2P 18650 pack went open circuit.

[Ian Field]

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

Thanks.

[mike]

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

[Ian Field]

"mike" <ham...@netzero.net> wrote in message
news:oufnf8$oh8$1...@dont-email.me...

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.

[mike]

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?

[Jeff Liebermann]

On Tue, 14 Nov 2017 19:22:17 -0000, "Ian Field"
<gangprobi...@virginmedia.com> 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 je...@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

[Bob Engelhardt]

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.

[Jeff Liebermann]

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>

[Ian Field]

"mike" <ham...@netzero.net> wrote in message

news:oug5uk$l7h$1...@dont-email.me...

> On 11/14/2017 1:44 PM, Ian Field wrote:
>>
>>
>> "mike" <ham...@netzero.net> wrote in message
>> news:oufnf8$oh8$1...@dont-email.me...
>>> 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.

[Ian Field]

"Jeff Liebermann" <je...@cruzio.com> wrote in message
news:9kin0d5cmed4i9gng...@4ax.com...

> On Tue, 14 Nov 2017 19:22:17 -0000, "Ian Field"
> <gangprobi...@virginmedia.com> 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.

[mike]

On 11/15/2017 10:00 AM, Jeff Liebermann wrote:
> On Wed, 15 Nov 2017 09:52:00 -0500, Bob Engelhardt
> <BobEng...@comcast.net> 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-Strong-Round-Disc-10x1mm-10x2mm-Magnets-Rare-Earth-Neodymium-N35/361874792648?hash=item54416b20c8:m:mVwQlu9k6vO_i4k0pOrvRVw
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.

[mike]

I wouldn't put a lot of faith in the assumption that your regulator
won't fail open. I suggest that a bad solder joint might be more likely
than an actual component failure.

The diode also solves the problem of disconnecting the power source while
the battery is connected.
>
>
But it adds another failure mode. A shorted diode will cause the battery
voltage to exceed the safe max voltage. I'd also worry about the forward
voltage vs forward current curve for the exact diode you're using.
Depending on the charging current and the capability of your diode
heat sink, the junction temperature might get well above ambient
and need to be considered.
A diode conducts all the way to zero volts. It's easy to assume that
the current is small enough to be ignored, but VERIFY that's the
case in your application. Look at the curves for your diode over
temperature. What's the maximum battery voltage if you left it
on charge for a week.

If you want to charge it as quickly as possible to the highest
capacity, typically 4.2V depending on chemistry, you might find
that it's not possible to do safely with a diode inline. Backing
the max voltage off 200mV to be safer seriously impacts run time,
but it's probably a good idea.

Another alternative is to set your shunt regulator to 4.2V and put
a resistor across the diode. You get quickly to 3.9V or so. Takes
longer for full charge but can be much safer.

Lithium batteries are usually charged right up near the destruction
limit. There isn't much margin for error.
If you have a limited supply of paranoia, charging lithium batteries
is a good place to allocate some.

[Jeff Liebermann]

On Wed, 15 Nov 2017 18:52:06 -0000, "Ian Field"

<gangprobi...@virginmedia.com> wrote:

>
>
>"Jeff Liebermann" <je...@cruzio.com> wrote in message
>news:9kin0d5cmed4i9gng...@4ax.com...
>> On Tue, 14 Nov 2017 19:22:17 -0000, "Ian Field"
>> <gangprobi...@virginmedia.com> 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.

That's another variation on my "Learn by Destroying". If you haven't
destroyed it, you don't understand it. My skool education was very
much like that. I would break something, and then take it apart to
see how it works. The skool would frown upon me taking apart
something that was still working, but offered little resistance if I
took apart something that was broken.

>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.

Bin? Don't you have a local recycling facility that takes batteries?

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

It might answer what happened, but not why. I've had brand new
battery packs, assembled by a reputable and experienced rebuilder,
trip the protector for no obvious reason. I recently had one go open
circuit during charging, which might offer a clue.

[Jeff Liebermann]

On Wed, 15 Nov 2017 15:21:44 -0800, mike <ham...@netzero.net> wrote:

>On 11/15/2017 10:00 AM, Jeff Liebermann wrote:
>> On Wed, 15 Nov 2017 09:52:00 -0500, Bob Engelhardt
>> <BobEng...@comcast.net> 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-Strong-Round-Disc-10x1mm-10x2mm-Magnets-Rare-Earth-Neodymium-N35/361874792648>

>for 3-cents each in hundreds.

Nice price. However, 10mm wide is MUCH too large for a button top
replacement. The eBay offering did not mention the size, but
measuring the one's I'm using produced:
6mm diameter x 0.84 mm thick.

Measuring the normal size of the stock button top on a typical 18650
cell, I get:
6mm diameter at the base x 2.5 mm thick.

>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.

