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

[T1 Terry]

Originally Posted by s/v Jedi

I wonder if we can find consensus on a summary that will help most readers of this thread. Let's say we have a sailboat with a 1,000Ah LA (incl. gel, AGM) house battery bank. They have just an AC powered battery charger and engine alternator. What are the steps to take, in simple terms? I think we should start with capacity needed to equal the old 1,000Ah bank, what cells are good for that etc.

ciao!
Nick.

1,000Ah of lead acid gives a safe useable 500Ah before the 50% state of charge (SOC) or depth of discharge 9DoD0, depending which end you look from. So I'm guessing you are looking for batteries that can safely and repeatable supply 500Ah.
If that is the case then LiFeP04 batteries can be taken down to 20% SOC or 80% DoD and still return a long cycle life, there is no data for deeper discharges against cycle life but the EV people take them down to 100% reasonably regularly without instantaneous failure but 80% is the figure the manufacturer uses so we should use that.
An Li battery pack of 600Ah would give a useable 480Ah at 80% DoD, even though this is 20Ah less than the figure for the lead acid at 50% DoD this would be roughly the equivalent battery size, the difference is that the lithium battery would still have a terminal voltage of around 13v even at 80% DoD but the lead acid would have a terminal voltage of 12.4v or lower at 50% DoD. The current and voltage supplied by the battery is measured in watts, watts is a measurement of work being done, 1 amp x 1 volt = 1 watt. Following this theory the lithium battery with a terminal voltage of 13v supplying 10 amps would be producing 130w but the lead acid battery at 12.4v supplying 10 amps would only be producing 124w. Not sure if I explained that very well.

What cells are good for that?
I would recommend using prismatic cells, batteries made up of cylindrical cells don't have the Ah capacity, they are designed for high discharge use, a bit like the difference between start batteries and deep cycle batteries in the lead acid format.
It is possible to buy 600Ah cells so 4 of these connected in series would supply 600Ah @ 12v. Personally, I wouldn't do it that way, it is the quickest and least complicated but if a cell should fail for what ever reason all the eggs are in one basket, you have no useable battery till the bad cell is replaced. I'm being a realist here, sometimes these things happen.
If multiple smaller capacity cells are connected in parallel to make up the capacity, say 6 x 100Ah cells to make 600Ah and 4 sets of these in parallel to make 12v would be a more practical approach because:
If a single cell fails only 100Ah was lost till the cell is replaced so the battery is still 500Ah and life can continue.
The single 100Ah cell would be a lot cheaper and easier to handle than the single 600Ah cell so packaging and transport cost would be a lot less.
By using 6 cells to make up the capacity the differences in manufacturing tolerance balance out better.

The down side is a lot more link plates to cover and protect from shorting out by something being dropped on them and more points to check for bolt tension during maintenance.

T1 Terry

[s/v Jedi]

Originally Posted by T1 Terry

It is possible to buy 600Ah cells so 4 of these connected in series would supply 600Ah @ 12v. Personally, I wouldn't do it that way, it is the quickest and least complicated but if a cell should fail for what ever reason all the eggs are in one basket, you have no useable battery till the bad cell is replaced. I'm being a realist here, sometimes these things happen.
If multiple smaller capacity cells are connected in parallel to make up the capacity, say 6 x 100Ah cells to make 600Ah and 4 sets of these in parallel to make 12v would be a more practical approach because:
If a single cell fails only 100Ah was lost till the cell is replaced so the battery is still 500Ah and life can continue.
The single 100Ah cell would be a lot cheaper and easier to handle than the single 600Ah cell so packaging and transport cost would be a lot less.
By using 6 cells to make up the capacity the differences in manufacturing tolerance balance out better.

The down side is a lot more link plates to cover and protect from shorting out by something being dropped on them and more points to check for bolt tension during maintenance.

T1 Terry

thanks Terry!

How would those cells be interconnected? Like 6x a 100Ah 12V bank or create 600Ah cells and put those in series?

p.s. I think that 50% usable capacity for LA is optimistic because most cruisers rarely charge to 100%.... if they charge to 90% than you would only have 40% usable...

ciao!
Nick.

[Surf City]

Thanks Terry for the great info.

