Solar charge controller, what for?

[bungawalbyn]

Hi Guys,
I'm new here so Hello to everyone from NE NSW Oz.
I need someone who knows to see if I've missed something in my analysis for charging LiFePO4 batteries. In this case it will be a 12V 4s bank of Winston 1000AHrs.
Due to LFP low resistance and hence voltage rising in direct relation to SOC and what would be the absorption phase in FLA is only for last 10%ish, which I don't want to use due to all the reasons of balance and life span problems, is there any reason to have a charge controller at all?
My panels will push out 18V but only against battery resistance.
I wish to run my batteries between 20% and 90% SOC, so the absorption phase needed to get to 100% is irrelevant. I'll be having the obligatory Hv and LV cut out protection + volt meters on each cell + full bank, HiLo voltage sensors to run cut outs at conservative parameters, a diversion to HWS for excess + Amp meter to monitor current, and a BMS (Non Balancing) for emergency.
I'm an obsessive meter reader so I'm happy to manually drive this system for the most part.
My panels give out about 100A max, so I'll be charging at < 0.1C
I plan to cut charge at 13.8 to 14V.

I saw it stated that the best way to get your head around LFP is to forget everything you know about FLA and start again. What have I missed?

[solar pete]

Hi Guys,
I'm new here so Hello to everyone from NE NSW Oz.
I need someone who knows to see if I've missed something in my analysis for charging LiFePO4 batteries. In this case it will be a 12V 4s bank of Winston 1000AHrs.
Due to LFP low resistance and hence voltage rising in direct relation to SOC and what would be the absorption phase in FLA is only for last 10%ish, which I don't want to use due to all the reasons of balance and life span problems, is there any reason to have a charge controller at all?
My panels will push out 18V but only against battery resistance.
I wish to run my batteries between 20% and 90% SOC, so the absorption phase needed to get to 100% is irrelevant. I'll be having the obligatory Hv and LV cut out protection + volt meters on each cell + full bank, HiLo voltage sensors to run cut outs at conservative parameters, a diversion to HWS for excess + Amp meter to monitor current, and a BMS (Non Balancing) for emergency.
I'm an obsessive meter reader so I'm happy to manually drive this system for the most part.
My panels give out about 100A max, so I'll be charging at < 0.1C
I plan to cut charge at 13.8 to 14V.

I saw it stated that the best way to get your head around LFP is to forget everything you know about FLA and start again. What have I missed?

Howdy bungawalbyn and welcome to Solar Panel Talk.
Always good to have another aussie running around the joint.

I think we will need more info about your system. Do you currently have a system up and running or are you planning a system? If you have a system up what are the details, what make and type of panel,how many, what make type inverter? How many KW/hrs does the system have to supply each day? Is the system grid tied or stand alone or hybrid?

[bungawalbyn]

As it stands and where I wnt to go

Hi Pete,
Stand alone.
I'm currently running 2 parallel 600ahr Raylight FLA's ( of different ages) running separate circuits, hooked up to 8 200W ebay panels. Forget the watts, they are rated at 11.1 amps which I have confirmed with my ammeters in max summer sun, perhaps a little more. This set up works OK in summer but fails badly in poor weather and is not doing at all well in winter. The main problem being keeping the batteries up on float long enough to give them a good charge. In the real world of constant daily usage, this just doesn't happen.
I use 2 elcheapo 1500W ebay modified square wave inverters which work everything OK, perhaps not as efficient as the u beaut cost an arm and a leg models, but not having standby means I can run an override thermostat on a chest freezer as a fridge. Works great.
Hence LiFePO4s. I was attracted to their ability to take all the charge I can throw at them, + the large % DOD without degradation and their liking of partial charge.
Power usage? I want more!!

So the new set up will be using the not so old panels and inverters, manual breakers on solar line and battery out put. next down the chain will be a programmable voltage relay (set to 14V) to operate a 120Amp SPDT relay as HV cutoff and possibly diverter to HWS (not yet decided) or another voltage relay to operate HWS (1000W custom element) through the system, using panel power when voltage approaches cut off. All this will be metered with volt and amp meters. For LV cut off I'm using a 400amp normally closed magnetic latching contactor that cuts ALL power from the batteries. This will be operated by a BMS (Non Balancing) sensing both individual cells and system voltage. This will be backed up by digital voltmeters on each cell. Power to these will also be cut if LV contactor is tripped.
I hope to make it a fairly simple set up with automatic cut offs backed up by manual cut offs for both high and low v in both cells and combined bank.

