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High drain NiCd - Sub C batteries for power tools (strapping tool)
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John Muchow
science forum beginner


Joined: 04 Apr 2005
Posts: 9

PostPosted: Tue Oct 18, 2005 9:39 am    Post subject: Re: High drain NiCd - Sub C batteries for power tools (strapping tool) Reply with quote

Quote:
thank you very much, I will substitute the stainless steel strips
(70microOhm.cm) and use nickel strips (much lower resistivity ~
8-10microOhm.cm) and see if this helps, if not, I will try soldering
them with Tin and will keep you updated Smile

Double-up on the strips. Every little bit helps. Smile
If you end up soldering the cells, be careful. It's very hard to do
right without damaging the cell. Lots of instruction on the Web
though. Use "battery bars" instead of the strips. They're thick
copper or silver-plated copper bars and when soldered on significantly
reduce the inter-cell resistances compared to spot-welded strips.

Quote:
What is the internal resistance of this IB3600 cells ? The ones I use
are around 7-8 mOhm
Around 2mOhm. But, if the Titanium cells are truly 7-8mOhm cells at

30A discharge over the entire useful discharge curve, then the problem
is definitely the tabs you're using for inter-cell connections.

John Muchow
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Jim Higgins
science forum beginner


Joined: 19 Jun 2005
Posts: 36

PostPosted: Wed Oct 19, 2005 6:04 pm    Post subject: Re: High drain NiCd - Sub C batteries for power tools (strapping tool) Reply with quote

On Tue, 18 Oct 2005 09:39:06 GMT, John <jmuchow@SPAMMENOTcamlight.com>
wrote:

Quote:
thank you very much, I will substitute the stainless steel strips
(70microOhm.cm) and use nickel strips (much lower resistivity ~
8-10microOhm.cm) and see if this helps, if not, I will try soldering
them with Tin and will keep you updated :)

Double-up on the strips. Every little bit helps. Smile
If you end up soldering the cells, be careful. It's very hard to do
right without damaging the cell. Lots of instruction on the Web
though. Use "battery bars" instead of the strips. They're thick
copper or silver-plated copper bars and when soldered on significantly
reduce the inter-cell resistances compared to spot-welded strips.

What is the internal resistance of this IB3600 cells ? The ones I use
are around 7-8 mOhm
Around 2mOhm. But, if the Titanium cells are truly 7-8mOhm cells at
30A discharge over the entire useful discharge curve, then the problem
is definitely the tabs you're using for inter-cell connections.


Yes, but bear this in mind. With an internal resistance of 7.5 mOhm
you will drop 0.23 volts per cell across the internal resistance of
the cells alone. That's a *BIG* drop for a Ni-Cd or Ni-MH cell. The
tabs just make an already bad situation worse.

Sounds to me like the device needs to be powered by a larger cell with
a lower internal resistance in addition to using lower resistance
tabs. OTOH, if the mfgr selected the tab resistance and maybe also
the cell internal resistance to control peak current, optimizing
either may damage the device.

I've missed out on most of this thread. If the changes are meant to
increase run time between charges, and especially if they are meant to
make up for the performance of older weaker cells, I think they may be
ill advised.
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John Muchow
science forum beginner


Joined: 04 Apr 2005
Posts: 9

PostPosted: Wed Oct 19, 2005 7:03 pm    Post subject: Re: High drain NiCd - Sub C batteries for power tools (strapping tool) Reply with quote

Good point about run time vs. limiting peak current. Hannes will have
to jump in on that one but it seemed like run time was the problem.

I was recommending a 2mOhm internal resistance cell to replace the one
he is currently using (and which is not working well for him with a IR
of 7-8mOhm.
John Muchow
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Jim Higgins
science forum beginner


Joined: 19 Jun 2005
Posts: 36

PostPosted: Thu Oct 20, 2005 3:02 pm    Post subject: Re: High drain NiCd - Sub C batteries for power tools (strapping tool) Reply with quote

On Wed, 19 Oct 2005 19:03:34 GMT, John <jmuchow@SPAMMENOTcamlight.com>
wrote:

Quote:
Good point about run time vs. limiting peak current. Hannes will have
to jump in on that one but it seemed like run time was the problem.

