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 April 15th 18, 10:18 PM posted to sci.electronics.repair
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Default Rechargeable battery question

On 4/15/2018 10:36 AM, Jeff Liebermann wrote:
On Sun, 15 Apr 2018 01:22:04 -0700, mike wrote:

I use nothing by the cheapest cells, which sucks because they usually
only have about half the capacity and lifetime of a decent cell.
However, they're cheap, and my use in mostly flashlight is not
critical.
https://www.ebay.com/sch/Rechargeable-Batteries/48619/i.html?_nkw=14500+li-ion+battery
I haven't tried this brand, but at $1/ea, it's worth trying.


Thanks, but the link takes me to page after page of cells.
Can you disclose exactly which link is the one you've verified as
reasonable cells?
Better the devil you know than to take a random shot.

I've had horrible luck with any 18650's with "ultra" or "fire" in the
name. I'd like not to repeat that with 14500's.


Sorry. I meant the link to show an example of typical LiIon batteries
of all sizes, brands, and qualities. I usually avoid making product
recommendations unless I've used or tested the product. I can't
provide a reliable source of 14500 cells because I have yet to
purchase any that I consider to be acceptable.

The problem with buying by brand name is that there are so many
counterfeit cells on the market, that chances are good that even an
honest vendor might be fooled by a disreputable distributor.
"Can you identify the fake LG HG2 18650 Battery?"
https://batterybro.com/blogs/18650-wholesale-battery-reviews/104619270-can-you-identify-the-fake-lg-hg2-18650-battery
Lots of articles on how to spot fake cells. For a while, I was having
too success by weighing the cells, but todays fakes are filled with
carefully measured amounts of sand making the fakes impossible to spot
by the weight. My best source of 18650 cells are used laptop battery
packs. The catch is that they don't have a "button top" on the +
terminal making them difficult to use in some holders.


Lotsa people recommending tiny magnets to replace the button top.
I asked about the series resistance and was assured it wasn't a problem.
I spot-weld a tab on top and fold it over until it's tall enough.

Best source for 18650 cells I've found is this:
https://www.lowes.com/pd/Kobalt-24-V...ery/1000090833

Has six 18650 cells. Only 1.5 Amp-Hours, but they're rated for 30A peak
discharge. Six for $10 is tough to beat.

If you saw the tabs in half, you can solder to the tab...if you're
quick about it.

The pack works great as a replacement for two series lead acids in my
weed whacker, but the voltage is too high for most things.
If my analysis is correct, there's no protection disconnect.
The reason the pack is cheap is that, it looks like,
they monitor the cells and send a bit stream to the tool.
The tool makes the decision about discharge protection.
The charger makes the decisions about charge protection...so it seems.
Good news is that there's a battery gauge. If you can use all 24V
and watch the gauge, you can keep from over-discharging
the cells...YMMV.

In 14500 cells, everything I've purchased on eBay has been lacking. I
haven't had time to run any discharge curves on the 14500 cells, such
as these for various 18650 cells:
http://www.learnbydestroying.com/jeffl/battery-tests/18650.jpg
I carry around a flashlight with 14500 cells that has a rather short
operating time and probably doesn't meet the printed specs.

To: John-Del
Before you run out and buy a pile of know to be good 14500 for
powering the unspecified device, I suggest you buy some cheap 14500
cells on eBay, which are sure to be inferior and possibly counterfeit.
Test the unspecified device and its charging system using cheap cells.
Once it's working, then go shopping for good batteries.

So, where to get good 14500 cells? I have no idea. I just checked
Digikey and Mouser. Nothing found.


AS I recall, there was a ban on individual cells in the US.
Don't know if it's true, but it's still a BIG liability issue
for sellers. People seem to throw in any battery that fits
and make smoke.
You can't rely on anything you read on EBAY.
You can't even buy one and test it. The next purchase of the same
part from the same vendor may be completely different.

