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Old 09-08-2011, 11:11   #46
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

Although I believe that I understand the overall advantages of using LiFePo4 batteries for a house bank, I'll be the first to admit that I quickly get lost in the technical details. Has anyone assembled a tutorial or something along the lines of "LiFePo4 for Dummies"?

Personally, I would find such a resource quite helpful. While my current bank of Sonnenschein gel cells is doing fine, I know that it's just a matter of time. Being a catamaran, I would love to both increase my usable daily energy budget while at the same time take a lot of weight off the boat. A discussion and "how to" guide would go a long way toward helping me feel more comfortable in making that transition.

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Old 09-08-2011, 17:31   #47
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

There is a lot of different avenues you can take with LiFeP04 battery banks, even more than with lead acid. Because Li batteries don't suffer the loss of capacity under heavy loads (Well heavy for house batteries) a large inverter can be powered from a small Li battery, something impossible to do with lead acid.
Li batteries charge much faster so a big alternator could can be better utilised for short runs rather than long slow recharges.
Li batteries can handle being semi discharged for long periods without any damage so 100% recharging each time is not needed. This means a recharge from 80%DoD (20% capacity) up to 20% DoD (80% capacity) or any combination between 80% DoD and fully charged. there is talk that staying between 70% DoD and 10% DoD gives an even greater number of life cycles but no ones worn a set out yet as house batteries so actual cycle life is really in the unknown. the manufacturer of Winston LYP cells claims 3,000 cycles to 80%DoD and 5,000 cycles to 70% DoD so if staying in the middle some where means they live even longer you may need to write them in your will.
They adapt readily to any good solar regulator that is fully adjustable and any good regulator is adaptable to Li batteries. by this I mean the batteries will stay reasonably balance with the gentle top charging a solar regulator gives as long as the max voltage is not greater than 3.5v per cell because solar will hold them at that voltage as long as it has the capacity and the sun is shining. I like to use 3.45v per cell, this equates to 13.8v for a 12v nom. battery pack and that's a common figure used by many battery charger manufacturers.
These cells adapt to series/parallel connection with ease, I.E. A 12v 4 cell 180ah battery can be made from 4 X 180ah cells, 2 X 90ah cells in series X 4 sets to make a 12v 180ah battery, even 3 x 60ah cells in series X 4 sets to make a 180ah battery. the combination is up to you and the space you have to fit them
Li cells need to be held in light compression to stop their sides from bulging. If the side bulge some capacity can be lost because the very thin plates that make up a cell start to separate and it's the close bond that makes these cells work so well. It's not a vice like crush, more a firm hold to keep the sides flat. The manufacturers make plate and band kits to bolt the cells together in packs but if you want to make a special configuration then some planning to include a side crushing mechanism is needed.

This probably caused more confusion but you maybe able to see why a one size fits all approach doesn't really work for Li batteries.
If you have an idea what you want to achieve, what space you have to fit the cells and how you plan to charge them just ask the question, I am and I'm sure there are many other happy to help you out with any guidance you need.
Here is a picture of a home made 360ah 12v battery pack, the comparison is a 100ah 12v AGM to the right and 125ah 6v agms to the left and behind. That pack behind is 250ah AGM lead acid, weighs 85kg the 360ah Li pack including the cradle weighs 57kg

T1 Terry
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Old 09-08-2011, 22:50   #48
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

Like ID, I have a good understanding of electric and mechanics, but not enough to jump into this new technology.

My new Salina has still the original battery bank which is 660ah in the stb engine room for the engine and the house and a 100ah in the port engine room for the engine only. All lead acid.

In time, I would like to add capacity and shift the batteries midship for better weight distribution.

I read an article where at the end of extensive tests and calculations, the author concluded that A/h for the $, lead acid are still coming in front even considering replacing the batteries after their useful lifespan.
Of course the premise was that you must use, discharge and recharge the batteries as per their specs (ie: never discharge lead acid more than 80%).

Has any of you more experienced done such an analysis?
Can you share your view on:
  • life-cost/ ah?
  • $/kg?
  • etc etc...
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Old 09-08-2011, 23:03   #49
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

Any idea what type LiFeP04 batteries were used for the comparison Stefano? I'm still looking for examples of real life cycling for LI batteries in a house battery situation. The only failures I,ve seen are from poor pack design or abuse, none that have come to the end of cycle life. That makes realistic comparisons extremely difficult.

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Old 10-08-2011, 06:12   #50
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

Terry,
I have searched everywhere for that article, I thought I had a PDF on my computer, but cannot locate it yet.
I think it was by Nigel Calder and it was published either on Professional Boatbuilder or Ocean Magazine.

