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Old 17-11-2022, 11:52   #1
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Mppt performance and Lifepo4 SoC%

If we do not want the cells to age quickly, we should not charge the Lifepo4 batteries up to 100% SoC level. There is now a broad consensus on this issue.

In order to cut off the mppt charge of Lifepo4 batteries at 90% SoC, it is necessary to set the charge cut-off voltage as 13.3-13.4 Volts. 13.6-13.7 volts is sufficient for 100% SoC.

To cut Mppt charging on the targeted SoC you need to lower the regulator's maximum charge voltage setting (If possible)

So when the max charging voltage is lowered, won't the performance of the mppt regulator decrease? With the low charge voltage setting, you can watch the mppt performance decrease from the coulomb meter.

We have to keep the max charge voltage of the Mppt regulator at the level where it works with the highest performance, which I think is 14.2 or 14.4 volts.

We need to turn off the mppt controller with a different control mechanism when the Lifepo4 batteries reach the targeted SoC%.

I think controlling the mppt regulator input line of the solar panels using a voltage sensitive relay will solve the problem.
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Old 17-11-2022, 11:56   #2
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Re: Mppt performance and Lifepo4 SoC%

I don't see how a lower charge output voltage would have any meaningful impact on MPPT performance unless your MPPTs are undersized and running up against their output current limit.
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Old 17-11-2022, 12:07   #3
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Re: Mppt performance and Lifepo4 SoC%

Quote:
Originally Posted by SOLAR SUPPORT View Post
So when the max charging voltage is lowered, won't the performance of the mppt regulator decrease? With the low charge voltage setting, you can watch the mppt performance decrease from the coulomb meter.
Yes, but if the batteries are full so what?

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Originally Posted by SOLAR SUPPORT View Post
We have to keep the max charge voltage of the Mppt regulator at the level where it works with the highest performance, which I think is 14.2 or 14.4 volts.
Why?

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Originally Posted by SOLAR SUPPORT View Post
We need to turn off the mppt controller with a different control mechanism when the Lifepo4 batteries reach the targeted SoC%.
I disagree. I don't want the MPPT turned off, because then any power supplied comes from the LFP. If the sun is still shinning then I want the MPPT to supply the power rather then use power from the batteries. Once the sun goes down, then allow the batteries to provide power. So the solution is a float charge lower than the fully charged voltage of the LFP which will supply the boat. Interestingly assuming the domestic loads are less than the solar panels output, then the MPPT will dial back the power they need to match the demand. Result full batteries at dusk to meet the nights demands.

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Originally Posted by SOLAR SUPPORT View Post
I think controlling the mppt regulator input line of the solar panels using a voltage sensitive relay will solve the problem.
I don't see what you are trying to achieve, but a float of 3.2.v per cell would do the same with the equipment you already have and in the event you really do take the batteries that low, then the MPPT will switch to bulk and absorption automatically.

I think you are over thinking this.

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Old 17-11-2022, 12:16   #4
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Re: Mppt performance and Lifepo4 SoC%

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Originally Posted by rslifkin View Post
I don't see how a lower charge output voltage would have any meaningful impact on MPPT performance unless your MPPTs are undersized and running up against their output current limit.
While charging my Lifepo4 drop-in batteries with mppt, I can change the settings of the regulator. While changing the max charge voltage setting, I personally observe that the charge current changes from the coulomb meter next to it.
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Old 17-11-2022, 12:22   #5
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Re: Mppt performance and Lifepo4 SoC%

Quote:
Originally Posted by SOLAR SUPPORT View Post
If we do not want the cells to age quickly, we should not charge the Lifepo4 batteries up to 100% SoC level. There is now a broad consensus on this issue.

In order to cut off the mppt charge of Lifepo4 batteries at 90% SoC, it is necessary to set the charge cut-off voltage as 13.3-13.4 Volts. 13.6-13.7 volts is sufficient for 100% SoC.

To cut Mppt charging on the targeted SoC you need to lower the regulator's maximum charge voltage setting (If possible)

So when the max charging voltage is lowered, won't the performance of the mppt regulator decrease? With the low charge voltage setting, you can watch the mppt performance decrease from the coulomb meter.

