The 20 hr rate would be 23a on 460ah
The 5 hr rate would be 70a on 350ah , and
The 3 hr rate would be 106a on 319ah
So my 90a draw would be a 3.6 hr rate on 330ah.
I have run this several times at 90a, getting to what I thought was 50% prior to testing my charging set-up, so these are real numbers-
I start with a full bank at 460 and run it down for 2.5 hrs at 90a and the Trimetric says I used 225ah so I think I am at 50%. SG and voltage is at least around the T105's 50% mark of 1.172 and 12.1v if not better.
How can this be? If the Peukert thing is right, then with a 90a draw the bank's capacity should be around 330ah. But I just took 225ah out, so that should be down to 32% SOC not somewhere near 50%.
Actually, since it took 2.5hrs to get to 50% (if it was at 50) then that would be the bank's 5 hr rate, so capacity should have been 350 using that chart, but then that goes with a 70a rate not a 90amp rate.
What's with that?
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The 20 hr rate would be 23a on 460ah
The 5 hr rate would be 70a on 350ah , and
The 3 hr rate would be 106a on 319ah
So my 90a draw would be a 3.6 hr rate on 330ah.
I have run this several times at 90a, getting to what I thought was 50% prior to testing my charging set-up, so these are real numbers-
I start with a full bank at 460 and run it down for 2.5 hrs at 90a and the Trimetric says I used 225ah so I think I am at 50%. SG and voltage is at least around the T105's 50% mark of 1.172 and 12.1v if not better.
How can this be? If the Peukert thing is right, then with a 90a draw the bank's capacity should be around 330ah. But I just took 225ah out, so that should be down to 32% SOC not somewhere near 50%.
Actually, since it took 2.5hrs to get to 50% (if it was at 50) then that would be the bank's 5 hr rate, so capacity should have been 350 using that chart, but then that goes with a 70a rate not a 90amp rate.
What's with that?
with the trimetric, what did you enter for battery AH?? The trimetric doesn't do any peukert correction. So if you used 460AH and discharged at 90A it assumes a 460AH capacity not the 330AH. Change the trimetric to 330AH capacity and repeat the test and see when the trimetric says your at 50%.
But I do agree, the SG and voltage measurements aren't consistent with the AH ratings for the 90A draw.
2011 Keystone Outback 295RE
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I do not set the Trimetric for capacity so don't get the percent used from it, just the accumulated amp hrs, which I use to calculate SOC myself. In the winter, I adjust the capacity for the cold to get a better estimated capacity.
My question is exactly about that mismatch wrt SG and voltage which IMO is greater than my "lab testing" margin of error. Tighter lab work might resolve some of it, but I think I could tell if I were at 32 percent vs maybe 45 from error thinking it was 50.
Maybe my batteries are really good and have more than their rated 458ah!
Peukert exponent is specific to each individual battery design. Trimetric does not know about that, but it can guess and be pretty close but only if that unit is programmed correctly.
You need to start working with specific gravity and temperatures to get real numbers that will be correct for your batteries.
If you look at you table, you will see that their US125 takes less of a beating during a hard-short drain than does US2200. This is what Trimetric has to be programmed to understand.
Did anybody bother to tell you that taking any lead/acid battery below a 50% charge will necessarily cause a permanent loss of capacity?
Matt
Matt & Mary Colie
A sailor, his bride and their black dog going to see some dry places that have Geocaches in a coach made the year we married.
Did anybody bother to tell you that taking any lead/acid battery below a 50% charge will necessarily cause a permanent loss of capacity?
Matt
You don't lose capacity (at least not right away) but you will lose some cycle life. If you look at the various battery manufacturers some will publish a cycle life curve for their batteries. Pretty much anything below 90% takes a LOT of cycle life from lead acids but 50% is the accepted level of discharge due to a compromise between battery cycle life and cash. Trojan says their batteries have a cycle life of ~3000 @ 90% but at 50% it's ~750. At 20% you still have ~500 cycles! I don't know about you but 500 cycles is WAY more than I and most other RVers will ever use (full timers may use more).
I go with Matt Colie's generalizations on this one. The mother of all error is assumption. Calibrate your meter TO a hydrometer reading not voltage amp/hours unless you like guessing or are forced to do so with a Valve Regulated battery. You don't need to wear a hydrometer in a hip holster. Use it merely to calibrate, verify, and diagnose. Like a doctor does to a patient.
OK, i'll stir the pot a little bit more
the hours/vs amps for total capacity of batteries, as listed by the MFG
was for a total discharge ? , down to 10.5v ?
so maybe ? between 50% and 100% the SG stays linear up to the C-5 rate and below 50% (or some other point) it drops off much faster creating the lower capacity
in other words, the chemical reaction process ability to maintain the higher rate drops drastically after a certain SG point
this would relate to SG density and thickness of plate sulfation,
voltage drops faster ( as the chemical reaction slows) and the test is terminated at the cut off point
this is nothing more than a possible theory
but it would explain why blf can read a 50% sG consistent with his 225amphr discharge test
it gives the mfG a reliable marker saying the battery can sustain x amps for y hrs
and they use total ampHrs created/consumed as the capacity rating for those hrs
I'm Not Knocking the system, just suggesting a possible explanation why on some batteries, you can draw a higher rate and still come up measuring an SG for the correct c20 50% capacity
OK mexi go ahead and explain where i'm wrong
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vs maybe 45 from error thinking it was 50.
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