From: jmuchow@SPAMMENOTcamlight.com (John Muchow)
Subject: Re: Reducing contact resistance for low volt use?
Date: Mon, 06 Jan 2003 06:20:59 GMT
Organization: MindSpring Enterprises
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X-Server-Date: 6 Jan 2003 06:22:45 GMT
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>>>>>>That's a misplaced assumption in this case. And I would love to read
>>>>>>a FM, or even a regular M, on such cells. But alas, no such document
>>> There ARE spec sheets on EVERY battery made that is made by a
You neglected to read the post carefully.
I said that there was no manual for Charles' assumption that I was
using a cell with connections designed for 100A of current. Since I'm
using standard Sub-C, C, and D-cells, there's no manual.
>>>>>>Sub-C, C, and D-sized NiCd and NiMH cells are regularly used at up to
>>>>>>100A discharge current levels by R/C plane, car, and combat-robot
>>> NOT from an individual cell, however. For one thing, they will NOT
>>>produce that much energy.
I never said that ONLY individual cells were used by those folks.
I've only mentioned packs when describing applications for the cells
we wish to test individually.
>>>>>> Typically, they are built in packs of 4-30 cells, soldered
>>>>>>together in series with copper battery bars and hefty leads.
>>> Such a battery pack MIGHT produce 100A. Silver plated teflon wire
>>>used for military applications would likely exhibit less resistance
>>>than the copper bars. It would weigh less as well.
The packs used by many BattleBot builders OFTEN deliver above 200A
(20-30 C-cells in series). Search past posts at the BattleBots Forum:
This is not done continuously, and often not by design (sometimes it's
a stalled motor), but it happens all the time.
Thanks for the teflon wire tip. Do you mean silver-plated copper,
teflon insulated wire? Or some type of specialized teflon core wire?
I didn't realize that the plating lowered the resistance that much for
DC applications. AC, yes, especially higher frequencies as more and
more of the current passes only along the outer portion of the wire
where the silver is.
Do you have a link to a chart for the DC resistances of silver-plated
cooper wire? I'd love to see the values.
>>>>>>cells don't survive very long at these discharge current levels, but
>>>>>>in the struggle to extract the maximum performance from the smallest,
>>>>>>lightest package, battery life is often only a minor concern.
>>> Then, what is your need? A 1600 mA/H battery is NOT going to
>>>produce 100 A at ANY load resistance, and the terminations for testing
>>>them individually does NOT need to be of such heft.
1600mAH? Where did that come from? Most of the cells used in these
high-current applications are 2400-3600mAH. And in 20-30 cell
strings, they most certainly do deliver a LOT more than 100A. I've
only discussed packs when mentioning these applications. We only want
to test individual cells though (for several obvious reasons).
My need is to have 100A flow through my constant-current load from a
1.2V or 2.4V (only measuring voltage-vs.-time for one cell though)
source. I can't possibly see the harm in having 100A-capable
terminations for a single or 2-cell test string of cells in case we
get close to, or even achieve, that 100A value. Even if we don't, how
the heck can having 100A terminations be a problem if there's 50A
flowing through them?
Since we won't know what the max discharge current level is until the
first test, IMHO it would be wrong to have smaller connectors on the
first unit. If we build a couple and both only give us a much lower
max current level, then any future units can be built to better match
the actual current flow.
>>>>>>I have regularly done destructive-test discharging at current levels
>>> Bullshit. A dead short on a single cell with copper or silver will
>>>NOT deliver such currents. If you are testing banks of cells, you are
>>>making a mistake.
I only ask that you read my post first before accusing me of a
lie. Please re-read the paragraph below, noting the now capitalized
"I have regularly done destructive-test discharging at current levels
above 100A. To date, this has been with SERIES CONNECTED BATTERY
>>>>>> To date, this has been with series-connected battery
>>>>>>packs. To test the real performance of different manufacturer's
>>>>>>cells, we need to test them individually to eliminate the variables
>>>>>>introduced by all the interconnects, soldering, etc.
