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

[Highland Fling]

First I thought this thread was for people who use LIFeP0$ OR are thinking about it.

I LOVE MY LIFeP04 battereies and my almost no change from the 14 year old Gel Cell LA house bank with my KISS LIFeP04 system.

I use them daily and hit them hard cooking using the batteries and a nice big inverter.....I can be upto (so far) 110AH down in the morning BUT still see 13.2+ volts on the house bank.

Unless I do a big batch cook during the afternoon when there is no sun, before 17:00 I have replaced all the AH used ONLY using solar.....and with only 400AH online.

Yesterday we went for a wee motor in total over the whole day about 90 minutes under engine, (60 mins in the morning and around 30 at 17:00) this was to meet up with a fellow cruising couple......

So I brought the other 200AH online and with the alternator outputting around 45+A and the solar the batteries got a nice big boost charge.......the solar only put out about 25A at most.

Pre that we have not run the engine for more than 30 mins at a time to move location nor have we run the generator since we lanuched in November.

I really dont get these marine service provider expurts who seem to say their way is the only way OR you are going to end up in real truoble.

That is just so much bollocks.

As a Electronics and Electrical engineer I am fully capable of desiging a complex system IF I felt that this was a requirement......I DON'T think it is at all.

I loved that complex complecated design write up and diagrams......I just don't see that as required at all, and all I can see there are complex maintenance issues down the road IF or WHEN something goes wrong.

For sure it is NOT for me.....

IF you want a lots of knobs bells and whistles system fine by me as this is your boat your life your choices.......I just don't see the need for any of that.

LIFePO4 seems to have become a revenue stream for a few people........who will tell you how complex and difficult it is to have a sound working system and how you need or your batteries need protected from...................all these nasty events just waiting to destroy your batteries

As well as keeping my Gel Cells working for 14 years I have at least 20+ years experience of using Lithium batteries in other mission critical applications.

Here is someone else talking some sense re LIFePO4 batteries

http://www.cruisersforum.com/forums/...tml#post466400.

I think I am done here as any useful info is being swamped by the overwhelming background noise.

[exMaggieDrum]

Originally Posted by T1 Terry

That is what I was trying to say, yes. As far as the 20mm bulge, is that per cell? 5mm rod is the biggest that will fit between the cells side by side with the narrow edges meeting, in the early days we constructed a pack this way and the pressure stripped the thread out of the stainless nut and distorted the thread on the rod so much a nut could no longer be wound past the damaged area. 4 cells will bend 50mm x 3mm steel strap, so we now use 3mm aluminium plates and stainless band strapping folded over each end cap and screwed through the end plate, 3 up each side. This will hold a pack in normal use but will not stop them from bulging if overcharged or completely drain and heat causes gassing to occurs. Once the cells have bulged a 10 tonne press would not flatten them until the vent cap was released..... that much pressure. I have seen them fitted in a confined space where the owner determined strapping was not required as there wasn't enough room for it and the confined space would act as the case for holding them together. In this case the owner was quite correct, they fitted into the space quite nicely and each swelled to the room available. The down side was he could not remove a cell from the group when he attempted to remove them to swap them to his new RV, they are there for life.

T1 Terry

Thanks for your informative posts!

Do you have a photo of your pack construction with the 3mm aluminum plate. It would be helpful.

I was considering using stainless strap to confine the cells but was concerned there would be too much pressure at the corners. I have also seen pictures of some type of plastic banding used. I was thinking of putting end plates that extended past the ends. The obvious problem with any plans I have seen is that the end cells would be much more constrained but the middle units would be able to push out, like Martin's stress analysis shows (nice!). Some kind of significant construction seems necessary to prevent this deformation at the middles. (If needed)

FYI - I have been quoted US $1.45/Ah by a supplier of cells in BC Canada, plus shipping. That includes end plates and lifting straps for each set of 4 cells.

[SailRedemption]

Not sure if my battery rack is what Terry is talking about but I feel it's pretty sufficient. When tightened nothing moves, they are held in place by compression and friction. Although on the sides the square tubing does have some help in the battery ridges.



See more @ redemptiverepair.com

[exMaggieDrum]

SailRedemption - very tidy installation and looks like a well done battery "box".

Design note: I have talked myself in to adopting part of the design that Martin (mbartosch - SV Entropy) has done regarding putting his alternator output to the load side of his install. My reasoning is that I will always be on the boat when running my alternators and available to react to a high voltage alarm manually by shutting down my DC genset alternator or my main engine alternator rather than relying on a charge disconnect with the charge side contactor. I would still hope that setting the alternator regulator parameters would prevent overcharging in the first place, but in the case there is a problem with that I could take manual action to deal with it with an alarm. If the BMS dies the load side contactor would open so it would still protect against an overcharge, or low voltage, situation.

