Looking for Input on LiFePo4 Batteries

[Lizzarro]

So, I finally got my van back and, after tearing everything out, I've begun to lay out my electrical system and it's needs. 

I have a few specific tech needs and plan to be be powering the following I'm trying to be generous with my estimates so that I'll end up with a good bit of wiggle room for future-proofing and rainy days.

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• Computer with monitor and accessories: ~125w during unladen use, ~300w under load. Approx 2hr/day and 3hr/day respectively. (around 100ah)
• Nikon charger: (1ah)
• Cell charger: 5W 2-3hr/day (1.25ah)
• Microwave (maybe): 700W >10m/day (9.3ah)
• Lights: 60w 4-6hr/day (30ah)
• Rear radio head unit: ~10a (max) 4-5hr/day (~45ah)

---

Total: ~187ah 
After inverter loss (~20%): ~224ah
Plus wiggle room (25%): ~280ah 

With 400w worth of panels on the roof, I figure I can clear that number on a sunny day and maybe squeak by on a partly cloudy day. However I don't want to deal with having to keep a vigil eye on my power consumption. I've heard about LiFePo4 batteries and that, while they're more of a hassle to set up and balance, they can offer a higher DoD than traditional lead acid batteries without the danger of thermal runaway that other lithium cells have. 

So all this brings me to my question. Could anybody tell me if these  3.2v 100ah wired in parallel would provide a decent battery bank for a 400ah system when wired in series? They're $112 apiece with the minimum order of 4 which would yield 12.8v when strung together. They're rated at 2,000 cycles at 80% DoD and weigh just under 8lbs apiece (a 110ah Lead/acid weighs around 70lbs) and can handle a nominal load of 300A (3600w). 

Is there something I'm missing here or is this actually a good idea? I'm fairly good with electronics and such but the thought of doing my own solar is intimidating. If this won't work is there another option that would meet my increased power needs? Much of my time using the computer is spent photo/video editing plus some gaming as well. I don't plan on being huddled up in my van all the time but I know there will be days when I need all that power, particularly after certain excursions. 

I'm really excited to have my van back and get to work but I want to plan like the dickens before I start spending time or money on something that doesn't work. 

Thanks in advance for your input!

-Lizzarro

 

[BradKW]

Its been a couple months since I was reading about it, but I recall there being more to creating a 12v bank than simply wiring some small cells together...can't remember what you have to "add" as I didn't understand it anyway. More recently, I keep reading that supply has become a real bottleneck for DIY'ers...orders placed that never arrive, calls and emails going without response for months, etc.

So make sure you're comfortable with supplier...your cost is on par with Blars: http://techno-viking.com/

And here's about everything you'll want to know about them in a mobile application: http://www.cruisersforum.com/forums...or-those-using-them-as-house-banks-65069.html

 

[IGBT]

Four 3.2V 100ah cells wired in parallel will give you a 3.2V 400ah battery.

You would either need to find stuff that runs on 3.2V (hard), wire them in series for a 12.8V 100ah battery, or buy 16 of them and make a 12.8V 400ah battery.

edit: I think maybe you meant you are buying 16 of them. Don't they make a bigger cell so you would only need four wired in series?

 

[MikeRuth]

I'm not sure but I think there may be a problem with your math.

These are a nominal voltage of 3.2V and a peak at charging of 3.65. you say each cell is rated at 100ah.
Given that then to obtain a working voltage of 12 volt system you will need to connect these in series. When you do that your total AH is still 100 AH, not 400 ah.
Wired in parallel you will only have a voltage of 3.2Volts, obviously not usable.

what I found was...as example
12.8V 100 AH built pack at $610.00.
3.2V 100ah individual cells, you build the pack to 12.8 with four at @$135.00 Each/$540.00

so again I'm thinking that to build a 400/ah pack is going to be much more expensive than you might have thought. 

Good luck in your search. 