I don't have much of a problem with current going through the magnet.
Perhaps if I were using the cells for a high discharge application,
but not for the typical small flashlight (about 1 amp) or E cigarette
application (about 2 amps max).

My ESR meter is in my office so I can't measure the resistance of the
battery right now. I'll try to remember to check tomorrow.

[mike]

On 11/15/2017 7:56 PM, Jeff Liebermann wrote:

>> Or you can get the ones not specified as battery extenders
>> https://www.ebay.com/itm/N35Super-Strong-Round-Disc-10x1mm-10x2mm-Magnets-Rare-Earth-Neodymium-N35/361874792648>
>> for 3-cents each in hundreds.
>
> Nice price. However, 10mm wide is MUCH too large for a button top
> replacement. The eBay offering did not mention the size, but
> measuring the one's I'm using produced:
> 6mm diameter x 0.84 mm thick.
>
> Measuring the normal size of the stock button top on a typical 18650
> cell, I get:
> 6mm diameter at the base x 2.5 mm thick.

click the size selector on that page.

[Jeff Liebermann]

Thanks. I missed that. Looks like 6mm x 1mm is available very cheap.
1pc for $1.08 and 100 pcs for $2.99.
I just ordered 100 each of 6mm dia x 1mm and 2mm thick magnets. Total
price was $7.01 (which was about what I paid for 10 magnets from the
previous vendor).

I managed to lose the magnet that I was measuring. It's probably
stuck to something on my desk, but I can't find it. Grumble.

[Ian Field]

"Jeff Liebermann" <je...@cruzio.com> wrote in message

news:ld1q0dht5jcs0ga8m...@4ax.com...

> On Wed, 15 Nov 2017 18:52:06 -0000, "Ian Field"
> <gangprobi...@virginmedia.com> wrote:
>
>>
>>
>>"Jeff Liebermann" <je...@cruzio.com> wrote in message
>>news:9kin0d5cmed4i9gng...@4ax.com...
>>> On Tue, 14 Nov 2017 19:22:17 -0000, "Ian Field"
>>> <gangprobi...@virginmedia.com> 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.
>
> That's another variation on my "Learn by Destroying". If you haven't
> destroyed it, you don't understand it. My skool education was very
> much like that. I would break something, and then take it apart to
> see how it works. The skool would frown upon me taking apart
> something that was still working, but offered little resistance if I
> took apart something that was broken.

The first powerbank I bought got destroyed by my curiosity - the second
donated its PCB to an LED bicycle light that I converted to lithium. Just
bought another to sit on the shelf just in case.

>>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.
>
> Bin? Don't you have a local recycling facility that takes batteries?
>
>>Plenty replacements to hand, I just assembled another battery pack - but
>>that seems to answer my question; what happened.
>
> It might answer what happened, but not why. I've had brand new
> battery packs, assembled by a reputable and experienced rebuilder,
> trip the protector for no obvious reason. I recently had one go open
> circuit during charging, which might offer a clue.

I suspect the charger - but it hasn't damaged any of the other batteries
rotated through it.

The cell I peeled had what looked like a popper disc in the top, but it was
malleable instead of springy - I suspect "resetting" it would compromise
safety.

[Wayne Chirnside]

If the battery has a protection circuit built in, you can tell by the dark
band at the negative terminal and a strip up the side to
the positive it will trip at something under 3 volts and refuse a charge
for safety sake.

You can put a very low current limited charge into the to get
them up to around 3.2 - 3.4 volts then and only then will
a lithium battery charger ( a proper one) attempt to charge it.

[Jeff Liebermann]

On Wed, 15 Nov 2017 19:56:22 -0800, Jeff Liebermann <je...@cruzio.com>
wrote:

>My ESR meter is in my office so I can't measure the resistance of the
>battery right now. I'll try to remember to check tomorrow.

I don't think there's a problem with pushing current through the
magnet if there is enough spring pressure on the contacts.

The 6mm dia x 1mm thick magnets show about 0.02 ohms measured with the
original Bob Parker ESR meter. It was fairly difficult getting a good
connection which required using two strips of nickel flat wire to get
a decent connection. I also had to apply some pressure to get a
reliable connection to the meter probes. Even so, the resistance
never climbed over about 0.30 ohms.

>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.

I don't have any square magnets and most everything that I could find
in the right size on eBay is round, but I'm sure they exist.

I'm (slowly) building a better spot welder suitable for welding tabs
onto batteries. I plan to buy some flat nickel wire at about 10 mm
width, and make replacement button tops in a small bench press, which
would then be spot welded to the top of recycled batteries.

Or, I could be crude, and just spot weld one end of a nickel strip to
the battery, and zig-zag the strip to simulate the button top. With
luck, it might act as a spring.

Sigh... yet another project.