I found one on the cost of producing energy on board: here he proves that for instance for air-conditioning, it's cheaper to use batteries and recharge them when depleted than use a genset at low load constantly.
I.E: Use the genset at high load to charge the batteries, then use an inverter to run the aircon. Then recharge. This is cheaper even taking into account the losses incurred through charging and inverting.
I cannot upload this article as it is 7MB.
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Old 10-08-2011, 09:49   #51
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If you do a straight comparison between LA an Li I don't think there is any doubt that LA are less expensive. There are other considerations that make Li attractive, if I could have fit in 8 - L 16 batteries I probably would not have considered the Li. In slightly more space than my 6-GC batteries I was able to put in 800Ah of Li. If you are sizing bank for worst conditions ie minimal solar and using engine or genset to charge batteries then Li gives you approximately double the effective Ah, so the 800 Ah of Li is giving me the capacity of 8 - L16s with less weight than the GCs.

The Li are much more efficient for Ah in/out so I get better return on my substantial investment in solar. As the Peukert's constant for Li is effectively unity you can efficiently use higher loads. This summer on a sunny days when my batteries are fully charged by 1:00 or so I'll run the water heater off the inverter for half hr or so, giving enough water for a couple of showers and washing the dishes, something I could not have done with the GCs.

Certainly getting the Li was risking a fair amount of $ as there is not really enough history to be certain how long they will last but for me the benefits out weighed the risks.

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Old 10-08-2011, 10:21   #52
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

The pdf is a bit long, but hopefully contributes some answers (or supplements some of great posts here). I use this in some Li vs. LA seminars I do. Sorry for any branding references...
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Old 10-08-2011, 17:07   #53
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

Thanks Bruce,
A good power point presentation. Do you mind if I post it on a few other forums? Regarding the alternator being run with no load, wouldn't it be easier to run the alternator output through the start batteries and then on to the house batteries? That way the start batteries act as a buffer so the alternator never sees a no load situation. What charging voltage do you use/recommend per cell? What is the Max. volts and min. volts per cell you use/recommend? Does your BMS operate off individual cells or terminal voltage?

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Old 11-08-2011, 01:41   #54
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

Sure T1, help spread the "Word" (lithium)...;-)

Excellent questions!

The "charge start batt first" idea is one way to go. However because the Li charge profile is different (never goes to lower float voltage), over a long period of charging (long motoring, etc.), and without the temp regulation that lead would like...it's less than ideal for the start batts (if they're lead/gel/agm). Best to have the alt protection built into the Li charging system but by no means mandatory if well options thought-out.

Genasun (for the cells they are using now) limit the max voltage per cell to 3.55V, and each BMS (typically there are two separate banks running in parallel) monitors and balances the individual cells in it's bank.

If any cell in a bank goes over 3.55V, first the BMS opens the alt field circuit, then (if the voltage keeps going up because it's some other charge source gone awry) then the BMS opens the charge bus relay to its bank (cutting it off from ALL charge sources). The other bank may still be charging (and the alt field still have a path). If BOTH banks have a cell or cells reaching 3.55V then both will cut the alt field and shut it off completely before cutting the 2nd charge bus relay.

So this system protects the batteries and alternator no matter what is going on with various charge sources (could be solar, AC/DC charger, genset, wind, hydro, whatever). Of course all sources should have their own regulation but if anything goes wrong with them it's good to know that the batt system looks after itself (and the alternator(s) without any human input.

It may sound complicated, but the idea is to make the installation virtually fool-proof for the user, to prevent over and under voltage. Hope all this is helpful....
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Old 11-08-2011, 02:48   #55
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

Thank you Bruce,
One small suggestion, when the field is cut to the alternator it should also open a relay in the solar + cabling before the regulator. This will protect the solar regulator from loosing the load path while the solar is still pumping amps in. With an MPPT regulator this often results in the regulator dumping every thing straight through because it no longer has a battery reference voltage, these units are generally multi voltage so often the highest possible voltage is selected anything still connected to the house circuit gets fried. There was mention of this happening a few posts back to McG I think. PWM controllers don’t change their voltage setting but they can let 20v panel open circuit voltage feed through when they loose battery sensing voltage.

Does the BMS have a hysteresis for HVC and LVC? Say HVC 3.55v open and 3.39v reconnect and LVC 2.5v and 3.1v reconnect or does it use a timer circuit?

I'm not a fan of active cell balancing as you already know but passive BMS in the form of cell protection is something Li cells/batteries definitely need because of the damage risk, just how complex is up to the buyers pocket size I guess.

To BMS or not to BMS is a very contentious and often heated subject so I’ll avoid going there, this has been a very good thread so far with lots of very good information, I’d hate to think I set off a flame war.