>>> No shit. You don't need 100 Amp connections either.
The sarcasm and foul language will be ignored.
I DO need 100A connections as that is one of the requirements for this
device. Please purchase a Sanyo N-3000CR cell, condition the cell
with at least 3 complete charge/discharge cycles, solder two short
lengths of #2 cable to each end, charge the cell fully, and short the
two wires together...measuring the current flow through them, of
course. Then get back to me with your recommendations..
If I have a requirement for 100A connections, then that's what I need.
Now, if you wanted to argue that a single sub-D, C, or D cell can't
deliver 100A...fine. But, that has nothing to do with my
requirements. If the cells can pass 100A in series strings (which
they definitely can), then I need a device that can handle 100A in
case I can get 100A from one or two in series. You're forgetting (did
you ever realize?) that the 100A from a single cell is a design goal.
A goal which I needed help from this group to achieve.
>>> Discharge the battery into a 0.1 ohm load that can handle the power
>>>level expected, and read the current with a voltmeter across the .1
>>>ohm resistor. Pretty simple. Reading across dead short loads will
>>>not give real data, and if you are reading current by way of a series
>>>shunt meter, you are dropping voltage on it anyway.
What the heck is that test supposed to do for me? 12A? You're right,
this test is simple. The problem is that it offers nothing to me. No
valid data, nothing.
Again, I plead with you to read my posts again carefully. See the
snipped paragraph below (with more capitalized letters to help you
"I've been moving forward with designing a CONSTANT-CURENT battery
So, your simple circuit only offers me 12A (max) of current, and isn't
even a constant-current load. I'm completely perplexed as to how you
think this a solution for the problem I came to the group for help
BTW, the load resistance of the motors often used is only about
50mOhms or so....pretty close to that dead short you mentioned. These
current levels I need will give me real data for real applications.
With 20-30 cells in series powering that motor, that's a lot more than
100A, even with wire and connection resistance. The motor can catch
fire, the insulation (or even the wire) melt, the batteries
practically explode, but it happens all the time as the builders of
these extraordinary machines push the limits on every component in
>>>>>>This lead to my desire to extend the functionality of the discharger
>>>>>>I'm working on to include 100A current levels with single-cells.
>>> Spot welded steel strips or hard soldered connections are your best
>>>bet. 100 A levels should not be expected from a single cell.
Thank you for the recommendations. This is why I posted my question.
Spot welded strips have been used before and just fried the cells as
it turned red from the heat at these high current levels. We've gone
to soldered silver-plated copper bars and they get *very* hot, but the
solder *usually* doesn't melt.
I've mentioned in my posts that we don't want to use soldered
connections. If we have to...fine. But, it's not something we want
We're only *hoping* to get 100A from one or two cells...hence my post
asking for help in achieving that goal. I've learned a lot from
others in the newsgroup about the difficulties I'll be dealing with
and I still think it's possible with a *lot* of care put into the
mechanical/electrical connections. If it's not possible, c'est la
>>> If you are getting 100 A out of 1.2V cells, and still read 1.2 volts
>>>on them, I want to know what brand they are.
Umm...so would I. Never said anything about the voltage-under-load of
these cells. But, for the record, it immediately drops to about
0.7V/cell and goes to zero (this is very, very bad in a pack) very
The 100A requirement is the extreme upper-end of the discharge
currents we want to use in this constant-current unit we're building.
Most of the time, the cells are used at 5A-50A levels. But, one way
to differentiate the performances of all the cells that are available
is to test them under extreme circumstances, like even higher current
levels. BattleBot builders would love this data, even if their cells
would only see it during a spinner-shell startup, or motor stall
I don't know why you took the tone you did in your response to me.
Most other posts of yours are merely to provide information (a good
thing). It's curious that you decided to be sarcastic for no reason
and call me a liar. Perhaps that's just your style. It is
interesting that you can be so adamant and opinionated about a post of
mine that you really didn't even read carefully.
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