LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

[sparrowhawk1]

Originally Posted by KTP

Seems really expensive to pay $600 for raw cells with no bms when packaged LFP solutions with warranties are $900 to $1000.

1/3 more is a deal? I can get a BMS for $30 that takes the higher voltage of one or more and puts it into the lower voltage cells. And bottom balances too. But if I stay away from the ends and periodically test, I shouldn't need one.
Edit. It also shows voltages and controls up to 8 cells

[sparrowhawk1]

Maybe in the future if I find I need auto balancingAttachment 194376

[john61ct]

The BMS included in many such "cheap" units introduce their own limitations, downsides and risks.

And who knows who the actual maker of the cells is? Huge variability in quality just in chemical purity, makes a great difference to longevity - if that factor is important to you.

The list of top-notch known trustworthy LFP cell makers is a **very** short one, and afaik none sell packaged systems to consumers, so far I have yet to talk to one willing to even recommend a suitable BMS!

[john61ct]

Originally Posted by sparrowhawk1

Maybe in the future if I find I need auto balancing

Yes many ways to do that, if ever needed.

So far doing so through the BMS seems the poorest value, riskiest way to go IMO.

ISDT makes great stuff. Have a look at FMA/Revolectrix Cellpro / PowerLab, and some Junsi iCharger as well.

There's also a German outfit a big quad using friend showed me says they really are top notch but of course pricey.

[sparrowhawk1]

Unfortunately this person doesn't have ratings yet but this seems like an awesome buy https://rover.ebay.com/rover/0/0/0?m...2F153535506369

100 amp hours for about $400 is my goal. Wish there was a way to use my current mppt controller without overcharging them.
PS seller joined eBay June 19th 2019

[CatNewBee]

Originally Posted by sparrowhawk1

So in a nutshell lithium batteries voltage vairies much less than lead acid having less differential at first but staying in bulk mode for much longer. Resulting in an average of 20% more amp hours. So I'm back to either buying an adjustable mppt controller ($150) or figuring out a way to use my 40a mppt controller that can only be set to sealed at 14.4 which when tested was actually 14.2 at the batteries when charging at 20 amps because the controller gets its reading off of the same leads that charge the battery. I'm just worried that at a lower amperage the voltage will be too high. Experienced people say different things. Keep in mind I'm planning on starting out small with maybe a hundred amp hour battery Bank that I can buy for less than $450 new. Free shipping. Same bank that Will Prowse used in his video.
Or even taking a gamble with used batteries with an eBay seller who has a high rating.

14.4V is OK for LFP. Just make sure, there is no temp compensation on, nor equalization program, that can fry the battery. 3.6V cell voltage is below the 3.65V for 100% SOC, no problem with balanced cells.
If not, the BMS will cut the charge bus anyway.

[Cpt Pat]

Originally Posted by sparrowhawk1

Maybe in the future if I find I need auto balancingAttachment 194376

I tried one of those just to monitor cell voltages with something more convenient than probing with my Fluke multi-meter. The voltage readings were all over the place. Very inaccurate. It ended up in the trash can. Worse than useless. A cell IM-balancer.

[john61ct]

They need to be calibrated, periodically just like the $600 tools, not hard to do.

And updating the firmware regularly is a good idea, the calibration user interface was one area improved a few times.

Talking about ISDT in general.

It's true that FMA PowerLab is better, IMO also the Junsi iCharger line

Found my note on the stellar German unit: Graupner Polaron EX

[newhaul]

Originally Posted by john61ct

.

It's true that FMA PowerLab is better, IMO also the Junsi iCharger line

please elaborate on this . What is the performance like on these ? What observations lead you to say they are better ?

Are there any links to the chargers in question ?

[sparrowhawk1]

First -closing a thread because it's too big doesn't make any sense to me.if you want to start another thread on particulars cool. Of course on a thread this long you're going to have repeating so here I go.On this YouTube Will says that hooking up his ($200+)controller to the BMS can harm it if the BMS disconnects it. which I pointed out before and that's why drop-ins make no sense to me especially if you're using an alternator to charge.he also shows hooking up the BMS for low-voltage to a separate switch that can handle high amperage. My question is why not attach that switch before the solar controller and have the BMS set to cut it off at a set voltage (measured at the highest cell). This way I can use my existing $200 plus mppt controller and have my batteries stop charging at a voltage of my choice. Also in the future I can charge my electric dinghy with solar panels with just the BMS and the switch https://youtu.be/_PgthByAYz4

[OceanSeaSpray]

Originally Posted by CatNewBee

14.4V is OK for LFP.
...
3.6V cell voltage is below the 3.65V for 100% SOC, no problem with balanced cells.
If not, the BMS will cut the charge bus anyway.

The BIG missing point is charge termination, the higher the voltage, the more quickly you do damage when not terminating properly.

The other one is that you will quickly find that, in practice, you need a balancing BMS to make charging at higher voltages manageable at all after a while or the charge bus will start dropping out all the time because of cell balance issues.

[tanglewood]

Originally Posted by sparrowhawk1

First -closing a thread because it's too big doesn't make any sense to me.if you want to start another thread on particulars cool. Of course on a thread this long you're going to have repeating so here I go.On this YouTube Will says that hooking up his ($200+)controller to the BMS can harm it if the BMS disconnects it. which I pointed out before and that's why drop-ins make no sense to me especially if you're using an alternator to charge.he also shows hooking up the BMS for low-voltage to a separate switch that can handle high amperage. My question is why not attach that switch before the solar controller and have the BMS set to cut it off at a set voltage (measured at the highest cell). This way I can use my existing $200 plus mppt controller and have my batteries stop charging at a voltage of my choice. Also in the future I can charge my electric dinghy with solar panels with just the BMS and the switch https://youtu.be/_PgthByAYz4

I think the issue with damaging the Victron MPPT is because the BMS opens the MPPT's ground when is disconnects. I remember (I think) reading a caution in the Victron manual about always grounding it first to prevent damage.



I haven't looked at many BMSes, but is it common for them to open the ground rather than the positive side? The few I have looked at open the positive.

[OceanSeaSpray]

Originally Posted by tanglewood

I haven't looked at many BMSes, but is it common for them to open the ground rather than the positive side? The few I have looked at open the positive.

Only Victron and junk Chinese ones on Alibaba as far as I have seen. From a BMS electronics point of view, it is much easier and cheaper to switch the ground because you do it using N-channel MOSFET transistors and these can be turned on with a gate voltage that is less than the battery voltage, so readily available.
To be fair, this can be fine if the installation is dead simple.

P-channel FETs to switch the positive side require more silicon to carry the same current, or they have higher "on" resistance and it makes them more costly to use. You turn them on by pulling the gate voltage down.

The best solution is switching the positive using N-channel FETs and it is possible, but it requires generating a gate voltage several volts above the battery voltage and adds circuitry and complexity for driving the FETs.

However, most BMS don't integrate solid-state switching of the battery current. This is done by an external device that can be sized for the installation.

[andyalford]

STRAW POLL ! Which would you buy ?
I have to choose between these two options for my new 800Ah LiFePo4 bank….

1/ Winston 8 x 400 Ah discounted to $3,200
WB-LYP400AHA direct from Winston with 1 year warranty

2/ CALB 16 x 200 Ah from AliBaba agent for $1,900
the new blue SE200FI - CALB don't manufacture a 400Ah cell any more
who promises to match cells within 200-204 Ah capacity and 0.2-0.3 mOhm resistance
offering 1 year warranty, but the batteries do not have original CALB manufacturing labels
he has 20+ 5-star reviews from USA / Canada / Aus authentic buyers
I believe the cells are a part batch manufactured some 2 years ago, but stored carefully

Winston

• most USA seem to go for the yellow batteries, but are they really any better?
• yttrium seems nice but I am cruising in the tropics so not a big issue
• 400Ah units are easier to install, and less stress with getting cells in right configuration 2p4s
• Number of life cycles is tempting, at 3 days for a cycle that is >> 20 years
  

CALB

• risky but I feel I can nearly trust the agent - he answers direct questions honestly but you have to ask the right questions!
• some the smaller 200Ah cells are more robust, although my Hylas 44 will give them a fairly smooth ride
• stress of 'which cell to put where?' in 4p4s with differing capacities and impedances? This is a concern
• at this price, I would buy 20 and configure the 'spare four' as a portable battery bank for hookah / electric bike / emergency engine start, etc - and still $700 in cash leftover
• if they 'only last 10 years', I will have the money I saved to buy the fancy current thing at the time

I have already decided upon

• Victron MultiPlus 12/3000/120, CCGX and 2x SmartSolar 100/50 - one 48V series, one 12V parallel.
• REC Active BMS for Victron CCGX / VE-Can
• Blue Sea 7700 bi-stable 500A contactors with CatNewBee's latching / LED circuit
• 850W solar which will mean a cycle should generally take 3 days between engine charging
• planning to add CMI's 200A large frame alternator to my 30 year old Yanmar 4JH-TE's fly wheel
• full time liveaboard, so extensive time at anchor, with watermaker, washing machine, movie projector and aircon to suck up excess power (!)

I have read everything I can find on the internet and now my brain is overflowing
Please help me decide….

[john61ct]

That "agent" is a huge unknown, I do not trust reviews through any selling platform. If you could actually make use of the warranty, local return **and** were set up to test thoroughly on arrival

or if fellow skeptical forum members without any self-interest vouch for a seller maybe I'd be more receptive the the CALBs.

Fewer cells and direct from factory are big pluses for the Winstons. Only downside is money, that's your call.

Have you tried to get CALBs direct or from a source located on the same continent as you?