So the question is, with all this, do I actually need a controller, with most of it's function either disabled or inappropriate? And if so Why?

[SunEagle]

Hi Pete,
Stand alone.
I'm currently running 2 parallel 600ahr Raylight FLA's ( of different ages) running separate circuits, hooked up to 8 200W ebay panels. Forget the watts, they are rated at 11.1 amps which I have confirmed with my ammeters in max summer sun, perhaps a little more. This set up works OK in summer but fails badly in poor weather and is not doing at all well in winter. The main problem being keeping the batteries up on float long enough to give them a good charge. In the real world of constant daily usage, this just doesn't happen.
I use 2 elcheapo 1500W ebay modified square wave inverters which work everything OK, perhaps not as efficient as the u beaut cost an arm and a leg models, but not having standby means I can run an override thermostat on a chest freezer as a fridge. Works great.
Hence LiFePO4s. I was attracted to their ability to take all the charge I can throw at them, + the large % DOD without degradation and their liking of partial charge.
Power usage? I want more!!

So the new set up will be using the not so old panels and inverters, manual breakers on solar line and battery out put. next down the chain will be a programmable voltage relay (set to 14V) to operate a 120Amp SPDT relay as HV cutoff and possibly diverter to HWS (not yet decided) or another voltage relay to operate HWS (1000W custom element) through the system, using panel power when voltage approaches cut off. All this will be metered with volt and amp meters. For LV cut off I'm using a 400amp normally closed magnetic latching contactor that cuts ALL power from the batteries. This will be operated by a BMS (Non Balancing) sensing both individual cells and system voltage. This will be backed up by digital voltmeters on each cell. Power to these will also be cut if LV contactor is tripped.
I hope to make it a fairly simple set up with automatic cut offs backed up by manual cut offs for both high and low v in both cells and combined bank.

So the question is, with all this, do I actually need a controller, with most of it's function either disabled or inappropriate? And if so Why?

Yes. You will still need some type of charge controller for those LiFePO4 batteries but not one of the normal ones that work on FLA or AGM batteries.

So before you go down the road with a different battery chemistry you may want to determine if your old system was properly sized or not.

I am a little confused of what you existing system consists of. You said you have 2 600Ah Raylite FLA batteries which are technically 6v so they must be wired in series and not parallel.

Next you have 8 200w panels each with an Imp of 11.1 amps which is correct for a Vmp of 18V. So that could mean you have 1600 watts total which is too much for a 12volt battery system.

But you have not mentioned what type of charge controller you are using so it is hard to know the reason your batteries do not work well in the Winter.

[bungawalbyn]

Hi Suneagle,

I have 2 separate 600 ahr 12V batteries, each running a different circuit in the house. This was due to a change from diesel gen with battery for day use, to 100% solar. I believe new batteries with old is a no no. Consequently at present the panels are split into 2 arrays of 800W. I was running 600w each but have added a couple more for the coming upgrade. they kick the Raylights up to float a bit quicker.
The old system is not properly sized, especially as the older set are going off a bit. They'll get a new life in the workshop where they'll mostly get to sit on float, unlike daily heavy cycling at the house.

The reasons they do not work well in winter is I live in a forest so I don't get much sun till 9.30 am and lose it at 2.30pm. I of course get some trickle either side but it's only about 5 amps. Consequently they never get enough time on float to really work up a good full charge, add to that more drain with shorter days.......
This is the main reason I'm switching to LiFePO4's. They bulk charge upto about 90%, They will take a lot of amps in a short period of time. And lets face it, FLA are crap. Even when treated really well, they are mostly ornamental.
Which is all beside the point.
The question at hand is, with hi + Lo V cut outs for protection, why do I need a charge controller rather than direct wire the panels. What benefits would it bestow? Main purpose on FLA is to hold voltage at float for ever, not a desirable function for LiFePO4's. My understanding is charge to voltage, shut it down.
You say I will still need a charge controller, but didn't state why.
I'm no expert, especially with LFP, so I'm really interested in the reasons so that I may understand, not just accept "the way it's usually done"

Thanks for your comments

[SunEagle]

Hi Suneagle,

I have 2 separate 600 ahr 12V batteries, each running a different circuit in the house. This was due to a change from diesel gen with battery for day use, to 100% solar. I believe new batteries with old is a no no. Consequently at present the panels are split into 2 arrays of 800W. I was running 600w each but have added a couple more for the coming upgrade. they kick the Raylights up to float a bit quicker.
The old system is not properly sized, especially as the older set are going off a bit. They'll get a new life in the workshop where they'll mostly get to sit on float, unlike daily heavy cycling at the house.

