Lithium batteries and new solar charger

[Slownsy]

I am replacing my 4 6V batteries I think 2 lithium, have never been impressed by the 30A PWM charger for my 600W solar, probably my fault for using 8 avg wire on a 9m run. Thinking if I get a Victron 100/75 MPPT controller I can go parallel and series for 24V and have less voltage drop and hopefully better charging, and also maybe adding 2 more panels. What say you.
Frank.

[full_mosey]

BFL13 wrote:

....

Voltage drop matters greatly with MPPT though. You benefit from the 24v needing thinner wire than 12v, but adding panels will increase the amps and it could be a wash so you could need fatter wire anyway.

Two LFPs will have fewer usable AH than four 6s, but with the solar you will only notice when there is an overcast for a couple of days so you need your battery bank as a "reserve" until the sun comes back out. It "depends" whether your two LFPs will be enough reserve, but it also "depends" whether the four 6s would be enough, so there is no way to be sure. You have to figure the odds on that. Obviously the odds are better in CA than in WA, eg.

1. With MPPT, you manage losses due to Voltage drop by increasing the solar output voltage by wiring panels in series. This is no 'big deal'. Even if you keep all the panels in parallel, the MPPT can outproduce PWM. In contrast, PWM cannot outproduce MPPT.

2. I have purchased 4 x 280Ah, 3.2V LiFePo cells to create a nominal 12.8V battery. If I were to use 8 cells I could have 2 12V batteries equaling 580Ahs. Wouldn't that be more Ahs that 4 x GC2's at 440Ahs?

HTH;
John

[StirCrazy]

BFL13 wrote:
Still no answer 😞

So if 10v is true zero and is 100AH down for the BB 100AH battery like it says, then people are fooling themselves thinking it is really a 120AH batt so they are not really going that low all the way to zero.

no one said for sure they were using 120AH to get 100, but the tear down test on you tube indicated they were using some extra capacity so I am not sure what is realy going on, but here is the only answer that matters.

using 100% of the capacity of the battery, (from 14.1V or what ever the top 100% is again to 10V) is one cycle of the battery.

you have aproximatly 3000 cycles like this in that battery (maybe more) so if you cycle your battery twice every weekend for the rest of its life it will last you 28.8 years. another company builds ther ebattery with extra capacity so they can give a longer usage so they get 5000 ccycles that will last 48 years... does it realy matter to the average guy? the price has dropped so much you can afford to use and abuse them as they will last longer than the adverage camper will...... I know anyone over 45 the burchases a battery has a pretty good chance of passing away before the batteries do.


Steve

[StirCrazy]

time2roll wrote:
The middle charge voltages in LFP are so flat it might be hard to impossible to really know on voltage alone what the charge level is. Generally a capacity test will be run top knee to bottom knee. The whole 50% discharged thing kind of fades away with LFP. It appears to me the charge level indicated by the BMS becomes more important.

it is flater than a normal battery but not that flat, you just need a better resolution voltage meter. every 0.1 seams to be aproximatly 10% so a reading of 0.01 change would be 1%. seams you can get pretty accurate with a deicent meter that is made for Li.

Steve

[StirCrazy]

BFL13 wrote:
Good points but missed my question (badly put maybe) so trying again:

Does the LFP voltage/SOC table in the BB blurb linked above apply to all capacity sizes of LFP that use the same type of cell?

sorry I thought this part was common sence and they way you stated it it looked like you were looking for somthing else. yes that chemistry type will have the same table no matter the size just like you do for lead acid and sio2.

Steve

[Almot]

1) 14.4-14.5 not sure, check your LFP specs. Full LFP would be ~13.5V. No, floating 13.8 is not needed, charging should stop when you hit whatever it says for 100% charge on LFP specs. You may set Float below what your LFP "full" voltage if your controller allows.

2) Yes, charge 100% "often", for balancing. The jury is still out on how often it should be. You don't want to shorten its life by overheating but you also don't want to leave cells unbalanced. Do 95% if you can.

3) Voltage at rear 7-pin plug? 13-something, doesn't matter because you shouldn't use this for charging LFP directly. You should install DC-DC charger between alternator and LFP.

[BFL13]

Ok the Op has a clue!

Yes the high discharge rate, the low weight, and the many life cycles are all worth something. Also no sulphation on solar while not getting to full every day. Watch out for high temps in the Oz interior with LFP AFAIK.

OTOH I can recharge my 460AH bank at 30% charging rate no issues though, as long as I have enough amps worth of chargers and a gen to run them along with anything the solar is doing at the same time.

