Are my lead acid batteries not charged well enough ?

[Jeroen Pasman]

Hello everyone.
I am a Dutchman living in the Philippines and I run 2 houses, both off the grid. The smaller house is a guesthouse that is for rent and every now and than we have guest to stay over for a couple of nights.
My problem is that my batteries barely make it overnight. I wonder if I made a mistake in my calculations.
My setup.
2 panels of 550w with a VOC of 47v in series. This will give me about 1100w at 90 plus volts.
40 amps 24v controller with 150v max 1120w max input.
2x 12v 100amps lead acid "solar" batteries in serie to create 24v.
24v 1000w inverter.

On the inverter I run a small fridge that use 60w.
I have a water pump that uses 268 w. Standby power is 0 watts. Than I have 1 outlet for aditional power use and USB charger.

Normally the battery power voltage starts at 24.5v in the morning. During the day, it charges up to 27.6v
After 6pm it's dark here, after 8pm the voltage dropped alkready to 26v. Somewhere at 4am the inverter shuts down.

I also run a 24v line directly from the battery. This power is used for all the lights and fans in the house. During the night, they are all off.

I added a watt / amp meter in the 24cand 130v circuit to check on power leaking. There is non in the 24v. Perfect 0 watts 0 amps. The 230v is using very low amps and the 60 to 65 w , if I turn the fridge and water pump off. The wattage and amp is 0.

Are my 6 months old lead acid batteries not good ? they never perform better this situation is since the beginning. Am I not charging them correctly ? Do I need to look for a lifepo alternative ?

Hope to receive some help. Thank you.

 

[rogerheflin]

ok. So you can only reasonably used 50% of lead acid cells.

If fully charged when most charging stops (say 5pm) then say you have to run 12 hours (5-6am) then that gives you a budget of 1200wh / 12hr = 100w/hour, so 60w for the fridge + lights + a tiny bit more and your have nothing left.

Your fridge uses 60w BUT someplace every 12 hours most fridges run through a defrost cycle and that defrost cycle (by itself) will almost deplete the batteries (typically 300-1000w for a while). You need to collect data with a watt-meter connected to it and see what the defrost cycle looks like.

Your panels being 11000w and say even 4 hours of sunlight then you have 4000wh and enough to easily charge the batteries, except on a cloudy day where you will only get 10% or so of the sunny capacity (400wh) and you won't be able to charge the batteries.

Everything seems to be close to undersized for a perfect sunny day and has no margin for bad sunlight days and/or someone using too many lights and/or even someone even opening the fridge too often causing it to draw slightly more power.

 

[OzSolar]

Normally the battery power voltage starts at 24.5v in the morning. During the day, it charges up to 27.6v
After 6pm it's dark here, after 8pm the voltage dropped alkready to 26v. Somewhere at 4am the inverter shuts down.

Can you adjust the low voltage disconnect on the inverter? No worries about the 50% limit at this point. You've already bought the batteries so you'd might as well get through the night.

Are these flooded batteries? If so you can check the specific gravity.

You really need something like the Victron Smart Shunt. Without one, it's like driving a car without a gas gauge.

I suspect the tare losses of your inverter are responsible for large part of of your energy usage.

 

[Jeroen Pasman]

ok. So you can only reasonably used 50% of lead acid cells.

If fully charged when most charging stops (say 5pm) then say you have to run 12 hours (5-6am) then that gives you a budget of 1200wh / 12hr = 100w/hour, so 60w for the fridge + lights + a tiny bit more and your have nothing left.

Your fridge uses 60w BUT someplace every 12 hours most fridges run through a defrost cycle and that defrost cycle (by itself) will almost deplete the batteries (typically 300-1000w for a while). You need to collect data with a watt-meter connected to it and see what the defrost cycle looks like.

Your panels being 11000w and say even 4 hours of sunlight then you have 4000wh and enough to easily charge the batteries, except on a cloudy day where you will only get 10% or so of the sunny capacity (400wh) and you won't be able to charge the batteries.

