Power in Flux
Likes Likes:  1
Results 1 to 10 of 10

Thread: Paralleling single turnigy cells

              
   
   
  1. #1
    Senior Member ARC EV Racing's Avatar
    Join Date
    Jun 2011
    Posts
    242
    Post Thanks / Like

    Paralleling single turnigy cells

    I'm looking for some advice from anybody on here who has built packs from single turnigy lipo cells (pretty sure there's at least someone on here who has). 2 questions regarding making parallel blocks from individual cells:

    Do I need to insulate between the individual cell pouches?

    Do I need to constrain the parallel blocks at the ends so as to provide some pressure to counter expansion?

    We've built A123 packs before and the answer to both of the above was 'yes' according to the manufacturer so I'll do that by default if nobody can advise.

    Thanks

    Sent from my AZ210A using Tapatalk

    www.arc-ev-engineering.co.uk

    ARCEVRacing on twitter

  2. #2
    Senior Member ARC EV Racing's Avatar
    Join Date
    Jun 2011
    Posts
    242
    Post Thanks / Like
    Thanks Ted I'll have a look at that thread when I'm on a decent connection.

    I saw the double sided tape too but in effect that is insulation. I won't be using tape as we have our own termination method that holds them together but I can slide in some acetate sheet if necessary.

    Sent from my AZ210A using Tapatalk

    www.arc-ev-engineering.co.uk

    ARCEVRacing on twitter

  3. #3
    Senior Member EVGator's Avatar
    Join Date
    Jun 2011
    Location
    Atlanta, GA
    Posts
    135
    Post Thanks / Like
    Quote Originally Posted by ARC EV Racing View Post
    I'm looking for some advice from anybody on here who has built packs from single turnigy lipo cells (pretty sure there's at least someone on here who has). 2 questions regarding making parallel blocks from individual cells:

    Do I need to insulate between the individual cell pouches?

    Do I need to constrain the parallel blocks at the ends so as to provide some pressure to counter expansion?

    We've built A123 packs before and the answer to both of the above was 'yes' according to the manufacturer so I'll do that by default if nobody can advise.

    Thanks

    Sent from my AZ210A using Tapatalk
    We are currently re-building our battery pack with individual LiPo cells, and built our last pack with them. I would recommend (as I have seen others do) that you have some sort of pressure on the entire outside surfaces of the cells. During testing last year, one of our pack designs allowed just the middle of the outside cells' surfaces to be exposed and sure enough, some of them swelled under heavy discharge. This was due to gas build up which normally happens when over charging cells, however, we did not overcharge EVER. It was a mistake to assume that putting force on the bottom and top sections of the cells would prevent this. I am sure that if you cruise endless sphere, you can find lots more LiPo info.

  4. #4
    Senior Member jonescg's Avatar
    Join Date
    Apr 2012
    Location
    Perth, Western Australia
    Posts
    399
    Post Thanks / Like
    Hey man, yeah I have been building many batteries from individual LiPo cells. I reckon it's the best way to use this particular variety of Li-Co pouches. If you wanted a race bike pack, they are a great option for their cost, power and size format. However for a road-going commuter I'd strongly recommend a larger format pouch.

    I solder them together with big copper busbars. These take the heat which is generated at the tab, and prevents the cells from soaking too much heat under normal use. I also ensure that they are enclosed inside a polycarbonate box.

    Compression is needed, but you aren't going to stop them from swelling if you plan on pulling high C rates for long periods. Over-spec the pack where you can. I'm pulling 10 C max and 5 C continuous on my bike, despite having "40C" cells.

    PM for any advice, or if you need some PCBs I can help you out.

    Chris

  5. Likes EVGator liked this post
  6. #5
    Senior Member ARC EV Racing's Avatar
    Join Date
    Jun 2011
    Posts
    242
    Post Thanks / Like
    Thanks for the advice guys. We've built our last 3 race bikes with these cells but using the 5s blocks, this will be the first we've done with single cells. This bike will pull 8C peak so the pack shouldn't be too stressed.

    So I'll build in some compression but what about insulation between cells - do you use anything Jones? After some experimentation this week I'm inclined not to bother.

