Originally posted by Peterng
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for money & that enerdrive half the cost is in the name & company overheads. The warranties are all small & they all use chinese cells & are slapped up.
Enerdrive units "shouldn't" be joined/paralleled due to bad bms design & want you to buy their more expensive larger banks. Their smaller units 100-125AH have undersized BMS.
Itechworld's BMS description is deliberately vague/useless & designed to deceive, trying to fool you into thinking you can just drop them in a wide range of charger environments with no need for an expensive quality charger. I wouldn't wan't the BMS in these cheap units controlling the voltage, that is the job of a quality battery charger. The fact is a quality charger is needed regardless of BMS. They dont care, that is why they offer a measly 2-3yr warranty.
A quick read over the offroad living all spark LFP and they are sprouting misinformation in various details. God only knows how they claim you can put one under bonnet. must be a catch somewhere. One thing is certain the small brands are so desperate they rely on heavy marketing & lies.
The achilles heel of these dropins is the questionable BMS they use, the wiring is usually undersized and so they can't take very high charge rates & end up being only marginally faster than AGM, which is pathetic. none of the bms ratings are in real world hot conditions like 40C minimum.
The Balancing components are said to be cheap & nasty and can fail & ruin the battery, not something you want in a batt you expect to get 8-10yrs out of, its also unclear if they are actually
neded at all over the lifespan with proper charging/use/sizing. Only time will tell if the BMS on dropins can hold up. Also only buy dropins that are made of large prismatic cells not many small individual 18650 or 25560 cells.
2000, 3000cycles to 100% or even 80%DoD are marketing lies and nothing more. Real tests on chinese lifepo4 to 100%DoD got about 1000cycles. That is controlled lab conditions, in real world it will be far less. Sorry but li-ion has reached its limits. Even lithium-titanate with its high cycle life still has the same average calendar life.
Cycle 100-10%Soc. It's kind of the equivalent to taking an AGM to just 50%.
Under heavy continually use you would be wise to stay between 85/90-20% only.
Proper Battery charging simplified:
stage 1= (bulk) aka constant current: I believe the name comes from lead acid days where a flat battery can take a fixed & high current rate up to about ~2/3 full without damage. this stage forces a fixed amount of current into batt. During bulk the batts internal voltage rises and bulk ends when a setpoint is reached (usually 14-14.4V).
stage 2= (absorption) aka constant voltage: when a lead battery gets about ~2/3 full it starts resisting how much current it can take, by the time its almost full its only accepting a very small amount of current. if you hold bulk up to full on a lead batt it will damage.
That is why this stage lets batt dictate how much current it takes. When current drops down to some small value the batt is full.
stage 3= (float) keeps battery full while supplying loads. this is exact same as stage 2 except lower voltage.
5, 7, 9 etc stages are just marketing & do nothing useful except for EQ on flooded batteries.
both Lead & LFP charge the exact same way only diff with LFP is the absorb stage comes latter because of its high acceptance rate up to almost full.
turn on charger, if batt is low enough it goes into bulk, if its only a bit low it goes into absorb. some chargers can still go into absorb & hold for a bit before going to float.
if you put a big load on a full rested batt for a minute, even though the batt is still almost full, because of the temp volt sag of the battery, when turned on the charger will go into bulk but briefly then back in absorb.
There really is only 2 stages CC & CV, all smart chargers do is manipulate these two charge modes to form a profile. Sadly the smarts in these are
often unreliable &/or more complicated than they need to be. Once you know basic charging you can sift through all the marketing & lies.
There is no such thing as the right voltage or charge rate.
Whether (AC charger, DC-DC or solar MPPT) you absolutely need to be able to set the absorb & float voltages and ideally absorption time. If you can't buy another charger that allows it, decent brands:
AC charger: sterling pro for wide range of output sizing, enerdrive in some ways have a better lifepo4 profile.
DC-Dc: enerdrive by far. have no clue about sterling
Solar charger: victron mppt by far. builtin mppt in DC chargers are really a gimmick & only good for a small panel setups on vehicle roof, not at all for big setups.
Don't even waste time with redarc dc-dc chargers old fashion clumsy and no custom settings/multichem.
