LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

[downunder]

Originally Posted by JoeFish

I've been looking at a couple different sources for batteries and I am considerng these:

Thunder Sky LiFFePO4 40Ah Cell

I am wondering if to get a proper 12v bank I need to get 3 or 4? There seems to be some variability in the voltage of these. That or I'm missing something, i.e. they can be made with voltages anywhere between those stated numbers.

Input?

This has pretty direct bearing on where I can put these things...

Thanks,

You need 4 to get 12V but 400AH will be equivalent to more than 800AH AGM.

What do you have now. 200 ah LI might be enough.

cheers

[JoeFish]

Had a chat with my AP manufacturer and with my new ram and the solenoid updates I can see as much as 75Ah a day in AP consumption or as little as 26. Obviously sea state dependent.

Was hoping to get 2-3 days between needing to top up the batteries. My instruments consume almost nothing and the laptop, when it's on only uses 85W. There is the refer and I haven't computed what the well insulated top loading refer will consume. We're upgrading the insulation and adding thermal reflective material to the cabinetry that houses it.

Only other power consumption is pumps, running lights (LED lopolights) and the sensibulbs in the cabin fixtures. Boat is pretty analog although I may add a small watermaker at some point.

Frankly I hate running the engine so the longer I can go without it the better

[sytaniwha]

Hi Joe,

I don't have any direct experience with ThunderSky - but T1Terry has and has written quite a lot in this thread about the history. If I remember correctly, he finds the cells to be good - but check back over his posts to verify that.

On the number of cells - you definitely need 4 cells to make a 12V nominal battery.

Just to explain: I think you're maybe confusing the maximum voltage operating range with the realistic discharge voltage. The link you provided just says "Operating Voltage: Min 2.5V, Max 4.2V". I think you're taking that as the "variability in the voltage" that you mention.

What you really need to look at is a discharge voltage curve. This will show you that in fact there is very little variability in the realistic discharge operating voltage. In fact LiFePO4 cells have a flatter discharge curve than lead-acid. The voltage through 90% of the discharge is between 3.4V & 3.0V - hence the "nominal voltage" rating of LiFePO4's of around 3.3V. Hence you need 4 cells to make up a 12V nominal battery (4*3.3V = 13.2V, which is very similar to an SLA battery nominal voltage).

To compare to lead acid. There are 6 cells in a 12V lead acid battery. A typical Operating Voltage Range is Min 10.5V (1.75v/cell) and Max 14.8V (2.7V/cell). That means you shouldn't discharge below 10.5V, or charge above 14.8V - hence the phrase "Operating Voltage". But on discharge a lead acid battery gives a usable voltage from about 13.2V (2.2V/cell) to 11.4V (1.9V/cell). Hence you need 6 to make a 12V battery with a useable discharge voltage range between 13.2V & 11.4V.

A 4 cell LiFePO4 battery has a useable discharge range between about 13.6V (3.4V/cell) and 12.0V (3.0V/cell). Slightly higher than a lead-acid battery, but very similar.

If you use 3 LiFePO4 cells, your usable discharge voltage would be between about only 10.2V (3*3.4V/cell) and 9.0V (3*3.0V/cell). Hence you need 4 cells.

Sorry, a bit wordy, but I think you need to understand the why before you put together a system.

Hope this helps.

Cheers,
Paul.

[JoeFish]

Paul,

Feel free to be as wordy as you like, I'm still learning about these batteries and I'm all ears.

Next step is to figure out how I can pump as much charge into them as quickly as possible without over doing it.

My boat (Bonne Amie) originally had a 17hp gas engine and it has been replaced during the restoration with a 26HP L26 three cylinder (same block as the Westerbeke of the same HP but custom built) of much lower weight. We use a 13" 3-blade Maxprop which pushes the boat easily at hull speed and because we can vary the pitch on the prop I can play around a bit here as we load it up with alternators, although when we race the boat offshore we run the engine in neutral, cruising we'll motor sail when charging.

