Simplified lifepo4 charging and care

[SunEagle]

Currently in an RV park (oh the shame and humiliation) and we are in total shade (get back about 600 kW-hours a day). Have paid attention to PNJunction and only hook up the 15 amp cord through the battery chargers when we get down -3500 W-HOURS

Reed and Elaine

That 600 kWh a day is probably a typo so I guess you are talking about 600 watt hour a day.

I am also curious as to how many watts of solar panels you have and how they are charging your batteries being in the shade or are the panels in the sun and your RV in the shade?

I'm not trying to be sarcastic. Just trying to understand what limitations I might see when my wife and I decide to do more RVing in the future that might take us to some dry camping places.

[reed cundiff]

Hmm, wish it were not a typo, or I could be running an EV down the road at 60 mph as long as the sun shone.

We are currently almost fully in the shade otherwise we would be charging around 500 W rate since the Fort Collins area is cloudy and rainy this week. We have gotten 1300 W to controller at mid-day in mid-summer and are to absorb by late morning. As noted in earlier post, we run Dometic refigerator (power hog) on AC 24 hours a day when dry camping in desert. This results in a -3 kW deficit by morning.

We have 1420 W of solar panels (6 x 235 W panels). They just do not do well in tree shade. I wrote on another thread (or earlier on this one) that we spent 6 days in Olympic Rain Forest and dropped about 50% DOD. Did call a NP CG and asked if they had any solar friendly sites. I was gently chided "Sir, this is a rain forest, your solar panels will not be very effective!" But the LFP battery bank does hold us well for quite a few days in shade using micro-wave and some forced air heater in the morning (in winter). Lasted another six days in deep shade at Portal NF CG in SE Arizona with no problems. We turn off the inverter when it is not in use in these situations since it draws around 60 W phantom

You have to choose your sites carefully for sun when dry camping. We do a lot of boondocking in western NM and eastern Arizona and there are few problems there (no trees, no shade). If there are trees, then we look for a site that will give us solar insolation through early afternoon and then shade in the mid afternoon to evening. Most FS CGs have a few sites with solar. Dispersed camping sites can be found in open terrain. Most folks want shade. Had great solar on beach in Yucatan and about two hours of solar when camped in jungle at north end of Lago Bacalar (it was sufficient with older 700 W solar system).

Dry camping/boondocking is what we prefer: quiet/solitude, wildlife, interesting people of the same general attitudes and interests. Almost everyone that boondocks has 100 to 1500 W or more of solar. Have had delightful times with these other folks. Battery banks are from two x 6V batteries to more than we have.

Please contact us if you have further questions on boondocking. RV.Net has a lot of threads on this as well.
Reed and Elaine

[SunEagle]

Hmm, wish it were not a typo, or I could be running an EV down the road at 60 mph as long as the sun shone.

We are currently almost fully in the shade otherwise we would be charging around 500 W rate since the Fort Collins area is cloudy and rainy this week. We have gotten 1300 W to controller at mid-day in mid-summer and are to absorb by late morning. As noted in earlier post, we run Dometic refigerator (power hog) on AC 24 hours a day when dry camping in desert. This results in a -3 kW deficit by morning.

We have 1420 W of solar panels (6 x 235 W panels). They just do not do well in tree shade. I wrote on another thread (or earlier on this one) that we spent 6 days in Olympic Rain Forest and dropped about 50% DOD. Did call a NP CG and asked if they had any solar friendly sites. I was gently chided "Sir, this is a rain forest, your solar panels will not be very effective!" But the LFP battery bank does hold us well for quite a few days in shade using micro-wave and some forced air heater in the morning (in winter). Lasted another six days in deep shade at Portal NF CG in SE Arizona with no problems. We turn off the inverter when it is not in use in these situations since it draws around 60 W phantom

You have to choose your sites carefully for sun when dry camping. We do a lot of boondocking in western NM and eastern Arizona and there are few problems there (no trees, no shade). If there are trees, then we look for a site that will give us solar insolation through early afternoon and then shade in the mid afternoon to evening. Most FS CGs have a few sites with solar. Dispersed camping sites can be found in open terrain. Most folks want shade. Had great solar on beach in Yucatan and about two hours of solar when camped in jungle at north end of Lago Bacalar (it was sufficient with older 700 W solar system).

