LiFeP04 Batteries for Solar & BMS

[PNjunction]

Well PN the irony of this whole thread and LFP batteries is it is only people like you and I who can work with them because we have the knowledge and skills to pull it off as long as we ignore cost. As for the public cannot be done because they do not have the knowledge or skills, not is there any automated equipment out there to work around that. Only thing out there now is Top Balance and it is expensive and is the root cause of battery failures.

Can't argue with that - realizing that American companies for the most part gave up on lithium-based batteries early on not so much from a technical standpoint, but from an inability to deal with the simplicity of lead that, um, just works even if THAT is often misunderstood. I think most who look into lifepo4 just realize it is not plug-n-play, or farm it out to others (or sharks) to do the job.

Well many folks with year old 3rd generation LFP cells are now starting to report capacity loss and failures. New package same ole line of crap. Failures are still being traced to over discharge using Top Balance, but capacity loss is a huge disappointment and set back. No matter what the manufactures say or do, calendar life still remains at 2 to 4 years regardless of cycles.

Yeah I've read those reports too, but only 100 messages later in the threads do we find out that they are using very old stock, abused their batteries early on testing and learning the right way .. and most importantly, using them in EV applications, not in a "Sub-C" solar storage application that I always harp about.

[PNjunction]

Does this mean my plan to use a window of 20%SOC to 90%SOC on a LFP bank, bottom balancing and a BMS, was all wet? We had discussed staying away from the knees. What am I missing, forgot, or never knew? Is my plan to use 70% of the capacity not realistic?

You CAN, but man, you had better have your power-budget calculations down to a tee if you plan to go there with an unstable source like solar only. One bad week or unexpected heavy emergency load means lights out.

I mean the sliding window of SOC that I talk about is cool and all, but is it practical for *you* ? Maybe so, but like taking lead to only 50% DOD many would argue not to go that far and shoot for maybe 35% max - it all depends on your power budget.

[PNjunction]

Orion is a centralized BMS with some smarts, but it does not have to be used as a BMS in the traditional sense. I use it as a battery monitor to turn off my battery charger. I Bottom Balance.

I believe the House Power BMS from CleanPowerAuto LLC has similar options. LVC, HVC, and passive top balancing that can be disabled I think. While the first thing I think of is top-balancing, being able to turn off the passive balancers and perhaps utilize the HVC to fire on the weakest cell after you do a bottom balance manually, might be something to look into.

Not for me, but maybe for others...

[Living Large]

I believe the House Power BMS from CleanPowerAuto LLC has similar options. LVC, HVC, and passive top balancing that can be disabled I think. While the first thing I think of is top-balancing, being able to turn off the passive balancers and perhaps utilize the HVC to fire on the weakest cell after you do a bottom balance manually, might be something to look into.

Not for me, but maybe for others...

I was looking at both House Power and Orion Jr for use with LFP and a bottom balancing approach. I believe I was considering the Orion for its added (at a small cost) ability to report the individual cell voltages via a CANBUS interface - but I don't honestly remember.

The House Power has a simple series loop where if any board goes open on charge or discharge it can trigger a HV or LV detect at the cell level of the first cell to hit the threshold, IIRC. I haven't looked at them for 3 months - this is from memory. I don't recall how that threshold would be programmed on each board though. There was a version with individual cell boards, and another with the electronics on a one board for multiple cells.

[PNjunction]

I think either one is a reasonable approach with some flexibility.

Just went to the Orion site and saw that it promotes their EMI protection - something sorely needed in today's environment. I wonder how many EV'ers may have had their bms go askew driving into areas of heavy FM Broadcast, NOAA, radio transmissions of every kind, and having the antennas, er balance leads picking all that up. Even in a fixed location environment, a neighbors plasma-TV may be a problem. I suppose you'd have to test for it before blaming it on this though.

I'm glad they are highlighting that since I think that's very important.

[Sunking]

PN EMI shielding is there to guard against the EV's motor controller, not external sources. External sources is chump change compared to what the motor controller can generate. Most DIY Ev builders uses a different battery to power the Controller to combat the problem. What Orion is done is allow you to use a DC-DC converter to run the controller off the HV Traction Battery.

