jonjo
regular
Reged: 27/02/2002
Posts: 2024
Loc: Cambridgeshire, UK
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Does anyone recall the battery drain test described in YM or PBO earlier this year? I think the procedure was to put a load of 5% of rated capacity on a fully charged battery for 10 hours providing the voltage under load does not drop below 10.xx volts.
I cannot remember what the minimum voltage was and currently I am on the boat but my pile of mags is at home.
(sent from the complimentary internet terminal in the Haslar marina office)
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William_H
regular
Reged: 28/07/2003
Posts: 3337
Loc: West Australia
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I think probably around 11 volts would be a good time to stop the discharge. If you get something like 50% of total capacity out of the battery that is pretty good. If you get 40 or even 30% out it is probably worth keeping the battery a bit longer before replacing. But if the test only produces like 10% then you know it is no good. I reckon the test will have pretty obvious results. good luck olewill
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alan
regular
Reged: 07/06/2001
Posts: 641
Loc: Nettuno, Italy
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There is a method described on the "Voltwatch" web site by a Mr. Attkins. Google for Voltwatch ( a battery volts indicator) and look for a page on technical information. I have used this method and it seems pretty good except that it performs all the volt measurements "on load", which I do not agree with.
http://www.attfield.dircon.co.uk/info-indx.html#Testing
Alan.
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Alan Cloke
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jonjo
regular
Reged: 27/02/2002
Posts: 2024
Loc: Cambridgeshire, UK
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I had misread the original battery crash test article, in the YM April 2008 issue Nigel Calder suggests a 5% load over a 20 hour-ish crash test down to 10.5 volts. I performed a 10 hour test.
The battery is a 140ah Bosch starting its 4th season of use. I applied a 7.3 amp load overnight. After 9 hours 54 minutes the link-10 monitor reported 70 amp hours consumed.
At test end the reported current had dropped to 7.0 amps and voltage under load was 11.53v. After 6 minutes of zero load, voltage recovered to 11.85v. I thought this indicated a healthy battery but the graphs here suggest my battery had lost 95% of its charge compared a theoretical 50%.
http://www.arttec.net/Solar_Mower/4_Electrical/Battery%20Charging.pdf
However this site below indicates that my rest 11.85v volts for an assumed 10 degrees c = around 40% remaining.
http://www.buchanan1.net/lead_acid.shtml
Whereas this Adverc chart below says 12.2v = 50% charge.
http://www.adverc.co.uk/technical/technical-soc.asp
What do you all think, one more season of use left?
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VicS
regular
Reged: 13/07/2002
Posts: 8383
Loc: Home: Kent. Boat: Chichester
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Quote:
What do you all think, one more season of use left
Impossible to say. It could fail tomorrow or it could soldier on for several more seasons. Any tests you perform only give you a snapshot of its condition at the time of the test.
With regard to the state of charge vs open circuit voltage the figures i use are: - around 12.7 to 12.8 = fully charged
- 12.2 = half charged
- around 11.7 = effectively discharged
All these readings apply after a resting period of 12hours and agree with the majority of published figures. The figures in the second of the two links you quote are vastly different and I would discount them! I cannot comment on a reading taken after standing for only 6 minutes except to say that it would have risen to a higher figure after 12 hours without doubt.
Battery capacities are normally quoted at a 20 hour rate so your discharge test would have been more appropriately done at a current of 3.5 amps with a view to taking 20 hours to discharge 140Ah. Discharging at a higher rate will give you apparently poor results although had you allowed 12 hours recovery time afterwards the open-circuit voltage reading (using my scale) would have given a better indication of the charge actually remaining and therefore enabled a better appraisal of the condition at that time.
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Old Chemists never die, they just fail to react
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halcyon
regular
Reged: 20/04/2002
Posts: 2690
Loc: Cornwall
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!!.53v under a 7 amp load would indicate a capacity of approx 30% left.
What voltage did you start at before you applied the load.
Brian
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Kddpowercentre designers and purveyors of fine charging systems for 30 years.
Powercentre spares and help line
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jonjo
regular
Reged: 27/02/2002
Posts: 2024
Loc: Cambridgeshire, UK
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Quote:
It could fail tomorrow or it could soldier on for several more seasons.
Ok in order to eek out the remaining capacity I should stop assuming it is ok to use 60AH of an assumed 140AH capacity. I will reprogram the Link-10 to assume the battery has an effective capacity of 90AH so it should bleep after 45AH of consumption.
Quote:
Battery capacities are normally quoted at a 20 hour rate so your discharge test would have been more appropriately done at a current of 3.5 amps with a view to taking 20 hours to discharge 140Ah.
Hmmm, Calder suggests a load of 10amps for a 20 hour crash test of a 200AH battery, maybe you suggested 3.5amps for a 20 hour test drain down to 50% of capacity?
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jonjo
regular
Reged: 27/02/2002
Posts: 2024
Loc: Cambridgeshire, UK
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Quote:
!!.53v under a 7 amp load would indicate a capacity of approx 30% left.
What voltage did you start at before you applied the load.
I failed to note that figure but the battery had been on a multistage mains charger for 2 days so I assume it was fully charged.
Next year I plan a long cruise of 2 to 3 months so my preference would be to fit a new battery next Spring, I will just have to treat the current one kindly this season.
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VicS
regular
Reged: 13/07/2002
Posts: 8383
Loc: Home: Kent. Boat: Chichester
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Quote:
maybe you suggested 3.5amps for a 20 hour test drain down to 50% of capacity?
No sorry a complete biocomputing malfunction  Normally the thing works Ok at that time of day.
7 amps obviously it should have been. The results therefore do not look so rosy.
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Old Chemists never die, they just fail to react
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