Battery Selection And Wiring Safety

[Rabbit]

OK, why go with 4-packs of prismatic cells rather than 12V drop-ins:

Drop-in 12V interior BMS is opaque, can't be adjusted or disabled, no communications to the outside, and they can suddenly isolate the battery with no warning.

Special steps must be taken to ensure this can't damage charge sources or sensitive load devices.

LFP is usually capable of accepting very high charge rates, no problem. To the point that 2-3 day's worth of energy can be pumped back into the bank in an hour or two if you have a high-current charge source available. But the cheap included BMS in drop-ins prevents that, restricts you to a slow charge (and discharge) rate.

If you follow their marketing BS for charging voltage (much too high) you'll be lucky to only get the rated #cycles' lifetime out of them.

If that, long after warranty expires. We don't have a large database on longevity reports as we do with the top prismatic manufacturers, and with those we know how to get House bank usage lifetimes well over double maybe 4-5x the rated 2000 cycles, so barring catastrophe well over a decade, maybe even two.

Putting more than 2-3 series strings (as each 12V unit is, 4S) in parallel can lead to shortened lifetimes from balancing issues.

Finally for a large bank they're rarely cheaper.

You have to understand, Drop-in is a lie if you want longevity, you need a ​good system, all the infrastructure designed for LFP from the ground up

not just BMS
over-current protection
LVD and HVD safety cut-offs
temperature protection

but also
100% PROGRAMMABLE charge sources
separate charge and loads bus

And the tools + knowledge required to try your best that investing 7-10x the price of a lead bank will pay off in many more years of service.

All of these last factors are true for any form of LFP bank.

Think about the fact that in the world of sailing yachts, 90+% of LFP installs are going into the racing boats, where lotsabuck$ are spent to minimize weight.

Even pretty wealthy liveaboard cruisers are hesitant about investing in a technology that has such a long ROI window, might be a lot less than a new set of sails, but still a lot of boat bucks to risk like that.

I suspect you hit an important nail on the head in speaking of the need for a "ground-up" system. I'm not an electrical expert by any means, but it's something I've seen again and again in new tech. There's a transition period when everything is wrongly-optimized to a soon-to-be-obsolete standard due to pure inertia.

I also suspect that as advanced a setup as you're describing is probably beyond my capabilities, as a beginner. In a few years, maybe. I've seen references to the prismatics here and there in my other research, but no one else explained them in such a way that I understood what the damn things even were. Thank you for your time, and for that especially. I accept that a drop-in system won't even be close to optimized, and that the ROI time is forever or beyond. But I think it's going to be all I ought to bite off for my first attempt. Maybe down the road, when I've learned more and the tech has matured, I can move up to a higher level.

 

[Rabbit]

Actually 13.8V is the magic maximum voltage for routine cycling, if your goal is longevity. Yes for drop-ins as well, even the little 18650 cells, chemistry is chemistry.

I have my LFP care summary blurb somewhere if you want me to dig it up let me know, also more links for further self-education.

I'm always eager to learn more, if you're willing to share. Thanks!

 

[jonyjoe303]

[font=Verdana, Arial, sans-serif][size=small]"I'm looking currently at $3-4k in Battle Born or another major brand, so... Yes, I plan to spend some serious money. Any info on an alternative and perhaps better way of doing things is most welcome, and thank you for taking the time."[/font][/size]

[font=Verdana, Arial, sans-serif]If you can build things, there are alternatives[/font]


This is what I used on my lifepo4, 80 of these tenergy cells connected in a 4s20p configuration gets you a little over 100ah. They cost me 154 dollars including shipping. All you need is a hot gluegun, tab welder and solder gun to put them together. So far I built 2 and was going to build one giant 200ah battery but never got around to it,  I barely use 1 of my batteries. After you build one battery the rest are easy. You can build 4 of these for the price of 1 battleborn. Performance so far has been excellent, I only drained it all the way down once during a week of cloudy weather and solar wasn't charging it every day, it took a week to charge it back up.
These are giant heavy batteries, bigger then a D battery, 80 of them weigh about 30 pounds.
They sell on ebay, they are out of tenergy, but they got fullriver brand but you get 60 for about 145, that only get you about 80ah.

Its an alternative and not that hard to put together, I build both of them inside my van where I have very limited space.

