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

[rainmaking]

Ebaugh-
True, diesels have no ignition but newer ones have electronic controls and injectors with big coils in them. Many boats also have fuel polishers, electronic engine instrumentation, tank level monitoring, navigation equipment, fuel pumps, water and waste systems, etc. that all add up to a pretty significant load. So the 10A is above your load? How do you arrive at that number? Could the batteries be burning that 140W of power just heating up?

Deck officer-
We can only fit about 200-250W of PV on the buggy top on the tower. Wish there was more we could do. Do you have that Kenyon electric grill?

Roetter-
I am no expert at this juncture but for me I would not mix chemistries in parallel. If you want to keep separate start batts I would hook them only to the starters and a small good LA charger driven by your large house bank. You are getting fancier with your system with battery isolators, etc. It's probably going to be fine but we are going to go the simpler route with three totally isolated banks, two active and one reserve. We will split our load up and be able to shift the load around a little to balance it but there won't be any connection between. Also, can't you get that victron to take care of the cutoffs without extra relays?

[ebaugh]

[QUOTE="rainmaking;1196055"]Ebaugh-
True, diesels have no ignition but newer ones have electronic controls and injectors with big coils in them. Many boats also have fuel polishers, electronic engine instrumentation, tank level monitoring, navigation equipment, fuel pumps, water and waste systems, etc. that all add up to a pretty significant load. So the 10A is above your load? How do you arrive at that number? Could the batteries be burning that 140W of power just heating up?
/QUOTE]

I don't pretend to know your load...my diesels are mechanical fuel injection and mechanical fuel pumps. If they are running, no further electric power of any kind is required to keep them running. Only the gauges need power to operate, but even with the batteries dead and alternators off line, the engines won't stop unless I shut off the fuel flow at the injection pump or somewhere else. I normally run the polishers only at anchor.

My running loads are refrigeration 24x7, lights and navigation/radar. Underway vs. at anchor might add 5-10A. Lights are mostly LED. I arrive at 25A running load, mostly based on the refrigeration, the biggest load. It takes 50A DC to run my 4 systems if they are all on, but they cycle on and off. The icemaker hibernates since I don't make ice underway. There is some guesswork involved? No question.

[rainmaking]

I had 3208's in a boat years ago that were like that....run no matter what so long as fed with fuel. Now I'm trusting a pair of gas outboards far offshore...go figure. I was just wondering if you had instrumentation showing that current going nowhere but into the cells.

[yamez4u]

Originally Posted by ebaugh

I disagree. 3.6V held indefinitely will lead to overcharge and reduced battery life. It's way high. The only formal specs available for LFP use 3.4 or 3.45V for float. .

Victron Energy, A company I trust a great deal list these setting for there lithium charge profile for a 48 volt pack:

Description| Absorption /absorption time| Float |Equalization(Default: off)
(LiFePo4) | 56,8V / 2h | 53,4V | off

Single cells would then float at 3.33 and charge(absorb) at 3.55 With no Equalization or temp adjustment. Next time I have the computer on my Victron Quattro I will make sure to check my numbers and make sure they match the recommendations.

[deckofficer]

Originally Posted by rainmaking

Ebaugh-

Deck officer-
We can only fit about 200-250W of PV on the buggy top on the tower. Wish there was more we could do. Do you have that Kenyon electric grill?

The Kenyon would deal with the elements better, but I went with the Meco 9210. Kenyon pulls 1300 watts, Meco pulls 1650 watts but boy can it BBQ a thick steak no problem, 5 minutes preheat, 10 minutes per side for thick meat. So for less than 800 w-hr, can cook (4) thick steaks. No more propane.

[wtmf]

My first thought was "oh no!!" Please use them the way they were intended. Think of it this way, how well do you work on your side?

[rainmaking]

We want built-in. I haven't heard good things about the Kenyon, mostly that it's slow. I like the idea of getting rid of the propane, but it takes a lot of battery. Glad you are making it work! It's probably healthier...

[hellosailor]

Battery Management Products - Battery Fuel Gauge - BQ27425-G2B - TI.com

Not intended for house banks, but these chips from TI may be of some interest to DIYers using Lithium batteries. It is a $2 chip designed to measure the state of charge based on a cell's impedance, at the single-cell level. TI apparently makes similar chips for lead batteries or cells as well.

With state of charge being measured by such a cheap chip, there are bound to be some interesting BMSes coming down the line.

[goboatingnow]

Originally Posted by FlyingCloud1937

terry,

It seems to me you answered you're own question.

If you stop go back and read back to yourself you're writing, you will see the light.

Charge cycle/Float/Standby.

It's done everyday.