Stop and think about it. A EV can draw up to 1000 Amps and uses PWM operating at 10 to 20Khz. That much current pulsed rings like Hell's Bell.

[karrak]

From my research and experience with an LFP battery that has been part of my off-grid power system for over two years now I am not so sure that bottom balancing LFP cells in off-grid systems and probably most power systems that rely on solar energy as their primary source of power is as good or as practicable as top balancing.

Firstly, In off-grid systems you want to charge the battery to as close to 100% when the weather is sunny while also maximising the lifespan of the battery, a tricky compromise. Usually this means fully charging the battery on a daily basis whenever there is sunshine. As has been mentioned in previous posts, bottom balancing a battery will mean that the individual cell voltages will be unequal every time the battery is fully charged which in this situation will mean on a daily or if not daily a very regular basis. I would think that this imbalance could lead to some cells ageing faster than others over the hopefully 10 year plus life of the battery.

Secondly, off-grid batteries relying on solar power to charge them spend most of their time above 50%SOC as you want to have as much power stored as possible for cloudy weather. It is only very rarely that a battery in a well managed off-grid systems gets to anything near 0% SOC where the protection given by bottom balancing has any impact. If you have cell level monitoring of the battery, imbalance in cell SOC at the bottom end is not an issue.

Thirdly, doing a bottom balance on a regular basis in an off-grid system is difficult if the battery is your main source of power, especially if you do not have an alternate power supply. I think it also subjects the battery to unnecessary stress.

I agree that for EV use bottom balancing cells has many advantages but the charge/discharge profiles, expectations and requirements for an EV battery and for a battery in an off-grid system are very different.

Simon

[Willy T]

From my research and experience with an LFP battery that has been part of my off-grid power system for over two years now I am not so sure that bottom balancing LFP cells in off-grid systems and probably most power systems that rely on solar energy as their primary source of power is as good or as practicable as top balancing.

Firstly, In off-grid systems you want to charge the battery to as close to 100% when the weather is sunny while also maximising the lifespan of the battery, a tricky compromise. Usually this means fully charging the battery on a daily basis whenever there is sunshine. As has been mentioned in previous posts, bottom balancing a battery will mean that the individual cell voltages will be unequal every time the battery is fully charged which in this situation will mean on a daily or if not daily a very regular basis. I would think that this imbalance could lead to some cells ageing faster than others over the hopefully 10 year plus life of the battery.

Secondly, off-grid batteries relying on solar power to charge them spend most of their time above 50%SOC as you want to have as much power stored as possible for cloudy weather. It is only very rarely that a battery in a well managed off-grid systems gets to anything near 0% SOC where the protection given by bottom balancing has any impact. If you have cell level monitoring of the battery, imbalance in cell SOC at the bottom end is not an issue.

Thirdly, doing a bottom balance on a regular basis in an off-grid system is difficult if the battery is your main source of power, especially if you do not have an alternate power supply. I think it also subjects the battery to unnecessary stress.

I agree that for EV use bottom balancing cells has many advantages but the charge/discharge profiles, expectations and requirements for an EV battery and for a battery in an off-grid system are very different.

Simon

Finally someone with a off grid system and not someone testing batteries on a bench or a golf cart. Be careful, the last off grid person got banned for talking about their system and being called a lot of names.

Do you have any issues with your CC triggering a full Bulk, Absorb, Float cycle until the voltage drops below 12.5. Sometimes my CC will not automatically re-trigger and it will limit the number of output amps and stops at the float setting unless the voltage drops below 12.5. I can set a bulk cycle, but that requires manual intervention.

[karrak]

Do you have any issues with your CC triggering a full Bulk, Absorb, Float cycle until the voltage drops below 12.5. Sometimes my CC will not automatically re-trigger and it will limit the number of output amps and stops at the float setting unless the voltage drops below 12.5. I can set a bulk cycle, but that requires manual intervention.

My MPPT charge controller is homemade so I can program it however I like. I have programmed it to start a new bulk charge at the start of each new day or if the battery voltage goes below 3.25 volts/cell (13 volts for a twelve volt system). What is the make and model of your charge controller?