So, I will install several banks of batteries to build up the the magical amp hour requirement. What do I need to charge up or better what voltage should I keep from over charging LI batteries? I have a Victron battery charger now which allows me to change the voltage for different batteries and a Outback 60 MPPT controller from the solar array. Do I need a different BMS to charge or regulate? How can you tell that your battery levels are low, if LI batteries maintain their level until dead? You mention a counter, what does it do?

Thank You

Wil

[downunder]

Originally Posted by s/v Jedi

thanks Terry!

How would those cells be interconnected? Like 6x a 100Ah 12V bank or create 600Ah cells and put those in series?

p.s. I think that 50% usable capacity for LA is optimistic because most cruisers rarely charge to 100%.... if they charge to 90% than you would only have 40% usable...

ciao!
Nick.

Terry,

Good info.

Would a better option be 3x 200Ah so as to cut back on number of link plates.

Cheers

[Whimsical]

For anybody in Australia that is interested.
I am getting together a group buy for CALB 180A/H cells. Price will be about 20% discount. Up to nearly 4,000A/H @12v now. Order will be placed early Dec most likely.

Mike

[downunder]

Just noticed the concept of a Regulator Decks are designed to eliminate wiring the wiring between cells and regulators thus creating a plug and play option.

Marine environment ??

At this american site Manzanita Micro

[Marqus]

Originally Posted by T1 Terry

If multiple smaller capacity cells are connected in parallel to make up the capacity, say 6 x 100Ah cells to make 600Ah and 4 sets of these in parallel to make 12v would be a more practical approach because:
T1 Terry

Erratum: Typo in there may confuse someone; Terry meant to say:

"If multiple smaller capacity cells are connected in parallel to make up the capacity, say 6 x 100Ah cells to make 600Ah and 4 sets of these in SERIES to make 12v ..."

[T1 Terry]

Connect the cells in parallel to build up the capacity, so 6 x 100Ah cells would make a 600Ah 3v battery, connect 4 of these together to make a 12v battery. This is the best way to have the least hassles. If you were to build multiple 12v batteries and connect them together in parallel the battery with the shortest cable and best connections and highest voltage cells would do all the work and be heading toward complete discharge before the next battery in the resistance scale starts to be discharged. Also each battery would need a cell logger.
By connecting the cells in parallel the high cells even out the low cells so the load is drawn fairly evenly across all 6 cells and therefore across all 24 cells not just the best pack of 4 cells. If you had a really flash BMS that could load balance and charge balance then it wouldn't be so much of an issue but then the BMS adds another possible failure point. Not saying they will fail but I don't think anyone would say for absolute certainty that they would never fail.

Hi Vic,
I recommend using a State Of Charge (SOC) meter with these batteries and avoid discharging them below 20% SOC. If things get busy and the SOC drops below 20% don't panic, they are tough, they will take it as long as you don't drag them dead flat, below 2v per cell, they will be ok. Cycle life maybe shortened but if it’s a life threatening situation then “such is life”. Below 2v per cell you are flirting with the risk of damaging a rather expensive set of batteries.

As far as setting your controllers, I don't think the outback has a setting for boost, only absorb and float.
2 similar options
(1) set absorb to 13.7v and float to 13.6v and equalise to 14v manual activate. This way you can be watching and listening for a high voltage cell when doing the equalise charge as this will bring all the cells above the 3.45v mark so they will all be 100% full. If you have a run away stop charging and drain some charge out of the run away cell, once below 3.4v start charging again till all cells are 3.45v of higher.
(2) basically the same as (1) but when a cell goes high use an inverter and wallwart or DC to DC 3.5v charger and bring the other cells up to 3.5v.

I think the Outback has an option that senses when the battery voltage drops below float voltage and resets the absorption mode, if I've got that right then enable that option so the solar goes back into full input each morning or if a heavy load is applied.

With the Victron, I'm guessing you would only use it when on shore power so I'd recommend setting it to a flat 13.6v for everything. Do the equalise balancing with the Outback unit.

For anyone who has a charger/solar control that has a Boost, equalise, float setting, if the battery is in balance or you will be in a position to do something if a cell goes into runaway the boost can be set to 14v, absorb at 13.9v and float at 13.8v. This setting with a load running on the batteries at all times while charging will self balance the batteries.

