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whoaru99 (Industrial) (OP)
28 Mar 06 20:02
Anyone familiar with the Midtronics conductance based battery testers?

Just wondering if these were the real deal.

Thanks,
Todd
B3188 (Military)
31 May 06 15:49
Not fam,iliar with theirs but you might want to
take a look at Enersys's white papers and ap notes.
Impedance matching of cells is covered.
They think matching by impedance quite important.
DanEE (Electrical)
31 May 06 22:51
Yes I'm familar with them, but rather than getting into a lengthy discussion of conductance testers, (as these things have been debated for years, if not decades).... Do a little reading of the pro and cons... The most informed writing I have found is here this link..

http://www.alber.com/TechLibraryPublishedPapers.htm

A major issue is around the use of AC impedance measurement techniques.. versus DC load testing..

Judge for yourself...

And, talk to the engineering people that design the batteries in question and ask if they will support a warranty claim based on conductance tests..

We talked to the engineering folks at two major manufacturers of industrial batteries the the answer was no.. They will only support warranty claims based on DC load test results..  Also ask if the same folks if they publish reference conductance values on their batteries.. again the answer was no..

We also talked to Alber..

We use only DC load test method at our customer sites..

------------------------------------------

In God we trust. All others state the facts and cite references.

B3188 (Military)
8 Jun 06 12:18
Well put.
We test capacity and charge/discharge efficiency.
Most specifications are for ampacity delivered..

We are looking into impedance matching for additional
data in building series parallel packs.

Having issues with a 42 cell pack (sealed lead acid)
arranged 3 cells parallel every stage, 17 stages.
Discharge rate, 2C;  CC mode charge rate at C/5.

Question is how do mismatches in the 3 cell parallel
banks effect the aging of the battery cells
over the design life.
Designed for 5 year life, getting 3 - 4.
Occasional packs show high corrosion from
outgassing and acid expulsion.
Corroded terminal cell location very random.

Thanks for the great reference.

B1388
justoneinthecrowd (Electrical)
14 Jun 06 10:50
WOW! Conductance vs. Impedance? There are only about a gazillion white papers on each side of this issue. The telecom world seems to prefer the conductance (Midtronics-type) while the Critical Data Power (UPS)world tends to prefer the impedance (Alber-type). Given that VRLA's are especially sensitive to temperature, pressure & hummidity and that most are 10 year design life at maximum; AND that VRLA's can fail quickly & dramatically (open circuit or short to open circuit), I don't think that it much matters which you use. Given that flooded fail gradually (almost never an open circuit, just a reduced ampacity/capacity), it probably does not matter much here either. Think of these measurements like a depth stick in a river. You just want to observe a radical change in level and be able to tell when the river is overflowing its banks!

With respect to parallel 3 cell monoblocks, the unequal resistance of course promotes deterioration of the better cells especially during equalize and charge cycles. But there is absolutely nothing that you can reasonably do about it. Even replacing a suspect block with a new "impedance-matched" one from the factory will never truly align the values. Run the string until it dies and make sure you have a redundant string, hopefully staggered in age. Replace the strings when their values or performance indicates. Max expectancy for 10 year VRLA is 7-8, for 20 year VRLA 10-15, for 20 year flooded, they can actually go beyond 20 if babied.

As far as warranty claims...these puppies are pro-rated so the warranty value is about as attractive as the one on your car battery.
btrueblood (Mechanical)
14 Jun 06 11:51
B3188,

Why parallel the cells?  I mean, why not run three independent strings that are common connected only at the +48V and ground terminals?

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