I've been considering a two alternator system with two equally sized large alternators.

Your thoughts here are appreciated. Keep in mind we need to be able to run the engine every couple of days to charge the house bank and only have 36 gallons of fuel. Transat could be 28-30 days.

[hellosailor]

Joe-
"Operating Voltage: Min 2.5V Max 4.2V"
No mystery there. All battery cells have a useful working voltage range. For a "12" volt battery there are usually six nominal ~2.11v cells. Their useful range is actually about 1.91 volts to 2.11 volts, which gives you a battery of six cells with a useful voltage range from 11.5-12.7 volts.
With those lithium cells, you can supposedly get useful power out of them through a wider range, so you could bolt up three of them to get a 12.6V fully charged battery...or bolt up four of them, and just don't charge them past 12.7 volts, i.e. only 3.2 volts each.
You CAN charge them up to 4.2V, what they are saying is that somewhere above that point, you'll blow 'em up. You can do that with common Nicads, too, just overcharge them and wait for the BOOM.
There are disagreements about how much of the voltage range you can or should use with any battery type. Some companies have come up with schemes that call for keeping the charge between 30-95%, or 40-90%, or other similar ranges not using the entire range of the cells. Others will tell you don't worry, just get your "12.7" and don't discharge them all the way.
Which comes back to why some folks say you must use a BMS to control the cycle depth, and others say don't worry about it as long as you stay inside the lines.
I'd suggest asking Thundersky how they would configure a "twelve" volt battery and how using a different charge range might affect battery life.

I'd expect that if you use 4/battery, the result would be more resistant to charge abuse, would hold a higher initial voltage, and would have more resistance to being killed by deep discharge. But that's just a guess.

This isn't unique to lithium batteries--even with wet lead, you'll find some people say a twelve volt battery can be taken down to 11.5, others say 10.5...

[sytaniwha]

I'm not an alternator expert, but I believe that they use about 1hp of engine power per 30A of charge current, plus a 1-2hp extra. So an alternator charging at 150A would use about 6-7hp.

So the first aspect of alternator size is how much extra hp you have to drive it.

After that, you need to know what your average total daily usage of Ampere-hours from your battery is (also useful to know high-end and low-end estimates). Depending on the size of your battery, you then know how many days you can go between charges.

Days between charges * daily average usage = ampere-hours you'll need to put back into your battery.

You then decide how many hours you want to run the engine to do that. Divide the amp-hours you'll need to generate by the time you want to run the engine, and you have how many amps you'll need your alternator to put out.

Remember that alternator output isn't the same at all rpm's, so you'll need to make sure the output at the rpm's you'll be running your engine at will be enough. It'll be different for every alternator (this is where continuous high-output alternators are better e.g. Zena).

That's the process, but because the variables and needs are different in each case you'll have to run the numbers.

How much diesel you'll use will depend on how your engine efficiency curve is at the power levels you're using it, and how many Ahrs you use over the total time. E.G if you use 100Ahr per day for 30 days, you'll need to generate 3,000 Ahr in total. If you run the engine with the alternator load only of 7hp (for 150A alternator output), and your engine uses 1/4 gallon per hour at that load, then you'll use 1/4 ga to generate 150Ahr, meaning that you'd need 5ga to generate 3,000 Ahr over your total trip.

But none of those relationships are linear so it all depends on your specific variables around your engine efficiency, engine use profile, alternator output at rpm's, Ahr used etc etc. So you'll need to do the calculations if you want to be certain.

Hope this helps.

[deckofficer]

Originally Posted by JoeFish

I've been looking at a couple different sources for batteries and I am considerng these:

Thunder Sky LiFFePO4 40Ah Cell

I am wondering if to get a proper 12v bank I need to get 3 or 4? There seems to be some variability in the voltage of these. That or I'm missing something, i.e. they can be made with voltages anywhere between those stated numbers.

Input?

This has pretty direct bearing on where I can put these things...

