Here are few of my experiences with Kokam 70 Ah pouch cells. Along the way I spent countless hours thinking about cell-clamping and other issues. Final pack turned out pretty good and has now worked for almost one year.
First and most important thing to remember:
!!! TAPE SIDES WITH KAPTON-TAPE !!!
and once again:
!!! TAPE SIDES WITH KAPTON-TAPE !!!
Belive me – they WILL leak if you do not tape them and allow them to contact other cells.
It seems that they have conductive foil left after cutting process at the factory. They will conduct electricity from sides when stacked together. And if you are using aluminum as your battery case material, disaster is ready … I ruined few 70 Ah cells and learned this the hard way.
Kapton-tape applied along the sides of the cells:
Second thing to remember -
!! KEEP THEM AT THEIR PACKING-BOXES AS LONG AS YOU CAN !!
Why ? Because they are very fragile to bending. Be extra careful when handling them. I had one cell ruined only by showing it to visitors at the workshop. Basically the cell was taken from it’s box, displayed to some visitors and put back to it’s box. And after few such “take from box, display, put back to box” events I discoverd that it had a hole in one corner. It seems that foil will very easily break if not handled extra carefully. So I recommend taking them from their box, taping them with Kapton-tape and then directly putting them to their final location at battery-box.
These unfortunate events happened while I was building 2 Kokam battery-packs for 2 different motorbikes – a Husqwarna Supermoto with about 5.2 kWh battery and a Cagiva Freccia (eCagiva) with 5.4 kWh battery. Both of them turned out fine and have quite good performance. They have Agni 95R DC-motors and Kelly DC-controllers. eCagiva has slightly more power with KDHE-series controller capable of 650A/120V.
Final version of cell clamping had Delrin (POM) clamping system with 4 mm stainless steel threaded rods and 3 mm Aluminum connectors. System doesn’t need any holes to be drilled to the cell tabs. Disadvantage is that it takes more space from between the tabs. Here is one picture of almost last version (last version had that welded clamping replaced with 3D printed ABS-plastic part):
Here is last version, with 3D printed ABS-plastic parts replacing those welded parts:
Those ABS-parts keep those stainless steel metal-parts from rising upwards when clamping is tightened with screws. Clamping force is distributed quite evenly and clamping seems to be adequate. This method does not need any holes to cell tabs. Clamping force is generated with 4 mm stainless steel threaded rod and screws.
Aluminum is 3 mm and was water-cutted. Delrin is 6/12 mm and was cut with CNC-machine.
Each cell was taped with very thin 100 mm wide 3M double-sided tape:
Tape roll is 100 mm wide:
Here is the finished eCagiva battery-box:
Wires are extra-fine thread high-quality silicone measurement cable. One cable connects to between 2 cells connects. BMS is conected to these cables.
Here are few shots showing actual bikes;
eSuperMoto has Agni 95R at the back-fork. We did some FEA-analysis for powers involved and this 10 mm Aluminum welded motor-stand seemed to withstand those forces well. It of cource adds a bit unsprung mass to back-fork but as it’s very near to “hinge-point” of the fork it does not affect so much (hopefully)…
First discharge tests were done with a 3-4 kW load. We replaced Agnimotor directly with DIY load-resistor and controlled discharge rate directly by twisting throttle Here is the load we used:
That’s it. Feel free to contact me if you want some more information and/or CAD-drawings of those components described above.
Few more pictures can be seen from: http://www.flickr.com/photos/yty/sets/72157628965069775/with/6735499795