The reasons they do not work well in winter is I live in a forest so I don't get much sun till 9.30 am and lose it at 2.30pm. I of course get some trickle either side but it's only about 5 amps. Consequently they never get enough time on float to really work up a good full charge, add to that more drain with shorter days.......
This is the main reason I'm switching to LiFePO4's. They bulk charge upto about 90%, They will take a lot of amps in a short period of time. And lets face it, FLA are crap. Even when treated really well, they are mostly ornamental.
Which is all beside the point.
The question at hand is, with hi + Lo V cut outs for protection, why do I need a charge controller rather than direct wire the panels. What benefits would it bestow? Main purpose on FLA is to hold voltage at float for ever, not a desirable function for LiFePO4's. My understanding is charge to voltage, shut it down.
You say I will still need a charge controller, but didn't state why.
I'm no expert, especially with LFP, so I'm really interested in the reasons so that I may understand, not just accept "the way it's usually done"

Thanks for your comments

Think of it this way. The panels are the power source but the batteries require some type of logic to control the charging process. Lithium batteries require some type of BMS or battery management system so all of the cells are charged equally. Hooking the panels directly to the LiFePO4 may put too much charge into one cell and not the others.

I use a charger that works on LiPo, LiFe and a few other battery chemistries for my RC planes. Most are 3S which is really 3 cells that charge up to 3.8volts each or 11.4 total. Each battery type have slightly different charging process so each "cell" stays balanced to 1/10th of a volt. An unbalanced LiPo is not going to discharge equally across the cells which usually means one cell gets much hotter than the others and you can reach a point of starting a fire.

I am not really sure what type of charge controller you will need but they are usually a little more complicated then a standard 3 or 4 level CC for FLA type batteries.

[bungawalbyn]

Think of it this way. The panels are the power source but the batteries require some type of logic to control the charging process. Lithium batteries require some type of BMS or battery management system so all of the cells are charged equally. Hooking the panels directly to the LiFePO4 may put too much charge into one cell and not the others.

I use a charger that works on LiPo, LiFe and a few other battery chemistries for my RC planes. Most are 3S which is really 3 cells that charge up to 3.8volts each or 11.4 total. Each battery type have slightly different charging process so each "cell" stays balanced to 1/10th of a volt. An unbalanced LiPo is not going to discharge equally across the cells which usually means one cell gets much hotter than the others and you can reach a point of starting a fire.

I am not really sure what type of charge controller you will need but they are usually a little more complicated then a standard 3 or 4 level CC for FLA type batteries.

These aren't LiPo, they don't burn.

Yeah I have the BMS, a non balancing monitoring unit, most of what I've seen suggests a well balanced to start 4s 12V pack kept between 20 and 90% SOC has little problem with cell drift, as it is mostly the higher voltage absorb phase to get that last 10% that causes most of the problems. I'll have everything metered up so I'll know if this is happening way before we get into the disaster zones (fingers crossed), and cut outs to isolate the battery if this should occur.

My understanding is that up to that absorption phase it's just CC and everyone who seems to have had some experience seems to want to cut off charge at about 13.8 to 14V which equates roughly to 90% SOC. NO FLOAT, as this evidently causes plating of the cathode/anode? which wrecks them.
This is what I plan to do. LiFePO4's are supposed to be tolerant and even like partial charging so we still haven't got to WHY a charge controller will perform these functions all that much better than direct. I understand some of the electronics can squeeze a bit of charge out of suboptimal conditions, but at the costs of 100AMP Charge controllers, YEOW, and the cheapness of panels, these minor gains are not cost effective.

[PNjunction]

My understanding is that up to that absorption phase it's just CC and everyone who seems to have had some experience seems to want to cut off charge at about 13.8 to 14V which equates roughly to 90% SOC.

That is a generic recommendation, which is quite safe. To be truly accurate, your voltage cutoff depends upon the charge current, but it is wise to be conservative.

