Simplified lifepo4 charging and care

Hey PNJunction. I read this entire thread. I will be installing an EVE 16s 280ah 48v bank to replace my 325ah Trojan L16s. I will be top balancing them in parallel with my CC/CV adjustable power supply. My Schneider Conext XW5548 inverter has settable LVD and HVD. The most I will be taking from these batteries during the darkest of winter is 150ah and a fraction of that when the place is vacant. I have the ability to remote monitor my Schneider equipment and have the Conext shunt based battery monitor for AH counting. I can also remote start my genset for charging if the panels get covered with snow.

When the place is vacant I leave the inverter on to run the fridge, security cameras and a few other low power devices. Batteries will be in an insulated box with a remote operated incandescent bulb so I can keep them close to 70 degrees Fahrenheit during the winter. There will be a second bulb for backup purposes. Both bulbs will be controlled using a simple but reliable Wifi plug through the Smartlife IOS app.

With all your LifeP04 experience over these last six years do you still think running without a BMS is practical for a setup like mine? I may eventually add the Orion Jr.2 BMS but want to get familiar with LifePO4 before getting too complicated.

Thanks for any advice.

I think 70F is too warm. 45 F is good enough, or even 50F if you want them more "lively"

I think an incandescent bulb is too unreliable (even 2 of them) I'd suggest a 50w heater pad or something like that, on an aluminum heat spreader plate at the bottom of the battery box (don't put the weight of the batteries on the heat pad)
google "silicone battery heater" for a bunch of ideas, Put a plate (thick enough to conduct heat) inder the batteries and extending enough on the side to stick the heater to. Much better than a light which will heat one battery and the otheres will be cool

Thanks Mike. So something like this? How thick do you think the aluminum plate needs to be? 1/4" work?

https://www.grainger.com/product/3CD...P7A1P:20501231

An alternative would be a seedling heat mat. Inexpensive ones that maintain about 70F are $20 and ones like this with adjustable thermostats are more: https://www.amazon.com/dp/B016MKY7C8..._1DBVFbZJTPAT9
Not sure that you would need an aluminum plate with the surface area of these pads. EVE says in their spec sheet that these batteries will perform from 0C to 60C which is 32F to 140F although I would never take them to those extremes. The charge and discharge tests are done at 25 C which is 77 F.

I would however follow EVE's recommendation for clamping the cells to extend their life. It does not need to be much but it reduces strain on the terminals if there is some swelling. I have 32 of these cells in a cabinet with 3/16" aluminum plate and 1/4" allthread. The clamping force I used is enough to compress a split washer. Not much is necessary.

I will defer to @PNJunction 's experience for the final word on running without a BMS. I can give you my experience with these EVE LF280 cells during the past six months in which I have been using them. I have a 2P16S pack with an Orion BMS. Mine is not a remote location but I am sometimes gone for a week at a time and I can remotely monitor the Orion BMS and my Outback Skybox inverter. I did do a parallel top balance but now realize that through errors in the meter I was using that I may have only taken them to 3.45 to 3.5 volts. I subsequently noticed that if I charged the pack to an average of 3.5 volts per cell I had some that were quickly runnning up to 3.65 volts.
I tried variations of charge current and Constant Voltage settings and the simplest solution was just to lower the voltage setting on the built in charger because I wanted to increase my odds of fully charging my pack from solar. That is why I kept the current high but it was still way below 1C.
That is why I would recommend that you use very conservative charging voltages until you do get a BMS, I had the advantage of several weeks of small increments while I could monitor my pack daily before I felt comfortable leaving it on its own. I did settle on 3.40 volts per cell which is a CV voltage of 54.4 volts for the pack. That is a conservative number but these cells seem to have a pretty steep charge curve after 3.4 volts. You are not leaving much capacity on the table and your pack life will be extended with that conservative voltage.

I have always used a BMS but I have not always used the the individual cell voltage cutoff to protect my pack. I have relied on using conservative charge parameters. Over time the small balancing currents of the BMS tend keep the cells balanced at the top but keep in mind, with these 250 Ahr cells it is going to take months to bleed off even a 10 Ahr balance difference between these large cells.