Mike R

 

[cyndi]

Blars has written extensively on the subject; both on his blog and here

https://vanlivingforum.com/Thread-Best-battery-for-full-time-boondocking-LiFePO4

http://techno-viking.com/

 

[blars]

As others have said, you need 16 in 4P4S to get 13.2v 400Ah. (3.2v is near full discharge, 3.3 is 80% charged.) Always parallel LiFePO4 before putting them in series.

I don't know anything about the FBC brand. I have 4 winston 260Ah cells in series, 450W solar, and use about 120Ah a day. Trees tend to limit power more than weather, but I don't need to run my generator often.

They do need a different charge regime than Lead, and there is a lot of misinformation out there. (Never charge them above 3.5v/cell.) Below 0.5C charge/discharge, I would not recommend any auto-balancing, it's more likely to cause problems than cure them.

See my blog for more info.

 

[Lizzarro]

You guys are right. I forgot my high school science course and that wiring them in parallel you stack amperage and in series you stack voltage. That'd make them way out of my price range. I'm going to keep looking though and I really appreciate everyone providing helpful links.

It appears that I either need to rethink my budget or my energy needs. Possibly finding a compromise on both.

Are there any exceptional Lead-Acid options that don't weigh a ton? I may start with that and upgrade down the road when the price on batteries (hopefully) falls in the next few years. Still, the prospect of having high DoD cycles is soooo tempting, even if it would cost me $1000 to do it.

 

[BradKW]

Are there any exceptional Lead-Acid options that don't weigh a ton? I may start with that and upgrade down the road when the price on batteries (hopefully) falls in the next few years. Still, the prospect of having high DoD cycles is soooo tempting, even if it would cost me $1000 to do it.

I think its one of those things where the better the quality, the heavier the battery. You'd want to go 6v golf cart x4 probably...something like these perhaps: http://bigtimebattery.com/store/Trojan_t-145_replacement_battery.html

 

[Almost There]

I'm running with 450 ah of batteries which is slightly more than you wanted.

I chose the Trojan T105 REs for their longer warranty and much higher cycle expectancy.

They only weight something like 6 lbs each more than T105s, and take up the same space.

Store front operations wanted considerably more for them than did an online store I used.

 

[johnny b]

"Store front operations wanted considerably more for them than did an online store I used."

How much was shipping?

 

[blars]

You'll need about 800Ah of Lead to have the same usable capacity as 400Ah of LiFePO4. I'd say cut back on usage and go with a smaller LiFePO4 bank.

 

[Patd4u2]

I have narrowed down my choice to one of these two. they are pretty good batteries and you don't have to worry about hydrogen gas when charging or keeping an eye on the water level.

http://www.amazon.com/dp/B00DDYM1UC...UTF8&colid=3Q36AGBYJNHEG&coliid=IVKP5WVXIPK2Y

http://www.amazon.com/Vmaxtanks-Vma..._UL160_SR152,160_&refRID=1X5JCZN2009K5CRSAX49

 

[BradKW]

In general, 2 x 6v outperform one 12v battery, and Lifeline seems to be acknowledged as one of the best: https://www.batterystuff.com/batteries/rv/agm/111-up-ah/gpl-31xt.html

Also in general, AGM's have the need for high amp charging cycles to keep them happy and solar alone doesn't provide this.

Sternwake on this forum has posted extensively about these topics...you'd do well to use "search" and work your way through some of his stuff before committing...

 

[Almost There]

"Store front operations wanted considerably more for them than did an online store I used."

How much was shipping?

They offered pick up at 7 different locations in AZ (each state will vary). The crazy part of it was that they couldn't tell me the availability in any one location until I placed the order and specified a pick up point. We played 'ring around the rosie' on the phone becuase I could pick them up in any one of 3 locations that they had that were all about equidistant from me.

The CSR finally got the message and when she placed the order for pick up in Yuma and I was told a month wait to get them, she arranged for them to be available to me the next week in Phoenix..duh!!

