You're going to be able to use 80%-90% of those 60Ah LFP cells with virtually no ill effect on their longevity, versus starting to adversely affect the life of the AGM batteries going much past 60% DOD.
60% of 75Ah is 45Ah, which is just 75% of 60Ah. So you have another 10% DOD (6Ah) on the LFPs compared to a 'safe' DOD on those AGMs. Many people use 50% instead of 60%, and in looking just now, I see one source saying 80% is okay for AGM. Not sure I buy that though. I certainly wouldn't leave it at that SOC for very long. I'd use 95% of an LFP before I'd use 80% of an AGM.
The considerably lower weight on the LFPs will also likely help your speed (marginally), and thus your range. Then there's the significantly-increased cycle count of LFPs over AGMs.
Do note that not every arrangement of prismatic LFP cells has such a nicely-fitting case for it. And, searching through many brands and sizes of cases can be time-consuming. Some time spent before pulling the trigger on the cells, trying to find a matching case (for some arrangement of them) could help avoid having cells for which no conveniently-sized case is made. I find between half an inch and one full inch on each side to be enough to compensate for the usual curvature at the bottom of the case. Alternatively, some spacers on the bottom of the case could get the bottoms of the cells up past where they interfere with that curvature (if a case with enough side space can't be found). A last resort would be an oversized case with spacer rails on the sides to match the cell arrangement dimensions.
From: electricboats@groups.io <electricboats@groups.io> on behalf of Skray775 <kelly@skraye.com>
Sent: Sunday, May 8, 2022 6:02 PM
To: electricboats@groups.io <electricboats@groups.io>
Subject: Re: [electricboats] LifePo4 build questions
Nice setup Bob. I have watched a ton of Will's videos and the build difference in these batteries is an eye-opener.
Now let me step back into reality for a moment...
I know that three group-31 Optima Blue Top batteries rated at 75Ah served me well for many years. I could fish all day without worry but I could not travel to the ends of the two reservoirs I frequent. While it would be nice to be able to do so, it is not something I have to have. So maybe you all can help me run the numbers so to speak.
How would 60Ah LifePO4 with Grade A Fortune cells in a 36-volt pack compare to the above Optima pack in terms of run time?
Assuming it is equal or a little better I could build a 12s 60Ah pack this year and if it turns out to not fit my needs I can add another 12 cells in parallel for 120 Ah next year. This seems more flexible / modular to me. I would fit all of this into a case similar to the one Bob showed in his video.
No comments:
Post a Comment