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LiFePo4 battery users
#1
Before I begin, let me say that I am interested in the actual experiences of users....not opinions of people who do not own and use these batteries.   (Too many uninformed opinions in the past]

I am running all electric systems.  No propane.   I have 650w solar on the roof and 600w on my awning.

But, my issue is about keeping my batteries full too much of the time.   Lithium (I am told) does not “like” being full all the time.   But...how much is too much?   How does that actually impact the life expectancy?    

I cook with an induction surface...coffee and lunch each day.  On a cloudy day I cook dinner with it too (1800w) For the last couple months I run the electric heat a couple hours each morning.  But, only full tilt about 30 minutes (1500w) otherwise it gets too warm, then turn it down to medium (900w). But, on a sunny day the batteries are back to full by 1-2 pm.  

Sometimes I just disconnect the solar completely for a day or two....but I always get back to full rather quickly....maybe too quick?

What experiences are other people having.   What do people do?  Disconnect the solar for days and watch the monitor?    What level do you look for before turning the charging back on? If you just keep them full, any idea how much shorter the battery life will be?  Any idea on how to calculate that?

One final question. What exactly is a cycle? Is a draw down to 95% then charge back to 100% counted as a cycle? Is it the same as if you had drawn down to 50% then back up? If every drop and rebound is considered a cycle...then I would have to say that I am probably cycling them a couple time a day. Doesn’t sound right.



1989 Honeywell motorhome
Ford E350 chassis.  460 engine
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#2
Here's a link to Technomadia's experience with lithium:
https://www.technomadia.com/lithium/
(03-14-2019, 05:23 AM)RoamingKat Wrote: What exactly is a cycle?   Is a draw down to 95% then charge back to 100% counted as a cycle?  Is it the same as if you had drawn down to 50% then back up?  If every drop and rebound is considered a cycle...then I would have to say that I am probably cycling them a couple time a day.  Doesn’t sound right.
Every battery has a finite number of cycles, so 95% would be a good approximation. Similarly 47% could be considered a half cycle. Therefore, if a battery is good for 1000 full cycles it then would be good for 2000 half cycles.
Tom
2005 Born Free 24' RB
Towing 2013 Smart Car
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#3
But...what is a cycle?

Does every dip below 100% and back up count as one cycle?

Also, techno article did not answer my questions.

Are you running LiFePo4 batteries? What is your day to day experience? How are you maintaining them? Full all the time? Etc.....



1989 Honeywell motorhome
Ford E350 chassis.  460 engine
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#4
(03-14-2019, 10:00 AM)RoamingKat Wrote: But...what is a cycle?  See below

Does every dip below 100% and back up count as one cycle?  No

I thought a cycle was already defined above.  A cycle is a full discharge, ie on lithium a 90%to 100% discharge would be 1 full cycle.  Likewise a partial discharge is a partial cycle.  I don't know how to simplify that any further.

I have AGM but the cycle thing is the same.  I have a 350 Ah bank that one cycle would be 50% of 350 or about ~170 Ah's.  I only take about 20% of my usable AH's which makes for partial cycles.  My batteries are now 8 years old and will need replacing soon.  I am on the fence about going to lithium.
Brian

2000 Roadtrek 200 Versatile "The Beast" (it has been tamed hopefully)  I feed it and it doesn't bite me.   Angel
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#5
If I counted 5% depth of discharges, as cycles, then I have many thousands of cycles on my lead acid battery.

I estimate I have about 1100 deep cycles to 60% SOC or less on the battery.

Lithium, I don;t know how to quantify as to what constitues a cycle.

I can say my Phone battery, when i was plugging it in all night overnight most every night, degraded much faster than when i replaced the battery and I simply plugged it in when it was low or I knew i was going to be away from a charging source for a while.

So I basically do not plug in my phone and keep it fully charged and the battery life seems to degrade less quickly.

how this correlates to prisimatic Lifepo4 cells, I do not know, and those who could definitively say so, obviously have to have experience with such batteries and the tools and wherewithall to actually test capacity and performance.

I would ask your question on the Cruisers forum and Wait for Mainesail's response. Do note you will see John61CT jump in on every thread as an expert as he would do here in his brief stay, or crvl . Seems a lot of people were calling him out on his zero experience BS there too. I kind of stopped visiting there much in part to seeing his BS responses on each and every thread, but it has some of the best technical gurus regarding Lifepo4 that I know of on the web. Basically Mainesail. That would be the guy I would always seek answers from as his experience and knowledge is unmatched, in my opinion.

http://www.cruisersforum.com/forums/f14/
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#6
I am using LiFePo4 in a VW based Campervan. I am not worried about the “too full” argument by charging to 14.1 Volts and discharging to 11.8 volts. According to me, that’s 90% full and 15% discharged. People into EVs tell me the 14.1 volts is closer to 85% and 11.8 is closer to 20%. I get very different opinions from some people using LiFePo4 in Motorhomes. Only been using Li for 20 months so cannot say anything about ‘life’.

