[EE] batteries, internal vs removable module vs removable cells

[James Cameron]

Soliciting opinions on overall industrial design for Lithium Polymer
batteries in a laptop;

1. internal, not user serviceable,

2. internal removable module, user serviceable with screwdriver,

3. external removable module, spring loaded retention clips,

4. external removable cells, spring loaded terminals, cover plate,


So far I've got;

- battery exchange with other laptops; easiest 3, easy 4, hard 2,

- third-party battery replacement; easiest 4, (e.g. 18650 cells),

- good isolation from system-generated heat; 3, 4,

- able to recover from embedded controller hang; easiest 4, easy 3,
hard 2, hardest 1,

- liquid spill protection; good 1 & 2, not as good 3 & 4.

- lowest cost of manufacturing; 1,

- lowest cost of connector; 1, 2,

- lowest cost of overcharge protection circuit; 1, 2, 3,

- lowest cost of discharge protection circuit; 1, 2, 3,

- lowest cost of cell balancing circuit; 1, 2, 3,

- lowest cost of thermal monitoring; 1, 2, 3,

- battery cycle life; best 1 & 2, medium 3, lowest 4,

Other phase-space axes?

[Sean Breheny]

I don't understand how you could do #4 and still pass safety requirements.
There are dangerous conditions which can exist in LiPo and other Li Ion
cells which are detectable only with knowledge of the history of the cell.
For example, a cell which has been overdischarged in the extreme and then
partially recharged is dangerous if fully recharged but there's no way to
detect that it is dangerous except to know that it was previously
overdischarged. If you allow the end user access to individual cells then
you may not be able to detect this condition and prevent further charging.

Also, in order to pass some of the shipping requirements you have to
demonstrate that various failures do not cause fire, and this generally
requires temperature monitoring of some of the cells, which in turn would
usually require bonding temp sensors to some of the cells in some way which
is not conducive to removable cells.

You could also be in for lots of trouble if people put some random cells in
there which are different from your originally-designed type. At a minimum
your BMS wouldn't know what the capacity of those cells is.

On the other hand, I also hate option #1 since it creates a definitely
planned obsolescence and forces the end user to buy a new device when the
battery fails.

Post by James Cameron
Soliciting opinions on overall industrial design for Lithium Polymer
batteries in a laptop;
1. internal, not user serviceable,
2. internal removable module, user serviceable with screwdriver,
3. external removable module, spring loaded retention clips,
4. external removable cells, spring loaded terminals, cover plate,
So far I've got;
- battery exchange with other laptops; easiest 3, easy 4, hard 2,
- third-party battery replacement; easiest 4, (e.g. 18650 cells),
- good isolation from system-generated heat; 3, 4,
- able to recover from embedded controller hang; easiest 4, easy 3,
hard 2, hardest 1,
- liquid spill protection; good 1 & 2, not as good 3 & 4.
- lowest cost of manufacturing; 1,
- lowest cost of connector; 1, 2,
- lowest cost of overcharge protection circuit; 1, 2, 3,
- lowest cost of discharge protection circuit; 1, 2, 3,
- lowest cost of cell balancing circuit; 1, 2, 3,
- lowest cost of thermal monitoring; 1, 2, 3,
- battery cycle life; best 1 & 2, medium 3, lowest 4,
Other phase-space axes?
--
James Cameron
http://quozl.netrek.org/
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