Everything seems to be close to undersized for a perfect sunny day and has no margin for bad sunlight days and/or someone using too many lights and/or even someone even opening the fridge too often causing it to draw slightly more power.

Thank you for your reply and the time you took to look into my system. Please correct me if I am wrong but since I am running a 24v system with 2x 12v 100amp battery in serie, should bring my watt hours to 24. Am I correct ? I choose these setting to have that 24 what hours so I double my needs. But still the battery runs empty so easy.

Maybe my charging settings are not correct. What would be a right charging voltage for this setup ?

I will look up the current settings on my display tomorrow and share them here.

Thanks allready.

 

[Jeroen Pasman]

Can you adjust the low voltage disconnect on the inverter? No worries about the 50% limit at this point. You've already bought the batteries so you'd might as well get through the night.

Are these flooded batteries? If so you can check the specific gravity.

You really need something like the Victron Smart Shunt. Without one, it's like driving a car without a gas gauge.

I suspect the tare losses of your inverter are responsible for large part of of your energy usage.

Thank you for your reply. Yes I can adjust the min voltage and restore voltage for the inverter. Also the charging voltage of the battery. I will check the current settings tomorrow. Will check the flood thing aswell.
I will come back on the shunt.

Thanks for helping me out.

 

[Jeroen Pasman]

Thank you for your reply. Yes I can adjust the min voltage and restore voltage for the inverter. Also the charging voltage of the battery. I will check the current settings tomorrow. Will check the flood thing aswell.
I will come back on the shunt.

Thanks for helping me out.

Just checked, the batteries I use are VLRA battery GEL type deep cycle for Solar Systems.

 

[rogerheflin]

Thank you for your reply and the time you took to look into my system. Please correct me if I am wrong but since I am running a 24v system with 2x 12v 100amp battery in serie, should bring my watt hours to 24. Am I correct ? I choose these setting to have that 24 what hours so I double my needs. But still the battery runs empty so easy.

Maybe my charging settings are not correct. What would be a right charging voltage for this setup ?

I will look up the current settings on my display tomorrow and share them here.

Thanks allready.

You have 1200wh USABLE. The battery capacity is 2400wh(100*24), but with lead acid using greater than 50% will significantly reduce the cycle count.

 

[OzSolar]

Just checked, the batteries I use are VLRA battery GEL type deep cycle for Solar Systems.

The next step is to make sure they are actually getting fully charged.

Actually the next step is to make sure both batteries are the same voltage. When batteries are series they can drift apart from each other. EG: One could be 12.2 volts and the other one 14.8 Volts and that would need to be remedied if that's what you find.

Fully Charger: You'll need to refer to the specifics for your battery but for now lets use the rule of thumb for sealed batteries. When you can hold your battery at 2.4 Volts per cell with 1 amp per 100 amp hours of capacity you battery is full.

In other words: If your battery can stay at ~28.8 Volts with ~2 amps then it's full.

 

[Jeroen Pasman]

You have 1200wh USABLE. The battery capacity is 2400wh(100*24), but with lead acid using greater than 50% will significantly reduce the cycle count.

Wow.... That was out of my calculations. 50 % holy cow. That's not good. Isa life po batt dieing better in this case ?

 

[Jeroen Pasman]

The next step is to make sure they are actually getting fully charged.

Actually the next step is to make sure both batteries are the same voltage. When batteries are series they can drift apart from each other. EG: One could be 12.2 volts and the other one 14.8 Volts and that would need to be remedied if that's what you find.

Fully Charger: You'll need to refer to the specifics for your battery but for now lets use the rule of thumb for sealed batteries. When you can hold your battery at 2.4 Volts per cell with 1 amp per 100 amp hours of capacity you battery is full.

In other words: If your battery can stay at ~28.8 Volts with ~2 amps then it's full.

Ok. 8 think we might have some room for improvement here.

