Matthew, I did not mention this in the last email, but I still use a lead acid battery for a dedicated start battery. I have my alternator connected directly to the start battery and I also use a battery combiner for charging the house bank. This was my simple solution for protecting the alternator from BMS disconnects, and since I already had a good start battery and a battery combiner, this was a no-cost safe LiFePO4 charging solution.
I do have the ability to use the LiFePO4 battery as a start back up. I would expect LiFePO4 batteries to perform fine as starting batteries. If anything, the constant 13.2V load voltage would keep your engine's starter happy. Low voltage drops are terrible for electric motors (i.e. starters and anchor windlasses). I have heard of some sailors using a LiFePO4 motorcycle battery for starting diesel engines. These batteries weigh about 2 lbs and while the capacity may only be ~5AH, they claim cold cranking amps (CCA ) of over 300A. I have little interest and am somewhat cautious about these claims, but at $60 they are cheap enough to test out and many have pretty good reviews. Check out the 5AH TPE Lithium Motorcycle Battery on Amazon. Since most marine diesel starters draw less than 150A, 5AH would amount to 5AH/150A*60m/H = 2 continuous minutes of cranking. That’s a lot of cranking and comparable to that of a 100AH rated lead acid battery (recall that a C/20 rated 100AH lead acid battery effectively provides only 10AH at 100A discharge load). I don’t have the interest in these for a start battery, but we do have some club racers who are suspected of removing every other screw and stripping down the boat to save on weight, so replacing 70 lbs with 2 lbs seems a bit starter. Paul - Paul E. 1981 C&C Landfall 38 S/V Johanna Rose Fort Walton Beach, FL http://svjohannarose.blogspot.com/ > >> On May 26, 2022, at 1:03 PM, Matthew via CnC-List <cnc-list@cnc-list.com >> <mailto:cnc-list@cnc-list.com>> wrote: >> >> >> This is excellent information. Thanks, Paul. >> >> One of the reasons I have hung on to my lead acid house batteries is that my >> charger has settings for AGM, lead, and maybe one other, but all three >> batteries must be of the same type. The lead acid starting battery is >> isolated (combined for charging) has good cranking amps, so I have continued >> to use lead acid for the house. How well do LiFePO4 batteries perform as >> starting batteries? >> >> From: Dreuge via CnC-List <cnc-list@cnc-list.com >> <mailto:cnc-list@cnc-list.com>> >> Sent: Thursday, May 26, 2022 3:24 PM >> To: cnc-list@cnc-list.com <mailto:cnc-list@cnc-list.com> >> Cc: Dreuge <dre...@gmail.com <mailto:dre...@gmail.com>> >> Subject: Stus-List Re: Batteries again >> >> Dave, >> >> As I mentioned in previously replies to the list, it no longer makes any >> sense to buy lead acid batteries(i.e. flooded, gel, or AGM) for a house >> bank. For lead acid, the AH capacity is highly dependent on the current >> load due to the Peukert Effect. Deep cycle lead acid batteries are rated >> at C/20. For a 100AH rated battery, this is 100AH/20H = 5A. This is often >> called the 20H rate, i.e. 5A * 20H = 100AH. If the actual load is 20A, >> then the same 100AH rated lead acid battery would only provide 60AH (or 10AH >> at 100A). And worse, one should only use 50% of a lead acid battery’s >> capacity as going below 50% substantially degrades the battery lifetime. >> This means that a 100AH lead acid battery has an effective 50AH @ 5A (or >> 30AH @ 20A). >> >> Let’s assume a 100AH lead acid battery price of $264 (the average of the >> Amazon prices), then 2 batteries would cost one $528 and one would get an >> effective 100AH (50%*200AH) at 5A loads. >> >> Now, the price of LiFePO4 batteries have come way down in the last few >> years and their performance and lifetimes are a magnitude better. A 100AH >> LiFePO4 battery is typically rated at 1C. That is they can deliver 100AH at >> 