LiFeYPo4 questions

[PNjunction]

The storage for lifepo4 would be about 3.1v per cell, measured with an accurate voltmeter.

I think we are over-engineering the actual storage voltage. I still haven't seen any comparative charts for cycle-life vs variable storage voltages, just that it is a best-engineering practice to store them somewhat discharged.

It dawned on me that the reason the powersports lifepo4 seem to be stored at only a shallow 80% SOC may be for operational readiness. That way when a rider takes the battery home and just replaces his old one, there will be enough power to start the vehicle. The manufacturer isn't counting on the consumer to charge the battery first with his own charger.

Had it been stored at the more commonly recommended 40% SOC, and sat around for 2 to 3 years, there may not be enough power to start the vehicle, and also drag the cells down too far on the very first start. Heh, I see this a lot with parking-lot swapouts at auto parts stores with lead too. Guy buys a quality brand, but old stock, starts vehicle, and does nothing but 5 minute coffee runs and ruins the battery by short cycling at low soc's. - of course swearing off brand-x batteries the rest of his life.

I'm not going to go bananas over the actual storage voltage. If I don't have the time to accurately get down to 50% I'll just make sure to at least get out of the top 10% of my capacity for running things for a little while. If that's the difference between getting only 2850 cycles vs 3000, at my sizes I'm not going to be too upset.

[tasman]

Just getting into lifepo4 batteries and don't have the tech nohow to really understand it yet, iv'e been looking at makng up a 200ah pack using lifepo4 3.2v cells and am a little confused.

Are these 3.2 cell suitable for a 12v pack and if soi what would be the low voltage level for proper use. In this thread it says 3.2-3.1, but the cells I'm looking at are only 3.2v. So how do you work out the best low voltage for them, or should I be looking at cells with a higher voltage. Thanks.

[PNjunction]

A series connected set of 4 LifePo4 cells (4S) at a "nominal" 3.2v rating is what you make a standard nominal 12v battery from.

As a set, assuming they are balanced to begin with, any charger that can bring the SOC to 14.0 to 14.6v will work. Since there is very little capacity from 90% SOC onwards, there is little need to go as high as 14.6v, and enhanced cycle life will result from lower voltages, although absorb will take just a smidgen longer. A happy medium would be to charge until reaching 14.2v / 3.55v per cell and let the absorb current drop to C/20 or thereabouts and shut off the charger (or solar charge controller). If you can't stop the charge immediately, it won't kill them outright, but don't let it stay that way forever.

At the low end, one shouldn't go past the 80% DOD mark, and for a 4S pack, that would be about 12.85v / 3.2v per cell. This is a "rested" voltage measurement of at least an hour or more.

At fractional charge / discharge rates <1C, you may not encounter severe out of balance issues, (again assuming they came balanced in the first place) however one should always monitor cell voltages individually on a regular basis in case action is necessary to balance the pack. Depending on who you talk to, what application you are doing, or how much quality monitoring is in place, (like EV, RC or other heavy duty motive power applications), then a dedicated BMS may be a wise choice. However one must weigh the consequences of a failed BMS taking out a perfectly good battery. BMS / No BMS is an endless internet thread.

As always, consult the manufacturer's own recommendations, but be sure to note that "hard limit" damaging voltages do not mean you should visit or get close to them regularly. Unless they indicate otherwise, I'd recommend staying within an 80% to 10% DOD ratio, ie 12.85v at the discharged end (3.2v cell), and 14.2v (3.55v) at the charged end.

Note that once you remove the charging source after a full charge, the cells will eventually settle down to about 13.3v or so on their own and stay that way for up to a year with no load. When dealing with Lifepo4 voltages one wants a voltmeter that has very good accuracy. We're talking about a Fluke 87V accuracy (not just the amount of digits) as being a minimum for anyone serious about lifepo4 care.

Float is not necessary nor needed on a lifepo4, but if you did have some sort of parasitic load that would drain the battery down dangerously, then you could "float" it at about 13.8 to maybe 14.0v at the most. Ideally, find and kill the parasitic load.

[tasman]

Thanks, that answers my question very well. be using a 200Ah bank in a converted bus, with 460/730w solar array, there's 460w 12v panels and a 250w 24v panel which can be switched from the start batteries to house, through an MPPT. Doing it as a learning tool for using lifepo4 systems and then will change over our 2kw house off grid system to lifepo4. We currently have a mix of AGM and gel, neither are satisfactory and gel seems very over rated.

Have started off with a 800cca lifepo4 start battery and a 38Ah lifepo4 for fridge/freezer and accessories in our Sahara. Found the start batteries didn't have the capacity to start and run accessories when the engine is off, so have both batteries in the battery holder and could fit another couple in as well.