A plus to putting the alternators on the load bus is that even if an over voltage occurs and the high voltage charge contactor opens, the alternators would still be connected to the battery. So no worries about a spike by losing alternator connection to a battery load. And the same for the inverte/charger (if that is even a concern). I suppose there might be some risk still if the BMS were to fail and the contactors were to go to NO while the alternators were running.

However, I would still connect the solar charge feed to the charge side contactor to prevent an overcharge from solar since that can be left on when I am not on the boat when I couldn't react to a high voltage alarm. This would still simplify my install as I could get rid of the large charge bus and connect the solar fuse and power lead direct to the contactor. If I had wind power generation I would put it on there as well (but no plans to do this right now).

My inverter/charger would also be connected to the load side bus even though the charger could overcharge if the parameters on it were to not prevent the overcharge. However, I will also use an AC solid state relay to cut off AC power to the inverter/charger (or standalone charger) in an overcharge situation - again like Martin has done and as noted by others.

I am now a convert to LiFePO4 and I am enjoying the challenge of designing the system. Wiring it will take some time but will just be an exercise in layout in the space available and using good installation technique with good parts/wire. My one big concern is if I have to sell the boat before I get to get some real use out of the system. I am going to be optimistic about that and would actually try to market the system as a plus should the boat have to be sold.

[evm1024]

I've been thinking off an on about the future of cruising power storage and thought to share some thoughts. Of course this is half cocked and only represents a bit of blue sky. There are many faults and presumptions. A significant presumption is that the cost if storage (be it LiFePO4 or some "New" storage technology). I would also presume that there is a BMS available that thoughtlessly and faultlessly (designed by and purchased from Ocean Planet of course) which keeps the storage bank within a know safe envelope.

As I transitioned from LA to LiFePO4 I had a number of LA habits to overcome (keep the cells fully charged for one). I have discovered another in the form of don't have more battery than you need or can charge. There are many reasons this is valid for LA but lose validity for LiFePO4. With that in mind and ignoring the cost let us explore having more storage than we need and how that could work.

As a baseline we can look at a 400 ah system that is discharged from 80% to 20% daily. This uses 240 ah and should have many years of cycles in it. It could be charged by 2 - 320 watt solar panels in 10 hours assuming an average output of 50%.

Now let's change the mix.

So to start with let's change the house bank to 2000 ah. We still use 240 ah a day and it still takes 10 hours to recover the 240 ah (2 - 320 w panels at 50% for 10 hours). But, now we are cycling from 56% to 44% and can presume that the cycle count (and thus battery life) is much greater than the (all ready) great life of the 400 ah bank. Plus we have 2.5 times the reserve capacity over the 400 ah bank - solar could fail for 2.5 days before we get to 20% SOC at our 240 ah/day rate.

1000 ah bank cycles between 62% and 38% which is also not bad.

With a full (at 80%) 2000ah bank we could go 5 days without a charge to get to 20% SOC.

It would be desirable for the charge controller for this bank to keep very good track of amps in and out. Having current measurements on only the battery negative lead or the charge in and load out leads or on all 3 may give advantages in accuracy and/or calibration factors. Who knows?... Very accurate voltage measurements also would be useful too.

The prediction of the 50% point that charging orbits around needs to be more precise with smaller capacity banks but becomes less so with larger banks. It may orbit 55% or 45% with a larger bank but still stay withing the 80%-20% desired range.

Initial calibration would be to top balance. Then drop to the 80% point. There would be times where you would want to re-calibrate. This assumes we have not come up with a good voltage vs SOC method. Just set the charge controller to charge until any cell reaches 3.8v (adjustable of course) and call it full. Also, track all cell voltages and keep a history of differences between cells. A lot you could do with that.

Anyway just a thought....

[darylat8750]

I am not an E/E and I didn't sleep in a Holiday Inn Express last night but....
It occurred to me that every bad thing that happens on a cell level seems to create heat and bulging. If that is correct would we get a measurable heat rise before significant damage is done? If so a simple disconnect charge bus for high pack voltage / disconnect power bus for low pack voltage / disconnect both for high temperature. Perhaps also or instead of a pressure sensor between the cells and case? I guess the real question is how much heat is generated how soon in a problem event?

[transmitterdan]

Originally Posted by darylat8750

I am not an E/E and I didn't sleep in a Holiday Inn Express last night but....
It occurred to me that every bad thing that happens on a cell level seems to create heat and bulging. If that is correct would we get a measurable heat rise before significant damage is done? If so a simple disconnect charge bus for high pack voltage / disconnect power bus for low pack voltage / disconnect both for high temperature. Perhaps also or instead of a pressure sensor between the cells and case? I guess the real question is how much heat is generated how soon in a problem event?

I think what you will find is that by the time the pack is hot the damage is done. It's a bit late to react to something that is already overheating the pack.

