Results 1 to 18 of 18
  1. #1
    mtbr member
    Reputation:
    Join Date
    Jun 2011
    Posts
    1,485

    need some schooling on PCB for unprotected cells.

    I have 2 light from Pucked up easy build and they work great. I bough 8 of the trustfire protected cells for that project.

    I have a supply of unprotected sanyo cells and want to build a couple packs for some future projects but need to leanr the pcb basics.

    I have a solar storm X2 on the way to play with and assume the batteries will crap out in good time.

    Im am assuming the X2 runs at 8.4v. Are the PCBs limited by the voltage you want or the number of cells (say I want to make a 4 cell 8.4 or a 2cell 8.4 or mabye an 8 cell 8.4?) Mabye I would want a 14v pack, would that requiers a different spec'ed pcb.

    Also any reading I can do to learn is always fun for me. I am very confident at wiring and have good understanding of the basics.

    Thanks

  2. #2
    mtbr member
    Reputation:
    Join Date
    May 2011
    Posts
    245
    Quote Originally Posted by machine4321 View Post
    Im am assuming the X2 runs at 8.4v. Are the PCBs limited by the voltage you want or the number of cells (say I want to make a 4 cell 8.4 or a 2cell 8.4 or mabye an 8 cell 8.4?) Mabye I would want a 14v pack, would that requiers a different spec'ed pcb.
    The PCBs used for DIY are purely voltage based &that depends on the number of cells in series, so 2s1p & 2s2p, 2s4p etc are all a nominal max voltage of 8.4v & all use the same PCB. A 1s_p, 3s_p or 4s_p would all use different PCBs.

    I found this site useful in understanding how to wire up a battery pack of any description

  3. #3
    mtbr member
    Reputation:
    Join Date
    Jun 2011
    Posts
    1,485
    Thanks for the link. That cleared up the balance wiring for me !
    Thanks for clearin up the cell# vs cell #, that is what I was thinking.
    Sonas ling as the pcb is rated for 8.4(or close to it) I can play with number of batteries I want.

    Now if the pcb supports balanced charging( dont think im going to get into that as I dont want to buy an exspensive charger) does it matter hom many cells you use?

  4. #4
    mtbr member
    Reputation:
    Join Date
    May 2011
    Posts
    245
    It doesn't matter all that much how many cells you have wired in parallel - cells wired in parallel have exactly the same voltage, which is why you wire up a pack like the pic on the right & not like on the right


    Balancing is a touchy subject - what you are doing is making sure the top group of cells have the same voltage as the bottom group. In an ideal world the cells in the top group are identical in capacity & discharge profile as the bottom group. It took me a while to get my head around the fact that out of balance is a symptom of a problem eg a pack I have now stopped using, the cells had aged differently so that one pair had a greater capacity that the other - if I balanced them at the top of the charge, they would be out of balance at the bottom of the discharge & vice versa.

    When fully charged, each cell is a bit under 4.2v, so 2s_p will be 8.4v. A simple charger brings the pack up to 8.4v & job is done. If however the two groups of cells get significantly out of balance, one might be 4V & the other 4.4V - ie dangerously overcharged.

    Similarly if you are using a cut-off of 2.5V per cell, the cut-off will be 5V. If the two groups are significantly out of balance, one might be 2.7V & the other 2.3V.

    A PCB is intended to protect you against both of these errors, but it is why I check the balance of my packs before and after every charge, even though I rarely balance them.

    Personally I would recommend using a hobby charger. They are not expensive - I got an "accucell 6" for a about $22 + shipping (I already had a suitable power supply) or you can get an imax B6 for $33 including a power supply & shipping. The value is not so much in balancing, but in being able to monitor the charging & set appropriate cut-offs, for example if the charge normally takes 2.5 hours, you can set a time limit of 3 hours. You can also charge various packs, battery types etc with the one charger.

  5. #5
    mtbr member
    Reputation:
    Join Date
    Jun 2011
    Posts
    1,485
    Thanks for the great info. Its funny as all of my series/parrallel wiring was done with speakers. I never would have thouth the left diagram was the wrong one. But I understand why it its done the "right" way.

    I will look into the charger for myself. 2 of my friends bought solar storms (trying to get them hooked on night riding for cheap) and I am planing ahead for when there batteries go bad. I guess I could use the pcb for the original pack and replace the cells with good ones. They could use the same charger as well.

