charge : CC 250mA CV 3.6V
    Cycle Life : > 500 cycles
    No C Rating given
    AW LiFePO4 3 Volt Lithium Rechargeable Battery


    RCR123A 3.0V (3.2V NOM) 750mAh LiFePO4 Rechargeable
    Up to 1000 cycles
    Working Voltage: 3.2V and Peak Voltage: 3.6V
    Charging cut-off voltage: 3.6V
    Discharge cut-off voltage: 2.2V
    Please never overdischarge battery below 2.2V/cell
    Charge the this battery with LiFePO4 RCR123A smart charger.
    Capacity - Nominal: 450mAh
    Maximum:750 mAh
    Maximum discharging rate:< 550 mA
    Maximum charge current: <550 mA
    Cell's dimension: 17mm Dia. x 34.5mm H.
    NOT COMPATIBLE WITH SUREFIRE FLASHLIGHT.
    DON'T USE THESE BATTERIES WITH ANY SUREFIRE FLASHLIGHTS.
    [apparently these test out at 4C or 5C with no problem, but leaves us with the issue of approving a battery for use at 5x the C rating]
    All-Battery.com: Tenergy RCR123A 3.0V (3.2V NOM) 750mAh LiFePO4 Rechargeable Battery
     
  12. AriM

    AriM Registered Supplier ECF Veteran

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    indeed, virtually ANY tube that can fit an 18650 can fit stacked 18350's. However 18350 is a size only available in IMR from AW. I am not sure it even fit's the true spec. for an "18350" size. That needs to be qualified.

    I listed them already in my nominations. If we are going to include sizes like 14500, 17600, 17340 etc....then we are opening up a can of worms....

    I say this specific topic should only include batteries that, when stacked, will equal the size of an 18650....it makes it a much easier subject to answer

    any thoughts on that?
     
  13. AriM

    AriM Registered Supplier ECF Veteran

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    yep those are my nominations, and I have all of those sitting in front of me, so I could qualify them with proper discharge/charge graphs
     
  14. rolygate

    rolygate Forum Manager Admin Verified Member ECF Veteran

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    Agreed.

    That keeps us with just the standard tube mod and that is what we need to handle right now.
     
  15. buGG

    buGG Ultra Member Verified Member ECF Veteran

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    I used several of these for years, and they served me well enough. However, if it's a matter of liability you may not want to approve a cell for an application that the manufacturer for one reason or another clearly states it isn't designed to handle.
     
  16. rolygate

    rolygate Forum Manager Admin Verified Member ECF Veteran

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    Yes, I'd be a lot happier if there are real good Li-FePo4 cells we could promote instead.

    Also I'd bet those Tenergy cells are among the most counterfeited out there. What you might end up with is a pair of reject Li-ion cells in your metal tube mod. Exactly what we are trying to avoid.

    Sometimes I think that 50% of the problem is actually getting your hands on the battery you think you have got. The supply chain is probably as critical as the label on the battery is.
     
  17. AriM

    AriM Registered Supplier ECF Veteran

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    IMO, we shouldn't recommend anything over 2c for any small battery. It keeps people safe, and still allows for the current we need for LR loads and 2 cell configs. A 2 cell (series) config doesn't double each cells C rating, it's more like 1.5 times.

    I would never endorse a rating of 5c on a small Li-Ion cell. Li-Poly, sure....but I don't see those as an option....
     
  18. AriM

    AriM Registered Supplier ECF Veteran

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    I only buy the tenergy LiFe's if they come in a tenergy blister pack. Even then, who knows....the genuine tenergy's seem to have a completely flat bottom. I have seen some "fakes" with a slightly raised section on the base.

    I have had really good luck with the AW LiFe cells....but I get them straight from AW. They all seem to have a slightly raised section on the bottom of the cell.

    I can take pictures of know real cells if it helps.....
     
  19. buGG

    buGG Ultra Member Verified Member ECF Veteran

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    By Lithium ion are we referring to LiCo only, or all chemistries (LiMn, LiFePO4, LiNiCo, etc.)?

    In the RCR123A size, with real mAh values at or around 500, the C rate is going to need to push 5 in a single cell configuration with a 1.5Ω low res atty. In series/stacked configurations, only the voltage is doubled, but shouldn't the amperage, capacity and then ultimately the C rate of the cell remain the same? A standard 510 or other atty in the 2.5Ω range would pull close to 2.4 Amps in a stacked (6V ~5.5V) setup, necessitating a 4-5C cell as well.

    If these sizes are recommended at all by ECF, wouldn't the recommendation need to state something like 4C/ 2.5A minimum for the discharge rate? Wouldn't this only be a LiMn in that size, and how many of them actually give the specs required for serious consideration?
     
  20. AriM

    AriM Registered Supplier ECF Veteran

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    Well I think it's hard to say, since there are so many variations on chemistry. In general though I would say LiCO, and LiFePO4. I think LiMn and LiNiCo2 could be stamped as high as 8-10c, but I wouldn't want to put my name on that endorsement.

    I think in rcr123 size we simply can't recommend a single cell as "adequate" for LR. I know we have all done it and continue to run such configurations (safely), but we are chasing a general recommendation. I think that a 2c rating is conservative and safe.

    When running in parallel we can safely double the C rating for each cell in the pack, but in series we can only bump the rating by 1.5 times. I think that we could safely recommend 3.2 ohm or greater for 6.4 v LifE stacks. I think going much lower would really diminish the life of the cell. I mean, I know we all run 1.5 ohm dual coils on life stacks, but it's really not good for the cells. Also keep in mind that the peak voltages are higher than stated on the cells, so the first few puffs exceed the c rating, until the cell flattens a bit

    Here is what i recommend to my customers, and I sell my kits accordingly

    4.8-5 volts NiMh - no less than 2 ohms (single coil)
    6.2-7.1 volts LiFe - no less than 3.2 ohms (single coil)
    7.2-8.4 volts Li-Ion (LiCo protected) - no less than 4 ohms (single coil)
    7.2-8.2 volts Li-Mn - 5 ohm dual coil


    RcR batteries really aren;t appropriate for PV's. I know we all use them, but IMO it's diminishing the performance and life of the cells. I am not sure if our recommendation is going to be based on the absolute limits of these batteries, or a more conservative and general suggestion....

    Also I am going out of my way to be VERY general on this topic....I think if we get too specific then the information won't be absorbed by people looking for a simple answer....sure there are case where a stacked 18350 LiMn could easily give you 5c plus, but it get's too specific IMO.



    any thoughts on that?
     
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