Battery Draw Bogus Math? Peukert UPDATE 2
Update- 11 Oct 20, Update 2- 12 Oct 20 Thinking one 100AH battery that can be drawn down to very low SOC gives you nearly the same "usable AH" as two regular AGM or Wet batts, as seen advertized, ...
Forum Discussion
I am comparing times at 5 amps between the one batt going down to 20% SOC at its 20hr rate ( 5 amps) which is 16 hours and 80AH (at its 20 hr rate)
With-- how long it would take to get to 60% SOC on the 200AH bank (at its 20 hr rate of 10 amps) but only drawing at 5 amps.
I am making a big assumption that you end up in the same place for SOC (at the 10 amp rate) ie at 60% either way -8 hrs at 10 amps or X hours at 5 amps.
"The amp rate is so low that perkuet is really not much of a factor, that comes into play at high amps decreased capacity, not much amphr capacity gain at low amp use"
That is what I am questioning. This table for a 105AH AGM seems to show that is wrong.
It is correct that the AH diff is not much, but look at the time diffs!
1 amp rate- 125AH = 125 hrs
1.18 a rate- 118AH = 100 hrs
5.25 amp rate- 105AH = 20 hrs
10 amp rate- 100AH = 10 hrs
So I claim the idea of comparing "usable AH" is smoke and mirrors. The real way to compare is by running times at the same amps.
It looks like drawing at half the 20 hr rate gets you about three times the running time. I am ASSuming that can be applied to the 10 amp 20 hr rate of the 200AH bank. So 8 hrs at 10 amps or 24 hrs at 5 amps.
I am worried this does not work for ending up in the same place for SOC at 60% on the 200AH bank at its 20 hr rate. Could be a problem here.
EDIT--could test for that with an open flooded using an hydrometer. Time it at 10 amps till 1.250 and then recharge to starting SG, then run it at 5 amps till 1.250 and note the time it took. Hmmmmm.
Reserve Capacity uses a fixed amp to compare battery times, 25 amps for RC of ordinary batts but then they use 75 amps for golf car batts, so that messes up comparing RCs.
With-- how long it would take to get to 60% SOC on the 200AH bank (at its 20 hr rate of 10 amps) but only drawing at 5 amps.
I am making a big assumption that you end up in the same place for SOC (at the 10 amp rate) ie at 60% either way -8 hrs at 10 amps or X hours at 5 amps.
"The amp rate is so low that perkuet is really not much of a factor, that comes into play at high amps decreased capacity, not much amphr capacity gain at low amp use"
That is what I am questioning. This table for a 105AH AGM seems to show that is wrong.
It is correct that the AH diff is not much, but look at the time diffs!
1 amp rate- 125AH = 125 hrs
1.18 a rate- 118AH = 100 hrs
5.25 amp rate- 105AH = 20 hrs
10 amp rate- 100AH = 10 hrs
So I claim the idea of comparing "usable AH" is smoke and mirrors. The real way to compare is by running times at the same amps.
It looks like drawing at half the 20 hr rate gets you about three times the running time. I am ASSuming that can be applied to the 10 amp 20 hr rate of the 200AH bank. So 8 hrs at 10 amps or 24 hrs at 5 amps.
I am worried this does not work for ending up in the same place for SOC at 60% on the 200AH bank at its 20 hr rate. Could be a problem here.
EDIT--could test for that with an open flooded using an hydrometer. Time it at 10 amps till 1.250 and then recharge to starting SG, then run it at 5 amps till 1.250 and note the time it took. Hmmmmm.
Reserve Capacity uses a fixed amp to compare battery times, 25 amps for RC of ordinary batts but then they use 75 amps for golf car batts, so that messes up comparing RCs.