For instance, lifepo4 is considered fully charged when the currrent drops to .05C. But consider that if you START out with .05C like you are close to, you are already charging at the absorb-rate, and a fully charged cell would actually be 3.45 to 3.47v! If you hammered the cells with 1-2C, then the voltage would actually be higher, like 3.6v. So yes, there is a difference, but for most of us charging at .05 to maybe .01C at best, the 13.8 - 14.1v limit seems the most reasonable.

LiFePO4's are supposed to be tolerant and even like partial charging so we still haven't got to WHY a charge controller will perform these functions all that much better than direct.

Basically you DO have a charge controller, but you DIY'ed it with the proper monitoring and voltage cutoffs. Others may try to emulate that with primarily lead-acid based chargers, where most of the features are disabled or tweaked by *knowledgeable* folks to accomodate lifepo4 properly.

Very simply, I use a Morningstar pwm controller for convenience on my small 20 / 40ah 4S batteries. BUT, I modified them to disable all temp-compensation, and chose the right voltage, which just happens to line up with the "gel / sealed" setting, even though the controller is not connected in any way to lead. I *verified* operation at 14.1v. But there is still a catch of TIME, something which may be controlled by a commercial controller in knowledgeable hands. My cells were initially balanced and in a "sub-C" application, they have been staying that way - BUT I manually monitor from time to time to make sure they are playing nice with each other.

In other words, if you know what you are doing, then you can diy. If you don't, then you'll be winging it and hoping that you don't $$$ get it wrong.

One thing diy'ers overlook is the TIME aspect of lifepo4. Basically charge it and get it over with. However, those who charge at less than .05C, or try to charge down to zero amps current, spend too much TIME trying to get that last bit of energy and what happens if you monitor the voltage closely enough, the cells will rapidly shoot UP in voltage after absorb with no current.

Why? Holding the voltage too high (even within the normal boundaries) FOR TOO LONG ends up heating the electrolyte. Not from current, but from exposure to high voltage over time. You have stepped out of the bounds of time for the battery and it no longer acts like a battery. Voltage shoots up, electrolyte is heating despite no current flow and eventually warpage and even venting. We're talking holding things higher than 3.45v for long periods. Obviously this pertains to those who top-balance.

Very simply, the smart guy will measure his cell voltage when the current reaches or just slightly drops from .05C in absorb when doing low-current charging. The unknowing might set their voltage too high, like 3.55v per cell which it may never reach at .05C! Oh but it will given enough time - that is from going past 100% charge to electrolyte heating! This is a fine line, but a serious one to watch. I wonder if some balancer circuits don't take into account the charge current - and in fact are un-balancing a cell charged by very low current which trips the balancer not by being fully charged, but by elevated voltage represented by electrolyte heating! Another thread another day perhaps.

I proved this to myself sitting like an idiot cross-legged on the floor for hours with Fluke in hand watching the characteristics of the charge process and lo and behold - those lifepo4 scientists were right! I was cool as a cucumber at 3.5v with .05C and dropping, and then a half-hour later - ZOOOM goes the heated electrolyte voltage.

Just take it easy with those 200ah cells and watch them like a hawk for the first few charges.

[bungawalbyn]

Thanks for that PNJunction,
I was just thinking that maybe I had phrased my enquiry wrong, as you point out, I have actually designed a "Charge controller" suited to my operating needs. Perhaps I should have asked "What do you guys think of this as a custom charge control set up for 100AMPS solar charging?" Or something of the like. I sometimes get the idea that fancy controllers with MPPT etc and data logging are seen as the only option even though most of their functions don't seem that applicable to LiFePO4. And they cost BIG$.

I've tried to design this to have 3 levels of protection
1st being having the cells and whole bank metered and manual cut offs at both PV in and battery in
2nd being the programmable hi lo voltage sensors to cut off relays on conservative settings
3rd being the BMS which will operate cutoffs at both cell and pack Hi Lo voltage at slightly wider settings than I'd like to keep things inside

The actual controllers that operate the cut offs are $AU20 boards from EBay Hong Kong, programmable for high and lo volts, similar I guess to a programmable thermostat like I use on my freezer to fridge conversion(Very Reliable). Most of the other bits like the HD relay the 400A latching contactor for battery isolation and the metering, bus bars and cabling I would want/need anyway

I plan to set the upper cutoff at a13.8 to 14V for the reasons you mention. I want to hold them back from the "Knee" this appears to be where most of the bad things that happen to these batteries occur. I have to figure out where to cut the charge back in, somewhere around 12.4? I have to look at the graphs again, I would like to let them work a bit, but also want to keep some charge in reserve for bad weather.