Lloyd

For LA yes not for lithium

Dave

[goboatingnow]

Ebaugh. Ill dig up the reading links again. There is a serious debate that is attempting to look at Li performance in pulse and recharge applications ( gsm power source ) , and also in backup battery situations with and without load sharing. There is evidence that any voltage above the nominal cell valve causes a charge action to take place, since the charge process is very unlike that of LA , one has to careful not to cross contaminate between the two chemistries. Li cobalt has fewer available cycles , ( but of course 16-20% higher energy density ) so much focus is on this technology as mini cycles have to be reduced. Li Ferrous is so new that the debate is suffering from lack of reliable data, but the increased cycle counts are in effect possibly masking the issue.

Furthermore there are research papers and " eminent opinion" that suggest float charging Li Cobalt technology is causing overcharging issues, though the newer preponderance of protected cells is again " dealing" with that issue. ( though not the mini cycles issue )

To some others posters. There is no absorption mode in Li. Its purely a CV charge to a cutoff. ( within the power of the charger ). Also unlike LA , there is in effect no acceptance rate, so matching charging with battery size is important.

Its great tech, but today it is really for people that want to wade into the technical details.

My advice would be to minimise mini cycles by dropping to a low float voltage at 3.2 -3.3 volts cell , or 13.2 V. The cell under any load will drop rapidly to its nominal voltage. In the absence of that , I would charge to whatever knee voltage you pick and then DISCONNECT the charge source, I would then manually reconnect the charge sources as required.

In my opinion re-entering charge mode , should be based not only on a lower voltage set point , but on actual amp counting, ie to ensure that recharging only begins when the battery is actually discharged and not when the charger might just be supporting a load.

I will accept that cycle life data is scare, so its remains to be seen

Dave

[FlyingCloud1937]

Originally Posted by goboatingnow

For LA yes not for lithium

Dave

Dave,

You and I are probably on the same page you just don't know it. Especially after I read the post, you made after the one above/below.

I believe Li-... should be charged to what ever knee voltage, to be determined, then float so that any Active BMS can do balance, then NO CHARGE after that I believe that Li... will benefit form a zero voltage circuit. That doesn't mean we can't have a charger acting as power supply.

All remote telco/radar sites use this topology ChargeCycle/Float/Standby.

When a charger is acting in stand-by/power supply mode once the float cycle has ended, then any loads that come online will cause the chager/power supply to step up and carry the load, after the load is gone the charger/power supply goes back to sleep, unless the bats are required to be charged.

It's done everyday at many sites by the thousands, the bat tech. has nothing to do with it, it's all in the PID Loop program.

Lloyd

One day we will have a dedicated marine PID charger.. but it's not here yet.

I believe Magnum is not far away, but I'll bet they won't be the first to market.

[sytaniwha]

Regarding Shore Chargers for LiFePO4.

We have a Victron Phoenix 12/50 (12v 50A max) charger being used as the shore charger for our 4*400Ahr CALB LiFePO4 battery.

This is a dedicated charger, rather than the charger/inverter combination. The reason is that it not only has global voltage/freq input capability, the outputs are also galvanically isolated from the input, meaning that we don't need an isolation transformer (all on-board AC supply is provided by the inverters from the batteries, so we don't use the shore power for anything but charging).

The charger has mostly user programmable settings, allowing a very good match to LiFePO4.

The charge regime is:

• Constant Current "Bulk" charge to 14.4V (3.6V/cell) not changeable (but max current is settable allowing good matching to battery capacity,
• Constant Voltage "Absorption" phase with settable voltage (ours set to 13.2V, 3.3V/cell). This is timed out at a calculated time of 5 * the time spent in "Bulk" phase - because it's a user settable voltage, it can never overcharge your cells if set correctly at the nominal cell voltage, or just below),
• A settable max time for the CV phase - this really isn't needed because of the settable CV voltage, but provides a back-up to prevent over-charge,
• A float voltage, which is settable (we have it set to 13V, 3.25V/cell), which operates for 24 hours if the charger doesn't kick in again,
• A reduced float voltage at an unchangeable 13V, 3.25V/cell which starts after 24 hrs (I know it's set at the same as our settable float, so is no different: I include it here for completeness),
• A settable delay time after which the charger kicks into the CV mode for a settable time period (we have that set at 15 days interval and 2 hours duration at the 3.3V/cell CV set=point)). This basically periodically replenishes any discharge currents experienced during an extended period on float e.g. from bilge pump, standby currents of various devices, leakage currents, etc. Since it's charging only at the nominal cell voltage (3.3V/cell) it won't overcharge, so you can set the period & duration to whatever you like - if you can measure the normal background current you can get quite accurate with this. If you're living on board, you can reduce the delay time to compensate for your usage patterns.

