Extremely Noob question about charging time for a single Chins 12V LiFePo battery

OK - almost embarrassed to ask this. I just bought 4 Chins 12V LifePo 100AH batteries. Eventually they will be in series configuration but first I am trying to fully charge each one individually to 100%. Chins says they are shipped mostly discharged.
I have a Dakota Lithium charger rated for 10Amps specifically for 12V LiFePo batteries. How long should it take to fully charge one battery? Should it be 100/10 = 10 hours?
Same topic: I also have a bench power supply which I set to 14.5 OC voltage and 5A max current. A series ammeter show it is pumping 5A into the battery but it seems to be taking forever (>12 hrs) to charge. When I hook up the bench supply, it indicates CC mode and the voltage drops to about 13.3.
Just not sure if I am doing it right.
Thanks in advance!

Sracer42 said:

OK - almost embarrassed to ask this. I just bought 4 Chins 12V LifePo 100AH batteries. Eventually they will be in series configuration but first I am trying to fully charge each one individually to 100%. Chins says they are shipped mostly discharged.
I have a Dakota Lithium charger rated for 10Amps specifically for 12V LiFePo batteries. How long should it take to fully charge one battery? Should it be 100/10 = 10 hours?

Click to expand...

Yep. Plus maybe 15-30 minutes at the end to completely top it off.

Legally, they must ship below 30% due to hazmat regs, so count on at least 7 hours @ 10A.

Sracer42 said:

Same topic: I also have a bench power supply which I set to 14.5 OC voltage and 5A max current. A series ammeter show it is pumping 5A into the battery but it seems to be taking forever (>12 hrs) to charge. When I hook up the bench supply, it indicates CC mode and the voltage drops to about 13.3.

Click to expand...

Per above, 14-20 hours charging @ 5A. LFP voltage doesn't hit peak until very near the end of the charge.

Keep charging. You'll get there.

sunshine_eggo said:

Yep. Plus maybe 15-30 minutes at the end to completely top it off.

Legally, they must ship below 30% due to hazmat regs, so count on at least 7 hours @ 10A.




Per above, 14-20 hours charging @ 5A. LFP voltage doesn't hit peak until very near the end of the charge.

Keep charging. You'll get there.

Click to expand...

Thanks - new to all this stuff

Sracer42 said:

Thanks - new to all this stuff

Click to expand...

Depending on the quality of the power supply connections (the stock ones are garbage), you may see the current drop before the battery terminals measure 14.5V but the supply reports 14.5V. If you've fabbed better leads, you're good to go.

Alternatively, since the batteries have a BMS, you can just set the voltage higher as they will cut off to protect themselves.

Sracer42 said:

OK - almost embarrassed to ask this. I just bought 4 Chins 12V LifePo 100AH batteries. Eventually they will be in series configuration but first I am trying to fully charge each one individually to 100%. Chins says they are shipped mostly discharged.
I have a Dakota Lithium charger rated for 10Amps specifically for 12V LiFePo batteries. How long should it take to fully charge one battery? Should it be 100/10 = 10 hours?
Same topic: I also have a bench power supply which I set to 14.5 OC voltage and 5A max current. A series ammeter show it is pumping 5A into the battery but it seems to be taking forever (>12 hrs) to charge. When I hook up the bench supply, it indicates CC mode and the voltage drops to about 13.3.
Just not sure if I am doing it right.
Thanks in advance!

Click to expand...

Hello, I got 8 and it takes a while, I started each one in the evening with a 10A charger too, and they were ready in the morning, rinse and repeat, remember that once you get them charged up you must set them up in parallel so that they can passively balance each other, they recommend 12 hours! But what I normally do is hook up the 12v charger while they are in parallel to speed things up, the next morning they are all equalized to the exact voltage; Now voltage is not an accurate way to determine the SOC of each battery so on my initial balancing cycle I went ahead and hood the capacity testers to each battery and got a good capacity reading from all of them, but that is optional I just wanted to make sure the batteries were within the specs, and it paid off because 2 of them ended up with lower capacity but still within spec. I got on the phone and explain the situation to the manufacturer and they issue a refund and said I could keep the batteries. I went ahead and adjusted the top and bottom voltages on my inverter to match the actual capacity limits of the bank and case solve. I'll keep them until the server type batteries drop in price and then I'll consider getting a few of those to check them out.

sunshine_eggo said:

Depending on the quality of the power supply connections (the stock ones are garbage), you may see the current drop before the battery terminals measure 14.5V but the supply reports 14.5V. If you've fabbed better leads, you're good to go.