[mike]

On 11/17/2017 10:13 AM, Jeff Liebermann wrote:
> On Wed, 15 Nov 2017 19:56:22 -0800, Jeff Liebermann <je...@cruzio.com>
> wrote:
>
>> My ESR meter is in my office so I can't measure the resistance of the
>> battery right now. I'll try to remember to check tomorrow.
>
> I don't think there's a problem with pushing current through the
> magnet if there is enough spring pressure on the contacts.
>
> The 6mm dia x 1mm thick magnets show about 0.02 ohms measured with the
> original Bob Parker ESR meter. It was fairly difficult getting a good
> connection which required using two strips of nickel flat wire to get
> a decent connection. I also had to apply some pressure to get a
> reliable connection to the meter probes. Even so, the resistance
> never climbed over about 0.30 ohms.

That was my concern. I could not get a reliable connection, as mesured
by a VOM, with casual contact to the magnet. I had to use pointy probes
and press very hard.

>> 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.
>
> I don't have any square magnets and most everything that I could find
> in the right size on eBay is round, but I'm sure they exist.

I'm not recommending square magnets for contact extenders in use.
Problem I solved was the lack of battery holders for charging cells.
If you wrap battery tab strips around the magnet, you can stick it
on any cell connection that's magnetic. The square magnet self-centers
in the rectangular cavity you created in the tab material.
Also works on most of the
power tool batteries that I have.

>
> I'm (slowly) building a better spot welder suitable for welding tabs
> onto batteries.

I'd be interested in your welder experiments.
I have a small arbor press with a 1/2" arbor. Turns out that a 1/2"
copper pipe cap fits nicely over the end. I soldered a circuit board to it
that holds spring-loaded contacts made from square brass tubing
and tips made of big copper wire. Gives some consistency to applied
pressure.

Bigger problem was consistency of applied energy.
I tried to use a microwave transformer.
I have some tips for dramatically increasing the reliability
of the weld from "useless" to marginally acceptable...sometimes,
if anybody's interested.

I tried discharging caps.
I could get some very nice welds, but the consistency was abysmal.
Don't think I ever built a battery pack with 100% good welds.
The voltage was just too low. Tiny variations in contact resistance
created MAJOR variations in weld quality.

I tripped over a small CD spot welder on ebay for cheap.
The thing delivers a pulse of energy, so it's much more tolerant
of contact resistance. It can put 7000 amps into a milliohm.
That terminated my work on the microwave transformer welder.

There are some relatively cheap CD spot welders on ebay.
I looked into a few of them. Although I never got any real info,
I surmised that they're still trying to switch relatively low
voltages.
A real CD spot welder switches 600V or so into a stepdown transformer.
I think the magic is in the design of the transformer.

I plan to buy some flat nickel wire at about 10 mm
> width, and make replacement button tops in a small bench press, which
> would then be spot welded to the top of recycled batteries.
>
> Or, I could be crude, and just spot weld one end of a nickel strip to
> the battery, and zig-zag the strip to simulate the button top. With
> luck, it might act as a spring.

That's what I do. If the cell was removed from a pack, there's already
enough tab left to fold over for a tip. You don't really need to zig-zag
it, just fold it over once and put a blob of solder underneath to raise
it to the desired height. Soldering the blob on both sides reduces the
resistance,
but risks overheating the cell top.

Zig-zag just gives it more opportunity to
fold to the side and cause problems. If you need a spring, it's often
part of the battery holder.

Hobby stores sell sheets of brass that can be cut to any size/shape.
Very easy to weld. I wouldn't use 'em in high current applications,
but they can work well at low current.
>
> Sigh... yet another project.
>

[Jeff Liebermann]

On Fri, 17 Nov 2017 12:18:42 -0800, mike <ham...@netzero.net> wrote:

>That was my concern. I could not get a reliable connection, as mesured
>by a VOM, with casual contact to the magnet. I had to use pointy probes
>and press very hard.

I did ok with points, the for higher currents, a flat surface with
many points of contact is better. This is my test fixture for
discharge testing various cells. The clamp is plastic so insulation
is not a problem:
<http://www.learnbydestroying.com/jeffl/LiPo/Ultrafire%2018650%20test.jpg>

>I'm not recommending square magnets for contact extenders in use.
>Problem I solved was the lack of battery holders for charging cells.
>If you wrap battery tab strips around the magnet, you can stick it
>on any cell connection that's magnetic. The square magnet self-centers
>in the rectangular cavity you created in the tab material.

Ok, that should work. Where did you find a small enough square shaped
magnet?

>Also works on most of the
>power tool batteries that I have.

For power tools, I use the spot welder. I tried battery holders only
once. The vibration from the tool caused are rather interesting form
of intermittent connection.

>> I'm (slowly) building a better spot welder suitable for welding tabs
>> onto batteries.
>
>I'd be interested in your welder experiments.