Dry camping/boondocking is what we prefer: quiet/solitude, wildlife, interesting people of the same general attitudes and interests. Almost everyone that boondocks has 100 to 1500 W or more of solar. Have had delightful times with these other folks. Battery banks are from two x 6V batteries to more than we have.

Please contact us if you have further questions on boondocking. RV.Net has a lot of threads on this as well.
Reed and Elaine

I appreciate the info. My wife and I will probably not "rough-it" in the beginning and go to places that have utility hook ups but I want to prepare for the day when we do go dry camping and understand what my small "solar system" might be able to do for me in case fuel becomes an issue.

I currently have about 500 watts of panels in various wattage (4x40, 2x80 and 2x90) with the 4 big ones (see pics) mounted to bases that fold down and can be stored in the RV. They then can easily be set up close enough to the batteries for charging. Not the best equipment but I purchased before I came here and read about what I really should have gotten.

Thanks for your help.
Vince
340 watts of pv panles.jpgBehind PV panels.jpg

[reed cundiff]

Vince

There are a lot of threads on permanently fixed on roof (flat versus tilted) versus ones you place on ground. The best reasons for ones placed on ground is that you can site your RV in the shade and place the panels in the sun - and then move them and tilt them as required. The main reason for fixed is convenience and the fact that they are charging battery bank while you are traveling.
Reed and Elaine

[PNjunction]

Reed - that's a nice collection of CALB cells for sure.

While I don't recommend you change your existing setup, nor have any comment on the quality of Manzanita Micro, it does add an additional point of failure and cost, even though it may work until the end of time. I'm sure it wisely includes an LVD and HVD, along with balancing.

The overall message I'm portraying here is that extreme balancing can be excessive when all we have to do is lower our overall charge voltage, and given the abundance of capacity we build into our systems as solar users, we also don't need to go nuts at the bottom like EV'ers do, stopping at a relatively conservative 80% dod maximum. That way if one cell is truly at 85% DOD due to a slight imbalance, we aren't going to worry too much since we don't plan on hitting an LVD every day. One may very well find that if the cells are properly charged at the factory, an extreme balancing procedure under OUR typical house-bank conditions may not be necessary at all.

In the case of KISS, an external LVD, along with the HVD as set by the CC or ac charger, may be all one needs.

Still, you have what appears to be a very nice setup.

[PNjunction]

Increasing capacity with multiple smaller cells

Example:

You ordered a 12v / 100ah lifepo4, but quickly realized you really needed 200ah.

What would be the worst thing to do? That would be to order another 100ah battery, and merely parallel them at the ends, much like you would with a lead-acid 12v battery simply because you have no other choice.

The rule of thumb here is:

"Parallel your cells to build up capacity first into groups, and then series-connect those groups together to get your voltage."

Schematically, our simple 12v / 4-cell would look like this, where "C" stands for a 3.2v cell, and "-" stands for a series link. Note that I'm not indicating any cross-connecting polarity needed when going from group to group to keep the visual simple.

C - C - C - C

But now you've received your additional cells. Merely expand upon this theme:

CC - CC - CC - CC

In this case, we are still at 12v nominal here, but the capacity is doubled. Now you have to make sure that they are banded / strapped together properly too.

One can expand upon this theme and come up with some operational advantages, (like a ship at sea that needs extreme redundancy) but this goes beyond the realm of KISS, and of course actually introduces more points of failure. At some point, it becomes ridiculous, much like trying to make your own bank out of hundreds of small cylindrical 18650's. If you want to retain your sanity and safety, don't go there.

Ideally, from a KISS standpoint, reduce your cell count if you can. Note that unlike lead-acid, an error in over-capacity won't cost you in battery life due to sulfation. It will just be heating up your wallet instead.

[reed cundiff]

PNJunction

You have provided quite a bit of useful information over the last few months of looking at this forum.

The BMS charges at 57.6 V in absorb but cuts off charging at 54.4 volts. float. Maximum voltage of the battery bank would be 62.4 V but the BMS cuts it off (as noted) at 54.4 V.

