battery protection components

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In a non-smart Lithium battery used in an oscilloscope.

BV3P1N SOP8 body - some kind of fet used back-back in series.

CGH1 SOT23 6pin possibly an undervoltage controller.

Any accurate info out there? At present the scope firmware interacts
with the battery at end of charge in a potentially life-shortening and
demonstrably firmware-corrupting manner.

No access to scope firmware....

RL

Re: battery protection components

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Usually the protection cuts discharging below 2.4V and charging above  
4.3 volts, with some temperature compensation.  A PTC fuse limits  
current.  There's nothing else to it - it's strictly for momentary fault  
protection.

An old battery may have a high impedance that's triggering firmware  
bugs.  Fancy chargers have a lockout timer for restarting a charge cycle  
to prevent constant top-offs of a failed battery that no longer appears  
to be charged.

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Re: battery protection components
On Sat, 12 Sep 2015 22:16:03 -0700, Kevin McMurtrie

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I expect these to be fairly simple devices, but need more accurate
info on what thresholds are expected, and method used to introduce
hysterisis etc.

This is a brand-dedicated series/parallel pack that expects ~constant
voltage charge limit ~ another issue of this end-use. Thermal fuse is
present (no ptc).

Even new packs have the same issue at end of discharge in these
scopes, though with less bizarre symptoms. Aim is to prevent firmware
from tripping over itself, even if it means external rework in
hardware.  

Batteries become 'aged' fairly rapidly under the circumstances, with
capacity halved in the first year, but they don't require a remote
depot servicing at inconvenient times, as a result.

RL

Re: battery protection components
Once upon a time on usenet Kevin McMurtrie wrote:
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4.2v is a better cutoff voltage for lithium cells, most are specced for  
4.2v. Charging to 4.3 will halve the life of the cells and only slightly  
increase capacity. (4.1v will increase cell life by about 20% but reduce  
stored energy by about 15%.)
--  
Shaun.

"Humans will have advanced a long, long way when religious belief has a cozy  
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Re: battery protection components

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The protection circuit is only for momentary faults, like a short to 0V  
or a high unregulated voltage.  I've never seen one that provides  
continuous protection.

From what I've read, 4.1 volts (temperature compensated) is the only  
safe trickle voltage and it never produces a full charge.  I'm using a  
pair of LTC4070 for a pair of solar charged LiPo cells.  So far, no  
explosion.

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Re: battery protection components
On Mon, 14 Sep 2015 22:30:32 -0700, Kevin McMurtrie

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The charging isn't the immediate issue, its interaction with the
hardware at end of charge I'm looking at, hence need for info on
internal UVLO circuit (assumed) components.

CGH1 SOT23 6pin

This is a series/parallel pack with trickle voltage speced at 8V4.
If charging is aging the cells prematurely, it would only mean that
EOC conditions were reached more often.

Distinct odor of outgassing from these devices, when plugged in, so
the charging circuit will need some looking into.

RL

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