Alternatively, since the batteries have a BMS, you can just set the voltage higher as they will cut off to protect themselves.

Click to expand...

I have a small (ish) follow up question(s)
i have a 2 x 12v 100AH lithium batts (with 50 amp BMS, over voltage, under voltage, short cct, and temp protection)
currently not setup on the off grid but will be set as 24v (2 batts in series)

Q1: i have a 5 amp CV/CC power supply, can i use this to slowly charge batts with the power supply set to 13.6 with it maxing out at 5amps

Q2: i also have a 20amp power supply, variable voltage (but no current control) can i use this to set at 13.6v and i presume it will pull 20 amps then current taper away as it reaches full charge.

Q3: i presume once the batt is fully the BMS will disconnect the inputs from the power supply`s?

Q4: not sure if this question will go here? can i set my inverter/charger to 27.2v (i can limit the charge current to 20AMPS) and let the BMS in the batts do the magic? I can turn off auto equalize. **Noting it`s not a "lithium" charger as such **
just figured i can let the BMS on the batts do the smarts of charging?
model: powmr hms-3k-24v

Cheers,
Richard

rgormley said:

I have a small (ish) follow up question(s)
i have a 2 x 12v 100AH lithium batts (with 50 amp BMS, over voltage, under voltage, short cct, and temp protection)
currently not setup on the off grid but will be set as 24v (2 batts in series)

Q1: i have a 5 amp CV/CC power supply, can i use this to slowly charge batts with the power supply set to 13.6 with it maxing out at 5amps

Click to expand...

If PS can be set to 14.4V, recommend you charge each to 14.4V until current drops below 2A

Then parallel and charge together @ 14.4V until current drops below 2A

rgormley said:

Q2: i also have a 20amp power supply, variable voltage (but no current control) can i use this to set at 13.6v and i presume it will pull 20 amps then current taper away as it reaches full charge.

Click to expand...

Should. Again, 14.4V is better.

rgormley said:

Q3: i presume once the batt is fully the BMS will disconnect the inputs from the power supply`s?

Click to expand...

No. The BMS does nothing unless a limit is exceeded. If the cell voltages do not go above limits, the BMS should do nothing.

rgormley said:

Q4: not sure if this question will go here? can i set my inverter/charger to 27.2v (i can limit the charge current to 20AMPS) and let the BMS in the batts do the magic? I can turn off auto equalize. **Noting it`s not a "lithium" charger as such **

Click to expand...

No. The BMS is safety equipment and should never be called to duty unless something goes wrong. Do not rely on it for routine termination.

Set charge to 28.8V and float to 27.0V.

ah ok thanks for all the answers
yes i mucked up my charge /float voltage (as you mentioned, i will set to Charge 28.8v and float at 27v)

rgormley said:

ah ok thanks for all the answers
yes i mucked up my charge /float voltage (as you mentioned, i will set to Charge 28.8v and float at 27v)

Click to expand...

i`m also assuming that the power supply that has a rated output of 20 AMPS will only push 20 amps into the batt, and once the voltages rises the current will taper off to around less than 2Amps ..... noting that i cant "set" the current, only the voltage (now at 14.4v)

my first charge with victron 15 amp took 2 hours at full 15 amps and then 2 hours on low to charge the last 5% for a total of 35 amp hours

sunshine_eggo said:

No. The BMS does nothing unless a limit is exceeded. If the cell voltages do not go above limits, the BMS should do nothing.

Click to expand...

After having the batts on the 5A PS (at this stage the volts was only set to 13.6 over night) the current dropped to 4.16 amps (with two batts paralleled.