Thanks,

3.2 volts nominal, and for 90% of its discharge curve will hang in there. You need (4) in series for a small 12 volt 40 a/hr pack. Do not increase capacity by running these cells in parallel, always stay with a series string.

[JoeFish]

Originally Posted by sytaniwha

I'm not an alternator expert, but I believe that they use about 1hp of engine power per 30A of charge current, plus a 1-2hp extra. So an alternator charging at 150A would use about 6-7hp...

I'm familiar with working out the budget, and most of what you are telling me is well understood, but the acceptance rate of these cells is what I'm curious about.

You can have two 150 amp alternators but if your bank can't accept a charge at that rate then there seems to be no point to generating this much at the engine as you'll have nowhere to put it.

This is what I'm most curious about.

Thanks!

J

[downunder]

Originally Posted by JoeFish

I'm familiar with working out the budget, and most of what you are telling me is well understood, but the acceptance rate of these cells is what I'm curious about.

You can have two 150 amp alternators but if your bank can't accept a charge at that rate then there seems to be no point to generating this much at the engine as you'll have nowhere to put it.

This is what I'm most curious about.

Thanks!

J

Size of your bank will have an effect. You have not indicated the size of LiFeO4 bank you need. 400ah,250ah or 200ah ???

[mrm]

Originally Posted by JoeFish

I've been looking at a couple different sources for batteries and I am considerng these:

Thunder Sky LiFFePO4 40Ah Cell

I am wondering if to get a proper 12v bank I need to get 3 or 4? There seems to be some variability in the voltage of these. That or I'm missing something, i.e. they can be made with voltages anywhere between those stated numbers.

Input?

This has pretty direct bearing on where I can put these things...

Thanks,

Definitely four. The maximum voltage quoted is the max. end of charge voltage (and not recommended anyway). Once charging is removed cells will quickly drop to their nominal voltage.

Marius

[sytaniwha]

I think all of the large prismatic (rectangular format vs round) LiFePO4 cells have similar charge characteristics.

For our CALB cells, they recommend 0.3C charging, which equates to 120A for our 400Ahr cells. The max charge rate looks to be about 1C, or 400A for our cells.

Personally I'd be a bit wary of charging these large prismatic cells at that rate. I'd probably limit the charge rate to 0.5C, or 200A.

LiFePO4 was developed to mitigate the fire risk associated with other Li_Ion chemistries. Some of the tradeoffs of this include slightly lower energy density, and lower possible charge/discharge rates. However both of these are still significantly higher than lead-acid. In addition, I think the geometry of the prismatic cells put another limiting factor on max charge/discharge rates compared to the cylindrical cells (this is also true with lead-acid, where the cylindrical cells like "Cyclone" have higher possible rates).

I have performance curves from CALB at the 1C rate, with very little decrease in capacity (a factor of the low internal impedance), so you could conceivably charge at that rate. But as I said, I personally would prefer to keep it to the 0.5C rate.

Anyway, if you're using 100Ahr per day from a 400Ahr battery, and charge at 0.5C (200A), then you're only running the engine for 1/2 an hour per day (or 1 hr every 2 days).

Also, to actually get 200A of charge current out of an alternator (or bank of alternators), at a decently low rpm rate (I assume you don't want to be cranking your engine at 3000rpm just to charge), you'll need alternators rated at least at 250A (probably more).

And if your charging gear is augmented by solar and/or wind, then it'll all be shorter times.

Cheers,
Paul.

[careka]

What are the Price around USA, Europa ?

i have a friend that got some of the first T.Prius that came to Norway many years ago,(10+) and it has now done more then 400.000km and still the same batt pack,

[gael]

Hi Joe,
I guess with have the same setup with NKE and L&S actuator.
During the last transat my dayly consumption was 35Ah(24V) in compass mode gain set to 3, but 80Ah in true wind mode with cross waves /25kt wind.