If you wanted to do this it would need some sophistication because it is the temperature differential between the pack and the nearby air that is important not necessarily the absolute temperature of the pack. So that adds a layer of complexity that is more easily managed by just watching the cell voltages. Cell level monitoring devices are pretty cheap these days.

[darylat8750]

Originally Posted by transmitterdan

I think what you will find is that by the time the pack is hot the damage is done. It's a bit late to react to something that is already overheating the pack.

If you wanted to do this it would need some sophistication because it is the temperature differential between the pack and the nearby air that is important not necessarily the absolute temperature of the pack. So that adds a layer of complexity that is more easily managed by just watching the cell voltages. Cell level monitoring devices are pretty cheap these days.

I thought that would most likely be the case or one of the smarter guys would have already tried it. I was thinking to put temp. sensors between all the cells and watch for any differential. I was given hope by Terry's comment that the cells in one installation swelled to fill the available space and are apparently still ok or at least still useable.

[transmitterdan]

The cells swell even without overheating. If the swelling is not contained then some internal damage to the cell ensues. So the admonition is to put something around the pack to keep it compressed so this "natural" swelling does not bulge the pack too much. This is a trade off the battery builders make which puts the onus on the pack container to provide the structural strength to withstand the pressure that normally occurs with LiFePo cells. If they made every cell with that much structural strength the cells would be twice the size and take up a lot more space.

[senormechanico]

I have never seen or measured any swelling or heating in my two LiFePo4 systems (1 in boat and 1 in house).
The boat (200 aH) max input capability is around 100 amps, and if I really tried, I could extract 200 amps over a few minutes with the Electroscan and inverter running a hairdryer and hot water tank.

In the house, 700 aH, max charge is 115 amps, max discharge might be about the same.
Both systems are clamped, but stay stone cold as measured with an infrared handheld and also battery temp probe systems.

[mcarling]

There is a huge difference between the > 10C discharge rates common in electric cars and the < 1C discharge rates typically seen on boats. Ideally, I would prefer to keep discharge rates below 0.1C if possible. I'm not convinced that compressing the batteries is necessary in low C rate applications, but it doesn't seem to add any risks so I do it for the potential reduction of risk.

[senormechanico]

Exactly.
The main reason I clamped the cells on the boat was to keep them from sloshing around in the battery compartment.
In the house, I did it just to keep them as one unit.
My installations are not as elegant as MainSail's so I'm not going to post pictures, but they're safe and perfectly operational.

[darylat8750]

Are there any other opinions whether temperature delta between cells could give warning before permenant damage would be done?

[mcarling]

Originally Posted by darylat8750

Are there any other opinions whether temperature delta between cells could give warning before permenant damage would be done?

If one could measure the temperature of the electrolyte, then probably yes. I think the best one could do with commercially available cells would be a temperature probe inside the bolts which clamp to the anode and cathode. I'm skeptical that could provide useful information in time to prevent a problem.

However, as has been posted many times in this thread by several experienced and knowledgable persons, LiFePO4 cells are extremely reliable if well-balanced, only subjected to fractional C charging and discharging, and are not overcharged or over-discharged. If you start with imbalanced cells, subject them to high C rate charging or discharging, charge them with voltages above 3.45V per cell, discharge them below 2.8V per cell, or connect them to a Battery Murder System that tries to actively balance the cells, then all bets are off.

[T1 Terry]

Originally Posted by exMaggieDrum

Thanks for your informative posts!

Do you have a photo of your pack construction with the 3mm aluminum plate. It would be helpful.

I was considering using stainless strap to confine the cells but was concerned there would be too much pressure at the corners. I have also seen pictures of some type of plastic banding used. I was thinking of putting end plates that extended past the ends. The obvious problem with any plans I have seen is that the end cells would be much more constrained but the middle units would be able to push out, like Martin's stress analysis shows (nice!). Some kind of significant construction seems necessary to prevent this deformation at the middles. (If needed)

FYI - I have been quoted US $1.45/Ah by a supplier of cells in BC Canada, plus shipping. That includes end plates and lifting straps for each set of 4 cells.

Attachment 117933
Not sure if it's easy to see in the photo but the strap is outside the aluminium plate and the screw goes through the strap and into a hole thread tapped into the aluminium plate. 200Ah cells actually require 2 plates, both rolled top and bottom and sized to fit one inside the other. Single plates rolled at the top and bottom level with the cell height works ok for 4 cells, but 6 cells or 8 cells requires double plates, and real strong arms to pick them up. You get easily fooled by the light weight of the 100Ah cells, 6 x 200Ah cells would be the equivalent of 12 x 100Ah cells and you wouldn't even dream of trying to carry that too far, but the 6 x 200ah cells look so much smaller and therefore lighter, till you slide them off the bench

T1 Terry