Cruisin via EV<ev@lists.evdl.org> 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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