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I think Eric is spot on. Victron smart shunts allow their smart solar and DC to DC chargers to end charging when reaching a specific tail current. I believe 3.45 volts per cell gives the fastest charging without driving cell imbalance. If you need to be above or below the knees in the charge curve you need a bigger bank.
I read Eric’s article. I understand ohm’s law and how batteries charge. However, Eric’ article is a bit too much for anybody wanting to go from lead acid to LFP. Eric is right – most people don’t understand or don’t know what they are doing or maybe don’t care. I honestly don’t believe that is going to change. The only thing Eric’s article does for me is convince me that I will never be able to properly charge a LFP battery or a lead acid battery for that matter.
The reality is that many of those individuals that don’t know anything about batteries are using them and mostly with some success. Boats, RV’s, golf carts, fork lifts, and many other users aren’t burning down or blowing up due to lfp failure. Maybe the batteries do not last the 6000 cycles because of improper charge/discharge but anything above 1000 is significantly better than an AGM battery. Due to the same ignorance, AGM or lead acid batteires significantly underperform.
Today you can buy very good LFP batteries assembled in cases with BMS’s that more than adequately manage charging and discharging. They may not be UL approved but are very good. Right now the cost of a fully assembled ready to go 12v 300ah LFP is the same ($450) as a reputable AGM (Northstar?) 31 105AH which at 50% is 20% of the LFP battery. You need 5 of those batteries to equal 1 12v 300AH LFP. Charging the AGM battery assuming you cannot wish away the float stage will take you 7-8 hours. The LFP at .5C is a bit more than 2 hours. A fancy 3 stage battery charger for AGM 24v 60A is over $1200. A fixed voltage 24v 50A charger/converter from Powermax is $350.
What we need is a common sense simple guide from a reputable source on how to incorporate LFP into your boat house batteries, especially if you already have large battery banks and maybe would like to have more. LFP prices keep going down and AGM prices go up? Maybe at the end you will not maximize the output or the cycles but then is that really an issue. We need to know if we do this and that (simple) the battery may only last so many cycles and how much is that going to cost vs an AGM batteruy also not properly managed.
Obviously, we need to build a system that protects all critical equipment such as instruments, auto pilot, bow thruster, start batteries, etc. However, most boats (> than 40ft) have seperate batteries for the above and house.
Hi George,
Sure, I agree that we don’t need to fully understand all of Eric’s article, at Nordkyn Design, that said, I do think we need to have a good understanding of all aspects of the system. As to a “common sense simple guide from a reputable source on how to incorporate LFP into your boat house batteries: that’s exactly how I see this Online Book: https://www.morganscloud.com/category/electrical/online-book-electrical-systems/
It will only take you about an hour to read, assuming you skip the stuff on lead acid, and I would argue that’s the minimum to impart the knowledge required to make good choices and install a safe, functional system.
That said, if you have further questions after the read though, please leave a comment.