I was recommending a 2mOhm internal resistance cell to replace the one
he is currently using (and which is not working well for him with a IR
of 7-8mOhm.

That much I did understand. Wink To clarify - I think you gave good
advice in direct response to a request, but it strikes me the
recipient of the advice probably shouldn't be wanting to do what he
wants to do the way he's talking about doing it.

If the strapping device doesn't run long enough on a battery pack,
either the pack is weak, the duty cycle exceeds the design limits of
the chosen strapper, or some other similar reason that points to
replacing the battery packs or the strappers, not redesigning the
packs.

And if the strappers work fine and last long on new packs, then ekeing
out a bit more performance from old weak packs is false economy.
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John Muchow
science forum beginner


Joined: 04 Apr 2005
Posts: 9

PostPosted: Fri Oct 21, 2005 8:07 pm    Post subject: Re: High drain NiCd - Sub C batteries for power tools (strapping tool) Reply with quote

Quote:
If the strapping device doesn't run long enough on a battery pack,
either the pack is weak, the duty cycle exceeds the design limits of
the chosen strapper, or some other similar reason that points to
replacing the battery packs or the strappers, not redesigning the
packs.

I agree. I interpreted his original post as saying that the packs
they have now are no longer working well, i.e., the capacity of the
cells had dropped too low and needed to be replaced. Along with
discussing which cells to be used for these replacement packs, we were
also discussing how these new packs should be designed as the first
set of replacement packs he put together we're not performing well
(IMHO due to high IR cells and spot-welded tabs).

Or have I misunderstood your post, it's been a lonnngggg day. Smile
John Muchow
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Amicus
science forum Guru Wannabe


Joined: 29 Jun 2005
Posts: 100

PostPosted: Sun Oct 23, 2005 1:45 pm    Post subject: Re: High drain NiCd - Sub C batteries for power tools (strapping tool) Reply with quote

On Fri, 21 Oct 2005 20:07:30 GMT, John <jmuchow@SPAMMENOTcamlight.com>
wrote:

Quote:
If the strapping device doesn't run long enough on a battery pack,
either the pack is weak, the duty cycle exceeds the design limits of
the chosen strapper, or some other similar reason that points to
replacing the battery packs or the strappers, not redesigning the
packs.

I agree. I interpreted his original post as saying that the packs
they have now are no longer working well, i.e., the capacity of the
cells had dropped too low and needed to be replaced. Along with
discussing which cells to be used for these replacement packs, we were
also discussing how these new packs should be designed as the first
set of replacement packs he put together we're not performing well
(IMHO due to high IR cells and spot-welded tabs).

Or have I misunderstood your post, it's been a lonnngggg day. Smile

You got it, John.
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Amicus
science forum Guru Wannabe


Joined: 29 Jun 2005
Posts: 100

PostPosted: Sun Oct 23, 2005 7:47 pm    Post subject: Re: High drain NiCd - Sub C batteries for power tools (strapping tool) Reply with quote

On Sun, 23 Oct 2005 13:45:47 GMT, Jim Higgins
<invalid@invalid.invalid> wrote:

Quote:
On Fri, 21 Oct 2005 20:07:30 GMT, John <jmuchow@SPAMMENOTcamlight.com
wrote:

If the strapping device doesn't run long enough on a battery pack,
either the pack is weak, the duty cycle exceeds the design limits of
the chosen strapper, or some other similar reason that points to
replacing the battery packs or the strappers, not redesigning the
packs.

I agree. I interpreted his original post as saying that the packs
they have now are no longer working well, i.e., the capacity of the
cells had dropped too low and needed to be replaced. Along with
discussing which cells to be used for these replacement packs, we were
also discussing how these new packs should be designed as the first
set of replacement packs he put together we're not performing well
(IMHO due to high IR cells and spot-welded tabs).

