Battery Questions.....

[DrumStick]

Hi Guys/Girls

I am a long time reader so before I post my questions I must thank you all here for your past posts and the the help you always give.

I am not too clued up on these things and since loadshedding is here to stay I have a few question regarding inverters and batteries. I have read threw most of the threads relating to them however there is something i have not seen answered yet:

I have gotten a Axpert 1kva inverter which runs at 12v, I will be running a total of 140 watts so she is more then capable.
I was looking at 12v 100 AH batteries and noticed these 6v batteries rated at 225AH
http://www.maidenelectronics.co.za/ProductInfo.aspx?productid=TROJAN%20T105

My question is would it make sense to get 2 6v batteries wired in series or are the 12v 100AH batteries wired parallel better, basically what are the pros and cons of using 6v batteries?

So far for the 6v batteries the following keeps popping up:
The prices are very reasonable considering the capacity.
The are much smaller then 12v batteries of equivalent capasity

Is there any reason using 2 6v batteries is a bad idea?

 

[mmacleod]

Remember that you need to halve the Ah when you double the voltage.
So a 6v 100Ah battery will give you only 50Ah @ 12v when you put a 12v load on it, or to put it differently you will need two of them if you want 100Ah at 12v...
Conversely a 50Ah 12V battery will give you 100Ah at 6V. (Ignoring conversion losses)

So you need double the amount of batteries if you are using 6V batteries, there are some possible benefits to 6v batteries vs 12v ones but they will likely end up more expensive not less expensive.

 

[The_Traveller]

How deep can those Trojan's be discharged ? also check the cycle chart on DoD.

 

[lived666]

yes, if you series two 6v batteries, if one has a problem or a shorter life or a charging issue, your system goes down. Look at the enertec 12v deep cycle 105ah - they a lot cheaper than the ones in your link. RGS batteries, I think they have them for under R1500 - make sure whatever you get, its the real deep cycle and not the truck heavy duty - the enertec is the green label one enertec 54105

 

[greg_SA]

Hi Guys/Girls

I am a long time reader so before I post my questions I must thank you all here for your past posts and the the help you always give.

I am not too clued up on these things and since loadshedding is here to stay I have a few question regarding inverters and batteries. I have read threw most of the threads relating to them however there is something i have not seen answered yet:

I have gotten a Axpert 1kva inverter which runs at 12v, I will be running a total of 140 watts so she is more then capable.
I was looking at 12v 100 AH batteries and noticed these 6v batteries rated at 225AH
http://www.maidenelectronics.co.za/ProductInfo.aspx?productid=TROJAN%20T105

My question is would it make sense to get 2 6v batteries wired in series or are the 12v 100AH batteries wired parallel better, basically what are the pros and cons of using 6v batteries?

So far for the 6v batteries the following keeps popping up:
The prices are very reasonable considering the capacity.
The are much smaller then 12v batteries of equivalent capasity

Is there any reason using 2 6v batteries is a bad idea?

I have the exact same inverter, running 2x 12V 100Ah Ritar AGM Deep Cycles in parallel, with 16mm2 battery cables (kept as short as possible). I paid R2250 each (inc. VAT).

Those 6V batteries are basically the same size as my 12V batteries. Mine are 50mm lower, but 60mm longer.

 

[desiganp]

Remember that you need to halve the Ah when you double the voltage.
So you need double the amount of batteries if you are using 6V batteries

:wtf:
I don't think that's correct.

My understanding is :
If you connect in series = voltage increases, capacity remains the same. (2 x 6V 225ah becomes 12V 225Ah)
If you connect in parallel = capacity increases, voltage remains the same. (2 x 6V 225ah becomes 6V 550Ah)

Is there any reason using 2 6v batteries is a bad idea?

Don't think there is any reason why it would be a bad idea. From the looks of it, looks like a good idea based on price and capacity. You should view the technical specs to be sure of life span based on DoD etc.

 

[mmacleod]

:wtf:
I don't think that's correct.
My understanding is :
If you connect in series = voltage increases, current remains the same. (2 x 6V 225ah becomes 12V 225Ah)
If you connect in parallel = current increases, voltage remains the same. (2 x 6V 22ah becomes 6V 550Ah)

I was not talking about connecting in series or parallel, I was talking about comparing the energy in the two batteries, i.e. basic laws of energy.
e.g. Say you ran them through a DC-DC converter to get the same voltage, the 12v 50Ah and the 6v 100Ah batteries are going to be roughly equivalent (ignoring inefficiencies and DoD differences etc.)

Anyway the end result is the same, you need 2x the amount of 6v batteries as you do 12v ones (if they are equal in terms of Ah), so for basic comparison purposes you should halve the Ah of the 6v batteries...

 

[DrumStick]

The only DOD specs i can find for trojan gives roughly 1000 cycles at 50% DOD.

My biggest concern is the size of the batteries, budget is R8000 for the set so I am looking for the batteries which will give me the best capacity in that price range. I am looking for a minimum of 300AH combined. I dont want to buy batteries now and have to replace them in a years time.

Can you guys post the links for the stores you bought the batteries you have for me to look at?

 

[lived666]

The only DOD specs i can find for trojan gives roughly 1000 cycles at 50% DOD.

My biggest concern is the size of the batteries, budget is R8000 for the set so I am looking for the batteries which will give me the best capacity in that price range. I am looking for a minimum of 300AH combined. I dont want to buy batteries now and have to replace them in a years time.

Can you guys post the links for the stores you bought the batteries you have for me to look at?

enertec 12v deep cycle 105ah. RGS batteries, I think they have them for under R1500, rgsbatteries.co.za

 

[elbow]

My biggest concern is the size of the batteries, budget is R8000 for the set so I am looking for the batteries which will give me the best capacity in that price range. I am looking for a minimum of 300AH combined. I dont want to buy batteries now and have to replace them in a years time.

If you want to compare different ways to assemble your batteries, I suggest you calculate the total watt-hours since that is directly comparable.

For instance:

• 2 x 12v 100AH batteries in series: 24v x 100AH = 2400WH
• 2 x 12v 100AH batteries in parallel: 12v x 200AH = 2400WH
• 4 x 6v 200AH batteries in serial: 24v @ 200AH = 4800WH
• 4 x 6v 200AH batteries in series/parallel: 12v @ 400AH = 4800WH

Obviously the voltage coming out of your pack needs to be compatible with your inverter. For high loads higher voltages are preferable otherwise the amps flowing (and therefore wire thickness, heat etc) become challenging.

Regards,
Elbow

 

[greg_SA]

If your planned load is 140W, then you won't need a huge battery bank.

2 x 12V 100Ah batteries (in parallel), will give you 2400Wh.

Even if you run for 4h, you DOD will only be about 25%, so the batteries will last well.

Is this for load shedding? Because then the number of cycles isn't very high. Should last for a few years.

I got mine from Mantech...

 

[DrumStick]

Yes this is for load shedding, my fear is that we get load shed more and more as time goes so I want to be prepared for at least 6 hours of load shedding should the need arise.

Thank you all for the help really appreciate all the feedback

Update:

I decided to go with THIS
Size wise perfect capacity good enough for approx 7 hours, will only need one then. Cost R5 550 at RGS Batteries (Thanks lived666 for the heads up about them)

Thanks for all your help again guys made the decision much easier and saved me some money too