The above regime basically fully charges the battery, without ever overcharging, and periodically cycles through a short CV charge period at nominal cell voltage which compensates for any discharge events if you leave the boat for an extended time.

The charger is triggered back into the CC (Bulk) phase if either the battery voltage falls 1.3V below the "float" set point (in our case that's at 11.7V, 2.925V/cell), or if the charger experiences a reset.

There's a slight chance that if you have a vary variable shore supply which resets the charger a lot (many times each day), you might get some overcharge since it'd start back at the CC to 14.4V (3.6V/cell) level. However this would be very rare because the minimum working voltage is 90Vac, and freq is 45Hz. Also, fully charged cells would rise to 3.6V/cell very quickly, then triggering the CV mode at your set point (3.3V/cell in our case), so it shouldn't cause any significant overcharge.

Is it the "perfect" LiFePO4 charger - no. But it's a pretty good one. We've been using it now for about 2 years with excellent results.

For any who have this charger, you need to set the "Battery Type" to "0" ("user defined") to have it use the settable points, as opposed to preset points for "Gel", Flooded, etc LA chemistries.

Cheers,
Paul.

[goboatingnow]

When a charger is acting in stand-by/power supply mode once the float cycle has ended, then any loads that come online will cause the chager/power supply to step up and carry the load, after the load is gone the charger/power supply goes back to sleep, unless the bats are required to be charged.

Yes FlyingCloud , my concern is that if you have load sharing, then the voltage of the charger is above the cell nominal voltage and all teh time the charger is supplying the load , it is also "recharging" the battery, even when full.

Dave

[ebaugh]

Originally Posted by goboatingnow

Ebaugh. Ill dig up the reading links again. There is a serious debate that is attempting to look at Li performance in pulse and recharge applications ( gsm power source ) , and also in backup battery situations with and without load sharing. There is evidence that any voltage above the nominal cell valve causes a charge action to take place, since the charge process is very unlike that of LA , one has to careful not to cross contaminate between the two chemistries. Li cobalt has fewer available cycles , ( but of course 16-20% higher energy density ) so much focus is on this technology as mini cycles have to be reduced. Li Ferrous is so new that the debate is suffering from lack of reliable data, but the increased cycle counts are in effect possibly masking the issue.

Furthermore there are research papers and " eminent opinion" that suggest float charging Li Cobalt technology is causing overcharging issues, though the newer preponderance of protected cells is again " dealing" with that issue. ( though not the mini cycles issue )

To some others posters. There is no absorption mode in Li. Its purely a CV charge to a cutoff. ( within the power of the charger ). Also unlike LA , there is in effect no acceptance rate, so matching charging with battery size is important.

Its great tech, but today it is really for people that want to wade into the technical details.

Dave

There are questions that need answering, but until the answers are known, I don't think it's that hard to program today's chargers to work. In the meantime, conservative values with only a slight reduction in capacity works around the issues.

Can you define "nominal cell value", used above? Is that 3.2V, the published nominal value, 3.4V the approximate full charge resting value, or something else?

Many Many pages back there is a link to a presentation by professor Dr. Jay Whitacre, explaining the chemistry in almost plain language. But what I got out of this...I think my own analogy though...is the charging/discharging process could be like a sand (electron) filled hourglass. Turn it one way to charge the other way to discharge, but always make sure there is some sand on both sides. Floating turns the hour glass on its side. Running out of sand on either side causes problems since there is no more sand to move. But theoretically, there is little "wear" caused by moving the sand until you run out.....

I think the floating issue is a need to discover the value that does not move sand either direction. So much research is done with the little 2Ah cells, but if you have 1200Ah, leave some sand to build a buffer. A few milliamperes takes a very long time to overcharge if you leave 100Ah on the top. And what is a micro cycle for a 1200AH cell? It would seem that capacity would have some impact, perhaps significant.

I promise to read anything you can provide links for....Bob

[daddle]

The charging and cycle characteristics are well understood and well documented in research papers. Unfortunately the "best practices" don't fit well with a cruising lifestyle. I think we will just have to live with the basic improvement over LA batteries and skip trying to find a solution to maximize LFP health. The EV industry faces a similar problem: what is good for battery does not fit well with the customers typical usage. Oh well.

One needs to factor this into the breathless fanboy superlatives here and elsewhere to figure if the improvement over LA is worth the added expense and technical attention. I think it probably is. But when one actually multiplies out all the factors, in a cruiser application, it is nowhere near the fabulous pop opinion of the early adopters, more of an incremental improvement.

Putting on flameproof suit...