Anything wrong with these multiplus settings?

[Solarfun4jim]

Looking at the settings above, do i need to change the absorption times at all? It is just that i was expecting, when charging from a low state of charge, that i would see bulk first, then absorption for 1 hour and then float mode, but what i'm witnessing is it going straight to float mode, pumping in 69Amps, which as far as i understood, when in float mode at only 27.00v, shouldn't be adding any charge to the system at all(ie below the 3.4v/cell threshold for charging). Can anyone tell me why this multiplus should go straight to float mode?

 

[snoobler]

What is your battery capacity?

 

[Solarfun4jim]

It is 280Ah.

I think i have sussed the issue anyways. I'm using the two signal bms assistant and at present i only have the discharge relay connected. Thus the charge relay going to the inverter is open(awaiting pins since no screw connections), so the assistant will default the charge to float mode. Doh...it is always the simplest of things that have you scratching your head....lol.

Thanks for stopping by anyways snoobler.

Why is it, one always realizes their mistake right after you post the question ?

 

[snoobler]

It's all good.

I would cut the absorption to 15 minutes. Since you're only charging at 0.25C, you're going to be nearly fully charged when you hit 3.55V.

 

[Solarfun4jim]

It's all good.

I would cut the absorption to 15 minutes. Since you're only charging at 0.25C, you're going to be nearly fully charged when you hit 3.55V.

@snoobler
1 hour is the minimum you can set it to :-(
What about the repeated absorption time? Should this be increased in value?

Or would it be better altogether, to target 3.5v/cell?

Thanks again

 

[mandrews44]

If you can't remove absorption time, can you lower the voltage closer to float? LiFePo4 does not need or want absorption. The further you stay away from the cell top voltage, the longer your cells will last. The issues is the membrane, they deteriorate faster as those ions get excited for long periods of time..

 

[Solarfun4jim]

If you can't remove absorption time, can you lower the voltage closer to float? LiFePo4 does not need or want absorption. The further you stay away from the cell top voltage, the longer your cells will last. The issues is the membrane, they deteriorate faster as those ions get excited for long periods of time..

I suppose i should move the 'repeated absorption time' from 1 hour to 24hours, so at least it only attempts this once in a daily cycle???

Also, i believed that if you float below 3.4v per cell, it wont charge the cell? My float is 3.375v/cell, so at least that should be ok?

 

[Solarfun4jim]

Still trying to figure, if the 'repeated absorption time' means the time between each successive absorption pulse or else is it the length of time that these subsequent pulses actually last for???

 

[snoobler]

1 hour is the minimum you can set it to :-(
What about the repeated absorption time? Should this be increased in value?

Or would it be better altogether, to target 3.5v/cell?

Thanks again

Did you try 0.25? My Quattro is set for 0.5. Your Multiplus should be no different.

Absorption time is the time in absorption following bulk.

Repeated absorption interval is the time between forced absorption if the battery is in float the entire time. If this is in a cyclic application, it's a non-issue. If this is stored on shore power for extended periods with no use at all, power should be removed.

You can click "Help" and "what's this" and then click on the field for context specific help.

If you can't remove absorption time, can you lower the voltage closer to float? LiFePo4 does not need or want absorption. The further you stay away from the cell top voltage, the longer your cells will last. The issues is the membrane, they deteriorate faster as those ions get excited for long periods of time..

This is not true as an absolute. It depends on charge current and the desired peak SoC. Charging at 0.5C will usually need at least a brief absorption current, particularly if you're charging at less than 3.65V.

I conducted tests and found I could get batteries charged to 92-95% @ 3.4V/cell, but it needed an absorption time of about 5 hours after an initial charge of 0.3C.

 

[Solarfun4jim]

Did you try 0.25? My Quattro is set for 0.5. Your Multiplus should be no different.

Absorption time is the time in absorption following bulk.

Repeated absorption interval is the time between forced absorption if the battery is in float the entire time. If this is in a cyclic application, it's a non-issue. If this is stored on shore power for extended periods with no use at all, power should be removed.

You can click "Help" and "what's this" and then click on the field for context specific help.



This is not true as an absolute. It depends on charge current and the desired peak SoC. Charging at 0.5C will usually need at least a brief absorption current, particularly if you're charging at less than 3.65V.