Or have I misunderstood your post, it's been a lonnngggg day. :-)

You got it, John.

Somehow I got the impression that the best of the bad cells were being
recycled vs all being replaced.

If I were the OP I'd still go slow with a design change that changes
the internal resistance of the pack significantly or he might see
damaged strapping machines.
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sventus@gmail.com
science forum beginner


Joined: 28 Sep 2005
Posts: 32

PostPosted: Mon Oct 24, 2005 7:06 pm    Post subject: Re: High drain NiCd - Sub C batteries for power tools (strapping tool) Reply with quote

Jim.... how do I measure the tabs resistance and the battery resistance
in an accurate way ? I would like to do that and then move one findind
the best tabs (nickel or nickel silver coated tabs which seem superior
than stainless steel tabs).

thanks,
Hannes

Jim Higgins wrote:
Quote:
On Sun, 23 Oct 2005 13:45:47 GMT, Jim Higgins
invalid@invalid.invalid> wrote:

On Fri, 21 Oct 2005 20:07:30 GMT, John <jmuchow@SPAMMENOTcamlight.com
wrote:

If the strapping device doesn't run long enough on a battery pack,
either the pack is weak, the duty cycle exceeds the design limits of
the chosen strapper, or some other similar reason that points to
replacing the battery packs or the strappers, not redesigning the
packs.

I agree. I interpreted his original post as saying that the packs
they have now are no longer working well, i.e., the capacity of the
cells had dropped too low and needed to be replaced. Along with
discussing which cells to be used for these replacement packs, we were
also discussing how these new packs should be designed as the first
set of replacement packs he put together we're not performing well
(IMHO due to high IR cells and spot-welded tabs).

Or have I misunderstood your post, it's been a lonnngggg day. :-)

You got it, John.

Somehow I got the impression that the best of the bad cells were being
recycled vs all being replaced.

If I were the OP I'd still go slow with a design change that changes
the internal resistance of the pack significantly or he might see
damaged strapping machines.
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Ian Stirling
science forum Guru Wannabe


Joined: 06 May 2005
Posts: 150

PostPosted: Mon Oct 24, 2005 9:23 pm    Post subject: Re: High drain NiCd - Sub C batteries for power tools (strapping tool) Reply with quote

Hannes <sventus@gmail.com> wrote:
Quote:
Jim.... how do I measure the tabs resistance and the battery resistance
in an accurate way ? I would like to do that and then move one findind
the best tabs (nickel or nickel silver coated tabs which seem superior
than stainless steel tabs).

You connect a DMM halfway along the tab, and to the cell case.
Now, draw 10A from the battery, measuring with another meter.
R=V/I.
Internal resistance is more complex to measure.
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Amicus
science forum Guru Wannabe


Joined: 29 Jun 2005
Posts: 100

PostPosted: Tue Oct 25, 2005 2:14 am    Post subject: Re: High drain NiCd - Sub C batteries for power tools (strapping tool) Reply with quote

On 24 Oct 2005 12:06:27 -0700, "Hannes" <sventus@gmail.com> wrote:

Quote:
Jim.... how do I measure the tabs resistance and the battery resistance
in an accurate way ? I would like to do that and then move one findind
the best tabs (nickel or nickel silver coated tabs which seem superior
than stainless steel tabs).

You would measure cell resistance independently of tab resistance in
the same way you did for your larger Ni-Cd cells, but measure the
voltage directly on the end terminals of the individual cells, not on
the terminals of the pack as a whole.

To measure the resistance of the interconnecting tabs, you would load
the cells with a known high current safe for a sustained discharge and
with an accurate voltmeter (millivolt meter) measure the voltage drop
across the tabs. Use Ohms Law to calculate resistance. I'd take the
voltage measurements across the end terminals of adjacent cells so you
include both the resistance due to the length of the tab as well as
the resistance of the spot weld. If you want just the resistance of
the tab without including the resistance of the weld, then measure
voltage across the tabs at the point they're tack welded to the cell.

