Thread: lithium ?
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Old 10-20-2019, 02:12 PM   #25
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City: Seattle
Country: USA
Vessel Name: Rendezvous
Vessel Model: Ocean Alexander 420 Sundeck
Join Date: Sep 2018
Posts: 306
Originally Posted by Gordon J View Post
After installing 900 amp hours of fire fly oasis batteries, I am curious about what you term to be their sensitivity to charge profile. I do not find them to be any more sensitive in set up then a normal AGM. Also, as you learned, they do charge faster than a normal AGM, and you can run them all the way to zero, without harming them. They advertise 4500 Cycles if only discharge to 50%. I reckon I will never have to buy batteries for this boat again.

About your lithium batteries, are they installed in the engine room. I am a bit concerned about the heat in my engine room and the coal location of my battery banks. My understanding was that lithium is even more sensitive to heat. Has that been your experience?
Hmmm, I remember the charge profile for Firefly batteries being more restrictive than, say, a Lifeline AGM battery. Has that changed?

I also do not remember that it is OK to discharge them to 0% without harming them - in fact, I believe that reduces the cycle life. Perhaps you meant to say that you could discharge a Firefly and not have it completely stop working vs. a traditional LiFePO4 without a BMS, in which case you'd most likely have a broken LiFePO4 battery.

Keep in mind the batteries I'm using have BMS's on them that prevent that, and the previous system had a BMS and control circuitry to do that as well. Firefly batteries don't have this at all, and in fact, I've seen more dead Firefly or AGM batteries because owners discharge them repeatedly to 0% accidentally. It makes the case for adding some of the same BMS/control circuitry that LiFePO4 banks have to a AGM or Firefly bank to make sure this wouldn't happen.

LiFePO4 is sensitive to heat just like any other battery. The ones I use now will trip the BMS and shut down if they are 135F or hotter. Victron LiFePO4 batteries have a max operating temp of 122F. Lifeline AGM says 160F max, and Firefly says 104F! Quite surprised at that low number for Firefly - I don't remember that from the original sets I installed.

My engine room sits at about 90-100F depending on the time of year, so I have not seen any issues. In terms of longevity, I'm sure there is an impact, but only time will tell.
Steve Mitchell - Editor
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1988 Ocean Alexander 420 Sundeck
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