  6. #6
    mtbr member
    Reputation:
    Join Date
    May 2011
    Posts
    245
    My way of thinking is that if the batteries are garbage, the PCB is probably not much chop either & same for the charger. I hadn't realised that you were building the packs for mates though - I probably wouldn't recommend a hobby charger unless I was confident my wouldn't do something stupid in connecting them up or selecting the wrong charge mode.

    How are you thinking of waterproofing the packs ?

  7. #7
    mtbr member
    Reputation:
    Join Date
    Jun 2011
    Posts
    1,485
    Heatshrink with the self sealing electrical tape. again this is just a "down the road" fix for them. But I have all of these cells around doing nothing.

  8. #8
    mtbr member
    Reputation:
    Join Date
    Apr 2006
    Posts
    594
    I used unbalanced packs for a time, then switched over to balancing every charge. Balancing extended run time by 20%. I use protection pcb's (almost sounds kinky) from all battery.com. I also add the balancing JST connector. About the best bang for the buck charger is a B6AC. That is a fairly cheap route. My last couple batteries were 100WHr @ 21 volt. 10 each 18650 cells in 2p5s. I shrink wrap the entire mess for impact and waterproofing.

  9. #9
    mtbr member
    Reputation:
    Join Date
    Jun 2011
    Posts
    1,485
    So the pcb doesnt have much to do with balance charging right. Balance wiring is just a way to charge individual cells, but to do this you need a proper charger since any protection is bypassed.

  10. #10
    mtbr member
    Reputation:
    Join Date
    May 2005
    Posts
    2,301
    Quote Originally Posted by machine4321 View Post
    So the pcb doesnt have much to do with balance charging right. Balance wiring is just a way to charge individual cells, but to do this you need a proper charger since any protection is bypassed.
    There are some protection PCBs that offer balancing. They are pretty expensive compared to a PCB that is for protection only. Check Batteryspace.com, I've seen them on their site.

  11. #11
    mtbr member
    Reputation:
    Join Date
    Jun 2011
    Posts
    1,485
    But I can still wire for balance charge even if the pcb doesnt support it. I just need a seperate connector.

  12. #12
    mtbr member
    Reputation:
    Join Date
    May 2011
    Posts
    245
    Quote Originally Posted by machine4321 View Post
    But I can still wire for balance charge even if the pcb doesnt support it. I just need a seperate connector.
    Yep that's the one. With a 2s2p battery (or 2s3p battery for that matter) you need a 3 pin connector pack +, pack - & centre. People commonly use a 3 pin jst connector like below, but there are others

  13. #13
    mtbr member
    Reputation:
    Join Date
    Jan 2007
    Posts
    754
    If you use top quality cells (such as Sanyo or Panasonic) that were bought together and haven't been individually charged or discharged, then you likely won't need to worry about balancing. Take a voltmeter and check the voltage of each cell before building the pack. Good quality cells that are the same age should have exactly the same voltage. If the cells have been used or charged individually, then you will need to get them in balance initially. Personally, I try very hard to avoid that case.

    Actually, most "balancing" hobby chargers aren't accurate enough to do a great job balancing and will often throw off the natural balance of a good set of high quality cells. To really get the balance precise, the balancer needs to be accurate to 0.001v and most hobby charger / balancers are only accurate to +-0.01v. Packs built with good cells will naturally stay in balance and when they start becoming unbalanced, it's a good idea to understand why they are going out of balance. It's usually an indication that something is going wrong with the pack.

    Now with that said, it's not a bad idea to put balance connectors on your packs. I sometime put them on my packs, most of the time I don't. I always use a protection PCB and yes you can have a balance connector and a protection PCB. But, it is a convenient way to check the voltage of each cell with a voltmeter by hand without having to take the covering off the pack. But I almost never use the balance connector to actually balance charge the pack. If you have a pack with good quality cells, I think you'll find that the balance will be spot on and it'll say that way without intervention.

    I just went through my set of 10 bike light packs a few weeks ago. They range in age from 1 to 8 year old. Two of them were built with less than top quality cells. I retired 3 packs this year that were all 8 years old with a lot of cycles on them. And I haven't had to retire any packs in quite a few years. Two of the retired packs were the ones built with 2nd tier cells. The third one was with Sanyo cells, but it was my fault why it died. I accidentally left it fully discharged at the end of last years night riding season and all the cells ended up discharging down to below 1V over the winter. The other 7 packs were all still perfectly balanced and in great shape and 3 of those are 6-year-old packs with lots of use.

