John Frum
Tell me your problems
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Nope the top in top balance means full.
Voltage best indicates state of charge at the extremes.
LiFePO4 charging voltage
- Thread starter krell313
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Voltage best indicates state of charge at the extremes.
krell313
New Member
This is where I got those numbers. I would probably use something like 90 to 95-20 or so
Ampster
Renewable Energy Hobbyist
I had to remind myself that this was a golf cart. I think his concept is to charge to 3.4 volts per cell and be conservative in deciding how far to drive. There is a persistant range anxiety among many of us EV drivers. We often don't use the full capacity of our batteries, especially when running errands. In fact I usually only charge to 80% unless I am going to need more than 200 miles of range.
Anectdotally, my wife got over her range anxiety when she ended up at a friend's house without enough estimated range to get home. She quickly figured out that if she drove slower the EV would go farther. She got home safely and plugged in and was pleased with her new found freedom.
Little did she know that the EV went into Limp mode for part of that drive.
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Ampster
Renewable Energy Hobbyist
My testing indicates 3.4 to 3.0 is much closer to 95% and 5%. Depending really on how long you keep it at 3.4v, it can also mean 98%.
topperharley
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Just got some cells, all 3.32. ive been charging using that charger from wills video, kind of a slow charger... What the average time it takes to charge up to 3.65v from that? Been charging for several hours, only up to 3.35v.
Dozens of threads with folks concerned about why the voltage isn't increasing.
Reason: almost all of the charging of LFP occurs between 3.3 and 3.4V.
Generally speaking as-received cells are at 50%. Assuming 280Ah cells, they each need 140Ah.
If you're charging at 10A, you'll need 14 hr/cell. You will think something is wrong and that nothing is working. "I'm certain something is wrong with my cells, they're just not charging!"
They are. It just takes patience.
topperharley
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Thanks for the info. My worry was leaving the charger on for too long, like over night or while I'm at work and it finish charging and I'm not there to turn it off. My cells are 200Ah so hopefully not much longer to go. I do see the voltage increasing, just not as quickly as i thought, expected cells to be at least 80% charged on arrival.
First, make sure your power supply is disconnected from the cells. Then using your meter, adjust the voltage on the power supply (not over 3.65 volts) and set the current to max. Then you can connect to the cells, and be confident you won't overcharge your cells. If you have good quality leads to connect to the cells with, your power supply should show max amps and the current cell voltage (don't adjust the voltage).
The resources section has an excellent tutorial, I highly recommend you read it and follow it, it answers 99% of your questions.
Top Balancing LiFePo4 Cells using a low cost benchtop power supply.
To get the paper, click on the orange at the top of this page. This is a tutorial with detailed steps on how I top-balance my LiFePO4 Cells using a low-cost benchtop power supply. To get the tutorial, click on the orange "Download" button...
diysolarforum.com
topperharley
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Yup, did all that, followed the steps from wills video. Even tho the amp slows down to milliamps, i was still worried about it charging for a while at that state of i couldn't get to it for a while or something, since they're no bms to cut the charge. I'll check out the link as well, thanks againFirst, make sure your power supply is disconnected from the cells. Then using your meter, adjust the voltage on the power supply (not over 3.65 volts) and set the current to max. Then you can connect to the cells, and be confident you won't overcharge your cells. If you have good quality leads to connect to the cells with, your power supply should show max amps and the current cell voltage (don't adjust the voltage).
The resources section has an excellent tutorial, I highly recommend you read it and follow it, it answers 99% of your questions.
Top Balancing LiFePo4 Cells using a low cost benchtop power supply.
To get the paper, click on the orange at the top of this page. This is a tutorial with detailed steps on how I top-balance my LiFePO4 Cells using a low-cost benchtop power supply. To get the tutorial, click on the orange "Download" button...
If it slows down to milliamps before the cell voltage is over 3.6v, you need better cables.
Even with better cables, if the power supply is set correctly (and doesn't die), it won't over charge. The voltage setting is the BMS in this instance, can't charge to over 3.65v if the power supply doesn't put out more than 3.65v. That's why it is critical you set the voltage correctly.