There are lots of different types of controllers and many methods of setting them up depending on how the operator would like the system to function. These batteries never need to be 100% charged for the batteries sake, it's only done to ensure the cells are balanced. If you have enough capacity to only charge to 90% or so, set the charge voltage to 13.6v. and leave the full 100% balance charge until you have the time to do it. It will take a little longer from 13.6v but the risk of a cell going high is minimised.

T1 Terry

[T1 Terry]

Originally Posted by Marqus

Erratum: Typo in there may confuse someone; Terry meant to say:

"If multiple smaller capacity cells are connected in parallel to make up the capacity, say 6 x 100Ah cells to make 600Ah and 4 sets of these in SERIES to make 12v ..."

Thanks for fixing that up for me, shouldn't rush posting but my proof readiing aways looks right to me anyway

T1 Terry

[senormechanico]

T1 Terry,
I have another noob question about Prismatic cells.
All the info I've read says they need support on the sides so they won't bulge during charge/discharge, but most of this comes from EV forums and videos.
At what charge/discharge rate does this become a factor?
I'm not going to be able to put in or take out more than 100 amps absolute max.
(100 amp alternator with single belt, and a Vitamix which draws 94 amps at full chat making smoothies).
Will some 90 degree angle 1"x1"x 1/8" aluminum at the corners connected with all thread and 1/8" aluminum sheet for side support be sufficient?
The batteries are in their own compartment away from the engine room on a sailboat.
I have a temp sensor installed as well.

Thanks in advance,

[T1 Terry]

Hi Steve,
The factory recommend plates each end with ripples rolled into them to stop them from bending and stainless straps to hold them together, you can buy the cells already strapped for a small extra cost from most distributors if you tell them what configuration you want them. Here is a photo of a friends 200Ah 4 cell pack without ripples in the plates.
The straps and plates more relate to discharging and charging that will crate heat stress. The plastic case gets hot, the electrolyte gases and the case bulges. Pulling the cells below 2v or charging above 3.5v for long periods will cause the electrolyte to heat up. Charging or discharging greater than 3C has the potential to cause either of these 2 voltages to be reached while still inside the 20% to 100% SOC safe area but more at the extreme ends, 2v at the 20% end etc.

Having said that I don't plan to take the risk anyway. this is my 16 x 90Ah cell pack confugured as 360Ah @ 12v.
The craddle is made from 3mm x 50mm angle and flat strap, this bits steel becauce my aluminum welding is crap and stainless was too expensive. The flat straps across the front are aluminium. The bolts are 6mm stainless threaded rod with stainless nuts and washers. They a tightened hand tight with the socket on a 1/2" extension held in the hand, no T bar or breaker bar handle. It really needs lock nuts or nyloc nuts to stop them rattling undone, the tension is that little. the craddle is massive over build but it will be hanging off the chassis of my bus so what the hell. All up with 360Ah of battery and the craddle it weighs 56 Kg, about 1 1/2 100Ah lead acid AGM batteries. The photo of the battery pack with battery around it are for size comparison, the 2 cells to the left and 4 behind are 6v x 125Ah Yuasa AGM and the one on the right is a Vision 100Ah AGM, same size as Fullriver etc.

T1 Terry

[sytaniwha]

Hi All,

Great to see that this thread has progressed so well since it started back at the end of July. I've been off sailing, and using my 4*400Ahr CALB house bank, so I haven't contributed anything since that first month, but I now have built up a bit of experience using these cells for sailing house-bank applications, so hopefully I can share some of that knowledge going forward.

Some initial observations from our usage are:

