Any Battery Guru's?

Submitted: Sunday, Apr 19, 2015 at 06:08
ThreadID: 117540 Views:2113 Replies:2 FollowUps:5
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Just wondering if any battery guru's can shed a little light on this topic.
I have a CenTech battery analyser. the type that measures internal resistance.

http://www.harborfreight.com/digital-automotive-battery-analyzer-66892.html

It compares voltage & internal resistance & comes up with a figure for a batterys CCA capacity.

I've tested it against new & known good batteries and the figures it comes up with seem pretty accurate.

But what about deep cycle batteries?
Is it possible to access their condition based on the voltage & internal resistance?
I know it's CCA figure is derived basically from a lookup table.

So what about say my Delcor DC-31?
5 minutes off the charger it showed about 12.9 volts & an internal resistance of 15.98 milliOhms.

Does anyone know much about what sort of internal resistance other types of batteries should have?

I'm doing a bit of Googling, but no real answers yet.

Cheers.
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Reply By: swampfox - Sunday, Apr 19, 2015 at 08:22

Sunday, Apr 19, 2015 at 08:22
HI
Although the unit may be ""reasonably accurate"". The best method I have found for wet lead acid is load tester[carbon pile ] and hydrometer . Many load testers will have cca and amperage scale . The amperage scale vs the voltage scale is compared to verify .Typically around 300amps [600 CCA] at at least 9.5 volts is an ok unit .
Hydrometer [approx.] over 1.250 is ok near full
Static voltage anything over 12.6 is ok
After many years the above is a little more accurate than the computer calculation method.
After all said and done batteries can and do sometimes exhibit unusual unexpected behaviour . These situations are hard to predict by any method .
So I guess this leaves us back at the beginning ha ha .
Hope this adds to your knowledge .
Cheers
swampfox
AnswerID: 552651

Follow Up By: Phil 23 - Sunday, Apr 19, 2015 at 20:40

Sunday, Apr 19, 2015 at 20:40
Hydrometer is always a good measure, but no go with sealed batteries.
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Follow Up By: swampfox - Monday, Apr 20, 2015 at 09:30

Monday, Apr 20, 2015 at 09:30
hi
primarily referring to wet/flooded [marine ,auto] lead acid re CCA.
Agreed ,but b4 u write off a battery as being sealed some do have a ""permanent ""cover that can be gently removed.

swampfox
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Reply By: Allan B (Member, SunCoast) - Sunday, Apr 19, 2015 at 13:40

Sunday, Apr 19, 2015 at 13:40
Hi Phil,

Using 'battery impedance' as a reference to battery condition is somewhat indefinite. It does have some value as a referential technique where changes in measured value are compared.

I have had useful results in managing large static battery banks by applying a load then measuring voltage across each cell where a significant high cell voltage may indicate high cell impedance and probable cell deterioration. Cell replacement can then be considered, but this is not practicable with a normal six cell 12v automobile battery.

Your analyser may be useful to compare a particular battery's impedance with previous records to indicate failing performance but care would need to be taken that each test was performed under the same conditions of temperature, charge state etc.

A more reliable assessment for a deep-cycle battery is obtained by measuring the battery's capacity by performing a controlled ampere hour discharge and comparing to manufacturer's specification and to previous test. This places the focus on capacity rather than high current ability.

It is difficult to obtain adequate engineering specifications from automobile battery manufacturers as their published data is limited to user interest such as CCA, Ah etc. This sort of information is more easily obtained from manufacturers in regard to industrial batteries.

To respond to your specific question, an internal resistance of "15.98 milliOhms" is suggestive of good condition in a 100Ah battery.

This Telstra Paper may provide some indication of the limitations and difficulty of assessment by measured battery impedance.
Cheers
Allan

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AnswerID: 552673

Follow Up By: Phil 23 - Sunday, Apr 19, 2015 at 20:35

Sunday, Apr 19, 2015 at 20:35
Left it charging overnight.
On 15.6 Volt Boost.

Disconnected it at 8:00 this morning.

Tested it a few times:-

8:00am 13.35V 4.61mOhm
9:00am 13.06V 3.92mOhm
10:00am 13.08V 4.09mOhm
11:00am 13.05V 4.11mOhm
12:00pm 13.04V 3.94mOhm
1:00pm 13.03V 3.98mOhm
2:00pm 13.04V 4.02mOhm
3:00pm 13.04V 4.00mOhm
4:00pm 13.02V 3.95mOhm
5:00pm 13.03V 3.99mOhm
6:00pm 13.03V 3.90mOhm
7:00pm 13.03V 3.98mOhm
8:00pm 13.02V 4.11mOhm

Interesting the tester reported it's capacity as 690CCA.
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Follow Up By: Allan B (Member, SunCoast) - Monday, Apr 20, 2015 at 09:45

Monday, Apr 20, 2015 at 09:45
Not sure what to make of that Phil.
Cheers
Allan

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Follow Up By: Phil 23 - Monday, Apr 20, 2015 at 10:35

Monday, Apr 20, 2015 at 10:35
Just out of interest....
tested it again this morning. 24 hours since removing from the charger.

8:00am 12.98C 4.06mOhms

The CCA showed as 651, but I know that's a looked up figure of sorts.

Also I think this battery is 4 yeears old now & has spent most of it's life maintained on a Ctek MX25.

It's also been abused a few times as it's the carry about one that powers the 2 Engels when I'm out.

Cheers

Phil.
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