I tried NewEgg and found the same
bogus brands as on eBay. Nitecore is probably a good (relabeled)
brand, but the price is too high:
https://www.amazon.com/TETC-1200mah-Rechargeable-Battery-charger/dp/B017IGL5HA
I found an article recommending brands:
http://www.25tobuy.com/electronics/top-9-best-14500-rechargeable-lithium-ion-batteries
but no sources. There's also the risk of buying counterfeits.

Bottom line... Sorry, I can't answer your question at this time.



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Old April 15th 18, 10:18 PM posted to sci.electronics.repair
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Default Rechargeable battery question

On Sat, 14 Apr 2018 18:56:46 -0700, mike wrote:

If there are 14 cells in series, there's a lot of opportunity
to have at least one cell reversed by the time you sense
any symptoms. Keep doing that and you'll kill 'em all eventually.


If that were true, then all the 19.2v laptop batteries, which consist
of 6 lithium ion cells in series, would also be dying from cell
reversal. I've seen dead cells in such battery packs, but usually
when the other cells are near death. It's just a question of which
cell blows up first.

You can kill series batteries several ways with cell reversal. The
most common is during discharge and charge. The problems can happen
with any chemistry if a cell is discharged to zero. Lithium Ion
batteries have battery protection circuitry (usually called a BMS or
battery management system) to prevent individual cells from dropping
below 2.7 to 3.0V which might kill the cell. Something like these:
https://www.ebay.com/itm/162735609854
https://www.ebay.com/itm/191978019369
A BMS will also protect against over voltage and over charging and
might include a charger and balancing circuit.

Keeping all the cells at the same voltage is also a problem. For
that, there is the "balanced charger" such as the Imax B6 V2 I
previously mentioned.
https://en.wikipedia.org/wiki/Battery_balancing
The battery pack has an extra connector with wired going to the
junction between adjacent cells. There are various schemes for
balancing. Most common is if the voltage across a cell is too high,
the balance charger adds some resistance across the cell to draw away
some of the charging current, so that the other cells can catch up.

Balance chargers are very common in the RC (radio control) and power
tool areas, where running unprotected LiPo batteries without BMS
boards is common.

The best strategy is to charge the cells externally in a proper
charger and put 'em
back in when you're ready to use it.


I agree, with one possible exception. The battery holders found in
consumer devices are not known for being rugged and reliable. The
springs make lousy connections, they become intermittent when banged
around, or they contacts go high resistance when an alkaline cell
leaks. This is not the best environment for precision LiIon charging.
I'm beginning to think that my suggestion of using 14500 cells in
series might be susceptible to these mechanical problems and that 5S
battery pack of 18650 cells, with welded nickel strips, and proper
XT60 connectors, might be a better choice.

There are many charging strategies, but depend heavily on
the usage patterns and actual cell configurations.


Yep. I don't know what's appropriate for a metal detector. If it's
lightly used, a single battery pack, as I mentioned above, would be
easy to remove when the device is not in use. (Anything is better
than fumbling with 14 cells, as I do with my MFJ-269 antenna analyzer.
The pack could also be charged externally. Hmmm... yet another
project.

--
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 April 15th 18, 10:50 PM posted to sci.electronics.repair
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Default Rechargeable battery question

On 4/15/2018 2:18 PM, Jeff Liebermann wrote:
On Sat, 14 Apr 2018 18:56:46 -0700, mike wrote:

If there are 14 cells in series, there's a lot of opportunity
to have at least one cell reversed by the time you sense
any symptoms. Keep doing that and you'll kill 'em all eventually.


If that were true, then all the 19.2v laptop batteries, which consist
of 6 lithium ion cells in series, would also be dying from cell
reversal.


Yet, you describe why that doesn't happen, for a protected battery pack,
in the next paragraphs.

