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What is the point in charging Lifepo4 all the way to 14.4v when we have about 99.8 SOC at 13.88 v ?

Danny

Danny

Solar Enthusiast
Joined
Sep 21, 2019
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I'm getting a bit frustrated because I'm finding many chargers are not custom programmable and they charge to 14.4 vdc pack voltage and my Calb 180ah charge cutoff at 3.6vpc or 14.4 pack voltage. Rod at Marinehowto.com has this chart https://marinehowto.com/wp-content/uploads/2015/09/28-LiFePO4-On-Boats.jpg and this article https://marinehowto.com/lifepo4-batteries-on-boats/ that states 13.88 is about 100% full. Yes. I top balanced my pack when I built it. To be safe, I just charge to 13.8 and I'm not giving up much SOC and my batteries will likely last longer. Am I missing something?
 
frankly i do not think a 0.5V will change something about the battery life.
An LFP can go up to 4.2v (so over 16V). if you feel the battery is heating too much at the end, you can stick to lower voltage to see if the temperature goes cooler.
 
nosys70 said:
frankly i do not think a 0.5V will change something about the battery life.
An LFP can go up to 4.2v (so over 16V). if you feel the battery is heating too much at the end, you can stick to lower voltage to see if the temperature goes cooler.
Click to expand...

The cell voltage needs to stay below 3.6 *if* all cells are the same and they are not in my case. Do you agree that not much is gained in energy storage above 13.88? Do you think I should cross the 3.6vpc line? What should my BMS be set to limit VPC? I must be not seeing something.

Capacity: 180Ah
Height: 280 mm (11.02 inch)
Width: 71 mm (2.80 inch)
Length: 180 mm (7.08 inch)
Weight: 5.6kg (12.35 lbs)
Bolt Size: M8
Voltage nominal: 3.2V
Charge voltage cut-off: 3.6V
Discharging cut-off: 2.5V
Life Cycle (0.3c Charging-Discharging, 80%DOD): 2000
Maximum Discharging Current (10 sec.):10C - 1800 Amps
Internal Impendance (1khz Ac, m-&#8486): Less Than 0.8
Chemistry: LiFePO4
Warranty Period: One year factory warranty on manufacturing defects.
 
your settings are ok on the high side, (you can even got up to 3.65) , you can also even go higher on the low side. 2.5V is pretty low.
 
smoothJoey said:
See this link powerstream
2 reasons I can see for charging to 14.4 or higher.
1. Force your pack to balance.
2. gets to absorption phase quicker.
Click to expand...
Good link . "Third, there isn't much difference in capacity when charged at 3.4V or 4.2 volts. Maybe 3% maximum. So surprisingly you can charge one of these cells at 3.4V and get almost the same capacity as charging at the recommended 3.65V. " Thanks. I don't want to risk my individual cells going above 3.65 so I'll stay at around 13.8. I'm not buying chargers hard set to 14.4 because I"m going to avoid untrusted balancing on my BMS. Thanks. Danny
 
Danny said:
Good link . "Third, there isn't much difference in capacity when charged at 3.4V or 4.2 volts. Maybe 3% maximum. So surprisingly you can charge one of these cells at 3.4V and get almost the same capacity as charging at the recommended 3.65V. " Thanks. I don't want to risk my individual cells going above 3.65 so I'll stay at around 13.8. I'm not buying chargers hard set to 14.4 because I"m going to avoid untrusted balancing on my BMS. Thanks. Danny
Click to expand...
I am with you Danny the only real reason I ever get my batteries to the top is to help balance them and then I watch them like a hawk.. Other than that it is not worth the extra effort and risk to max them out.
 
Craig said:
I am with you Danny the only real reason I ever get my batteries to the top is to help balance them and then I watch them like a hawk.. Other than that it is not worth the extra effort and risk to max them out.
Click to expand...
I bought my used batteries for $400 and I've watched my individual cells go 20mv of balance above 13.85 pack voltage where they are nearly full. Your statement perhaps out of context... "it is not worth the extra effort and risk to max them out".. Is my impression is what should be told to beginners and DIY pack builders as best practice. My used batteries are in balance otherwise +-5mv. Maxing out appears to be the way many chargers are programmed by default and I don't think it is the best way based on charge curve evidence. Too often the DIY beginner is not warned about the risk. Marinehowto.com has exposed the risk vs the reward but but don't understand why very smart knowledgeable people continue to to charge to 14.4 relying on their BMS to balance when this can be avoided almost without sacrificing any (very little) SOC. I'm going to give up on my quest to expose this issue. I guess It is not as important as Rob at marinehowto.com makes it out to be. Some very smart people are not afraid of maxing out their vpc so I must be over reacting. Thanks for your time in this discussion. You are very knowledgeable.
 