Projecta have poor cooling, some faults/glitches and no customization. Both= not recommended on $$ LFP
any (bulk,absorb,float only) charger should charge LFP as long as it doesn't have a lead acid specific profile, if so it may not be ideal & may not reengage bulk or absorb until the LFP is almost flat. flooded profiles may have auto EQ and over absorbing. brands that use lead acid or lfp specific only profiles are just another rip, a charger that allows custom voltages and absorption duration eliminates the need for chemistry specific profiles (just doing the basic bulk, absorb, float thing)
* Charge voltage AKA absorb voltage. Set between 13.8-14V, going higher only stresses the cells and gives only noticeable faster recharge times with no extra real capacity. 14.4- 14.6V is way too high and only needed for balancing. when you see battery charger manufactures using 14.5- 14.6V this is because they had no clue when making their chargers & probably refuse to change (to costly). Only now are some of the top brands lowering their recommendations.
You can over time actually overcharge LFP with as little as 14V with low charge rates 0.1C (solar) even if the bank is not even full. LFP likes 0.3-0.4C current rates.
Some say LFP has no absorption stage, not true. the absorb stage is just more steep and ends faster than Lead acid which is more flater and gradual. Still AGM is no slouch charged from 50-100%.
higher charge voltage means less absorb duration. for example at decent current rates if you charge to 14.6V the absorb period is virtually just a few minutes, at 13.8V it may 30-60mins.
At just 14V using higher charge rates mean absorb stage (absorb voltage set point) comes earlier, low rates later. at 0.5C it comes around ~70%SoC and at 0.1C 95%SoC. but because of LFP high acceptance rate the practical diff between CC/Bulk & CV/absorb is blurred alot more.
High V is faster, but low voltage at higher rates can also be fast even though the absorb stage has hit very early at 70%soc. That last 30% taper period will act almost like CC.
* float voltage & floating. Set anywhere between 13.4-13.6V. Floating a LFP is not bad and for casual infrequent use is no problem at all. as long as it's low like 13.6v max
The bad thing with LFP is keeping them in a high soc &/or high temps for long periods, not floating itself.
For longterm floating on mains power for example you can float at a lower desired soc, for example 13.2v on mine means it keeps the battery at 50-60% Soc depending on loads or not.
*The absorption problem: The charger cant possible know how long absorb duration should be. (it doesn't know the capacity or what the loads are doing)
solution 1- One size fits all, projecta use this timer. its based on length of bulk & few other things. It usually results in the charger going into float early which means it takes a bit longer to get to full. This can be a problem when every minute is valuable like using a genny. A charger that allows custom voltages with this type of absorption timer usually means lower voltages ~13.8V can make charger go to float far too early.
2- absorb stage ends based on a tail current setting. enerdrive chargers use this. Problem is if you got a big load always on the charger will stay in absorb overcharging batt overtime.
3- Custom duration setting: Arguable the best approach to avoid charger getting confused but the catch is you need to know what situation your in to know what duration to set. victron mppt allow this.
as general rule: ac power you set duration to zero, as LFP will easily get to full on float.
As for solar there isn't usually enough sunhours in a day for any significant overcharge at 13.8-14V. Short sun hours keep long. But if your in a place with 5-6hrs average of hard sun with large panel wattage keep duration to zero or just about 30mins max.
LFP is not as easy as people make it seem, one major problems I ran into:
1- LFP really needs a battery monitor or else you are going in blind. You simple cannot judge SoC in most of the curve like 20, or 80% SoC by voltage. 0.1V can be spread across as much as 20-30% of the soc. Voltage is only useful when the batt is flat or almost full during charge/discharge.
Precise voltage is still not reliable as it will vary with loads. The voltages will also be different for every battery as who knows what manufacturer of cells they are using. Also each battery monitor, volt meter, gives a slightly diff voltage as they are not accurate gear. Some only show 1 digit past the decimal point which is useless.
This is the beauty of lead acid as a cheap volt meter is good enough to know where your batts are at.
The big problem with monitors is they require baby sitting & a steep learning curve, you really need to know the LFP's real capacity (by capacity testing) and just entering the labelled advertsied capacity is not good enough. Doing so will give an inaccurate soc, I know I have tested & confirmed many times.
I can tell you 100% having used 3 monitors (sg200, BMV 712 & enerdrive's phone app)
they all stuff up a fair bit and need to get back to full 100% frequently to reset. They usually only work well in a controlled environment like discharge deeply, stop. full recharge. That doesn't happen alot in real world.
without monitor:
a-Manually count & keep track of amps in & out of batt. you wont have time for that while enjoying yourself.
c- size so you want go too low. May work like constant traveling with frequent Dc-Dc charging, but in fails in base camping, sizing doesn't work well at all, too many variables, clouds, number of people etc.
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