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 04-13-2012, 04:06 PM #71 (permalink) EcoModding Lurker   Join Date: Mar 2012 Location: Ft. Lauderdale FL Posts: 32 Thanks: 18 Thanked 4 Times in 4 Posts I thought I did but maybe it did not post sorry. Endless-sphere.com • View topic - Bottom balancing? In any case the whole matter can be resumed in one sentence: Don't let the cells go over or under and you'll be fine. That's all.
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Ok, thus you already posted the link but I was looking for a blog

I looked the curves, and personnally I am unable to conclude anything :

On the 2 first curves, Y axis are not the same, we cannot easily compare voltages, and on which criteria is based the 0% SOC !? It seems to be based on the global pack voltage for an average cell voltage of approx 2.1V.

On the first curve, we can deduct that the weakest cell (with the lower capacity) is the cell 4 : it reach the theoretical 2.1V LVC before other.

On the second curve, we can deduct the same thing, cell 4 is the weakest cell, because at the begin of the decharge it has the higher voltage, and thus it's this cell which triggered the HVC and stopped the charge.

Thus in the 2 cases (bottom balancing and top balancing), it's always the same cell which is completely charged AND completely discharged (voltage level range from HVC to LVC). It's totally logical, because it's the cell with the lower capacity.

Because of this, if the pack is discharged in the same condition for the 2 tests, the curve of this cell number 4 cannot be different between top or bottom balancing curve in the range of HVC/LVC (3.65/2.1V range).

But we can see that the cell 4 curve is completely different in the 2 graph, there is a mistake somewhere !
And the Y axis should be time and no SOC, because which is interesting is to calculate the Wh that the pack output (knowing the continuous current discharge).

For the 2 other curves, cannot conclude anything, because the same discharge measurement is needed after a bottom balancing charge procedure, and there is not ! From this curve we can just conclude that I say above is true : the weakest cell is alway used on its full HVC/LVC voltage range in the 2 cases, thus the discharge curve of this cell cannot be different in same discharge rate condition.

Quote:
 In any case the whole matter can be resumed in one sentence: Don't let the cells go over or under and you'll be fine. That's all.
Absolutely, it's what I alway said, it's the primary goal of a BMS. It's why bottom balancing or top balancing during pack assembly is really not a primordial question, the final result will be exactly the same in term of Ah capacity because the global Ah of the whole pack will alway be the Ah of the weakest cell.

I think this bottom balancing debate only concern guys which want to use their pack without BMS during discharging and do the LVC cutoff on global pack voltage only.
But imo it's an error to think the pack will be bottom balanced all its life, because cell are not completely identical (temperature, internal resistance, ...), with peukert effect and thus charge after charge and discharge after discharge, voltage variation will appear on individual cells when cutoff on global cell voltage will trig.

 The Following User Says Thank You to nlc For This Useful Post: TadhBijou (04-18-2012)
 04-25-2012, 09:47 AM #73 (permalink) Deyan Stoev   Join Date: Jan 2012 Location: Bulgaria Posts: 6 Silver Slut - '95 Renault Laguna Thanks: 104 Thanked 1 Time in 1 Post Congrats!!! I am far from my conversion, but will wait with interest evolving... I am deep fan of board computers (ordinateur du bord) - in my Renaults I watch them frequently... especially l/100 momentary consumption - helps me to have a light foot on a gas pedal ... Also you know approximately haw far you can go...
 04-25-2012, 09:51 AM #74 (permalink) EcoModding Lurker   Join Date: Jul 2011 Location: France Posts: 90 Thanks: 3 Thanked 61 Times in 28 Posts Hi deodeo, I actually work on the dashboad, just validated the direct TFT screen drive with the microcontroller :
 The Following User Says Thank You to nlc For This Useful Post: deodeo (04-25-2012)
 04-25-2012, 01:18 PM #75 (permalink) Deyan Stoev   Join Date: Jan 2012 Location: Bulgaria Posts: 6 Silver Slut - '95 Renault Laguna Thanks: 104 Thanked 1 Time in 1 Post Yeah, it would be great!
 04-25-2012, 01:20 PM #76 (permalink) Deyan Stoev   Join Date: Jan 2012 Location: Bulgaria Posts: 6 Silver Slut - '95 Renault Laguna Thanks: 104 Thanked 1 Time in 1 Post I know that in the 80's some of the dashboards of Renault are digital (http://www.youtube.com/watch?NR=1&v=...ture=endscreen) - I've seen myself dashboard from R21 w digital speedometer etc at junkyard... but it was too big for my Clio, so I took dash from R19 with digital board computer and put it in the Clio. You know that in 90's Clio plug-in electric are produced - there are some left in EValbum... But is it possible to be homemade such dash? PS Did you noticed that this ordinateur speaks like Alpha60 from Godard's Alphaville!?! Last edited by deodeo; 04-25-2012 at 01:26 PM..
 04-26-2012, 06:04 AM #77 (permalink) EcoModding Lurker   Join Date: Jul 2011 Location: France Posts: 90 Thanks: 3 Thanked 61 Times in 28 Posts With the TFT screen of the master board I develop, there is the possibility to emulate a digital dashboard like this
 04-27-2012, 05:57 PM #78 (permalink) EcoModding Lurker   Join Date: Jul 2011 Location: France Posts: 90 Thanks: 3 Thanked 61 Times in 28 Posts A little question, is someone is a software developer and is able to develop a very small QT application ? It's to emulate a TFT touchscreen and lets me develop, test and validate all the master software on my computer (with a clean HAL interface for low level accesses) instead directly develop on the microcontroller target.
 06-03-2012, 06:54 PM #79 (permalink) EcoModding Lurker   Join Date: Jul 2011 Location: France Posts: 90 Thanks: 3 Thanked 61 Times in 28 Posts My work on this BMS project continue, the slave board are totally finished (hardware+software), now just need real dynamic testing on a pack. I currently work on the master board, because I think I will not sell any slave board without a master board to use them. This master board will be very evolutionary with a lot of possible functionalities. Here is the general diagram of the board : The schematic design is almost completely done, in some days I will reach the routing step I found a great enclosure for this master board : I am a on this project but there are no enough day in a week
 The Following User Says Thank You to nlc For This Useful Post: mrbigh (06-03-2012)
 11-01-2012, 05:44 PM #80 (permalink) EcoModding Lurker   Join Date: Jul 2011 Location: France Posts: 90 Thanks: 3 Thanked 61 Times in 28 Posts These last day I worked again on my BMS project, I simplified it but it also implements a lot of thing : - +12V permanent supply - +12 Ignition input to power up the board - Mains 110/230VAC input for charger presence detection - 2 relay outputs 110/230V/12A (charge authorization and discharge authorization) - 2 LED outputs for status - 2 open collector free outputs - RS232 serial port for firmware upgrade, configuration, and bluetooth module option connection (configuration, log and management with a smartphone) - 1 BMS slave interface (up to 255 slaves) - 2 universal analogic/digital inputs (for current sensor for example, throttle, ...) - 2 analogic output (0-5V), for external baragraph or analogic jauge for example - 1 SD card support, for datalogging - 1 CAN bus, to interconnect on a CAN bus, to do a lot of thing in the future ! I finished to solder the prototype this morning : The first firmware with minimum functionalities is well advanced Attached Thumbnails   Last edited by nlc; 11-01-2012 at 05:59 PM..
 The Following 2 Users Say Thank You to nlc For This Useful Post: mrbigh (11-04-2012), sawickm (11-02-2012)