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Hi Reed - looks like you are doing good so far. I've got some additional GBS cells headed my way, so your timing is good.
When you say you've reached float, I hope that your float voltage (which is unnecessary for lifepo4,) is not high, and low enough to be benign, although still active. If you could disable float, that would be even better.
In regards to your question - this brings up something I'm researching right now about "micro-cycle" life degradation of LFP. From what I've garnered so far, doing a micro-cycle repetetively leads to higher internal resistance and loss of capacity. But what exactly a micro-cycle is for LFP I'm still researching. Is it 10% DOD, 20%, 30% ?? Maybe Sunking can help us out here.
This is a different issue than overall charge voltage, which hopefully you've lowered to around 3.45 - 3.5v per cell. No need to go higher unless you need that for balancing purposes.
While I'm researching the micro-cycle DOD issue, I'm going to try and achieve at least 20-30% DOD per cycle to CYA. Perhaps it is less, I don't know yet. T1 Terry may have more info than I do about it. Heh, in your case with over-capacity, perhaps an even lower voltage would be advisable, like 3.4 volts so you cycle starting from 20% DOD right off the bat in a PSOC environment. Maybe just a weekly 3.5/3.6v higher voltage to check balance.
Interesting update: I found on some recent CALB spec sheets, in addition to the normal HVC and LVC damage points, along with "recommended" normal use voltages, suddenly there appeared a spec for "recommended DOD" cycling! Guess what - they list as 10-90% DOD, emphasizing the need to not always charge up to 100% SOC. Personally, I'm not going to go as low as 90% DOD, as I find that I'm well into the steep discharge knee at that point. (at least with my GBS cells).
When you say you've reached float, I hope that your float voltage (which is unnecessary for lifepo4,) is not high, and low enough to be benign, although still active. If you could disable float, that would be even better.
In regards to your question - this brings up something I'm researching right now about "micro-cycle" life degradation of LFP. From what I've garnered so far, doing a micro-cycle repetetively leads to higher internal resistance and loss of capacity. But what exactly a micro-cycle is for LFP I'm still researching. Is it 10% DOD, 20%, 30% ?? Maybe Sunking can help us out here.
This is a different issue than overall charge voltage, which hopefully you've lowered to around 3.45 - 3.5v per cell. No need to go higher unless you need that for balancing purposes.
While I'm researching the micro-cycle DOD issue, I'm going to try and achieve at least 20-30% DOD per cycle to CYA. Perhaps it is less, I don't know yet. T1 Terry may have more info than I do about it. Heh, in your case with over-capacity, perhaps an even lower voltage would be advisable, like 3.4 volts so you cycle starting from 20% DOD right off the bat in a PSOC environment. Maybe just a weekly 3.5/3.6v higher voltage to check balance.
Interesting update: I found on some recent CALB spec sheets, in addition to the normal HVC and LVC damage points, along with "recommended" normal use voltages, suddenly there appeared a spec for "recommended DOD" cycling! Guess what - they list as 10-90% DOD, emphasizing the need to not always charge up to 100% SOC. Personally, I'm not going to go as low as 90% DOD, as I find that I'm well into the steep discharge knee at that point. (at least with my GBS cells).
but thanks for the info! Perhaps others might be interested!
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