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Most useful article I've ever found on LFP battery charging

So...from a discharge, charge to 50% (let's say), then I leave it for weeks. Isn't that exactly the condition described in paper as creating the memory effect? That's the source of my confusion.

I thinks it's the repetitiveness that people think causes the problem...daily cycles to the exact same charge level. One charge or discharge to storage voltage should not be a problem, and is better than the alternative (permanent capacity loss from storing at full charge).
 
Re Memory effect. If I plan to store a LiFePO4 bank for weeks or months how should I treat it? Full-charge (using the paper's definition of full-charge, a CC phase followed by a CV phase that ends at C/20 or lower current)? I thought leaving LFEs at full charge shortened their life? Full charge followed by a shallow discharge (maybe down to 90%?)
What are LFEs or do you mean LFP for LiFePo4?
 
Nothing wrong with trying to understand LFP before getting them, now that you have them put the batteries in to some sort of real life daily use to see how they actually behave instead of confusing yourselves reading other noobies non sencicle no experience post. ;)
 
confusing yourselves reading other noobies non sencicle no experience post. ;)

When they are discussing in a thread about a couple of papers written by someone who obviously did their homework, I don't think that comment is very nice, sarcastic or not. As you mention in the first part of your reply: "nothing wrong with trying to understand LFP".
 
When they are discussing in a thread about a couple of papers written by someone who obviously did their homework, I don't think that comment is very nice, sarcastic or not. As you mention in the first part of your reply: "nothing wrong with trying to understand LFP".

Assuming that we (meaning all of us posting) have used quality parts throughout the entire system and have the proper safe guards in place for protection of individual components and have proper safe guards set up for the batteries or cells. The next step is pick your poison (voltages) for daily operation. Take notes if you must for comparison down the road and to refresh your memory/ experience for the behavior of the system as a hole or batteries at misc voltages with loads.

Here is sample of something that I posted in another thread (post 30) that I use. There is more info in my excel sheet but not all will fit when doing a screen shot from my tablet that It's recorded on. I also have recorded in another excel sheet daily power produced and used from my pv system going back 3 years. The only thing I wished I would of done is started from day 1.

 
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I'm not arguing against that at all. As I mentioned before in a post, I don't think it's a major issue, or that the sky is falling. However as new, properly sourced data presents itself, as an engineer, looking at it without prejudice is a must. Therefor calling everyone doing that "noobies non sencicle no experience" is what triggered me. If we look at the data objectively and it allows us to make better systems because our knowledge of the systems get better, then we should strive to do this.
 
So...from a discharge, charge to 50% (let's say), then I leave it for weeks. Isn't that exactly the condition described in paper as creating the memory effect? That's the source of my confusion.

If I understood the article correctly *and* based on what a lot of the manufactures say about storage. It sounds like the best way to store would be to start from a full charge (ideally full charge is detected by current) and then discharge to 40-60% before storage.
 
If I understood the article correctly *and* based on what a lot of the manufactures say about storage. It sounds like the best way to store would be to start from a full charge (ideally full charge is detected by current) and then discharge to 40-60% before storage.
Thanks @FilterGuy for your astute logic. My block chains are now back in proper order.
 
We still need what is effectively a "equalization" charge periodically and I have no idea of how to automate that with my Midnites. I might have to rig something up with a power supply and long duration time delay relay control boards for once a month or so after the system gets inspected by the county after install is complete.
Not always. If allowed to under charge long enough, it may become a permanent loss.
Connect your pack and charge it while watching the ammeter, when the ammeter drops to zero or within a amp or so disconnect the charging source. Don't let it 'float' at max capacity as that degrades the battery.
Watch the voltage while charging, if it goes over 3.6v/cell reduce it.

So, exactly what @Steve_S has in the Chargery BMS,
Over Voltage Disconnect, controlled by BMS at user programmable set point.
Under Voltage Disconnect, controlled by BMS at user programmable set point.
Both using line relays for positive disconnect.

Controlled Amp rate charge based on 'C' rating,

Balancing both during charging and discharging...

Oh my God, red line has slightly deviated from the black line, call the Nobel Prize committee, we discovered that sky is falling on all LFP batteries.
This will be chewed, regurgitated, chewed again and again until no longer recognizable in all social media for the next 10 years.
You guys are a funny bunch... :ROFLMAO:

*IF* there were more people building (and less talking) these issues would be hammered out (like Steve_S has already done),
And the conversation would be about which charge controllers/BMSs have which options the user can program.

You would be talking charge balancing, discharge balancing, disconnect voltage both upper and low, 'C'/Amperage rates in charging, and lets not forget not only the bottom temp charge shutdown, but temp of cells as they charge.
 
Really interesting reading on memory effects of LFP in the Nordkyn articles. I am just starting with my BYD 24 v batteries which appear to have a memory effect in place. I use a MeanWell power supply feeding power into my only two charge controllers: ToolKitRC M8S and ISDT T8. They have very different high voltage protection functions. The M8S allows me to set a high voltage cutoff in a very limited range of (3.55 - 3.65). When the first cell reaching that voltage it disconnects itself from the battery. However, the MeanWell just keeps happily sending power to the M8S which just ignores it. For an automated system this would not work. The ISDT on the other hand uses the high voltage disconnect setting to keep the first cell at that voltage and then continues to charge up the other cells until all cells are at that same voltage. The current is indeed drastically reduced to about 0.5 - 3 amp (down from 10 amp bulk charge) during this time bringing the cells to the same voltage. So the T8 is a great top balancing charge controller whereas the M8S is NOT. Neither one actually STOP the charging process in the sense of turning off all charging power. They do however disconnect themselves from the battery, so for manual supervision like I am doing now it works fine.