I then hooked the 20 AMP power supply and set the volts to 14.4v across one battery, the battery drew initially drew 16 amps then dropped away after 15 minutes and was sitting on 10amps for 10mins i went away for a few mins and i came back and the charging had stopped ( batt volts at 14.4v (open voltage of PS) with zero current flowing to the batt

hhmmm i disconnected the PS and measured the volts on the battery...zero!! looks like the BMS disconnected the PS and stopped charging??
left the batt to sit for 10 mins and the volts were back at 13.73 .....

Q: is this all good and expected?
Q: why did the BMS drop the charging?

the battery spec sheet says charge at 14.6v so i was actually under this value....

i`m charging the other batt now with the same 20AMP PS set at 14.4v it`s been on for 15 minutes and the current is sitting on 16 amps and slowly dropping (volts across batt 13.67)

UPDATE: after 45 minutes as soon as the volts hit 14.4v current at 3.85 amps (i was watching it) the charge current stopped...hhhmmm is this normal?
open no load volts with the PS disconnected is 13.62v

yes and this is why i have posted in the someones newb thread...

should i try dropping the charge voltage to 14.3v and see it it charged that little bit longer


or is the battery fully charged? simple as that?

.

What you are seeing is normal as the BMS is shutting down due to cell overvolts. Many 'drop in' batteries do not have fully balanced cells and at high charging volts a small variation in cell capacity will cause one cell to reach protection level. Once the charger is removed the cell voltages will fall and once below the recovery voltage the BMS will reactivate the charge path.

You could consider the battery fully charged.

When you make up the series battery assembly the charging voltage used should not cause protection in any of the 12v batteries, so 28.8 volts may be too high for a 24 volt system.

In series as a 24 or 48 volt pack it's probable the batteries will become out of balance as 'batteries' over time, as its very unlikely they will be matched in performance.
Mid point balance devices may need to be installed.

For a 24 or 48 volt system it's more ideal to use 24 or 48 volt batteries rather that strings of 12v batteries.

Mike

mikefitz said:

What you are seeing is normal as the BMS is shutting down due to cell overvolts. Many 'drop in' batteries do not have fully balanced cells and at high charging volts a small variation in cell capacity will cause one cell to reach protection level. Once the charger is removed the cell voltages will fall and once below the recovery voltage the BMS will reactivate the charge path.

You could consider the battery fully charged.

When you make up the series battery assembly the charging voltage used should not cause protection in any of the 12v batteries, so 28.8 volts may be too high for a 24 volt system.

In series as a 24 or 48 volt pack it's probable the batteries will become out of balance as 'batteries' over time, as its very unlikely they will be matched in performance.
Mid point balance devices may need to be installed.

For a 24 or 48 volt system it's more ideal to use 24 or 48 volt batteries rather that strings of 12v batteries.

Mike

Click to expand...

thanks Mike for the info...
i have a 5 amp balancer on order to help with the series linking out of balance problem,, (HC01) from fleebay

as a further observation, as i was watching the batts charge in real time when it hit excatly 14.4 the charge stopped (it was charging at 2 amps)

i left to do some other stuff then came back 5 minutes later and it reconnected and started to charge again, very quckly went to 14.2v charging at 1,3 amps then hit 14.4 and stopped again.

waited 3-4 minutes and it is charging again went to 14.39v and charging at 300mA been like that for 15 minutes
now toggling 14.3 /14.4v at 250mA
-20 minutes now and still at 14.3v / 14.4v 240mA

it like its "topping" up the last bit of the battery..???

---14.4v @245mA and holding....
maybe the BMS cant detect the negative delta voltage curve this time as the charge current and voltge rise is so small/slow?? hence why it`s not terminating the charge

I presume the 200 mA now is not going to worry the battery if i leave it on overnight? (100ma per bat as i have 2 in parr at the moment)
maybe just powering the BMS only?

