Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems.

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Old November 14th 17, 08:22 PM posted to sci.electronics.repair
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Default 2P 18650 pack went open circuit.

Just curious about the failure mode - the cells really weren't worked that
hard.

Thanks.


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Old November 14th 17, 10:32 PM posted to sci.electronics.repair
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Default 2P 18650 pack went open circuit.

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?
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Old November 14th 17, 10:44 PM posted to sci.electronics.repair
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Default 2P 18650 pack went open circuit.



"mike" wrote in message
news
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.

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Old November 15th 17, 02:39 AM posted to sci.electronics.repair
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Default 2P 18650 pack went open circuit.

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


"mike" wrote in message
news
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?
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Old November 15th 17, 06:09 AM posted to sci.electronics.repair
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Default 2P 18650 pack went open circuit.

On Tue, 14 Nov 2017 19:22:17 -0000, "Ian Field"
wrote:

Just curious about the failure mode - the cells really weren't worked that
hard.


Here's how to fix it:
https://www.youtube.com/watch?v=IhUtKvCV6fs
https://www.youtube.com/watch?v=1w3Tv1Jg0ps
https://www.youtube.com/watch?v=AWmu3U7tndA
https://www.youtube.com/watch?v=YOi0hepEtYo
Something may have shorted one or both cells.

If you're having problems charging cells which exhibit low terminal
voltage (under about 2.5v), try this:
https://www.youtube.com/watch?v=tbEfhPbqTDE

--
Jeff Liebermann
150 Felker St #D
http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558


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Old November 15th 17, 03:52 PM posted to sci.electronics.repair
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Default 2P 18650 pack went open circuit.

On 11/15/2017 12:09 AM, Jeff Liebermann wrote:
...
If you're having problems charging cells which exhibit low terminal
voltage (under about 2.5v), try this:
https://www.youtube.com/watch?v=tbEfhPbqTDE


I came away with this clever tip: use small magnets to hold test leads
to the ends of cells.
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Old November 15th 17, 07:00 PM posted to sci.electronics.repair
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Default 2P 18650 pack went open circuit.

On Wed, 15 Nov 2017 09:52:00 -0500, Bob Engelhardt
wrote:

On 11/15/2017 12:09 AM, Jeff Liebermann wrote:
...
If you're having problems charging cells which exhibit low terminal
voltage (under about 2.5v), try this:
https://www.youtube.com/watch?v=tbEfhPbqTDE


I came away with this clever tip: use small magnets to hold test leads
to the ends of cells.


Yep. However, I suspect that may have been an accidental discovery.
When one salvages 18650 cells from a laptop battery pack, the
resulting cells do not have a projecting button top on the positive
electrode. Getting such a cell to make a proper connection in a
battery holder or flashlight is problematic. So, someone determined
that a tiny magnet will stick to the positive terminal and provide a
suitable button top contact (and test lead connection):
https://www.ebay.com/itm/New-15pcs-Battery-Magnet-Spacer-Convert-Flat-to-Button-Top-All-Lithium-ion-/282548150944

--
Jeff Liebermann
150 Felker St #D
http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558
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Old November 15th 17, 07:44 PM posted to sci.electronics.repair
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Default 2P 18650 pack went open circuit.



"mike" wrote in message
news
On 11/14/2017 1:44 PM, Ian Field wrote:


"mike" wrote in message
news
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



Yes - a tact switch salvaged from the front panel of a Sky box.

You're saying that the shunt regulator failing open can't harm the
battery?


It helps if you read before replying.

A shunt regulator failing short circuit (the most likely fault) wouldn't do
the battery any good at all - A SB diode in the feed makes that accident
unlikely.


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Old November 15th 17, 07:52 PM posted to sci.electronics.repair
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Default 2P 18650 pack went open circuit.



"Jeff Liebermann" wrote in message
...
On Tue, 14 Nov 2017 19:22:17 -0000, "Ian Field"
wrote:

Just curious about the failure mode - the cells really weren't worked that
hard.


Here's how to fix it:
https://www.youtube.com/watch?v=IhUtKvCV6fs
https://www.youtube.com/watch?v=1w3Tv1Jg0ps


Every day is a school day.

I might have to rummage those cells out of the bin and do an autopsy - but
conscious enough of potential hazards to not bother re using them though.

Plenty replacements to hand, I just assembled another battery pack - but
that seems to answer my question; what happened.

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Old November 16th 17, 12:21 AM posted to sci.electronics.repair
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Posts: 1,129
Default 2P 18650 pack went open circuit.

On 11/15/2017 10:00 AM, Jeff Liebermann wrote:
On Wed, 15 Nov 2017 09:52:00 -0500, Bob Engelhardt
wrote:

On 11/15/2017 12:09 AM, Jeff Liebermann wrote:
...
If you're having problems charging cells which exhibit low terminal
voltage (under about 2.5v), try this:
https://www.youtube.com/watch?v=tbEfhPbqTDE


I came away with this clever tip: use small magnets to hold test leads
to the ends of cells.


Yep. However, I suspect that may have been an accidental discovery.
When one salvages 18650 cells from a laptop battery pack, the
resulting cells do not have a projecting button top on the positive
electrode. Getting such a cell to make a proper connection in a
battery holder or flashlight is problematic. So, someone determined
that a tiny magnet will stick to the positive terminal and provide a
suitable button top contact (and test lead connection):
https://www.ebay.com/itm/New-15pcs-Battery-Magnet-Spacer-Convert-Flat-to-Button-Top-All-Lithium-ion-/282548150944

Or you can get the ones not specified as battery extenders
https://www.ebay.com/itm/N35Super-St..._i4k 0pOrvRVw
for 3-cents each in hundreds.

If you get some square magnets, you can wrap a piece of battery tab
material around them. Leave some sticking out so you can
solder a wire or put a clip on it. Works for charging all types
of batteries with magnet-attractive connection points. And the current
doesn't go through the magnet or depend on the surface plating.



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