I used to think that couldn't be, due to Peukert, but apparently it can be, because that is what happens.
Doesn't the Trimetric use 1.3 for its Peukert exponent? If it does, then it accounts for Peukert.
I set my Magnum for Lifeline batteries but it is not putting out the voltages recommended by Magnum.
If you've been boondocking with those batteries and you do the routine of only charging to 90% while you're boondocking (which we all do...well most of us do) THEN you go home, hook up to shore power and let them charge to 100%, your batteries will lose capacity after a time. With this type of usage, Lifeline recommends a conditioning charge (the 15.5V thing, which your Magnum will do properly) when you notice capacity loss. Some others disagree with me AND Lifeline (LOL!) but I think I'll go with what Lifeline says on this one. If I were you, I would verify that there is indeed capacity loss first. You can do your own load test.
Batteries are rated at the 20 hr rate. You COULD fully charge them, let them sit for 24 hrs with NO load. Take voltage reading, if at 12.8V commence test. You could load them with their 20 hour rate and they should get down to 50% SOC in 10 hrs or so. If they get to 50% in 10 hrs then you know they're ok, if not then they're sulfated and you should run the Magnum's equalizing charge (need to use the Lifeline AGM setting for this to work). Lifeline, I believe, recommends 8 hrs but I think the Magnum does 4 hrs so you may have to run it twice.
I don't know whart the Trimetric does--ISTR somebody posted an article from the company on why it does not bother with Peukert.
bigfootford posted this in a previous discussion on this topic:
".... Bogart Engineering Trimetric 2020 states: "it should also be noted that effective capacity of the battery is less at high current draw--although this is not significant for the "typical" rates in renewable energy systems--it becomes more significant at discharge rates exceeding C/5 rates". Read section C4 page 9 about higher than average discharge rates and programming. Bogart Engineering Trimetric 2020 programming and install"
Anyway, 90 amps on my 458AH bank is C/5 and the OP's draw of 140 on his rated at 765ah would be C/5.4 so that may explain why I can't see much Peukert happening based on the above quote re C/5.
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Mr Wiz, I know the capacity should be less and it is not linear. In fact I used to post how I thought a monitor couldn't possibly work right because of Peukert. I agree it doesn't make sense what I was saying, but the Trimetric seems to work ok.
I may not be seeing the truth also because in a typical test, I recharge at 100 amps after discharging at 90 and sure enough a 50-90 comes out right for AH going back the other way.
The only thing I can think of that could be throwing me off is when picking the 50% mark using SG, my hydrometer accuracy could be better. Also the rebound in voltage to 12.2 is an estimate based on when the rising v slows right down. I could be at a lower SOC than I think.
T-105s use 1.172 SG and 12.1v at 80F at their 50%. My 27s testing worked best using 1.200 and 12.2v. Not sure what my G135s and GC2 XHDs should be at so I pick something in there.
The advice given me above is in effect to do a better job observing AH vs SG at the supposed 50% mark so I will try to do that.
* This post was
edited 06/30/12 11:01pm by BFL13 *
I'm reading all these replies and trying to learn. I wanted to answer this one as the poster asked a couple of questions.
Water Pump: I didn't run it an hour. Just used it to fill a big container for each microwave run. Tried to estimate the AH it was run after I determined its amp rate.
Loads: I ran the microwave 12 times for 5 minutes and measured during and after each time.
Batts: They are cabled correctly, I believe, with the proper size cable. The cable between the batteries and the inverter is 0000 (4 ott).
Not sure about the rest yet. Thanks.
Kustom Koach Class C 28'5", 256 watts Unisolar, 875 amp hours in two battery banks 12 volt batteries, 2500 MSW watt inverter.
Thanks again to everybody. I read up on the Peukert and have a general understanding of it. i.e. Battery will have less capacity as the discharge rate is raised. (the Peukert constant for the Lifelines is 1.12).
Yesterday, I plugged in and let it charge to "full charge" and 0 amps according to the Magnum display. That took around 4 hours (started at 12.4 volts). I disconnected the batteries this morning and am going to let them sit until tomorrow morning. Then I'll read the voltage and should know if I am really at a full charge (12.8 or more according to Lifeline).
Pianotuna: I never thought about the surge factor of the microwave. Thanks. Re a balanced battery installation, now I see what you mean. My installation most closely resembles #2 with the batteries strapped together with 000 and positive to coach on one end and negative on the other.
Mena661: We boondock a lot, about half the time. e.g. Last time out we were gone about 2 1/2 months and spent about half the time dry camping. I did equalize the batteries during our last time out after getting the OK from Lifeline. I'd like to do the 20 hours rate test you suggest. Lifeline documentation indicates that my three 8DA batteries will take 13.7 hours to discharge to 50% at a 25 amp rate. So how would I create that 25 amp draw? Just turn on stuff until I get to 25? Thanks.
unless the magnum does some sort of maintenance current
Thanks. It has four stages. The float is supposed to provide 13.2-13.4 compensated by temperature. Then it goes to "full charge" which turns the charger on when the voltage drops to 12.7. Then it floats for four hours.
Printed out smk's chart (thanks). Pretty amazing. Also read up on the effect of temperature. My setup is supposed to compensate. Yesterday, for example, the batt compartment was about the same as ambient temp, around 110.
Now I'm going to find that post on the Magnum issues.
I'd like to do the 20 hours rate test you suggest. Lifeline documentation indicates that my three 8DA batteries will take 13.7 hours to discharge to 50% at a 25 amp rate. So how would I create that 25 amp draw? Just turn on stuff until I get to 25? Thanks.
Yea pretty much. Do you have something that you can run from the inverter that draws about 250W? That should get you close.