"kits" for 18650 or 26650 cells
- Thread starter tome
- Start date
Actually I have been working on such kit for some time now. It is still early to reveal design ideas, but I will do so when it is ready. Thermal management and per-cell fuses are on the feature list. It's for 18650 cells, as I don't see a point in investing into 26650 due to availability.
Not a DIY kit, but shows the tech.
New High capacity Li-Ion high cycle count
New High capacity Li-Ion high cycle count
circuit said:
You can buy A123 ANR26650 cells for $9.75/ea (there are qty discounts) from buya123batteries.com which have some impressive specs. There are also Feilong 26650 3.7V 4000mAh available (as well as FeiLong 32650 3.2V 5000mAh).
I am not arguing that 18650 aren't more common, just that 26650s are certainly available...
Tom
I was reading the A123 "Cylindrical Battery Pack Design, Validation, and Assembly Guide" document. It explicitly discourages mechanical fastening of cells on their ends. They discourage holding cells from their ends for two reasons, one because you cannot cover up the venting area of the cell and two because vibration transferred to the cell through the top/bottom shortens cell life. Below are relevant snippets from the document. The pack referenced in this link: http://endless-sphere.com/forums/viewtopic.php?f=14&t=39980 would seem to violate A123's design criteria, but I haven't seen the inside of it. I can think of ways to mitigate these issues in a mechanical clamping design, but I am skeptical that this pack does it. Also, they claim it is waterproof, which is great but is there a way to vent the gas if a cell vents?
This is the A123 document: http://assets.buya123batteries.com/images/a123/Battery_Pack_Design_Guide_Rev_07.pdf
"Cell Support
Secure the cells in place by supporting their outside cases, not their terminal ends. The vibration induced between the terminal ends and the rest of the case has been shown to be detrimental to the life of the cell, causing internal and external cell damage. The intercell terminations must be light enough not to cause vibration-induced damage to the cell."
"Never use pressure at the top and bottom of the cell to hold cells together in a way that leads to blocked cell vents. If the vents are blocked, the gas cannot exit the cell in case of cell failure. Cells shall be mounted in the application, in a way that will not interfere with the vent function on the cell."
"Thermal Events
Proper battery pack design is essential to allow the safety features of A123 Systems’ cells to function as designed.As a safety feature, overheating A123 cells vent gases to relieve dangerous pressure buildup to disperse into the environment. However, an improperly designed battery pack can prevent the gases from safely dispersing, or prevent the cells from venting altogether.
Adding an ignition source to improperly-vented gases can create a dangerous thermal event. You must ventilate these expelled gasses from the environment itself after the gases are vented from the cell itself.
"
This is the A123 document: http://assets.buya123batteries.com/images/a123/Battery_Pack_Design_Guide_Rev_07.pdf
"Cell Support
Secure the cells in place by supporting their outside cases, not their terminal ends. The vibration induced between the terminal ends and the rest of the case has been shown to be detrimental to the life of the cell, causing internal and external cell damage. The intercell terminations must be light enough not to cause vibration-induced damage to the cell."
"Never use pressure at the top and bottom of the cell to hold cells together in a way that leads to blocked cell vents. If the vents are blocked, the gas cannot exit the cell in case of cell failure. Cells shall be mounted in the application, in a way that will not interfere with the vent function on the cell."
"Thermal Events
Proper battery pack design is essential to allow the safety features of A123 Systems’ cells to function as designed.As a safety feature, overheating A123 cells vent gases to relieve dangerous pressure buildup to disperse into the environment. However, an improperly designed battery pack can prevent the gases from safely dispersing, or prevent the cells from venting altogether.
Adding an ignition source to improperly-vented gases can create a dangerous thermal event. You must ventilate these expelled gasses from the environment itself after the gases are vented from the cell itself.
"
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