My few cents wrt charging LiFePO4 batteries :

Some 12.8V (4S) LiFePO4 BMSs cannot handle the higher voltages that can occur if you put them in series to get a "24"V or higher voltage system.
as mentioned above -better to use a battery bank with BMS prepared for the total system voltage (so an 8S BMS for a 24V system).

What a BMS will do is constantly monitor lowest voltage cell and highest voltage cell. When charging it is the the cell with the highest voltage which is at risk at overcharging (if excessive with risk of damage, fire ...) so a charger should have ïnter active communication to be aware of this and stop charging.
A limitation on the total charger voltage can -if blind (=not informed by BMSs) not be aware that although total voltage appears to be OK for a healthy battery there could be -in case of unbalanced cells- still be a dangerous situation in which some cells are far from full another cell is above its "safe" limit (at which charging should be stopped).

If BMSs also have active cell balancing the adjacent cells (lower voltage) around the higher voltage cells will transfer some of their respective charge to the cells who still can absorb more to reach a proper full charge level. But this rebalancing happens with relatively low current so it can cause the charger to switch off (and on) several times before cells under control of BMS are properly balanced..

LiFePO4 batteries do have several advantages versus conventional lead acid batteries but they are more dangerous when charging is continued when "max"cell voltage of one voltage is reached (while for liquid lead acid batteries you 'll just have to add some distilled water if required.. Also trying to charge LiFePO4 batteries at temp below 5 degree Celcius can seriously damage them or kill them... so the system "around" them should take care of that...

rgormley said:

it like its "topping" up the last bit of the battery..???

Click to expand...

Sorta. It's topping of the lower cells as the BMS burns off excess from the high cells.

rgormley said:

---14.4v @245mA and holding....
maybe the BMS cant detect the negative delta voltage curve this time as the charge current and voltge rise is so small/slow?? hence why it`s not terminating the charge

I presume the 200 mA now is not going to worry the battery if i leave it on overnight? (100ma per bat as i have 2 in parr at the moment)
maybe just powering the BMS only?

Click to expand...

This is fine. The battery BMS is balancing the cells. You should be able to charge to 14.4V without triggering BMS over-volt protection.

After the full charge and balance last night with the two batts in parrallel i hooked the two batts in series and connected them into the system

hhmmm i have a problem i think... ??

the batts are charging and disharging (cycling) every 10 -15 minutes pulling 20 amps from the batts then sags in voltage ..

once it hits the 25.5v (inverter low set point to start the charger again) it then charges at 20 amps and once it it hits the high set point (28.5V) it stops charging and repeats the cycle (discharge back down to 25.5V)

when on charge the voltage rises back to 28.5 (14.2 per batt) in the space of 10 min or so.

i would have thought that pulling 20 amps from the two batts would give me a much longer run time..

any thoughts on what i can do/test/ adjust?

attached is a screen shot of my inverter settings (i`m a newb at this so they may be tattlay wrong??)

thanks in advance....

What gauge wire are you using, and have you confirmed that all connections are of high quality and properly torqued?

the main feeder cables from the batts to the shunt / DC breaker and then back to the inverter are 16mm sq
the link cabel betwwen the two batts is a 70mm SQ

all crimped with a professianal crimp tool

are you thinking voltage drop? i can go and measure across the cables to see if there is anything significant?

The low set point seems to be set too high at 25.5. You may have cable and fuse/ breaker volt drops to also deal with.
Any DC breaker in the feed is suspect unless a quality item.
Try reducing to a lower value, 24.0 volts or even lower at 23.5 volts.
28.5 volts charge may be causing BMS protection to cut off the charge.

16mm2 cable has 0.025 volts drop per meter at 20 amps so the cable itself shouldn't be an issue.

Mike

rgormley said:

the main feeder cables from the batts to the shunt / DC breaker and then back to the inverter are 16mm sq
the link cabel betwwen the two batts is a 70mm SQ

all crimped with a professianal crimp tool

are you thinking voltage drop? i can go and measure across the cables to see if there is anything significant?

Click to expand...

