Keeping batteries in series in balance

[Helimadness]

Hi, Going to set up a total off grid solar system for our holiday house that is in a remote location. Going for 1.8kw panels and was going to get 4 x 200ah 12v lead carbon batteries in series to get 48v to keep the current down.
As we will not be on site for a lot of the year I am concerned about not being able to keep a close eye on the batteries and making sure they stay balanced. Is there a way of making sure the 4 x 12v batteries stay balanced within the 48v series system ?
Cheers

[Mike90250]

t 2 x 200ah 12v lead carbon batteries in series to get 48v to keep the current down

That's going to need to be 4 , 12V batteries in series, to get 48V @ 200ah

2 batteries will get you 24V @ 200ah

[Helimadness]

That's going to need to be 4 , 12V batteries in series, to get 48V @ 200ah

2 batteries will get you 24V @ 200ah

Sorry Typo meant to be 4 x 12v. Got it right on the second half of the post Have edited thanks

[NorthRick]

If the batteries are wired in series they will stay in balance on their own. Even in parallel on a system that spends most of it's time in float they won't tend to get out of balance.

[jflorey2]

Hi, Going to set up a total off grid solar system for our holiday house that is in a remote location. Going for 1.8kw panels and was going to get 4 x 200ah 12v lead carbon batteries in series to get 48v to keep the current down.
As we will not be on site for a lot of the year I am concerned about not being able to keep a close eye on the batteries and making sure they stay balanced. Is there a way of making sure the 4 x 12v batteries stay balanced within the 48v series system ?

Charge using the voltages and times recommended by the battery manufacturer. They will stay in balance. Lead acid batteries in series "self balance" during charging.

[Sunking]

Hi, Going to set up a total off grid solar system for our holiday house that is in a remote location. Going for 1.8kw panels and was going to get 4 x 200ah 12v lead carbon batteries

Start saving your money to replace the carbon batteries.

[Helimadness]

Start saving your money to replace the carbon batteries.

Not a fan of the carbon batteries ? From what I read they have much better life and can be discharged to a higher rate than lead acid.

I am a big fan of Lithium and have made several smaller 18650 packs for some RC stuff that have preformed amazing. Will be for down the track when we are living on site but. Need something a bit more off the shelf for now

[Helimadness]

Charge using the voltages and times recommended by the battery manufacturer. They will stay in balance. Lead acid batteries in series "self balance" during charging.

I totally get how batteries in parallel will stay in balance but dont understand how batteries in series can. Dont really have any experience with larger banks in series. The battery voltage read is only the total voltage yeah. So 4x12v = 48v. So the charger can only see the 48v. What happens if 2 batteries are at 11v and 2 at 13v Its still 48v total which is what the charger will see but 2 will get over charged and 2 over discharged yeah ?

I found this HC02 Equalizer. Looks like a good thing to have ?

https://www.amazon.com/Battery-Equalizer-Voltage-Balancer-support/dp/B01JJ4X8CO

Cheers

[Sunking]

I totally get how batteries in parallel will stay in balance but dont understand how batteries in series can.

No you do not understand anything abou thow batteries charge them from this statement. All batteries except Lithium are self balancing. When one cell becomes charged up, the curent is still passed along to lower cells to charge up. Simple Series Law. !1 = I2 = I3...... The cells that are fully charged stop charging and start heating up, but they still pass current. Try that with Lithium and you will have an explosion.. Last thing you want is Lithium Ion Batteries on a solar system. Buying any battery Balancer is like buying Lithium Ion Batteries for Solar. You just throw away good money.

[Helimadness]

No you do not understand anything abou thow batteries charge them from this statement. All batteries except Lithium are self balancing. When one cell becomes charged up, the curent is still passed along to lower cells to charge up. Simple Series Law. !1 = I2 = I3...... The cells that are fully charged stop charging and start heating up, but they still pass current. Try that with Lithium and you will have an explosion.. Last thing you want is Lithium Ion Batteries on a solar system. Buying any battery Balancer is like buying Lithium Ion Batteries for Solar. You just throw away good money.