 

[Weight]

Here is a link to CALB lithium cells. http://store.evtv.me/products.php?cat=10 Many consider them among the best. No welding involved. But if a person has limited experience, it would be expensive and difficult to build a bank. I don't know why John didn't refer you to this comprehensive thread about LiFePo battery banks. http://www.cruisersforum.com/forums...or-those-using-them-as-house-banks-65069.html

 

[highdesertranger]

for 3-4k, I could be into 6v batteries for the rest of my life and still have 1-2k left over for other things. just saying. highdesertranger

 

[John61CT]

I don't recommend cobbling together hundreds of small cylinder cells.

And again, the "drop-ins" may well never payback, not cheaper, still want the same level of care below, and resulting longevity is completely unknown IRL.

For you OP, I recommend sticking to the FLA Deka GCs at $1/AH

_______
Here's my "boilerplate" LFP summary, mostly from marine electrics discussion forums involving long-term users and professionals, with special thanks to Maine Sail (see below).

Any and all feedback is welcome, especially if more "canonical" information from the links cited conflict with my summary.

______
Systems: OceanPlanet (Lithionics), Victron, MasterVolt, Redarc (Oz specific?)

Bare cells: ​Winston/Voltronix, CALB, GBS, A123 & Sinopoly

Best to size your cells for two parallel strings for redundancy, unless you have a separate reserve/backup bank. Don't go past three, or you may see balancing issues that affect long-term longevity, maybe four in a pinch.

Note nearly **every** vendor, also those of ancillary hardware touted as "LFP ready", gives charging voltages **way too high** for longevity.

My (conspiracy) theory is that manufacturers would prefer their cells get burned out in under 10 years.

EV usage is very different from much gentler House bank cycling. Most EV people talking "lithium-ion" mean other chemistries not as safe as LFP, much shorter lifetimes, and with completely different setpoints and behaviors.

My charge settings for LFP: 3.45Vpc, which = 13.8V max for 4S "12V".

The point is to look at the SoC vs Voltage chart, and avoid the "shoulders" at both ends, stay in the smooth parts of the curve.

Either "just stop" charging when voltage is hit, or if you want another couple % SoC capacity, stop when trailing amps **at your spec'd voltage** hits endAmps of .02C, or 2A per 100AH. 

Note even at the "low" max charge voltage, letting the charge source continue to "push" even low currents long past the endAmps point is **over-charging, and will** greatly reduce lifecycles.

So if you can't then "just stop", set Float well below resting Full voltage, at say 13.1V, but that is a compromise, and *may* shorten life cycles.

With LFP, you don't need to fill up all the way at all, as far as the cells are concerned. In fact, it is bad for them to sit there more than a few minutes. Therefore only "fill up" if consumer loads are present, ready to start discharging, ideally right away.

Store the bank as cool as possible and at 10-20% SoC, or maybe higher to compensate for self-discharge, if not getting topped up regularly (I would at least monthly). 

Letting the batts go "dead flat" = instant **permanent unrecoverable** damage.

Same with charging in below 32°F / 0°C freezing temps.

Persistent high temps also drastically shortens life.

Charging at 1C or even higher is no problem, as long as your wiring is that robust, vendors may spec lower out of legal caution.

Again, going above 14V won't add much AH capacity, but will shorten life cycles dramatically.

And of course, we're talking about gentle "partial C" House bank discharge rates, size appropriately and be careful feeding heavy loads like a winch or windlass.

Following these tips, letting the BMS do active balancing is unnecessary and potentially harmful, just look for LVD / OVD and temp protection. Multiple layers of protection are advised if it is a very expensive bank, so you don't rely on any one device to keep working.

Check cell-level voltage balance say monthly to start, then quarterly, finally every six months if there are no imbalance issues, but only if that seems safe to you.

This thread is long but informative http://www.cruisersforum.com/forums...or-those-using-them-as-house-banks-65069.html

, make sure to give both Maine Sail and Ocean Planet your close attention.

Also MS' summary notes here
https://marinehowto.com/lifepo4-batteries-on-boats/

**Everything** at that site is worth reading, very valuable. He also has great articles in Practical Sailor. His new site under development transitioning the pbase content is here

https://marinehowto.com/support, feel free to make a donation to help with those expenses.

Best of luck, and do please report back here!

 

[John61CT]

When comparing prices make sure to find out shipping costs.

Last big batch of CALBs cost me ~$250 cross country, and that was to a commercial loading dock. Manual unloading to a residence was going to be $50 more.

With lead GCs you should be able to pick up locally, preserving that $1/AH

 

[Weight]

thanks John. I will add, letting Li cells discharge too low can reverse the charge, neg becomes pos. All kinds of bad.
LiFePo cells are fairly safe to use, but many bad things have happened to users of other Li chemistry. Especially bad is using cells from recycled automotive such as Chevy Volt. Those A123 cells are difficult to build a reasonable sized bank. Also some of them are not LiFePo.
Read Maine Sail's carefully researched information and make a donation or buy something from his store.