The Tri-Star monitor gives the charging rate in amps (48 V nominal) and watts.

The Manzanita monitor gives: voltage of each cell (16) and of battery bank, charging (discharging) rate, Watt-hours above/below full charge. Happily, the Manzanita and Tri-Star Monitors give the same voltage values for the battery bank to tenth of a volt

Reed and Elaine

[Sunking]

This is an excellent example of what is not our application. High voltage - and high current.

Huh? It is smaller than a solar 48 volt system. V1 is 48 volts @ 100 AH, and V2 is 96 volts @ 100 AH which is the equivalence of 48 @ 200 AH using the exact same batteries you are using. How is that any different?

I charge both at C/2 but could easily drop that down to C/10 or lower if I desired. LFP batteries were developed for EV's like most of the R&D going into lithium chemistry. Solar is just a side show. When I cruise around in the cart I am only pulling 20 to 30 amps depending on grade of road surface. It only uses high amps when accelerating or climbing a tree. No offense but i am not sure what you are driving at. LFP is LFP regardless of how it is being used. Only difference in my mind is justifying the cost of using LFP. I cannot do that for solar application other than maybe a niche mobile application where weight is a concern. FLA cost 1/4th of LFP and only last half as long as FLA making them roughly 8 times the operating cost. So sorry if that were me using LFP on solar other than say small scale, dang right I will use a BMS to protect that investment and get as much life out of it as I can.

So help me out on what I am missing?

[PNjunction]

Nice.

If that were my bank, I'd simplify by charging at no more than 56V (3.5v per cell max ideally), and not sweat small deviations, as long as they stayed under 3.6v under charge. I might tweak any outrunners by a simple individual discharge for a little bit, but that's about it.

But I can understand those that need the assurance of an external circuit. Remember, I love to use my Flukes.

[Sunking]

Nice.

If that were my bank, I'd simplify by charging at no more than 56V (3.5v per cell max ideally), and not sweat small deviations, as long as they stayed under 3.6v under charge. I might tweak any outrunners by a simple individual discharge for a little bit, but that's about it.

But I can understand those that need the assurance of an external circuit. Remember, I love to use my Flukes.

OK so you are saying you never take your batteries to 100% SOC.

[PNjunction]

Exactly!

Unlike an EV where space is at a premium, and capacity is paramount limiting the size / and trying to maximize the DOD of the bank, in a solar house bank where one still designs for a 50% DOD just like lead-acid, that large cushion of being able to go down to 80% DOD without harm allows you to do a slight tradeoff of running from 10-60% DOD, where balance (unless it is just whacko from the start) won't be much of an issue. It also cuts down on accumulative parasitic reactions, albeit slight every cycle. (electrolyte oxidation, SEI layer growth)

Still, the warning here is that even a first timer who just throws a bare pack on a 13.8v charge source, still needs to babysit the very first charge just to make sure that the distributor didn't miss charging a cell close to the others. Stuff happens.

It really is weird to deal with lifepo4 at first, since we are trained at birth to always achieve 100% SOC otherwise bad things happen. And with no sulfation, no penalty for psoc. I knew this going in, but once I got a first-hand taste of it, wow. It is all the options it opens up that freaks you out. You just figure out what tradeoffs work best for your installation.

[Sunking]

OK PN but still at some point the cells will become unbalanced and need corrected.

What I am driving at if you only monitor string voltage, all 16 cells in series, does not ell you what is going on with each cell. That can get you into trouble when battery voltage gets low because on eor more cells can fall below minimum threshold.

[reed cundiff]

Our system does have fairly good BMS. Manzanita Micro monitor does show voltage of all 16 cells. I am to OCD to be happy without BMS and monitor

[SunEagle]

Our system does have fairly good BMS. Manzanita Micro monitor does show voltage of all 16 cells. I am to OCD to be happy without BMS and monitor

Reed

Care to share any pictures of your battery system?

[reed cundiff]

Suneagle

Will do so tonight. We are anecdotards. Our son and grandson have done the design and fabrication. I am of the hammer, crowbar WD40/Duct tape school of home/RV repair
Reed