Cheap 4kwh LiFePO4 batteries from Battery Hookup

[Keith C]

That's interesting. I'll check that out Jason.
Thanks.

 

[GVSolar]

Did my first charge/discharge cycle with 3 paralleled pre-assembled TechDirect/BYD units: They were fully charged to the internal BMS cutoff of 28v. Using a 500w heater @ approx 18amp discharge the batteries lasted for 17 hours 12 minutes - using a cut-off voltage of 24.0v.
Didn't want to press the voltage any lower on my first discharge cycle. At 24.v my meter read: 8.14Kwh, 315Ah.
That would represent 2.71kwh/105ah per battery. It's not 4Kwh per battery, but it's a start, and there may be some operator error in there.
I've started the recharge cycle and will be more rigorous in my measurements next time - we'll see if the capacity increases with each "wake up" cycle. I will also push the discharge voltage a little more aggressively - perhaps as low as 23volts. Best to all.

 

[jasonhc73]

Here I am now, 27 days on the BMS...

I don't know what setting I did to make it do what it is doing now, but:
After the bulk charge, my BMS turns off the battery.

This at first annoyed me, but after 3 days of doing it, I also noticed my Voltage on the battery is staying higher, instead of near-instant return to 52.9V. 2 days in a row steady at 53.4V, the Cell Difference is only 0.006. I use them a steady 7-8 hours a day, and normally end the day at 52.2 or 52.3V. Each BMS records... 6.5 to 7 AH of use, for a total of about 26-27AH per usage. Hardly any usage for that 8-ish hours use. I have a total set of 800 AH.

 

[Sojourner1]

Here I am now, 27 days on the BMS...

I don't know what setting I did to make it do what it is doing now, but:
After the bulk charge, my BMS turns off the battery.

This at first annoyed me, but after 3 days of doing it, I also noticed my Voltage on the battery is staying higher, instead of near-instant return to 52.9V. 2 days in a row steady at 53.4V, the Cell Difference is only 0.006. I use them a steady 7-8 hours a day, and normally end the day at 52.2 or 52.3V. Each BMS records... 6.5 to 7 AH of use, for a total of about 26-27AH per usage. Hardly any usage for that 8-ish hours use. I have a total set of 800 AH.

Does your bms protect individual cells? Is it possible that a cell is climbing in voltage while charging and shutting down to protect the batteries?

 

[Refinished]

I have five of them that I have been cycling individually. No BMS yet, but I have been monitoring the cells externally. So far, all packs have been behaving in more or less the same ways.

Some observations that I have not really started to put together into a long term charge strategy:

• Like jasonhc73, my batteries always return to between 26.4 and 26.6v within a few minutes to an hour after a bulk charge to higher voltages. I tried a charge to 29v with 60 minutes of absorb time on one of them to see if I could get that voltage to hold a little higher and it didn't seem to have an effect.
• My charger data logs, so I have been able to see the voltage profile over time on charge cycles from 22.5v to 29v and the classic LFP knees are evident. The shape and voltage levels of the curves are pretty much the same at 5a as at 50a. The fall-back voltage referenced above is pretty much where the upper knee starts it's vertical climb. The pack voltage always slides right back down the steep part of the curve.
• The balancing seems quite good across the five and I've done nothing specifically to balance them other than the cycling. At the top end, the cells are generally closer than 0.05v and at the low end they start to diverge and some packs develop a very predictable (as in the high/low cell diverges a very predicable/repeatable amount) variance as much as 0.3v. The divergence does not start until the pack starts to fall off the low end knee. I am new to LFP, but this seems like it is probably not worrisome at all.
• The cycling I've done has been increasingly aggressive. I started with a narrow voltage range and low amps and have been widening the range to a 29v top end and a 22.5v low end at 50a. So, far each battery has only one cycle at that aggressive profile and they are giving me 3.3kwh to 3.6kwh reliably. Being new, I should have sought some advice before starting this wake up regimen, but what the hey.... I am eager to know if anyone with a more intimate knowledge of the physics at work here can think of the right way to get more kwh out of them.

