Re: (ET) Wanted, information on installing Lithium cells in my EGT 200

["David Roden" <etpost drmm net>]

On Jun 1, 2013, at 4:00 PM, John Jeno <jjjeno hotmail com> wrote:

> As to BMS systems as far as I know they do not monitor each cell. 

On 1 Jun 2013 at 17:42, dave wrote:

> no. the bms monitors every cell ...

Dave is correct.

John may be thinking of the BMS systems that have been used with lead 
batteries.  Most of those balance at the module level - that is, 6, 8, or 
12v modules, not individual cells.  (In this context a "module" or 
monoblock 
is what some folks call a battery, and the "battery" is what some call a 
"battery pack."  Sorry for the confusion.)

That isn't ideal, but it's better than nothing at all.  It helps because 
all 
the cells in a module are manufactured at the same time, so they're 
somwhat 
matched in capacity.  

Monitoring at the cell level is less expensive with a lithium battery 
partly 
because, with a nominal 3.3vpc (LiFePO4) vs 2.0vpc for lead, there are 
fewer 
cells for a given battery voltage.

The other thing which has made lithium BMSes more affordable for the 
average 
guy (not independently wealthy) is - I hate to say this - cheap Chinese 
design and manufacturing.  The price of a truly competent lead BMS from 
the 
early 1990s would make your head spin.  IIRC the Badicheq was about $3k 
for 
a 10-module battery.  Today with inflation that would be almost $5k.  They 
were building them by the dozens, not the thousands, so that had something 
to do with the price too.


David Roden - Akron, Ohio, USA

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