Correct battery setup for 2x 48v banks

[Daniel128]

Good day everyone

My name is Danie I live in the centurion area.

Thank you for accepting me to join the forum im really new to the solar industry but willing to learn as much as I can.

I have already looked through some of the content on the forum and have gained some vital knowledge from it.

We have recently bought a house where a solar backup system was already installed or they were busy because it looks a bit confusing and half completed.

It looks like a Axpert 5kva inverter and 2x micro care mptt chargers one 60amp and the author 100amp but their not connected at the moment.

I have 9x Tenesol te230-60p+ panels and 3x small Tenesol te95-36m panels not connected at the moment.

8x sbs170f agm batteries 12v 170ah/c

But I have difficulty finding the correct way to connect the battery banks together to be able to utilise them to their best or full potential.

Another question what is the correct bulk charging volts and amps that I must look at also the correct float voltage and amps.

At the moment the charging amps is set to 20amp the bulk charging is set to 54volts and the float voltage is at 52v

Ill attach some pictures to help.

[ibiza]

Welcome to the forum Dannie !

Your batteries look lime mine. Narada. If so bulk charge is 56.7V and float set on 54V.

[Daniel128]

7 minutes ago, ibiza said:

Welcome to the forum Dannie !

Your batteries look lime mine. Narada. If so bulk charge is 56.7V and float set on 54V.

Thank you ibiza

I had a look at the brand again and it was power safe sbs but thank you for the info.

[ibiza]

 

[ibiza]

[ibiza]

You should set your charger on 40A.

13% of 340AH is 44A but Axpert can't set on 45A which is proper charging current for your bank

[ibiza]

 

[Daniel128]

1 minute ago, ibiza said:

You should set your charger on 40A.

13% of 340AH is 44A but Axpert can't set on 45A which is proper charging current for your bank

Thank you Ibiza I thought it might be too low will that charging rate be the sale on utility and solar?

[ibiza]

...

[ibiza]

Both, overcharging as well as undercharging are not good for the batteries.

Don't worry for the safety of the charger, it can take 40A easily.

[ibiza]

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[ibiza]

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[ibiza]

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[ibiza]

For proper advice wait for our wannabe state president TTT, he has more knowledge re, batteries

[Guest]

Wannabe ... Gmpf ... I just need more votes BUT seeing as the DA is kicking some arse, the pressure is off! 

 

As ibiza says, to much is bad, to little is bad. 

Note: The higher the amps the more water the batts are going to use, if they are lead acid. So keep an eye out with lead acid batteries. At least once a month.

There is a diffirence, on my experiences, between off-grid and batteries as backup / used only max of 20% DOD.

Using 5.5 hours of full sunlight:
Charging batts at 5-8% is good for weekend use, take a week to charge the batts.
10% is good for daily cycling.
13% is good for off-grid, you want to get the batts charged fast in other words.

Seeing as I do not go below 20% DOD I am at 10% for I have the whole day to charge the batts, whilst powering the load.

In off-grid scenario's, if the batts are only fully charge once a week, that is fine. But then equalize them also every 30 days or so.

Try to not to go below 50% DOD, only if you need to, but if you have to, once in a blue moon, that is ok.

[Daniel128]

44 minutes ago, ibiza said:

Both, overcharging as well as undercharging are not good for the batteries.

Don't worry for the safety of the charger, it can take 40A easily.

What is the best way to connect the 2 battery banks some sites say    +- +- +- +- to build a 48v bank and then they say to connect the one banks + and - to the author and then then one cable to the inverter?

[Daniel128]

25 minutes ago, The Terrible Triplett said:

Wannabe ... Gmpf ... I just need more votes BUT seeing as the DA is kicking some arse, the pressure is off! 

 

As ibiza says, to much is bad, to little is bad. 

Note: The higher the amps the more water the batts are going to use, if they are lead acid. So keep an eye out with lead acid batteries. At least once a month.

There is a diffirence, on my experiences, between off-grid and batteries as backup / used only max of 20% DOD.

Using 5.5 hours of full sunlight:
Charging batts at 5-8% is good for weekend use, take a week to charge the batts.
10% is good for daily cycling.
13% is good for off-grid, you want to get the batts charged fast in other words.

Seeing as I do not go below 20% DOD I am at 10% for I have the whole day to charge the batts, whilst powering the load.

In off-grid scenario's, if the batts are only fully charge once a week, that is fine. But then equalize them also every 30 days or so.

Try to not to go below 50% DOD, only if you need to, but if you have to, once in a blue moon, that is ok.

Than you for the help TTT

What does dod mean sorry imp still learning.

My current system runs most of my appliances tv fridge freezer lights 24/7 charging in the day and using and at night running on batteries only so will that be considered to be a  off-grid setup?

[Guest]

2 minutes ago, Daniel128 said:

What does dod mean sorry imp still learning.

My current system runs most of my appliances tv fridge freezer lights 24/7 charging in the day and using and at night running on batteries only so will that be considered to be a  off-grid setup?

DOD is Depth of Discharge. 20% being the best for most batteries.

Yes, that is off-grid as you do not use any Eskom to charge the batteries.

You just need to make very sure how much of the batteries are used at night. If it is 20% or less, brilliant. If it is like 50%, oops, if it is more than that, OMW, HKGK. 

Do you know the DOD? Do you have a BMV Battery Monitor?

[Daniel128]

Just now, The Terrible Triplett said:

DOD is Depth of Discharge. 20% being the best for most batteries.

Yes, that is off-grid as you do not use any Eskom to charge the batteries.