We have to keep the max charge voltage of the Mppt regulator at the level where it works with the highest performance, which I think is 14.2 or 14.4 volts.

We need to turn off the mppt controller with a different control mechanism when the Lifepo4 batteries reach the targeted SoC%.

I think controlling the mppt regulator input line of the solar panels using a voltage sensitive relay will solve the problem.
Completely wrong approach. You BMS is the masterbrain in your LifePo4 System and Controlling all your charge sources. BMS is the only one that knows the real SOC of the bank AND each cell, your MPPT only the total voltage at the moment it’s measuring it, it doesn‘t even know how much voltage really „arrive“ at the bank (cable, fuses,shunts…) and 0,1V matters here plus has no glue about the current…and if one cell is at 3,6V while the other is at 3,4V, in total it’s still 14,0V.
So the BMS sets the voltage and SOC when the MPPT should stop charging and restart again on cell level. My system runs at 3,55V=14,2V or 100%SOC charge cut off, doesn’t matter which source is charging as amps are amps. The re-engage charge is only at 3,30V to discharge the bank deeper (as mine is massively oversized) but I only done that after a month at 3,40V so SOC and cells are very balanced (4mV difference). If on passage I raise cut off to 3,6V and re-engage at 3,45V to have the bank as full as possible for security reasons. That also keeps the bank balanced, from time to time, I would say 1 month, it’s good to have it really full and cycle for 3 days a lot microcycles around 3,45v to 3,6V as this really top balances the bank and calibrates the BMS well.
Yes 3,55V it’s actually around 95% SOC of the bank but that’s security overhead while balancing still works well.I could also calibrate it to 3,65V with 100% SOC but well I prefer security and give away 5% capacity for that.
You also cannot go too low eg 3,4V which is 13,6V as no real balancing can happen and your cells in the bank start to differ as the balancing only really works in the steep knee above 3.5V.
What would make a difference is if you could modify the calibration and restart cycle of the BMS to something else then 24H, the only BMS I know that’s possible is the Tao BMS. For the typically oversized bank in a boat that would allow to discharge the bank deeper and cycling it less. Well for the price difference of the Electrodacus to Tao I can buy 4 cells EVE 280AH, which gives me 5000cycles more, so makes no sense. If I would have Winston cells, I would get the Tao BMS.

If you treat your cells well, means max 0.3C dis-/charge, don’t go below 30% keep as cool as possible and balanced the calendar aging has a much bigger effect then your MPPT charging.
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Old 17-11-2022, 12:23   #6
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Re: Mppt performance and Lifepo4 SoC%

Quote:
Originally Posted by SOLAR SUPPORT View Post
While charging my Lifepo4 drop-in batteries with mppt, I can change the settings of the regulator. While changing the max charge voltage setting, I personally observe that the charge current changes from the coulomb meter next to it.

If you have a lot of solar relative to the size of your batteries, you may be hitting the max charge acceptance of the batteries. Batteries will generally accept less power at a lower voltage. It's less extreme with LFP, but the effect is still there. That, or there's something weird going on with your MPPT controllers.



Out of curiosity, what MPPT controllers are you using? And how much solar and what size battery bank?
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Old 17-11-2022, 12:38   #7
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Re: Mppt performance and Lifepo4 SoC%

Quote:
Originally Posted by rslifkin View Post
If you have a lot of solar relative to the size of your batteries, you may be hitting the max charge acceptance of the batteries. Batteries will generally accept less power at a lower voltage. It's less extreme with LFP, but the effect is still there. That, or there's something weird going on with your MPPT controllers.

Out of curiosity, what MPPT controllers are you using? And how much solar and what size battery bank?
It should be noted that I do not use a very special and advanced mppt regulator for performance evaluation. In this regulator, you only set the maximum charge voltage, there is no battery type etc selection. The voltage setting determined by the user can be changed while the device is running, and I can monitor the result from the coulomb meter.