Question: are there actually Grid powered chargers that will STOP charging and turn themselves off when a user set HVC value is reached? This question is germane to this thread because if we need twice per year to charge up to 3.6 VPC and at other times be more conservative and charge only up to a 3.4 - 3.5 VPC cutoff then we have to have a charger that will directly allow that.

Note I have not yet ever installed or used a BMS on my BYD batteries. But from Will's videos and other info my understanding is that a BMS will disconnect the battery from either charging or discharging upon user controlled HVC and LVC and H/L temperature cutoff. But a BMS cannot switch off inverters, chargers, or SCC except through relay connections to their on/off switches. Is this understanding correct?
 
Hi, I am planning a 10 kWh system for a tiny house that will operate off grid. The battery is large compared to the number of panels. So, the maximum charging current will be about only 0.05C. In that case there is not really a need for an absorption phase. You can just stop charging when the cut-off voltage is reached. So, it is probably okay to work with a cut-off voltage of 3.5 or 3.55V normally, and occasionally set it to 3.6 or 3.65V.
I am just not sure what would be the best strategy to decide when to start charging again. Using a lower voltage to start charging again is tricky because voltage will depend on loads (the inverter will be quite a load and could trigger the charger again).
Maybe counting coulombs until 5% of the charge has gone?
I will be building a solar charger based on an arduino, so I can implement any strategy that I can think of.
 
Hi, I am planning a 10 kWh system for a tiny house that will operate off grid. The battery is large compared to the number of panels.

I'm curious what factors influenced your decision to build such a large battery bank relative to your solar array?
 
Well, the tiny house is for my daughter, who is building it now. They have a full-size washing machine, fridge, and she works on the laptop the whole day. She has calculated to use about 1800 Wh per day. In the winter they will live in Austria or Norway and there will be periods when there will not be much sun. The roof area for panels is very limited. So, the more capacity the better. And with some over capacity, you can run the cells with a low DOD which will be good for the lifetime of the battery.
 
Well, the tiny house is for my daughter, who is building it now. They have a full-size washing machine, fridge, and she works on the laptop the whole day. She has calculated to use about 1800 Wh per day. In the winter they will live in Austria or Norway and there will be periods when there will not be much sun. The roof area for panels is very limited. So, the more capacity the better.
And with some over capacity, you can run the cells with a low DOD which will be good for the lifetime of the battery.

I agree with you, but the benefit of overcapacity comes down to the ratio between battery capacity and consumption between charges, not battery capacity vs solar input.

If roof space is the limiting factor, there isn't much you can do to get around that, but there are vans with 1 kW of solar on the roof, so I would be surprised if there weren't a way to fit more than 500 watts. If I were in here shoes, I would be concerned with that small amount of solar. It may be just enough, but its cutting it really close. At the end of the day power in must exceed power out, a larger battery bank can extend the length of time you can run at a deficit, but it can't make it sustainable.

At 90% efficiency and 5 hours of full sun she is looking at generating 2250 Wh per day, At 70% efficiency she's looking at 1750 Wh per day. At 4 hours of sun those numbers drop to 1800 and 1400 respectively. How much sun can be counted on in a Norwegian Winter? Her array may be just enough to cover her needs, but its cutting it close, and leaves very little excess for recharging the batteries after prolonged periods of little or no sun. But maybe the 1800 Wh figure she calculated already has a big margin of safety built in.

Sorry I didn't intend to distract from your initial questions.

One way or another, I'm pretty envious of your daughter spending winters in a tinyhouse in Norway and/or Austria sounds pretty idyllic!
 
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I would go with the Austrian locale, much warmer with fantastic solar gain and putting up with walabees is a small price to pay.
 
I agree with you, but the benefit of overcapacity comes to the ratio between battery capacity and consumption between charges, not battery capacity vs solar input.
Not quite sure what you mean exactly here. If you increase battery capacity, you will increase both ratio's and gain from lower DOD and you will be able to overcome a longer period of cloudy days with a deficit.

The panels will have a (peak) capacity of about 1800W. So, the 0.05C that I mentioned could be 0.18 in theory. But in reality it will probably be much lower. With sunny days she will have plenty capacity to recharge, but on winter days with no sun, it will not be enough. I think in the winter, she will only be able to recharge on days with some sun, and you can have periods of 1 or 2 weeks with hardly any sun.
The extra capacity does not really cost any money, as it will extend the lifetime of the battery:
If you double your capacity, the lifetime should more than double. Because of the lower DOD the lifetime in cycles increases and each cycle will be twice as long.

So regarding to charging strategy, I figured that an absorption phase is not really required. With expected winter charge-rates of around 0.05C stopping charging at a cut-off voltage is equal to charging with a higher current and an absorption phase. And at occasional higher currents (like 0.15), you will miss only a very small charge.
 
The panels will have a (peak) capacity of about 1800W. So, the 0.05C that I mentioned could be 0.18 in theory. But in reality it will probably be much lower. With sunny days she will have plenty capacity to recharge, but on winter days with no sun, it will not be enough. I think in the winter, she will only be able to recharge on days with some sun, and you can have periods of 1 or 2 weeks with hardly any sun.

Oh okay now I get it, I assumed your array was 500w (0.05c x 10kWh) based on your earlier comment, but as I understand it now its an 1800W array, that you are estimating might output 500W on an average bad weather winter day? This makes much more sense, and seems like a much more reasonably sized solar array.

So regarding to charging strategy, I figured that an absorption phase is not really required. With expected winter charge-rates of around 0.05C stopping charging at a cut-off voltage is equal to charging with a higher current and an absorption phase. And at occasional higher currents (like 0.15), you will miss only a very small charge.

This is an interesting point, I see your logic, I hadn't connected those dots before
 
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