Battery drain test.

[jonjo]

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)

 

[William_H]

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

 

[alan]

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.

 

[jonjo]

Re: Battery drain test - result

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?

 

[VicS]

Re: Battery drain test - result

[ QUOTE ]
What do you all think, one more season of use left

[/ QUOTE ] 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: <ul type="square"> [*]around 12.7 to 12.8 = fully charged [*]12.2 = half charged [*]around 11.7 = effectively discharged [/list] 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.

 

[halcyon]

Re: Battery drain test - result

!!.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

 

[jonjo]

Re: Battery drain test - result

[ QUOTE ]
It could fail tomorrow or it could soldier on for several more seasons.

[/ QUOTE ]
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.

[/ QUOTE ]
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?

 

[jonjo]

Re: Battery drain test - result

[ 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.

[/ QUOTE ]
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.

 

[VicS]

Re: Battery drain test - result

[ QUOTE ]
maybe you suggested 3.5amps for a 20 hour test drain down to 50% of capacity?

[/ QUOTE ] No sorry a complete biocomputing malfunction /forums/images/graemlins/blush.gif 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.