Do these batteries look appropriate? Great deal.

[Mike90250]

Beware of the "BMS trap". A BMS system has limits, and many different possible features. Some work by bleeding high voltage cells down. Some work by disconnecting the charger when the pack reaches a preset max voltage(HVD) . Some provide Low Voltage Disconnect too (LVD) All require interaction with the Charge controller, and you cannot simply disconnect the controller from the battery, without damage to the controller. Sometimes it's desirable to disconnect the solar PV from the controller.

Frankly, for a neophyte, most LFP systems are too risky and complex, unless you spend months learning the lingo before purchasing a thing. Things like, do any of those 10 spaghetti leads need fuses for protection against shorts? Can the wire harness be laid out in a safe manner? Is the BMS well engineered to not be a problem in it's self ?

If Karrak gives incomplete or wrong information, as in his enthusiasm for Lithium, he'll get a couple days in the cooler.

KARRAK - you are on notice, foisting a Li battery onto a neophyte, without a completely compatible BMS, CC & Load control is DANGEROUS. Expecting a neophyte who does not know what questions to ask, is borderline criminal.

[rw3iss]

Thanks for the info guys, very useful.

You could use this BMS

Cool... karrak, can you tell me briefly how a BMS sort of works in regards to maintaining the charge/discharge level for each individual cell? The device you linked has about 10 leads coming out of it. Are each of these designed to be hooked to one individual pack (ie. one pack of 48V, 20Ah or something), so can support only up to 10 packs? Or is it designed for individual cells, ie. 10 cells (and not packs of them)? All of the battery packs I'm looking at say they have a BMS, which I thought meant some complicated circuit hooked up to each individual cell, but haven't done much BMS research yet.

[karrak]

I am just putting together a third LFP based system. It is based around 200Ah CALB cells configured with two in parallel and then 15 in series (2p15s) to give 48V with a capacity of ~10kWh. In Australia the cost of these cells was ~US$3,700 which includes 10% tax. You could use this BMS

A word of warning, you will need some technical understanding and do some research on how to put a system like this together.

Battleborn make LFP batteries with an inbuilt BMS.

When comparing Lead Acid and LFP batteries bear in mind that an LFP battery can run much larger loads with a smaller battery, can be left partially full and that the usable capacity for long life is > than 50% of the rated capacity compared to LA's ~25%.

Simon
Off grid 24V system, 6x190W Solar Panels, 32x90ah Winston LiFeYPO4 batteries installed April 2013
BMS - Homemade Battery logger github.com/simat/BatteryMonitor/wiki
Latronics 4kW Inverter, homemade MPPT controller

[jflorey2]

Thanks. Will definitely consider. I suppose the weight isn't a huge hurdle when the whole system is under 15kwh. Maybe we're talking a difference of 100 pounds between FLA and Li-Ion at that size, but I'm guessing. Will do some more research.

More like ~500 lbs. LiFePO4 beats lead acid by about 3 to 1 in terms of wh/kg. But of course it's more expensive.

[Sunking]

I suppose the weight isn't a huge hurdle when the whole system is under 15kwh. Maybe we're talking a difference of 100 pounds between FLA and Li-Ion at that size, but I'm guessing.

Yep you are guessing wildly.

I will not tell what the weight difference is, but I will tell you how to figure it out. The figure or spec you want to know is called Specific Energy (also can be called Energy Density with respect to batteries) and is measure of energy for a given mass expressed as watt-hours / kilogram w-h/Kg. FWIW those high energy density lithium ion batteries come with danger. More energy in a given space is less stable and more dangerous. A barrel of HEX explosive makes a lot bigger hole in the ground than a keg of gun powder or fertilizer.

Lead acid batteries vary from about 40 wh to 60 wh/Kg, just call it 50 wh/Kg. Lithium Ion batteries run the gauntlet from as low as 40 wh/Kg (LTO cells) to 240 wh/Kg (NCA cells) or a factor of 6. Cells safe for consumer use are LiFeP04 or LFP for short. LFP specific energy runs on the low side of 80 to 100 wh/Kg. Just call it 90 wh/Kg so almost twice the density. So a 15 Kwh Pb battery weighs in around ????

15,000 wh / 50-wh/Kg = 300 Kg or 660 pounds. I will let you figure out what the same capacity is for LFP.

[rw3iss]

If weight is an issue consider LiFePO4. A lot lighter than lead acid and less dangerous than li-ion. There are several vendors out there that do 12 and 48V blocks. SimpliPhi is one but they are hideously expensive. The LG RESU10 is another. You can also roll your own with cells and a BMS - but with a much higher risk of destroying the cells.