    Sent from my AZ210A using Tapatalk

    www.arc-ev-engineering.co.uk

    ARCEVRacing on twitter

  7. #6
    Moderator Nuts & Volts's Avatar
    Join Date
    Aug 2010
    Location
    Columbus, OH
    Posts
    1,794
    Post Thanks / Like
    Yea I think you'll be ok without insulation. Just make sure you can prevent movement between the cells. Maybe kapton tape between every 10 cells. Also don't stack too many together both to prevent too much weight on each cell and to prevent excess stress on cell tabs.

    Sent from my SCH-I605 using Tapatalk
    Whats under my tank may shock you!!! R6 Build, Blog/, [/URL] OSU Current webpage

  8. #7
    Senior Member ARC EV Racing's Avatar
    Join Date
    Jun 2011
    Posts
    242
    Post Thanks / Like
    No chance of movement or excess stress, each parallel block is discreet with its own bus bars and terminals. Each block interlocks with its neighbour and there are copper link bars to make the series connections. Brendan spent about 3 months milling all the bits to make enough for our next pack for the TT bike and now I've got to build them up. It all goes in a carbon fibre battery box.

    I'll stick some pictures up when I get time. Thanks again for the info, I'll go with compression on each block of cells but leave out the insulation between cell pouches.

    Ted the low cost is what drew us in but a lot if that is eaten up when you buy single cells and have to come up with a packaging system. This also trades off a bit in terms of weight and volume but the performance should be unreal. I've never used the hard cases though, only the 5s packs and now single cells. Do you have a link?

    Sent from my AZ210A using Tapatalk
    Last edited by ARC EV Racing; 09 February 2014 at 1648.

    www.arc-ev-engineering.co.uk

    ARCEVRacing on twitter

  9. #8
    Senior Member jonescg's Avatar
    Join Date
    Apr 2012
    Location
    Perth, Western Australia
    Posts
    399
    Post Thanks / Like
    The reason I started buying single cells, despite their higher cost (go figure) was that I had more control over which cells get put in parallel. Hardcases, 6s packs - they're all made from a pile of cells you or I have no idea what their quality is. Plus they solder them tab-to-tab, so there's no nice big lump of copper to soak the heat.

    I had considered using M3 screws to clamp the tabs down, but it loses the space gains that I'd made with soldering. Plus you can still unsolder some dud cells if you really have to, it's just a PITA.

    Here is a 28s3p pack I made for Entecho. We use three of these for the hoverpod test flight pack.
    http://www.endless-sphere.com/forums...rt=250#p830663

  10. #9
    Senior Member ARC EV Racing's Avatar
    Join Date
    Jun 2011
    Posts
    242
    Post Thanks / Like
    That's a nice, efficient looking pack build. Our method does clamp the tabs and it puts an open frame around the cells, so not as volume efficient as that but probably easier to build.

    What form of testing did you do with your cells? I've just been doing ir test and voltage check, then I'll weed out any poorly performing blocks once we get them in the bike. I plan to strip the pack down between testing anyway since we didn't prototype on the same scale as this.

    I couldn't bring myself to cycle each individual cell to measure capacity the way I did with the 5s packs, there are just too many and not enough time.

    Sent from my AZ210A using Tapatalk

    www.arc-ev-engineering.co.uk

    ARCEVRacing on twitter

  11. #10
    Senior Member jonescg's Avatar
    Join Date
    Apr 2012
    Location
    Perth, Western Australia
    Posts
    399
    Post Thanks / Like
    My main QC effort is checking voltages. All of the cells are charged to 3.90 V when they leave the factory, so any cells which have self-discharged back to 3.83 V or less are put to one side. Also, no cells with obvious defects are used in any pack, and if I am short of a few cells and I do need to dip into the reject pile, I put them to one end where it's easiest to remove if I have to.

    The other thing I do is package them inside a rigid polycarbonate box. There is also a thin layer of plastic between the two cells, as there is a good 100 V between one cell edge and the next. Any potential chaffing would lead to an epic arc. The box is important, as physical trauma is a pouch cell's worst enemy.

Bookmarks

Posting Permissions

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