I conducted tests and found I could get batteries charged to 92-95% @ 3.4V/cell, but it needed an absorption time of about 5 hours after an initial charge of 0.3C.

Thanks snoobler.
1Hr is the minimum the multiplus will go to. I'm going to drop my charge rate to 3.48v/cell equiv, so the 1hr absorption shouldn't be too bad. This will only be used in an infrequent cyclic application.
I've still to determine if at 27.84v target, i have enough headroom to get there before my high delta cell hits the ceiling when charging at 0.25CA. Have the BMS set to 3.64v HVD, so hopefully this is good...will find out in due course.

The nice 10mv delta when charging at 0.05A goes right out the window when doing 0.25A (delta bouncing about anywhere up to 91mv)

 

[mandrews44]

Sorry, I am lost.. With LFP, BMS is master. The longer you keep the voltage at the top of the knee, the worse off your battery life will be. This isn't SLA or LA at all.. It is more of a tub of water, near 100% efficiency that does not like anything SLA or LA related because it harms the battery. They do not need topped off, do not lose life because they are not fully charged and actually the opposite.. I set all of my BMS's lower than max, never charge over 14.2 and do not allow the bank to go below 12.8 on a 16kW battery bank used as a Power wall for a whole house UPS / Solar storage. The higher the voltage on that pack is, the higher pressure you are putting on that thin membrane keeping your battery alive and there is very little to no benefit in doing so..

 

[snoobler]

Sorry, I am lost.. With LFP, BMS is master. The longer you keep the voltage at the top of the knee, the worse off your battery life will be. This isn't SLA or LA at all.. It is more of a tub of water, near 100% efficiency that does not like anything SLA or LA related because it harms the battery. They do not need topped off, do not lose life because they are not fully charged and actually the opposite.. I set all of my BMS's lower than max, never charge over 14.2 and do not allow the bank to go below 12.8 on a 16kW battery bank used as a Power wall for a whole house UPS / Solar storage. The higher the voltage on that pack is, the higher pressure you are putting on that thin membrane keeping your battery alive and there is very little to no benefit in doing so..

You're speaking from your perspective and desire. I'm not saying you're wrong. I'm saying your statement isn't right without qualifiers. If you want to fully charge a LFP cell, you must have an absorption charge if you are charging at anything over 0.05C. If you are charging at 0.05C, then you don't need an absorption phase.

These have a 2000+ cycle life operating between the 2.5 and 3.65V limits. Restraining these cells to prevent case expansion nearly doubles their full-range cycle life to about 3500. If you want to treat your batteries even more gently, charge to 13.6, and you'll never exceed 95% SoC, but it will take all day to get there.

BTW, if you've seen actual numbers that demonstrate LFP experiences notable cycle life increases with reduced SoC range operation, please link it. I personally haven't. For the more aggressive Lithium Chemistries, there are lots of references, but I haven't found any with LFP. One wants to assume you get more cycle life with LFP as you DO with LMO/NMC/NCA chemistries.

 

[Solarfun4jim]

Sorry, I am lost.. With LFP, BMS is master. The longer you keep the voltage at the top of the knee, the worse off your battery life will be. This isn't SLA or LA at all..

Sorry, I don't quite understand. I always viewed the charge controller as master and the BMS is only there as a failsafe if a cell runs. So in my scenario i thought 3.48v/cell(27.84v) would be a reasonable compromise on the charge controller. What would you recommend as a reasonable compromise between capacity gained and speed of charge? Keeping in mind, my normal mode of operation 90%+ of time will be solar charging for 4-5 hours/day @ 28A output max.... so anything i can do to speed up the rate at which the energy goes into the cells the better....imo.

With my absorption mode being fixed at 1 hour, there has to be an ideal voltage target, that charges as quickly as possible, at 0.25CA grid(very infrequently) and 0.1CA solar, inputs. Unfortunately i'm still tweaking, trying to find that number.

Thanks for the input folks

 

[mandrews44]

You're speaking from your perspective and desire. I'm not saying you're wrong. I'm saying your statement isn't right without qualifiers. If you want to fully charge a LFP cell, you must have an absorption charge if you are charging at anything over 0.05C. If you are charging at 0.05C, then you don't need an absorption phase.