Regarding the cell count, the packs have a 3 slopes V/I transfer curve.
"flat V/I" between 27 down to 25.5V
Near 90% charged from 27 and above till 28V
Near 10% charged from 25.5 down to 23.5V
This with 8Cells per packs. The cells come from CALB.
Fyi the 16 cells have shiped prelaoded and with a very little voltage spread around the 16 units - less than 10mv if I well remember .
So for a 12V pack you can divide by two to get the useful range of operation.

An other parameter I had measured is the charge efficiency. For my regular usage, I have measured 97% yeld. so for 100Amp loaded, you will get back only 97Amp. this parameter is required in my battery monitoring system.

cheer
gael

[LiFeTech Energy]

For those people in or around Brisbane, Australia next week there is a presentation day next Friday with demonstrations of several different LiFePO4 complete battery packs, cells, chargers, solar chargers, etc. which is being put on at the offices of W2Power. Interested parties can email John Hocken from W2Power and Knowledge Consulting for an invitation-
Knowledge Consulting
Waste²Power | Home
You will learn everything you ever wanted to know about lithium batteries.

[ebaugh]

I've read this thread twice now from end to end. I think most of it has sunk in, but I'm not sure. So I'd like to see if this is a reasonable plan. And ask a few questions.

My house bank is presently 12 6V lead acid golf cart batteries. We use 400-500 amp hours a day at anchor. I know that's a lot. It's mostly refrigeration (4 110V Systems) and reducing consumption is a topic for a different thread. We are an all electric boat, and have to run the generator for cooking, so we charge at the same time with paralleled inverter chargers, with a maximum rate of 200 amps. A typical day we charge 1-2 hours in the morning and 1-2 hours in the evening, normally at 150 amps bulk due to other generator loads.

We live aboard and spend 80 percent of our time at anchor. The golf carts work OK, but their service life is about 18 months due mostly to cycle life. The days we miss one of the charging cycles we go from 80-85 percent SOC to around 30. I'm hoping this investment will see at least a 5 year service life. Does this seem reasonable for a lithium swap out? I'd also be interested in what you think the efficiency difference might be given the data below. Less generator time daily would save some fuel.

I'm considering installing 16 Sinopoly/Thundersky 260 Ah cells. First connected 4P for 3.2V then 4S for the house. BMS will be the inverter. HVC by setting the max charge voltage to 14.4 V and LVC by turning off the inverter at 11.5 V. Almost all loads are AC. Underway, the alternators (adjustable charge voltage, but no smarts) are presently set to 13.2 V to keep from overcharging on multi day runs.

One of my inverters allows a custom charge profile, the other one is either 14.4 or 14.6 bulk/absorption and 13.2 float. Both have temperature compensation. I'm planning to remove the sensors to eliminate that variable. Underway, the ambient temp is about 115-120 degrees F. At anchor its more like 90 to 95F. Set both to 14.4 bulk. How long should 14.4 be held during the absorption phase? I can set this time for both inverters. Both are timers without consideration for charge rate. The adjustable inverter can have a different float voltage, mostly for marina time, what should this be set to?

I suppose ideally you have a system that keeps track of power used and replaced, but I don't have that. So it has to be voltage and time based.

After breaking in of a few cycles, I might tinker with using 14.6 bulk if the cells are close. But unless I keep them the same value, one will stop charging once the bulk value is reached. Would this change the absorption time?

The average load is about 20 amps, peaks to as much as 250 amp with other loads intermittently. I also start the mains off this bank, about 600 amps for a few seconds. Batteries interconnected with copper bus bar 3/4 wide by 3/8 thick. Installed in old golf cart battery box. Plan to secure with wood wedges to prevent movement, is banding required? Balancing resistive path to each cell by connecting at opposite corners of each 4P 3.2V cell.

Initial cell balancing per this thread by charging in a temporary 4 single cell series configuration and manually loading the high cell until balanced.

It seems too easy, am I missing something? Thanks for you help!

Bob