Cycles - the tables supplied by AGM suppliers show several cycle depth to life graphs. If you only ever discharge 20%, you get to do that lots of times, as a prediction of Life. If you always discharge to 80%, you get to do that much fewer times before you run out of Life. You will notice that the total energy you get to draw from the battery is about the same no matter whether you cycle up and down 20% or 80%.

My power needs in the campervan are modest. I have two identical Li batteries. I charge and discharge one at a time. So for me, a cycle is 75% of nominal capacity, every time. When the batteries “die” some time in the future, I will offer some data on how long they lasted.
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#7
Something to think about if deciding what your low voltage cutoff should be with LiFePo4. At the bottom of a discharge cycle, terminal voltage drops from well above 12 volts towards the high 11s very quickly. I incorporated that knowledge into my decision of how low to go by understanding that the difference between a low point of 11.8 is only a tiny percentage difference in depth of discharge to, say, 11.5. I could have decided on 12 volts as my low voltage point and not lost much usable capacity.

High end point. Still playing with that by charging to 14.1 then watching what the terminal voltage settles at after the battery is rested, that is, left sit not connected to anything. I have one 7 year old AGM that I charge with 14.4 volts. When I rest that battery, it settles out to 12.63 volts. The charge voltage is only relevant to the time it takes to charge the battery, not the level or amount the battery can store.
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#8
(03-14-2019, 10:00 AM)RoamingKat Wrote: But...what is a cycle?

Does every dip below 100% and back up count as one cycle?

A 'cycle' is a fuzzy term, and can be confusing.

Lithium batteries are also rated in 'lifetime amp hours', which you rarely see for lead acid batteries.

A typical 100 ah lead acid battery might have a lifetime amp hour rating of 30,000. Maybe 50,000.

Meaning you can draw (then recharge) 30 (or 50) amp hours, 1000 times. (in theory, ideal conditions)

A typical 100 ah lithium battery will have a lifetime amp hour rating of around 300,000.

Meaning you can draw the same, for 10,000 times. (again, in theory).

At the end of those lifetime amp hours, the lead acid battery will be near the end of its usable life, where the lithium battery might have lots of usable life left. 

The way you are using your lithium batteries sounds fine to me, and the reason they recharge quickly on your system is because that's exactly one of their primary advantages: quick recharge time. 

In other words, if it aint broke, dont fix it!
Wondering about Wandering.
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#9
I like the idea of total lifetime amp hours rating, or better yet lifetime KWH in terms of expected battery life, instead of cycles which can be so vague.

while many AGMs are heavier and come in at a lower AH rating for the same size battery, if one were to rate them in KWH, since they usually maintain higher voltage under discharge, they would likely come out ahead on the total capacity rating, but in AH only, it artificially makes the flooded battery appear to have higher capacity for less$$ and less weight when the AGM, if properly recharged would have been able to power more for longer anda larger lifetime AH/WH

Also the 50% rule with lead acid gets smeared out of place, with people thinking that if they go below 50% then the battery is doomed, but in relity as long as it is not brought down o 20% and left there for days on end, the total lifetime KWH is likely the same as if one observed the 50% rule.

i've got hundreds of cycles well below 50% on my AGM but proper and full recharges are done often. Its lifetime KHW is no doubt impressive so far, but I could only roughtly guestimate the amount if i were to put the thought into it and run some numbers, hich I will not bother with.

If Lifepo4 are really finicky about living fully charged, perhaps lower the absorption voltage or take a panel or two off line after sundown when sunny skies are expected the next day, Whether taking panes offline in direct sun when making lots of amps is detrimental to panels, well it is a possibility, and one I avoid and recommend be avoided when possible.

One reason i have not pursued lithium is one supposedly has to unlearn the get it full asap keep it full for best service life of lead acid mentality. i guess the only time you really need to fully charge lithium is when you need their full capacity for that next discharge.

Looks like someone could heat a good amount of water electrically with their excess solar and keep the lithium from sitting full all afternoon.
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#10
First : Stop stressing about counting anything Huh .

This basically applies to all battery types AFAIK.
(I'd need to save a lot more to get experience on anything above lead acid.
But it's treated me pretty good over all these years of life on those round spinny things...)


Look at the big picture.
In real life use , depth of discharge varies just as your use does.
So does charging , especially if you're relying on solar to do all or most of it. Wink

Deeper discharges count more than light discharges
but the exact amount of each matters less than the overall
total.

>>>>>>>>AND proper charging of any battery is the holy grail. Angel <<<<<<<<<<<<<<<<<<

A full charge every time as soon as possible is the true meaning of (battery) life............... Wink

EMVOT.....everybody's mileage varies on this.. Cool
Stay Tuned
rvpopeye



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