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Thread: IMR LI-Mn 18650 Cells

  1. #1

    IMR LI-Mn 18650 Cells

    Hello Group,
    Today I am posting about a new battery pack I constructed from CHEAP IMR-18650 cells. I say cheap because these are on the cheap side of the market. I am a vapor and I often buy IMR cells for my vaporizer which are of much higher quality than these. The first thing I noticed when I took them out of the package was that they were very light compared to the higher quality ones I am used too. I suspect that they have lied about the capacity and filled them with far less active material than the quality cells used in vaping products, hence they are cheap. I knew that going in however and I wanted to see what could be done with them even if they do not have the advertised capacity.

    This pack is constructed from 72 cells. I have three parallel sections of 24 cells which are then put into series to create a 12.6v pack at full charge. The cells were rated at 2500mah but as I have said I doubt they actually have that much capacity. My cost per cell with the two plastic end caps that form an interlocked frame was 76 cents per cell so this pack is roughly a 55 dollar investment.

    Here are some shots of the top and bottom:

    IMRPack_2.jpg

    IRMPack_3.jpg

    I have just completed the build and am currently doing a few initial test runs. I will be covering the exposed connections with shrink tape later on once I am sure I don't need access to that area anymore. Each of the three parallel string has a pos and neg lead connected via deans plugs so that I can check each string individually for balancing. Later on if I build more packs I can simply remove that and make some cross connections to convert the whole pack into a single parallel pack that would then become part of a series in a larger pack. That is why I laid them out physically all in the same direction instead of inverting the middle row.

    I choose the IMR cells because with their chemistry they are able to handle large current drains and have a reputation for being much safer than ICR which is the typical Li-ION cell that has been out longer and is widely used for things like laptop batteries. For example in my vaporizer with the good cells I use IMR's and it takes two cells in series. When using the device I run a .25 OHM coil on it which results in about a 15A draw every time I take a puff. Granted this is not continuous but the point is that IMR's can give a lot of current. The downside of using IMR is that it inherently has much lower capacity. Generally you will only find IMR's up to about 2500mah but other lithium cells can go into 6000 and higher, they don't handle high draws well though.

    I have not decided on exactly how I will use this pack but one idea I had is to pair it up with this little 400 watt inverter. I would only be pulling the battery pack down about half each time because it cuts off at 10.5v or so, but that would be very safe for the pack. In reality the IMR cells are nominal 3.7v with 4.2v being the top and 3v considered drained.

    IMRPack_1.jpg

  2. #2
    Senior Member John_Koorn's Avatar
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    Jul 2012
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    Melbourne, Australia
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    Nice work as usual Bob. I am currently also building an 18650 pack from used electric bike battery packs.

    If if you or anyone else wants to seriously get into 18650 builds, especially your own powerwall this forum has plenty of info: http://www.diypowerwalls.com/index.php

    John K.

  3. #3
    Thanks for the tip John. I might check that out.

    This pack is turning out to be a bit disappointing. It seems to be around a 10AH pack, I have drained it at 4A and 2A and get almost the same results with the 2A being slightly better. I need to really think about the value of this, I know they were cheap cells but if they had the capacity they are marked with this *should* be a 60AH pack.

    I know these 18650 packs can be very good if good cells are used but I do not have access to a bunch of salvage and the *good* new cells are 5 bucks a piece at a minimum. When I look at the AH and the cycle life I need to consider if I could do better with other packages.

    Anyway it is not a total waste, this pack will be used for light duty but it is nowhere near what I had hoped for.

    Here is a discharge curve. The pack was charged to 12.3v after it rested. I could have pushed it a bit higher and maybe I will try that next time.

    LiMnPack_1.JPG

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