The next obstacle is to find a decent amp solar controller with adjustable low and high voltage cut off, so far haven't found one, they all seem to high and to low. Then have to find a 2500-5000 inverter with the same ability. Our current inverter works well and is wired into the buses 240v system, can switch it fro inverter to grid when we have power on the road which saves lots of messing round.

Buying a ready made 200Ah lifepo4 battery from china with included BMS and will learn from that installation, then hope to builds my own house bank, with an adjustable BMS.

[Mike90250]

.... We currently have a mix of AGM and gel, neither are satisfactory and gel seems very over rated....

GEL is not suited to solar, and I'm surprised someone sold you on it. (well, actually, not, but it never should have happened)

[tasman]

G'day Mike, bought the gel 4 years ago before I knew anything about them and they were recommended for a solar set up in a bus. Had nothing but trouble, they seem to be at full charge, but lose it rapidly when used and haven't worked out why. Though it may e the controller, so have changed that a few times, or maybe the panels weren't providing the proper input, but they are working fine.

You're the first one to tell me gel isn't good for solar, but form using them would have to agree and don't even know why. Be interested to find out why, what they are good for and whether I can get better service from them until we can change over to lifepo4.

Found the answers in the battery forum, thanks. I've been battling these things for years and lucky they are still alive, can't wait to get my lifepo4 set up.

[inetdog]

G'day Mike, bought the gel 4 years ago before I knew anything about them and they were recommended for a solar set up in a bus. Had nothing but trouble, they seem to be at full charge, but lose it rapidly when used and haven't worked out why. Though it may e the controller, so have changed that a few times, or maybe the panels weren't providing the proper input, but they are working fine.

You're the first one to tell me gel isn't good for solar, but form using them would have to agree and don't even know why. Be interested to find out why, what they are good for and whether I can get better service from them until we can change over to lifepo4.

Found the answers in the battery forum, thanks. I've been battling these things for years and lucky they are still alive, can't wait to get my lifepo4 set up.

For those who are watching the thread and not doing their own research through the forums, the main drawback with GEL is that they cannot (with maybe one possible exception stated by one manufacturer) be charged at a high C/N rate.
Any substantial gassing inside a GEL battery can cause gas bubbles to form in the GEL and even though the gas may recombine back to water and not cause the cell to vent, the void in the gel at or near the surface of the electrode will cause a permanent loss in cell capacity (both current and AH) from which the cell cannot recover.

[reed cundiff]

RV with LFP

Read every post on this thread and found them informative and interesting. We are full time RV'ers with four (4) Manzanita Micro 180 amp-hour (13.5 V) in series for a 180 amp-hour (54.5V) battery set. This is about 9.8 kWh total of which 80% should be usable. The batteries fit nicely into the forward baggage compartment. We have about 1.4 kW in solar. This was expensive but older son is in solar business and he wanted to see if he could design and fabricate a solar autonomous RV. The battery set allowed us to sit out a snow storm for four days with the forced air heater going almost full time (15 F). We have also been able to run the a/c for 3.5 hours as combination of solar and battery suite. We did not go below 60% energy storage in either case. This means dispersed camping in National Forest lands without a generator to annoy the birds and animals. We had two young Bull Moose "fighting' within 25 meters of the rig near Vedauwoo, Wyoming this last August. I slept late and missed most of it. The rest of the family was enthralled. We boondock as "dispersed camping" 90% of the time. The rest of the time we are "camped" in our kids backyards without using hookup.

Weight/cube is critical in a 5th wheel and equivalent usable energy storage with PbS would have probably been in excess of 750# as opposed to the 250# for the Mazanita batteries and BMS. 750# would have placed us in excess of rear axle loading of dualie 4x4. There would be no room to place such PbS batteries.

If we catch fire and burn to the ground, we shall report it, if possible.
Reed and Elaine

[PNjunction]

No worries about catching fire if those cells from Manzanito Micro are actually lifepo4 like the CALB's. Poor / insufficient wiring infrastructure, or bms failure perhaps, but the batteries themselves would have to be insanely abused since they are not the temperamental lithium-cobalt.

The yttrium versions of lifepo4, ie lifeYpo4 are similarly safe as they are still in the lithium-iron phosphate family.

With the battery balanced, have you tried just running from an 80% to 10% DOD ratio without a bms - that is staying out of the extreme charge / discharge knees? (In a nominal 12v system, that would be about 12.85v to 14.2v) In our fractional-C application, you may never need a balance unless the cells themselves are grossly mismatched to begin with.

[reed cundiff]

RV with LFP

The battery suites fabricated by Manzanita are apparently quite good for electric vehicle usage.l The BMS, controller and monitor are designed for electric vehicle usage (high drain rate) and not for RV (moderate to low drain rate).