Yes, that Granger heater pad is the sort of thing. Look for one with some sort of CE or UL certification, you want reliable & safe, not cheap. Seed bed heaters would also work I suppose,

Think of unattended conditions, the cost of the batteries, and the consequences of a failure. Will your charge controller block charging if the temps fall below 34F ?

Be sure to inhibit charging by disconnecting the solar panels from the controller, - don't allow the BMS to disconnect the battery from your controller, or you may fry the controller.

As long as the battery weight does not crush/damage the pad. Greenhouse pads are expecting 1 or 2 inches of soil. Keep us posted

Absolutely, don't let them get away

There is no setting that I am aware of to have the Conext MMMP 60 150 shut down on low temp. The Orion Jr. 2 BMS can do it though. I have spoken with the Orion techs and their Jr.2 BMS can shut down the XW5548 and my CC separately over the Xanbus. And just as important restart the inverter and CC when the cell voltage or temperature is back in normal range. It also allows cloud based monitoring for a few hundred more as well a Coulomb counting. So the batteries cost $1,446 including shipping. The BMS would be approx. $700 including the cloud internet module and Coulomb counting.

If we lived there full time I would probably skip the BMS. But $700 is worth it for the piece of mind when the place is vacant.

Thanks for all the advice.

I have an off grid system consisting of 900w solar array through an “Outback 80Amp controller”. I was using only 1 LiFePO4 200w battery set for 12 Volts. Recently I purchased another identical (Make and Watts) battery.
Fitting them in series I set charging volts to 29.2 (14.6 recommended charge per battery) . The new battery does not want to charge up to the same voltage as the original one. In circuit I am getting a maximum 13.32 volts on the new battery and 15.69 on the original. The combined voltage comes up as 29.01 Volts, seemingly ideal, but 15.69 is too high for one and 13.32 is too low for the other. Should the BMS have allowed this?
I assume one of the batteries is faulty but which? As I’m new to lithium I’m betting on the new one, but...? The original battery is only one month old. Now I wonder if the 15.69 has damaged the battery.I would appreciate any help with this problem.

Maurie

What is the make of your drop in Battery?. Does the manufacturer recommend putting them in series? 15.69 volts is definitely too high for a LFP battery of four cells. If it was operating correctly the internal FETs on the BMS should have disconnected it when voltage hit 14.6 volts (3.65 per cell). When FETs fail they often fail closed so that may be the issue. The only help I could offer would be to open it up and diagnose the BMS and measure the individual cell voltages but that would probably void the warranty.
This sounds like a warranty issue that you should discuss with the manufacturer.

Hi Ampster

The Batteries are VoltaX 200 Ah LiFePO4. They do say up to 4 batteries in series. I agree it's a warranty problem and like all warranty situations I want as much information and understanding of the problem. Sadly many manufacturers try to negate claims, so opening the battery is not a viable option.
The same battery functioned well as single 12volt system. So the problem only came about with the addional battery.

I would run an individual test of each battery to document and prepare for the conversation with the manufacturer. I can only frame a hypothesis that the battery that went to 15 volts is the faulty one. I would see if I could duplicate the problem using a 12 volt power supply. You may have to drain the battery first a little but presumably it settled below 15 volts. Normal resting voltage is 3.32 per cell or about 13.3 volts. Coincidentally that is where the new battery either stopped charging or came back to resting voltage. Initially set the power supply to 14.6 volts volts and measure charging current. Current should taper as voltage gets near the cutoff. If it just keeps taking current, that would duplicate the scenerio and be a pretty good clue that the BMS is faulty.
I would verify all your charger settings to better inform your conversation with the manufacturer. Normally those drop in batteries should open the circuit if either battery goes above the charging voltage. The reason for using a power supply versus your charge controller is to get a more consistent current measurement for the documentation, It may also eliminate your charge controller as a variable.

I might add that it might be a good idea to put those two batteries in parallel for a day or two. It would be best to put 14.4 volts on them so they get current and have a better chance of balance at the top of the charge curve. That would eliminate any big balance issues that might have complicated the original scenerio. They won't balance in series because as soon as one of them hits the high voltage cutoff the BMS should drop it off and the other one will also lose power so it would never catch up. They could also appear to be in balance at resting voltage but that is not a good measure like it would be at the upper knee at 14.4 volts.