These have a 2000+ cycle life operating between the 2.5 and 3.65V limits. Restraining these cells to prevent case expansion nearly doubles their full-range cycle life to about 3500. If you want to treat your batteries even more gently, charge to 13.6, and you'll never exceed 95% SoC, but it will take all day to get there.

BTW, if you've seen actual numbers that demonstrate LFP experiences notable cycle life increases with reduced SoC range operation, please link it. I personally haven't. For the more aggressive Lithium Chemistries, there are lots of references, but I haven't found any with LFP. One wants to assume you get more cycle life with LFP as you DO with LMO/NMC/NCA chemistries.

As long as your charge voltage is >= 14.2v, it will charge at what you are giving it. I can set the voltage to 14.2v and the top cycle to 13.6 and it will charge at 100 amps. It all depends on your application. If you are using the batteries for backup / storage and are not cycled, it is best to keep them no higher than 75% capacity when stored for > 3 months and not cycled. For Cycle usage, I prefer the 80/20 rule but allow my packs to get up to 13.6v as a max. Once they reach 13.6v, I dump the as much solar energy as available into AC circuits in the house to reduce the charging. If you google it, you will find research papers on this that includes fairly conclusive lab testing, not just someone in their basement. I've also seen videos so youtube may also help you with this. LFP has an issue when voltages are at the top of the charging range and many studies have shown that you do not want to keep LFP cells at that high voltage.. ever.. Not for cycle, not for storage..

Unlike LA, LFP offer not having the fully charge them for cycle usage, the downside is they hate being fully charged.

 

[mandrews44]

Sorry, I don't quite understand. I always viewed the charge controller as master and the BMS is only there as a failsafe if a cell runs. So in my scenario i thought 3.48v/cell(27.84v) would be a reasonable compromise on the charge controller. What would you recommend as a reasonable compromise between capacity gained and speed of charge? Keeping in mind, my normal mode of operation 90%+ of time will be solar charging for 4-5 hours/day @ 28A output max.... so anything i can do to speed up the rate at which the energy goes into the cells the better....imo.

With my absorption mode being fixed at 1 hour, there has to be an ideal voltage target, that charges as quickly as possible, at 0.25CA grid(very infrequently) and 0.1CA solar, inputs. Unfortunately i'm still tweaking, trying to find that number.

Thanks for the input folks

If you can set your boost and absorption to the same voltage, it will be best. Anything over 28.4 (14.2) will give you 100% charge current. If you can not set bulk and absorption the same voltage, set bulk to 14.1 and absorption to 14.2. That way, you are canceling the absorption cycle.

Here is a thread that explains this.. Absorption is for SLA (LA) and is required for LA due to it's chemistry and does not apply to LFP and it not changed can do damage to LFP batteries.

Constant 14.6 Volts and no reduced float charge for 12v LiFePO4?

I just got a Progressive Dynamics "PD9145ALV 12V Lithium Ion Battery Converter/Charger - 45 Amp" charger off Amazon. Amazon says "Electronic Current Limiting – Automatically reduces output voltage to prevent overheating and possible damage". But the manual that came with it says "When...

diysolarforum.com

Absorb phase of AIMS inverter/charger only runs for ~10 seconds, not 10X bulk charge time as manual states (3000W, 48V)

I recently set up a 48V off-grid UPS, using the AIMS Global LF Series Pure Sine Wave 4000W 48V inverter/charger. It has multiple battery types, and I've rotated that selector to LiFePo4, which is supposed to bulk charge at a fixed current, until the bank (4S Battle Born 100 AH) reaches 57.6 (=...

diysolarforum.com

don't understand Lifepo charging, seems like voltage/time-based charging is flawed?

I decided to do the Cerbo GX with the touch 50 screen and I didn't want the extra screen that came with the 712. The cerbo has a couple relays and multiple inputs for temp and tank levels and also some digital inputs (which I doubt I'll ever use). It can connect to the inverter and solar...

diysolarforum.com

Hope this helps.. LFP only has one cycle.. Charge / Discharge..

 

[Solarfun4jim]

If you can set your boost and absorption to the same voltage, it will be best. Anything over 28.4 (14.2) will give you 100% charge current. If you can not set bulk and absorption the same voltage, set bulk to 14.1 and absorption to 14.2. That way, you are canceling the absorption cycle.

Here is a thread that explains this.. Absorption is for SLA (LA) and is required for LA due to it's chemistry and does not apply to LFP and it not changed can do damage to LFP batteries.