When the charging voltage is low, the charging current is low. As the charging voltage rises from 13.5 volts to 14.2-14.4 volts, the charging current transferred to the batteries increases significantly. My batteries are 2x200Ah Lifepo4 drop-in type. Solar panels are 600 Wp. Charge controller 40A mppt.
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Old 17-11-2022, 12:46   #8
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Re: Mppt performance and Lifepo4 SoC%

That sounds like it's not a real MPPT controller at all.
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Old 17-11-2022, 12:50   #9
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Re: Mppt performance and Lifepo4 SoC%

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Completely wrong approach. You BMS is the masterbrain in your LifePo4 System and Controlling all your charge sources. BMS is the only one that knows the real SOC of the bank AND each cell, your MPPT only the total voltage at the moment it’s measuring it, it doesn‘t even know how much voltage really „arrive“ at the bank (cable, fuses,shunts…) and 0,1V matters here plus has no glue about the current…and if one cell is at 3,6V while the other is at 3,4V, in total it’s still 14,0V.
So the BMS sets the voltage and SOC when the MPPT should stop charging and restart again on cell level. My system runs at 3,55V=14,2V or 100%SOC charge cut off, doesn’t matter which source is charging as amps are amps. The re-engage charge is only at 3,30V to discharge the bank deeper (as mine is massively oversized) but I only done that after a month at 3,40V so SOC and cells are very balanced (4mV difference). If on passage I raise cut off to 3,6V and re-engage at 3,45V to have the bank as full as possible for security reasons. That also keeps the bank balanced, from time to time, I would say 1 month, it’s good to have it really full and cycle for 3 days a lot microcycles around 3,45v to 3,6V as this really top balances the bank and calibrates the BMS well.
Yes 3,55V it’s actually around 95% SOC of the bank but that’s security overhead while balancing still works well.I could also calibrate it to 3,65V with 100% SOC but well I prefer security and give away 5% capacity for that.
You also cannot go too low eg 3,4V which is 13,6V as no real balancing can happen and your cells in the bank start to differ as the balancing only really works in the steep knee above 3.5V.
What would make a difference is if you could modify the calibration and restart cycle of the BMS to something else then 24H, the only BMS I know that’s possible is the Tao BMS. For the typically oversized bank in a boat that would allow to discharge the bank deeper and cycling it less. Well for the price difference of the Electrodacus to Tao I can buy 4 cells EVE 280AH, which gives me 5000cycles more, so makes no sense. If I would have Winston cells, I would get the Tao BMS.

If you treat your cells well, means max 0.3C dis-/charge, don’t go below 30% keep as cool as possible and balanced the calendar aging has a much bigger effect then your MPPT charging.
I guess we don't have the same type of batteries. My system is pretty simple. My mppt regulator is directly connected to Lifepo4 batteries. Drop-in Lifepo4 batteries trigger HvCutoff at 13.9V. I've never seen cells go above 3.47V. I pass the batteries to capacity test every month.
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Old 17-11-2022, 12:52   #10
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Re: Mppt performance and Lifepo4 SoC%

If your charger is hitting your voltage limit then switches to absorption phase and slowly lowers the current then you're still at your set voltage. There's not much to worry about.

Say you hit your 80% SoC voltage then the current trickles down for 4 hours. You still have your voltage limit right?

I came to the conclusion these things aren't worth worrying about. Full cycles from 20% to 80% would be best but it's not practical. Set your voltages to 80% and be done. How much lifetime are you truly going to lose?
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Old 17-11-2022, 12:59   #11
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Re: Mppt performance and Lifepo4 SoC%

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Originally Posted by Pete7 View Post
Yes, but if the batteries are full so what?



Why?



I disagree. I don't want the MPPT turned off, because then any power supplied comes from the LFP. If the sun is still shinning then I want the MPPT to supply the power rather then use power from the batteries. Once the sun goes down, then allow the batteries to provide power. So the solution is a float charge lower than the fully charged voltage of the LFP which will supply the boat. Interestingly assuming the domestic loads are less than the solar panels output, then the MPPT will dial back the power they need to match the demand. Result full batteries at dusk to meet the nights demands.



I don't see what you are trying to achieve, but a float of 3.2.v per cell would do the same with the equipment you already have and in the event you really do take the batteries that low, then the MPPT will switch to bulk and absorption automatically.

I think you are over thinking this.