I invested in a DC power supply the other day so I can bench test everything before going live.

Thanks for your reply and advice.

[bungawalbyn]

update

I picked up the batteries from the freight depot yesterday. All in good order. The Chinese really know how to crate. Pity they don't use screws for more than just the lid, getting them out means beating up the boxes some, which is a pity.
I had them top balanced and they arrived at 1 cell at 3.62 1 @ 3.63 and 2 @3.65 so not far apart.
On what I've read and advice from here, I felt uncomfortable leaving them up that high for the probable couple of weeks it will take to put it all together (waiting on parts), so I have put them together and have them metered up and running a 12V soldering iron.
After maybe an hour the little soldering iron has dropped bank voltage by 0.5V so they must be well up the knee. Not many watts on 1000AHR batteries. The discrepancy between cells appears to be narrowing a little.
I want to bring the voltage back down to the flat so I'm making up temp cables to run an inverter to pull a bit more juice. By the looks of the graphs the drain down will slow as it approaches nominal voltage.

After that it's back to nutting out the most-ish efficient way to board up the bits and pieces of the controls.
Pics may follow

[PNjunction]

I had them top balanced and they arrived at 1 cell at 3.62 1 @ 3.63 and 2 @3.65 so not far apart.

OUCH! From this distance I have to throw up some red-flags unless you are making typos. A fully charged cell after at least 12 hours rest should measure about 3.38 to 3.42v or so. Granted, you had them charged beforehand, and some huge capacity cells, but if they are *resting* at 3.6v or more, that is NOT good and means they were overcharged to begin with. Normally cells that have not been charged come sitting somewhere in the flat part of the curve, at about 3.2v, which of course does not mean balance. In your case, I surely hope that those big cells were not overcharged.

Either way, DISCHARGE those cells NOW to about 3.2v each. This simple video (going too low but for extreme capacity testing) might help showing some simple loads. At the very least, an automotive bulb can be applied to each cell do drop that voltage now... :

https://www.youtube.com/watch?v=oJ8AfJsOhsM

Of course, I have to ask - after spending all that on the batteries, I hope you aren't using a shirt-pocket $20 multimeter. Invest in a good quality Fluke or similar.

Keep in mind that as a non-professional speaker I get tongue tied, so I'll try to simplify and reiterate the above when using low-current charge rates, like .05 - .10C ...

No matter what voltage you choose as your HVC, be it 3.47 to 3.6v, given enough time your cells WILL fully charge to 100% SOC, so once again voltage is not a TRUE indicator of full charge. Keep an eye on absorb current. Basically, no matter the voltage, once your cells just start to dip into / below .05C absorb, STOP no matter what. Those that try to charge well below .05C, or spend waaaay too much time at .05C will eventually witness the change from battery charging to electrolyte heating.

That is one thing a commercial controller has the advantage with - safety timeouts as compared to just a simple voltage / current triggering bms. Ie, even my simple Morningstar pwm will only spend 1 hour at absorb before falling back to float. Yes, we're talking a Pb charger, but at least it does something which I accommodate and shoehorn into the wrong application.

Example - on a cloudy day, I could possibly supply ridiculously low currents, say .0025C which isn't enough to drive my cells to the 3.5v cutoff. BUT, if I don't use the batteries and they get this treatment day after day, they *could* sit at 3.45v for a week, eventually fully charge, but still never reach the 3.5v cutoff. So it spends a whole week basically in absorb - and eventually on day 5 they go into electrolyte heating mode which does finally trigger the hvc... I think you get the idea. Sometimes too little current can be damaging according to the environment / application at hand. Hard to account for all the variables in a forum ...

[PNjunction]

I invested in a DC power supply the other day so I can bench test everything before going live.

Forgot to mention that this is great for your needs.

Just know, that if for some reason your bms fails or for whatever reason you go beyond say 85% DOD down into the deep part of the discharge knee, which happens relatively FAST, the OPPOSITE is true for coming out of it. That is, below about 85% DOD one should apply no more than about .01C until the cells reach 3.2v again, and THEN you can apply your normal charge current. Kind of a gentle absorb only in reverse!

