Thanks Alan! I have been looking at the chips supposedly used in the Tesla product lineu= p: http://www.ti.com/product/bq76pl536a Also Linear's latest you are talking about: http://cds.linear.com/docs/en/datasheet/680412fb.pdf and I found products by Maxim Integrated, but all say do not use for new Designs: http://www.maximintegrated.com/en/products/power/battery-management/MAX1106= 8.html Apparently the standard way of balancing a pack is to parallel a FET as a current path to those cells that are getting over their full voltage. I don't think that is a satisfying solution for me! I have been looking at the Linear data sheet and haven't been able to tell = if you should be able to toggle the 'balancing outputs' by program control, and how fast that could be done? You know if you looked at the prezi I mentioned in the initial post, that my idea of balancing is slightly different than paralleling a resistor to waste excess energy... I am planning to invest heavily in sub miliohm FET such as Infineon IPT004N03L at down to .4mOhm Rdson. two of them per parallel cell level, one to disconnect those cells and one to bridge it short to the rest of the pack. The idea is that I respect my sources of energy - be them solar on the roof of the vehicle or regenerative breaking. Equally how do I protect my cells otherwise if I want to keep going and some are exhausted and need a break? And then the most time critical aspect! I figure I can If I am fast enough shorten out the pack ideally each parallel cellstack simultaneously and disconnect the cells if the external short was to hit! Dreadful thought but needs to be executed anyway! So I wonder how far this can be implemented if not automated with this chip= ? Thanks and pleasant Sunday! Tobias On 2/1/15, alan.b.pearce@stfc.ac.uk wrote: >> Hello wizards of electronics ! >> I made great advances on my electric trike in the last few weeks, and my >> own >> battery build is rising in priority very fast! >> >> To keep costs down I am now considering to create a hybrid between my >> proposed cell level protection scheme ( >> https://prezi.com/qibqej3sqqy1/open-source-battery/ ) and a more >> conventional BMS where one circuit monitors the whole pack. >> So I know there are BMS chips that can measure the voltage of series of >> cells. >> I wonder how it is done? Maybe a charge sample moved around by a variety >> of FET? >> For a beginning I want to work with a 24S LiFePO4 (72V or full at >> 87.6V) But a flexibility of the circuit would be even better! I still wa= nt >> to >> bridge cells in or out of the circuit to protect them either from >> overcharge or >> deep discharge! What I think is smart to avoid in this first iteration i= s >> to have >> one microcontroller per cell level with all the communication hassle thi= s >> might >> imply! >> Thanks for all comments they are appreciated ! > > Linear Technology makes chips that monitor each individual cell in a stri= ng. > From memory they can be stacked beyond the number of cells an individual > chip can handle. IIRC they have an I2C or SMB interface, which can be > isolated for big cell stacks. IIRC they were originally designed for lapt= op > battery stacks, but I think they also talk about electric vehicle stacks > which is why they have made the chips intelligent enough to go beyond the > number of cells an individual chip can handle. > > > > -- > http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist > --=20 Tobias Gogolin Tel. D1 (49) 0151 5187 5210 Tel. D2 (49) 0152 0839 5060 skype: moontogo messenger: usertogo@hotmail.com You develop Sustainable Ranch Technology at http://tech.groups.yahoo.com/group/SURA-TECH an Open Source Electric Motor/Alternator at http://groups.yahoo.com/group/Performance_Axial_Flux and an Open Source Motor Controller at http://groups.yahoo.com/group/GoBox --=20 http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .