On 11/14/2017 1:44 PM, Ian Field wrote:


"mike" wrote in message
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On 11/14/2017 11:22 AM, Ian Field wrote:
Just curious about the failure mode - the cells really weren't worked
that hard.

Thanks.
You're gonna have to be a LOT more descriptive about the 'pack'.
passive/active/protected?
What did it power?

Just a bare 2P 18650 pack powering an e-cig with a 1 Ohm coil.

The only electronics is a power MOSFET where there used to be a
microswitch for the fire button.

Charging is controlled by a shunt regulator, there is a feed SB diode so
the shunt failing short can't harm the battery.

That seems to contradict the statement the the only electronics is the
MOSFET. I don't know what to make of that... And something has to
control the MOSFET

You're saying that the shunt regulator failing open can't harm the battery?
You're saying that the SB diode, guessing that it's a series diode
from regulator to cells, can't fail short and harm the battery?

The 18650 cells they put in cordless drills can do 30 amps each.
The cells you get on ebay for cheap may not like 4 amps at all.


Assuming this is a commercial battery pack and not
something you cobbled together.
Assuming that the cells are bare unprotected cells.
Assuming that you're measuring the cells directly at the cells and they
are open.

There's not much that can go wrong.
There's typically a pressure switch inside the cell that opens
if the pressure gets too high or the positive terminal gets too hot.

Some people believe that you can take random cells, solder wires
on 'em and you're good to go. That dramatically increases the
failure rate, assuming you don't set them on fire while soldering.

I'm not a smoker, but it's hard to imagine a successful e-cig
that's as big as a pair of 18650's.
Is there more to the story?