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Old 11-08-2011, 10:48   #56
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

T1, since you brought it up... Actually Genasun's main business is MPPT solar controllers. They have no problem with a load cutoff and are used all the time with the Genasun BMS. Besides, all the loads/devices you might be worried about would be on the LOAD bus anyhow...not the CHARGE bus. So they would never see a voltage spike even if there was one.

And yes, the load bus relays have a higher HVC than the charge bus, so that the loads stay on in a HVC; and the charge bus LVC is lower than the load bus, so that charging can stay on in a LVC.

Thanks for the great questions and input!
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Old 11-08-2011, 16:00   #57
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

Had me thrown there for a minute Bruce but I checked out the Genasun website and it appears they deal in small solar stuff. My system is a little over 1.5kw of solar and the voltage spike resulting from cutting off that off at full tilt would destroy a regulator quick smart that’s why I suggested cutting the solar input before the regulator.
The reason for the hysteresis question was a concern about relay flutter or chatter. If the HVC had say a 3.55v per cell or 14.2v in a balanced 12v nom. pack without some hysteresis (differential) between open and close as soon as the solar stopped the voltage would drop resulting in the relay closing and the whole cycle repeating, virtually creating a PWM regulator using a relay. If it wasn't a solid state type the contacts would last in the minutes range before the relay was stuffed, especially if it was a high voltage MPPT type, the arc across the contacts when opened would not be a good thing to repeat too often.
The idea of using a separate charge and discharge bus requires everything to go through the battery so monitoring would require 2 shunts and a unit that could accurately do the math that included any losses to give you an accurate State Of Charge. This is the real gauge for battery monitoring to determine when charging is required. That magic 20% SOG or 80% DoD is the safety point so the operator really needs to know what that figure is at a glance to know if all is well or the generator is going to need a run to give a safety margin. I guess it's not so much an issue on a boat out at sea but in a motorhome starting the generator up in free camp after about 4pm or before about 10am results in a sudden drop in popularity and if you were to do it in the middle of the night a good chance of reduced life expectancy.

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Old 12-08-2011, 01:20   #58
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

Hey T1,
There are a few details I forgot that effect your worries. There are many of these systems working perfectly on top yachts.

1) Genasun uses a small MPPT controller on EACH panel (or one each on smaller groups) vs. running to one big controller. This is much more efficient on yachts as each controller can optimize the output of it's own panel's shading condition. Obviously this isn't the way you'd do it for residential or land-based PV where there is usually not the shading issues we have on yachts. They can handle the load cutoff no problem.

2) Since the battery banks are two parallel (or in some cases, three) banks, one always tends to have an HVC before other so you get the BMS alarm and some warning before the other goes off. So you may not even have a comeplete load cutoff for the controllers before you recognize there's a regulation problem. In may experience this rarely happens anyway except on new boats where they haven't finished adjusting the various charging sources regulation (inverter/chargers, etc.)

3) Using a regular neg. shunt monitor (like a Victron BMV602/s) in the common neg, it is simple to monitor and track the entire bank's SOC %-wise. Do it all the time. You can program in your alarms as you like; whether voltage or percentage-based.

Sorry for the slow reply, I'm in Lanzarote polishing up a battery system (920Ah x 24V) and new alternators on the Volvo 70Telefonica. Fun stuff!
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Old 12-08-2011, 07:50   #59
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

Now there's a problem that I hadn't thought about but obvious now you mention it, the shade from sails. I guess the panels are separated in the best vantage positions around the boat so inter connected wiring in series with a single controller wouldn't be a logical move so your system is tailored to suit sailing boats in particular.
Each system has it's own set of problems, on a motorhome it's aerials, satellite dishes vent hatches, roof top airconditioning and trees in all the best camping spots :lol:
Do boats more rely on generator charging and solar as a top up? Do many use wind or water driven turbines?

920ah @ 24v, that is a serious system, is it for propulsion or just house power? I guess air conditioning would be run off a system that size because the near zero Peukert’s factor of Li cells would make that more efficient than an engine driven unit.
Thought about the controller per panel idea but the cost would be prohibitive on my type of set up, too many panels. Ultimately the final plan for my system is 3 X 48v 180ah Li battery pack that can be switched from parallel for house power to series to provide 144v nom for a hybrid drive set up with regen braking and solar for recharging.

T1 Terry
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Old 12-08-2011, 13:32   #60
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

Quote:
Originally Posted by T1 Terry View Post
Ultimately the final plan for my system is 3 X 48v 180ah Li battery pack that can be switched from parallel for house power to series to provide 144v nom for a hybrid drive set up with regen braking and solar for recharging.
What would be the advantage of switching from the 144 V series combination to the 48 V parallel for extracting 12 V house power? In either case a DC to DC converter would be needed so why bother with the switching?
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