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MPP Solar "premature float bug"

JAS

Solar Enthusiast
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Jan 16, 2020
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Hey all,

So I assume from searching the forum (as well as a general google search), that the so called "premature float bug" still exists with all MPP Solar units.

Question: Is this as big of a deal if using LFP? Or is it more of an issue with Lead Acid?

And does it apply only with solar charging or also with the AC grid charging?

Thanks,

Jeff
 
https://diysolarforum.com/threads/problem-charging-battery-with-mpp-solar-lv5048-inverter.3261/


The root cause of the problem is the setting 32 "Bulk Charging Time". There is a bug in the firmware that when this setting is set to "Automatuic" the charger does not charge the batteries correctly. This bug is known as the premature float bug. I had open a case on another forum where they explained to me what it is etc. Take a look at it at https://powerforum.co.za/topic/4838...bank-with-all-in-one-inverter-from-mpp-solar/

Since there is no fix to this problem for the MPP LV5048 you need to work around it by doing the following:

- Setting 5 "Battery type" must be set to User defined
-Make sure Setting 26 "Bulk Charge Voltage is set 58.4V (Maximum Voltage)
-Setting 27 "Floating Charge Voltage " is set to 53.4V
-Change Setting 32 "Bulk Charge Time" from automatic and set it to fixed amount. You can start with 360 or 420 minutes ( by changing it form automatic to a fixed value you will be either overcharging or undercharging it) So you will need to play around with the minutes. But since the max bulk charging voltage is 58.4V and not 60V and also as you state you cannot equalize the batteries the damage of overcharging is minimum (makes sure that you always have enough water in the batteries) and is less harmfull then undercharging.

Start with the above and measure the gravity at the end of the charge cycle (once the Battery voltage goes back down to the float charge voltage 53.4V) it should be somewhere around 1.275.
 
https://diysolarforum.com/threads/problem-charging-battery-with-mpp-solar-lv5048-inverter.3261/


The root cause of the problem is the setting 32 "Bulk Charging Time". There is a bug in the firmware that when this setting is set to "Automatuic" the charger does not charge the batteries correctly. This bug is known as the premature float bug. I had open a case on another forum where they explained to me what it is etc. Take a look at it at https://powerforum.co.za/topic/4838...bank-with-all-in-one-inverter-from-mpp-solar/

Since there is no fix to this problem for the MPP LV5048 you need to work around it by doing the following:

- Setting 5 "Battery type" must be set to User defined
-Make sure Setting 26 "Bulk Charge Voltage is set 58.4V (Maximum Voltage)
-Setting 27 "Floating Charge Voltage " is set to 53.4V
-Change Setting 32 "Bulk Charge Time" from automatic and set it to fixed amount. You can start with 360 or 420 minutes ( by changing it form automatic to a fixed value you will be either overcharging or undercharging it) So you will need to play around with the minutes. But since the max bulk charging voltage is 58.4V and not 60V and also as you state you cannot equalize the batteries the damage of overcharging is minimum (makes sure that you always have enough water in the batteries) and is less harmfull then undercharging.

Start with the above and measure the gravity at the end of the charge cycle (once the Battery voltage goes back down to the float charge voltage 53.4V) it should be somewhere around 1.275.
I have two MPP LV6548 units. Never heard of this bug, nor am I experiencing any issues with Lishen and CATL cells, with Heltec/JK 200amp BMS's
My float is at 54V, my charge is at 55.2V. Cells stay within .008V of each other. The Inverters are in parallel.
 
@Sanwizard

Good to know. So maybe this "bug" is not as important in relation to LifePo4 batteries?

What do you have for your setting #32?
 
There is no menu item 32. It skips over 32. 31 is equalization voltage, which Inhave at 56V (my float is set at 54V, and charge at 55V), and item 33 is eqalization time, and that is set at 5 min.
Basically, it never goes into that mode, as charging completes at 55V, and it then floats at 54V.
My BMS has a 2 amp active balancer, and that keeps the cells balanced.
 
There is no menu item 32. It skips over 32
So according to time2roll's link, that implies your unit acts the same as if setting 32 is set to auto. Hence, supposedly your unit is also subject to this bug. And after re-reading the linked thread, it appears that this also affects LFP as well. (Although, I'm not certain if it is as detrimental to LFP like it could be to LA). But, I'm also not sure I understand the dynamics of charging all that well yet either o_O
 
I am not familar with LV6548 operation but it sounds like the 'automatic' mode of absorb exit may be based on charge current taper down level instead of a timed absorb phase. Likely an exit trigger based on 5% or 10% of charger bulk current setting. Perhaps PV charging is not included in the charge taper current measurement when grid inverter charging is contributing to battery charging. With PV supplying the battery absorb taper down current, the inverter thinks the battery charge current has tapered off in current and exits absorb. This is a guess on my part. Would have to know exactly what 'automatic' mode is doing to be more certain.

For LFP batteries charged at less than 0.2 CA rate, zero absorb time will not make much difference in achieving full charge. With low charge rate the absorb taper down current period is very short in time.

For LFP batteries with BMS that does not balance a cell until it rises above 3.4v, using current taper down absorb exit can result in insufficient balancing time on battery array. Best to use an absorb voltage of 3.50-3.55v per cell x number of series cells, which is a voltage that can be tolerated for some time without much battery stress, and use timed absorb phase to ensure enough cell balancing time.
 
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Not sure about all that, as I keep my system off the grid as much as possible. I keep the grid breaker to the AC in side of the inverters off. Been off since I installed them, so I have no experience with grid charging with my units. That being said, I have had zero issues, and the DIY LFP batteries (26KW) work fine.
 
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