 

[SolarRat]

A lot of you guys are saying the same thing: these batteries drop down a lot after charging at higher voltages.

I'm in the skeptic camp when it comes to lithium batteries having a memory, but isn't this a classic symptom of what would happen if the battery has a memory of constantly being undercharged?

 

[nebster]

All LFP cells, even brand new fresh ones, will drop down to around 3.33Vpc when at 98% or lower SOC and even a tiny load is present.

26.4V doesn't sound too far off to me. That they fall back down a little faster maybe, even under zero load (true?), and to a few tenths of a volt lower, probably is par for the course with a cell that has lost a good bit of its capacity.

Charging to 29V is pretty high for day-to-day use, and discharging to 22.5V is also a bit too low. Especially without a BMS to watch for the inevitable spiking cell.

 

[jasonhc73]

Does your bms protect individual cells? Is it possible that a cell is climbing in voltage while charging and shutting down to protect the batteries?

Yes,
I've watched the BMS stop everything when one gets low volt, high volt, and even too much volt spread.
I doubt I will ever get into temp protect, but it has 4 temp sensors with the possibility to have two more. But that means soldering something you need extreme skills to do a super tiny connect.

I just fitted my 3 of 4 BMS into a double pack of 16 cells, my set is affectionately known as 20 and 21.
The cell difference was 0.002V of the 16 cells across both packs! <-- = OMG!

A lot of you guys are saying the same thing: these batteries drop down a lot after charging at higher voltages.

I'm in the skeptic camp when it comes to lithium batteries having a memory, but isn't this a classic symptom of what would happen if the battery has a memory of constantly being undercharged?

Click the link I have in my signature... LiFePO4 simply has no memory. Nickel-cadmium batteries certainly do. They are an entirely different chemical process.

 

[jasonhc73]

I have five of them that I have been cycling individually. No BMS yet, but I have been monitoring the cells externally. So far, all packs have been behaving in more or less the same ways.

Some observations that I have not really started to put together into a long term charge strategy:

• Like jasonhc73, my batteries always return to between 26.4 and 26.6v within a few minutes to an hour after a bulk charge to higher voltages. I tried a charge to 29v with 60 minutes of absorb time on one of them to see if I could get that voltage to hold a little higher and it didn't seem to have an effect.
• My charger data logs, so I have been able to see the voltage profile over time on charge cycles from 22.5v to 29v and the classic LFP knees are evident. The shape and voltage levels of the curves are pretty much the same at 5a as at 50a. The fall-back voltage referenced above is pretty much where the upper knee starts it's vertical climb. The pack voltage always slides right back down the steep part of the curve.
• The balancing seems quite good across the five and I've done nothing specifically to balance them other than the cycling. At the top end, the cells are generally closer than 0.05v and at the low end they start to diverge and some packs develop a very predictable (as in the high/low cell diverges a very predicable/repeatable amount) variance as much as 0.3v. The divergence does not start until the pack starts to fall off the low end knee. I am new to LFP, but this seems like it is probably not worrisome at all.
• The cycling I've done has been increasingly aggressive. I started with a narrow voltage range and low amps and have been widening the range to a 29v top end and a 22.5v low end at 50a. So, far each battery has only one cycle at that aggressive profile and they are giving me 3.3kwh to 3.6kwh reliably. Being new, I should have sought some advice before starting this wake up regimen, but what the hey.... I am eager to know if anyone with a more intimate knowledge of the physics at work here can think of the right way to get more kwh out of them.

Magic is happening... I dunno, but for the last three days in a row, the packs are sitting idle at 53.4V (26.7V).
By accident, I discovered one of the settings in the BMS and what it actually does.

• Cell unit voltage Gap Protection
  • The default is 1.0V - I thought I set it to 0.8V. However, I set it at 0.08V.
  • Every time when the packs charged, as soon as one cell got out of line, everything just took a pause and about an hour later the out of parameter cell equalized to the rest. This is on the packs known as 40 and 41. This is the pair that has been on BMS for 28 days.

I think this might be key to getting a bit more juice into the cells, very slow charging, any out of spec, just pause and wait some time, then continue.

