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Old 28-01-2013, 14:55   #1621
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

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Originally Posted by typhoon View Post
" C " I take it, means the total capacity of the house bank , so if I had a 400 ah bank 0.5C would be a discharge rate of 200 amps and visa versa.
Correct.

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So basically you want to size your total AH house bank twice what your highest load in amps would be and also your daily requirement in Amp hours .

Correct me if I'm wrong
I'm not suggesting that as a rule of thumb, but sizing the battery bank to at least 2 hours at peak load would maximize battery life. There are many other factors to consider in sizing the battery bank including cost, weight, space available, charging sources, etc.

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These batteries really are a godsend for us sailors.
Thank Poseidon!
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Old 28-01-2013, 15:03   #1622
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

My Lifeline AGMs were barely cycled, rarely below 80% SoC. Got 300 cycles out of them. I figure even the crappiest LFPs will do twice as well.
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Old 28-01-2013, 15:23   #1623
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

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Originally Posted by diugo View Post
My Lifeline AGMs were barely cycled, rarely below 80% SoC. Got 300 cycles out of them. I figure even the crappiest LFPs will do twice as well.
Now imagine what it was like on a boat when Lifeline originally told us to cycle to 80% DOD....... 300 cycles would have been a dream come true for some AGM users...
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Old 28-01-2013, 17:40   #1624
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Quote:
Originally Posted by Lagoon4us View Post
Bob's blog www.ebaugh.net is an excellent learning point, iv'e read it three times now getting bits out...

Now i have a question on high the batteries going into high voltage, correct me if i'm wrong:-
1). Are we are more concerned with a cell or cells going into a higher voltage causing an imbalance causing damage to the cell?

OR

2). Are we concerned that a higher output will cause damage to sensitive equipment?

Cheers.
There is little concern for equipment, since it will easily handle the maximum safe voltage for LiFePO4.

The concern is too high of a voltage, possibly even an old systems style normal one of 14-14.4V held too long. Either case can cause overcharge. Overcharge gets translated to lower capacity and shorter cycle life. Extreme cases CAN cause cell death and POSSIBLY, too much heat generation.
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Old 28-01-2013, 18:01   #1625
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

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nimblemotors,

You won't be seeing me complain after the results of these tests. At a low amp draw, when I can see 65% more a-hr than the cell's rating, I'm a happy camper. If I see 2000 cycles @ 80% DOD before the battery only holds 80% charge, again happy camper.
yep, the current LiFe cells are excellent, it is great to see their prices finally get reasonable. The early ones lived short lives, very poor C rates. AGM's have the ability to discharge at very high rates, but their lifetime has always been poor, just the opposite of what you need for a boat house battery. The current generation of LiFe are well suited for boats.
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Old 28-01-2013, 18:03   #1626
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

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Now imagine what it was like on a boat when Lifeline originally told us to cycle to 80% DOD....... 300 cycles would have been a dream come true for some AGM users...
I respect your knowledge when it comes to batteries and I know you don't think much of AGM's. I just wonder if Lifeline AGM is your main experience? I have used Odyssey AGM and they have been quite good for the applications I used them on. 17 years (and still going) as a cranking battery for my hot rod and that was a small 15 lb PC-680, and 5 years (and also still going) for my race scooter, where it got cycled deep and had 400 amps pulled a lot on a 48 volt series string of PC-680's.


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Old 28-01-2013, 18:05   #1627
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I basically agree with MaineSail's comments on cycle life. I saw 600 or so cycles, mostly in the 50-85% range, and ended up with 70-80% of bank capacity at the end on my T105's before lithium. But I did that in 16 months.

Someone who uses their boat less than 3 months a year needs to think hard before they invest the time and energy switching. Especially if they are happy with lead acid batteries. Or guys with big solar/wind generation capabilities unless aboard full time.

Regardless, install at least 20% more capacity than you think you need to allow for aging.

According to the professor in the video linked to way back in this blog, in a theoretical lab, they can cycle almost forever. But in real life, I think that's extremely optimistic. I do think we may find eventually that shelf life may turn into at least an equal factor in useful life onboard a boat, as cycle life is. But all of this is unproven, and we have to wait and see,

It's very encouraging and perhaps even contradictory to see the guys buying older cells from Balqon and observing greater than rated capacity in their testing.
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Old 28-01-2013, 19:34   #1628
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

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Originally Posted by deckofficer View Post
I respect your knowledge when it comes to batteries and I know you don't think much of AGM's. I just wonder if Lifeline AGM is your main experience? I have used Odyssey AGM and they have been quite good for the applications I used them on.

I find the Odyssey batteries to be doing better than other AGM's but I still doubt they will be as good as GEL...They are pretty amazing AGM batteries though and if I had to choose an AGM it would be Odyssey.


That said I have just completed my seventh cycle to 50% DOD and back to full. I am charging to 14.0V/3.5V per cell and considering that my "full". After seven cycles using a 100A load, the cells are still in amazing balance.

Cell #1 = 3.346
Cell #2 = 3.346
Cell #3 = 3.342
Cell #4 = 3.344

Measured with a calibrated Fluke 179 after 100A load applied for 30 seconds then allowed to rest for 2 hours...

On thing I notice is that at the top end of charge the voltage drifts a little bit and one cell might be 8-15mA higher than another. The minute you slap a load on it, and then measure voltage, they come right back in-line. Any good explanation for this?? I can live with the 8-15mA drift as it still keeps me well below the danger zone, but I find it odd that it vanishes once you apply a load and the cells come back to within +/- 4mA of each other.....
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Old 28-01-2013, 20:36   #1629
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

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Originally Posted by Maine Sail View Post

That said I have just completed my seventh cycle to 50% DOD and back to full. I am charging to 14.0V/3.5V per cell and considering that my "full". After seven cycles using a 100A load, the cells are still in amazing balance.