Im all new to this and find this very interesting. I have yet got anything built but when I do and if need to be program my BMS as it should be or what is practical.
 
The only time that I wish that I spent the time trying to make heads or tails out of my SCC's poorly written charge profile programming instructions is when my BMS shuts my lifepo's down due to low voltage at the very moment that Captain Picard is giving the order to launch photon torpedoes towards where he thinks that a cloaked Klingon warship may be hiding. Other than that I don't care about an extra 6/10 of a volt maximum charge.
 
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tim0shel said:
Im all new to this and find this very interesting. I have yet got anything built but when I do and if need to be program my BMS as it should be or what is practical.
Click to expand...
The problem is if your cell voltages vary when at a full state of charge, your BMS will shut off your pack if you go above say.. 3.65 vpc and the Captain will be caught with his shields down. Turning down your charger charge voltage to say 13.8 will avoid this potential problem but most people don't worry about this apparently. I like my shields up.
 
offgriddle said:
The only time that I wish that I spent the time trying to make heads or tails out of my SCC's poorly written charge profile programming instructions is when my BMS shuts my lifepo's down due to low voltage at the very moment that Captain Picard is giving the order to launch photon torpedoes towards where he thinks that a cloaked Klingon warship may be hiding. Other than that I don't care about an extra 6/10 of a volt maximum charge.
Click to expand...
Scotty, What is your BMS cell vpc cuttoff to keep the dilithium crystal cells from melting down. My crystals don't like vpc above 3.65? If the cutoff hits on the high end you will lose your shields!
 
you also need to take in account that voltage measured on the charger is not always what your get at the battery terminal
 
nosys70 said:
you also need to take in account that voltage measured on the charger is not always what your get at the battery terminal
Click to expand...
Right! This is a good point and this may be why more batteries are not blowing up because most chargers are reading themselves and the actual battery terminal voltage is lower because of wire voltage drop etc. The latest DC DC charger from Renology Will reviewed does have a separate voltage sense wire but chargers at 14.4 and this could cause and issue. My balmar 614 and Sterling B 2 B chargers all have voltange sense for battery voltage. My victron MPPT CC is using smart battery sense.
 
Danny said:
The cell voltage needs to stay below 3.6 *if* all cells are the same and they are not in my case. Do you agree that not much is gained in energy storage above 13.88? Do you think I should cross the 3.6vpc line? What should my BMS be set to limit VPC? I must be not seeing something.

Capacity: 180Ah
Height: 280 mm (11.02 inch)
Width: 71 mm (2.80 inch)
Length: 180 mm (7.08 inch)
Weight: 5.6kg (12.35 lbs)
Bolt Size: M8
Voltage nominal: 3.2V
Charge voltage cut-off: 3.6V
Discharging cut-off: 2.5V
Life Cycle (0.3c Charging-Discharging, 80%DOD): 2000
Maximum Discharging Current (10 sec.):10C - 1800 Amps
Internal Impendance (1khz Ac, m-&#8486): Less Than 0.8
Chemistry: LiFePO4
Warranty Period: One year factory warranty on manufacturing defects.
Click to expand...
I don’t understand your question I guess... with a cutoff voltage of 3.6v/cell, you are charging to 14.4

what is the question I guess?
 
Supervstech said:
I don’t understand your question I guess... with a cutoff voltage of 3.6v/cell, you are charging to 14.4

what is the question I guess?
Click to expand...
My cells are not all 3.6 volts at the upper part of the knee on charging curve. In fact I have a 4S and cell 1 is 200mv above my lowest cell. Pushing the pack voltage charge to 14.4 can bring my highest cell above 3.6 for no good reason. Better to let your charge voltage for lifepo4 lower if there is no gain to be had by charging above 13.88 pack voltage. See the article reference links about it explains it what my situation is. Thanks for your response.

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