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8x 6v vs 4x 12v to get 48v


viceroy
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My two Axpert 5kva inverters arrived this morning, so next step is to start looking at batteries.

I'm on a bit of a budget so looking to get the best bang for buck.

 

My first question is which is better and why.

 

6v * 8 = 48v

or

12v * 4 = 48v

 

Not taking into account that you usually get more ah from the 6v batteries, which configuration is better?

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2V x 24.  If one cell dies or get damaged for whatever reason, you only replace the single cell.  Only my opinion though.

 

If you look at pictures of all the big installations you will mostly see 2V cells and sometimes 4V or 6V batteries.  Capacity wise a 12V battery would also get quite bulky and heavy.  The other option is to connect multiple serial strings of 12V batteries in parallel to get the same AH rating.

 

Since you are going to use 2 x 5KVA inverters you are probably looking at at least a 2000AH battery bank - in that case I'll try to get very high AH 2V cells in order to have a single serial string instead of lower AH batteries in multiple serial strings connected in parallel.

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I would say it is more a question of AH size vs battery size.

The bigger the AH rating, the lower the voltage of the battery become.

I think the goal is too keep the weight down to below 100kg.

 

So, 600AH you only going to find in 2Volt cells.

100AH in 2Volt is not worth it, so they pack it in a 12V cell.

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These Are my thoughts as well.

 

2V x 24.  If one cell dies or get damaged for whatever reason, you only replace the single cell.  Only my opinion though.

 

If you look at pictures of all the big installations you will mostly see 2V cells and sometimes 4V or 6V batteries.  Capacity wise a 12V battery would also get quite bulky and heavy.  The other option is to connect multiple serial strings of 12V batteries in parallel to get the same AH rating.

 

Since you are going to use 2 x 5KVA inverters you are probably looking at at least a 2000AH battery bank - in that case I'll try to get very high AH 2V cells in order to have a single serial string instead of lower AH batteries in multiple serial strings connected in parallel.

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you could consider the US solar battery or the Trojan 6v cells at 232 /242ah. I fid they work well on my installs as does the Willard 2v 762ah or the Raylight 2v 1060ah, but pricey.

US Solars i get from JHB at R1950 excl, the 2v cells are around R4400 and have a 6 week waiting period

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and some reading:

 

Battery Types

Battery types and technologies are almost as bountiful as the brands in the market and all of them claim to be superior in some way or another. This letter will only explain a few aspects to take into consideration when deciding on a technology and does in no way pretend to be a comprehensive explanation of all the technologies in the market. Some of the most commonly available technologies for standby systems are as follows:

  • -       Valve Regulated Lead Acid (VRLA)/Sealed Lead Acid, 3-5yr design life
  • -       Valve Regulated Lead Acid (VRLA)/Sealed Lead Acid, 7-10yr design life
  • -       Gel
  • -       Lead Crystal
  • -       LiPo (Lithium Polymer)
  • -       LifePo (Lithium/Iron Polymer)

For the purposes of this discussion we will only discuss the first three types of batteries and the way in which they are specified.

Basic Specifications:

Batteries are rated on a few basic specifications that are important to us:

  • -       Capacity
  • -       Design Life
  • -       Number of discharge Cycles

Capacity:

Batteries are first and foremost rated on how long they can deliver a specified load. This is reported in Amp Hours or Ah. So if a battery is rated at 100A/h it theoretically means that the battery will be able to supply a 100A load for 1 hour, or 50A for 2hrs, or 200A for

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Getting back to replacing bad cells....

My UPS guy reccomend we replace a complete string if one battery is bad.

The one bad battery can cause the other cells to overcharge.

We have also lost a complete ups due to a fire caused by a bad cell :(

Also the new cell will react diffrently than the new cells. That could cause the new cell to overcharge again.

 

That is the main reason for a warrenty. Replace everything!!!

 

But again it is easy for a corporation with loads of money to do that, but can you afford to do that?

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The best value for money 2V cell I have priced to date is the Deltec BI-XILF 23 tubular traction cell.

Cost is around R3300 for a 600AH unit. At 2200 cycles at 50% DoD it is a good buy.

Problem is the total cost!

 

Next would be the Willard RT13, also 2V. Cost about R2400 for 400AH. Also 2200 cycles at 50% DoD.

Problem is the total cost!

 

Next on my list would be the Trojan T-105. Cost R2200 for 225AH @ 6V. Rated 1200 cycles at 50% DoD.

Two strings of these will still cost less than the Willard RT13, but you have the same capacity.

Thing is, it is nearly 50% of the life cycle time.

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The best value for money 2V cell I have priced to date is the Deltec BI-XILF 23 tubular traction cell.

Cost is around R3300 for a 600AH unit. At 2200 cycles at 50% DoD it is a good buy.

Problem is the total cost!

 

Next would be the Willard RT13, also 2V. Cost about R2400 for 400AH. Also 2200 cycles at 50% DoD.

Problem is the total cost!

 

Next on my list would be the Trojan T-105. Cost R2200 for 225AH @ 6V. Rated 1200 cycles at 50% DoD.

Two strings of these will still cost less than the Willard RT13, but you have the same capacity.

Thing is, it is nearly 50% of the life cycle time.

 

Last price I got for the T-105 was R1 653.00 incl. each - that was on 12 Feb 2015

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  • 2 months later...
  • 3 weeks later...

Gel battries is ok, but once you draw too much amps from them and they start forming bubbles, you screwed.

This means that with gel you have to make sure you NOT overloading or overcharging the battries.

 

I got the Trojan's for a good price and they were in stock, so I took them.

I have them now for 3 months and to date did not need to refill any of the cells.

As they only used for loadshedding, they not working hard or cycling very much.

Basically just on standby 24/7.

 

I would say a lot depends on your aplication and what you can afford to spend.

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As an aside, im trying to figure out how long batteries take to charge. Is there a guide or something?

My thinking is ...

Infinisolar max charge 25Amp

Sonic gel must be charged at 24A (my understanding)

4 x 100ah sonic gel battery bank 48v

Assume 50% dod

Assume 80% efficiency of charger

10-12 hours?

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Hi Haggers,

 

If you already have the Infini Solar unit, you can really go with any battery you like, as you can program the unit to not abuse your battries like with a bi-directional invertor and MPPT charger.

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