Interfacing Lead Acid batteries with inverter

[Avier]

Hello Friends,

is there any device to pair simple lead acid battery to modern inverters?

I have a Solis S5-EH1P6K-L. The vendor told me lead acid work fine but I won't be able to see the charge level on screen.

@peufeu do you know anything about it?

Thank you everyone!

 

[Hedges]

Device?

The data sheet says lead-acid is supported. Read the manual and find how to set charging parameters. Battery data sheet should give preferred voltages, current, time.

https://www.ginlong.com/uploads/file/Solis_datasheet_S5-EH1P(3-6)K-L_Global_V2,5_2022_12.pdf

For lead-acid, there should be a temperature sensor. See if that is mentioned.

 

[Avier]

The data sheet says lead-acid is supported.

Yes, it is, but lead acid don't have CAN BUS for communication. I was wondering whether those need some kind of interface (CAN BUS equipped) which allows the inverter to work with them the way it does with Li-ion batteries.

 

[Hedges]

No, inverters using lead acid only know voltage, current, temperature, and time.

Some models may be better than others at guessing when an equalization charge (for FLA) should be performed. What you can do is periodically check voltages of individual cells (if terminals available) or of 6V or 12V batteries. And specific gravity of cells using a hygrometer.

When configuring the system, you should be able to set voltage (per cell, or for whole battery) for absorption, float, equalization, low-voltage disconnect. Set charge current, and time for absorption and for equalization. If VRLA not FLA, the settings should prevent equalization. Instead of BMS communicating what it wants, you program that up front.


I suppose you've considered advantages of lead-acid vs. lithium and decided lead-acid is what you want?

 

[Avier]

I suppose you've considered advantages of lead-acid vs. lithium and decided lead-acid is what you want?

Just happened I got them used. I might end up switching to lithium after these.

Instead of BMS communicating what it wants, you program that up front.

And yet I thought that after all there could have been some interface around that can manage automatically all of these parameters and feed them back to the inverter via CAN BUS as if it was a lithium system.

My main concern obviously is knowing when the batteries are approaching 50% (dis)charge so that I can prevent it to go further.

 

[Hogheavenfarm]

I just run a shunt with a battery monitor in between. No automated way of shutting down the loads at 50% though, not that I have found, they will "alarm" at your preset voltage though.

 

[Hedges]

No communication (unless it works with a smart shunt). Inverter should track amp hours in/out, also consider instantaneous voltage and current, to determine SoC. Accuracy of algorithms will vary.
The inverter should have low voltage disconnect setting and probably low SoC disconnect setting.

With lead-acid more than lithium, it is important to avoid sitting at low SoC and important to fully and properly recharge. Which means when you run it down vs. when charging is available will matter. Find a way to shed loads before they discharge it too much, try to operate some loads when there is surplus production.

 

[peufeu]

Yes in the Solis the lead battery is the manual mode, user should enter all parameters via the GUI. I think there's a temperature probe supplied with the inverter.

 

[Avier]

Inverter should track amp hours in/out

Was thinking the same, and if that is not precise enough installing a dedicated wi-fi energy meter on batteries.

Thank you all so much for the info. I will post an update once I do the actual connection.

 

[Avier]

Finally yesterday we did the connections.

So we have x8 of these



They are 2 series of 4 connected in parallel to the inverter.
Am I doing the calculation right if I consider each series being 7.2 kW (150*48), for a total of 14.4 kW?

These is what the inverter gave me back once I selected the right type of battery (lead acid):



Each of these parameters can be modified. I haven't touched any of them.

Yes in the Solis the lead battery is the manual mode, user should enter all parameters via the GUI. I think there's a temperature probe supplied with the inverter.

I am not sure the probe has been supplied but yes, the inverter expects it to be connected via CAN (normally used for lithium communication). However, in case there is not a temperature probe the inverter lets us choose between three preset temperature scenarios: hot +- 45 °C, warm +- 25 °C and cold +- 5 °C. We chose option "warm" as we are in a fresh basement.

Here is how it looks like in the main page. It shows the SOC and gives the current Voltage.




What I am wondering is:

Can I improve performance and accuracy by modifying some of the above parameters?
For example what you see above is the max (0.53 kW) the battery can charge. Can that be increased?
How accurate is the SOC i see in the picture?

Hope I am not mixing things up.
Thank you for your time and help!!

 

[Hedges]

For one, you could change battery capacity to 300 Ah.

Float voltage 13.62 x 4 = 54.48V

You'll need to see manual or data sheet for charging voltage.
Inverter doesn't list "boost", only "equalize" which normally means FLA over-charge done occasionally.
56.4V / 4 = 14.1V per 12V battery, lower than I would expect for normal charge of AGM. Is it correct for gel? RTFM (battery).
Does inverter go to what it calls "equalize" every cycle, or maybe every month? RTFM (inverter). Lead-acid wants full charge, including absorption for couple of hours, every time.

 

[peufeu]

They are 2 series of 4 connected in parallel to the inverter.
Am I doing the calculation right if I consider each series being 7.2 kW (150*48), for a total of 14.4 kW?

12V 150Ah
4S = 48V 150Ah
4S2P = 48V 300Ah or 14.4 kWh so this is correct.

If you want lead acid batteries to last a long time, it is necessary to not discharge them below about 50% capacity, so you will only get half that capacity. Maximum depth of discharge for long life should be specified in the battery manual. Discharging below that will significantly shorten the life of the battery. Over-discharging, even once, will ruin it.

