Yes there is. If you connect an alternator straight to a lithium bank and the BMS opens, you are likely to blow the diodes at best or do a lot of damage with a voltage spike at worst. Besides for that, since lithium batteries can accept a high rate of charge for a long time, they look like a dead short more or less to a small alternator.
Since the charging profile for lithium is different than any lead battery including the fact all lead batteries should have temperature compensated charging parameters and lithium does not do this, to correctly charge lead batteries and lithium batteries from the same alternator, there is going to have to be a DC-DC charger in there somewhere that uses the correct parameters for the bank it is charging, either lead>lithium or lithium>lead. In my case with a 60 amp alternator on an Atomic 4, I believe my best plan is to charge the start battery and use DC-DC for the lithium bank. See https://www.moyermarineforum.com/forums/attachment.php?attachmentid=16228 <https://www.moyermarineforum.com/forums/attachment.php?attachmentid=16228&stc=1&d=1651155864> &stc=1&d=1651155864 * the A4 is a special case for charging. The pulley that drives the alternator is small, so the alternator spins slower than on almost any other engine. Max current at low RPMs is hell on alternators, that makes them run hot with less cooling air from the slower turning fan. Even with a 120 amp alternator on the engine and loading up with a hair dryer that sucks 90 amps, I have never seen more than 45-50 amps from any alternator. I could mess around with my regulator and set it up for lithium, the temp sensor on the alternator should cause it to back off when very hot, but that still doesn’t solve the BMS issue and I still need to charge the start bank somehow. Joe Della Barba Coquina C&C 35 MK I Kent Island MD USA From: David Risch via CnC-List <cnc-list@cnc-list.com> Sent: Friday, May 27, 2022 1:46 PM To: Stus-List <cnc-list@cnc-list.com> Cc: David Risch <davidrisc...@msn.com> Subject: Stus-List Re: [EXTERNAL] Re: Batteries again Joe, We charge house then, a via “Digital Duo”, the start battery. That seems to be the norm DC to DC. Any reason you are doing it otherwise? From: Della Barba, Joe via CnC-List <cnc-list@cnc-list.com <mailto:cnc-list@cnc-list.com> > Sent: Friday, May 27, 2022 11:14 AM To: Stus-List <cnc-list@cnc-list.com <mailto:cnc-list@cnc-list.com> > Cc: Della Barba, Joe <joe.della.ba...@ssa.gov <mailto:joe.della.ba...@ssa.gov> > Subject: Stus-List Re: [EXTERNAL] Re: Batteries again My batteries are pretty well shot, so this is all good info for me as well. I always liked gels myself, but they are getting pretty hard to find now. I have been getting pretty tempted to go for a 300ah lithium, it will fit right in and give me a TON more amp-hours. If I go that way I am going to swap the alternator cable to the start battery and use a DC-DC charger for the house bank. One perhaps not appreciated feature of lithium batteries is that they are “stiff”, you maintain around 12.8 volts most of the way to being dead. Wednesday morning I went to check into the Waterway Net and the SSB wasn’t real happy to be seeing 12.4 volts, this would not be an issue with a lithium bank unless it was down to its very last bit of juice. Joe Coquina From: Korbey Hunt via CnC-List <cnc-list@cnc-list.com <mailto:cnc-list@cnc-list.com> > Sent: Thursday, May 26, 2022 11:12 PM To: Stus-List <cnc-list@cnc-list.com <mailto:cnc-list@cnc-list.com> > Cc: j...@dellabarba.com <mailto:j...@dellabarba.com> ; Korbey Hunt <kampf2...@hotmail.com <mailto:kampf2...@hotmail.com> > Subject: [EXTERNAL] Stus-List Re: Batteries again I highly recommend Lifeline group 31 Get Outlook for Android <https://nam12.safelinks.protection.outlook.com/?url=https%3A%2F%2Faka.ms%2FAAb9ysg&data=05%7C01%7C%7Ce6db60abfa6447c5e26208da3ff37fd5%7C84df9e7fe9f640afb435aaaaaaaaaaaa%7C1%7C0%7C637892612292527463%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&sdata=LNio5EVZQmyWD8G8Qg%2B8MAClJ8dzNAjh5gYLQM6luMU%3D&reserved=0> _____ From: Joe Della Barba via CnC-List <cnc-list@cnc-list.com <mailto:cnc-list@cnc-list.com> > Sent: Thursday, May 26, 2022 9:40:31 AM To: 'Stus-List' <cnc-list@cnc-list.com <mailto:cnc-list@cnc-list.com> > Cc: j...@dellabarba.com <mailto:j...@dellabarba.com> <j...@dellabarba.com <mailto:j...@dellabarba.com> > Subject: Stus-List Re: Batteries again There is a lot of reason to be concerned about off brands. Pretty much all cycling batteries of the same size will be about the same AH rating. There is no magic in lead batteries, the AH per pound is pretty consistent. What matters *hugely* is the number of cycles that they can endure before being trashed. The various cheap Chinese imports are highly variable to say the least, their reviews are all over the place. Lifeline is usually considered the best AGM maker. FYI – Deka makes all the West Marine AGMs, you might call around your local battery shop and see what they charge. They are worse than Lifelines, but if they crap out after a week at least you can return them to the store 😉 Joe Della Barba Coquina C&C 35 MK I Kent Island MD USA From: David Knecht via CnC-List <cnc-list@cnc-list.com <mailto:cnc-list@cnc-list.com> > Sent: Thursday, May 26, 2022 11:25 AM To: CnC CnC discussion list <CnC-List@cnc-list.com <mailto:CnC-List@cnc-list.com> > Cc: David Knecht <davidakne...@gmail.com <mailto:davidakne...@gmail.com> > Subject: Stus-List Batteries again 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