We (our son with me watching at times) exercised system running both air conditioning and microwave simultaneously and the batteries were being drained at 3 kW. We have not run the batteries below 50%. The monitor gives the voltage of each of the 16 sub-cells as well as that of the total suite. It was below freezing last night and the forced air heater ran quite a bit and we are down -1600 kWh (down to 75% capacity) with suite voltage down to 52.4v and individual cells around 3.3V. Cut-off is 49.1V for suite and 3.1V for individual. Float is 54.4V for suite and 3.4V individual cell

This is the best answer I can give to your question of "...With the battery balanced, have you tried just running from an 80% to 10% DOD ratio without a bms - that is staying out of the extreme charge / discharge knees?"

I do not believe system has been exercised without BMS

When little sunlight is expected, we turn off the inverter at night which saves quite a few Wh (1.5 amps at 54V). We run the refrigerator on ac during the summer during daylight hours even though propane is much more efficient. We have changed to all LED lights except for the one below the microwave stove.

Our older system utilizing glass mat batteries was in wreck near Orizaba Mexico on March 15 of last year which totaled vehicle and trailer in 70 car pileup in heavy fog at 8500'. Mexican Insurance paid for truck (engine torn loose and frame bent to ground - no amount of Bondo would fix that) and finally agreed after one year (two days ago) that the trailer with bent, warped and cracked frame is totaled. The panels, batteries, and inverter were still attached. Son Cary and grand-daughter Sonya drove 1700 miles from Las Vegas, NM to haul our personal items back to US. We noticed that the brake breakaway was "broken-away" which dumps 10 amps (12 V) to hold the electro-magnetic brakes. Cary just clipped and isolated the wires and the system immediately began charging at 20 amps - and is probably still working great at some wrecking yard in Hidalgo, Mexico. The Onan generator was smashed and pushed back through the main baggage compartment - but the batteries, inverter and controllers were placed further back and were not damaged.
Reed

[PNjunction]

Wow - first of all I'm glad everyone is ok!

As a side note about crashing, if you smell a sweet-perfume like scent that is BAD. That means electrolyte is cooking, or perhaps one of the vents if they are covered has come off and is not immediately visible. Stop everything and be safe while inspecting. Lifepo4's are generally safe, but like any battery are a danger after an incident like that until inspected and verified for safety.

50% DOD - you'll have great cycle life. One thing to note is that although your bms should protect against this, but if you drop below 80% DOD for some reason, then do NOT apply a charge current larger than 0.1C to it until it comes back to the 80% DOD mark - once it does, THEN you can continue on with your normal current charge. Some small 12v-nominal lifepo4 specific chargers do this, like the little 5A Optimate TM-291 lithium.

[reed cundiff]

Son Cary has stuck a card in the control panel cabinet where we can monitor the system that stated "49.6 V" turn-off. It is a nominal 48 V system but operates generally 52 to 54.6 V. This is four "12 V" battery packs in series. He generally designs and fabricates for commercial purposes and voltage loss is an important consideration. There is also supposed to be an audio alarm when it gets near that voltage. As I have noted in a previous post, we run the refrigerator on electric during the day. If we expect strong solar insolation the following day, we leave it on 110v overnight and get up with about a - 3kW-hour deficit. If it is a bright day, we are up to full charge by noon. We did have 1400 W to controller a few days ago when we let it drop to about -4500 W-hours and didn't get the snow off till 1 pm, aka full insolation on a right day. It was fully charged in about 4 hours. Elaine thinks I am OCD with checking the instrument panel during the day, and perhaps she is correct.
Reed and Elaine Cundiff

[inetdog]

...Elaine thinks I am OCD with checking the instrument panel during the day, and perhaps she is correct.
Reed and Elaine Cundiff

Well, given the cost of the batteries and the risk to food, etc. I would have to say that you are not at all OCD. Maybe after some months of good performance I might cut back a little. But only if I were confident that the alarms, etc. work properly.
Unless you check at the exact same clock time each day. In that case I would say that you are actually CDO. (That's OCD but with the letters in alphabetical order like they should be.)

[Mike90250]

the fact that the TS-MPPT-60 can be set to a custom charge setting and will down convert my panel's 24 volts to the battery bank's 12 volts, but what charge settings would I program into the TS-MPPT-60 for a LiFeYPo4 battery bank?

Can indeed be programmed, I use the serial port and and usb translator to get to my laptop, along with MS View software to program.

[reed cundiff]

As noted above, we are full time RVers (caravaners) and are solar autonomous with LFP battery suite. The solar generally has the battery suite at float until near nightfall and they are almost always at 80 to 90% charged/10 to 20% DOD) at dawn. There were remarks earlier on this thread about problems in keeping LFP at to high a charge. Should we discharge them more fully.
Reed and Elaine