I just finished building a charger out of a solar yard light and a USB power supply. I was using it to charge the lifepo4 14500 cells they sell at walmart. It works fine for charging cells but it does not stop charging them when they are done. So at what voltage should I pull them off at? I left one in for 12 hours straight and it went up to 4.8 and then stopped so is that safe? Thanks.
Hey Scaru, I didn’t know those yardlight batteries were 14500. Are they any good?I don’t know anything about LIfepo4 chemistry…so I can’t help you with the termination charge voltage.What are you using these cells for?-Rick
Not all of them are. I had got this one on sale for 2 dollars and was surprised to see the lifepo4 in it. As to the quality it sucks. It had one 10 mm LED in it and it barely turned on. The battery was fine though it was 400 mah and it is currently in my 14500 minimag.
I think I saw the batteries being sold in packs of two….I ’ll have to check later, I noticed they were AA sized…but assumed they were 1.2volts.Gotta run…have a great afternoon!-Rick
Charge LiFe PO4 to 3.6V (3.4V for a long term float charge). Discharge to 2.5V There is very little capacity between 3.0V and 2.5V. For longest life, set the LVC to 3.0V
Here is some of my testing of the A123 M1 cells:
Thanks. I guess I'll just hook up my multimeter to it so I can keep and eye on the charging.
If you set the charger voltage to 3.4V … 3.6V then you can pretty much just let them sit on charge. When the cell gets full, the charge current drops to close to zero and it stops charging (particularly at 3.4V, the recommended float charge voltage). I charge my single cells with a current limited lab supply set to 6A, 3.6V
I don't have anything that complicated. This is an old yard light where I wired it up to USB to power it to charge the battery.
I just checked my iCharger’s Standard Battery Parameters on LiPo, then on LiFe
LiPo / LiFe
nominal voltage: 3.7V / 3.3V
Max charge voltage: 4.2V / 3.6V
Storage voltage: 3.85V / 3.3V
Allowable fast charge: 1C (max) / 4C
Min. discharge voltage cut-off level: 3V / 2.0V
But I’m not sure about the difference between a LiPo and and and LiFe4
Uh… It’s not LiPo4. It’s LiFePO4.
The difference is that “Po” in LiPo is short for Polymer (so LiPo = Lithium Polymer), while “PO4” in LiFePO4 is chemical for “phosphate” (so LiFePO4 = Lithium Iron Phosphate)
Sorry Scaru,
Your post was made while I was editing my original post.
You really cant determine the proper storage condition or state of charge for a LiFePO4 cell from its voltage. Almost all the capacity (90% down to 10%) is from 3.3V to 3.1V (with 3.2V nominal).
Above 3.3V is almost certainly an almost full cell. Below 3.0V would be an almost empty cell. You really can’t say with any certainty between those two voltages.
You want to store them at 50% charge. The only way to properly storage charge them is to:
- discharge the cell
- fully charge the cell and measure the mAh you put in
- drain half that amount of mAh from the cell.
If you have only a volt meter, then 3.1V would be a better value to use.
Do any of you know can Lifepo4s vent with flame? Mine went up to 4.8 but it came back down to 3.4.
Does anyone know the difference between a ‘regular’ liFe and the LiFePO4?
My RC friends use the LiFe batts on their electric helis and planes. Discharge rates up to 45C !
It’s possible, but not likely. The chemistry is very stable and does not have the positive feedback/thermal runaway characteristic of LiPO. Flames come from the electrolyte solvent catching fire. One can always imaging ways for that to happen. I’ve seen A123 cells charged at over a 100C rate (under 60 seconds) without any drama.
Overcharging to 4.8V definitely is not a good thing.
LiFe is just another name for LiFePO4.
LiFe is just the way HobbyKing wrongly labels their Turnigy LiFePO4 batteries.