Specs from my setup ,
Controller :

Batt : sla
Voltage grade : auto
Charge voltage : 27.6 volt
Charge current: 39 amp
Limit voltage :21 volt
Float charge :27.6volt
Egg charge : 29 volt

Discharge

UV recov : 25 volt
UV protect : 21 volt
OV recov : 29 volt
OV protect :32 volt

Setting on the inverter are very minimal

Low voltage protection :23.4 volt
Low voltage restore : 25.6 volt.

I checked the balance of the batt when I bought them and twice now during 7 months of use . They voltage is the same.

 

[crossy]

Wow.... That was out of my calculations. 50 % holy cow. That's not good. Isa life po batt dieing better in this case ?

Yes, lithium iron phosphate (LiFePO4) batteries can go to pretty well 100% capacity without damage (and they have electronics in the BMS to prevent you over from discharging), although treating them gently does increase their lifespan.

 

[seneysolar]

Charging at 27.6v will likely not get you a full charge.

Check with your battery specs but most sealed batteries should be able to go to 28.5v in bulk phase, 27.6 would be a normal absorbtion phase after that.

 

[Jeroen Pasman]

Charging at 27.6v will likely not get you a full charge.

Check with your battery specs but most sealed batteries should be able to go to 28.5v in bulk phase, 27.6 would be a normal absorbtion phase after that.

Thank you for your confirmation of my thoughts.. so I need to change my settings. Can you point me I to the right direction and give me some advise ?

 

[seneysolar]

Thank you for your confirmation of my thoughts.. so I need to change my settings. Can you point me I to the right direction and give me some advise ?

What is the make and model of your batteries? Have you looked up their recommended charge rates?

 

[Supervstech]

Keep in mind, your inverter is pulling some wattage ALL the time.
Figure 25 to 75 depending on quality of the inverter.
During the day, its no problem, but as soon as the sun stops producing, say at 6pm, the watts add quick.
25x12 is 300Wh gone just from the inverter being on.
Add in any use from the fridge, amd usb, and it wont take long to eat up 1200Wh.
And if you have been draining below 50% for long, the batteries will be degrading.

 

[Jeroen Pasman]

What is the make and model of your batteries? Have you looked up their recommended charge rates?

The brand name is solar homes. I tried to find specs but I can't find anything. I am asking now at dealers for the charge settings.

 

[seneysolar]

The brand name is solar homes. I tried to find specs but I can't find anything. I am asking now at dealers for the charge settings.

It appears these are a Philippines only battery... Likely rebranded but either way i cant find any data on them.

I would not hesitate to set your charge voltage at 28.4 for the bulk phase and see if you get any improvement. Personally id try an equalization charge but i cant instruct you to do that without manufacturer data and the right equipment.

You are on the edge of not enough battery. And your inverter has to draw something to be on, all do. Most dont measure or display their own consumption. For estimate sake id probably assume 40w for now.

 

[adrasto2006]

It appears these are a Philippines only battery... Likely rebranded but either way i cant find any data on them.

I would not hesitate to set your charge voltage at 28.4 for the bulk phase and see if you get any improvement. Personally id try an equalization charge but i cant instruct you to do that without manufacturer data and the right equipment.

You are on the edge of not enough battery. And your inverter has to draw something to be on, all do. Most dont measure or display their own consumption. For estimate sake id probably assume 40w for now.

I think the problem is not enough usable energy. Consider

2x 12V 100Ah lead-acid batteries in series, giving 24V and 100Ah total capacity (2.4 kWh).

Usable capacity: Lead-acid batteries should not be discharged below 50% to avoid damage, so you have about 1.2 kWh of usable energy.

Your battery bank has 1.2 kWh usable energy, but your fridge alone consumes about 1.44 kWh/day, which already exceeds the usable capacity.

If you add the water pump and any additional loads, it's clear the batteries are undersized for the demands.

 

[Jeroen Pasman]

It appears these are a Philippines only battery... Likely rebranded but either way i cant find any data on them.