For unmonitored series connections, the shape of the discharge
curve matters.
Lithium voltage decreases gradually. By the time you trigger
shutdown, the cells may be unbalanced, but likely not damaged.
NiMH has a flatter voltage that drops suddenly at the end.
Minor imbalance can cause one cell to drop by more than a volt
before any symptoms are visible.
For 14 in series, one cell can go from 1V to 0V with only about 7% change
in voltage.

For unmonitored devices like NiCd or NiMH cordless drills...
The speed drops, but you've got only one more hole to drill.
That last hole damages a cell. That weakened cell is the first to
go next time. Increase in self-discharge also means that if it
sits on the shelf for a month before you need it again, it
runs out of charge far faster than the other cells,
compounding the problem. Eventually it shorts. Now, all the rest get
overcharged.
I suggest that practice is why most unmonitored drill batteries fail.

I've seen dead cells in such battery packs, but usually
when the other cells are near death. It's just a question of which
cell blows up first.

Yep.

You can kill series batteries several ways with cell reversal. The
most common is during discharge and charge. The problems can happen
with any chemistry if a cell is discharged to zero. Lithium Ion
batteries have battery protection circuitry (usually called a BMS or
battery management system) to prevent individual cells from dropping
below 2.7 to 3.0V which might kill the cell. Something like these:
https://www.ebay.com/itm/162735609854
https://www.ebay.com/itm/191978019369
A BMS will also protect against over voltage and over charging and
might include a charger and balancing circuit.

Keeping all the cells at the same voltage is also a problem. For
that, there is the "balanced charger" such as the Imax B6 V2 I
previously mentioned.
https://en.wikipedia.org/wiki/Battery_balancing
The battery pack has an extra connector with wired going to the
junction between adjacent cells. There are various schemes for
balancing. Most common is if the voltage across a cell is too high,
the balance charger adds some resistance across the cell to draw away
some of the charging current, so that the other cells can catch up.

Balance chargers are very common in the RC (radio control) and power
tool areas, where running unprotected LiPo batteries without BMS
boards is common.

The best strategy is to charge the cells externally in a proper
charger and put 'em
back in when you're ready to use it.


I agree, with one possible exception. The battery holders found in
consumer devices are not known for being rugged and reliable. The
springs make lousy connections, they become intermittent when banged
around, or they contacts go high resistance when an alkaline cell
leaks. This is not the best environment for precision LiIon charging.
I'm beginning to think that my suggestion of using 14500 cells in
series might be susceptible to these mechanical problems and that 5S
battery pack of 18650 cells, with welded nickel strips, and proper
XT60 connectors, might be a better choice.

There are many charging strategies, but depend heavily on
the usage patterns and actual cell configurations.


Yep. I don't know what's appropriate for a metal detector. If it's
lightly used, a single battery pack, as I mentioned above, would be
easy to remove when the device is not in use. (Anything is better
than fumbling with 14 cells, as I do with my MFJ-269 antenna analyzer.
The pack could also be charged externally. Hmmm... yet another
project.


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Old April 16th 18, 04:05 AM posted to sci.electronics.repair
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Default Rechargeable battery question

On Sun, 15 Apr 2018 14:18:39 -0700, mike wrote:

Lotsa people recommending tiny magnets to replace the button top.
I asked about the series resistance and was assured it wasn't a problem.
I spot-weld a tab on top and fold it over until it's tall enough.


I bought an assortment of magnets to replace the button top on an
18650 cell. They're not quite the right size, but work well enough in
my various flashlights. My spot welder died and I haven't bothered to
work on its replacement. When I get something working, I'll go back
to spot welding fake button tops (made by pounding a home made die set
with a big hammer). I measured the resistance of the magnet with a
ESR meter and found the resistance to be negligible. I forgot the
exact value. Bug me if you want the numbers.

So, where to get good 14500 cells? I have no idea. I just checked
Digikey and Mouser. Nothing found.


AS I recall, there was a ban on individual cells in the US.
Don't know if it's true, but it's still a BIG liability issue
for sellers. People seem to throw in any battery that fits
and make smoke.