Cell #1 = 3.346
Cell #2 = 3.346
Cell #3 = 3.342
Cell #4 = 3.344

Measured with a calibrated Fluke 179 after 100A load applied for 30 seconds then allowed to rest for 2 hours...

On thing I notice is that at the top end of charge the voltage drifts a little bit and one cell might be 8-15mV higher than another. The minute you slap a load on it, and then measure voltage, they come right back in-line. Any good explanation for this?? I can live with the 8-15mV drift as it still keeps me well below the danger zone, but I find it odd that it vanishes once you apply a load and the cells come back to within +/- 4mV of each other.....

I don't know the answer to your question, but my cells do the same except the variance is higher (50mv).

After reading about your charging (3.5V/cell) I was wondering if you have 3.6V balance boards or 3.8V ? It seems you would need to charge at a bit higher voltage if you have the 3.8VBalance boards and want to activate the balance function.

Cheers,
JM.
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Old 28-01-2013, 21:12   #1630
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Re the low voltage cutoff. One might avoid the huge interrupter solenoid with a bit of wiring. The small house panel loads can be interrupted with a common solenoid or remote breaker. What are the big loads? Windlass, starters, inverters... The windlass and starter loads can be effectively disabled by interrupting the smaller control circuit. E.g. The engine panel, windlass control relay. Not so sure how to disable an inverter with a low current 'signal'. Perhaps put the interrupter on the AC side.

Just submitting an idea to avoid the 300A interrupter issue.
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Old 28-01-2013, 22:03   #1631
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

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Originally Posted by Maine Sail View Post
I find the Odyssey batteries to be doing better than other AGM's but I still doubt they will be as good as GEL...They are pretty amazing AGM batteries though and if I had to choose an AGM it would be Odyssey.


That said I have just completed my seventh cycle to 50% DOD and back to full. I am charging to 14.0V/3.5V per cell and considering that my "full". After seven cycles using a 100A load, the cells are still in amazing balance.

Cell #1 = 3.346
Cell #2 = 3.346
Cell #3 = 3.342
Cell #4 = 3.344

Measured with a calibrated Fluke 179 after 100A load applied for 30 seconds then allowed to rest for 2 hours...

On thing I notice is that at the top end of charge the voltage drifts a little bit and one cell might be 8-15mA higher than another. The minute you slap a load on it, and then measure voltage, they come right back in-line. Any good explanation for this?? I can live with the 8-15mA drift as it still keeps me well below the danger zone, but I find it odd that it vanishes once you apply a load and the cells come back to within +/- 4mA of each other.....
Once the cells are full, they are full, the voltage will rise rapidly. This means if one cell reaches full even 0.1Ah ahead of the others it will hit 4v easily if a simple system of replacing the Ah that came out with the same number of Ah back in. This is why I recommend restricting the charging voltage to 13.8v float and 14v end of boost charging AND have the secondary back up of the cell logger with the alarms set at 3.6v and 2.8v, simply to protect the cells from harm.

T1 Terry
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Old 28-01-2013, 23:57   #1632
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

So really Bob based on most yachts being left with solar only running whilst ashore it would be best to put a CelLog activated 100amp solenoid to cut the Solar panel out if an over voltage situation is detected. (This is if the reg has malfunctioned.)

Load will only help bring the voltage down, the alarm will cause the owner to act and find out why?

Charging by other mechanical sources means we are on board and can sort the problem once the alarm notifies.
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Old 29-01-2013, 03:37   #1633
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

One thing to note here is that that we have spent a lot of time on HVC. Its very important to have a LVC , arguably more so. All Li technologies are very badly damaged by extreme discharge and actually generate a lot of heat near the end ( as they are damaged). As far As I can see most unexplained fires seem to have more to do with uncontrolled discharge then overcharge. LiF can withstand a greater degree of overcharge then others, but of course nothing like LA.

My experience with cylindrical LiF ( and other LI) is that at fractional C discharge and re charge, cell voltage seem to converge and do not diverge. I suspect in time all this top balancing BMS stuff will die away. Cell voltage monitoring is a good idea though. ( good idea for any battery bank).

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Old 29-01-2013, 05:20   #1634
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

The cells will only be damaged if dragged below 2v and held there for an extended time. They will heat up and damage themselves but certainly no where near as much as they heat up from over charging. It's simple volts x amps equals watts stuff, all the amps and volts above fully charged creates heat in watts, at the bottom end the volts are less and the amps just aren't there to be had so the total watts are much less, much less heat is generated.
An inverter is the thing that is likely to drag out the amps, it will shut down at 10.5v, it can't get one cell out of 4 below 2v and hold it there, maybe 1.5v for a very brief period if the other cells remain at 3v but the inverter will still shut down and the low cell will recover. Maybe an incandescent bulb left turned on for a very long time could do it, but would anyone leave their battery system connected for that long if they didn't have solar recharging?
A simple alarm set up if a cell goes low is quite sufficient, sophisticated battery disconnects for low cell voltage is really overkill for a house battery.

T1 Terry
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Old 29-01-2013, 05:28   #1635
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

If you want to get the longest life from the cells rather than a low voltage disconnect a 20% SOC disconnect of all but essential loads is a much better idea. There are a number of battery monitors on the market that have a relay driver that can be programmed to switch at a predetermined state of charge, you wouldn't want to loose everything, but non essential load shedding would extend the time till recharging reached the desperation level.

T1 Terry
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