 

[jimindenver]

The discussion is so focused on batteries that it isn't dealing with the rest of the grail. I obtained the grail years ago and may be one of the first considering all I read and heard before that was it could not be done. I have some bad news for your basic numbers though. I have 1185w of solar and with 435w tilting and tracking the sun it is more like 1600w of flat mounted panels. I have 675 AH of Lifeline AGM's that are 7 years old that can suck up a charge rate that isn't practical to produce even on shore power. It is rare to see a bank of that age out here and I'd bet mine will outlast most of the banks I have seen recently even though they are newer. This isn't because Lifelines are the cream of the crop in AGM's, it's because it takes a lot more than settings and gear. It takes personal experience with your batteries and gear in relationship to your needs and conditions. It is nothing that can be Googled and regurgitated, read on a forum or taken from another's experiences from their system and applied to yours. Those are starting points to consider, that's all.

The one thing I can tell you is that 1200w of solar is not going to produce enough power to run even the smallest window A/C during the day AND recharge the batteries after running it at night too. You might stand a chance if it is tilting and tracking on a good summers day but you will be behind the 8 ball with one bad day and the shorter days of low sun in the winter are hell. Even with my system the best I could do is use my tiny generator to run the A/C during the day while the solar replenishes the batteries that can run it over night. The other option is a shorter run in the morning of a big generator pushing a big converter/charger replenishing the bulk of the overnight use while the solar finishes the charging while running the A/C at the same time.

So the grail is obtainable but only if you get a handle on your needs first. You will need a bank that can support not only the total haul but also large draws. You need not only enough solar to cover those needs but also a back up that can produce enough of a charge to bring your bank up in a reasonable amount of time. Lithium may save you weight but you are going to pick it right back up in a high output charger and the generator to run it.

Every choice you make is going to affect the rest of the choices in one way or another. You need to find a set of options for each part of your system and work out how each option not only fulfills your needs but also how it plays with the other portions of your system. You can do this by working it all out before making any decisions or building it all by advice and replacing as it fails.

Things to consider from the advice isn't if a persons bank last forever and is always recharged by this much solar, it is how much power do they use daily. Why? Because they may be only cycling the bank lightly and have way more solar than they need to replace what they use. The same system deep cycled daily will last a much shorter amount of time and the solar doesn't stand a chance at keeping up. A 100 Ah lithium battery that can't be kept at 100% isn't a 100 Ah battery. A shunt that doesn't know the true starting point, doesn't consider that batteries age or know the difference between what the battery produces/accepts vs what the solar runs straight off the panel isn't really accurate. All cool concepts on the surface but each has its flaws.

So start with your needs. I can't believe that the A/C is going to be the only thing you will want to run. You will need to know how big of a A/C it will require to cool the space, research units of that size and then add in the rest of the loads. A 12v fridge sucks up a lot of power and a cell booster can pull 24 or more Ah's Ah's a day. To give you a idea, I use on average 250 Ah's a day and that's without running the A/C. I have a large system and use a lot of power but it took years to work it all out. Take your time to find the balance and you will be a lot happier in the long run.

 

[B and C]

^^^ Good advice

 

[John61CT]

many bad things have happened to users of other Li chemistry.

Yes LFP is the only Li chemistry I'd recommend, both for safety and longevity.

EV car packs are not LFP, and lots of reasons to avoid them, at least for now.

 

[tx2sturgis]

In addition to all the wisdom stated in this thread, I'll toss this tidbit out there:

If you can partition off part of the trailer just for sleeping, TV watching, internet surfing, what have you, then you can reduce the amount of AC needed. (the AC can run much less if its cooling a very small room)

Super insulate that section.

No need to put the burden of cooling the entire trailer, including the warmer kitchen area, on an AC unit and the associated power system.

Or do you really want and need to cool the ENTIRE trailer?

 

[Rabbit]

In addition to all the wisdom stated in this thread, I'll toss this tidbit out there:

If you can partition off part of the trailer just for sleeping, TV watching, internet surfing, what have you, then you can reduce the amount of AC needed. (the AC can run much less if its cooling a very small room)

Super insulate that section.

No need to put the burden of cooling the entire trailer, including the warmer kitchen area, on an AC unit and the associated power system.

Or do you really want and need to cool the ENTIRE trailer?