You just need to make very sure how much of the batteries are used at night. If it is 20% or less, brilliant. If it is like 50%, oops, if it is more than that, OMW, HKGK. 

Do you know the DOD? Do you have a BMV Battery Monitor?

Thanks for the help now I know for future reference. No unfortunately not om still trying to get the system to work properly and to get all the author fuse and safety items in place first before im going to expand.

 

But I have measured with a multi meter every battery after a day’s charge is around 12.56v and in the morning before I go to work some of them are around 12.10v to 11.95 but I have noticed my author batteries bank is 12.20v to 12.35 each why do you think one bank will drained more than the author one? Might it be because I haven’t connected the batteries correctly.

[Guest]

If would connect the 2 x 48v banks to busbars.

And I would suggest, as the guys have done on the forum, to put battery balancers on the banks.

[___]

Faaark, that battery wiring is terrible. It looks like some kind of effort went into making the lengths of the paths the same (with that terrible insulation tape connection in the middle of the "bus"), but I would actually advise that you connect them like the picture you posted above. Two 48V strings, then put those in parallel, and then cross the inverter cables so it takes the negative from one bank and the positive from the other. That way the extra length of cable that links the two banks together cancel each other out. Put a fuse between the battery and the inverter (or does the Axpert include an internal fuse? The Victron's do, but I still have mine fused externally).

For those AGM batteries, absorption voltage would be 57.6V, float at least 53V (52 is WAY too low). For extended floating 53V will be better, for daily cycling go a bit higher. Basically, whatever the spec sheet of the battery says. The above is just some common sense. After a while you know the numbers by heart: 12.8V is a full battery at rest, 13.2V for a maintenance float, 13.8V for float, 14.4V for absorb, 15V for equilisation, but do watch out for variations, eg Lead-Calcium is slightly different, as is AGM, Gel, etc.

A hint, to adjust thought processes: When the charger goes to float, the battery isn't full yet. It's about 90% full. It needs to spend some time on float every day to get to 100% SoC (state of charge, the inverse of DoD). This time that it spends on float... this is the most inefficient most wasteful part of the daily cycle... which is why TinkerBoy will tell you how much more he makes now that he traded the Axpert for an Infini :-)

[___]

Oh, and author vs other. I know it is bad form to be spelling Nazi but it drives me nuts when people spell the word correctly but it is completely the wrong word... :-)

[Chris Hobson]

 

1 hour ago, Daniel128 said:

What is the best way to connect the 2 battery banks some sites say    +- +- +- +- to build a 48v bank and then they say to connect the one banks + and - to the author and then then one cable to the inverter?

What you need to ensure is that the cabling connecting the one string is equal in length to the cabling connecting the second string so that each string of batteries has the same resistance and that they charge evenly. Havign uneven length of total cabling or mixing and matching battery types or chemistry (yes I have seen this) put paid to any hope of even charging. 

For two strings this is probably (after a busbar) the best setup. 

 

Notice the cables connect individual batteries are all equal in length and two bridging cables are slightly longer but they in turn are the same length.

26 minutes ago, The Terrible Triplett said:

I would connect the 2 x 48v banks to busbars.

The correct way of connecting multiple strings is with a busbar but for two string I feel that it is an overkill. 

[Chris Hobson]

 

1 hour ago, Daniel128 said:

What is the best way to connect the 2 battery banks some sites say    +- +- +- +- to build a 48v bank and then they say to connect the one banks + and - to the author and then then one cable to the inverter?

What you need to ensure is that the cabling connecting the one string is equal in length to the cabling connecting the second string so that each string of batteries has the same resistance and that they charge evenly. Havign uneven length of total cabling or mixing and matching battery types or chemistry (yes I have seen this) put paid to any hope of even charging. 

For two strings this is probably (after a busbar) the best setup. 

 

Notice the cables connect individual batteries are all equal in length and two bridging cables are slightly longer but they in turn are the same length.

52 minutes ago, The Terrible Triplett said:

I would connect the 2 x 48v banks to busbars.

The correct way of connecting multiple strings is with a busbar but for two strings I feel that it is an overkill. 

[Daniel128]

15 minutes ago, plonkster said:

Faaark, that battery wiring is terrible. It looks like some kind of effort went into making the lengths of the paths the same (with that terrible insulation tape connection in the middle of the "bus"), but I would actually advise that you connect them like the picture you posted above. Two 48V strings, then put those in parallel, and then cross the inverter cables so it takes the negative from one bank and the positive from the other. That way the extra length of cable that links the two banks together cancel each other out. Put a fuse between the battery and the inverter (or does the Axpert include an internal fuse? The Victron's do, but I still have mine fused externally).

For those AGM batteries, absorption voltage would be 57.6V, float at least 53V (52 is WAY too low). For extended floating 53V will be better, for daily cycling go a bit higher. Basically, whatever the spec sheet of the battery says. The above is just some common sense. After a while you know the numbers by heart: 12.8V is a full battery at rest, 13.2V for a maintenance float, 13.8V for float, 14.4V for absorb, 15V for equilisation, but do watch out for variations, eg Lead-Calcium is slightly different, as is AGM, Gel, etc.

A hint, to adjust thought processes: When the charger goes to float, the battery isn't full yet. It's about 90% full. It needs to spend some time on float every day to get to 100% SoC (state of charge, the inverse of DoD). This time that it spends on float... this is the most inefficient most wasteful part of the daily cycle... which is why TinkerBoy will tell you how much more he makes now that he traded the Axpert for an Infini :-)

Wow thank you so much for all your feedback and advice Plonkster