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Old 18-10-2019, 07:09   #1
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Firefly Oasis voltage sag?

Can anyone comment on voltage sag for the Firefly Oasis batteries? I know they can be discharged to 80%-100% SOC without affecting the batteries capacity, but do the batteries still produce useful voltages at these SOCs? Right now we're debating lithiums or a set of L15 Fireflys. Thanks!
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Old 18-10-2019, 11:12   #2
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Re: Firefly Oasis voltage sag?

They still sag.
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Old 18-10-2019, 11:59   #3
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Re: Firefly Oasis voltage sag?

I have three L15+, they sag like AGM batteries, which they are.
Lithium is the only way to minimize or almost eliminate voltage sag.

I still love them. When they wear out, I'll upgrade to a larger bank of LiFePO4.
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Old 18-10-2019, 13:07   #4
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Re: Firefly Oasis voltage sag?

Thanks for the replies. I'm planning on redoing all of the charge systems on the boat as part of a refit anyway, so it sounds like I might as well go with LiFePO4 at the same time.
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Old 18-10-2019, 13:12   #5
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Re: Firefly Oasis voltage sag?

I wasn't willing to replace all of my charge sources so the L15+ made sense.
It turns out I almost exclusively charge with four solar controllers, not two alternators (two engines) and shore power connection. In your case, I would definitely go LiFepO4 now.
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Old 18-10-2019, 20:55   #6
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Re: Firefly Oasis voltage sag?

Voltage **dropping** as SoC falls, more than LFP does, is inherent in lead, even at low discharge C-rate, say C/20.

Voltage **sag** is the temporary drop from drawing at higher C-rates.

A separate phenomenon, but only solution with any lead bank is to increase Ah capacity to reduce the C-rate.

If you really need to that is, neither is in itself a problem as such, unless hitting a LVC disconnect setpoint or something.

Going to LFP for just that reason may well not be required, a very expensive jump, certainly in the US market.
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Old 18-10-2019, 21:09   #7
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Re: Firefly Oasis voltage sag?

When I needed new batteries two years ago, I did quite a bit of analysis and concluded that Firefly was the way to go for MOST sailboats over Lithium. I redid that analysis for a client recently, and nothing has changed.

https://fetchinketch.net/2019/09/24/...-marketing-bs/

If the weight is very important to you, go with Li. If you have a way of actually generating 0.5C or 1C charging currents, maybe Li makes sense.

For everybody else you get more than 80% of the benefit of Li for less than 50% of the cost with the Firefly batteries.

I have no economic dog in this fight, just data sharing.
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Old 19-10-2019, 00:29   #8
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Re: Firefly Oasis voltage sag?

Quote:
Originally Posted by billknny View Post
If you have a way of actually generating 0.5C or 1C charging currents, maybe Li makes sense
Doing so regularly in cool, or even mild temps can **greatly** shorten cycling lifespan.

At the lower end of that range, if the cells are getting up to 30C or higher, you should be OK, but I'd still only do so with strong reasons, not all the time.

Otherwise 0.4C is my max charge rate, 0.2-3C when they're getting cooler, even lower in true cold weather.

And conversely, while **not** charging and when not actively cycling, the cells should be kept as cool as practical, calendar life is **drastically** shortened by high temps.

Most owners may consider these issues not worth the trouble resolving, but better to know about them rather than not.
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Old 24-10-2019, 02:27   #9
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Re: Firefly Oasis voltage sag?

I am replacing my Optima Yellow Tops with Firefly Series 31s. My question is my ProTech1240iPLUS 40 amp charger "floats" at 13.3v and I read somewhere that Firefly batteries "float" at 13.2 and then I read again somewhere that Firefly batteries "float" at 13.4.

Is this 1/10th of a volt a big issue when maintaining a charge?
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Old 24-10-2019, 05:20   #10
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Re: Firefly Oasis voltage sag?

No that will be fine.

Best is no Floating at all though.
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Old 24-10-2019, 06:57   #11
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Re: Firefly Oasis voltage sag?

Quote:
Originally Posted by john61ct View Post
Doing so regularly in cool, or even mild temps can **greatly** shorten cycling lifespan.

At the lower end of that range, if the cells are getting up to 30C or higher, you should be OK, but I'd still only do so with strong reasons, not all the time.

Otherwise 0.4C is my max charge rate, 0.2-3C when they're getting cooler, even lower in true cold weather.

And conversely, while **not** charging and when not actively cycling, the cells should be kept as cool as practical, calendar life is **drastically** shortened by high temps.

Most owners may consider these issues not worth the trouble resolving, but better to know about them rather than not.
When you say '0.4C is your max'.

Is this what you are physcally doing yourself? Or it is just your opinion from what you have read other people saying on forums.

If you could note your source, or a write up of your experience that would be appreciated.
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Old 24-10-2019, 09:45   #12
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Re: Firefly Oasis voltage sag?

Note that the post you quoted from was about charging rates vs temperature wrt LFP chemistry cells *only**, nothing to do with FF AGMs.

I was responding to a member suggesting

> generating 0.5C or 1C charging currents

without qualifying the critical part temperature plays in whether such high rates are safe or not wrt cell longevity.

Before Maine Sail warned us off such high charging rates last year, I believe in a thread started by @rgleason,

I did indeed used to also regularly go that high.

The fact that high cell temperatures can make doing so safe has been documented in several research papers, but I don't have links.
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Old 24-10-2019, 12:37   #13
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Re: Firefly Oasis voltage sag?

Quote:
Originally Posted by George DuBose View Post
I am replacing my Optima Yellow Tops with Firefly Series 31s. My question is my ProTech1240iPLUS 40 amp charger "floats" at 13.3v and I read somewhere that Firefly batteries "float" at 13.2 and then I read again somewhere that Firefly batteries "float" at 13.4.

Is this 1/10th of a volt a big issue when maintaining a charge?
"Reading somewhere" isn't such a great approach; best to check with Firefly for actual recommended charge voltages.

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Old 24-10-2019, 13:13   #14
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Re: Firefly Oasis voltage sag?

latest, straight from the horse's mouth
http://www.cruisersforum.com/forums/....php?p=3001851
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Old 24-10-2019, 14:54   #15
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Re: Firefly Oasis voltage sag?

We have been cruising full time for the past 2 years with Firefly batteries. They are great batteries, but they are NOT Li Ion. The voltage sag is significant and affects all things like the watermaker and anything rotating (like pumps). To say that they can be discharged to 20% SOC is unrealistic. We will be converting the entire boat to Mastervolt Li Ion because the voltage sag with the Fireflies is very annoying. I was hoping they would be a "Li Ion Like" battery but nope.
I would still prefer and recommend Firefly batteries over AGM because of their resilience to being not fully charged and don't suffer from deep discharge events. For a cruiser it is nice to know that you have resilient batteries.
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