View Single Post
Old 03-04-2013, 07:43 AM   #387
_cy_ OP
Beastly Adventurer
Joined: Sep 2011
Location: Tulsa, Oklahoma
Oddometer: 5,940
Originally Posted by JoelWisman View Post
I see what your saying. The balance circuit that earthX is using will prevent the kind of over voltage damage that occurs when a series of cells is badly out of balance through shunting from one cell to the next provided that the charging voltage does not exceed normal charging voltage. Yes I agree 100%

But this isn't actual BMS over-voltage protection and will do nothing to stop the whole battery from being destroyed from over-voltage if the charging voltage becomes excessive.

Something not that uncommon on a modern shunt regulated bike with a PM charging system is for the shunt to fail or the shunt ground to go bad. In this case system voltage climbs above 20 volts and even at idle, the F800GS for example has 11 amps of excess current available with all accessories switched off.

In this case the earthX battery is likely to dramatically fail just as any other LiFePO4, or lead/acid battery for that matter because it does not have actual BMS over-voltage protection, nor for that matter does any other LiFePO4 or lead/acid battery for power sports i'm familiar with.

amazing how far modern electronics has come. should be easy enough to key trigger point for said MOSFET to open/close at say when an over voltage condition exists.

LiFePO4 reaches full charge at 3.65v per cell, 4s = 14.6 .. 4s x however many stacks in parallel = 13.2v nominal with a max charge voltage of 14.6v needed to achieve full charge.

as you've found out during over voltage abuse tests ...cylindrical LiFePO4 cells will absorb an amazing amount of abuse and still keep working. li-ion cylindrical cells typically contain safety valves designed to open at set temps to release internal pressures. vs prismatic cells will balloon to vent pressures.

normal 12v charging system operate 13.8v to 14.2v ... so if said MOSFET triggers at say 14.8v or what ever voltage slightly over 14.6v full charge condition.

above would prevent battery from being destroyed by severe overcharge conditions like say when F800's voltage regulator fails. then when volts drops below say 14.8v, MOSFET goes back to it's Normally closed condition.

_cy_ screwed with this post 03-04-2013 at 07:53 AM
_cy_ is online now   Reply With Quote