Charging LFP battery from AC-DC unit

[Almot]

Tried to charge LFP from Meanwell se-200-15.

Lynac Lithium 120AH battery marketed as 100AH, you discharge to 80% DOD and get 100AH. Was partially charged already, resting 13.1V. Battery manual suggests charging to 14.2V. I understand they mean 14.2 under charge, not resting.

Set Meanwell to 14.2V, connected LFP. Voltage went up quickly to 14.1, then slowly climbed to 14.15 and refused to go any higher for a couple of hours.

Meanie got hot, I stopped the charging, disconnected LFP, set Meanie to 14.23, connected LFP. In a couple of hours voltage went up to 14.19 and didn't go any higher. Disconnected again.

Connected LFP to portable DC fridge, voltage under load immediately dropped to 13.28, slowly discharged to 12.49 (80% DOD as per manual), discharge took more than 24 hours, disconnected. After 1 hour resting voltage climbed to 12.52.

Set Meanie to 14.22, connected LFP.
Voltage immediately jumped to 13.8 and was going 13.8-14.05 for half an hour (this up and down didn't look normal to me), then settled at 13.95. Meanie got really, really hot, was giving off a smell and making a quiet high-pitched buzz - not an alarm buzzer, but I got the message and disconnected it. Experiment lasted ~40 minutes. Didn't measure current, but Meanie is rated only 14A so couldn't be too high since it didn't go up in smoke.

Connected Meanie to solar controller input and LFP to controller output. Voltage under charging 13.1, controller output 11A. After a few hours voltage climbed to 13.4, current dropped to 10A. Now everything goes as it should.

Bad Meanie.

EDIT - Update:
After total 5 hours of charging it's still 13.4V, sitting at this voltage for 3 hours now. Current dropped to 5A and is fluctuating between 4.5 and 5.5A every second. Hmm...

Edit - Update:
Yay! It has made it to 14.2V (the value suggested in the manual). Current dropped to 1A, and in a few minutes - to 0A, at which point V dropped to 14.1

Despite being set to Gel 14.2 V Abs, 13.8 V Float, Epever controller did NOT enter Float. The current was 0 anyway so I pulled the plug.

Controller input reads 1.5 KWH total, this is ~105 AH @13.6V, battery 120AH discharged to roughly 15 AH, so - the numbers match.
Voltage was rising from 13.1 to 14.2 and stayed the longest in the section 13.4-13.6.
Meanwell input to controller all the time was 15.1V - it's 15V rated, I didn't want to push it.
1 hour after disconnect resting V dropped to 13.7.

Bad news:
Charging lasted 16.5 hours, in solar terms = 3 days of sun. On sunny day 200W panel would generate ~13A starting current with empty battery, so maybe 2 days and a half.

I'm disappointed with what looks like low acceptance of current, - a few hours in when battery climbed out of the "knee" and reached 13.4V, current dropped from 11A to 10A and was gradually decreasing since then. BUT... up to~13.5V I was able to increase the current by tweaking Meanwell voltage up from 15.05 to 15.15, this was enough to increase the current by more than 0.5A. So there was a margin for current increase, I was just afraid that Meanwell would go up in smoke if I increased the voltage more.

[Almot]

BFL, thank you. I am looking at the charge curve for my particular battery https://www.lynaclithium.com/wp-content/uploads/2020/10/12.8V-100Ah-True-Series-Quick-Sheet.pdf. Long Absorption stage here is a gradually rising voltage from 13.3 to 13.6, at this point it's ~80% full - I was wrong earlier, it's 80% not 60. Hard to tell when the curve is almost flat.
Should be having a spike now but it's been hanging on at 13.6 for 3 hours. KWH counter on the controller input now reads 1.3 KWH, this is 80% full for 120AH battery. Will give it another several hours.

One article (which LFP folks here liked or hated depending on their moods of the day) said if you charge at less than 14.6 that was ok; it just meant you got a longer Absorption Stage.

Do you mean that it takes longer when voltage is lower, regardless of how many AH you're pumping in there every hour?

Also, how can empty battery be 14.X at the beginning of charging? Max recommended voltage for my battery is 14.2. This is where it eventually arrives with charger still connected (and then drops to 13.8 resting).

[BFL13]

https://batteryuniversity.com/learn/article/charging_lithium_ion_batteries

Not clear where you are at, but Figure 3 might apply. You could be in a long Absorption Stage and you could be off in your SOC notions from using voltage instead of an AH counting meter. Just guessing though.

You might be getting along in the "flat" voltage curve and soon to finally see a spike in voltage if you keep going. Just guessing on that too.

One article (which LFP folks here liked or hated depending on their moods of the day) said if you charge at less than 14.6 that was ok; it just meant you got a longer Absorption Stage. Might be what you are seeing?