> I am not sure the probe has been supplied but yes, the inverter expects it to be connected via CAN

They're cheating a little bit: the CAN connector has 8 pins, but CAN doesn't use all 8 pins. So they kept 2 pins for the probe, which is a simple analog sensor (probably thermistor).

> For example what you see above is the max (0.53 kW) the battery can charge. Can that be increased?

Yes, given the high Ah capacity you can probably charge much harder than this. You should check the battery manual for what charge current you can use.

 

[Hedges]

Some batteries tolerate 70% or 80% depth of discharge without significantly reducing total life-cycle Ah.
That can let you get your money's worth sooner by wearing them out sooner, or tolerate occasional deeper discharge.
I planned my SunXtender for 70% DoD (grid backup). But need to shed some excess loads and get some panels aimed SE in order to operate through without low battery shutdown.

 

[Avier]

RTFM (battery)

Right! An here it is

https://www.monbat.com/wp-content/uploads/2022/03/Data-sheet-12MVR150.pdf

If I wanted to follow parameters on data sheet shall I modify the following:
Floating Voltage for each battery is (2.27*6=) 13.62 V. Being 4S2P, should it be set to (13.62*4=) 54.48 V instead of 53.5 V?
Likewise for Equalization charge voltage (2.32*6=) 13.92*4= 55.68 V instead of 56.4 V

Inverter doesn't list "boost"

Can Force Charg Voltage have anything to do with "boost"?
How about ForceChg PLmp?

Does inverter go to what it calls "equalize" every cycle, or maybe every month?

No chance to find it out on Solis manual IMO..

Yes, given the high Ah capacity you can probably charge much harder than this.

I believe so. For some reason either the inverter is limiting charging pow according to some incorrect info I have been giving or the batteries have some problem. Hope for the first.

If you want lead acid batteries to last a long time, it is necessary to not discharge them below about 50% capacity

I set the limit at 55%. Not sure the inverter will comply though.

Some batteries tolerate 70% or 80% depth of discharge without significantly reducing total life-cycle Ah.

How can we tell if that is the case?

 

[Hedges]

Right! An here it is

https://www.monbat.com/wp-content/uploads/2022/03/Data-sheet-12MVR150.pdf

View attachment 152464

If I wanted to follow parameters on data sheet shall I modify the following:
Floating Voltage for each battery is (2.27*6=) 13.62 V. Being 4S2P, should it be set to (13.62*4=) 54.48 V instead of 53.5 V?
Likewise for Equalization charge voltage (2.32*6=) 13.92*4= 55.68 V instead of 56.4 V

Battery says 2.4V/cell for Boost. That's daily charging. Need to figure out where in inverter to set that.
Also absorption time. But how long should that be? Graph shows continuous (from time = 4 hours to time = 24 hours). I'm accustomed to "2 hours" before it drops voltage to float. That's for cyclical use.

Temperature adjustment is given: "Temperature correction:-4mV / cell / oC"

For float usage (sitting indefinitely on a grid charger, just for power fail backup like UPS), in that case it uses the reduced float voltage.

The battery I use has more detailed manual.

https://sunxtender.com/pdfs/Sun_Xtender_Battery_Technical_Manual.pdf

Can Force Charg Voltage have anything to do with "boost"?
How about ForceChg PLmp?

I suspect that refers to using grid or generator, rather than waiting for PV.

How can we tell if that is the case?

RTFM.

 

[Avier]

Battery says 2.4V/cell for Boost. That's daily charging. Need to figure out where in inverter to set that.

Haven't found it so far.

Temperature adjustment is given: "Temperature correction:-4mV / cell / oC"

Is that in the data sheet?

RTFM

The battery data sheet doesn't seem to mention anything about how low DoD can be on that battery.

Anyways, I modified a few parameters, like capacity (300 Ah instead of 100 Ah), Floating Voltage and Equalization charge voltage. These last two as stated in my last post. I haven't notice any big change: max power on charge is still 0.5 kW. I'd say they barely reach 80% after a full day of charge and get as low as 20% after the night. I'm considering to let them charge for two days, unplugging them at night.

What else can I try to increase the charge?

 

[Hedges]

What voltage does it reach after a full day of charging? Or does it reach some high, then drop lower?

You could try setting equalization to 2.40V per cell and frequency of equalization daily. That would be a full charge.

 

[Avier]

?‍?‍?‍ I couldn't see it.

Is Temperature correction supposed to be what they called Temperature Compensation in Solis battery setup?
If 4mV is intended per cell, that means 24mV per battery and 24*4 if the batteries are 4 in series?

I luckily solved the 0.5kW max charge.
I just had to modify I_Max Charge. I set it gradually at 60A checking the battery temperature. At 60A the batteries could absorb about 3.5kW reaching what is seemed full charge in about 4h. It charged something like 11kW, so that meant batteries weren't faring that well. Hope they didn't take too much damage.
Is it safe to increase further the Ampere limit on charge and discharge and let the batteries behave with their factory limits?

While I was at it I seemed to understand what Equalizing Voltage is: as soon as the batteries reached full charge they started a loop to limit intake current from PV - the voltage was going up rapidly to 57V to then going back at around 52V and at the same time cutting absorption from PV.
I then brought Equalizing Voltage to 53V. Result: battery voltage wasn't exceeding 53V.

 

[Hedges]

Temperature compensation is -4 mV per cell, not +4 mV per cell. Voltage should be increased for cold temperature, decreased for hot temperature.