Originally Posted by smac999
which with a 800ah+ battery bank at 50 soc and a small 60-80a could be 4+ hours before the combiner turns on. there is no way I'd want an engine running without the engine battery being charged. not for more then a min. that is just asking for problems. and a dead and stalled engine at some point. some engines take 10+ amps while running.
A 60A alt on an 800Ah bank.....
Why would any "competent" installer do such a thing...?
That is 4.6 hours just to get to 85% SOC from 50% SOC. Of course that does not include charge efficiency or the alt actually getting hot and putting out 40A, rather than 60A, which would now result in about 8.4 hours to go from 50% SOC to 85% SOC. An 800Ah bank on a 60A alt or main "fast charge" source is simply poor system design not an issue of the ACR or combiner.
7.5% of "C" is about as useless as tits on a bull
unless it is solar and you have DAYS to wait for a full charge.....
If it takes you four hours to raise the voltage to 13.0V on an 800Ah bank you simply need to go back to the drawing board on the system design.
Even so I would bet that a diminutive 7.5% of "C" charge source could still hit combine in under 40 minutes, but it is still a horrible system design....
A healthy bank charged with 20% of "C" source will raise the voltage to combine
levels (13.0V) in about 12-15 minutes. Done this test many times, with many different lead acid batteries and scaled it both up and down...
It is getting beyond the combine voltage that becomes harder, but 13.0V is pretty easy for a well designed
system to hit......
If you have an 800Ah bank and don't have 20% of "C" from your alternator or charging system it may take longer to combine.... If you can't provide 20% of "C" then that is simply a poor design unless you have lots of time to charge, which on sailboats is rarely the case.....
An Echo Charger
or Duo Charger
also don't turn on until 13.0V so there is no difference in that regard. The Sterling battery to battery charger, their version of an Echo or Duo, does not turn on until 13.3V...
This is some collected data from a test I ran a few years ago. The battery was a healthy, but broken in, 125Ah Group 31 "Deep Cycle" battery fed by a 20% of "C" charge rate, or 25A, this after being discharged to 50% SOC. This was also after a controlled 20 hour capacity test confirming the capacity of the bank.
It took 1.7 Hours in bulk or constant current charging to hit absorption voltage but just 10 minutes at 20% of "C" to hit combine
voltage. This was done at 75F....
2 Min = 12.59V / 25A = BULK / Constant Current
10 Min = 13.0V / 25A (ACR would make after 90 seconds)
20 Min = 13.12V / 25A
30 Min = 13.22V / 25A
40 Min = 13.33V / 25A
50 Min = 13.45 / 25A
60 Min = 13.6V / 25A
70 Min = 13.76 / 25A
80 Min = 13.95 / 25A
90 Min = 14.16V / 25A
100 Min = 14.39 / 25A
102 Min = 14.4V / 24.5A = ABSORPTION VOLTAGE / Attained Voltage Limiting