Pete
Pete, the float voltage is an approach I have to try but how as the BMS has no float to set. To set re-engage higher means I just microcycle the bank at around 95%SOc and during night it starts mostly in the morning with 85% (if the admiral doesn‘t do a cooking marathon after sundowner)…means I cycle it between 85 and 95%, not good. That’s why I went down to 3,3V reengage charge to get to 60-95%. Wish I would have the Tao BMS to set the calibration cycle to 60hours instead 24h like all other BMS do, so it doesn‘t start to charge bank to 95% SOC each day.
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Old 17-11-2022, 13:04   #12
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Re: Mppt performance and Lifepo4 SoC%

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Originally Posted by WaldPinkler View Post
If your charger is hitting your voltage limit then switches to absorption phase and slowly lowers the current then you're still at your set voltage. There's not much to worry about.

Say you hit your 80% SoC voltage then the current trickles down for 4 hours. You still have your voltage limit right?

I came to the conclusion these things aren't worth worrying about. Full cycles from 20% to 80% would be best but it's not practical. Set your voltages to 80% and be done. How much lifetime are you truly going to lose?
80% is around 3,4V which means no top balancing happing and your bank will get out of balance and weakest cell the most wear. You reach the opposite what you want.
Optimum would be charge it once a week to 3,55V, the rest of the week it cycles between 40 and 70%. The only BMS that can be set is the TAO BMS.
All other BMS start a full cycle every morning when the first charge kicks in.
On anchor I try to get near to it by playing with the parameters in my setup at the moment. Well i need around 200AH/ day and have a 1100AH bank.
Great would be a BMS that has 3-4 different profiles you could simply switch.
One would be „anchor summertime“ where the above once a week to 95%, Rest between 40-70%. Anchor Winter time/bad weather 95% once a week, Rest between xx and 80-90% and „passage“ with daily 98% and xx% till 98% plus a „storage“ profile with 40 till 50% cycling.
That would optimize cycling and lifetime but give you all capacity when you need it.
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Old 17-11-2022, 13:06   #13
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Re: Mppt performance and Lifepo4 SoC%

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That sounds like it's not a real MPPT controller at all.
I don't know but it can pump 30+ amps to my Lifepo4 bank. Here is the video I took when its working with 600 Wp solar panels.

https://youtu.be/ORXeFtJ59gM
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Old 17-11-2022, 13:16   #14
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Re: Mppt performance and Lifepo4 SoC%

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Originally Posted by WaldPinkler View Post
If your charger is hitting your voltage limit then switches to absorption phase and slowly lowers the current then you're still at your set voltage. There's not much to worry about.

Say you hit your 80% SoC voltage then the current trickles down for 4 hours. You still have your voltage limit right?

I came to the conclusion these things aren't worth worrying about. Full cycles from 20% to 80% would be best but it's not practical. Set your voltages to 80% and be done. How much lifetime are you truly going to lose?
The mppt device I use does not have bulk, float, absorption voltage settings. You just set the max charging voltage. Therefore, the transition voltage changes between the phases you mentioned are not present. You already see the performance change I mentioned when you change the max voltage setting at the same time.
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Old 17-11-2022, 13:30   #15
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Re: Mppt performance and Lifepo4 SoC%

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I guess we don't have the same type of batteries. My system is pretty simple. My mppt regulator is directly connected to Lifepo4 batteries. Drop-in Lifepo4 batteries trigger HvCutoff at 13.9V. I've never seen cells go above 3.47V. I pass the batteries to capacity test every month.
Well that’s a bad System design and not suitable for a boat, even a drop in should be able to steer external charging. That’s the reason I didn‘t use drop ins and never will because you don‘t know what’s inside and they are sealed, means your 5$ BMS in that drop in fails (mostly the case) and you can throw the whole battery away. You get what you pay for…

1100A LifePo4 means 16x272AH Lishen cells Tier1 A+ quality calibrated with Electrodacus BMS was 2600Euro delivered to slip in Mallorca incl. all. Ok 300 Euro for the watertide case and 1cm by 2cm thick tinned Cooper busbars for 600A continuous draw on top plus other peanuts makes it 3000Euro for the whole system, AGM would have been more expensive
Like this I know what’s inside and know how System really works and can replace every component.
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