12 v switch to 24v system

[thirteen]

I am getting my solar panels this week and in 10 days I plan on mounting them on my wood shed for the start of my system. I will still have a few items that will be 12v until late next year when I will add more solar panels. At this time I will have 2 -12v battereis 8d  for my system. When I get them hooked up on my 24 v system I will need to use one for a 12 v supply for a pump and some lighting and a grinder (meat). I would like to use the last battery for my 12v supply. I am wondering if I should switch batteries every couple of months to balance the drawdown preasure on the batteries? I will be going into winter where I will only get limeted sun light maybe 2 hrs daily. I will be able to charge them with a generator every couple of days if needed. Any ideas.
13

[ChrisOlson]

When you're pulling an unbalanced load off a 24V system, I would definitely rotate the batteries now and then.  The problem is going to be charging - say you have one battery at 60% and the other at 80% SOC - and charge them at 24 volt at say 30 volts for absorb.  While the system voltage will be 30, the one that's lower on SOC will lag behind on bulk at say 28 volts, and that's going to run the other one 32 volts.

So keep tabs on the individual voltages of the batteries so you don't over-boil the one that's higher on SOC and run it out of water.
--
Chris

[gww]

13
Would a dc to dc converter draw more evenly from the batteries?
gww

[DamonHD]

Yes

[thirteen]

GWW could you explain a dc to dc converter for what I am trying to make work. 13

[Frank S]

I don't know if this would work for you but if you could find a wrecked toyota Pirus and get the converter out of it they boost  202v to 500v should be more than heavy duty enough for even a large bank

[Bruce S]

13
 A dc-to-dc converter basically grabs the 24Vdc and steps it down to 12Vdc, in buck fashion.
This way the system still sees it as a 24Vdc draw across the entire battery setup rather than from just one battery that could cause an unbalanced setup.
Hope this helps
Bruce S

[gww]

I am sorry I missed your question.  I was thinking of something that took 24 volts and put it out as twelve volts.  I can not tell you of a spicific product but I know that a mppt charge controller does this as It takes higher voltage and converts it to charge lower voltage batteries.  I believe with an internet search you would find something much cheeper out there for your exact needs but I have not did one in sometime.
Hope this helps
gww

Maby look here   http://www.bing.com/search?q=dc+to+dc+converter+24+to+12&src=IE-SearchBox&FORM=IE8SRC

[XeonPony]

thats a dc to dc converter, pick an amperage and order one from powerstream or any other such venders, or hell make one, they aren't that hard!

[thirteen]

thank you for the info 13