Check out the Renogy DC-DC charger that has a buck/boost for the voltage for your alternator charging. I have the 20 amp size for my TC rig, and it can be set using its dip switches for various types of battery. It has a whole setting thing for LFPs, so that should solve that, regardless of your up and down alternator voltages.

[Slownsy]

Ok please calm down, right over my head, the batteries may only have 80A usable energy each but I can purchase a 3 and still have 240A usable, the whole point is they are lighter and should last a long time and not much more $ than the flooded, about $600 per 100A. The attraction is also there higher discharge and charge rate. I can’t discharge a flooded at 300A or change at 100A. My concern is with my existing chargers being able to charge within the lithium batteries perimeters, 14.4-14.5 main 13.8 and 13.2 floating. It has also been said they need to be fully charged every so often to balance the cells. Another thought just got thrown in, the charge rate of smart alternator, my vehicle is 2015 F350 6.7 diesel with a 200A alternator with a 30A supply to rear supposedly , anyone know what voltage is at rear ?
Thanks Frank

[BFL13]

When even with my Grade 6 math I can see something doesn't match up, it red-lines my BS meter.

There may well be honest explanations, but there is so much Advertising using silly numbers you have to wonder what is going on. Too much like when they had the tail fins on cars, as I mentioned before.

There are apparently some real benefits to LFP, but IMO there is no need for the BS that seems to be part of it all. Meanwhile the True Believers want to burn anybody at the stake who questions any aspect of it all during this seeming frenzy.

So, it is all down to being over 21, and keeping your eyes wide open. If you flunked Grade 6, then too bad! 🙂

[time2roll]

Well you can't fake the voltage. All you can do is test it with a monitor and see what you get. You may get 120 or maybe 100. The specs say 100 so this could be the minimum depending on the randomness of the individual cells placed in the battery you get. Seems to be a lot of variation depending on what happens in the clean room.

Not sure who is saying 120 but they would be the ones that should demonstrate and prove out what they get. We don't know what is in the magic box.

[BFL13]

Still no answer 😞

So if 10v is true zero and is 100AH down for the BB 100AH battery like it says, then people are fooling themselves thinking it is really a 120AH batt so they are not really going that low all the way to zero.

[time2roll]

It is a consumer battery with a warranty. If you want max factory cell rating available you will need to roll your own.

I have four cells (310 Ah) on the way from China right now. Not complicated but there are a lot of moving parts to the DIY LFP batteries. Virtually no warranty, just risk.

BattleBorn: 100 Ah $950
time2roll: 310 Ah $700 +labor and minor supplies and 60-90 days for delivery and build.

[BFL13]

time2roll wrote:
If the battery is rated 100 Ah it is just 100 Ah.... not 120 Ah.
If you get more fine but why are you expecting 120?

Because so many are saying they are really 120 not 100. If 10v is zero, then it can't be true.

The story has been that they make "zero" above the real zero so you can run the batts down 100AH and not get to the real zero. So the fake zero would not be 10v, it would be 12v.

It would not matter except apparently some LFPs don't use a fake zero. In that case the voltage/SOC for the fake zero AH batt would be different from the LFP's that uses a real zero.

If you are setting your low as you dare to go operating limit using a voltage setting that is supposed to represent the SOC you picked, it would be useful (!) to have the right voltage for that!

[time2roll]

If the battery is rated 100 Ah it is just 100 Ah.... not 120 Ah.
If you get more fine but why are you expecting 120?

[Itinerant1]

time2roll wrote:
10.000 volts is considered flat dead and well into the lower knee that commonly would not be used. Going to drop fast from 12.0 to 10.0 volts as there is not much energy here. Energy and voltage is not linear but rather an exponential curve at these points.

This is true for all sizes of LFP batteries. You can have one or one-thousand in parallel and it is still 10.0 volts. 10 Ah cell or 310 Ah cell same thing at 2.5v per cell and there are 4 series cells in a LFP battery. The BMS will cut power based upon the lowest cell hitting 2.5 volts so power could be cut before 10.0 volts. But again there is no real reason to go below 12.0 volts except to prepare for system shut down.

I was going to bring that up but his mind is spinning don't blow it up.

[BFL13]

"Yes it does. Why would you think it doesn't?"

(for the umpteenth time) because the Battle Born 100AH has that table showing 10v is zero, but the story is that it is really 120AH so when it is down 100 the voltage should still be 12v, not 10v.