I hadn't heard of any such ban and couldn't find anything searching
with Google. There are various limits to how many cells can be
shipped and how they should be packages, but no ban that I could find.
https://about.usps.com/postal-bulletin/2012/pb22336/html/updt_004.htm
https://www.ups.com/assets/resources/media/us_lithium_battery_regulations.pdf
http://images.fedex.com/us/services/pdf/LithiumBattery_Overview_2018.pdf
http://www.dhl.com/en/express/shipping/shipping_advice/lithium_batteries.html
http://www.iata.org/whatwedo/cargo/dgr/Pages/lithium-batteries.aspx
http://www.batteryspace.com/Lithium-Battery-Shipping-Regulations.aspx

You can't rely on anything you read on EBAY.


I prefer "Trust, but verify".

You can't even buy one and test it. The next purchase of the same
part from the same vendor may be completely different.


Well, I bought 10 cells on eBay twice from the same vendor and
received the same junk cells twice. Like these but from a different
vendor:
https://www.ebay.com/itm/202070101554

I just realized that I don't have any 14500 data, so I dug out the
West Mountain Radio CBA-II discharge tester and ran a graph:
http://www.learnbydestroying.com/jeffl/battery-tests/14500%20SkyWolfsEye%201200.jpg
The cell is labeled 1200 ma-hr. Nominal, normal, or typical for a
14500 LiIon cell is 750 ma-hr. My test produced about 225 ma-hr
capacity, which is well below 750 ma-hr nominal. The cell is junk.

Also, there's a problem. Capacity is measured at 0.2C. For a nominal
750 ma-hr rated capacity, 0.2C would be 150 ma test current. That
would require 5 hrs to run the test. It's also well below where I
normally run these batteries in my various flashlights. Testing the
battery at operating conditions makes more sense, so I measured the
current of my cheap junk Chinese flashlight at 850 ma and ran the test
at 850 ma which would only require 1.1 hrs. If I had run it at 150
ma, it capacity would have been somewhat higher, but nowhere near the
nominal 750 ma-hr.



--
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 April 16th 18, 04:31 AM posted to sci.electronics.repair
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Default Rechargeable battery question

On 4/15/2018 8:05 PM, Jeff Liebermann wrote:
On Sun, 15 Apr 2018 14:18:39 -0700, mike wrote:

Lotsa people recommending tiny magnets to replace the button top.
I asked about the series resistance and was assured it wasn't a problem.
I spot-weld a tab on top and fold it over until it's tall enough.


I bought an assortment of magnets to replace the button top on an
18650 cell. They're not quite the right size, but work well enough in
my various flashlights. My spot welder died and I haven't bothered to
work on its replacement. When I get something working, I'll go back
to spot welding fake button tops (made by pounding a home made die set
with a big hammer). I measured the resistance of the magnet with a
ESR meter and found the resistance to be negligible. I forgot the
exact value. Bug me if you want the numbers.

So, where to get good 14500 cells? I have no idea. I just checked
Digikey and Mouser. Nothing found.


AS I recall, there was a ban on individual cells in the US.
Don't know if it's true, but it's still a BIG liability issue
for sellers. People seem to throw in any battery that fits
and make smoke.


I hadn't heard of any such ban and couldn't find anything searching
with Google. There are various limits to how many cells can be
shipped and how they should be packages, but no ban that I could find.
https://about.usps.com/postal-bulletin/2012/pb22336/html/updt_004.htm
https://www.ups.com/assets/resources/media/us_lithium_battery_regulations.pdf
http://images.fedex.com/us/services/pdf/LithiumBattery_Overview_2018.pdf
http://www.dhl.com/en/express/shipping/shipping_advice/lithium_batteries.html
http://www.iata.org/whatwedo/cargo/dgr/Pages/lithium-batteries.aspx
http://www.batteryspace.com/Lithium-Battery-Shipping-Regulations.aspx

You can't rely on anything you read on EBAY.


