Arlo1 wrote:Hats off for DIY SMD work. Sorry I skimmed your thread and did not see how this works. Do they use current when the battery is at rest? I think I read they just send ground signal if LVC is reached? So it could be used to pull the throttle low? But will not cut power to the controller?
Very nice build IM excited to see this.
When at rest (ie between LVC and HVC points) there is a small current draw through a voltage divider on the TL431 ref input. The resistors on this input are in the 100k range total, so divide 100k into the cell voltage and you'll get an approximation of the steady state draw. For LiFePO4 it's around 40 microamps.
[EDIT] The TL431 actually draws more current than I anticipated, in the range of 200-400 microamps depending on cell voltage. Still small, but not as small as I had hoped. 200 microamps constant draw is about 1 Ah every 7 months. Even the worst case 440 uA draw would still take close to 3 years to deplete a 10Ah pack, although this is a very conservative estimate since the TL431 current load drops off as the cell voltage drops. At the nominal 3.2V for LiFePO4, total current draw would be around 250-300 microamps, or around 4-4.5 years to deplete a 10Ah pack. Hardly a problem in my opinion, but greater than I hoped for.
LVC and HVC both send a ground signal (via an optocoupler). At LVC it's used to cut out the controller by simulating pulling the brake lever, or anything else that triggers on a low signal. It could also be used to trigger a fet array to cut off current, or whatever else you want. I didn't include it since it adds complication and the brake input is sufficient for most people.
The LVC/HVC signal can also be used to limit charge current when below LVC or above HVC.
flez1966 wrote:re the voltage difference jumper possibility, why a jumper, as you say its large and costly also, just go for a pair of solder pads ppl can drop a blob of solder on...
I just bought my first 4*4s packs, and i have one crappy b6, charging is a pain.
I have spent a week trying out different designs in a simulator but think as you have all the work done best just to pay up lol
can i charge a 4s pack with a 19v supply with this design of yours, I know 4/5v isnt much of an overhead.
I'd suggest investing in a decent charger that is adjustable or will only supply up to the max pack voltage. 19V for 4S is 4.75V per cell, way over the safe limit for any chemistry. No BMS will protect against everything. Unless your charge current is less than or equal to the balance shunt current (~150mA for mine) then you will still over charge the cells.
:thumbup:
Lipo porn! 