• The cells were shipped to us @60% SOC approx (240Ahr). We didn't install them for about 6 months and during that time they just sat in storage with no charging at all. On the first charge they took only 170Ahr @ C/10, indicating virtually no self-discharge in that 6 month storage time. Conversely, the reason we bought these cells was because our previous SLA Trojan cells had been left without their trickle charge on for 4 months by contractors who forgot to re-connect the charger, and they were dead in that time. This is a huge benefit for sailors - no more worrying about self-discharge killing cells when you're not on the boat.
• Our cells were sent direct from the factory and were closely matched for both capacity and impedance. In fact, their serial numbers show they were consecutively manufactured on the same day, also. Despite this (and maybe because of the 6 months non-use) we had to do an initial balance process to make sure that they were all at closely matching SOC. What we found was that 3 were almost identical, and 1 was quite different. I consider this initial balance process to be critical - it's very easy to do.
• We have run without a "traditional" cell-level BMS, and have not experienced problems thus far. This is because our rates of charge and discharge are so low in a yacht house-bank situation (typically charge @ C/10 or C/4, discharge @ <C/10 90% of the time, and almost never above C/4). BMS' were created for the EV applications where both charge & discharge rates are high.
• The other point about housebank applications vs EV is that we typically have A LOT less cells than EVs. An EV might have hundreds of cells in combined parallel & series connection. We have 4 cells in series, and even if you take the approach that Terry suggests, you'll only have a few more. This makes individual cell management less necessary in my opinion.
• We do use battery bank level management for both high voltage and low voltage conditions, and I think that's essential for sailing applications regardless of whether you're using Li tech or SLA. For high end, we use a Victron smart charger for shore power, and a Sterling smart regulator for the alternator. Both are have programmeable voltage levels and fail "off". For discharge protection we use a Vetus discharge alarm and cutoff relay. We've found these to be more than adequate once the cells are balanced. I also have a cell level voltage recorder which I check periodically to monitor any imbalance. I haven't noted any yet.

Cheers,
Paul

[sytaniwha]

Here's a picture of our battery, with one of the old (and very dead) lead batteries beside it. The lead battery is a 120Ahr Trojan wet cell. As you can see the Li pack takes up about the space of 3 lead batteries, weighs about the same as 2 lead batteries (57kg), and gives the usable Ahr of about 7. Here in South Asia, the landed cost was about the same as 8 lead batteries.

You can also clearly see the "C" beams which CALB shipped with the cells to make them into a pack (the black bars on the lower side in the photo). There are two beams on each of the 2 long sides, connected by threaded rods.

[T1 Terry]

Looks neat Paul, are they 400Ah cells? They don't look much bigger than the 200Ah cells in my last photo but compared to the Trojon the 4 cells are neary as wide so the must be a lot thicker . All 16 cells in the the pack in the other photo only add up to 360Ah.
Just to clarify

This is because our rates of charge and discharge are so low in a yacht house-bank situation (typically charge @ C/10 or C/4, discharge @ <C/10 90% of the time, and almost never above C/4).

by C/10 do you mean 0.1C or one tenth of the capacity, in this case 40 amps into a 400Ah battery? So if I got that part right then C/4 is 100 amps?

T1 Terry

[sytaniwha]

T1 Terry,

Your battery pack and holder look great - it'd be good to have a custom made holder like that.

I'd like to make one suggestion based on your photo (which you may have already done).

As you said in one of your posts, your 4p4s pack is a good way of assembling a battery for a number of reasons, and I totally agree with your comment that you should absolutely NOT connect 4 series strings in parallel, but SHOULD connect 4 parallel strings in series, as you have done (for anyone who doesn't see why this is, draw a diagram of each - that's what I did. It then becomes very evident that a series first pack will be likely to create imbalanced cells quickly).

It looks like you have connected the parallel strings together at the cells at the bottom of the picture, and that you have also taken the +ve & -ve connections off at those points also.

It may be worth you considering the following:

1. add another set of connectors between the parallel strings at the top cells in the photo, and move your +ve & -ve take-off connections to one of the middle 2 cells, OR
2. move your connections between parallel strings to one of the 2 middle cells in each string, and your +ve & -ve take-off wires to the same cell.

The reason for this is that the most balanced battery is created by making the electrical paths for each cell identical. By linking the parallel strings through one of the end cells, there is a small extra resistance for the other cells in each string through the connectors in the parallel arrangement. The cells at the far end (top in your photo) have the biggest resistance because they deliver their power through the most connector links.

It's not a very big resistance if you're using really good connectors, but could become significant if you have a high rate alternator or use inverters (which have high discharge rates @ 12V).

The ideal situation would be to have a connector at each of the 4 cell pairs between adjacent parallel strings, and then 4 identical take-off wires at each end wired to a +ve and -ve post or buss. But that may be over-kill.

I think in this situation I'd probably go for 2 links between each parallel string on the end cells, and then 2 idenitcal take-off wires each for +ve & -ve brought to a common post.

This isn't a LiFePO4 only concept. The same theory is appropriate for any electrical parallel/series arrangement (lead batteries, resistors, etc).

Anyway, just an idea that I thought you might find useful.

Cheers,
Paul.