I prefer "Trust, but verify".

You can't even buy one and test it. The next purchase of the same
part from the same vendor may be completely different.


Well, I bought 10 cells on eBay twice from the same vendor and
received the same junk cells twice. Like these but from a different
vendor:
https://www.ebay.com/itm/202070101554

I just realized that I don't have any 14500 data, so I dug out the
West Mountain Radio CBA-II discharge tester and ran a graph:
http://www.learnbydestroying.com/jeffl/battery-tests/14500%20SkyWolfsEye%201200.jpg
The cell is labeled 1200 ma-hr. Nominal, normal, or typical for a
14500 LiIon cell is 750 ma-hr. My test produced about 225 ma-hr
capacity, which is well below 750 ma-hr nominal. The cell is junk.

Also, there's a problem. Capacity is measured at 0.2C. For a nominal
750 ma-hr rated capacity, 0.2C would be 150 ma test current. That
would require 5 hrs to run the test. It's also well below where I
normally run these batteries in my various flashlights. Testing the
battery at operating conditions makes more sense, so I measured the
current of my cheap junk Chinese flashlight at 850 ma and ran the test
at 850 ma which would only require 1.1 hrs. If I had run it at 150
ma, it capacity would have been somewhat higher, but nowhere near the
nominal 750 ma-hr.


If you use magnets you might consider grabbing the magnets out of a dead
hard drive, neodymium is IIRC the strongest fixed magnet made, and it
has very low resistance.
https://e-magnetsuk.com/neodymium_ma...teristics.aspx

What do you like for a small spot welder? I've been thinking of getting
one.



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Old April 16th 18, 08:54 AM posted to sci.electronics.repair
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On Sun, 15 Apr 2018 20:31:34 -0700, Mike S wrote:

If you use magnets you might consider grabbing the magnets out of a dead
hard drive, neodymium is IIRC the strongest fixed magnet made, and it
has very low resistance.
https://e-magnetsuk.com/neodymium_ma...teristics.aspx


Those magnets are much too big I have a fairly large pile of such
hard disk magnets that I bought at a local flea market. Very handy,
but not for making button tabs.

The magnets I bought were some of these:
https://www.ebay.com/itm/282388785539
in 6mm x 1mm and 6mm x 2mm. 1mm is a bit thin but works for most
battery holders. 2mm is a bit too thick but works ok in a few
holders. The magnets stick fairly well to the stainless battery case.
I had to punch out a few sticky back vinyl "washers" to keep the
magnets centered.

What do you like for a small spot welder? I've been thinking of getting
one.


I looked at what was available and decided that I didn't like anything
that was also affordable. So, I'm building my own. Nothing fancy.
The biggest automotive starting battery I can find (I want cold
cranking amps), a large high current relay, a less than 1 second timer
board to drive the relay, a foot switch to start the timer, some heavy
gauge wire, and some machined parts for the copper electrodes. It
didn't take much testing to determine that if I wanted to weld
something, I want DC, and to use AC if I wanted to blow a hole in
something. There are several YouTube videos describing how to throw
something together. For example:
"Simple and dirt cheap Spot Welder for lithium cells"
https://www.youtube.com/watch?v=UU7QC5Uby6M
It needs 2 electrodes, no ground clamp, and heavier gauge wire.

--
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 April 16th 18, 11:01 AM posted to sci.electronics.repair
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Default Rechargeable battery question

On 4/16/2018 12:54 AM, Jeff Liebermann wrote:

What do you like for a small spot welder? I've been thinking of getting
one.


I looked at what was available and decided that I didn't like anything
that was also affordable. So, I'm building my own. Nothing fancy.
The biggest automotive starting battery I can find (I want cold
cranking amps), a large high current relay, a less than 1 second timer
board to drive the relay, a foot switch to start the timer, some heavy
gauge wire, and some machined parts for the copper electrodes. It
didn't take much testing to determine that if I wanted to weld
something, I want DC, and to use AC if I wanted to blow a hole in
something. There are several YouTube videos describing how to throw
something together. For example:
"Simple and dirt cheap Spot Welder for lithium cells"
https://www.youtube.com/watch?v=UU7QC5Uby6M
It needs 2 electrodes, no ground clamp, and heavier gauge wire.