It's only a 6x12, but I've planned to partition it if I need to.

 

[Rabbit]

So start with your needs. I can't believe that the A/C is going to be the only thing you will want to run. You will need to know how big of a A/C it will require to cool the space, research units of that size and then add in the rest of the loads. A 12v fridge sucks up a lot of power and a cell booster can pull 24 or more Ah's Ah's a day. To give you a idea, I use on average 250 Ah's a day and that's without running the A/C. I have a large system and use a lot of power but it took years to work it all out. Take your time to find the balance and you will be a lot happier in the long run.

In two words, thank you.

I went with 1200 watts because that's the maximum amount of panels I could physically fit on top of my rig. Even 1200 extends an inch or so beyond the rest of the trailer-body in all directions. So what you're telling me, pretty much, is that it isn't going to happen. This is what I needed to hear at the earliest point possible. I can spend more money, but I can't make more physical mounting space short of using ground-panels, which is a place (for complicated reasons) that I'm not willing to go.

I have much refiguring and redesign to do from here. Again, thank you. And congratulations on the grail!

 

[tx2sturgis]

Ok...well maybe just an insulated curtain around the bed might help....thinking of ways to reduce the cooling load. 

I dont know if you can put enough batteries and solar on a 6x12 to do the job....I'll let others figure out the how to's on this one.

I do know there are some low BTU AC units for cooling teardrop trailers, kiosks, and dog houses...but they are much more expensive than the common, mass-produced, window units...

 

[Rabbit]

Ok...well maybe just an insulated curtain around the bed might help....thinking of ways to reduce the cooling load. 

I dont know if you can put enough batteries and solar on a 6x12 to do the job....I'll let others figure out the how to's on this one.

I do know there are some low BTU AC units for cooling teardrop trailers, kiosks, and dog houses...but they are much more expensive than the common, mass-produced, window units...

We'll see what develops. This is a back-burnered project, not an abandoned one. Impossible for now, maybe not forever.

Thanks to everyone for all the help!

 

[jimindenver]

Oddly the low BTU units do not use any less power than the 5000 BTU energy star unit I use, in fact some use more.

My grail was running the little A/C directly off the power produced by the panel mid day. I travel in the desert in the winter and at high altitude in the summer so I am more likely to use the furnace at night than the A/C. (arthritis sucks)

One thing to know is 5000 BTU is not a monster when it comes to cooling. I need to anticipate the heat by starting the A/C before it gets hot and using it to keep the trailer cooled down, not cool it down. I have it mounted mid trailer and honestly it was better up front with a box fan pushing the cool air back to a exhaust fan pulling hot air off the ceiling. It would cool the tint bedroom wonderfully but struggles now unless I cordon off the bedroom, bunks and bathroom. Such is life in a poorly insulated trailer.

 

[Rabbit]

Oddly the low BTU units do not use any less power than the 5000 BTU energy star unit I use, in fact some use more.

My grail was running the little A/C directly off the power produced by the panel mid day. I travel in the desert in the winter and at high altitude in the summer so I am more likely to use the furnace at night than the A/C. (arthritis sucks)

One thing to know is 5000 BTU is not a monster when it comes to cooling. I need to anticipate the heat by starting the A/C before it gets hot and using it to keep the trailer cooled down, not cool it down. I have it mounted mid trailer and honestly it was better up front with a box fan pushing the cool air back to a exhaust fan pulling hot air off the ceiling. It would cool the tint bedroom wonderfully but struggles now unless I cordon off the bedroom, bunks and bathroom. Such is life in a poorly insulated trailer.

Good to know!

I have rapidly-worsening arthritis, plus a serious birth defect in my heart that no one caught until I was too old to have it repaired. So... I'm trying to get out while I can still move, and stay cool once I'm there. The good news is that if I'm going to be generator-dependent regardless, I can use a larger btu unit if I must.

 

[tx2sturgis]

Oddly the low BTU  units do not use any less power than the 5000 BTU energy star unit I use, in fact some use more.

That's probably true, being less likely to be energy-star tested, which means they most likely use power hungry components....maybe even the same compressors from the 5000 BTU air conditioners.

 

[SalsaDog]

Have you looked into getting a bigger ac and throw an extra starting capacitor (Easy Start) on the compressor? It
works like a charm. A motor runs on a fraction of the starting (in rush) current.

If you need an ac for health reasons; get an ac. I built a collapsible four panel wall for our generator. I glued acoustic
foam to the walls. It blocks about half of the sound at 100 ft. IMO, a neighbor should not be closer than that.