While going below 85% DOD doesn't do the cell any favors, applying too much current coming out of the deep discharge does secondary damage. I hope the op in the video above with extreme capacity testing took it easy recharging initially. In other words, don't go into a panic and hammer the bank with your genny if you have gone too far. Use your controlled power supply instead to recover back to a normal state. Once again, an 80% DOD max is the right choice overall as even a moderate solar system capable of .05C is too much when the bank has gone too far down the slope to recover nicely.

Of course if you flatten your batteries, this extreme low current revival applies too, BUT you MUST get to them ASAP. Staying too long in a deep discharge from a safety / recovery standpoint has been discussed elsewhere, but this is a gentle reminder when your adrenaline might be flowing.

I'd love to see pics of your project and keep us updated...

[bungawalbyn]

[QUOTE=PNjunction;163084]OUCH! From this distance I have to throw up some red-flags unless you are making typos. A fully charged cell after at least 12 hours rest should measure about 3.38 to 3.42v or so. Granted, you had them charged beforehand, and some huge capacity cells, but if they are *resting* at 3.6v or more, that is NOT good and means they were overcharged to begin with. Normally cells that have not been charged come sitting somewhere in the flat part of the curve, at about 3.2v, which of course does not mean balance. In your case, I surely hope that those big cells were not overcharged.

I thought that might spin your dials. I had them top charged before delivery to what the factory and distributor recommend. I take your point about leaving them like that so have been bleeding off charge all afternoon.
Ive got the bank sitting at 13.24, and the voltage drop has slowed right up, I think I'll take them down to abot 13.2 or a touch lower. Interesting to note virtually no voltage bounce back when loads switch off, Also individual cell voltages stay within 0.02 but each time I measure they alternate ranking. Curioser.
Hopefully this will put them on the "Flat" cause they will have to sit for a week or two

My system gets a regular daily workout, when I go away it's good for the FLA's they get some good float time, but with these I think it would be best to turn everything off.

So I'm not overly concerned with them sitting on high states of charge for long

P1060715.jpg

This was the start of drain down. I since hooked up an inverter and wired in a voltmeter I can see through the window. I've been going out to do the cells regularly.

Ya gotta laugh!!

Not long after I first hooked it all up I went to check the voltages and was feeling the temp of the cells when white plasticy smoke wafted over the batteries. I had contractions. When the moment of panic subsided I searched for the source. I'd stood on the soldering iron, I was making a burnt offering of my sole.
Phew!

[inetdog]

The main problem with leaving out the charge controller is that you are then depending on getting a precise, consistent voltage output from your panels.
That will not happen, since Voc and Vmp both depend weakly on the insolation at a given time and strongly on panel temperature.
If you want to be able to drive full current from the panels during the Bulk phase, you will have to be able to size you panels so that Vmp is close to the low SOC battery voltage while Voc is not any higher than your target charge cutoff voltage.
Since the difference between Vmp and Voc for that typical crystaline silicon panel is about 20%, you may not be able to hit the values you need. And the variation of both voltages with temperature can be as much as 25% in a very cold winter climate and a high summer panel temperature.

And you would be completely ruling out the opportunity to select your panels for best power per watt, which an MPPT CC would make possible.

[bungawalbyn]

The main problem with leaving out the charge controller is that you are then depending on getting a precise, consistent voltage output from your panels..

Am I? How so? If panel V is less than batteries, no charge, if greater, some charge. LifePO4's especially of large cell size will take all my panels will put out and MANY times more amps, with minimal resistance, doesn't this keep the operating voltage at about SOC of the battery? Doesn't this mean that the voltage will only rise to cut out when the battery reaches the SOC of this voltage?
Remember these are not FLA and operate quite differently under charge due to their very low internal resistance.

Why do I want the Voc to be no higher than my target cut off voltage? I'm not relying on the charge just fizzling out due to voltage equalisation, I've got sensors and cutouts for that.

The business I bought the batteries from turns out to be doing something similar to what I propose, having previously done comparisons between "direct connect" and using MPPT controller and found little difference. These guys, one would hope, have greater knowledge and experience in using LiFePO4 batteries. They do EV cars, and run their workshop on a 'direct connect" set up.




The batteries after draw down are now sitting at 3.31v all cells after an overnight rest. so the balance is very good. Sweet.