Stable/controlled pressure is very important.
You can make a serviceable electrode pair from a small arbor press
and some hobby store brass. I use #6 solid copper wire for the
electrode and a file
to shape the end. The trick is to make sure that the current doesn't
go thru any part of the probe actuation assembly.
I could put up some pix if anybody cares.

You need a lot of energy in a short time to melt the nickel without
overheating the bottom of the cell. At the risk of repeating myself,
the secret is to use an energy pulse, not a current or voltage pulse.

I started with a microwave transformer and some logic to count full
cycles of 60 Hz. to keep the transformer from saturating arbitrarily.
I used 4-6 cycles for a weld. If you try to do it without the full
cycle counter, the transformer ends up at some arbitrary point on
the B-H curve and saturation effects can raise havoc with your welds.
Repeatability was horrible.
I could make some very nice welds, but not enough in a row to make
a battery pack.
Starting the pulse at a zero crossing and counting cycles improved
repeatability dramatically, but it was still crap.
Problem is the low voltage is very intolerant of contact resistance
variation.

I tried discharging a cap, but at the time, I didn't have anything
that would switch the required current. And I didn't have a
storage scope so I could see what I was doing. Turns out that it's
harder than I thought to instrument a welder. When the pulse fires,
everything on the bench jumps. Getting a scope to trigger on
a specific part of the waveform was just wishful thinking.

I tripped over a Unitek CD welder for $17 shipped on EBAY and snapped it up.
It can put 7V across a milliohm. Welds got instantly very much more
repeatable. Since it's an energy pulse rather than a current pulse,
it's much more tolerant of resistance variations.
It's only 125 Watt-Seconds, so it works great on thin nickel for low
current stuff. It won't weld the thick links for high current stuff.

Turns out that hobby store brass sheet can be cut into battery tabs.
It welds very easily. I wouldn't use it for anything high current tho.


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Default Rechargeable battery question

On 4/16/2018 3:01 AM, mike wrote:
On 4/16/2018 12:54 AM, Jeff Liebermann wrote:

What do you like for a small spot welder? I've been thinking of getting
one.


Forgot to mention that rebuilding battery packs rarely works these days.
Back in the NiCD days, there was a chance.
With Lithiums, not so much.

IF you remove the battery, the protection chip goes into disabled mode.
Even if the cells are good, the laptop won't work.
I only succeeded on ONE Lithium battery pack because it used a PIC
processor and I was lucky that resetting the PIC restored control.

I haven't tried, but I expect the same applies for Lithium cordless tools
and most everything else.

That's not a problem for this thread, but might influence your
motivation for building a welder.

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Old April 16th 18, 12:21 PM posted to sci.electronics.repair
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Default Rechargeable battery question

On 4/16/2018 6:01 AM, mike wrote:
...
Turns out that hobby store brass sheet can be cut into battery tabs.
It welds very easily.* ...


Since the brass melts at a much lower temperature than the
nickel/stainless steel, is it actually a weld (both metals melted)? Or
is it more of a braze, with only the brass melted?
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Old April 16th 18, 05:11 PM posted to sci.electronics.repair
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Default Rechargeable battery question

On 4/16/2018 4:21 AM, Bob Engelhardt wrote:
On 4/16/2018 6:01 AM, mike wrote:
...
Turns out that hobby store brass sheet can be cut into battery tabs.
It welds very easily. ...


Since the brass melts at a much lower temperature than the
nickel/stainless steel, is it actually a weld (both metals melted)? Or
is it more of a braze, with only the brass melted?

You can pick all the nits you want.
It makes the connection.


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