You seem to spend a lot of time on these Ni-Cd problems. What is your
function at the company where you're having these problems?
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sventus@gmail.com
science forum beginner


Joined: 28 Sep 2005
Posts: 32

PostPosted: Wed Oct 26, 2005 3:38 pm    Post subject: Re: High drain NiCd - Sub C batteries for power tools (strapping tool) Reply with quote

Thanks Jim,

I measured the voltage drop passing a 10A current throught the cells,
for Ni strips the voltage drop was around 10mV and for stainles steel
strips it was around 50mV :)

I'm a researcher, this is just part of a cost reduction process I plan
to introduce in my company. Actually I make research in new materials
(MMCs for example). I actually have someone to help me with this stuff,
so I don't have to make the hard dirty work (just at the beginning, but
when it becomes repetitive I have a colleage hired just for this
purposes).

Regarding the measurements accros the end terminals of adjacent
cells... would I not inclusde also the resistance of the 2 cells beside
the resistance of the strip and spot weld ? Would it not be best just
to measure the voltage drop at the positive and negative cells where
the strip is spot welded ?

I'm making progess on the lard NiCd cells too. Just received a brand
new package and will measure internal resistance on this too Smile as well
as capacity.

sincerely,
Hannes
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sventus@gmail.com
science forum beginner


Joined: 28 Sep 2005
Posts: 32

PostPosted: Wed Oct 26, 2005 3:47 pm    Post subject: Re: High drain NiCd - Sub C batteries for power tools (strapping tool) Reply with quote

Thanks Ian!

I did that and worked fine... internal resistance I measured as Mr John
Buchmann suggest in his book (used to different resistances in parallel
with the cells and measure the voltage drop and current - the
difference gave me the internal resistance).

sincerely
Hannes
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Amicus
science forum Guru Wannabe


Joined: 29 Jun 2005
Posts: 100

PostPosted: Fri Oct 28, 2005 8:26 pm    Post subject: Re: High drain NiCd - Sub C batteries for power tools (strapping tool) Reply with quote

On 26 Oct 2005 08:38:09 -0700, "Hannes" <sventus@gmail.com> wrote:

Quote:
Regarding the measurements accros the end terminals of adjacent
cells... would I not inclusde also the resistance of the 2 cells beside
the resistance of the strip and spot weld ? Would it not be best just
to measure the voltage drop at the positive and negative cells where
the strip is spot welded ?

That's what I meant. Measure across the terminals to which the strips
are attached. With no load, that voltage will be zero. I think that
removes all ambiguity. ;-)

Quote:
I'm making progess on the lard NiCd cells too. Just received a brand
new package and will measure internal resistance on this too Smile as well
as capacity.

Best of luck.
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wsemajb
science forum beginner


Joined: 04 Nov 2006
Posts: 1

PostPosted: Sat Nov 04, 2006 5:07 pm    Post subject: Reply with quote

Since I'm looking at similar amp hour rating and battery type, may I throw in a question here?

Recently I researched costs for rebuilding the 14.4v NiCd milwaukee batteries for the shop. I'm not well versed in battery tech and there is soooo much apocryphal detrius out there. Just about the best deal I could find was at my local Batteries Plus outlet. They would rebuild to the same spec or switch me over to a higher (3.4?) amp hour NiMH. I went ahead with the "upgrade" but am beginning to wonder if I should have. My chargers are standard little milwaukee units of 9.6v to 18v NiCd/NiMH, but I am unsure of the amp rating of the charger itself. I only had one battery rebuilt at Batteries Plus. Since I dropped the battery off yesterday for rebuild, I'm suddenly finding quite a bit of negative comment on the web about NiMH.

I think I'll order a good brand of 12 x 2.4ah NiCd sub-c cells and rebuild another on my own to compare side by side. Someone suggested using a heavy de-solder braid to connect the tabs.

After a week or two of use, which one am I likely to be happier with? Should I have just stayed with the 2.4ah NiCd?
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