I would not hesitate to set your charge voltage at 28.4 for the bulk phase and see if you get any improvement. Personally id try an equalization charge but i cant instruct you to do that without manufacturer data and the right equipment.

You are on the edge of not enough battery. And your inverter has to draw something to be on, all do. Most dont measure or display their own consumption. For estimate sake id probably assume 40w for now.

Thank you for this.
In my solar controller i could not find a lot of setting to play with until I changed the voltage recognition from auto to 24v.
Now I can change the charging to 28.4 volts.
As soon as I did that, the battery voltage jumped from 27.6v to 28.4v in the solar controller. I was like. Huh. What the heck....got my voltage meter and measured the battery. 28.4 volts...
In my book a 24v 100ah battery setup can not jump from 27.6v to 28.4 v in 1 second.. this leaves me with the fact that the battery set was always 28.4v but the settings in the controller are playing funny games ? I also measured the batt separated and there is a difference. 14.3 on 14.1 volt. I will check this the coming days.

 

[Jeroen Pasman]

It appears these are a Philippines only battery... Likely rebranded but either way i cant find any data on them.

I would not hesitate to set your charge voltage at 28.4 for the bulk phase and see if you get any improvement. Personally id try an equalization charge but i cant instruct you to do that without manufacturer data and the right equipment.

You are on the edge of not enough battery. And your inverter has to draw something to be on, all do. Most dont measure or display their own consumption. For estimate sake id probably assume 40w for now.

Manufactor date is may 11 2024

 

[Jeroen Pasman]

I think the problem is not enough usable energy. Consider

2x 12V 100Ah lead-acid batteries in series, giving 24V and 100Ah total capacity (2.4 kWh).

Usable capacity: Lead-acid batteries should not be discharged below 50% to avoid damage, so you have about 1.2 kWh of usable energy.

Your battery bank has 1.2 kWh usable energy, but your fridge alone consumes about 1.44 kWh/day, which already exceeds the usable capacity.

If you add the water pump and any additional loads, it's clear the batteries are undersized for the demands.

This can be very true since I never calculated the 50% discharge..
Maybe I will end up with investing in a 24v life po battery. With only very little % loss on discharge a 100ah might be enough. But if I want to go bigger I need to calculate how many amps I can still charge with my setup. 2x 550w 45v panel on a 40amps controller..

 

[wpns]

Personally id try an equalization charge but i cant instruct you to do that without manufacturer data and the right equipment.

I’m not sure about how to do an equalization charge on a gel battery, so I would be cautious without manufacturer data as well. More than a couple cycles all the way down to zero on lead acid batteries will essentially destroy them.

I think you need to start with a system design that will cover your loads and have some margin without a lot of supervision.

If you do get LFP batteries, make sure you get 24 V batteries and not 12 V batteries in series, and that your solar charge controller can be set for LFP or the appropriate equivalent voltages.

 

[adrasto2006]

This can be very true since I never calculated the 50% discharge..
Maybe I will end up with investing in a 24v life po battery. With only very little % loss on discharge a 100ah might be enough. But if I want to go bigger I need to calculate how many amps I can still charge with my setup. 2x 550w 45v panel on a 40amps controller..

Are the batteries hitting 100 soc everyday during the day?

 

[Jeroen Pasman]

Are the batteries hitting 100 soc everyday during the day?

No. Not always, on a bright sunny day yes they will. Meanwhile I changed 2 major settings. The batteries are now charging to I higher voltage level , 28.4v instead of 27.6v and I changed the setting in the fridge. This was at the highest setting and that's not needed. I bring it back to setting 1, and that is cold enough. Now the fridge is using only 35w instead of almost 60. I ha e no more stop out during the night, Evey morning there is still 26.5v left for now it's good enough. If we will receive more bookings and have payed guests in our guesthouse I will upgrade to a 24v 100amp life po battery to extend the standby time.




Thank you for all the help.

 

[Bluedog225]

Consider upgrading the whole deal to 48 volts.