Yes, I had to drive from Quartzite to Phoenix for them and pay a $35.00 fee but it was still a whole lot cheaper than paying the local RV dealer what they wanted. If I had only been buying 2 then it wouldn't have worked out cheaper because my gas and the pick up fee wouldn't have changed. With 4 of them it made more sense to do it this way.

 

[Lizzarro]

You'll need about 800Ah of Lead to have the same usable capacity as 400Ah of LiFePO4.  I'd say cut back on usage and go with a smaller LiFePO4 bank.

I think this will be where I end up going. There are some models that I could run for about 2-2.5x my planned costs. The initial cost will be steep but I feel I will be better off in the long run.

 

[SternWake]

You confusion between hooking batteries in series vs parallel might make setting up and properly caring for Lifepo4 batteries a bigger piece of pie than you plan on.


Lead acid are quite forgiving, in comparison, to Lifepo4.  One serious overcharge or overdischarge might reduce their capacity to uselessness.

No doubt Lifepo4 is a better battery, but proper implementation is a necessity to prevent overcharge or overdischarge.  Since their voltage under load only sags right at the end, it is easy to go from appearing fine one moment, to overdischarging the next.

Prematurely Killing a Lead acid battery is much less financially painful than committing batterycide on Lifepo4.

http://www.pbase.com/mainecruising/lifepo4_on_boats

http://www.cruisersforum.com/forums...or-those-using-them-as-house-banks-65069.html

And yes, AGM batteries are often seen as the Super Lead acid battery, but in reality, compared to a true deep cycle flooded lead acid battery, they are much more petulant in regards to their charging current, and partial state of charge cycling.

AGMs like recharge currents upto their stated maximums, if they list one.  Usually 30 amps per 100AH of capacity like for those Vmaxtanks.  They do not like the low and slow solar only recharge, when discharged to 50%, or deeper but are likely OK in the 75%+ ranges.

If one can feed a depleted AGM a near 30% charge rate when most depleted, AND have the solar top off the battery each and every cycle, then they can achieve that super battery status that most people imbue them with, due to their  pricetag.

Feed an AGM improperly and it will not last as long as a flooded battery in the same usage, and cost twice as much for the privilege of living a shorter useful lifespan.

Reduction of power requirements is wise too.  Get a Kill a watt meter, see how much your stuff really draws, you might not need the capacity you think you do.

I once had 345AH total capacity.  Years later I use more electricity and have only 90AH capacity total and can achieve excellent number of cycles from the hard working high$$ AGM battery, for less $$ per cycle achieved, compared to having 3 flooded group 27 marine batteries.

 

[Lizzarro]

You confusion between hooking batteries in series vs parallel might make setting up and properly caring for Lifepo4 batteries a bigger piece of pie than you plan on.

This is why I'm asking questions. I'm familiar with electronics in general but have never built a solar system before. Some of this stuff relies on knowledge I haven't used in awhile.

 

[SternWake]

This is why I'm asking questions. I'm familiar with electronics in general but have never built a solar system before. Some of this stuff relies on knowledge I haven't used in awhile.

  Well, as long as you know that Lifepo4 is not just a simple lead acid drop in replacement that simply costs more upfront.  The whole charging system needs to be tailored to their profile, and preventing overcharge and overdischarge are prime considerations.

And Lifepo4 can cook your alternator as they have such low resistance and can greedily ask for everything it can make up until nearly fully charged.  Leadacid batteries start limiting current at~80% charged and take about 4 hours to get from 80% to 100%.

Newbies to living on 12vDC battery power are usually battery murderers as they have little idea how much power they require, nor how much recharging ( time at the correct charging voltages) needs to occur to repeat the abuse of the lowly lead acid ancient technology. 

 A Newb paying out the premium for Lifepo4 better have a firm grasp on what they require to be safe and long lived.