Norm,The number of cells we had is hazy, but I think somewhere around 220-240 seems to stick in my mind.
Reactor accident analysis determined what actions were required to render the reactor safe under all designed accident scenarios. There had to be enough electricity in the bank to provide the power necessary to meet these accident scenarios. Plus some.
So, one can assume that the battery capacity was designed to meet these requirements throughout the battery bank's designed life (as measured in cycles and years) before replacement was warranted. So, to keep it all simple, as long as the bank met these design accident requirements, it was good to go. So, in theory, we were testing to the battery spec, in a round about sort of way..
Our AH meters had a calibration capability and meter adjustment was possible. You could do the same. Turn on a known unwavering DC load (like a string of DC lights that are all the same wattage) for a period of time that allows battery voltage to drop something like 0.2-0.3 VDC and then stop the discharge and compare what was read vs what was recorded. If there is no adjustment possible, than a scaling factor can be calculated.
Do this over two different voltage ranges if you really are bored. Should be little difference.
Or, use your calibrated hydrometer to determine 100 % full and something less (maybe 60% or so?) and then using the capacity figure of your cells, see if amps out calculated is close to indicated.
Re-perform test if after equalization, the reading appear to be different from the last time....
As for how we got so many years out of these cells, we had low pressure air agitation to keep the electrolyte mixed, temperature and humidity controlled battery compartment, a team of sailors who cleaned the place, measured carefully, checked inter cell connection torques, etc etc etc.
On my last boat, i had Interstate 4Ds (3 of them) as my house bank and 2 group 31's for the engine starting bank. When i installed the 4Ds, i filled them with distilled water and electrolyte solution and charged them per Interstate's directions on a bench. Then, installed, and used distilled water to keep them full (checking bi-weekly in July and august, monthly otherwise), posts clean, connections tight, and batteries strapped down so no movement was possible. Never discharged below 50% and never recharged if the indicated capacity was above 75%. Equalized at the beginning and end of the season, and measured and recorded each cell's specific gravity with a hydrometer that I had just checked at the local battery shop for accuracy. At year one, battery capacity was just over 100%. When i sold the boat 4 years later, battery capacity was ~104 % with 134+ cycles on the bank.... Go figure...
[Update: I forgot to state that I never left my charger on once the battery was charged. I believe that the slight charging current cannot be good for the battery. In the Navy, we used a 5 amp trickle discharge rate once the battery was fully charged. In the winter, after the battery was fully charged, I isolated them from the dc circuit and kept the engine room warm with a 100 watt light bulb. I measure the specific gravity monthly and as long as batteries never strayed below 50%, i did not charge them. I think that in fact, the battery bank was somewhere just above 70% capacity at the end of the 7 month winter storage period....Lee]
In the battery bank I want for my trawler, I am asking for 2.2 VDC cells. The inverter has a DC input range of something above 19 VDC so if I do end up with a bad cell or two, I could jumper and live that way until I could arrange for a replacement.....
Lee On Nov 22, 2008, at 1548, Norm of Bandersnatch wrote: Lee, Thank you for the great information about the submarine batteries. Itcorrelates well with the information I have read in Home Power magazine......
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