Ensure proper torque. 16mm should be fine for the 20A you're pulling, but it would be a good idea to check for voltage drop.

mikefitz said:

The low set point seems to be set too high at 25.5. You may have cable and fuse/ breaker volt drops to also deal with.
Any DC breaker in the feed is suspect unless a quality item.
Try reducing to a lower value, 24.0 volts or even lower at 23.5 volts.
28.5 volts charge may be causing BMS protection to cut off the charge.

Mike

Click to expand...

Agree with this. Wanted to check connections/cabling first before I mentioned it.

Your charger also appears to be like the Growatt that starts at low voltage and immediately terminates once high voltage has been achieved - no absorption. If that's the case, you should raise your charge voltage to 28.8V to make sure you're getting close to full charge.

mikefitz said:

The low set point seems to be set too high at 25.5. You may have cable and fuse/ breaker volt drops to also deal with.
Any DC breaker in the feed is suspect unless a quality item.
Try reducing to a lower value, 24.0 volts or even lower at 23.5 volts.
28.5 volts charge may be causing BMS protection to cut off the charge.

16mm2 cable has 0.025 volts drop per meter at 20 amps so the cable itself shouldn't be an issue.

Mike

Click to expand...

had to go to sleep last night ...
anyway this morning measured the volt drop across the entire system
batt volts 27.1 pushing 18 amps into the batts
see the attached photo it shows all the voltage drops in mV across each section. measured on the bolt or connection ternimal screw
inverter/charger powmr hms-3k-24v yeah i know.....buy crap get crap.... but it`s so far so good! mppt works well

--udate 4:15pm--

pannels been in full sun all day
have the bulk charge set to 28.6 and the float at 27.6
couple of things i did and noted...

1: if i disconnect and reapply the PV source (off for 30 seconds then re-connect) the inverter switches over and runs purely on bateries (expected)
2: during this period the batts dip to 26.6v and pulling 22amps from the bank. (couple of fridges and misc items running)
3: once the inverter sees the panels back on and MPPT kicks in it will charge at 20A untill the batts hit the bulk voltage of 28.6 within 2 minutes, then the inverter will drop the charge rate and it will settle back down on 27.6, (float) at around 2 or 3A

Q: I presume that batteries are fully charged that`s why when it pushes the 20 amps up to the bulk charge voltage and then sinks back to float voltage within minutes.

does this sound all normal??

it will be interesting to see what happen when the sun goes down... i have the chargeer low voltage "recharge" set at 24V so i presume i will see the power draw down to this level and then the mains part of the inverter/charger will kick back it and float them??

sorry, you guys must roll your eyes at us.... but we all started from a low base...
thanks....

rgormley said:

does this sound all normal??

Click to expand...

Yes.

rgormley said:

it will be interesting to see what happen when the sun goes down... i have the chargeer low voltage "recharge" set at 24V so i presume i will see the power draw down to this level and then the mains part of the inverter/charger will kick back it and float them??

sorry, you guys must roll your eyes at us.... but we all started from a low base...
thanks....

Click to expand...

Consider that your inverter likely consumes 40-50W ALL THE TIME. That's 1080Wh/day or 45Ah of your battery capacity. This happens even if you don't pull any loads from it. If you have two 100Ah batteries in series, your inverter is consuming almost 50% of your battery capacity.

my mdel is not a growatt it`s a powmr HMS-3K-24V
inverter spec mentions no load and power saving consumption
i presume this is the power consumed when it`s turned on but doing nothing anything... if so how do i know how much power it using when actually inverting and and doing it`s job? eitherway it`s a mute point as i cant do anything about that, other than adding more storage..




Also this may be a huge "no no" but i will ask.....

As mentioned my batts may not be getting a full charge as the charger aspect of the inverter may stop charging as soon as it`s hits the upper bulk voltage.
so what about i set a "safe" equalzastion charginging phase time say for 2 hours?? i can set a few parameters in this setting..
say
EQ volts 28.8
EQ time 2 hours
EQ time out 2 hours
EQ interval every day

or is this something that i should not go near as it will damage my batts. (although i presume the BMS will cover that concern?)
this screen grab from the manual/PDF...