It's nothing special. Cazapitor discharge systems are ok, but I think
I can do as well with a LiIon (or LiPo) battery for power storage. My
big worry is that as the battery discharges, the energy delivered to
the weld will decrease. So, I'm trying to measure the current and
adjust the duration accordingly. I don't have this part working yet.

Another nice thing about using a battery instead of CD is that I can
spot weld as fast as I can push the foot switch. I don't need to wait
for the cazapitor to charge. At this time, it's just a simple eBay
timer board driving a automobile starter relay controlled by a foot
switch.
<https://www.ebay.com/itm//111983136980>
It took about 3 weeks to arrive. The starter relays I bought surplus
many years ago. Get the biggest you can find. I'll post photos when
I get something that's reliable.

>I have a small arbor press with a 1/2" arbor. Turns out that a 1/2"
>copper pipe cap fits nicely over the end. I soldered a circuit board to it
>that holds spring-loaded contacts made from square brass tubing
>and tips made of big copper wire. Gives some consistency to applied
>pressure.

I use two 1/4" copper rods mounted on drilled fiberglass insulators.

>Bigger problem was consistency of applied energy.
>I tried to use a microwave transformer.
>I have some tips for dramatically increasing the reliability
>of the weld from "useless" to marginally acceptable...sometimes,
>if anybody's interested.
>
>I tried discharging caps.
>I could get some very nice welds, but the consistency was abysmal.
>Don't think I ever built a battery pack with 100% good welds.
>The voltage was just too low. Tiny variations in contact resistance
>created MAJOR variations in weld quality.
>
>I tripped over a small CD spot welder on ebay for cheap.
>The thing delivers a pulse of energy, so it's much more tolerant
>of contact resistance. It can put 7000 amps into a milliohm.
>That terminated my work on the microwave transformer welder.
>
>There are some relatively cheap CD spot welders on ebay.
>I looked into a few of them. Although I never got any real info,
>I surmised that they're still trying to switch relatively low
>voltages.
>A real CD spot welder switches 600V or so into a stepdown transformer.
>I think the magic is in the design of the transformer.

I think the secret is in the ESR or internal resistance of the power
source. New quality LiIon cells run about 150-400 mohms (milli-ohms).
Older cells and eBay crap batteries are much higher. The series
connectors, switch, SCR, wire, probes, and relay all add to the series
resistance.

>> Or, I could be crude, and just spot weld one end of a nickel strip to
>> the battery, and zig-zag the strip to simulate the button top. With
>> luck, it might act as a spring.
>
>That's what I do. If the cell was removed from a pack, there's already
>enough tab left to fold over for a tip. You don't really need to zig-zag
>it, just fold it over once and put a blob of solder underneath to raise
>it to the desired height. Soldering the blob on both sides reduces the
>resistance,
>but risks overheating the cell top.

I do ok with soldering to NiCd and NiMH cells. However, LiIon cells
are stainless steel and difficult solder. With enough flux, I can do
a tolerable job. However, I tend to overheat the cell trying to get a
decent connection, which is both dangerous and irritating when the
battery pack eventually fails.

>Zig-zag just gives it more opportunity to
>fold to the side and cause problems. If you need a spring, it's often
>part of the battery holder.
>
>Hobby stores sell sheets of brass that can be cut to any size/shape.
>Very easy to weld. I wouldn't use 'em in high current applications,
>but they can work well at low current.
>>
>> Sigh... yet another project.
>>

[~misfit~]

I used to do that until one part-unfolded as I put a cell into my favourite
flashlight, shorted against part of the top of the flashlight referenced to
negative and and cooked the switch into oblivion. :-/

> Sigh... yet another project.

I know the feeling.
--
Shaun.

"Humans will have advanced a long, long way when religious belief has a cozy
little classification in the DSM*."
David Melville (in r.a.s.f1)
(*Diagnostic and Statistical Manual of Mental Disorders)

[Ian Field]

"~misfit~" <shaun.at...@gmail.com> wrote in message
news:ove4i0$64a$1...@dont-email.me...

If I have to - I tin a m3 nut and solder it on. some applications have a
contact spring at both ends, so it isn't an issue.

[mike]

You can reduce that by coiling the strip in the direction that reduces
the length of unsupported strip. Coil can't fold over as easily.

[~misfit~]

Yep, I've got it sussed now thanks.

[~misfit~]

I'm always a bit shy about soldering onto a cell - worried I'll cook it.
That's why I left the nickel strip on in the first place, so it'd be there
if I needed to solder the cell somewhere.

[Ian Field]

"~misfit~" <shaun.at...@gmail.com> wrote in message

news:p1o1uc$5km$2...@dont-email.me...

The bus strip is a little more thermal resistance on the way to the cell.

A strong active flux helps make the joint quickly so damage is minimised.

[~misfit~]

Cheers,