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
This time at 23 amps vs 11.5 (the 20hr rate) it took 1 hr 18 minutes (instead of 1 hr and 30 minutes for half the 3 hrs it took at 11.5,) and the Trimetric said 31.2AH instead of 34.3 AH to get down to 1.275 from 1.295
All subject to margins of error best I can do. I do not have Peukert info to say if that is as expected for amount, but it does seem to show the Effect.
ASSuming that is all reasonable for test results, it means the SG is a valid marker for SOC regardless of capacity.
I note that the "usable AH" idea is based on SOC, where they allow going down to 50% each on the two ordinary batteries and 100% (almost) on the fancy one.
BUT---SOC is not the same as AH. It is only the same when you use 100AH batteries. Part of the smoke and mirrors.
So with 10 amps as the load for equal "use" where 5 amps is the 20 hr rate on the single fancy batt, you can go down to 20%, SOC but that will not be 80AH, but less for less time, which going down to 60% SOC each on the 200AH bank would be 80AH, since that is at the 20 hr rate for that bank.
EDIT--"phemens" in another thread running here, introduces a wrinkle in all this--What if the fancy battery does better in cold temps, not losing as much capacity? That might help even things out some in cold temps.
All subject to margins of error best I can do. I do not have Peukert info to say if that is as expected for amount, but it does seem to show the Effect.
ASSuming that is all reasonable for test results, it means the SG is a valid marker for SOC regardless of capacity.
I note that the "usable AH" idea is based on SOC, where they allow going down to 50% each on the two ordinary batteries and 100% (almost) on the fancy one.
BUT---SOC is not the same as AH. It is only the same when you use 100AH batteries. Part of the smoke and mirrors.
So with 10 amps as the load for equal "use" where 5 amps is the 20 hr rate on the single fancy batt, you can go down to 20%, SOC but that will not be 80AH, but less for less time, which going down to 60% SOC each on the 200AH bank would be 80AH, since that is at the 20 hr rate for that bank.
EDIT--"phemens" in another thread running here, introduces a wrinkle in all this--What if the fancy battery does better in cold temps, not losing as much capacity? That might help even things out some in cold temps.