Ok so the high batteries naturally slow down due to getting inefficient and let the low ones catch up. My concerns were because it might be left for 6+ months at a time unattended I wanted to make sure it was safe over time. Planning on setting up a security system I can monitor remotely and will try and work out a what to get the solar and battery info remotely as well so I can at least monitor.
Cheers

[Mike90250]

For extended absence the most critical thing is preventing the batteries from going dry and exposing plates.
Set your Absorb times to something low, 10 min, and locate what the FLOAT SERVICE voltage settings are, since you won't be cycling these. There are NO loads while you are absent, correct?
Inverter powered off ?

[Helimadness]

For extended absence the most critical thing is preventing the batteries from going dry and exposing plates.
Set your Absorb times to something low, 10 min, and locate what the FLOAT SERVICE voltage settings are, since you won't be cycling these. There are NO loads while you are absent, correct?
Inverter powered off ?

The Lead carbon batteries I was looking at are so called "Maintenance free" So I assume no need or option to top up liquids.
I was thinking of leaving the system live. Maybe just having a outside light on a timer so the place doesn't look totally abandoned. Also will give power to things like cameras I can connect to remotely and will look at setting up remote monitoring for the solar and batteries. So will have very minimal current draw. There is a neighbour I can call on if things start to go pear shaped.

I also love the tech side so the remote monitoring thing is the nerd coming out in me

Cheers

[Sunking]

My concerns were because it might be left for 6+ months at a time unattended I wanted to make sure it was safe over time.

Well then you do not have much to worry about. Batteries become unblalanced from being used. Batteries on a Float Charger never become unbalanced. Telephone companies have batteries in service up to 40 years, and never ever have an EQ charge except for one time when they were installed.

As for monitoring battery voltage. A waste of time and money with any lead acid battery.

[jflorey2]

I totally get how batteries in parallel will stay in balance but dont understand how batteries in series can.

Ironically the opposite is true with lead acid.

Dont really have any experience with larger banks in series. The battery voltage read is only the total voltage yeah. So 4x12v = 48v. So the charger can only see the 48v. What happens if 2 batteries are at 11v and 2 at 13v Its still 48v total which is what the charger will see but 2 will get over charged and 2 over discharged yeah ?

At first, yes. The 2 that are higher voltage will start to outgas. They will not charge any further, and will convert that extra energy to chemical energy (i.e. will split water into hydrogen and oxygen) and heat. The 2 that are lower will continue to charge until they are back in balance.

This means that lead acids have a mechanism that allows them to come back into balance, at the cost of some lost electrolyte. A well balanced pack (i.e. all purchased at the same time) will need to self-balance very rarely so you won't lose a lot of electrolyte.

However, if you put batteries in parallel, then the "stronger" (lower ESR) strings will take most of the current, leaving little for the "weaker" strings. There may not be enough current to completely charge the lower cells in the weaker strings. This is one of the reasons why multiple parallel strings are a bad idea.

[Helimadness]

Ironically the opposite is true with lead acid.

At first, yes. The 2 that are higher voltage will start to outgas. They will not charge any further, and will convert that extra energy to chemical energy (i.e. will split water into hydrogen and oxygen) and heat. The 2 that are lower will continue to charge until they are back in balance.

This means that lead acids have a mechanism that allows them to come back into balance, at the cost of some lost electrolyte. A well balanced pack (i.e. all purchased at the same time) will need to self-balance very rarely so you won't lose a lot of electrolyte.

However, if you put batteries in parallel, then the "stronger" (lower ESR) strings will take most of the current, leaving little for the "weaker" strings. There may not be enough current to completely charge the lower cells in the weaker strings. This is one of the reasons why multiple parallel strings are a bad idea.

When you say lead acid I assume lead carbon respond the same ?