Simon

[Willy T]

My MPPT charge controller is homemade so I can program it however I like. I have programmed it to start a new bulk charge at the start of each new day or if the battery voltage goes below 3.25 volts/cell (13 volts for a twelve volt system). What is the make and model of your charge controller?

Simon

The CC is a FM60 and a FNdc all connected to a GFX 1312. I have tried a lot of settings and with and without the FNdc controlling the total system and it still seems to happen. Maybe I haven't found the right combination yet. It's like the system just doesn't want to reset because the voltage is to high and it wants to stay in Float. Sometimes integrated systems aren't all that they are cranked to be. It could be something in the algorithm that is fixed. I said 12.5, it's hard to tell exactly, it could be 12.7. I'll have to watch it again to see. Just getting everything calibrated has been a pain within the voltage range of LiFep04 batteries.

[karrak]

The CC is a FM60 It's like the system just doesn't want to reset because the voltage is to high and it wants to stay in Float. Sometimes integrated systems aren't all that they are cranked to be. It could be something in the algorithm that is fixed. I said 12.5, it's hard to tell exactly, it could be 12.7. I'll have to watch it again to see. Just getting everything calibrated has been a pain within the voltage range of LiFep04 batteries.

I had a quick look at the FM60 manual. It is not very clear to me (pretty poor manual!) but I think the FM60 should go back to Bulk charge after what they call 'Sleeping' then 'Zzzzz...' then 'Snoozing'. 'Sleeping' starts when the panel voltage is 2 volts below the battery voltage, then after 3 hours of 'Sleeping' it should go to 'Zzzz...' then when the panel voltage gets 2 volts above the battery it should go to 'wakeup' then I assume on to bulk.

I would check that it is going through this cycle each night. I couldn't work out if the battery voltage needs to go below the 'Rebulk Voltage' at night before the FM60 will go back to 'Bulk' mode when it wakes up, maybe someone else can help here.

Simon

[Sunking]

Firstly, In off-grid systems you want to charge the battery to as close to 100% when the weather is sunny while also maximising the lifespan of the battery, a tricky compromise. Usually this means fully charging the battery on a daily basis whenever there is sunshine. As has been mentioned in previous posts, bottom balancing a battery will mean that the individual cell voltages will be unequal every time the battery is fully charged which in this situation will mean on a daily or if not daily a very regular basis. I would think that this imbalance could lead to some cells ageing faster than others over the hopefully 10 year plus life of the battery.

You are missing the big picture and still stuck using lead acid battery techniques. Keeping LFP batteries at or near 100% shortens their lives, not maximize as you mistakenly said. That is a lead acid world thing. Keeping LFP at 100% are taking them their daily accelerates their aging. Keeping LFP cell voltages equal are not important at the top as it does not tell you anything about them or has no benefit.

Secondly, off-grid batteries relying on solar power to charge them spend most of their time above 50%SOC as you want to have as much power stored as possible for cloudy weather. It is only very rarely that a battery in a well managed off-grid systems gets to anything near 0% SOC where the protection given by bottom balancing has any impact. If you have cell level monitoring of the battery, imbalance in cell SOC at the bottom end is not an issue.

Again you logic is flawed and stuck in a Pb world. In a Bottom Balance system every cell has the same capacity, and the system is charged up referencing the weakest cell in the string. In a Top Balanced system the capacity of the pack is determined by the weakest cell. Example in a 100 AH system your AH capacity, cell values are going to range from 100 to 120 AH. The weakest is 100 AH. Bottom Balance them at at any point every cell has the same capacity. You charge them up using the weakest cell. Say 95 AH.

If you Top Balance not only do you stress every cell every time you charge, you run a very high risk of over discharging and destroying the weaker cells. In a Bottom Balanced system you eliminate those risk.

Thirdly, doing a bottom balance on a regular basis in an off-grid system is difficult if the battery is your main source of power, especially if you do not have an alternate power supply. I think it also subjects the battery to unnecessary stress.

Regular basis? What are you talking about? You do it one time initially at the beginning.

[karrak]

Maybe I haven't found the right combination yet. It's like the system just doesn't want to reset because the voltage is to high and it wants to stay in Float.

