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Thread: Newbie pack and PCB build/rebuild questions

  1. #1

    Thumbs up Newbie pack and PCB build/rebuild questions

    Hey people
    So here's the project - I'm building a battery pack from an underwater diving light.
    I have a problem identifying a replacement PCB as the original ones malfunctioned and I can't find the exact same part anywhere.
    I will be building an exact same copy of the pack seen in the pictures and need help with locating an alternative to the original PCB. I have the same type Samsung batteries.

    Can you guys help me identify what's going on? I'm good with the mechanical part but not so good with the electronics.
    What is the voltage of this pack? What is the amperage of the PCB? In the last photo you can see the PCB's that were recommended to me - will they work as a replacement if I wire everything in exactly the same way?

    Thank you and sorry for the dropbox fotos I don't have anywhere else to upload them!






    Last edited by DonSilvio; 10-08-2019 at 06:02 AM.

  2. #2
    Flashaholic* DIWdiver's Avatar
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    Default Re: Newbie pack and PCB build/rebuild questions

    Hi, and welcome to the forum!

    First about the pics. If you change the 'www.dropbox' part of your URL to 'dl.dropboxusercontent', you can paste the URL in the 'insert an image' dialog and the pictures will appear in your post. Don't forget to size them to no more than 800x800 pixels, though, or the moderators will be on you to fix them.

    Most people would call that an 11.1V pack, using the somewhat standard 3.7V per cell, times 3 cells in series. Others might call it as high as 12.6V, using the maximum 4.2V per cell.

    It looks like you actually have two packs in parallel. Each one is 3S2P, meaning you have 3 in series, 2 in parallel. Putting 2 packs in parallel makes it essentially a 3S4P, but having two protection boards gives you twice the max current.

    Speaking of current, the 26F cells are rated at 5.2A, so 2 in parallel would be rated at 10.4A, but it's unlikely the protection circuit would allow that. The protection has an over-current limit, and I would guess that it's between 3 and 8A. Two packs in parallel would give you 6-16A.

    Another way to approach the current question is to know, estimate, or measure how much current the light draws. If you knew the runtime of the light, or the true (not the hyped) lumen output, we could estimate it from that.

    What you need from the new board is the following:
    1. Must be for LiIon cells
    2. Must be for 3 cells in series (or 2-3, or 2-4, or something like that).
    3. Must have a current limit high enough to support your light.
    4. Should have a current limit no higher than 10.4A.
    5. Must fit.
    6. You must know how to wire it properly.

  3. #3

    Default Re: Newbie pack and PCB build/rebuild questions

    Thank you so much!!! What a great reply
    It seems I have most of the information to make the project work. I need to sit down and look at all the parameters you so kindly provided.

    The light is a 21w led and is supposed to burn 3.5 hours on a new pack of 2500mAh 18650's
    As far as true lumens go... well it's supposed to be 2000lmns, I think it's close to that.

  4. #4

    Default Re: Newbie pack and PCB build/rebuild questions

    I've built a few 6 cell li-ion packs with protection boards. If you are doing 3 series with 2 parallel its 3S2P as was mentioned. You get the same voltage as 3S, but double the capacity (mah rating) and current handling. But be careful because your protection hoard needs to handle the load. Your batteries might take it, but when they sag under load below the low voltage threshold of your protection board, it will shut down the whole thing until the cells recover. eBay is a good place for protection boards. I say, go with a rating higher than you think you'll need since the accuracy of cheap boards can vary. If you think you need 5A, go 10A or even 20A. The voltage doesn't matter. Wiring it up is easy. Just follow the directions on the board for each series connection...3.7v, 7.4v, 11.1v, batt+, batt -

  5. #5
    Flashaholic* DIWdiver's Avatar
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    Default Re: Newbie pack and PCB build/rebuild questions

    Quote Originally Posted by DonSilvio View Post
    The light is a 21w led and is supposed to burn 3.5 hours on a new pack of 2500mAh 18650's
    As far as true lumens go... well it's supposed to be 2000lmns, I think it's close to that.

    2500 mAh times 3.7V times 12 cells gives 111 w-h, which should run a 21W lamp for 5 hours. Getting 2000 lm at that power level is not hard. You might have a very conservatively rated light.

    Unless you are talking about only one of the two 3S2P packs you showed, which would give you about half that run time. That would be more in line with how most manufacturers seem to rate lights. If the brightness tapers off at the end, you can end up with a quite long, quite dim 'tail'. They advertise maximum brightness, and total run time, not how long it stays at max.

  6. #6

    Default Re: Newbie pack and PCB build/rebuild questions

    Ok I've finally had the time to equalize the batteries and soldered them together.
    Each 3s2p pack of six gives about 11.2V

    I tried putting it together with the 12V PCB - everything OK but no output current from either of the packs 0v...
    Current does not leave the terminals of the PCB.

    What could be the reason for this?
    Last edited by DonSilvio; 10-09-2019 at 09:52 PM.

  7. #7

    Default Re: Newbie pack and PCB build/rebuild questions

    I noticed that the original pcb has a resistance module labeled 030. The new pcb's I got have the same module labeled 010. I just couldn't find an exact pcb match. Could this be the issue?

  8. #8
    Flashaholic* DIWdiver's Avatar
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    Default Re: Newbie pack and PCB build/rebuild questions

    I doubt it. That's a current sense resistor, 0.030 and 0.010 ohms, respectively. That, combined with the chip, determines what the current limit of the board is.

    It's possible that you have to charge the pack a bit to enable it before you can draw power from it.

  9. #9

    Default Re: Newbie pack and PCB build/rebuild questions

    Thank you very much for the info and suggestion I will try it!!!

  10. #10

    Default Re: Newbie pack and PCB build/rebuild questions

    Ok yeah so for some reason the original charger does not like the new PCB, so I can't even charge the pack.
    I finally gave up and soldered one of the original PCB's (that are very abused), seen in the image above... And Lol and behold. Charger likes it, charges, the light turns on.
    There's no voltage on the P+/P- on the PCB without the light!!!

  11. #11

    Default Re: Newbie pack and PCB build/rebuild questions

    Soldered half of the pack and got it working with the old PCB. 6 batteries on one pcb - reads fine on the terminals, charges, powers the light for more about 90mins.
    The other PCB does not work. I can't order it from anywhere. Only available in Europe and Alibaba. I don't understand why this PCB is sooo special.

  12. #12

    Default Re: Newbie pack and PCB build/rebuild questions

    Update: got an alternative PCB that is being used by the manufacturer of the light lately, got the other half of the pack going. Hope I can find another one so that I have the same pcb's on both halfs. Will see how it works when I join them - hopefully will be fine.

    Does anyone know of any quality pcb suppliers in the U.S.?? I looked on amazon but mostly the reviews for the pcb's are realllyyyy mixed

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