Constant 14.6 Volts and no reduced float charge for 12v LiFePO4?

I just got a Progressive Dynamics "PD9145ALV 12V Lithium Ion Battery Converter/Charger - 45 Amp" charger off Amazon. Amazon says "Electronic Current Limiting – Automatically reduces output voltage to prevent overheating and possible damage". But the manual that came with it says "When...

diysolarforum.com

Absorb phase of AIMS inverter/charger only runs for ~10 seconds, not 10X bulk charge time as manual states (3000W, 48V)

I recently set up a 48V off-grid UPS, using the AIMS Global LF Series Pure Sine Wave 4000W 48V inverter/charger. It has multiple battery types, and I've rotated that selector to LiFePo4, which is supposed to bulk charge at a fixed current, until the bank (4S Battle Born 100 AH) reaches 57.6 (=...

diysolarforum.com

don't understand Lifepo charging, seems like voltage/time-based charging is flawed?

I decided to do the Cerbo GX with the touch 50 screen and I didn't want the extra screen that came with the 712. The cerbo has a couple relays and multiple inputs for temp and tank levels and also some digital inputs (which I doubt I'll ever use). It can connect to the inverter and solar...

diysolarforum.com

Hope this helps.. LFP only has one cycle.. Charge / Discharge..

@mandrews44

Thanks for your help, however i have changed my settings from previous....takes a bit of tweaking to get the best out of it, applying possible worst case scenario's.
My settings now are absorption 27.20v and float 27.00, (That is the only settings you can adjust) however this implies the charging going through the following states......bulk 3.40v(27.2v), absorption 1hr @3.40v(27.20), float 3.375v (27.00v).
On the discharge, settings are 3.07v (24.60v), reset 26.60v
These were worked out applying a low current input(simulate a cloudy day) and high current draw to simulate worst case when battery is getting low. Bms HVD set at 3.60v and LVD set at 2.60v, basically to guard against the cell runners, but i shouldn't think they will ever come into play. Just in the process now of guaging what likely capacity i would get from these values applying average usage. Hopefully around 5% up to 85% or 80% in total????
I didnt actually want to drop as low with the discharge level, however there is a minimum 2v addition to the value before the inverter will reset and allow power to be drawn again....which means, if i set the discharge limit any higher, then effectively you would then need to charge the battery back up to full before you got to use it again :-( As it is, it needs about a 33% charge up before it hits 26.60, resetting the inverter.

The other thing i'm thinking of doing, is resetting my BMV712 from its original settings, which were based on initial capacity testing, assuming 280Ah and 3.65v/cell charging. Now that i want it to syncronise as full, when it hits 3.4v and 0.5A, if the capacity at that level is say 85%, i thought about recalibrating the BMV712 to 238Ah , with the charged voltage set as 27.1v, tail current set at 2%(to account for cloudy days) and Time set at say 10 minutes, just to make sure, it is not passing clouds. I should then synchonise to 100% at this stage, ie 100% of useable, not 100% of total capacity. I would just leave my chargery BMS at the original capacity settings, simply to monitor votages and provide protections, nothing else, so not to worried if the capacity on that gets out of sync somewhat, as i wont be reading that one.

Any downsides to my planned set up?

Thanks for any input offered.

 

[mandrews44]

External Reference: How to find happiness with LiFePo4

 

[Solarfun4jim]

External Reference: How to find happiness with LiFePo4

The issues are not so much the principles(have read most of the referenced articles), but more to do with the configuration of the actual unit itself.
Thanks anyways for your help.

 

[mandrews44]

If you are using this for cycling, not storage, you can use your load to keep the voltage in the battery from exceeding the upper knee.. 28.4v. As previously posted, if you charge at 13.6 (27.2v), your charge will slow once you get anywhere near this value in your bank. What I was trying to convey was, you can control how high the cell voltage gets without reducing your charge voltage. Does this make sense? I.E. set your BMS to stop charging and go to float of 13.6v once your cell voltage gets to 28.4 (3.55v) and keep your charge voltage at 28.4v. If you power usage is about the same as your solar availability, you might not ever have to worry about it as this only comes into play when there is a surplus.

 

[mandrews44]

BTW: BMS shutting down charge will force the SCC to go to float..