However I just put the 3rd BMS on tonight and it was sitting there 0.002V cell difference. I am pretty sure it said "Sup, how you doin?" and winked.

 

[HMR]

Summary of charge/discharge cycles of two of my four BYD batteries. I am charging up until the first cell goes over 3.5 amps (where I set my charge controller to cut off). My charge rate has been either 5 amp or 8 amp. I discharged until the first cell goes below 2.8 amp. My discharge rate has been 29 amp. Here are my results so far:
(Note: edited to include battery voltage values)
Battery Number one
Cycle 1: charge: 3.54 KwH; 133 Ah 26.64 V discharge: 2.76 KwH; 110 Ah 23.31.V
Cycle 2: charge: 3.18 KwH; 120 Ah 26.58 V discharge: 2.94 KwH; 116 Ah missing
Cycle 3: charge: 3.19 Kwh; 120 Ah 26.59 V discharge: 2.87 KwH; 114 Ah 23.5 V

Battery Number 2:
Cycle 1: charge: 2.64 KwH; 99 Ah 27.6 V discharge: 2.29 KwH; 91 Ah 22.5 V
Cycle 2: charge: 2.77 KwH; 104 Ah 27.0 V discharge: 2.57 KwH; 101 Ah 23.9 V
Cycle 3: charge: 2.79 Kwh; 105 Ah 27.3 V discharge: 2.56 KwH; 101 Ah 23.3 V

GVsolar above reported 2.71 Kwh / 105 Ah. Refinished above reported 3.4 - 3.6 Kwh. Nice to see these numbers roll in now. So far it looks like my battery number 2 brings up the rear, my number 1 is about like GVSolar's results, and Refinished has the top end of the spectrum. Any thoughts?

 

[Refinished]

I may be pushing mine harder than some others since I am using overall pack voltage to determine start and stop and my C rates may be higher on charge. Effectively, I am allowing the average cell voltage to reach 3.625 on charge and 2.8 on discharge to get that output. Since the cells are all pretty tight on balance, I have not been too worried about this. I am still waiting for Moses to appear on the mountain with the perfect BMS from heaven. Disclaimer: Don't consider anything I write as advice. I am not a moron, which may be debatable, but I have no experience with LFP batteries, which is not debatable. Anyway, here is what I've done:

1. Charge to 27 @15a @60m absorb
2. Drain to 22.5 @30a
3. Charge to 28 @25a @15m absorb
4. Drain to 22.5 @30a
5. Charge to 29 @45a @1m absorb
6. Drain to 22.5 @30a
7. Charge to 27 @40a @1m absorb <- This one is just to hold the battery over in case work pulls me away for an extended time

 

[HMR]

I may be pushing mine harder than some others since I am using overall pack voltage to determine start and stop and my C rates may be higher on charge. Effectively, I am allowing the average cell voltage to reach 3.625 on charge and 2.8 on discharge to get that output. Since the cells are all pretty tight on balance, I have not been too worried about this. I am still waiting for Moses to appear on the mountain with the perfect BMS from heaven. Disclaimer: Don't consider anything I write as advice. I am not a moron, which may be debatable, but I have no experience with LFP batteries, which is not debatable. Anyway, here is what I've done:

1. Charge to 27 @15a @60m absorb
2. Drain to 22.5 @30a
3. Charge to 28 @25a @15m absorb
4. Drain to 22.5 @30a
5. Charge to 29 @45a @1m absorb
6. Drain to 22.5 @30a
7. Charge to 27 @40a @1m absorb <- This one is just to hold the battery over in case work pulls me away for an extended time

You report absorb figures. What do these mean. What charger/charge controller are you using and does it have this absorb setting that you can leave on?

 

[Refinished]

Samlex EVO programmed with a two stage profile. The stages are Bulk (constant current) then Absorb (constant voltage). The absorb stage holds the target voltage steady and allows the amps to drop per the uptake of the battery at that voltage. The absorb stage can end based on a countdown timer or the amps taken up by the battery dropping below some threshold. There is a lot of talk about the place of CC and CV in LFP charging out there, though it is not all consistent. My use of absorb is based on my trying to translate what I read out there as best practice for a daily charge cycle to waking these batteries up from long storage. I have not seen anything that is written with apparent knowledge that addresses 'waking up' this chemistry.