100A for 1H(or 5A at 20H or 20A at 5H). They can also charge at amps up to >> 100A which is impossible for a lead acid battery. And LiFePO4 batteries >> live 5 times longer. That is, one would expect to replace 5 sets of lead >> acid batteries before replacing a LiFePO4 battery. Yes, LiFePO4 batteries >> are more complex as they require a battery management system (i.e. BMS), but >> there are companies which provide 12V drop in replacements with the BMS >> built internal to the battery. Top companies like Battle Born sell a 100AH >> LiFePO4 for $874 and provide a 10yr warranty. Renogy sells a 100AH LiFePO4 >> for $765. A company, CurrentConnected.com <http://currentconnected.com/>, >> sells a SOK 100AH LiFePO4 battery for $569 and it has a 10 yr warranty! >> YouTuber Will Prowse rates the SOK as the best value LiFePO4 12V drop in >> replacement (see https://www.mobile-solarpower.com/lithium-batteries.html >> <https://www.mobile-solarpower.com/lithium-batteries.html>). There are a >> plethora of cheaper 100AH LiFePO4 batteries that can be found on Amazon, >> Ebay, AliExpres, …, but one gets little service and limited warrantees, so >> I would recommend avoiding these. >> >> Rather than buying 2 100AH lead acid batteries for $528 at a total weight of >> 140lbs(70lbs each) , one could just buy 1 100AH LiFePO4 for $569 weighing >> only 28lbs and get a better performing battery. That is basically the same >> price. If one takes into account the increased lifetime, the saving is >> HUGE! >> >> If one builds their own DIY LiFePO4 battery, the savings is much much >> greater. Last year I replaced 2 100AH lead acid batteries with one DIY >> 560AH LiFePO4 battery for a little over $900 (see my blog link below). The >> DIY LiFePO4 battery occupies the same location and physical space as the >> previous 2 lead acid batteries, it weighs much less (95 lbs vs 125 lbs), but >> has 5 TIMES the capacity. >> >> I recently gave a talk on off-grid solar systems a local amateur radio >> society meeting. The discuss the battery as the heart of the system and >> make the case for LiFePO4 batteries. My slides from the talk are available >> on my blog: >> >> >> https://svjohannarose.blogspot.com/2021/10/solar-off-grid-system.html >> <https://svjohannarose.blogspot.com/2021/10/solar-off-grid-system.html> >> >> >> Also, the details of my DIY 560AH LiFePO4 are posted at the link below which >> includes details about alternator charging. >> >> >> https://svjohannarose.blogspot.com/2021/06/adding-new-lifepo4-to-house-battery.html >> >> <https://svjohannarose.blogspot.com/2021/06/adding-new-lifepo4-to-house-battery.html> >> >> >> >> >> >> - >> Paul E. >> 1981 C&C Landfall 38 >> S/V Johanna Rose >> Fort Walton Beach, FL >> >> http://svjohannarose.blogspot.com/ <http://svjohannarose.blogspot.com/> >> >> >> On May 26, 2022, at 11:24 AM, David Knecht via CnC-List >> <cnc-list@cnc-list.com <mailto:cnc-list@cnc-list.com>> wrote: >> >> I have been following the battery discussion and have a question. I need to >> replace my two 9 year old AGM batteries this season. I have separate start >> and house batteries which can be combined if needed. I don’t have large >> power needs (electronics, autopilot and fridge when cruising). I have been >> reading and researching this and I am unsure of what to purchase. From what >> I have read, AH is the important number to focus on. Last time, I got >> Lifeline AGM group 27 from Defender. Defender has 3 different group 27 >> batteries >> Powertech rated at 92AH which cost about $330 >> Lifeline rated at 100AH for 432 >> Northstar rated at 92AH for 457 >> >> From Amazon, I can get a VMAX group 27 with 100AH for $289 or a Universal >> with 110 AH for $239. Is there any reason to be concerned about less known >> (to me) brands from Amazon or does it make sense to just focus on the >> numbers? Thanks- Dave >> >> S/V Aries >> 1990 C&C 34+ >> New London, CT >> >> <pastedGraphic.tiff>
