ProstheticHead
Newly Enlightened
- Joined
- Oct 3, 2011
- Messages
- 13
Firstly, please forgive any ignorance that may become obvious in this post - I'm pretty new to directly handling lithium ion cells.
One of the concerns I have with the 'protected' 18650 cells I've recently started using is that they have a conductive metal strip running down the side of the cell which is only insulated by weak film coverings. This strikes me as particularly dangerous with a relatively high likelihood of leading to a short. After searching I found this issue has already been mentioned several times on these forums.
I may be being ignorant, but it seems unnecessary to me. I know that the protection circuitry requires power and hence connection to both terminals of the cell, however I don't see why it needs to take the form of a thick, high current capable copper strip with such poor protection. Surely the actual control circuitry only requires a tiny amount of power and as such could be serviced by a VERY thin wire in place of the usual thick strip. This would have several advantages; firstly, it would be incapable of carrying sufficient current to represent a serious safty hazard in the envent of a short it would simply burn out like a fuse. Secondly, it's smaller size could allow it to be better insulated and protected (even that hair thin magnet wire one can buy has a durable non-conductive coating). I don't see any reason why that should cost any more to implement than the normal copper strip arrangement.
Last point, most cells I've encountered are coated in very fragile and easily damaged film material, leading to exposure of conductive spots along the sides of the cells, clearly not an ideal safety situation. Much stronger polymer films are available and the per cell cost difference would be minimal, it seems odd to me that even 'premium' cells have such poor coatings.
I may well have missed or failed to understand something, if so please let me know. If not, does anyone have any idea why the cells are made as they are when there appear to be cheap and easy ways to improve safety?
Thanks!
One of the concerns I have with the 'protected' 18650 cells I've recently started using is that they have a conductive metal strip running down the side of the cell which is only insulated by weak film coverings. This strikes me as particularly dangerous with a relatively high likelihood of leading to a short. After searching I found this issue has already been mentioned several times on these forums.
I may be being ignorant, but it seems unnecessary to me. I know that the protection circuitry requires power and hence connection to both terminals of the cell, however I don't see why it needs to take the form of a thick, high current capable copper strip with such poor protection. Surely the actual control circuitry only requires a tiny amount of power and as such could be serviced by a VERY thin wire in place of the usual thick strip. This would have several advantages; firstly, it would be incapable of carrying sufficient current to represent a serious safty hazard in the envent of a short it would simply burn out like a fuse. Secondly, it's smaller size could allow it to be better insulated and protected (even that hair thin magnet wire one can buy has a durable non-conductive coating). I don't see any reason why that should cost any more to implement than the normal copper strip arrangement.
Last point, most cells I've encountered are coated in very fragile and easily damaged film material, leading to exposure of conductive spots along the sides of the cells, clearly not an ideal safety situation. Much stronger polymer films are available and the per cell cost difference would be minimal, it seems odd to me that even 'premium' cells have such poor coatings.
I may well have missed or failed to understand something, if so please let me know. If not, does anyone have any idea why the cells are made as they are when there appear to be cheap and easy ways to improve safety?
Thanks!