Hi Paul and All,
According to a long history using batteries Lee is
exactly correct.
Doing it bottom balancing it bringing all the
batteries to a common charge at say 5% based on the particular cell's voltage
chart. While in the middle of the pack voltage can't be trusted, at both ends
they change rapidly, can be used to make each cell the same % charged,/balanced.
I'll put all my cells in parallel and discharge
until the 5% charge voltage is reached. Only then can you rely on them to work
together without an each cell BMS when assembled into a pack. You can do
similar top balancing but I believe the biggest danger is on discharge so I
chose that one.
Next you need to have some way of finding out if a
cell, etc is going bad, out of balance as eventually like Lee said, the cells
will age and divert in spec. Or could from a weak cell early on. But it will
happen.
Luckily Lee's BattBridge circuit splits a pack or
even 2 cells and if half gets out of balance, it'll give a light warning or
triggering something like cutting or reducing power/charge.
Along with the Lightobject meter, it's adjustable
relays and for fuel gauge, charging cut off and displaying recording energy
use and a person who knows how to run it is good, low cost, risk. I might
even get 2 of them. It likely can be used to balance cells one at a time
BTW Lee has forgot more about EV's that you'll
likely ever know so when he writes something it's usually the best advice
you'll get. He is an original source so it's according to him, is rather hard
to beat.
Many have tried, lost by not listening to him on
EV's, many other things.
Jerry Dycus
On Monday, October 13, 2014 9:05 PM, Paul Dove via EV <[email protected]> wrote:
According to whom?
Sent from my iPad
> On Oct 13, 2014, at 1:55 PM, Lee Hart via EV <[email protected]> wrote:
>
> Cruisin via EV<[email protected]> wrote:
>>>> Using a meter to turn off a charger at a pre-programmed voltage
>>>> can be very risky.
>
> Paul Dove wrote:
> >> Problem is no one has actually proved that with experimentation.
> >> Not in any of my reading. You can believe what ever you like.
> >>
> >> I have used ammeter for 2 years now. The voltage always end
> >> exactly the same. The next day the pack is the pack is exactly 147
> >> volts.
>
> Martin WINLOW via EV wrote:
>> The problem I have with relying on simple pack voltage measurement
>> to control the charger is that eventually, as the pack ages, one or
>> more cells are going to go out of balance, become the 'weakest link'
>> and cause the capacity of the pack as a whole to unnecessarily
>> reduce. From a safety perspective (safety of the pack) I suppose the
>> Light-meter method is as good as any but it is the vagueness of its
>> operation that is the issue for me.
>
> When the pack is new, and if the cells are already well balanced, then
> measuring the overall voltage works.
>
> But, the cells might NOT be initially well balanced. If you bought them from
> the cheapest source, they almost certainly didn't take the time to balance
> them for you.
>
> Just because the cells are at the same voltage doesn't mean they are
> balanced. Voltage is not a good indicator of state of charge for lithium
> cells.
>
> Then, the cells are going to age. Time is not likely to improve them; instead
> it's almost certain to make them worse.
>
> Finally, consider this. You *will* use the pack until it fails! And the
> failure modes of lithium cells can be catastrophic (early destruction of an
> expensive pack, serious fires, etc.) With no BMS, nothing will detect, warn,
> or prevent disastrous failures.
>
> --
> Failure is only the opportunity to begin again more intelligently.
> -- Henry Ford
> --
> Lee Hart's EV projects are at http://www.sunrise-ev.com/LeesEVs.htm
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