What does the “bulk charging voltage” of a hybrid inverter mean (MPP Solar LVX 6048)?

[alejnavab]

I have an inverter, brand MPP Solar, model LVX 6048. It is a hybrid inverter, as in having an AC input, AC output, PV input, and battery input/output. I'm using it with lithium batteries. On the manual, it says the program (setting) #17 is the “bulk charging voltage”, as shown in the screenshot below. Here is the user manual.



I would like to know what does that mean.

I'm using the inverter with lithium batteries, so I've already set program/setting #14 (battery type) to USE (user-defined), so that I can adjust the value of program #17.

I know that the (re)charge cycle/process of a secondary/rechargeable battery consists of a bulk stage, absorption stage, float stage, and optionally an equalization stage once every 1-6 months. The bulk charging stage of a battery is done at constant current while the voltage increases from its current SoC (state of charge) to about 70%-80% of its full charge. In other words, the battery voltage is not constant during this stage. Hence, I don't think the “bulk charging voltage” setting of the previous inverter refers to the voltage to be supplied to the battery, because it is in reality varying as the batteries charges more and more.

But I think it may refer to the voltage at which the bulk stage ends (and so the absorption stage begins). Is this the case? If not, what does the "bulk charging voltage" mean?

 

[Samsonite801]

Yeah I would lean towards that assumption too, that it would be the trigger voltage to move to absorption, since bulk is a CC stage. That's usually how I always interpreted it when reading the charge stage voltages in manuals too because often times, they list a voltage number under the 'bulk' column...

 

[wattmatters]

But I think it may mean is the voltage at which the bulk stage ends (and so the absorption stage begins). Is this the case?

Yes.

 

[time2roll]

Bulk voltage will climb to the set point during bulk, amps are constant. When amps taper, battery is in absorption and voltage remains constant at that set point.

Next question is how long to hold the voltage in absorption before dropping to float.

 

[alejnavab]

Next question is how long to hold the voltage in absorption before dropping to float.

While the end point of the bulk stage is specified as a voltage (since it is increasing in this stage), the end point of the absorption stage should be specified as a current (since it is decreasing in this stage), right? As shown in the following figure (taken from this video):

 

[time2roll]

Yes there is often a tail current as a trigger or a simple timer. Maybe both.

 

[robby]

Bulk voltage will climb to the set point during bulk, amps are constant. When amps taper, battery is in absorption and voltage remains constant at that set point.

I read about that also but the current is not really constant since they vary a lot depending on what the PV is bringing in. Mine goes anywhere from 1Amp per pack to 30Amps if I am getting full PV power.

Next question is how long to hold the voltage in absorption before dropping to float.

As far as I can see the Float stops when the batteries are no longer trying to pull anymore current.

 

[time2roll]

I read about that also but the current is not really constant since they vary a lot depending on what the PV is bringing in. Mine goes anywhere from 1Amp per pack to 30Amps if I am getting full PV power.

"Constant in Bulk" with solar would be the maximum available amps.

 

[Zwy]

I have an inverter, brand MPP Solar, model LVX 6048. It is a hybrid inverter, as in having an AC input, AC output, PV input, and battery input/output. I'm using it with lithium batteries. On the manual, it says the program (setting) #17 is the “bulk charging voltage”, as shown in the screenshot below. Here is the user manual.

View attachment 105667

I would like to know what does that mean.

I'm using the inverter with lithium batteries, so I've already set program/setting #14 (battery type) to USE (user-defined), so that I can adjust the value of program #17.

I know that the (re)charge cycle/process of a secondary/rechargeable battery consists of a bulk stage, absorption stage, float stage, and optionally an equalization stage once every 1-6 months. The bulk charging stage of a battery is done at constant current while the voltage increases from its current SoC (state of charge) to about 70%-80% of its full charge. In other words, the battery voltage is not constant during this stage. Hence, I don't think the “bulk charging voltage” setting of the previous inverter refers to the voltage to be supplied to the battery, because it is in reality varying as the batteries charges more and more.

But I think it may refer to the voltage at which the bulk stage ends (and so the absorption stage begins). Is this the case? If not, what does the "bulk charging voltage" mean?

There won't be absorption or equalization on USE, just bulk and float. Bulk is where you want to stop charging, it needs to be set high enough to trigger cell balancing in the BMS or balancer.

Float is where the SCC will attempt to maintain battery voltage by using PV or grid power.

It's best to set float about 0.5V below bulk setting due to the flat SOC voltage readings with LFP.