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mid north Matt

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Joined: 06/01/2011
Location: Australia
Posts: 58

Posted: 09:44am 24 Feb 2011

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hi all
saw some trogan 8 volt golf cart batties at the dump and they measured 6.5,4.4 and 4.6 volts,how do you measure the impedence of the batteries to check for shorted/dudd cells? what would be typical readings for good and bad cells?

Pt Wakefield Matt

Tinker

Guru

Joined: 07/11/2007
Location: Australia
Posts: 1904

Posted: 02:33pm 24 Feb 2011

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Hi Matt,

Your question caused me some embarrassment as I should know the answer, I guess its been too long since I finished trade school

.

Anyway, Google got me many answers, here is one battery impedance

All I remember is that the impedance of a good battery is very low <<1 Ohm, that is why a spanner quickly vaporizes if you drop it across the terminals

Klaus

mid north Matt

Regular Member

Joined: 06/01/2011
Location: Australia
Posts: 58

Posted: 01:41am 25 Feb 2011

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hi Tinker
thanks for the info and link,think i'll do the ohms test with a cheap meter in case the magic smoke wants to get out and do it on a good and bad batteries so ill know what reading's i should get,yeah it's been a while since i finished my auto trade course too but they didnt teach us much about batteries

Pt Wakefield Matt

CraziestOzzy

Senior Member

Joined: 11/07/2008
Location: Australia
Posts: 135

Posted: 04:06am 25 Feb 2011

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My uninformed answer on your question regarding testing a depleted battery, is to get a hydrometer and measure each cell of a battery and that will give you an idea as to if the battery is good or not.

http://cr4.globalspec.com/member?u=25757

http://www.instructables.com/member/OzzyRoo/

Barry T Coles

Senior Member

Joined: 30/07/2009
Location: Australia
Posts: 109

Posted: 05:53am 25 Feb 2011

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One simple way to test if a battery has dropped a cell is to remove all the caps from the refill openings, put the + lead of your multimeter on the + battery terminal & place the - lead in the fluid of each cell.
Start from the cell closest to the + terminal& check each one individually if the battery is OK you should see the voltage rise as you progress through the cells, if you get one that doesnt increase then thats the cell that has died.

Cheers
Barry

I need to learn from the mistakes of others.
I dont have the time to make them all myself.

mid north Matt

Regular Member

Joined: 06/01/2011
Location: Australia
Posts: 58

Posted: 10:23am 25 Feb 2011

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hi c/ozzie
yeah i know about the specific gravity test being a small engine/motorcycle mechanic and i know how to detect shorted cells by voltage readings but most batteries out the tip have been sitting a long while and dont come out fully charged to do those tests hence wanting to know about battery impedence as that is easy to do without acid going over me or my car

but at 85c a kilo ill wait till they go out to one of the scrappies and get them at the right price with full refund if they dont come up to capacity @ 40c a kilo

hi Barry
never thought of that way of testing for shorted cells but will give it ago,but what about sealed wet cells and gell cells as they get a few out the tip?

Pt Wakefield Matt

Alasdair
Regular Member

Joined: 12/01/2011
Location: Australia
Posts: 62

Posted: 02:16pm 05 Mar 2011

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Hi matt
the simplest and most accurate test of battery impedance is
simply done by measuring terminal voltage at two different
charge currents, the voltage change relative to the current
change at close to the same time will give you the formula
data for overall impedance. Just keep the higher current
within the battery limits, use R=E/I with E being the differential
voltage and I being the differential current. Eg, a battery with
13 volts @ 1A and 14.5v @ 10A has 1.5v @ 9A difference,
or 0.16 ohms impedance. This formula will work both ways and
as such can be measured using discharge currents and voltage
drops instead of charge, as long as the battery is in it's normal
delivery range and state of charge and temperature. The impedance
will vary quite a bit with temperature, so around 20degrees C is
probably ideal.
Regards Alasdair.

Amc-elec

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