Might be worth changing the 'Rebulk Voltage' in the Advanced menu to 13.0 volts to get the FM60 to go back to 'Bulk' charge at a more realistic battery SOC, 12 volts (3.0 volts/cell) is nearly fully discharged for an LFP battery. Could you tell me what your 'Absorbing' and 'Float' voltages are from the Charger Screen and also 'Absorb Time Limits' and 'Absorb End Amps' from the 'Advanced Menu', also what are the 'Equilization' settings.

[Willy T]

Might be worth changing the 'Rebulk Voltage' in the Advanced menu to 13.0 volts to get the FM60 to go back to 'Bulk' charge at a more realistic battery SOC, 12 volts (3.0 volts/cell) is nearly fully discharged for an LFP battery. Could you tell me what your 'Absorbing' and 'Float' voltages are from the Charger Screen and also 'Absorb Time Limits' and 'Absorb End Amps' from the 'Advanced Menu', also what are the 'Equilization' settings.

Bulk / Absorb 13.7, Float 13.1 re-float 12.7v Time limit 30 minutes and ending amps of 20 amps. The EQ setting is set to 14.3 that gets me above 3.55 on the BMS and used to balance if necessary.

I tried to bottom balance @ 2.6 on 4 cells. As I recharged them I found that once the voltage gets above 3.460 one cell would climb very fast while the rest were 3.2 -3.3 v. As I watched them the high cell went to 3.785 and the lowest was still at 3.4 v. That let me know that the safest high charge voltage would have to be 3.4 and even that would be to high to be safe. So if I used 3.3v that would make my bulk at 13.2 v and to me that is way to low and giving up to much capacity, so I decided to top balance. I have no idea how temperature effects voltage, I am watching them close until I get a handle on them. I am trusting the BMS, it's better than losing a cell. I have not cycled them yet to see what the lowest safe voltage is yet. It won't be that low, since the lowest it can go is 12.7 before it will recharge off another system.

Real life trumps theoretical BS.

[karrak]

You are missing the big picture and still stuck using lead acid battery techniques. Keeping LFP batteries at or near 100% shortens their lives, not maximize as you mistakenly said. That is a lead acid world thing. Keeping LFP at 100% are taking them their daily accelerates their aging. Keeping LFP cell voltages equal are not important at the top as it does not tell you anything about them or has no benefit.

I find this rather amusing as I have never used Pb batteries in my off-grid system, NiCd and LFP yes, Pb no.

If you are off-grid you have to keep your battery as close to 100% full as possible during sunny weather as you don't know how long you will have to live off your battery storage when cloudy weather occurs. What voltage would you suggest that you charge an LFP battery to under these circumstances.

Again you logic is flawed and stuck in a Pb world. In a Bottom Balance system every cell has the same capacity, and the system is charged up referencing the weakest cell in the string. In a Top Balanced system the capacity of the pack is determined by the weakest cell. Example in a 100 AH system your AH capacity, cell values are going to range from 100 to 120 AH. The weakest is 100 AH. Bottom Balance them at at any point every cell has the same capacity. You charge them up using the weakest cell. Say 95 AH.

No they don't all have the same capacity, the weakest cell only has 100ah and the strongest cell has 120ah. Using your example, the weakest cell is charged to 95% of its capacity while the strongest cell is only charge to 79% of its capacity. With bottom balancing you only charge the stronger cells up to the same level as the weakest cell's fully charged state, so you loose the extra 20ah of the strongest cell at the top end. With top balancing it is exactly the same but the 20ah is lost at the bottom end.

If you Top Balance not only do you stress every cell every time you charge, you run a very high risk of over discharging and destroying the weaker cells. In a Bottom Balanced system you eliminate those risk.

Top balancing does not mean that you charge them all to a high voltage >3.6 volts/cell. It means that they are all balanced at the voltage that you do charge them too. You do not run a very high risk of over discharging the cells in an off-grid system as the battery spends the vast majority of its time more than half full and as an emergency backup you have some sort of cell monitoring which will shut down your load or notify you when the weakest cell is flat.

Regular basis? What are you talking about? You do it one time initially at the beginning.

What if the cells age and loose capacity at different rates. If this happens the bottom balance will have to be redone just as it has to with top balancing.

Simon