Battery bank sizing

[Nemo]

Ok, check the numbers for me folks, for some reason my brain goes to mush when I start trying to figure this stuff out <img src="/images/boards/smilies/smile.gif" border="0" align="absmiddle"><br><br>Ok, I've decided that I want/need to increase the size of my battery bank simply for entertainment after the sun goes down &lt;grin&gt;&nbsp; my laptop runs about 11 amps, I use a single 1 amp light, and a portable dvd player that uses under 1 amp.. so have chosen my target storage&nbsp; capacity as 300AH capacity minimum..&nbsp; (15 amps X 10 hours = 150) X 2 (to keep the batteries above half)<br><br>Now.. this (to me) appears to work fine as a calculation, but it doesnt even come close in reality.. not counting inverter inefficiencies, I currently am carrying 110AH usable now on my pair of trojan T105s, and they are NOT lasting long at all with the above mentioned load.&nbsp; Hmm.. just occurred to me that they are rated at 6v and I'm pulling 12.. perhaps I should have thought of that &lt;grin&gt;<br><br>ok, so if I get 12v Trojans, is it reasonable to plan for a bank of 350AH in order to safely get a daily draw of 150?<br><br>Lookin for thoughts of others here, I dont trust myself on this stuff &lt;grin&gt;<br><br><br>

 

[blars]

Are you mixing amps at 120v with amps at 12v?&nbsp; Your inverter will pull at least 10 times (more like 12 with inefficenncy) the amps at 12v that it puts out at 120v.&nbsp; Also, you seem to be assuming your batteries are fully charged -- how are you charging them?&nbsp; (Note that charging rate tends to go down, so if you can get them from 50% charged to 80% charged in 4 hours, it may take 12 more hours of charging to get them to 100%.)<br>

 

[Nemo]

to the best of my knowledge, I'm not mixing amp reading.. the 10 amps that I require for the laptop is taken by how much my PV panels take in when i'm at float, and running the laptop.. it probably takes about 9 when it's fully charged, but usually the amount being sent to the batteries reads near 10amps when fully charged and I turn it on..&nbsp; so making a bit of an assumption there.<br><br>I am currently running 410 watts of solar, through a 45amp MPPT charge controller, so charging is not a problem.&nbsp; In the summer I can run all day and still have full batteries at night, but once the sun goes down, I have to watch and will only have a couple hours of full usage.. thats what I want to fix.. hence the original question <img src="/images/boards/smilies/smile.gif" border="0" align="absmiddle">&nbsp; With usage as described, a laptop, light, and possibly portable dvd player, how big of a battery bank would I need to have to be able to run for 10 hours?<br><br>

 

[sl1966]

How much do those items you have consume in AH's and how many AH's does your current setup support? I mean the full AH's and not just the 50% threshold.

 

[akrvbob]

Hey Nemo, hope all is well with you and your family!! I'm sending best wishes. It has been my experience that every time someone does these calculations, and then tries to live with them, they are dissappointed. What I've decided is that manufacturers are terribly optimistic&nbsp; in their ratings, and real world use doesn't match up. If the calculations say you can get by with 220 ah total, then you need to get 440 ah total. that has been my experience over and over again.<br><br>If one pair of Trojans isn't getting you through the night, I'd add a second pair. It's 1000 times better to have too much battery storage then too little. Over the long run the batteries should last you so much longer it won't cost you more. Bob<br>

 

[4x4tour]

You never want to run 6-volts and 12-volts together in the same&nbsp;house-bank system (regardless of how they're connected).&nbsp; Anyone tells you its okay, stop reading their post... <br><br>I would get the same battery type that you already have, AS LONG AS those other 2 are in 90% or better condition.&nbsp; If not, the two older batteries will suck&nbsp;that new one down all the time, to the point where the new 3rd battery will&nbsp;only always be at 90%,&nbsp;follow me? <br><br>If the&nbsp;current rear batteries are over 2 years&nbsp;old, I go to a junkie and get a couple of similar type,&nbsp;on the cheap, and not have to worry about&nbsp;mis-matching battery types. &nbsp;<br><br>6-volts are a PAIN IN THE ASH.&nbsp; I prefer Military&nbsp;type Odyssey AGM's, but that's just me.&nbsp; When I buy a battery, I dont wanna mess with it for many years... Plus, a 5 year free replacement, doesnt get any better than that. <br><br>Odyssey makes them for Sears, who sell them as Platinum P-2's (3 group 65's for me, a group 27 would be a different item number etc...). &nbsp; <br><br>Informative web info here: <br><br><A href="http://www.badgertrek.com/sportsmobile/electrical.shtml" target=_blank>http://www.badgertrek.com/sportsmobile/electrical.shtml</A><br><br><br>

 

[VanTramp]

Hey Nemo, Seemed like you may have a little confusion about the 6V, 12V thing and amp hours. &nbsp;If your current setup (no pun intended, really) is 2 6V T105's in series for 12V, the voltage doubles but the ah stays the same. so whatever ah rating it is for 1 of the 6V batts, it's still that rating even with 2. Okay, you may realize that so onward...<div><br></div><div>I agree with Bob. Get twice what you think you will need. Especially with the room you have. Temperature, water level, weak sun, bad weather, whatever, there are a number of reasons why you may fall short.charging &nbsp;for any length of time, might as well have enough on reserve that you can still do what you want.&nbsp;</div><div><br></div><div>I know many people don't like 6V batteries in their banks, but honestly, they have thicker plates and are really well suited for what we use them for. Just have to keep adding them in parallel as series wired pairs of course <img src="/images/boards/smilies/smile.gif" border="0" align="absmiddle"> &nbsp;&nbsp;</div>

 

[Nemo]

Thank ya all )&nbsp; gonna have to at least double up my 225ah, that just wont hold me, now have to figure out what I'm willing to spend on it!!<br><br>Thanks for the good wishes Bob, things have been really up and down lately, but going as well as can be expected <img src="/images/boards/smilies/smile.gif" border="0" align="absmiddle">&nbsp; <br><br>