    For the other 2 packs that were out of balance, itís because one or more of the cells had lost capacity and were also starting to self-discharge at a higher rate than the others. Thatís typically what happens when cells get near the end of their life. I could have made them work a little longer by balance charging them, but simply balancing the pack wouldnít fix the real problem that the real world capacities of the cells were inconsistent and ranged from 2200 to 1500mah. Balance charging would make the packís state of charge ďbalancedĒ when the pack was fully charged, but it canít fix the fact that the weakest cells are still going to run down first, cause the protection PCB to shutdown when the first cells drops to 2.5v, and hence make the pack unpredictable. I donít like unpredictable packs, so I take them out of service when they get to this point.

    If you are building packs out of poor quality cells or a collection of inconsistent cells, then you donít have much choice than to balance charge them. But my experience is that itís a lot of trouble, the packs are typically inconsistent, and in the long run Iím not sure itís any cheaper than building a pack out of top quality cells thatíll work well for many years.

    And if you really want to make a pack last a really long time, you can employ some of the same techniques used to make the battery packs in satellites and electric cars last a really long time. But, this post is already too long, so Iíll save that for another time.

  14. #14
    mtbr member
    Reputation:
    Join Date
    Jun 2011
    Posts
    1,485
    That was a good read, thanks.

    The cells I have are sanyo 18650a. I belive they are2250mah and are mostly new. Some are used but they come from a unit that keeps them in an ideal charge ( theyvare used as backup batteries) they are wired for individual monitoring but the pcb that is in the pack limits voltge to around 6 volts so it cant be used. Nice thing is there is tabs already welded on, so its just a matter if deciding if i want them skinny stacked or fatter.

  15. #15
    mtbr member
    Reputation:
    Join Date
    Jan 2007
    Posts
    754
    Just keep in mind that li-ion cells lifetime is based on both age and cycles. Even if the cells haven't been cycled many times, if they are fairly old, they will have lost capacity. If they are really 2250mah cells, then they are probably pretty old. Sanyo hasn't made that capacity in quite a while.

  16. #16
    mtbr member
    Reputation:
    Join Date
    Jun 2011
    Posts
    1,485
    I unpack them as new couple times a week they may be old stock or somthing, some are in use but i have the choice. They are free and there is tones of them around. They have to he better then the china specials they will be replacing.

  17. #17
    mtbr member
    Reputation:
    Join Date
    Jun 2011
    Posts
    1,485

  18. #18
    mtbr member
    Reputation:
    Join Date
    Jan 2007
    Posts
    754
    Quote Originally Posted by machine4321 View Post
    I unpack them as new couple times a week they may be old stock or somthing, some are in use but i have the choice. They are free and there is tones of them around. They have to he better then the china specials they will be replacing.
    Well, if I had a choice I'd always go with unused cells over ones that have been used. Unused cells typically sit at 3.7 volts. Cells that are used typically sit at a higher voltage most of the time and the higher voltage accelerates the aging process. If you have ready access and they are cheap or free, build a pack and do a little testing. It only takes one charge / discharge cycle to get a really good idea of the kind of shape they're in. You'll get a really good idea of capacity based on how long the light runs and if the voltage of each cell stays close together at the end of the discharge, then you'll know the cell capacities are well balanced.

Similar Threads

  1. New guy needs schooling on tires!
    By Samblam in forum Wheels and Tires
    Replies: 4
    Last Post: 07-09-2013, 06:36 AM
  2. need some schooling, best bang for the buck?
    By keith13 in forum 29er Bikes
    Replies: 7
    Last Post: 02-06-2013, 02:34 PM
  3. More Schooling Needed
    By jbone ll in forum 29er Components
    Replies: 7
    Last Post: 01-26-2013, 06:18 AM
  4. Quick Roadie between cells
    By GoGoGordo in forum California - Norcal
    Replies: 4
    Last Post: 12-01-2012, 10:58 PM
  5. Help identifying salvaged cells?
    By adrenalnjunky in forum Lights DIY - Do It Yourself
    Replies: 7
    Last Post: 10-08-2012, 07:49 PM

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •