LiFePo4 batteries

[Handsome]

Hey team.

I am redoing my electrical system this year an am looking at using lithium for my house/leisure battery. For me the discharge curve outweighs the potential of fire as i will be using a  dedicated lithium dual charger (solar plus a 12v input.) called a BCDC1240D from an Australian company -redarc. the system i am going for is 300w solar if my room will allow the 12v input to the solar charger will either be fed by my alternator or shore power if plugged in(will use a 240v-12v power supply and change over relays to switch the input). all loading on the battery will go through a low voltage disconnect to prevent over discharge of the battery. the load will be a 1000w inverter with one high voltage outlet, a 12v fridge, 5 lights(LEDs) , 3 usb charging ports and a small stereo system(probably run off an old tablet i have laying round with an amp to run speakers). Not sure on the total loading to calculate how long the battery will last but my main priority is to get the maximum time from my inverted so i can charge my laptop and game if i wanted to.

If anyone has any input that would be appreciated

 

[John61CT]

LFP holds much less fire danger than all the other lithium chemistries.

I would advise a fully user-adjustable DC-DC charger - Sterling BB series - rather than that Redarc charger. And a separate dedicated solar controller.

No inverter is needed for charging most laptops, find the right 12V "car charger" much more efficient.

Same with other screen devices, USB and entertainment, stick to DC native much as possible.

 

[DLTooley]

The RedArc combined isolater/charger is an interesting take on combing charging AND battery systems, but its spendy. at around $400. When I upgraded my system I split the two systems entirely, but left the cable in place for emergency or future upgrade.

When recharging the laptop wait a few hours after peak solar in order to maximize your solar. Having an inline ammeter, a functionality the dedicated Victron charger's provide helps to understand the relative importance of this to your system and current conditions. Using the 15 amp max load terminal also helps maximize solar charging when there are concurrent loads of any sort.

 

[jonyjoe303]

Get a TK15  LCD coulombmeter, you can find on ebay for about 23 dollars (DC 8-80V 50A High Precision LiFePO / Lithium / Lead Acid Battery Tester Coulomb)
You need it for lifepo4. Lifepo4 voltage reads 13.1 throughout the day. It only read higher or lower when its charging or its discharging. The coulombmeter you set the batterys AH hour rating, if its 100ah you set it to that. What it does it counts all the amps going in/out of battery so you always know exactly how much capacity you have left.
Without this meter, a couple of days of cloudy weather and your battery will be depleted, since it always reads 13.1 volts, you might think its being fully charged every day. The above model measures up to 50 amps, but they sell ones that can measure in the 100s of amps.
You just connect the module between the battery minus output and and battery minus input. Easy to hookup and very accurate, been using mine for over a year and never drained my battery yet. 
Before I had this meter I drained my lifepo4 where the bms cutoff power suddenly, I actually thought I had a full battery. It was after several days of cloudy weather when the battery wasn't getting fully charge everyday but it always read 13.1 volts. The only warning you get your battery is almost empty is when you see a voltage under 12.9 volts with no load, from there to totallly empty is maybe 10 amps. It happens quickly.
I have these on all my lifepo4's.

 

[John61CT]

Ampacity must be higher than the maximum current.

A 500A or even 1000A version is not that much more expensive.

 

[DLTooley]

How well do the absorption based solar charge controller algorithms work on LiFePo4 batteries?

 

[John61CT]

Not sure what you mean.

LFP needs no regulated "stages", a simple on/off power supply works fine.

They should not sit full, and floating can harm them, or at least reduce longevity.

But acceptance stays high right up the charge curve, so given enough power you can fully recharge in under an hour.

Best for a fully-adjustable BMS to control the bank's connection / isolation from charge sources, separately from connection / isolation from loads, based on voltage, current amps, temperatures and calculated SoC.

 

[John61CT]

The real key is for all charge sources' setpoints to be user customizable, nearly every one I've seen advertised as LFP ready has its default voltage set way too high.

Most proprietary cells+BMS packaged systems are set up so they last a much shorter lifespan than they could.

Maybe 6-8 years if the warranty period is 5 years

 

[DLTooley]

I'm using sloppy language I'm sure. Maybe 'acceptance rate' is the better term? I'm thinking of the amps 'accepted' by the bank, in this case LiFePo4. Once below a certain rate you could program the float voltage at a relatively low level - allowing you to use the excess solar in your system without draining the battery at all.

 

[Handsome]

Sorry i havent been near wifi in the past couple of days.

The reason im headed towards the redarc is that i can get it at a much cheaper price than usual - close to 30% off. i plan using it in conjunction with some kind of current shunt battery monitoring system so i can detect my batteries current status. ive used victron before on some previous projects( solar radio repeater in the outback) and it worked great, only it dosent incorperate alternator charging or 240 charging. i think i can use a computer power supply to feed the red arc controller when shore power is available(i even got the power supply and external plug for free - only need a contact breaker).

i have compared the charge output of the redarc product with the cell i plane to get(https://aasolar.co.nz/AA Solar Lithium Deep Cycle Batteries.html) and it is within the accepted range. I understand what you are saying - a adjustable charger is best once you know what your battery likes, but i haven't found one with the 12v input in new zealand at a decent price.

 

[John61CT]

3.45Vpc or 13.8V for 4s is the highest I'd advise going in daily use. A bit higher for occasional maintenance purposes like testing, balancing etc.

Much much longer lifespan, sacrificing very little top-end capacity.

 

[ronzey2+]

Hey team.

I am redoing my electrical system this year an am looking at using lithium for my house/leisure battery. For me the discharge curve outweighs the potential of fire as i will be using a  dedicated lithium dual charger (solar plus a 12v input.) called a BCDC1240D from an Australian company -redarc. the system i am going for is 300w solar if my room will allow the 12v input to the solar charger will either be fed by my alternator or shore power if plugged in(will use a 240v-12v power supply and change over relays to switch the input). all loading on the battery will go through a low voltage disconnect to prevent over discharge of the battery. the load will be a 1000w inverter with one high voltage outlet, a 12v fridge, 5 lights(LEDs) , 3 usb charging ports and a small stereo system(probably run off an old tablet i have laying round with an amp to run speakers). Not sure on the total loading to calculate how long the battery will last but my main priority is to get the maximum time from my inverted so i can charge my laptop and game if i wanted to.

If anyone has any input that would be appreciated

 

[ronzey2+]

Lipo4 ,very stable chemistry,Ron in AJ,AZ.

 

[tripper]

I've been using the stock LiFePo4 profile in the Victron controller recently, it matches the manufacturers specs on my LIFEPOs pretty closely, it seems a bit high but works (14.4 bulk/absorb and 13.5 float). I know it seems a bit high, but I heavily use power during the day and it works well. I turn down both numbers a lot when storing. I found when turning bulk down low, like 13.8 volts that it seriously reduced the available AH on the battery. I know what all the lithium theory says, but in use I found it was way too low. If you are a light user of the batteries, or have a bunch of them, maybe that would work.

LFP batteries are not going to catch on fire. Don't use 18650s or other RC car/e bike batteries, they are dangerous.

If you are going with solar, just get a Victron controller, it works extremely well for charging any battery type, and they are fairly inexpensive.

 

[John61CT]

If you actually do a 20-hour load test, you will find you're actually giving up 5-8% from maximum, maybe 2-4% from their rated capacity.

If that's worth sacrificing thousands of lifetime cycles to you, go for it. Difference could be 2000 vs maybe 8000, we just don't know yet.

Of course if you're old enough, might figure that you won't last that long yourself

 

[tripper]

I haven't done a load test, but I do extensively real world use the battery / solar system. I have found a considerable drop in available AHs when I run the bulk less than 14.2 volts. I do not have a SOC meter, but I can tell by the resting voltage on the battery in the morning about where it is. I am fairly well read on lithium batteries, having been into RC cars in the past and owned 3 e bikes and now using lifepo in my rv. I just know from using it what works. I think people with large lithium banks would not care or notice but since my AHs are very limited it is noticeable when I do not get the system charged enough. I have tried various iterations of bulk/absorb float voltages, and I really do see a larger than expected gain in useable AHs when running the bulk voltage that high.

 

[John61CT]

Not cycling so deeply - especially if you actually see resting voltage change much at the low end of the curve - will also extend lifetime by triple or more, above and beyond the life extension of avoiding the top shoulder. Going below say 15% SoC is IMO very risky, dead flat is instant death, scrap EoL.

Me personally, I'd go to a bigger bank.

If you've cared for it well otherwise, and are now at less than a couple hundred cycles, matching the mfg date won't IMO be critical, as long as they are otherwise identical cells.

But as long as you're consciously making the choice, obviously it's your rig. . .

 

[John61CT]

And why wouldn't you invest in a good shunt-based BM?

Or at least a cheapie AH counter, maybe $40-60?

 

[jonyjoe303]

"LFP batteries are not going to catch on fire" I have to make one observation on this. I always read and heard that lifepo4 were safer and started moving to them. 

But I also build my own lithium battery packs using laptop, powertool batteries (18650) and lifepo4 using the 32650 and 26650 cells. I was taking apart a lifepo4 battery pack to reuse the cells, while doing this I punctured one of the lifepo4 cells, I heard the pressure escaping and then it caught on fire. Luckily I threw water on it and that put the fire out. It was my fault for rushing to take the pack apart but I did learned a valuable lessen.

My observation is lifepo4 is just as dangerous as laptop batteries as far as fire hazard. I'm still going to use them but I won't treat them as more safe then the laptop batteries. They might be safer if you accidentally overcharge them but I'm always careful in that regard.

But one recommendation is that they are securely stored in a area where they won't get punctured. You punctured a lifepo4 and it probably will catch on fire, from my first hand experience I can guarantee that it will catch on fire. Never had a laptop battery catch on fire thats why it surprise me to see the lifepo4 go up in flames. 

Lifepo4 being safer is a myth. But the tremendous power from them is just too good not to use them. I wouldn't discourage anyone from using them but they aren't any safer than other lithiums as we been lead to believe.

 

[John61CT]

What a crock of sh1t, sorry but really.

When the statement is made, no one's talking about hobbyist mad scientist projects, hacking homemade packs from little cylinders or salvage EV.

Purchase properly engineered systems, yes thousands of dollars.

Or most DIY level, purchase new prismatic cells and figure out your LVD / OVD and temp protection, but that is getting risky.

Not from thermal runaway, just losing your investment.

Puncturing a lithium cell is just silly, would you say messing around with a jerry can of gas is dangerous if you're shooting rounds through it.

Really, the mind boggles.