[Test-Equipment] "Conductance" battery checker

[J. Forster]

You can probably cobble up a simple test fixture to make a meaningful
measurement.

Get a switch, a couple of load resistors, and a DMM

Hook up the resistors in parallel, with the switch in the lead of one. Put
this dummy load across the battery and monitor the voltage with the DMM at
the battery terminals.

Measure the battery terminal voltage with one, and with both resistors
loading it, then calculate the internal resistance.

The two load resistors are because you want to get away from an open
circuit voltage to avoid funniness.

For a 12V 7 A-H battery, I'd choose resistors of about 25 Ohms, so the
load current is about 1/2 and 1 Amp.

Best,

-John

===================




> My application is for SLA batteries, specifically 12 V 7.2 Amp,
> typically used in UPS apps at less than 3KVA.
> Ray, W4BYG
>
> -----Original Message-----
> From: test-equipment-bounces at mailman.qth.net
> [mailto:test-equipment-bounces at mailman.qth.net] On Behalf Of rbethman
> Sent: Wednesday, March 16, 2011 3:13 PM
> To: Discussion of Electronic Test Equipment
> Cc: Grant, Ken
> Subject: Re: [Test-Equipment] "Conductance" battery checker
>
> This paper refers specifically to "lead acid" batteries.
>
> !) I do NOT know if this is the type of batteries or cells being
> discussed.
>
> 2) My specific usage referred to NiCads, and their testing for
> capacity.  I test them from initial purchase, and keep records to
> understand their *state* after use to determine whether or NOT to take
> them out of use.
>
> I do NOT know the TYPE of battery being considered for "conductance"
> testing.
>
> This *could* be apples vs. oranges.
>
> Bob - N0DGN
>
> On 3/16/2011 2:50 PM, Grant, Ken wrote:
>> Hi guys,
>>
>> Have a read of this paper:
>>
> http://www.lordconsulting.com/images/stories/TechnicalPapers/Battery-Man
> agem
>> ent.pdf . It describes evaluating a battery's condition by measuring
> its
>> internal impedance and comparing it to the value of a fresh battery.
> There
>> are several inexpensive testers available that use this principal.
>>
>>   Usually, you measure Zint by applying a constant alternating current
>> (around 1 KHz) to the battery and measuring the resultant AC voltage
> drop.
>> Zint is then E / I. Conductance (if you wish to think in a less
> intuitive
>> way), is then 1 / Zint.
>>
>>   Pay special attention to graph #3. It shows that when Zint is about
> 150% of
>> its initial value, the battery is at 80% capacity and 'heading south'
> real
>> quick.
>>
>> Ken, VE3FIT
>>
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