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| Cold Cranking Amps oddity |
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| awemawson:
Yesterday I went to do some work on my 'New to Me' Ford 4600 tractor - only had it a few days so much of it is an unknown quantity. It's been a very good starter, on the button each time and much better than my Ford 4000 (which is basically the same engine) This time just a slight click and nowt else. Battery flat as a fluke - blast must have left something like a light on un-noticed. Fortunately a friend was with me to help lift the battery out as it's an unbelievably heavy lump. |
| awemawson:
Dragged it into the welding shop to put it on charge, but my fancy modern battery charger wouldn't put anything into it at all. Battery volts were 11.5. Dug out my old and simple 'non-smart' battery charger which is only rated at 6 amps, but it only shoved 3 amps in on charge. Presumably something a bit high resistance in the battery - bit of sulphation or what ever. After a few minutes charging I discharged it a bit with an old WW2 Aldis lamp (5 amps at 12 volts) then it started charging at a much more sensible rate, but still the modern charger was no use. Left it charging for several hours and then dug out my 'Cold Cranking Amps' tester. This has proved invaluable over the years I've had it to sort useless from good batteries. Now the oddity. Quite repeatably, if I measured cold cranking amps having just taken the battery off charge I got something like 450 (should be 880) BUT if I discharged the battery for a few minutes the cold cranking amps rose to 550 if tested with load removed. |
| awemawson:
Now I don't know how that tester works - obviousy somehow it's measuring the internal resistance of the battery and deriving CCA from that. Googling tells me there are several methods including testing using short duration high current pulses and and other way is using AC across a range of frequencies. However it works, as I say it has proved over time to be a reliable and consistent tool. Now the good news is having gone through a few charge / discharge cycles (only slight discharge for maybe ten mins at 5 amps) the battery was able to be charged using the fancy modern charger and was left over night charging until all cells were lightly gassing. The even better news is that I now am measuring a CCA of 900 amps - (battery is rated 880) :ddb: |
| awemawson:
Being single handed today, refitting the battery involved some nifty driving with the fork lift truck (how ever did I manage without it). So battery gets re-installed - checked for discharge when everything is supposedly turned off (none) and low and behold the engine springs into life at the first jab of the starter - just as it was. Battery volts monitored when engine on fast tick over - they rise to 14v - so the alternator is charging ok. But the question remains - why did the CCA seem to rise after discharge and return to the lower value after charging during the process even though eventually rising to the correct figure. My guess is that there was light sulphation on the plates which was eventually removed by what I did and maybe this was influencing things. |
| hermetic:
Hi Awemawson, If the battery has been stood, suphation occurs on the plates, and this insulates the plates from the electrolyte. Putting a reasonably heavy discharge on the battery will destroy the sulphate layes, so the battery can then deliver more current. Problem is that some of the sulphate will not be reconverted into lead and will sink to the bottom of the battery, so you have lost some of the "ultimate chemical capacity" of the unit The old style fork lift batteries used to be put on a heavy discharge cycle once or twice a year to prevent this. As to the CC ammeter, I am shocked that you have not pulled it to bits to see how it worked;-) Phil |
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