Charging with lower initial amps would not matter as long as your voltage was sufficient AFAIK--it just means it takes longer to get it done. LFP guys will have to confirm, but AFAIK there is no "minimum" charging rate such as with some (all?) AGMs in some situations

[Almot]

When charging directly from Meanwell and voltage got stuck at 14.15, it was directly on Meanwell output terminals. I installed a small meter on the Meanwell. Not at the end of a long wire to battery.

Voltage is still fluctuating now +/- 1V on the controller output with Meanwell feeding the controller, and Meanwell at 6A post-MPPT is just "warm", not hot. I think this fluctuation is the battery behavior, not Meanwell thermal protection mode.

Battery went up to 13.6V after 10 hours of charging at the average 8A, this is only 60% full or 72 AH. It will not get much better current with 200W solar. This is what worries me because Meanwell output measured by controller is now 1.1 KWH, this is 75 AH even after all imaginable losses. Battery was previously discharged to 12.5, which according to their manual is 90% DOD,12 AH remaining. 87 AH input and only 72 AH in the battery?

Has it been established that there is an adverse effect of low current on LFP charging? The only restriction on charging in the battery manual is max 0.2C or 24A in this case, and they allow a higher current for a short time.

[MEXICOWANDERER]

Landy used some of my suggestions on his Meanwell. The chokes develop the most heat. A 600 watt uses a blow out fan but a 80mm suck in fan in front connected to the original fan electrically lowers internal temps 40°F. I have a 150 watt 36 volt meanwell that warms up too much on a 50 watt LED load. No fan.

I original 36-amp Megawatt was souped up to provide 56 amps continuous at 15.5 volts. It's on it's 4th year. Nicknamed the HYPERWATT. The Delta power distribution on pos and neg are similarly inversed into 3 into 8 gauge power wires.

The 14 amp is a garden hose on a fire truck.

[2112]

Yea, I tried to dig up Landyachts screwy31 thread but couldn't find it. I recall him using a 30A Megawatt as well as a lesser quality unit that smoked.

[BFL13]

ISTR Landyacht posted about his version of that kind of charger. He had to modify it with a fan , a heat sink, and fatter wires to get it to work right IIRC.

It has such low amps compared with what the LFP can accept, IMO , it is not worth using, when there are way better options. EG this one is low cost, reliable, and does 45 amps (close to the .5c rate for your battery), and it has adjustable voltage so you can pick any voltage you want and change it to float at any voltage you want.

https://www.boatandrvaccessories.com/products/powermax-pm3-45lk-45-amp-12-volt-power-supply-with-led...

You can probably also use your RV's converter, depending on which one you have, instead of that low amp gizmo.

[2112]

Almot wrote:


Set Meanwell to 14.2V, connected LFP. Voltage went up quickly to 14.1, then slowly climbed to 14.15 and refused to go any higher for a couple of hours.

There is current flowing through your cables between the power supply and the battery creating a 0.05V drop across the cables. The higher the current the higher this voltage across the cables will be. This is known as IR. Your Meanwell doesn't have sense lines so you will have to accept this.

Meanie got hot, I stopped the charging, disconnected LFP, set Meanie to 14.23, connected LFP. In a couple of hours voltage went up to 14.19 and didn't go any higher. Disconnected again.

You need to put a fan on it.

Set Meanie to 14.22, connected LFP.
Voltage immediately jumped to 13.8 and was going 13.8-14.05 for half an hour (this up and down didn't look normal to me),then settled at 13.95. Meanie got really, really hot, was giving off a smell and making a quiet high-pitched buzz - not an alarm buzzer, but I got the message and disconnected it.

My guess is it's going into thermal protection. It overheated, turned the output off, battery voltage dropped to 13.8V, it cooled down, turned output back on and battery voltage climbed back to 14.05V. If you were measuring the current you would have seen it go to 0A then back to 14+A with the voltage changes.You really need to put a fan on the power supply.

Connected Meanie to solar controller input and LFP to controller output. Voltage under charging 13.1, controller output 11A. After a few hours voltage climbed to 13.4, current dropped to 10A. Now everything goes as it should.

This is limiting the power supply current output, creating a very slow charge profile. Your power supply is happy with this, but is your battery?

Your 14A Meanie is a little underrated for the task. Are you getting the proper charge profile to protect your $800 investment?

Wire a 120V fan or 2 on the power supply input and use them to cool the power supply. I wouldn't wire 12VDC fans on the output because you need every mA you can get to charge the battery.

[Almot]

Don't see any fan through the many small holes.

In the setting with controller at 10-11A/13V controller output, Meanwell was still "very warm or hot" to my subjective feeling. Not as hot as when plugged directly into battery, no smell and no odd sounds.

Cranked Meanwell up to V=15.12 (it's 15V rated, don't want to push it), current went up from 5A to 6A. Unplugged for the night.

[MEXICOWANDERER]

Does your meanwell have a fan?

[Olivaw]

Following.