Thanks. Will definitely consider. I suppose the weight isn't a huge hurdle when the whole system is under 15kwh. Maybe we're talking a difference of 100 pounds between FLA and Li-Ion at that size, but I'm guessing. Will do some more research.

[jflorey2]

I'm trying to find the most affordable solution to about 10kwh power reserve for my RV. Li-Ion seemed to be the way to go considering weight and the more modern technologies, but maybe I should reconsider FLA.

If weight is an issue consider LiFePO4. A lot lighter than lead acid and less dangerous than li-ion. There are several vendors out there that do 12 and 48V blocks. SimpliPhi is one but they are hideously expensive. The LG RESU10 is another. You can also roll your own with cells and a BMS - but with a much higher risk of destroying the cells.

[rw3iss]

Right on, was looking for Li-Ion though!
The second quote seemed pretty reasonable, for the different battery I shared last, isn't it? 48V 300Ah = 14.4kwh @ $3480. That is reasonable, no? For comparison, the Tesla Powerwall 2 is about $5500+$1k install for about the same amount of power (15kwh @ 50V).
From my research here it seems like FLA batteries are just a little cheaper than the Li-Ion offerings these days.

For comparison, here is some pricing I received on some Carbon AGM batteries:

http://www.hotspotenergy.com/solar-batteries/

The price is:
REXC-200 = 9.6kwh @ 48V = $3,830

Granted, it has a longer lifespan, but the price is a lot higher for the capacity. Any thoughts?
I'm trying to find the most affordable solution to about 10kwh power reserve for my RV. Li-Ion seemed to be the way to go considering weight and the more modern technologies, but maybe I should reconsider FLA.

[Sunking]

What is wrong with 2,000 cycles? I thought most Lithium Ion cells/packs are rated around 2,000 cycles, typically?
How is it not easy to parallel? There are two leads coming out... rig something to put them in parallel to others, no?
So what is really so bad about these batteries?

Like I said is this a joke.

Many FLA batteries exceed 2000 cycles for 1/4 to 1/10 the cost and actually come with a much longer warranty you can actually claim in the USA. Good luck with that from Chi-Com manufacture from China E-Bay junk peddler.

[rw3iss]

Thanks Mike.
Well, they do include a BMS (don't know why the page doesn't say, but the woman I'm talking to said they do).
What is wrong with 2,000 cycles? I thought most Lithium Ion cells/packs are rated around 2,000 cycles, typically?
How is it not easy to parallel? There are two leads coming out... rig something to put them in parallel to others, no?
So what is really so bad about these batteries?

My application is simply a small off-grid/RV power system, max draw of maybe 500-750W, running at 48V, about 10kwh total power storage.

The second best deal I found so far, for a more typical Li-Ion pack is:

https://www.alibaba.com/product-detail/12v-24v-36v-48v-10ah-20ah_60567239963.html

They quoted me at:
48V 200AH lithium module:$2480/set including the metal box/BMS and LCD meter
48V 300AH lithium module:$3480/set including the metal box/BMS and LCD meter

Would that be a far better choice? For what reason other than it being in a more standard container or something?

[Mike90250]

I'd say considering the batteries you linked to, is a joke.
Only rated 2000 cycles, small capacity, no easy way to parallel, no BMS no no NO !

And definitely NO for a starter system. Almost a guarantee for failure.

if you tell us what you are wanting to do, maybe we can help, but for starting out, not this.

[rw3iss]

What, you or my message?

[Sunking]

ROFL. Is this a joke?

[rw3iss]

Heyas, I was talking to some suppliers on Alibaba, and ended up finding a great price for some NMC Lithium Ion cells.
Here they are: https://www.alibaba.com/product-deta...693596464.html

The quoted price is $354 for a 12V 160Ah cell. That seems pretty amazing and is the cheapest I've found.
Cost breakdown:
12V 160Ah = 1920Wh = $354 ($184/kwh)
48V = (above * 4) = 7680Wh = $1416
15.36kwh = $2832

The person I'm talking to tells me they're used for solar charging of utility poles, and maybe not appropriate for off-grid storage, but to me, they look like any other NMC Li-Ion cell, though I am by no means an expert.
Does anyone see any possible downside to using these in series for a 48V off-grid system that would draw a maximum of 500W-750W or so of power at a time, or in general? The specs say the maximum discharge power is 40W, so maybe that is what will kill the deal, but I'm not sure myself.