 

[HMR]

Samlex EVO programmed with a two stage profile. The stages are Bulk (constant current) then Absorb (constant voltage). The absorb stage holds the target voltage steady and allows the amps to drop per the uptake of the battery at that voltage. The absorb stage can end based on a countdown timer or the amps taken up by the battery dropping below some threshold. There is a lot of talk about the place of CC and CV in LFP charging out there, though it is not all consistent. My use of absorb is based on my trying to translate what I read out there as best practice for a daily charge cycle to waking these batteries up from long storage. I have not seen anything that is written with apparent knowledge that addresses 'waking up' this chemistry.

Can you be more specific on the charger? I quickly looked up samlex 24v chargers and landed on ones specifically for Lead Acid batteries not LFP? Thanks.

 

[Refinished]

Can you be more specific on the charger? I quickly looked up samlex 24v chargers and landed on ones specifically for Lead Acid batteries not LFP? Thanks.

AFAIK, all of the EVO line work with LFP. Steve_S has a thread that he started with discussion about these models.

 

[nwillitts]

Yes,
I've watched the BMS stop everything when one gets low volt, high volt, and even too much volt spread.
I doubt I will ever get into temp protect, but it has 4 temp sensors with the possibility to have two more. But that means soldering something you need extreme skills to do a super tiny connect.

I just fitted my 3 of 4 BMS into a double pack of 16 cells, my set is affectionately known as 20 and 21.
The cell difference was 0.002V of the 16 cells across both packs! <-- = OMG!

View attachment 6366 View attachment 6367


Click the link I have in my signature... LiFePO4 simply has no memory. Nickel-cadmium batteries certainly do. They are an entirely different chemical process.

do you have the BMS main wires both hooked up to negatives?
could you take a real close up pic of how you have them wired?i dont know where to plug in the LCD.no freaking instructions.

 

[davissd]

Just received my BYD today. I'm sure it sat at the Fedex terminal all night in the 12 Deg. F temperatures. How long do you think it will take to get up to room temperature before I start to charge it?

 

[jasonhc73]

Just received my BYD today. I'm sure it sat at the Fedex terminal all night in the 12 Deg. F temperatures. How long do you think it will take to get up to room temperature before I start to charge it?

29

 

[davissd]

"ITS IMPORTANT TO HAVE BALANCING IF YOU PLAN ON FULLY CHARGING AND FULLY DISCHARGING. JUST SEARCH ALIEXPRESS FOR "8S ACTIVE BALANCER". OR YOU CAN USE AN 8S BALANCE CHARGER WITH THE BALANCING FEATURE.

NOMINAL VOLTAGE IS 25.6V
FULLY CHARGED IS 29.2V
FULLY DISCHARGED IS 20V"

Charging to 56 (instead of 100% 58.4)
Returning to the utility at 44 (instead of 40) - No BMS!
(I have grid-tied solar. These inverters (LV5048sj) support 8 kW each, 4x2 solar inputs)
View attachment 3933View attachment 3934View attachment 3935
1st test!
S - U - C - C - E -S - S

Whole house on battery! YES!!!!!! 1st test.

View attachment 3936View attachment 3937

I can't figure out the software monitor yet though, I guess it only works WiFi, but I'm connected USB and nothing.

Were you able to get the software to work via USB? I had the same issue running windows 10 until I right clicked on the .exe file and selected "Run as Administrator" Much easier to configure the unit through the software. I'm working now installing the linux version on a Raspberry Pi so I can have full time monitoring

 

[jasonhc73]

Were you able to get the software to work via USB? I had the same issue running windows 10 until I right clicked on the .exe file and selected "Run as Administrator" Much easier to configure the unit through the software. I'm working now installing the linux version on a Raspberry Pi so I can have full time monitoring

The Offgrid Guy in Hawaii(https://www.youtube.com/channel/UCVn2ng2ythNsotzk4IT42NA) is making a really nice looking Raspberry Pi reporting program. Maybe combine some brainpower and see what the outcome happens.